Loss of mains protection or anti islanding

P a g e | 1
Loss of Mains Protection or anti-islanding
Osama Alshhoumi
17/08/2018

P a g e | 2
ABSTRACT
Our world is changing massively and there are challenges to overcome regarding to develop
the existing conventional methods of producing, transmitting, distributing and protecting the
system to meet the requirements of future demands. Penetration of renewable energy such
Wind, solar, hydro power, fuel cell, geothermal energy and micro-turbines. Poses tremendous
operational challenges to overlay. From operation point of view it is all about data, forecast
ability, and ability to model everything that may or may not happen in the network by
implementing different scenarios to make sure that the network is robust to transfer and
product power. The traditional unidirectional (radial) systems now exhibit bidirectional
current flow during normal and short-circuit conditions which rise the challenges of power
system protection.
Islanding phenomena or loss of main become very interesting topic in the last 2 decades. And
this is due to that the risk of islanding phenomena if it is not planned could cause damages on
both the utility and customer’s equipment. In most the world countries islanding is forbidden.
But in the last recent years there are studies encourage that regarding to make the system stable
the current standards must be review.
This thesis includes a survey on the loss of mains detection methods, focusing mainly
on the inverter-based generators. And then implementing and comparing between the current
conventional techniques, in this case for the active methods sandia frequency shift (SFS) and
slip mode frequency shift (SMS) are been applied. And for passive methods rate of change of
frequency (ROCOF) been applied.
The performance of these methods is tested. Then comparison between these methods is
presented.

P a g e | 3
Table of Contents
Table of Figures.......................................................................................................................................4
1. Introduction: ....................................................................................................................................6
1.1 Research Background ..............................................................................................................6
1.2 PROBLEM STATEMENT......................................................................................................7
1.3 OBJECTIVES OF THE RESEARCH ...................................................................................14
1.4 THE SCOPE OF THE RESEARCH .....................................................................................14
1.5 ORGANIZATION OF THE THESIS ...................................................................................15
2 LITERATURE REVIEW ..............................................................................................................16
2.1 LOSS OF MAINS DETECTION METHODS......................................................................16
2.1.1 PASSIVE METHODS...................................................................................................17
2.1.2 ACTIVE METHODS ....................................................................................................35
2.1.3 COMMUNICATION-BASED METHODS (REMOTE METHODS) .........................42
3 METHODOLOGY ........................................................................................................................45
3.1 INTRDUECTION..................................................................................................................45
3.2 LOM PROTECTION PERFORMANCE REQUIRMENTS: ...............................................45
3.2.1 Sensitivity ......................................................................................................................46
3.2.2 Stability..........................................................................................................................46
3.3 Unintentional LOM test.........................................................................................................47
3.4 NON DETECTION ZONE (NDZ)........................................................................................49
3.4.1 Non-Detection Zone for Sandia Frequency Shift (SFS) method...................................51
3.4.2 Non-Detection Zone of SLIP MODE FREQUENCY SHIFT (SMS) ...........................53
3.5 Case Study .............................................................................................................................53
3.5.1 Case Study 1 ..................................................................................................................54
3.5.2 Case Study 2 ..................................................................................................................62
4 Conclusion......................................................................................................................................66
4.1 Future work............................................................................................................................67
4.1.1 Technical challenges......................................................................................................67
4.1.2 Economic challenges .....................................................................................................69
4.1.3 environmental and political developments ....................................................................69
4.1.4 Social challenge.............................................................................................................70

P a g e | 4
Table of Figures
FIGURE 1-1 SCHEMATIC REPRESENTATION OF PV IN PARALLEL WITH THE GRID [1]....7
FIGURE 1-2 PROTECTION BLINDING ISSUE [7].............................................................................9
FIGURE 1-3 MISCOORDINATION ISSUE [7] ....................................................................................9
FIGURE 1-4 AUTO-RECLOSER FAILS TO RECLOSE [7]................................................................9
FIGURE 1-5 TYPICAL EQUIVALENT TOTAL SYSTEM REPRESENTATION IN THE UK [2].11
FIGURE 1-6 TYPICAL PROTECTION ARRANGEMENT FOR AN LV GENERATOR
CONNECTED TO A DNO HV SYSTEM AND DESIGNED FOR BOTH INDEPENDENT
OPERATION AND PARALLEL OPERATION [2] ....................................................................11
FIGURE 1-7 THE TRADITIONAL ELECTRICITY SYSTEM IN THE UK [3]................................12
FIGURE 1-8 THE CHANGING IN THE ELECTRICITY SYSTEM IN THE UK [3]........................13
FIGURE 1-9 THE VISUALISATION OF THE FREQUENCY CONTROL PROBLEM FOR
POWER SYSTEMS. [4]................................................................................................................14
FIGURE 2-1 THE COMMONLY USED MODEL IN LOSS OF MAINS DETECTIONS [10]........16
FIGURE 2-2 LOSS OF MAINS DETECTION METHODS................................................................17
FIGURE 2-3 PV ARRAY CONNECTED TO THE MAIN GRID. [11]..............................................18
FIGURE 2-4 CHARACTERISTICS OF VOLTAGE AND FREQUENCY IN AN ISLANDING [12]
.......................................................................................................................................................18
FIGURE 2-5 THE RANGE AND THE ACTION RESPONSE TO THE LARGE POWER
MISMATCH IN THE EVENT OF LOM [12]..............................................................................19
FIGURE 2-6 VOLTAGE DIP IN THE EVENT OF LOSS OF MAINS [12].......................................20
FIGURE 2-7 VOLTAGE AND FREQUENCY RESPONSE SYNCHRONOUS GENERATOR [12]
.......................................................................................................................................................21
FIGURE 2-8 THE VOLTAGE CO-ORDINATION [12] ....................................................................21
FIGURE 2-9 THE FREQUENCY CO-ORDINATION [12]...............................................................23
FIGURE 2-10 RATE OF CHANGE OF FREQUENCY [14]...............................................................24
FIGURE 2-11 LOM EVENT [13].........................................................................................................26
FIGURE 2-12 ROCOF NEGATIVE DF/DT [12].................................................................................27
FIGURE 2-13 ROCOF POSITIVE DF/DT [12] ...................................................................................27
FIGURE 2-14 THE EQUIVALENT CIRCUIT AND THE VECTOR DIAGRAM OF GRID
CONNECTED GENERATOR [12] ..............................................................................................28
FIGURE 2-15 EQUIVALENT CIRCUIT AND THE VECTOR DIAGRAM OF AN ISLANDED
GENERATOR [12] .......................................................................................................................29
FIGURE 2-16 WAVELET FILTER BANK ANALYSIS [27].............................................................34
FIGURE 2-17 THREE LEVEL DISCRETE WAVELET TRANSFORMATION DECOMPOSITION
[27].................................................................................................................................................34
FIGURE 2-18 IMPEDANCE DETECTION SCHEMATIC.................................................................36
FIGURE 2-19 BLOCK DIAGRAM REPRESENTATION OF THE SANDIA’S ANTI-ISLANDING
ALGORITHM [38]........................................................................................................................39
FIGURE 2-20 BLOCK DIAGRAM HIGHLIGHTING THE SFS COMPONENT OF THE
SANDIA’S ANTI-ISLANDING ALGORITHM [38]. .................................................................39
FIGURE 2-21 NATURE OF WAVEFORMS CAUSED BY THE SFS ALGORITHM [38].............39
FIGURE 2-22 BLOCK DIAGRAM HIGHLIGHTING THE SVS COMPONENT OF THE
SANDIA’S ANTI-ISLANDING ALGORITHM..........................................................................41

P a g e | 5
FIGURE 2-23 SLIP MODE FREQUENCY SHIFT AND PARALLEL RLC LOAD PHASE
RESPONSE CURVE [39] .............................................................................................................42
FIGURE 3-1 LOM SENSITIVITY ISSUE ...........................................................................................47
FIGURE 3-2 LOM STABILITY ISSUE...............................................................................................47
FIGURE 3-3 UNINTENTIONAL LOM TEST IEEE STANDARDS 1547.........................................49
FIGURE 3-4 NDZ OF THE OVP/UVP ...............................................................................................50
FIGURE 3-5 NDZ OF THE OFP/UFP..................................................................................................51
FIGURE 3-6 EQUIVALENT PV CELL CIRCUIT WITHOUT LIGHT .............................................55
FIGURE 3-7 CHARACTERISTICS OF PV ARRAY..........................................................................55
FIGURE 3-8 BLOCK-DIAGRAM OF THE MODEL .........................................................................56
FIGURE 3-9 POWER OF THE GRID, LOAD AND PV, THE PV VOLTAGE FOR THE MODEL 57
FIGURE 3-10 THE PV SYSTEM INTEGRATED WITH THE UTILITY GRID..............................57
FIGURE 3-11 POWER OF THE GRID, LOAD AND PV, THE PV VOLTAGE FOR THE MODEL
BEFORE LOM AND AFTER LOM.............................................................................................58
FIGURE 3-12 IMPLEMENTATION OF SANDIA FREQUENCY SHIFT (SFS) ..............................58
FIGURE 3-13 IMPLEMENTATION OF RATE OF CHANGE OF FREQUENCY (ROCOF) ..........58
FIGURE 3-14 VOLTAGE AT PCC, GRID CURRENT, LOAD CURRENT AND THE INVERTER
CURRENT FOR THE MODEL BEFORE AND AFTER LOM ..................................................59
FIGURE 3-15 RATE OF CHANGE OF FREQUENCY (ROCOF) .....................................................59
FIGURE 3-16 RATE OF CHANGE OF FREQUENCY (ROCOF) WITH TIME DELAY ................60
FIGURE 3-17 RATE OF CHANGE OF FREQUENCY (ROCOF) WITH TIME DELAY ................60
FIGURE 3-18 THD BEFORE AND AFTER LOM..............................................................................60
FIGURE 3-19 VU BEFORE AND AFTER LOM ................................................................................60
FIGURE 3-20 SANDIA FREQUENCY SHIFT (SFS) LOM DETECTION........................................61
FIGURE 3-21 PCC VOLTAGE AND INVERTER CURRENT WHICH IS APPLIED SFS METHOD
.......................................................................................................................................................61
FIGURE 3-22 CASE STUDY 2 MODEL.............................................................................................62
FIGURE 3-23 SMS IMPLEMENTATION...........................................................................................63
FIGURE 3-24 SMS CODE.................................................................. ERROR! BOOKMARK NOT DEFINED.
FIGURE 3-25 SMS FREQUENCY AND SMS DETECTION. ...........................................................65
FIGURE 3-26 VOLTAGE FREQUENCY AT PCC AND SMS FREQUENCY. ................................65
FIGURE 3-27 PCC VOLTAGE AND INVERTER CURRENT WHICH IS APPLIED SMS
METHOD ......................................................................................................................................65
FIGURE 4-1...........................................................................................................................................68
FIGURE 4-2...........................................................................................................................................68
FIGURE 4-3...........................................................................................................................................69
FIGURE 4-4...........................................................................................................................................70

