Power Quality-Report-5

Study and interaction with industry
for application of power electronics
in electricity distribution system
for improvement in power quality.
-A REPORT
NESCL, Noida
Engg. Department
(2012-13)

NESCL/ NTPC MoU/R&D/Power Quality NESCL:Engg. Page 2 of 43
A study report on application of power electronics
in electricity distribution system for improvement in power quality
A REPORT
On
“Study and interaction with industry
for application of power electronics
in electricity distribution system
for improvement in power quality.”
By
M. Nageswar Rao (Manager)
S.Lokanatham (Manager)
Under the guidance of
Shri C.D. Murthy (HOD-Engg)
Shri A.K. Parhi (AGM-Engg)
Shri B.M. Singh (AGM-Engg.)
ENGINEERING DEPARTMENT
NTPC ELECTRIC SUPPLY COMPANY LIMITED

ACKNOWLEDGEMENTS
We are thankful to Shri C.D. Murthy, HOD (Engg.), NESCL for his
valuable suggestions in accomplishing this project. We express our
sincere thanks and acknowledge with deep sense of gratitude for the
guidance and encouragement rendered by Shri A.K. Parhi (AGM-
Engg.), NESCL and Shri B.M. Singh (AGM-Engg.), NESCL for sparing
their valuable time at every stage besides their friendly co operation
and guidance to complete our work successfully.
NESCL expresses its sincere gratitude to M/s L&T, M/s ABB, M/s
P2Power Solutions for their valuable support extended which helped
in preparation of the report.
Finally, we would like to thank all the people who directly and
indirectly co operated us in completing our study successfully.
Power Quality Study Team
NESCL-Engg.

PROFILE OF NTPC ELECTRIC SUPPLY COMPANY
LIMITED
NTPC Electric Supply Company Ltd. (NESCL) a wholly owned subsidiary of
NTPC was formed in the year 2002, as the electricity distribution arm of power
generation major, NTPC Ltd. NESCL, is engaged in the Rajiv Gandhi Grameen
Vidyutikaran Yojana (RGGVY) of Govt of India and other Consultancy works in
the electricity distribution sector.
NESCL has also been associated in the field of design, engineering and turn-key
execution of various works in the area of construction of EHV substations and
transmission lines from concept to commissioning. Some of the works executed
by NESCL as well as those under execution are as indicated below:
 Project management and engineering consultancy work including site
supervision for BPCL Kochi refinery for setting up 220/33 kV
Substation with 2X50 MVA 220/33 kV power Transformer along with
33 kV Gas insulated substation for supply arrangement of BPCL Kochi
refinery.
 Power supply arrangement for International Container
Transshipment Terminal, Vallarpadam on behalf of Cochin Port Trust.
 Execution of Power supply arrangement of all the five coal mining
projects of NTPC. NESCL has already taken up works related to Pakri-
Barwadih Coal mines in Jharkhand state involving construction of 220
kV Transmission Line and 220/33kV substation with 2X50 MVA
220/33 kV Power Transformer and associated 220/33 kV switch
yard.
 Construction of 66 kV transmission lines (both underground and
overhead) along with 66/11 kV substation in UT Chandigarh,
commissioned in year 2007-08.
 Turnkey execution of 3x10 MVA power transformers along with 33 kV
line at Mega Sports Complex, Hotwar Ranchi, commissioned in Dec
2008.

 Turnkey execution of following substation works on behalf of UT-
Chandigarh is under implementation:
1. 2X20 MVA, 66/11 kV Grid Sub Station at Raipur Kalan.
2. Augmentation of 66/11 KV Sub Station at Sec-52 with 1x30
MVA Power Transformer along with the associated bay.
 The company is also involved in providing supply of electricity in 5
km. area around NTPC power plants under a Government of India
scheme.
 NESCL has also positioned itself in providing consultancy and
advisory services for assisting Electricity Department of Union
Territory of Pondicherry in preparation and filing of Annual Revenue
Requirement petition and its submission/presentation and defense
before the concerned Regulatory Commission.
 NESCL has offered its services to Orissa Power Transmission
Corporation Limited (OPTCL) for rendering Pre-Award Contract
Management Services in respect of major capacity addition
undertaken by OPTCL by putting up new EHT substation, associated
lines and associated works for eleven such packages. NESCL has also
extended its services in the area of Quality Assurance and 3rd party
inspection of stock material to UPCL, UHBVN, MPMKVVCL,
MPPoKVVCL, MPPKVVCL and all the Discoms of Karnataka.
The entire gamut of services offered by NESCL is tailored to meet the
individual needs of the customer and we have created a benchmark being
receptive to our customers in dealing with various cultural issues related to
Quality Assurance, Project Management, System orientation and
Management Information System.

Table of Contents
Page No.
INTRODUCTION .......................................................................................................8
1.Background ...................................................................................................8
2.Validation of the Report ................................................................................8
3.Introduction...................................................................................................8
4.Roadmap .......................................................................................................9
5.Power Quality Study Team: ...........................................................................9
1. POWER QUALITY ...............................................................................................10
1.1 Introduction .........................................................................................10
1.2 Effect of poor Power Quality.................................................................10
a. Utility concerns..............................................................................11
b. Industrial consumer concerns .......................................................11
c. Commercial/ Residential consumer concerns................................11
1.3 What is Power Quality..........................................................................11
a. Voltage sag (dip) ...........................................................................13
b. Voltage swell..................................................................................14
c. Interruption ..................................................................................14
d. Undervoltage ................................................................................14
e. Overvoltage...................................................................................14
f. Waveform distortion (Harmonics) ................................................15
i. Sources of Harmonics...............................................................15
ii. %THD .......................................................................................16
iii. Recommended Limits ...............................................................17
g. Voltage Imbalance.........................................................................18
h. Voltage Fluctuations......................................................................18
i. Power Frequency Variations..........................................................19
2. POWER ELECTRONIC SOLUTIONS ....................................................................20
3. DISTRIBUTION STATIC VAR COMPENSATORS (D-SVC)...................................21
3.1 SVC using TCR/ FC................................................................................21
3.2 SVC using TCR/ TSC..............................................................................24
4. DISTRIBUTION STATIC SYNCHRONOUS COMPENSATORS (D-STATCOM) or
ACTIVE -FILTERS...........................................................................................25
4.1 Principle of operation...........................................................................25
4.2 Topology...............................................................................................26
4.3 Operating characteristics.....................................................................27
4.4 Modes of D-STATCOM operation ..........................................................28
a. Load compensation mode..............................................................28
b. Voltage regulation mode ...............................................................30
4.5 Product Survey .....................................................................................31

5. Dynamic Voltage Restorer (DVR) ......................................................................32
6. Power Quality Measurements............................................................................33
6.1 CASE STUDY-1: NTPC EOC Substation..................................................33
6.2 CASE STUDY-2: M/s Goldwyn Ltd., NSEZ, Noida...................................35
6.3 CASE STUDY-3: M/s Karna Apparel, NSEZ, Noida................................40
6.4 Observations:........................................................................................43
6.5 Recommendations: ................................................................................43
6.6 Conclusions:..........................................................................................43

INTRODUCTION
1. Background
As per MoU for the year 2012-13 finalized by MoP, GoI, NESCL is required to
take up this study and interact with industries and to prepare a report on
application of power electronics in improving power quality in electricity
distribution systems.
2. Validation of the Report
As a part of validation, a technical paper has been prepared based on this report
and has been submitted to CPRI, Bangalore for presentation in a conference
“National Conference on Power Distribution” organized by CPRI during 8-9th
Nov’2012.
Upon scrutiny by Technical Review Committee of the CPRI, the paper was
selected for presentation in the conference vide their mail dated 16.10.2012. A
copy of the mail is attached herewith at Annex-I.
Accordingly, the paper was presented in the Conference held at CPRI,
Bangalore on 8th Nov’2012. The technical paper presented in the CPRI
conference is attached herewith at Annex-II.
3. Introduction
Power Quality mainly deals with supply voltage magnitude disturbances (short
term) and waveform distortion of supply voltage and currents. Power quality
can only be maintained with combined effort of utilities and the consumers.
Utilities have to maintain quality supply even under increased renewable
generation and grid disturbances. Similarly, consumers have to prevent the
electrical disturbances and distortions from spreading into the distribution
system.

EN 50160 defines the quality of power and the max. acceptable levels at the
consumer’s supply terminals. Also, IEEE 519-1992 stipulates max. acceptable
levels of harmonic distortions.
This paper discusses about the spectrum of power quality, causes of power
quality problems, solutions using various power electronic technologies
suitable for distribution systems. Also, this paper presents case studies
conducted with measurements taken at three industries.
4. Roadmap
As a part of this study, following industries have been interacted to understand
various technologies and power electronic products available those help in
improving power quality in electrical distribution sector.
a) M/s P2Power Solutions, Noida
b) M/s L&T, New Delhi and
c) M/s ABB, New Delhi.
Also, Literature survey was conducted and had a detailed study of various IEEE
papers, text books, journals and industry brochures.
A detailed report has been prepared with documenting theory, various
technologies and products helpful in improving power quality in electrical
distribution system.
5. Power Quality Study Team:
Members of team are
Sh. M.Nageswar Rao Manager (Engg.), NESCL, Noida
Sh. S.Lokanatham Manager (Engg.), NESCL, Noida
The team worked under the guidance of
Sh. C.D.Murthy HOD (Engg.), NESCL, Noida
Sh. A.K.Parhi AGM (Engg.), NESCL, Noida
Sh. B.M.Singh AGM (Engg.), NESCL, Noida