P a g e | 6
1 Introduction:
1.1 Research Background
Loss of mains or islanding phenomena in electric power system is when the distributed
generator start to feed the load under balance conditions, and in stand-alone situation after
losing the connection with remainder of the Total System. In some cases, the islanding could
be planned. If generating plant permitted to do so, further detailed studies must have considered
which is related to load flows, voltage regulation, frequency regulation, voltage unbalance,
voltage flicker and harmonic voltage distortion to ensure islanding section is stable and it will
not cause any hazardous situation on the utility and customers equipment. In the UK if the
generating plant will have separated from the remainder of the Total System a contractual
agreement between the DNO and Generator must be in place and the legal liabilities associated
with such operation must be carefully considered by the DNO and the Generator. However,
when the islanding is not planned (unintentional). It could cause undesirable impacts on both
utility and customer equipment. Failure to detect unintentional loss of mains for period of time
larger than the recommended time setting, may lead to hazardous situation where personnel
safety could be in concern. However, even if the LOM period time is short, the chance of
exposure to side effects on the power quality still be a concern. For these reasons the risk
assessments study for unplanned loss of mains is very important to make sure that the risk of
unintentional loss of mains kept low. In the UK Applicable standards such as ENA Engineering
Recommendation G59 which been published by the Energy Networks Association (ENA).
Which has been prepared and approved for publication under the authority of the Great Britain
Distribution Code Review Panel. Which require that the Generator’s protection should detect
a LOM situation and disconnect the Generating Plant in a time shorter than any auto-reclose
dead time. Which include the circuit breaker to operate minimum 0.5s and for auto-recloser,
LOM protection should detect and disconnect the islanding in 2.5s due to that the auto-recloser
dead time is 3s. Furthermore, for the American standards such as IEEE 1547 and IEC 62116
require that a DG detect an unintentional islanding condition and cease to energize within 2s.
Regarding to understand the form of unplanned loss of mains, Figure 1-1 illustrate the
schematic representation of the DG which in this case is PV plant which is inverter-based DG,

P a g e | 7
controlling output current magnitude and phase with respect to terminal voltage.; a local load;
circuit breaker; and the utility grid. [1][2]
Figure 1-1 schematic representation of PV in parallel with the grid [1].
1.2 PROBLEM STATEMENT
According to G59 Issue 3 Amendment 3 in the requirements of 10.3.5 it state that
‘’ Where the amount of Distribution System load that the Generating Plant will attempt to pick
up following a fault on the Distribution System is significantly more than its capability the
Generating Plant will rapidly disconnect, or stall. However, depending on the exact conditions
at the time of the Distribution System failure, there may or may not be a sufficient change of
load on the Generating Plant to be able to reliably detect the failure. The Distribution System
failure may result in one of the following load conditions being experienced by the Generating
Plant:
A. The load may slightly increase or reduce, but remain within the capability of the
Generating Plant. There may even be no change of load;
B. The load may increase above the capability of the prime mover, in which case the
Generating Plant will slow down, even though the alternator may maintain voltage and
current within its capacity. This condition of speed/frequency reduction can be easily
detected; or
C. The load may increase to several times the capability of the Generating Plant, in which
case the following easily detectable conditions will occur:

P a g e | 8
• Overload and accompanying speed/frequency reduction
• Over current and under voltage on the alternator
Therefore, worst case scenario to detect sustained unplanned loss of mains which can be
explained from Figure 1 when the circuit breaker is opened, the utility grid current is equal to
nearly zero at the moment when the circuit breaker is opened. which means that the PV output
and the local load demand are balanced closely and matched in both terms active and reactive
power If such a balance does exist, then the LOM protection may fail to detect the unplanned
islanding due to that the inverter cannot tell the difference if the output current of the PV
flowing into the load creates a voltage that appears sufficiently similar to the grid voltage. The
loading condition that could result in unintentional islanding is referred to as a non-detection
zone (NDZ) as denoted in the requirements of 10.3.5 point A. whereas, in the case of points B
and C when the circuit breaker opens either the voltage or the frequency will vary remarkably
outside of normal operating range, and the islanding phenomena can be detected easily.
Nowadays, due to the high penetration of distributed generators and due to the Significant
retirement of conventional generation like coal, gas and nuclear power for the following
reasons:
• Environmental Protection regulations
• Low cost natural gas availability
• Age
Which will increase the issue of dependability and sensitivity of LOM protection due to that
the traditional protection techniques are designed for unidirectional (radial) systems but now
exhibit bidirectional current flow during normal and short-circuit conditions. Figure 1-2 shows
the protection blinding issue, Figure 1-3 shows the miscoordination issue and Figure 1-4
illustrate the auto-Recloser fails to reclose due to voltage on line on account of DG’s [7].

P a g e | 9
Figure 1-2 protection blinding issue [7]
Figure 1-3 miscoordination issue [7]
Figure 1-4 auto-Recloser fails to reclose [7]
Distributed generation is term refer to the electric power source integrated within distribution
network, near the point of use. Distributed generators usually connected to medium or low
voltage grid. Normally they are less than 30 MW [8] Distributed generation are opposite the
electricity supply system, in UK the electrical network established in 1920s starting as many
independent regional systems, in 1950s was the construction of the national grid which in
decades, the technology progress enabled the construction of large and efficient plant outside
the city centre. The energy sector is extensive, it involves many parties, supports many

P a g e | 10
functions and comprises complex dynamics between commercial, policy and technical
landscapes. It is also undergoing an unprecedented change. More static and centralised energy
systems which was built last century are transforming into new flexible, sustainable and user-
focused energy systems. Shaping this transition involves more stakeholders than ever before
[9]. IEEE defines Distributed generation as ‘’ Generation of electricity by facilities sufficiently
smaller than central plants, usually 20MW or less, so as to allow interconnection at nearly any
point in the power system as Distributed resource’’.
Distributed generation contribute economic advantages to scale down the amount of energy
lost in transmission lines furthermore, the integration of distributed renewable energy sources
i.e., bio-energy, wind energy, hydraulic energy, solar energy and so on, into the traditional
electric power system, can solve the environmental issue, by reducing the emission of the
greenhouse gases. Figure 1-5 illustrate the typical equivalent total system representation in the
United Kingdom According to Engineering Recommendation G59/3. Furthermore, Figure 1-6
shows the typical protection arrangement for an LV generator connected to a DNO HV system
and designed for both Independent Operation and Parallel Operation [2]. Table 1 shows the
Applied voltage and frequency settings in the UK according to the engineering
recommendation G59. Considering the changes that are already penetrated the grid as illustrate
in Figure 1-7 and Figure 1-8 which shows the traditional electricity system and the Changing
in the electricity system respectively, increase the issue of the protection due to the penetration
of different sources. Which is related to the significant increase in DG's in the network
especially in the distribution network level, which increase the risk of rapid changes to
frequency, which may consequence unhealthy tripping on the electricity network. Therefore,
as high growth rate of renewable non-synchronous generation technologies in energy market,
such as, solar and wind, protection engineers facing tremendous challenges to preserve the 50
Hz frequency stability on the transmission system [3].

P a g e | 11
Figure 1-5 typical equivalent total system representation in the UK [2]
Figure 1-6 typical protection arrangement for an LV generator connected to a DNO HV system and designed for
both Independent Operation and Parallel Operation [2]

P a g e | 12
G59/1 G59/2 (Small LV
connected DG)
(G59/3) (Small power
station – LV)
Setting Time delay Setting Time delay Setting Time delay
UV stage 1 –10% Vn 0.5 s –13% Vn 2.5 s –13% Vn 2.5 s
UV stage 2 - - –20% Vn 0.5 s –20% Vn 0.5 s
OV stage 1 +10% Vn 0.5 s +10% Vn 1.0 s +14% Vn 1.0 s
OV stage 2 - - +15% Vn 0.5 s +19% Vn 0.5 s
UF stage 1 47.0 Hz 0.5 s 47.5 Hz 20 s 47.5 Hz 20 s
UF stage 2 - - 47.0 Hz 0.5 s 47.0 Hz 0.5 s
OF stage 1 50.5 Hz 0.5 s 51.5 Hz 90 s 51.5 Hz 90 s
OF stage 2 - - 52 Hz 0.5 s 52 Hz 0.5 s
Table 1 the Applied voltage and frequency settings in the UK [2]
Figure 1-7 the traditional electricity system in the UK [3]

P a g e | 13
Renewable energy technologies challenges are linked to the system stability as they do not
provide reliable inertia, which mean they cannot help maintaining system frequency. Figure 1-
9 illustrate the Visualisation of the frequency control problem for power systems. The water
level in the bucket stands for the system frequency and the water body for its inertia. The system
operator monitors the water level and regulates the water inflow with the tap so that it meets
the water outflow [4]. Protection engineers will require to adjust the protection schemes to
mitigate the new challenges related to speed of frequency response to keep the system stable.
[5]. The traditional large thermal plants dominated GB generation were easily controllable and
could be switched on and off in response to patterns of demand. Therefore, nowadays engineers
facing new challenges due to the rapid growth of new technologies of inverter-based generation
[6].
Figure 1-8 the Changing in the electricity system in the UK [3]

P a g e | 14
Figure 1-9 the Visualisation of the frequency control problem for power systems. [4]
1.3 OBJECTIVES OF THE RESEARCH
The objectives of the research are as follows:
• Review of loss of mains methods.
• Identification of main issues associated with loss of mains
• Comparison of current techniques and listing the advantages and disadvantages with
each technique.
• Creation of power system using Matlab/Simulink and study of LOM phenomena and
faults in the system to Investigate the sensitivity and stability issue with LOM
phenomena
• Analysis of data from different simulation scenarios
1.4 THE SCOPE OF THE RESEARCH
This research conducted initial investigation on the LOM phenomena. Focusing on the different
techniques used nowadays, and what the pros and cons of these methods. Moreover, after
creating power system model using MATLAB/Simulink focusing mainly on inverter-based
generators to evaluate the performance of the conventional methods used in the UK to detect
the loss of mains phenomena. And the impact of the remote faults on the system to Investigate
the sensitivity and stability issue with LOM phenomena.

P a g e | 15
After the loss of mains event occur, Sandia frequency shift method (SFS) and rate of change
of frequency (ROCOF) are implemented to detect the loss of mains event. Moreover, an
implementation of slip mode frequency shift (SMS) is presented to explain and simulate the
performance of this method. And the reason behind this is due to that this method is widely
used in the inverter-based generators to detect the loss of mains phenomena.
1.5 ORGANIZATION OF THE THESIS
This thesis consists of four chapters, which are as follows:
Chapter 1 Introduction
Chapter 2 Provides a deep investigation about the methods used to detect the loss of mains phenomena.
the pros and cons of these methods.
Chapter 3 Describes the methodology used to evaluate the performance of the loss of mains
techniques. And also describes the steps to implement these methods.
Chapter 4 Presents conclusions on the achievements of this project and possible scenarios on the
developments of the smart grid in the future to meet 2050 target.

P a g e | 16
2 LITERATURE REVIEW
In this chapter, a detailed description of different islanding detection methods reported in the
literature are defined and reviewed, mainly focusing on the inverter-based generators.
furthermore, Comparison of current techniques and listing of the advantages and disadvantages
existing. Communication based detection method (remote methods) and local techniques are
presented as well. The selection of LOM detection methods will depend on the selection of
suitable DG model. Figure 2-1 illustrate the commonly used model in loss of mains detections
studies. By forming islanding scenarios as result of the opening of the circuit breaker at the
point of common coupling (PCC).
Figure 2-1 the commonly used model in loss of mains detections [10]
2.1 LOSS OF MAINS DETECTION METHODS
Loss of mains detection methods can be subdivided to 3 categories as shown in Figure 2-2.