1. POWER QUALITY
This chapter discusses importance of power quality in electrical distribution
system. Also, this chapter discusses about harmonics, their sources and
methods of estimation of them. Also, but not the least, the effects of poor power
quality are also discussed in this chapter.
1.1 Introduction
Power Quality has gained tremendous concern in distribution utilities as well as
consumers, and is also mandated by international standards like EN 50160 and
IEEE 519.
Generally, the power quality disturbances are caused by industries like
Automobile, Cement Steel/ foundries, Pulp processing, Printing press etc. Also,
wave form distortions are generally caused, as identified by IEEE 519:1992
standard are power converters, arc furnaces, static VAR compensator, inverters
of dispersed generation, electronic phase control of power, switched mode
power supplies and Pulse wide modulated drives.
1.2 Effect of poor Power Quality
The poor power quality in turn increases the losses in the system as well as
technical losses in the electrical product/ equipment itself. The electrical
disturbances & distortions caused by one consumer/ industry are not only
pollutes the power supply of other equipment of his own, but also pollutes the
power supply of neighboring consumers. And all the distortions are transmitted
back to the source through distribution transformers, distribution &
transmission network, thereby polluting the entire system.
Poor power quality affects badly to Utilities as well all consumers in the system,
as follows:

a. Utility concerns
i. Frequent failures of equipment
ii. Reduced life time of equipment
iii. Reduced safety levels of installations
iv. Increased carbon footprint
v. Increased kWh losses in network components like DTs and cables
etc.
vi. Reduced system capacity
vii. Nuisance tripping of safety devices
viii. Vibration and audible noise in electrical machines like motors,
transformers etc.
ix. Large neutral currents
b. Industrial consumer concerns
i. Production loss
ii. Non-compliance with utility regulations
iii. DG hunting
iv. Frequent failures of equipment
v. Reduced life time of equipment
vi. Vibration and audible noise in electrical machines like motors,
transformers etc.
vii. Low p.f. and hence penalty
c. Commercial/ Residential consumer concerns
i. Increased kWh consumption and billing charges
ii. Low p.f. and hence penalty
iii. Reduced life time of equipment
1.3 What is Power Quality
Power quality is defined by
a) Magnitude variations in fundamental voltage of power supply, and
b) Waveform distortion of fundamental voltage and current of power supply.

The term Power Quality is rather nebulous and may be associated with
reliability by electric utilities. Power Quality refers to those characteristics of
power supply that enable the equipment to work properly. Reliability refers to
the non-availability of electricity supply to consumers because of sustained
interruptions.
The common power quality issues are
a) Transients
b) Short-duration variations
a. Voltage sag
b. Voltage swell
c. Momentary interruptions
c) Long-duration variations
a. Interruption, sustained
b. Under voltages
c. Over voltages
d) Voltage unbalance
e) Waveform distortions
a. Harmonics, Inter-harmonics
b. Notching
c. Noise
f) Voltage fluctuations
g) Power frequency variations

IEEE 1159-1995 stipulates typical characteristics like time duration and voltage
magnitude variations of the above power quality distortions, as tabulated
below.
Instantaneous
(0.5–30
cycles)
Momentary
(30 cycles–
3 s)
Temporary
(3 s–1
min)
Sustained
(>1 min)
Others
Voltage sag 0.1–0.9 pu 0.1–0.9 pu 0.1–0.9 pu -- --
Voltage swell 1.1–1.8 pu 1.1–1.4 pu 1.1–1.2 pu -- --
Interruptions -- <0.1 pu <0.1 pu 0.0 pu --
Under
voltages
-- -- -- 0.8 pu --
Overvoltage -- -- -- 1.1–1.2
pu
--
Waveform
distortion
-- -- -- Steady
state
Voltage
fluctuations
-- -- -- Intermit
tent
0.1–7%
Power
frequency
variations
-- -- -- <10 s
All the above power quality issues are described below in detail.
a. Voltage sag (dip)
A Voltage sag (dip) is defined as a decrease in the root-mean-square (rms) voltage
at the power frequency for periods ranging from a half cycle to a minute.
It is caused by voltage drops due to fault currents or starting of large motors.
Sags may trigger shutdown of process controllers or computer system crashes.

b. Voltage swell
A voltage swell is defined as an increase up to a level between 1.1 and 1.8 pu in
rms voltage at the power frequency for periods ranging from a half cycle to a
minute.
c. Interruption
An interruption occurs when the supply voltage decreases to less than 0.1 pu for a
period of time not exceeding 1 min.
Interruptions can be caused by faults, control malfunctions, or equipment
failures.
d. Undervoltage
An Undervoltage is a decrease in the rms ac voltage to less than 90% at the power
frequency for duration longer than 1 min.
These can be caused by switching on a large load or switching off a large
capacitor bank. Undervoltages are sometimes due to a deliberate reduction of
voltage by the utility to lessen the load during periods of peak demand. These
are often referred to by the nontechnical term brownout.
An undervoltage will lower the output from capacitor banks that a utility or
customer will often install to help maintain voltage and reduce losses in the
system by compensating for the inductive nature of many conductors and loads.
e. Overvoltage
An overvoltage is an increase in the rms ac voltage to a level greater than 110%
at the power frequency for a duration longer than 1 min.
These are caused by switching off a large load or energizing a capacitor bank.
Incorrect tap settings on transformers can also cause undervoltages and
overvoltages.

As these can last several minutes, they stress computers, electronic controllers,
and motors. An overvoltage may shorten the life of power system equipment
and motors.
f. Waveform distortion (Harmonics)
With the increased use of non-linear loads like electronic goods, Switch mode
Power supplies, power electronic switching of power supplies, in these modern
years, the quality of power supply has been disrupted and distorted heavily.
Any distortion caused in the wave shape of voltage or current is analyzed and
synthesized (by Fourier series expansion) using harmonics.
A harmonic component in an AC power system is defined as a sinusoidal
component of a periodic waveform that has a frequency equal to an integer
multiple of the fundamental frequency of the system.
Sub-integral multiple of fundamental frequency of voltage & currents are called
Inter-harmonics or Sub-Harmonics.
i. Sources of Harmonics
Sources of harmonics are broadly categorized as follows
b) Supply side harmonics : mainly causes voltage quality distortion,
c) Load side harmonics : mainly causes current quality distortion.
Supply side harmonics are mainly caused because of
i. Generator torque pulsations, eccentricity, non-sinusoidal winding
patterns etc. causes distortions in voltage generated. No generator
can generate perfect sinusoidal voltage.

ii. Power transformer & Distribution transformers, because of non-
linear (B-H curve) magnetic properties of core, causes severe
distortions in secondary voltage and currents as shown below.
Figure 1: Harmonics Generated by Transformers
Load side harmonics are mainly caused by electrical consumers deploying
equipment/ machines having
i. Electronic switching of power supplies (SMPS) or
ii. Power electronic switching of power supply (power conditioning
devices etc.).
iii. Adjustable speed drives
ii. %THD
The most common harmonic index, which relates to the voltage waveform, is
the THD, which is defined as the root mean square (r.m.s.) of the harmonics
expressed as a percentage of the fundamental component, i.e.
1
2
2
V
V
THD
N
n
n
 ….Eq.(1)
where,
Vn is the single frequency r.m.s. voltage at harmonic n,
N is the maximum harmonic order to be considered,
V1 is the fundamental line to neutral r.m.s. voltage.

Current distortion levels can also be characterized by a THD value but it can be
misleading when the fundamental load current is low. A high THD value for
input current may not be of significant concern if the load is light, since the
magnitude of the harmonic current is low, even though its relative distortion to
the fundamental frequency is high. To avoid such ambiguity a total demand
distortion (TDD) factor is used instead, defined as:
R
N
n
n
I
I
TDD

 2
2
…Eq.(2)
This factor is similar to THD except that the distortion is expressed as a
percentage of some rated or maximum load current magnitude, rather than as a
percentage of the fundamental current. Since electrical power supply systems
are designed to withstand the rated or maximum load current, the impact of
current distortion on the system will be more realistic if the assessment is
based on the designed values, rather than on a reference that fluctuates with
the load levels.
iii. Recommended Limits
As per IEEE 519-1992, the recommended limits for Voltage THD for various
classes of loads are depicted below.
Application Class THDV % (max.)
Special System 3%
General System 5%
Dedicated System 10%

Also, the same standard recommended limits for current harmonic distortions
and %TDD are as given below.
.
where,
Isc: Maximum short-circuit current at the Point of Common Coupling (PCC).
IL: Maximum demand load current (fundamental) at the PCC.
g. Voltage Imbalance
Voltage imbalance (unbalance) is defined as the ratio of a negative- or zero-
sequence component to a positive-sequence component.
The voltage imbalance is due to single-phase loads. Uneven distribution of
single phase loads on 3-ph system leads to heavy voltage unbalance and large
neutral current.
h. Voltage Fluctuations
Voltage fluctuations are defined by their rms magnitude expressed as a
percentage of the fundamental magnitude.
Loads that exhibit continuous, rapid variations in load current can cause voltage
variations erroneously referred to as flicker. ANSI C84.1-1992 recommends that
the system voltages should lie in the range 0.9–1.1 pu.
Arc furnaces are the most common cause of voltage fluctuations in the
transmission and distribution system.

i. Power Frequency Variations
At any instant, the frequency depends on the balance between the load and the
capacity of the available generation. When dynamic balance changes, small
changes in frequency occur. In modern interconnected power systems,
frequency is controlled within a tight range as a result of good governor action.
Frequency variations beyond ±0.1 Hz are likely to occur under fault conditions
or from the loss of a major load or generating unit.

2. POWER ELECTRONIC SOLUTIONS
Conventional solutions like APFC panels, Voltage boosters, Static Balancer
Transformer etc. have poor dynamic response and are limited in improving
power quality. On the other hand, with improvement in Power Electronic
systems and microcontroller development, various solutions have been evolved
for power quality in electrical distribution systems.
The Power electronic solutions for power quality improvement can generally be
categorized in two Shunt controllers and series controllers.
a) Shunt controllers:
a. Distribution Static VAR Compensators (D-SVC)
b. Distribution Static Synchronous Compensators (D-STATCOM)
(or) Active -Filters
b) Series Controllers
a. Dynamic Voltage Restorer (DVR)
Shunt controllers protect the utility electrical system from the unfavorable
impact of customer loads. They are recommended mainly for mitigation of the
causes of disturbances, and not their effects in distanced nodes of a power-
electronics system. Series controllers are preferred in case when reduction of
disturbances effects is required, that leads to protection of sensitive loads from
the deterioration in the supply-side voltage.