P a g e | 17
Figure 2-2 LOSS OF MAINS DETECTION METHODS
2.1.1 PASSIVE METHODS
Passive methods are depending on monitoring and measuring the parameters of the DG’s
terminal voltage, and react upon if the selected parameters exceed the threshold setting. The
reason of defined this method as passive is due to that LOM protection scheme does not actively
try to manipulate the parameters being measured, it simply processes the measured parameters
and react upon the designed algorithm.
The basic requirements for this method protection are laid out in DPC7.4 of the Distribution
Code. The requirements of EREC G59 are as follows:
2.1.1.1 OVER/UNDER VOLTAGE AND OVER/UNDER FREQUENCY METHODS
The grid voltage and frequency limit setting are given in Table 1. The (UVP/OVP) and
(UFP/OFP) protective relays are normally placed on the feeders. Behaviour of the system at
the event of loss of mains is depend on the ∆𝑃 and ∆𝑄 at PCC. Figure 2-3 shows the PV array
as DG source connected to the main grid.
(1)
If ∆𝑃 ≠ 0, the voltage at the inverter terminal will vary remarkably and (UVP/OVP) will
detect loss of mains event and trip
LOSS OF MAINS DETECTION METHODS
PASSIVE METHODS ACTIVE METHODS REMOTE METHODS

P a g e | 18
If ∆𝑄 ≠ 0, the frequency at the inverter output current will vary remarkably and (UFP/OFP)
will detect the loss of mains event and trip. [11]
Figure 2-3 PV array connected to the main grid. [11]
Figure 2-4 illustrate the characteristics of voltage and frequency in an islanding event case for
synchronous generator. And Figure 2-5 illustrates the range and the action required to response
to the large power mismatch immediately after loss of mains phenomena [12].
Figure 2-4 characteristics of voltage and frequency in an islanding [12]

P a g e | 19
Figure 2-5 the range and the action response to the large power mismatch in the event of LOM [12]
2.1.1.1.1 Under Voltage
Under voltage protection setting [2] should help to maintain the total system stability.
According to the new requirements of EREC G59 the setting of Under Voltage protection is
with 2 stage to facilitate fault ride through capability (except where local auto-reclose dead
times are 1s or less as a reclose on to a fault is more likely to destabilise generation that is still
recovering stability from the first fault). The main aim of 2 stages setting is to ensure that DG’s
in not disconnected from the distributed network unless there is disturbance in the system.
EREC G59 denoted the 2-Stage under voltage protection are as follows:
1. Stage 1 should have a setting of -13% (i.e. 10% to cater for a future low voltage
statutory voltage limit and an additional 3% to provide immunity from 3% Step Voltage
Changes permitted under EREC P28) and a time delay of 2.5s.
2. Stage 2 should have a setting of –20% (i.e. to detect a major Distribution System
disturbance), with a time delay of 0.5s.
From Figure 2-6 it can be seen that the voltage dip in the event of loss of mains, due to that the
power demand in term of active power is greater than the generators output.

P a g e | 20
Figure 2-6 voltage dip in the event of loss of mains [12]
2.1.1.1.2 OVER VOLTAGE
In case of the system is operating abnormally [2], and as result of the presence of DG within
the distribution network, this could increase the risk of the limit being exceed Over Voltage
Protection is intended to detect islanding. Over voltage are more dangerous than under voltage.
EREC G59 requirements (Grid Code CC6.3 provides further details) for over voltage
protection with 2 Stage to be applied as denoted in EREC G59/3 for LV and HV is as follows:
A. In low voltage:
1. Stage 1 (LV) should have a setting of +14% (i.e. the LV statutory upper voltage limit
of +10%, with a further 4% permitted for voltage rise internal to the Customer’s
installation and measurement errors), with a time delay of 1.0s (to avoid nuisance
tripping for short duration excursions);
2. Stage 2 (LV) should have a setting of +19% with a time delay of 0.5s (i.e. recognising
the need to disconnect quickly for a material excursion).
B. In High voltage:
1. Stage 1 (HV) should have a setting of +10% with a time delay of 1.0s (ie the HV
statutory upper voltage limit of +6%, with a further 4% permitted for voltage rise

P a g e | 21
internal to the Customers Installation and measurement errors), with a time delay of
1.0s to avoid nuisance tripping for short duration excursions);
2. Stage 2 (HV) should have a setting of +13% with a time delay of 0.5s (i.e. recognising
the need to disconnect quickly for a material excursion).
Figure 2-7 illustrate the voltage and frequency response in case of synchronous generator, the
voltage rises in the event of loss of mains, due to that the power demand in term of active power
is less than the generators output. Moreover, it can be seen the impact of the governor
comparing to when there is no governor.
Figure 2-7 voltage and frequency response synchronous generator [12]
Figure 2-8 illustrate the voltage co-ordination, which indicate how that the characteristics of
the thresholds of the passive detection methods cannot discriminate between the islanding and
anti-islanding events in case if the active power mismatch close to zero [12].
Figure 2-8 the voltage co-ordination [12]

P a g e | 22
2.1.1.1.3 Over Frequency
For all DG’s which are connected in low voltage level (LV) and high voltage level (HV), it is
very important to prevent the unhealthy tripping. For this reason, the ‘’Distribution Code
DPC7.4.1.3’’ required that over voltage protection for both medium power stations and large
power stations to remain connected to 52 Hz, regarding to provide the necessary regulation to
control the Total System frequency. As denoted by EREC G59 requirements. A 2-stage
protection is to be applied as follows:
1. Stage 1 should have a time delay of 90s and a setting of 51.5 Hz. The 90s setting should
provide sufficient time for the NETSO to bring the Total System frequency below this
level. Should the frequency rise be the result of a genuine islanding condition which
the LOM protection fails to detect, this setting will help to limit the duration of the
islanding period.
2. Stage 2 should have a time delay of 0.5s and a setting of 52 Hz (ie to co-ordinate with
the Grid Code and Distribution Code requirements with a practical time delay that can
be tolerated by most Generating Plant). If the frequency rises to and above 52 Hz is the
result of an undetected islanding condition, the Generating Plant will be disconnected
with a delay of 0.5s plus circuit breaker operating time.
As shown in Figure 16 it can be seen that the frequency initially decreases in the event of loss
of mains, due to that the power demand in term of reactive power is less than the generators
output.
2.1.1.1.4 Under Frequency
In [2] the EREC G59/3 requirements for small power stations is to not disconnect with the
system unless the frequency falls below 47.5 HZ for 20 seconds. For both low voltage level
(LV) and high voltage level (HV). Under frequency protection is required to apply the
following 2 stage as denoted in 10.5.6:

P a g e | 23
1. Stage 1 should have a setting of 47.5 Hz with a time delay of 20s;
2. Stage 2 should have a setting of 47.0 Hz with a time delay of 0.5s;
In the UK, these settings are in line with the Distribution Code requirements.
Figure 2-9 illustrate the frequency co-ordination, which indicate how that the characteristics of
the thresholds of the passive detection methods cannot discriminate between the islanding and
anti-islanding events in case if the reactive power mismatch close to zero [12].
Figure 2-9 the frequency co-ordination [12]
2.1.1.2 RATE OF CHANGE OF FREQUNCY (ROCOF)
In UK RATE OF CHANGE OF FREQUNCY (ROCOF) is the most widely used technique, to
detect a genuine LOM event [13]. ROCOF relay measures the rate of change in frequency
caused by any difference between prime mover power and electrical output power of the
embedded by using the following equation [13]:
(2)
Where:
ROCOF: Rate of Change of Frequency [Hz/s]
∆𝑃: Active power variation during LOM event [MW]
f: system frequency [Hz]

P a g e | 24
S: DG’s rating [MW]
H: inertia constant of the generator [s]
In [2] it denoted that ROCOF protection is generally only applicable for Small Power Stations.
Table 2 illustrate the setting of ROCOF protection relay for power stations less than 5 MW.
Whereas, Table 3 shows the setting of ROCOF protection relay for power stations greater than
5 MW [2]
Figure 2-10 rate of change of frequency [14]
ROCOF setting for power stations < than 5 MW Registered Capacity
Date of Commissioning Asynchronous Synchronous
Generating Plant
Commissioned before
01/02/18
Not to be less than K2 x
0.125 Hz/s
and not to be greater than
1.0Hz/s, time delay 0.5s
Not to be less than K2 x
0.125 Hz/s
and not to be greater than
1.0Hz/s, time delay 0.5s
Generating Plant
commissioned on or after
01/02/18
1.0Hz/s, time delay 0.5s 1.0Hz/s, time delay 0.5s

P a g e | 25
Table 2 the setting of ROCOF protection relay for power stations less than 5 MW [2]
Date of Commissioning Small Power Stations Medium Power
Stations
Asynchronous Synchronous
Generating
Plant
Commissioned
before 01/08/14
Settings
permitted until
01/08/16
Not to be less
than K2 x 0.125
Hz/s
and not to be
greater than
1.0Hz/s, time
delay 0.5s
Not to be less
than K2 x 0.125
Hz/s#
and not to be
greater than
0.5Hz/s, time
delay 0.5s
Intertripping
Expected
Settings
permitted on or
after 01/08/16
1.0Hz/s, time
delay 0.5s
0.5Hz/s, time
delay 0.5s
Intertripping
expected
Generating Plant commissioned
between 01/08/14 and 31/07/16
inclusive
1.0Hz/s, time
delay 0.5s
0.5Hz/s, time
delay 0.5s
Intertripping
expected
Generating Plant commissioned on
or after 01/08/16
1.0Hz/s, time
delay 0.5s
1.0Hz/s, time
delay 0.5s
Intertripping
expected
Table 3 the setting of ROCOF protection relay for power stations greater than 5 MW [2]
Where k1 and k2 are LOM constants:

P a g e | 26
K1 = 1.0 (for low impedance networks) or 1.66 – 2.0 (for high impedance networks)
K2 = 1.0 (for low impedance networks) or 1.6 (for high impedance networks).
More details can be found in DPC7.4 in the ‘’Distribution Code’’ where ROCOF may be used,
and what the differences are between Scotland and England and Wales.
During a genuine loss of mains phenomena, ROCOF depends on the value of power mismatch
between the local load and the generator output at PCC. Due to that the Non-Detection zone
(NDZ) of ROCOF is large in the event of islanding, and when the generation meets the local
demand in term of both active and reactive power, ROCOF fails to detect the LOM events [13].
Moreover, if more than 70% of the load are been supplied from inverter-based generation
source, in [13] the NDZ of ROCOF protection could not be assessed. The reason behind this is
due to that after a small transient in voltage magnitude and frequency, the system become quite
stable for constant impedance loads. During the event of loss of mains, a voltage drop at the
DG terminal occurs which has a stabilising effect. As the load is represented by a constant
impedance, its power adjusts according to the square of the voltage and the system reaches a
new steady state condition. Figure 2-11 illustrate the event of islanding when using 2 inverter-
based generation techniques.
Figure 2-11 LOM event [13]
The threshold setting of ROCOF can be defined depending on the NDZ, which is relative to
the minimal difference in the production over the consumption in islanding event by using the
following equation [13]:
(3)
(4)