3. DISTRIBUTION STATIC VAR COMPENSATORS (D-SVC)
The Static VAR Compensators have been widely used by utilities since the mid
1970s in the world. SVC provides reactive power, load balancing, power factor
improvement, and also helps in reducing voltage variations and associated light
flicker due to arc furnace loads.
SVC is based on conventional capacitors and inductors combined with thyristor
switching facilities. Basically, there are two variations of SVC as follows:
i) SVC using a TCR/ FC
ii) SVC using a TCR/ TSC
3.1 SVC using TCR/ FC
In this arrangement, two or more FC (fixed capacitor) banks are connected to a
TCR (thyristor controlled reactor) through a step-down transformer, as shown
in the figure below.
The rating of the reactor is chosen larger than the rating of the capacitor by an
amount to provide the maximum lagging VARS that have to be absorbed from
the system. By changing the firing angle of the thyristor controlling the reactor
from 90° to 180°, the reactive power can be varied over the entire range from
maximum lagging VARS to leading VARS that can be absorbed from the system
by this compensator.

It is common to use wye–delta transformers with SVCs because the delta
windings provide a path to circulate zero-sequence components of the
fundamental and other harmonic currents.
If all the three-phase currents are balanced even though they are distorted with
harmonics, then all the triplen harmonics are of zero-sequence nature.
However, if all the three-phase currents do not contain balanced harmonic
currents, then the triplen harmonics not only contain zero-sequence
components but will also contain both positive- and negative-sequence triplen
harmonics. Positive- and negative-sequence components of the triplen
harmonics can still flow into the system from nonlinear harmonic-producing
loads even with wye–delta transformers.
The sinusoidal steady-state characteristics such as voltage–current (or voltage
and MVArs supplied by the SVC) relationship of an SVC is shown in Figure
below. It consists of three parts. In the regulated region, the voltage and current
are linearly related. Outside the regulated interval, output current (VAR) versus
voltage characteristic of the compensator is the same as that of the capacitor
(low voltage) or an inductor (high voltage).

Disadvantages:
a) The main disadvantage of this configuration is the significant harmonics
that will be generated because of the partial conduction of the large
reactor under normal sinusoidal steady-state operating condition when
the SVC is absorbing zero MVAr.
These harmonics are filtered in the following manner. Triplex harmonics
are canceled by arranging the TCR and the secondary windings of the
step-down transformer in delta connection. The capacitor banks with
the help of series reactors are tuned to filter fifth, seventh, and other
higher-order harmonics as a high-pass filter.
b) Further losses are high due to the circulating current between the
reactor and capacitor banks. The losses in these types of SVCs are shown
in Figure below.
c) These SVCs do not have a short-time overload capability because the
reactors are usually of the air-core type. In applications requiring
overload capability, TCR must be designed for short-time overloading, or
separate thyristor-switched overload reactors must be employed.

3.2 SVC using TCR/ TSC
This compensator comprises of Thyristor controlled reactor and Thyristor
switched Capacitor.
This type of SVC overcomes two major shortcomings of the earlier
compensators by
a) reducing losses under operating conditions and
b) better performance under large system disturbances.
Figure below shows the arrangement of this SVC with a TCR in parallel with
several TSC banks (say, n).
In view of the smaller rating of each capacitor bank, the rating of the reactor
bank will be 1/n times the maximum output of the SVC, thus reducing the
harmonics generated by the reactor. In those situations where harmonics have
to be reduced further, a small amount of FCs tuned as filters may be connected
in parallel with the TCR.

4. DISTRIBUTION STATIC SYNCHRONOUS
COMPENSATORS (D-STATCOM) or ACTIVE -FILTERS
D-STATCOM and Active filters are synonymously called. Development & design
wise, it is called as D-STATCOM and the same is called as Active filter in the
industrial market. By topology of the circuit, D-STATCOMs are called as shunt
Active filters.
D-STATCOM is the most important controller for distribution networks. It has
been widely used since the 1990s.
D-STATCOM helps in precisely
i) regulate the system voltage
ii) Improve voltage profile
iii) Reduce voltage harmonics
iv) Reduce transient voltage disturbances, and
v) Load compensation.
In most applications, a DSTATCOM can use its significant short-term transient
overload capabilities to reduce the size of the compensation system needed to
handle transient events. The short-term overload capability is up to 325% for
periods of 1 to 3 seconds, which allows applications such as wind farms and
utility voltage stabilization to optimize the system’s cost and performance.
Due to its lesser power handling requirement, PWM converters (at higher
switching frequencies) are used (with IGBTs in D-STATCOM as compared to
Thyristors used in STATCOM (FACTS controllers).
4.1 Principle of operation
The equivalent circuit of a power system with a DSTATCOM is shown below.