P a g e | 27
Where:
𝑃 𝑃𝐶𝐶: Real power imbalance across PCC [MW]
𝑄PCC: Reactive power imbalance across PCC [MVAr]
𝑆DG : DG’s rating [MVA]
Choosing the correct threshold setting for ROCOF is hard. The threshold setting depends on
the network parameters. [14] Figure 2-12 shows ROCOF detection for negative 𝑑𝑓/𝑑𝑡 and
Figure 2-13 shows the ROCOF detection for positive 𝑑𝑓/𝑑𝑡
Figure 2-12 ROCOF negative df/dt [12]
Figure 2-13 ROCOF positive df/dt [12]
2.1.1.3 Vector shift
The voltage vector shift technique tries to detect the shift in the voltage vector caused by a
sudden change in the output of Generating Plant or load over one or two cycles (or half cycles)

P a g e | 28
[2]. Figure 2-14 illustrate the equivalent circuit and the vector diagram of grid connected
generator. And Figure 2-15 shows the equivalent circuit and the vector diagram of an islanded
generator [13].
In UK, Vector shift protection have been removed from the LOM protection requirements. In
the last update in EREC G59/3-3, and also, new setting for ROCOF has been applied. The
reason behind this update, is due to that in early 2017 investigations denoted that vector shift
protection is less effective at detecting LOM phenomena, and it is susceptible to spurious
operation during voltage disturbances caused by faults on the transmission system [2].
Moreover, on the On the 22nd of March 2013 Northern Ireland was exposed to a severe snow
storm which resulted in a significant number of faults on the distribution and transmission
system. During three 15 minute blocks, the electricity system lost generation of 24 wind farms
due to the unhealthy tripping of LOM protection, causing shortage in totalling approximately
316 MW of generation from the system over a 15 h period and a total of 171 MW in a single
15 minute period. The investigation conclude that the wind farms which disconnected from
the system were only those with the VS element of their LOM protection activated, in the other
hand the wind farms which employed the rate of change (ROCOF) protection remained stable
[15]. For these reasons, in the latest update of EREC G59/3-3 vector shift has been removed as
loss of mains detection technique and applied new settings for ROCOF protection.
Figure 2-14 the equivalent circuit and the vector diagram of grid connected generator [12]

P a g e | 29
Figure 2-15 equivalent circuit and the vector diagram of an islanded generator [12]
Table 4 shows the Historic Vector Shift Settings.
Historic Vector Shift Settings
Historic Vector Shift
Settings
Small Power Station Medium Power
Stations
Asynchronous Synchronous
Settings permitted
for Generating Plant
commissioned
before 01/02/18
K1 x 6 degrees K1 x 6 degrees# Intertripping
Expected
Settings permitted
for Generating Plant
commissioned on or
after 01/02/18
Vector Shift not allowed as LoM in these
Power Stations
Intertripping
Expected
Table 4 Historic Vector Shift Settings [2]
Where K1 and K2 are LOM constants:
K1 = 1.0 (for low impedance networks) or 1.66 – 2.0 (for high impedance networks)
K2 = 1.0 (for low impedance networks) or 1.6 (for high impedance networks).

P a g e | 30
2.1.1.4 Voltage or current harmonic distortion (THD)
In event of islanding, this method depends on measurement of total harmonics distortion (THD)
at the point of common coupling (PCC). By using the following equation for THD:
𝑇𝐻𝐷 = ට
σ 𝐼ℎ
2𝐻
ℎ−2
𝐼1
∗ 100 (5)
Where 𝐼ℎ is the rms of the harmonic components and 𝐼ℎ is the rms value off fundamental
component.
Due to that in the normal condition, THD is negligible because the impedance of the grid is
small. Whereas, in the event of islanding, the inverter output current harmonics and transformer
hysteresis effect are transmitted to the load will aggravate harmonic distortion at PCC. Current
harmonics produced by the inverter and hysteresis effect of transformer will further. This
method used two parameters to detect islanding event, which are THD and the main harmonics
(3rd, 5th, and 7th) of the PCC voltage or current. However, this method poses challenges to
select threshold. And this is due the fact that grid disturbance is easy to cause error detection.
This method may fail to detect LOM if NDZ is large for loads with a large quality factor Q.
[16] [17]. The definition quality factor Q can be found in [18]. By using the following equation,
the value of the quality factor is:
𝑄 = 𝑅ට
𝐶
𝐿
(6)
Where RLC are all in parallel loads:
R: is the effective resistance.
C: is the capacitance.
L: is the inductance.
Q is equal to 2π times the ratio of the maximum stored energy at the resonant frequency to the
energy dissipated of a cycle at that frequency. When the resonant frequency of the load closes

P a g e | 31
to the grid rated frequency, such as 50 Hz or so, the value of Q has great influences on the size
of NDZ and detection accuracy can be confusing because it is used for different quantities in
electrical engineering. It is used for the reactive component of complex power, as in the
equation:
𝑆 = 𝑃 + 𝑗𝑄 (7)
However, to avoid mal-operation with this method, to distinguish between the islanding and
non-islanding situation, a new criterion is proposed in [20]. By measuring the deviation of THD
from steady state and normal loading condition as shown in the equation:
(8)
Where:
𝑇𝐻𝐷𝑠: is the initial set for the steady-state before islanding
𝑇𝐻𝐷𝑠𝑡𝑎𝑏𝑙𝑒: is the stable value right after three power cycles after events of loss of mains
To avoid the transient period. Then the rule of islanding is proposed as follows:
(9)
If the monitoring parameters has been satisfy as shown in (9), then it will be treated as
occurrence of Islanding and make a trip signal.
For the harmonic-based methods, the NDZ is depend on the RLC parallel resonant. In case of
a huge variation of harmonics amplitude, this method has a small NDZ.
The harmonics distortion of the grid voltage depends on the grid impedance.
Table 5 illustrate the maximum amplitude of the grid voltage harmonics [20].

P a g e | 32
Harmonic
order (h)
3 5 7 9 11 13
Amplitude
(%)
5 6 5 1.5 3.5 3
Table 5 the maximum amplitude of the grid voltage harmonics
2.1.1.5 Voltage Unbalance Variation (VU)
Voltage negative components are widely used to detect fault and unbalanced conditions in
transmission system. Voltage unbalance factor is based on the negative and positive sequence
of the DG output voltage components of three-phase. In [21] the definition of voltage
unbalanced factor is ‘’ the ratio of negative sequence voltage component to the positive
sequence voltage component’’
By using the following equation, the voltage unbalance Variation is:
(10)
Moreover, to avoid mal-operation with this method, to distinguish between the islanding and
non-islanding situation, a new criterion is proposed in [21]. By measuring the deviation of VU
from steady state and normal loading condition as shown in the equation:
(11)
Where:
𝑉𝑈𝑠: is the initial set for the steady-state before islanding
𝑉𝑈𝑠𝑡𝑎𝑏𝑙𝑒: is the stable value right after three power cycles after events of loss of mains
To avoid the transient period. Then the rule of islanding is proposed as follows:

P a g e | 33
(12)
If the monitoring parameters has been satisfy as shown in (9), then it will be treated as
occurrence of Islanding and make a trip signal.
2.1.1.6 Various harmonic pattern recognition methods, using spectral techniques
Some of the most widely used techniques for various harmonic pattern recognition methods
are is fellow:
1. Fast Fourier Transformation
2. Kalman Filters
3. Wavelet-based Islanding Detection Method
This thesis will focus on the wavelet transformation. FFTs and Kalman filters spectral
techniques are beyond the scope of this thesis.
2.1.1.6.1 Wavelet-based Islanding Detection Method
Wavelet spectral techniques is widely used in power system, like feature detection, feature
extraction, de-noising and data compression of power quality waveforms, power system
protection [22] [23]. Wavelet analysis is very useful tool in power system, due to that that it
can extract some high frequency components in the transient event, which they cannot be detect
when using conventional methods on a power frequency. The transient waveforms of currents
and voltages provide very important information to analysis the fault [24].
Wavelet transformation function is an efficient tool to describe a signal, by decomposing it into
its constituents at different frequency bands (or scales), which are known as wavelet
coefficients [25]
Figure 2-16 illustrate Structure of wavelet filter bank analysis. The coefficients of wavelet are
being obtained by passing the signal through a low pass filter with impulse response𝑔, the first

P a g e | 34
level of DWT of objective signal 𝑥(𝑛) is calculated, resulting giving the approximation
coefficients (𝑎1(𝑛)), and passing through a high pass filter ℎ, resulting giving the detail
coefficients (𝑑2(𝑛)). The filter outputs are then subsampled by 2. Then this process can be
repeated to decompose more levels of the approximation coefficients with high and low pass
filters and then subsampled by 2 as similar. Moreover, Figure 2-17 show the 3-level Discrete
Wavelet Transformation decomposition [27]
Figure 2-16 wavelet filter bank analysis [27]
Figure 2-17 Three level Discrete Wavelet Transformation decomposition [27]
The equations below explain the calculation of approximation coefficients and detail
coefficients [26].
(13)

P a g e | 35
Where 𝑎𝑚(𝑛) represents the approximation coefficients at level 𝑚, wavelet coefficients (detail
coefficients) 𝑑𝑚(𝑛), represents signal detail at level 𝑚.
In [26], the author conclude that the wavelet-transform method is not adapted to detect
islanding, but it can be used to detect or distinguish between the islanding or non-islanding
event.
2.1.1.7 Summary:
There are other passive methods beside the methods that already been mentioned above, such
as rate of change of output power, rate of change of frequency over power, comparison rate of
change of frequency, rate of change phase angle difference, phase jump detection and rate of
change of voltage. In general, all passive methods suffer from difficultly to obtain a unique
threshold or patterns to detect LOM phenomena. And the reason for this fact is that due to in
passive methods it is hard to eliminate all NDZs. The performance of passive methods is
difficult to predict when multiple inverters are present in the potential island. Unfortunately,
the majority of reports which is related to the loss of mains detection methods focus on the
passive methods with dynamics generators. In the short term that is fine but in the long term
due to the penetration of the inverter-based generators this could be an issue. Moreover, in the
UK it can be seen it is far behind the target of 2050 comparing with USA and Germany, most
of studies focus on the performance of rate of change of frequency which is in my opinion will
have no future in the long term. Also most of the studies do not considers the inertia issue due
to the penetration of inverter-based generators which will have an impact on the total system
inertia. Which will be decrease in the future.
2.1.2 ACTIVE METHODS
The similarity between the passive and active methods is that both methods are depending on
the threshold settings. The difference between these two methods is in active methods the
applied algorithm takes an active role in driving the system state toward that threshold. Overall,
active methods are more efficient than the passive methods to detect in the event of LOM. And

P a g e | 36
this is due that active methods tend to destabilize the potential island by making the generation-
load balance more difficult to achieve [1]. Active methods include the following:
2.1.2.1 Impedance detection.
In impedance detection, the inverter periodically perturbs its output current and checks to see
whether there is a corresponding change in voltage, thereby measuring the source impedance
as seen from the inverter. If the detected impedance is too high, the inverter trips. The method
normally used as backup protection. From Figure 2-18 it can be seen that impedance detection
method is usually installed on the grid distribution. Specifically, a low-value-impedance,
usually a capacitor bank is installed on the grid system inside the potential LOM [29].
Figure 2-18 Impedance detection schematic.
This method is based on the reactive power equation [28]:
(14)
In normal situation the capacitors switch is disconnected. But, in the event of LOM capacitor
switch is commanded to close after a short delay. The time delay between the grid
disconnection and the capacitor insertion is important and this is due to that the system is not
in a situation of reactive power balance. In [28] system would automatically trip out without

P a g e | 37
the need of capacitor insertion. In the other hand if there is not short time delay, this method
may fail to detect the LOM phenomena, and this due the fact that the immediate capacitor
connection could compensate the reactive power absorbed by the inductive load. Moreover,
the value of the absorbed reactive power by the capacitor ( 𝑄𝑐 ) determines different time of
the over/under frequency islanding protection operation. This method is highly effective to
detect and prevent the LOM phenomena. But, comparing to other methods, this method is more
expensive, and because it is necessary to install extra hardware on the grid side of the PCC.
Moreover, the time delay may increase the impacts of unintentional LOM which could request
the modification of the value of the capacitor bank.
2.1.2.2 Positive feedback based methods
The inverter in these methods employs positive feedback on voltage or frequency, then detects
the changes in one of these parameters. By pushing these parameters in the same direction,
trying to drive it out of bounds. If it can, the inverter trips. The positive feedback based methods
include the following:
2.1.2.2.1 Active Frequency Drift (AFD)
This method is based on injecting slightly distorted current into the PCC then detecting the
frequency response. If the grid is connected the injected distorted current will not affect the
grid frequency. But if the grid is disconnected then the injected distorted current this
perturbation will affect the frequency. the frequency response will vary which will will
continue until exceed the thresholds of under frequency or over frequency. The ‘’chopping
fraction’’ defined as fellow:
𝑐𝑓 =
2𝑡 𝑧
𝑇 𝑉𝑢𝑡𝑖𝑙𝑙
(15)
Where:
𝑡 𝑧: is the ratio of the dead or zero time.
𝑇 𝑉𝑢𝑡𝑖𝑙𝑙
2
: half of the period of the utility voltage waveforms.

P a g e | 38
𝑐𝑓: chopping fraction.
The pros of this method is that its implementation is easywith microprocessor-based controller.
Whereas, the cons of this method is that it introduces a distortion into the system which will
affect the power quality. Moreover, the NDZ of this method is depends on the chopping fraction
value. [40][41][42].
2.1.2.2.2 Sandia Frequency Shift (SFS)
Sandia frequency shift method (SFS) is basically the developed version of active frequency
drift (AFD). which is basically nothing but, AFD with positive feedback. Figure 2-19 illustrate
the block diagram representation of the Sandia’s anti-islanding algorithm by using the positive
feedback to detect the event of LOM Figure 2-20 shows the block diagram highlighting the
SFS component of the Sandia’s anti-islanding algorithm. The principle of operation is that
when the inverter is connected with the grid amplifying small change in the frequency, then
detecting the response of the grid. The philosophy behind it, is that due to that frequency is
considered as system issue if the inverter tries to change the grid frequency in the normal
healthy situation the stability of the grid will prevents it. But, in the event of LOM the frequency
response will vary remarkably thus LOM phenomena will be detected by detecting the phase
error produced by the frequency. This process will continue until exceed the thresholds of under
frequency or over frequency. Figure 2-21 illustrate the nature of waveforms caused by the SFS
algorithm. The ‘’chopping fraction’’ defined as:
𝑐𝑓 = 𝑐𝑓0 + 𝑘(𝑓 − 𝑓𝑔) (16)
Where:
𝑐𝑓: is the chopping fraction.
𝑐𝑓0: is the initial chopping fraction.
𝑘:is the feedback gain constant.
𝑓: is the frequency at PCC.
𝑓𝑔: is the grid frequency.

P a g e | 39
Thus, the new inverter angle is given as:
𝜃𝐴𝐹𝐷𝑃𝐹 = 𝜋𝑓𝑡 𝑧 =
𝜋𝑐𝑓
2
𝜃𝐴𝐹𝐷𝑃𝐹 =
𝜋𝑐𝑓(𝑓)
2
(17)
Figure 2-19 Block diagram representation of the Sandia’s anti-islanding algorithm [38].
Figure 2-20 Block diagram highlighting the SFS component of the Sandia’s anti-islanding algorithm [38].
Figure 2-21 Nature of waveforms caused by the SFS algorithm [38].
The pros of this method is that it has the smallest NDZ comparing with the other active methods
used to detect the islanding phenomena. Moreover, this method provides a good compromise
between the LOM detection effectiveness, quality of the output power and transient effects of
the system. In the other hand, cons of the applied method are that it’s required that the quality

P a g e | 40
of the output power of the inverter will slightly decrease in case of the inverter is connected
with the grid. And this is because the positive feedback will amplify changes in the grid.
Furthermore, if the utility is weak. there is possibility that the feedback could lead to transient
behaviour. Which is considered to be one of the major challenges in the near future when there
is more grid inverter tied generators [34][35][36].
2.1.2.2.3 Sandia Voltage Shift (SVS).
This method depends on the voltage measurements at PCC, by detecting the reflection of the
voltage variation at PCC on the output current, in the scenario where the inverter is connected
with the grid the extra output power of the inverter is absorbed or realised by the grid.
Therefore, regarding to detect the LOM phenomena this method uses positive feedback to
manipulate the magnitude of the output current. The RMS measurement value of the voltage
in half cycle is updated to the next cycle. Then, the current per unit value is modified relating
to the change in voltage. Furthermore, the limit of this changes is limited so it will not cause
any damages in the inverter. The equation of current used to update the reference is:
𝐼 𝑝𝑢 = 1 + 𝐾𝑠𝑣𝑠(𝑉𝑟𝑚𝑠 − 𝑉𝑟𝑚𝑠(𝑘−1)) (18)
Where:
𝐾𝑠𝑣𝑠: is feedback constant, which used to accelerate the response exponentially until voltage
trip occurs.
𝑉𝑟𝑚𝑠: is the RMS value of voltage in half cycle.
𝑉𝑟𝑚𝑠(𝑘−1): is the RMS value of voltage in the previous cycle.
Figure 2-22 illustrate the Block diagram highlighting the SVS component of the Sandia’s anti-
islanding algorithm. The drawback of this method is that the feedback injunction in the grid
creates a reduction on the inverter efficiency. But, it has small impacts on the utility power
quality and system transient response [31][32][33].

P a g e | 41
Figure 2-22 Block diagram highlighting the SVS component of the Sandia’s anti-islanding algorithm.
2.1.2.2.4 Slip Mode Frequency Shift
The principle of this method is to change the phase angle of the inverter output current
(𝜃𝑆𝑀𝑆,𝑘), then by detecting the voltage frequency variation comparing to grid nominal
frequency as shown in the equation:
𝜃𝑆𝑀𝑆,𝑘 = 𝜃 𝑚 𝑠𝑖𝑛 (
𝜋𝑓 𝑘−1−𝑓0
2(𝑓 𝑚−𝑓0)
) (19)
Where:
𝑓𝑚: is the frequency at which the maximum phase shift 𝜃 𝑚
𝜃 𝑚: is the maximum phase shift
The maximum value of 𝑓𝑚 − 𝑓0 is normally taken as 3 Hz.
To process of this method is when losing the connection with the grid the voltage frequency
at the PCC will slightly increase, therefore the current phase angle will increase as well, and
so on, until they reach the over frequency threshold setting. Whereas, when the voltage
frequency at the PCC decrease after LOM, frequency will decrease until exceed the under
frequency threshold setting [37]. Figure 2-23 illustrate Slip Mode Frequency Shift and
parallel RLC load phase response curve.

P a g e | 42
Figure 2-23 Slip Mode Frequency Shift and parallel RLC load phase response curve [39]
2.1.2.3 Summary
Most commercial inverters nowadays use the techniques mentioned above. As these techniques
shows high sensitivity to detect loss of mains event and high stability to remote faults. But due to the
fact that the inverter-based generation comparing to the other generation technology still low. But in
the future it can be seen that the energy sectors will depends more on these techniques. The majority
of studies focus on the performance of these method to detect the LOM phenomena. But there is a
shortage on the impact of these techniques on the overall system stability and this is due that the
detection principle these techniques depends on sending disturbance to the PCC and then observe
the feedback. For now, this is not big issue but when these renewable energies increase the overall
impact may lead to power quality issue.
2.1.3 COMMUNICATION-BASED METHODS (REMOTE METHODS)
The operation principle of this method depends on the communication between the distributed
generator and the utility. Which is in other words the tripping signal is centralized to detect whether
an island has been formed [1]. The advantages of these methods is that they do not have NDZ. But,
they are very costly and it will depend on the DNO to decide whether or not they can be used after
presenting risk assessment with further investigation. Communications-based methods include the
following:

P a g e | 43
2.1.3.1 Power line carrier communications (PLCC).
In this method power line carrier communication principle of operation is to send low energy
communication signal via the power line itself. And due to that there is a receiver installed at
point of common coupling. Then the PLCC transmitter will sends via the power line to the
receiver to evaluate the continuity of the line. The pros of this method is that is highly effective
to detect the LOM event and this due the fact that the non-detection zone of this method is zero.
Furthermore, this method has no effect on the output power quality and has high reliability. In
the other hand the cons of this method is that it is quite expensive [48].
2.1.3.2 Transfer Tripping scheme (TTS)
This method depends on monitoring all the circuit breaker and re-closer that may lead to cause
islanding on the distribution system which is achievable by using SCADA system. In other
words, when the substation detects islanded section in the distribution network. TTS will
indicate the event of loss of mains and send signal to the distributed generator. The advantages
of this method is that, its operation principle is simple in case of the radial system with small
integration of DGs and thus few circuit breakers. But if the system is more complex this method
will suffer from non-detection zone if the implementation was wrong or the system is not
updating and this due that this method required configuration.
2.1.3.3 Supervisory control and data acquisition system (SCADA)
This technique is straight forward by keeping an observation on the status of the circuit breaker. And
then SACADA depending on the collected parameters if it is sufficient it will decide if the loss of
mains event occur or not. This method collects the parameters by using sensors which are linked to
the substation. And depending on the signals received from the sensors the system will decides if
there is need of necessary precautions [49].

P a g e | 44
2.1.3.4 Phasor Measurements units (PMU)
By using standard code Phasor Measurements units may be supplied directly from a time broadcast
such as GPS or from a local clock using. The received signals are stamped before sent to the receiver
to determine if the if the distributed generator in synchronized with the grid. This can measure
50/60 HZ AC waveform at rate of 48 samples per cycle. It need analogue to digital transformer for
each phase. If the phase-locked oscillator used with GPS it could provide high speed synchronized
sampling with 1 microsecond accuracy [49].
2.1.3.5 Summary
This method is very sensitive to detect all types of faults. And this is due that it has zero non-
detection zone. But, it is very expensive comparing with the other methods. Most of the
research in this topic are related to the communication techniques. But, most of research did
not investigate the influence of the industrial internet of things (IIoT) which is can decrease the
cost of these techniques. In the near future in the UK there isn’t any deep investigation on the
impact of the industry 4.0 comparing with the USA and Germany.