DSTATCOM generates a variable voltage, Vd, that is very nearly in phase with
the source voltage, Vs. The inductance in this simplified circuit, L, consists of the
inductance of the coupling transformer and filter. The voltage across the
inductance, VL, equals Vs-Vd and is small in per-unit terms. . . of the order of 5-
20%.
If Vs > Vd, VL is in phase with Vs and current IL lags Vs by 90°; DSTATCOM, acting
as a generator, produces leading (inductive) reactive current.
If Vs < Vd, VL is antiphase with Vs and current IL leads Vs by 90°; DSTATCOM
produces lagging (capacitive) reactive current.
4.2 Topology
DSTATCOM controllers can be constructed based on both VSI and CSI
topologies, as shown below.

The VSI converter is connected to the feeder via a reactor Lf and has a voltage
source (Capacitor CD) on the dc side. On the other hand, the CSI converter is
connected on the AC side via capacitor Cf and has a current source (inductor LD)
on the dc side.
In practice, CSI topology is not used for D-STATCOM due to
a) Higher loses on the dc reactor compare to the dc capacitor of VSI
b) Requirement of reverse-blocking semiconductor switches, which have
higher losses than reverse-conducting switches of VSI.
c) VSI has advantage that Inductance of coupling transformer (if present)
adds to Lf (of ac filter), thus reducing the size of ac filter inductance.
4.3 Operating characteristics
The static V-I characteristic of D-STATCOM reactive power is symmetrical as
shown in Fig. below.

Assuming lossless operation, the averaged (but not instantaneous) active power
has to be zero. There are no similar limitations for reactive power, because it is
only exchanged between phases, and is not converted between the AC and DC
sides of D-STATCOM VSI.
4.4 Modes of D-STATCOM operation
There are two modes of D-STATCOM operation: load compensation in current
control mode and voltage regulation in voltage control mode.
a. Load compensation mode
In the load-compensation mode, D-STATCOM is controlled in current mode. In
this current control mode, the feeder currents are made proportion to the
fundamental, positive component of terminal voltage. The control system of D-
STATCOM has to generate
i) reference currents,
ii) compensating harmonic, unbalance and fundamental reactive
components of non-linear load supply currents.
The required rated power of load-compensating D-STATCOM depends only on
i) reactive power,
ii) harmonic distortion and
iii) power of the compensated load.

In general, D-STATCOM is capable of compensating current disturbances from
harmonics to long duration effects, including active power transients.
The possibility and effectiveness of compensation of a particular voltage-quality
problem depends on
i) the topology and
ii) rated power of the controller, as well as on
iii) the capacity of the energy-storage (ES) system connected on the D-
STATCOM DC side.
Load compensation provides also a reduction of voltage distortion related with
the feeder voltage drop. The level of distortion reduction depends on
i) the configuration of the distribution network, as well as
ii) The ratio between the power of the compensated nonlinear load and the
feeder short-circuit power.
The block diagram of a control system for load compensating D-STATCOM is
given in the Figure below.
Despite current compensation, a D-STATCOM controller can be used at the
same time for AC/DC power conversion, for example providing a supply for a

DC feeder or micro-DC distribution system, especially in distributed generation
systems.
b. Voltage regulation mode
The idea of voltage regulation using D-STATCOM is consistent with D-SVC,
discussed in previous chapter. It is realized by compensating reactive power
(i.e. by injecting or absorbing reactive power). The advantage of D-STATCOM
over D-SVC is also V-I characteristics and dynamics, but this controller is more
expensive.
D-STATCOM in voltage regulation mode, requires higher compensating power
than for load compensation.
The block diagram of a voltage-regulating D-STATCOM is presented in Figure
below.

4.5 Product Survey
PureWave DSTATCOM of M/s S&C Electric Company utilizes ±1.25 MVA / 3.3
MVAR PWM Inverters in a modular arrangement. The product specifications are
as follows:
Specifications
System Voltage Continuous Output 480 V to 35 kV, 50 or 60 Hz
Short-Term Current Rating
264% for 2 seconds, ramping to 100% at 4 seconds; or
264% for 3 seconds, stepping directly to 100%
Reactive Current Response Time 2 to 4 milliseconds
Inverter IGBT, pulse-width modulated at 4860 Hz
Temperature Range -40° to +50° C
Efficiency >98% typical
Cooling Ambient air cooling

5. Dynamic Voltage Restorer (DVR)
DVR is a series power electronic controller, protects sensitive loads from all
supply-side disturbances other than outages. They are connected in series to
the feeder between supply and load. They operate as synchronous voltage
source and inject voltage into the feeder in phase with supply voltage and with
required waveform to mitigate supply side disturbances, and thereby
maintaining quality power at the load side. A typical location and operation
principle of DVR is shown in figure below.
DVRs can be divided into two groups with and without energy storage (ES). ES
devices like batteries, capacitors or flywheels are used to store and deliver
energy during disturbances. In cases of DVR without internal ES, the energy is
taken from the supply grid during disturbances.