P a g e | 45
3 METHODOLOGY
3.1 INTRDUECTION
In order to investigate stability and sensitivity issue of LOM, Sim Power Systems will be used
to model power system components. In this project, simulation will be used to model a
simplistic section of power network, with a model of a widely used protection scheme for loss
of mains. The proposed model will investigate the probability of islanding in the network
distribution level to evaluate the performance of DG focusing mainly on inverter-based DG
with an initial investigation on the different scenarios. Then, initial analysis of data from
multiple simulations and identification and demonstration of alternative methods of identifying
loss of mains conditions. The most challenging scenario is to assess non-detection zone when
using inverter-based Distribution. Slip mode frequency shift is considered as one of the most
effective method to detect the phenomena of LOM when using photovoltaic as distributed
energy source. This detecting method used to improve the NDZ by using positive feedback.
The NDZ criteria depends on the quality factor 𝑄 𝑓 and the RLC Load resonant frequency. The
equation of NDZ of SMS as mentioned in chapter 2 equation 19 to detect LOM are preformed
using MATLAB/SIMULINK. Two cases studies are applied to test this method. The
integration includes PV and three phase grid working parallel, PWM current control.
This chapter introduce LOM protection requirements, definition of quality factor, NDZ. Then,
the model description, implementation of active method by designing and testing SMS. And
implementation of passive method ROCOF, THD & VU. Then after the model description the
results will be presented and discussed.
3.2 LOM PROTECTION PERFORMANCE REQUIRMENTS:
The requirements from protection function and setting is to prevent the DGs supporting an
islanded section of the distribution system. Risk of unintentional LOM are as follows:
• malfunction or damage of network and customers’ equipment due to exceeding of
acceptable limits for the voltage, frequency, unbalanced, harmonics, flicker and active
and reactive power parameters
• Un-cleared faults (earth or phase faults).

P a g e | 46
• Out-of-phase due to re-closing of circuit breaker which increase transient inrush
relevance for network with automatic re-closing facility.
• Electric shock due to touching of live conductors which assumed to be dead (in LV
network).
Therefore, as mentioned above when there is a risk of unintentional LOM, which may or would
pose a hazard to the Distribution System or Customers equipment. In the UK. LOM protection
required to detect LOM phenomena according to the requirements of Engineering
Recommendation G59. In the other hand, in the last update of ENA Engineering
Recommendation G59 Issue 3 Amendment 3 2018, modified the setting to overlay the issue of
nuisance tripping, by requiring the need of 2 steps approach by when there is a long time delay
for smaller excursions that may be experienced during normal Distribution System operation
which will increase the stability of LOM protection, but with a faster trip for greater excursions
which will increase the sensitivity of the LOM protection [2]. The requirement of LOM is as
fellow:
3.2.1 Sensitivity
LOM protection required to be sensitive and dependable under all generation and load
scenarios which in specific situation when the local load closely follows the generator output
both in terms of active and reactive power can represent serious challenge for unintentional
islanding as shown in Figure 3-1.
3.2.2 Stability
LOM protection required to be stable and secure for remote faults cleared by the utility
protection device and stable and secure under system dynamic events to prevent unhealthy
tripping which will leads to the unnecessary disconnection of the generator as shown in Figure
3-2

P a g e | 47
Figure 3-1 LOM sensitivity issue
Figure 3-2 LOM stability issue
3.3 Unintentional LOM test
The purpose of the unintentional LOM test is to verify if the distributed generator in the
islanding event cease to energize the network. Therefore, for this purpose as shown in Figure
3-3, the procedure is designed to mitigate the influence of the islanding phenomena. By
adjusting the islanded load circuit in Figure to provide a quality factor 𝑄𝑓 of 1.0 ± 0.05 (when
𝑄𝑓 is equal to 1.0
The value of 𝑄𝑓 is to be determined by using the following equations as appropriate:

P a g e | 48
𝑄 𝑓 = 𝑅ට
𝐶
𝐿
(20)
Or
𝑄 𝑓 =
√𝑃 𝑞𝐿∗𝑃 𝑞𝐶
𝑃
(21)
Where:
𝑄𝑓 is the quality factor of the parallel (RLC) resonant load
𝑅 is the effective load resistance.
𝐶 is effective load capacitance (F),
𝐿 is effective load inductance (H),
𝑃𝑞𝐿 is the reactive power per phase consumed by the inductive load component.
𝑃𝑞𝐶 is the reactive power per phase consumed by the capacitive load component.
𝑃 is the real output power per phase of the unit.
𝑓 is frequency.
The inductance and capacitance are to be calculated using the following equations:
𝐿 =
𝑉2
2∗𝜋∗𝑓∗𝑃∗𝑄 𝑓
(22)
𝐶 =
𝑃∗𝑄 𝑓
2∗𝜋∗𝑓∗𝑉2 (23)
Where:
𝐿: is effective load inductance (H),

P a g e | 49
𝑉: is the nominal voltage across each phase of the RLC load (V) (for loads connected phase to
phase, V: is the nominal line voltage; for loads connected phase to neutral, V is the nominal
phase voltage).
𝑃: Is the real output power per phase of the unit (W),
𝑄𝑓: is the quality factor of the parallel (RLC) resonant load,
𝐶: is the effective load capacitance (F),
𝑓: is frequency.
The make the islanding circuit within the over frequency and under frequency trip setting the
reactive load should be balanced to make the resonant frequency close to the nominal as
possible [43]. In this chapter, this test will be considered as the guide to check the functionality
of the designed techniques to detect the LOM phenomena.
Figure 3-3 unintentional LOM test IEEE standards 1547
3.4 NON DETECTION ZONE (NDZ)
The NON-Detection Zone (NDZ) is used as criteria to evaluate various islanding detection
methods. Therefore, NDZ is when the LOM detection scheme fail to detect the event of LOM.
NDZ is defended by using the following equation [13]:

P a g e | 50
(24)
(25)
Where:
𝑃 𝑃𝐶𝐶: Real power imbalance across PCC [MW]
𝑄PCC: Reactive power imbalance across PCC [MVAr]
𝑆DG : DG’s rating [MVA]
One of the biggest issue related with the passive islanding detection methods is that it suffers
from large non-detection zone. Passive methods such as G59, which depends on monitoring
the measured parameters such as voltage amplitude or frequency and comparing it with a
predetermined threshold. Moreover, NDZ is depends as well on the used control techniques.
Two mainly used control schemes in DG system are Constant power control and constant
current control are the two mainly used control schemes in DG system [44]. Figure 3-4 and
Figure 3-5 illustrate the NDZ of the OVP/UVP functions and NDZ of the OFP/UFP functions
for current controlled DG system respectively.
Figure 3-4 NDZ of the OVP/UVP

P a g e | 51
Figure 3-5 NDZ of the OFP/UFP
However, in the active methods for LOM detection. Due to that these methods depends on
drifting the frequency of the islanded section to reach the UFP/OFP, resonant frequency 𝑓0of
the RLC load has significant effect on the frequency of the islanded section and on the unity
power factor [45].
In this chapter there will be 2 case studies. In the first case study, active method in this case
Sandia Frequency Shift (SFS) and passive method which is rate of change of frequency
(ROCOF) will be used to study and evaluate the LOM phenomena. In case study 2, the active
method in this case slip mode frequency shift (SMS) will be used to evaluate and study the
LOM phenomena. Therefore, the NDZ for these methods are evaluated as follow:
3.4.1 Non-Detection Zone for Sandia Frequency Shift (SFS) method
The principle of Sandia Frequency Shift (SFS) detection method is depending on accelerating
the frequency dip then measuring the influence of the step on the system by using the feedback
loop. As it is known that the frequency is a system issue. In other words, if the system is
connected this mean if the inverter tries to drift the frequency it will fail. On the other hand,
when the system is islanded frequency will drift. This method is implemented by using the
concept of zero current segment regarding to accelerate the frequency drift of the measured
voltage at point of common coupling (PCC). Zero segment current or chopping factor is

P a g e | 52
nothing but the ratio between the lengths of zero segment of half cycle. Therefore, the SFS
block as shown in the Figure, has been successfully designed to detect the LOM phenomena
by controlling the inverter output current. The performance of this method is controlled by
frequency difference gain (KSFS) [46]. Regarding to evaluate the NDZ of this method. The
following equations are used to calculate the phase angel of the inverter output current
𝜃𝑆𝐹𝑆 =
𝜋𝑐𝑓(𝑓)
2
=
𝜋
2
(𝐶𝑓0 + 𝐾(𝑓 − 𝑓𝑙𝑖𝑛𝑒) (26)
Moreover, the frequency boundaries are given as follow
𝑓 = (𝑓0 ∓ ∆𝑓) (27)
Where:
∓∆𝑓: is the increasing and decreasing in frequency from its nominal value
By substituting equation 26 and equation 27 into the following equation:
𝑓02
+
tan 𝜃 𝑖𝑛𝑣𝑒𝑟𝑡𝑒𝑟(𝑓)
𝑄 𝑓
𝑓0 − 𝑓2
= 0 (28)
For +∆𝑓 the obtained equation is as follow:
𝜋
2
(𝐶𝑓0 + 𝐾(+∆𝑓) = 𝑄 𝑓 (
𝑓0+∆𝑓
𝑓0
−
𝑓0
𝑓0+∆𝑓
) (29)
+∆𝑓 =
𝑓0
2𝑄 𝑓
൤
𝜋
2
𝐶𝑓𝑚𝑎𝑥 − 2𝑄 𝑓 + ට(
𝑓0
2𝑄 𝑓𝑚𝑎𝑥
)2 + (2𝑄 𝑓)2൨ (30)
Where:
𝐶𝑓𝑚𝑎𝑥 =
𝜋
2
(𝐶𝑓0 + 𝐾(𝑓𝑚𝑎𝑥 − 𝑓0) (31)
And for −∆𝑓

P a g e | 53
−∆𝑓 =
𝑓0
2𝑄 𝑓
቎
𝜋
2
𝐶𝑓𝑚𝑖𝑛 − 2𝑄 𝑓 + ඨ(
𝑓0
2𝑄 𝑓𝑚𝑖𝑛
)2 + (2𝑄 𝑓)2቏
(32)
𝐶𝑓𝑚𝑖𝑛 =
𝜋
2
(𝐶𝑓0 + 𝐾(𝑓 𝑚𝑖𝑛 − 𝑓0) (33)
3.4.2 Non-Detection Zone of SLIP MODE FREQUENCY SHIFT (SMS)
This method depends on phase perturbation or frequency to detect the LOM phenomena. By
destabilize the inverter output and observing the response of the frequency by measuring the
feedback. From equation (19). It can be seen that phase of current relative to the voltage can
be changed which will disturb the frequency of the voltage at PCC if the grid is disconnected
from the islanded section. Depending on the fact that the inverter output current and grid
voltage having zero-degree phase different when operate at the unity power factor. Therefore,
this method uses the frequency as function of the voltage at PCC. Which is designed in way
that the inverter phase will increase and decrease more rapidly that the RLC load, which will
make the inverter unstable. Due to the fact that the feedback closed loop are used, small
disturbance on the frequency will cause the error to increase which will accelerate the fault to
reach the OFP/UFP threshold setting. This method is easy to implement as it will be shown
later case study 2, and this is because that it can be implemented by writing code and then
observing the impact of it. The NDZ of this method is very small comparing with other active
methods. But, if the phase response of the load is faster than inverter. In this case NDZ will
exists [47].
3.5 Case Study
Figure 1-1 illustrate the schematic diagram used the study the LOM phenomena. This thesis
will focus mainly on using inverter-based generator in this case photovoltaic has been used as

P a g e | 54
distributed generator which is integrated with the utility grid. When the circuit breaker at point
of common coupling is open. The LOM event will occur and NDZ will depends on the quality
factor of the RLC load as mentioned in section 3.3 unintentional LOM. In case study 1 the
quality factor will be hold at 1. Which in this case the conventional detection methods
(OVP/UVP, OFP/UFP and ROCOF) will fail to detect the LOM phenomena. However, Sandia
Frequency Shift (SFS) will be used to detect LOM. In case study 2 the quality factor will be
hold at 2.5, then by using the active method in this case SLIP MODE FREQUENCY SHIFT
(SMS). To detect the event of LOM.
3.5.1 Case Study 1
3.5.1.1 PV and three-phase grid working parallel
In the recent years PV cells employed widely to generate electric power, they can be used
independently or with other sources. [1] Figure 3-6 illustrate the equivalent PV cell circuit
without light, the PV cell is lit up, the characteristic shifts by the photocurrent 𝐼 𝑝ℎ
𝐼 𝑑 = 𝐼 𝑑0 ቄ𝑒𝑥𝑝 ቂ
𝑞𝑉1
𝐾 𝑏 𝑇𝑐 𝐴(1−𝑏 𝑡(𝑇𝑐−𝑇𝑐𝑟
ቃ − 1ቅ, (34)
Where:
𝐼 𝑑: is the diode saturation current (A)
𝑞: is equal to 1.602 ∗ 10−19
𝐶 is the electron charge.
𝐾𝑏: is equal to1.38 ∗ 10−23
𝐽/𝐾 is Boltzmann’s constant,
𝑇𝑐: is the PV absolute temperature.
𝑇𝑐𝑟: is the nominal temperature.
𝐴: adjusting factor.
𝑏𝑡: is the voltage temperature coefficient.

P a g e | 55
Figure 3-6 equivalent PV cell circuit without light
As shown in Figure 3-7 Characteristics of PV array, the magnitude of the photocurrent
controlled by the irradiance level and on the temperature, and it can be taken as:
𝐼 𝑝ℎ = 𝐼𝑠𝑟ሼ1 + 𝑎 𝑘(𝑇𝑐 − 𝑇𝑐𝑟)ሽ
𝑄
100
, (35)
Where:
𝐼𝑠𝑟: is the photocurrent under the nominal condition
𝑇𝑐= 𝑇𝑐𝑟 : Usually 298K
𝑎 𝑘: is the current temperature coefficient.
𝑄: is the irradiance level
Figure 3-7 Characteristics of PV array

P a g e | 56
Figure 3-7 illustrate the characteristics of PV array. The volt-ampere characteristics under
various conditions and also power curve as well.
Figure 3-8 shows the inverter, the reactor, the load, and the AC source 𝑉𝑔𝑟which is three-phase
source. The phase-phase RMS value of 𝑉𝑔𝑟is 220 v, and the load will be adjust to have quality
factor of 1. By using the Thevenin's theorem as shown in equation (21). The PV unit has 750
PV cells in series and 50 PV cells in parallel. In this model when the irradiance level 𝑄𝑟 =
75%, the load will supplied from the PV unit only; when 𝑄𝑟 < 75% the load is supplied from
the PV unit and the grid; when 𝑄𝑟 > 75% the power surplus is sent to the grid. The controller
used in this model is hysteresis current controller. Figure 3-9 illustrate the changes of the
powers of the load, the grid and PV, together with the PV voltage. In this model when the
irradiance level 𝑄𝑟 = 1, PV power is equal to 157 KW.
Figure 3-8 Block-diagram of the model
For islanding condition, the breaker is opened at second 2. The local load is implemented by a
parallel load with quality factor equal 1. Figure 3-10 illustrate the PV system integrated with
the utility grid. However, the irradiance level was fixed at 100% to make the PV output power
at 157 KW in the 2 second the section will be islanded. As shown in Figure 3-11 after the LOM
event the power mismatch between the PV output power and the load power are almost zero.
Figure 3-12 Illustrate the implementation Sandia Frequency Shift (SFS) detection method.
And, Figure 3-13 shows the implementation of rate of change of frequency (ROCOF). Due to
that the power mismatch is small the G59 protection will fail to detect the islanding at the

P a g e | 57
recommended time setting. Figure 3-14 Shows that after the LOM event the converter still
energize the islanded section.
Figure 3-9 Power of the grid, load and PV, the PV voltage for the model
Figure 3-10 the PV system integrated with the utility grid

P a g e | 58
Figure 3-11 Power of the grid, load and PV, the PV voltage for the model before LOM and after LOM
Figure 3-12 implementation of Sandia Frequency Shift (SFS)
Figure 3-13 implementation of rate of change of frequency (ROCOF)

P a g e | 59
Figure 3-14 voltage at PCC, grid current, load current and the inverter current for the model before and after LOM
3.5.1.2 Results
For the passive methods when using the rate of change of frequency (ROCOF) with time delay,
ROCOF fail detect the event of islanding, as shown in Figure 3-15. When using ROCOF with
time delay it will make false tripping serval of times before the occur of LOM event. As
mentioned in [13] For ROCOF protection with time delay the NDZ could not be assessed The
system seems to be quite stable for constant impedance loads. During the islanding, when the
connection with the grid is lost, a voltage drop at the DG terminal occurs which has a stabilising
effect. Which make sense due to that ROCOF is effective in the dynamics DG, because it
depends on the system inertia as shown in equation (2-2). Therefore, using different passive
method in this case total harmonics distortion (THD) and voltage unbalance (VU) as shown in
Figure 3-17 and Figure 3-18 It can be seen that these two techniques show high sensitivity for
LOM, but they suffer from the instability for remote faults which causes unhealthy tripping.
Furthermore, choosing proper setting for these method is very hard in complicated and it
required using Wavelet transformation to detect the features and then extract the features.
Figure 3-15 Rate of change of frequency (ROCOF)

P a g e | 60
Figure 3-16 Rate of change of frequency (ROCOF) with time delay
Figure 3-17 Rate of change of frequency (ROCOF) with time delay
Figure 3-18 THD before and after LOM
Figure 3-19 VU before and after LOM
In the other hand, active methods in this case Sandia Frequency Shift (SFS) was implemented
successfully and it shows robust sensitivity for LOM event and also stable for the remote fault.
And this is due that the principle of this method it depends on the fact that is an accelerated
frequency drip with positive feedback. In the presence of grid, the frequency will not be drifted;
on the contrary when the grid is missing the frequency will drift. As shown in Figure 3-20 by
using equation (17) which takes 0.18 seconds to detect the LOM event. And as it is known that
due to that the frequency is considered to by system issue which in other word when the inverter
tries to change the frequency before the occur of LOM. The system will prevent it from drifting

P a g e | 61
the frequency. But when losing the connection with the system the inverter will manage to drift
the frequency to the OUFP setting. Figure 3-21 illustrate the voltage at the point of common
coupling and inverter output current which is applied SFS method
Figure 3-20 Sandia Frequency Shift (SFS) LOM detection.
Figure 3-21 PCC voltage and inverter current which is applied SFS method
From above it can be seen that for the inverter-based generators passive methods cannot be
reliable and stable and this due that these conventional methods depend on the system inertia
which in the case of PV system cannot be satisfied. In the other hand Active methods are more
sensitive for LOM phenomena and more stable for remote faults and have small NDZ. But,
there is possibility that the feedback could lead to transient behaviour. Which is considered to
be one of the major challenges in the near future when there is more grid inverter tied
generators.

P a g e | 62
3.5.2 Case Study 2
In this case study. One of the most advantages methods used to detect LOM phenomena. The
model been used is very simple as shown in Figure 3-22 which is for simplicity the source is
DC source instead of PV and then controlling the DC/AC inverter. The purpose from this case
study is to evaluate the slip mode frequency shift (SMS) which is one of the active methods
widely used in commercial inverter and this is due that this method is easy to implement as
shown in Figure 3-23, and this is because that it can be implemented by writing code (as shown
in Figure 3-24) and then observing the impact of it. small disturbance on the frequency will
cause the error to increase which will accelerate the fault to reach the OFP/UFP threshold
setting. This method depends on phase perturbation or frequency to detect the LOM
phenomena. By destabilize the inverter output and observing the response of the frequency by
measuring the feedback. In this case the power quality equal to 2.5. and the LOM occur when
opening the circuit breaker at 1 s.
Figure 3-22 case study 2 model

P a g e | 63
Figure 3-23 SMS implementation
3.5.2.1 Results
The detection of LOM is shown in Figure 3-25. It can be seen that this method takes around
0.16 seconds to detect the LOM event. In this is when quality factor of the load is equal to 2.5.
Moreover, Figure 3-26 illustrate the comparing between the grid frequency and the SMS
frequency. However, from this graph it can be seen that after the LOM. And, due to the fact
which when losing the connection with the grid the grid voltage frequency at the PCC will
slightly increase, therefore the current phase angle will increase as well, and so on, until they
reach the over frequency threshold setting. Whereas, when the voltage frequency at the PCC
decrease after LOM, frequency will decrease until exceed the under frequency threshold
setting. Figure 3-27 illustrate the voltage at the point of common coupling and inverter output
current which is applied SMS method. As mentioned previously this method is easy to
implement and it has very small NDZ comparing with other methods. Most of commercial
inverter in the USA and Europe uses this method to detect the LOM event. Furthermore, this
method is very stable for remote faults. But if the system is weak this method may force the
OUFP to trip.