6. Power Quality Measurements
Power Quality Measurements were carried out at following locations on Low
voltage side of the incomers.
1. NTPC EOC Substation (33/0.4 kV)
2. M/s Goldwyn Ltd., NSEZ, Noida- An LED manufacturing unit
3. M/s Karna Apparels (P) Ltd., NSEZ, Noida- A garment factory
6.1 CASE STUDY-1: NTPC EOC Substation
Measurements were carried out at 33/0.4kV substation of NTPC EOC building
on the low voltage side of incomer 9R using Power analyser KRYKARD.
The results of the measurement are tabulated as follows:
R Y B N R Y B R Y B R Y B PF1 PF2 PF3
INCOMER OF 9R(27july) #1 307 360 348 53 5 6 6 240 240 240 1.3 1.4 1.4 0.86 0.84 0.81
#2 270 308 327 15 15 14 255 256 254 1.9 2.1 1.8 0.82 0.82 0.74
#3 91 105 86 71 59 68 257 256 257 3.2 3.3 3.1 0.52 0.75 0.59
INCOMER OF 9R(28july) #4 202 229 254 44 13 13 13 247 248 246 2.1 2.1 2.2 0.88 0.86 0.78
CASEContents
Arms iTHD% Vrms vTHD% PF
The phase currents variations are recorded and are as follows:
R Phase Y Phase B Phase N Phase Critical Points
Legend

100.0
150.0
200.0
250.0
300.0
350.0
400.0
A
3:29:30.000 PM
7/27/2012
12:40:58.000 PM
7/28/2012
4 h/Div
21:11:28 (h:min:s)
The current THD% of the three phases is also recorded and is as follows:
5.000
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
55.00
60.00
65.00
70.00
75.00
80.00
85.00
%
3:29:30.000 PM
7/27/2012
12:40:58.000 PM
7/28/2012
4 h/Div
21:11:28 (h:min:s)
Observations:
It is inferred from above measurements and recordings that
i) % Unbalance of phase currents is very high, of the order of 15%.
ii) Loads are highly non-linear and pulsating.
iii) % Current THD increases to abnormal values upto 75%.

6.2 CASE STUDY-2: M/s Goldwyn Ltd., NSEZ, Noida
Measurement was carried out on incomer LT cables housed inside the LT
distribution panel. These LT cables are run from the 11/0.433kV Distribution
Transformer and are 2 runs of single core type for R-ph, Y-ph, B-ph and Neutral.
These 2 runs of cables are terminated on common LT busbars inside the panel.
Due to limitation in clamp-on CT diameter, measurement was conducted in 2
stages. One set of data recorded on one set of cables and the other set of data on
the 2nd set of cables inside the panels. Neutral current was calculated by the
Instrument, based on the three phase current measurements.
Measurements on 1st set of cable (R1,Y1,B1) and 2nd set of cable (R2,Y2,B2)
are as follows:
Measurement on 1st set of cable (R1,Y1,B1):
Figure 2: Measurement results on 1st set of cables
Note: -ve sign in currents & power is due to clamp of meter CTs in reverse
direction, hence they should be considered +ve for power drawal from UPPCL.
The voltage waveform measured is as follows:

Basic scope / File: 43.DAT
-400
-360
-320
-280
-240
-200
-160
-120
-80
-40
0
40
80
120
160
200
240
280
320
360
400
U1 I 1 U2 I 2 U3 I 3
Figure 3: Voltage waveforms on 1st set of cable
CT current setting in the meter was 10A whereas the clamp on CT used with the
instrument was of 1000A rating, hence multiplying factor was derived as 100
(1000A/10A).
-2
-2
-2
-1
-1
-1
-1
-1
0
0
0
0
0
1
1
1
1
1
2
2
2
U1 I1 U2 I2 U3 I3
Figure 4: Current waveforms on 1st set of cable
M.F. for current readings = 100.
Measurement on 2nd set of cable (R2,Y2,B2):

Figure 5: Measurement results on 2nd set of cables
Note: -ve sign in currents & power is due to clamp of meter CTs in reverse
direction, hence they should be considered +ve for power drawal from UPPCL.
The voltage waveform measured is as follows:
-400
-360
-320
-280
-240
-200
-160
-120
-80
-40
0
40
80
120
160
200
240
280
320
360
400
U1 I1 U2 I 2 U3 I 3
Figure 6: Voltage waveforms on 2nd set of cable

-2
-2
-2
-1
-1
-1
-1
-1
0
0
0
0
0
1
1
1
1
1
2
2
2
U1 I1 U2 I2 U3 I3
Figure 7: Current waveforms on 2nd set of cable
M.F. for current readings = 100.

Harmonic measurement was also carried out, and the current-harmonic
spectrum was recorded. The bar-graphs for 1st set of cable (R1,Y1,B1) and 2nd
set of cable (R2,Y2,B2) are as follows:
Pha
se
Current Harmonic spectrum (measured)
1st set of cable (R1,Y1,B1) 2nd set of cable (R2,Y2,B2)
R-
ph
Harmonics / Curr Ph1 / File:43.DAT
0 4 8 12 16 20 24 28 32 36 40 44 48 52
0
3.3
6.7
10.0
13.3
16.7
20.0
23.3
26.7
30.0
33.3
36.7
40.0
43.3
46.7
50.0
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56
0
3.3
6.7
10.0
13.3
16.7
20.0
23.3
26.7
30.0
33.3
36.7
40.0
43.3
46.7
50.0
Y-
ph
H armonics / Curr Ph2 / File:43.DAT
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56
0
0.7
1.3
2.0
2.7
3.3
4.0
4.7
5.3
6.0
6.7
7.3
8.0
8.7
9.3
10.0
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56
0
0.7
1.3
2.0
2.7
3.3
4.0
4.7
5.3
6.0
6.7
7.3
8.0
8.7
9.3
10.0
B-
ph
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60
0
1.3
2.7
4.0
5.3
6.7
8.0
9.3
10.7
12.0
13.3
14.7
16.0
17.3
18.7
20.0
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56
0
3.3
6.7
10.0
13.3
16.7
20.0
23.3
26.7
30.0
33.3
36.7
40.0
43.3
46.7
50.0
NOTE: %THD(I) is displayed in the bar-graphs at 64th harmonic no.

6.3 CASE STUDY-3: M/s Karna Apparel, NSEZ, Noida
Measurement was carried out on incomer LT cables of both LT feeders
separately.
a) 1st LT feeder is that connected on 250kVA distribution transformer with
sanctioned load of 175kVA.
b) 2nd LT feeder is that connected on common 1000kVA distribution
transformer (common to 4 neighboring industries). Sanction load for M/s
Karna from this transformer is 89kVA.
The measurements on 1st & 2nd LT feeder are carried out separately, and the
meter recordings are as follows:
Measurement on 1st LT feeder:
The phase-wise electrical parameters are recorded in the meter, and are as
follows:
The scope of waveforms of voltage and currents of all phases is as follows:

Basic scope / File: 01_01_01.DAT
-400
-360
-320
-280
-240
-200
-160
-120
-80
-40
0
40
80
120
160
200
240
280
320
360
400
U1 I 1 U2 I 2 U3 I 3
M.F. for voltage & current readings = 1.
Measurements carried out on 2nd LT feeder:

Scope:
Basic scope / File: 01_01_05.DAT
-400
-360
-320
-280
-240
-200
-160
-120
-80
-40
0
40
80
120
160
200
240
280
320
360
400
U1 I 1 U2 I 2 U3 I 3
Also, the current harmonics are recorded for both 1st & 2nd LT feeders and are
as follows:
Phase Current Harmonic spectrum (measured)
1st LT feeder source 2nd LT feeder source
R-ph
Harmonics / Curr Ph1 / File:01_01_01.DAT
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
0
1.3
2.7
4.0
5.3
6.7
8.0
9.3
10.7
12.0
13.3
14.7
16.0
17.3
18.7
20.0
H ar monics / C ur r Ph1 / File:01_01_05.DAT
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
0
1.3
2.7
4.0
5.3
6.7
8.0
9.3
10.7
12.0
13.3
14.7
16.0
17.3
18.7
20.0
Y-ph
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
0
3.3
6.7
10.0
13.3
16.7
20.0
23.3
26.7
30.0
33.3
36.7
40.0
43.3
46.7
50.0
H armonics / Curr Ph2 / File: 01_01_05.DAT
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
0
1.3
2.7
4.0
5.3
6.7
8.0
9.3
10.7
12.0
13.3
14.7
16.0
17.3
18.7
20.0

B-ph
Harmonics / Curr Ph3 / File : 01_0 1_01 .DAT
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
0
1.3
2.7
4.0
5.3
6.7
8.0
9.3
10.7
12.0
13.3
14.7
16.0
17.3
18.7
20.0
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
0
1.3
2.7
4.0
5.3
6.7
8.0
9.3
10.7
12.0
13.3
14.7
16.0
17.3
18.7
20.0
6.4 Observations:
In all the above case studies, it found that the
a) load currents are generally polluted with heavy harmonic currents.
Current THD levels are predominantly higher than 15%, much higher
than recommended limit of 5%.
b) Loads are unbalanced.
6.5 Recommendations:
Because of above observations, it is recommended in all the locations with D-
STATCOM (active filter), as it can mitigate load unbalance, harmonic currents.
Also, the solution provides dynamic reactive support.
6.6 Conclusions:
It is generally observed from the case studies conducted that the current
distortions are very high at consumers’ PCC, and the loads are high unbalanced.
Also, due to increased use of computers, switch mode power supplies and
controlled supplies, lot of harmonics are being injected into the system.
It is high time for distribution utilities as well as consumers to install power
electronic controllers to mitigate power quality problems and to restrict the
disturbances from spreading into the system.
---*---*---

Power Quality-Report-5

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