P a g e | 64
function [sys,x0,str,ts] = SMS2(t,x,u,flag)
switch flag,
case 0,
[sys,x0,str,ts]=mdlInitializeSizes;
case 1,
sys=[];
case 2,
sys=[];
case 3,
sys=mdlOutputs(t,x,u);
case 4,
sys=[];
case 9,
sys=[];
otherwise
error(['Unhandled flag = ',num2str(flag)]);
end
% mdlInitializeSizes
function [sys,x0,str,ts]=mdlInitializeSizes
global f_i f_vo arg_i arg_vo arg_io isIslanding theta_SMS_latest
f_i=50;
f_vo=50;
arg_i=0;
arg_vo=0;
arg_io = 0;
isIslanding=0;
theta_SMS_latest = 0;
sizes = simsizes;
sizes.NumContStates = 0;
sizes.NumDiscStates = 0;
sizes.NumOutputs = 5;
sizes.NumInputs = 2;
sizes.DirFeedthrough = 1;
sizes.NumSampleTimes = 1; % at least one sample time is needed
sys = simsizes(sizes);
x0 = [];
str = [];
ts = [1e-4 0];
function f=theta_SMS(f_vo)
f=5*pi/180*sin( (pi/2) * (f_vo-50) );
function sys=mdlOutputs(t,x,u)
global f_i f_vo arg_i arg_vo isIslanding
arg_vo=u(2);
if abs(arg_vo)<0.04 % µçÑ¹ÏàÎ»Îª0Ê±¸üÐÂÆµÂÊ
f_vo=u(1); %%%
end
if(isIslanding==0)
if abs(arg_vo)<0.04
if (f_vo>50.5) || (f_vo<49.5) %ÅÐ¶ÏÆµÂÊÊÇ·ñÔ½½ç
sys=[0 1 0 0 0 ];
isIslanding=1;
else
f_i=f_vo;
arg_i=theta_SMS(f_i);
end
else
arg_i=arg_i+2*pi*f_i*1e-4;
end
sys(3)=sin(arg_i);
sys(4)=sin(arg_i - (2/3)*pi);
sys(5)=sin(arg_i + (2/3)*pi);
else
sys(3)=0;
sys(4)=0;
sys(5)=0;
end
sys(1)=f_vo;
sys(2)=~isIslanding;
Figure 3-24 SMS code

P a g e | 65
Figure 3-25 SMS frequency and SMS detection.
Figure 3-26 Voltage frequency at PCC and SMS frequency.
Figure 3-27 PCC voltage and inverter current which is applied SMS method

P a g e | 66
4 Conclusion
Risk assessment of unintentional islanding is very important to decide whether or not there is
need of loss of mains protection. In practical there are some cases where it can be said that
islanding is so unlikely to occur. For instant when it is not possible to balance the reactive
power supply and demand within the potential island area. If both active and reactive power
demand of the load and power system components are not balanced loss of mains phenomena
cannot be sustained. Therefore, depending on the fact that most loads and power system
components absorb reactive power. Thus if there is no reactive power source in the potential
islanded area loss of mains phenomena cannot be occur. Nowadays, most of commercial
inverters operate at unity power factor, but, due to the increasing demand on the future
requirements to meet 2050 target, larger inverters are being used and they operate at a fixed
power factor. In other words, inverters in this case could source or sink reactive power which
could lead to that the risk of unintentional loss of main is almost zero. And the reason behind
this is if this was the case. Then, the reactive power mismatch at PCC is large which mean that
the frequency will vary remarkably, thus OUFP will detect it. Furthermore, if the of the ratings
of all the distributed generators in the area where could suffer from the unintentional loss of
mains is less than two third of the minimum load within the section where it could potentially
be islanded. Then physically it is not possible. And this is due that When ∆𝑃 at PCC is large
voltage will vary remarkably, thus OUVP will detect it. Therefore, it can say that for all the
previous situation G59 protection or the passive methods will satisfy the requirements to detect
the loss of mains event. In the other hand, there are some cases when should be considered that
the risk of unintentional loss of mains is hard to detect for instant when the potential area that
could suffer from unintentional loss of mains contains large capacitors in is tuned such power
factor in this section close to 1. If this was the case passive methods could fail to detect the
event of loss of mains. But, when using active methods and due that these methods will tries
to manipulate the system by sending disturbance signals. any imbalance in the reactive power
is enough to detect the loss of mains events.
Table 6 illustrate the pros and cons of each method.

P a g e | 67
Table 6 comparison between LOM detection methods
4.1 Future work
The drivers behind the change in the transformation of energy systems in the future smarter
grid must maintaining the energy supply affordable and reliable to meet the need to protect the
environment (Energy Trilemma) which introduce energy challenges to interpolating the
implication of the following:
4.1.1 Technical challenges
Considering changes that are already penetrated the grid. Which is related to the significant
increase in DG's in the network especially in the distribution network, boosts the risk of rapid
changes to frequency, which may consequence unhealthy tripping on the electricity network.
Therefore, as high growth rate of renewable non-synchronous generation technologies in
energy market, such as batteries storage, solar and wind (DFIG), power system protection

P a g e | 68
engineers dial with challenges to preserve the 50 Hz frequency stability on the transmission
system. Renewable energy technologies challenges are linked to the system stability as they do
not provide reliable inertia, which mean they cannot help maintaining system frequency.
Engineers will require adjust the schemes of protection system to meet the new challenges
related to speed of frequency response to keep the system stable. Which was mitigate in the
last update in the Engineering recommendation G59 issue 3 Amendment 3 – Feb 2018. The
traditional large thermal plants dominated GB generation were easily controllable and could
be switched on and off in response to patterns of demand. Therefore, nowadays engineers
facing new challenges due to the rapid growth of new technologies of non-synchronous
generation which are inverter-based generation.
Figure 4-1 renewable energy
Figure 4-2 system inertia

P a g e | 69
4.1.2 Economic challenges
The main purpose from the development plan is to facilitate the entrance of innovative and new
technologies and business models into balancing market services and mechanism which
introduce challenges particularly plans to balance service market are hard to understand
because they are not very transparent. Therefore, to make the market easier to understand by
assessing the value proposition to facilitate the transition to a low carbon network and lower
cost to the consumers in an increasingly complex operational environment.
Figure 4-3 Balancing mechanism unit
4.1.3 Environmental and political developments
The 2020 Renewable Energy Directive which requires the EU to fulfil at least 20% of its total
energy needs with renewables by 2020 and the 2050 carbon reduction target. Has been
supported through environmental and energy policy by leverage new technologies to create
visible impact and opportunities

P a g e | 70
Figure 4-4 Distributed generation installed capacity
4.1.4 Social challenge
As a part of the effort to engage the public with this target, and the planning process, for
example the UK government throw the 2050 team at DECC, with the support of Sciencewise-
ERC, commissioned Delib to create an interactive Simulation, whereby the public can create
their own solution to meet the 2050 target.

P a g e | 71
References
[1] A. E. M. Ropp, “Suggested Guidelines for Assessment of DG Unintentional Islanding Risk,”
Sandia National Laboratories, California, March 2013.
[2] E. R. G. I. 3. A. 3, “RECOMMENDATIONS FOR THE CONNECTION OF GENERATING PLANT TO THE
DISTRIBUTION SYSTEMS OF LICENSED DISTRIBUTION NETWORK OPERATORS,” © 2018 Energy
Networks Association, London, February 2018.
[3] e. n. association, “ENA EREC P28 ISSUE 2 KEY TECHNICAL MODIFICATIONS GRID CODE AND
SQSS MODS,” LONDON, 2018.
[4] K. B. C. N. Jens Bömer, “ALL ISLAND TSO FACILITATION OF RENEWABLE STUDIES,” EirGrid Plc,
DUBLIN, 2010.
[5] U. o. M. a. t. U. o. Strathclyde, “Enhanced Frequency Control Capability (EFCC) Project,”
NATIONAL GRID, LONDON , 2017.
[6] N. GRID, “Future Energy Scenarios,” NATIONAL GRID, LONDON, 2018.
[7] SIMENS, “RELIABLE GRID PROTECTION, CHALLENGES, DRIVES, SOLUTION AND BENEFITS
SIEMENS,” SIMENS, NEWYORK, 2018.
[8] H. L. Willis, “Distributed Power Generation: Planning and Evaluation,” CRC Press, 2000.
[9] IET, “An overview of Britain's changing energy sector,” IET, LONDON.
[10] D. T. D. C. B. Dr Adam Dyśko, “Assessment of Risks Resulting from the Adjustment of Vector
Shift (VS) Based Loss of Mains Protection Settings PHASE 2,” Institute for Energy and
Environment Department of Electronic and Electrical Engineering University of Strathclyde,
GLASGOW.
[11] W. G. Rohit S. Kunte, “Comparison and review of islanding detection techniques for distributed
energy resources,” IEEE, 2008.
[12] E. Ltd, “ASSESSMENT OF ISLANDED OPERATION OF DISTRIBUTION NETWORK AND MEASURES
FOR PROTECTION,” CROWN COPYRIGHT, 2001.
[13] D. a. D. A. Tzelepis, “Impact of distributed generation mix on the effectiveness of islanded
operation detection,” Sixth Protection, Automation and Control World Conference (PAC World
2015), GLASGOW, Technology and Innovation Centre, University of Strathclyde..
[14] Z. M. Marijan Lukac, “Anti-islanding protection of distributed generators with regard to
sensitivity in a balance and power system stability,” IET, 24th International Conference &
Exhibition on Electricity Distribution (CIRED), 2017.

P a g e | 72
[15] A. Dyśko, D. Tzelepis, C. Booth, J. Pollock and D. Hill, “Practical risk assessment of the relaxation
of LOM protection settings in NIE networks' distribution system,” UNIVERSITY OF
STRATHCLYDE, Belfast, 2018.
[16] C. Li, “A review of islanding detection methods for microgrid,” 2014.
[17] K. A. J. N. A. Ku Nurul Edhura, “A review of the islanding detection methods in grid-connected
PV inverters,” Renewable and Sustainable Energy Reviews, 2013.
[18] S. REPORT, “DEVELOPMENT AND TESTING OF AN APPROCH TO ANTI-ISLANDING IN UTILITY-
INTERCONNECTED PHOTOVOLTAIC SYSTEM,” SANDIA NATIONAL LABORATORIES, 2000.
[19] K. S. I JANG, “AN ISLANDING DETECTION METHOD FOR DISTRIBUTION GENERATION USING
VOLTAGE UNBALANCE AND HARMONIC DISTORTION OF CURRENT”.
[20] M. L. A. D. a. A. P. Francesco De Mango', “Overview of Anti-Islanding Algorithms for PV
Systems. Part I: Passive Methods,” IEEE, 2006.
[21] G. Y. B. S. ARFAT SIDDIQUE, “EFFECTS OF VOLTAGE UNBALANCE ON INDUCTION MOTOR,” IEEE,
2004.
[22] S. S. U.D.DWIVEDI, “A WAVELET BASED APPROACH FOR CLASSIFICATION AND LOCATION OF
FAULTS IN DISTRIBUTION SYSTEM,” IEEE, 1999.
[23] DAUBECHIES.J, “THE WAVELET TRANSFORMS, TIME FREQUENCY LOCALIZATION AND SIGNAL
ANALYSIS,” IEEE, 1990.
[24] M. G. M. M.R.VATANI, “A NEW FAST AND RELIABLE METHODS FOR ISLANDING DETECTION
BASED ON TRANSIENT SIGNAL,” SECOND IRANIAN CONFERENCE ON SMART GRID, TAHARAN,
2012.
[25] S. U.D.DWIVEDI, “ENHANCED DETECTION OF POWER QUALITY EVENTS USING INTRA AND
INTER-SCALE DEPENDENCIES OF WAVELET COEFFICIENTS,” IEEE, 2010.
[26] U. D. M. K. M.HANIF, “WAVELET BASED ISLANDING DETECTION OF DC-AC INVERTER
INTERFACED DG SYSTEMS,” UPEC, 2010.
[27] O. C. J. W. D.C ROBERTSON, “WAVELET AND ELECTROMAGNETIC POWER SYSTEM TRANSIENT,”
IEEE, 1996.
[28] M. L. a. A. D. Francesco De Mango', “Overview of Anti-Islanding Algorithms for PV Systems.
Part II: Active Methods,” IEEEE, 2006.
[29] W. A. M.ROPP, “EVALUATION OF ISLANDING DETECTION METHODS FOR PHOTOVOLTAIC
SYSTEM RESEARCH AND DEVELOPMENT,” SANDIA NATIONAL LABORATORIES, 2002.

Loss of mains protection or anti islanding

Loss of mains protection or anti islanding

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Loss of mains protection or anti islanding

Similar to Loss of mains protection or anti islanding (20)

Recently uploaded

Recently uploaded (20)

Loss of mains protection or anti islanding