Over-Current-Earth

1. Slide 1
6th Comprehensive Protection Training Program
at Pearl Continental L AHORE in 2012
A TYPICAL POWER SYSTEM
NETWORK

2. Slide 2
SIEMENS
LECTURE ON
OVER CURRENT & EARTH FAULT RELAY
SETTING CALCULATIONS
AT
PEARL CONTINENTAL HOTEL
LAHORE
ON 04-09-2012
BY
SIEMENS PAKISTAN ENGINEERING COMPANY
LTD

3. Slide 3
RELAY SETTING CALCULATIONS
A guide for the calculations of the Relay
Settings for:
Over current and Earth fault Relays
a) Definite Time Relays
b) Inverse Time Relays
For Power Transformers & 11kv feeders

4. Slide 4
RELAY SETTING CALCULATIONS
1. Enlist the technical data required in network study and
calculations of relay settings.
2. Ask from clientconsultant to provide essential technical data
relating to the existing network and equipment needed in the subject
matter.
3. Study carefully the protection schemes designed for the
project.
4. Enlist the protection relays with their functions to be used.
5. Chalk out which type of documents are agreed to submit to
consultant/client.
6. Arrange the content/index sheet of the relays, need to settings'
calculations.
7. Submission of proposed relay settings to the consultantclient for
approval.
8. Arrange a meeting to clarify technical and disputed points
regarding to the submitted document for the approval.
9. Finalize the relays setting calculations with duly signed from
clientconsultantcontractor.
10.Upload the parameters in the relays according to the calculations
at site for pre-commissioning and testing.

5. Slide 5
RELAY SETTING CALCULATIONS
Please note that
- Minimum generation is considered for
relay setting calculations. (pick up,trip)
&
- Circuit Breaking capacity is calculated
for maximum generation possible.

6. Slide 6
PAKISTAN
G
G
1 2
3
4
POWER HOUSE STATION A
132 kV
STATION B
132 kV
Boundary of Protection Zones are decided by Location of CT’s
X Circuit Breaker
1 Generator Protection Zone
2 Generator Transformer Unit Protection Zone
3 Bus Bar Protection Zone
4 Transmission Line Protection Zone
PROTECTION IN SMALL ZONES
USING OVERLAPPING PRINCIPLE

7. Slide 7

8. Slide 8
Definite Time Over current Characteristic

9. Slide 9
Inverse time Over current Characteristic

10. Slide 10

11. Slide 11
Normal Inverse time characteristic of relay 7SJ60

12. Slide 12
SETTING DEFINITE TIME OVERCURRENT
RELAYS
Over current Relays has a wide range of applications. It can be
applied where there is an abrupt change of current due to faulty
condition.
These relays are used for protection of Motors, Transformers,
Generators and Transmission Lines etc. In distribution networks
these are the main protection whereas in HV and EHV systems,
these are used as back up protection. Although there is no hard
and fast rule for use of definite time or inverse time relays and
one can decide by looking into the site requirements.
NTDC and the utilities in Pakistan
however have standard practice to use
Inverse time relays for back up of Motors,
Transformers and Generators. For HV and
EHV lines, definite time over current relays
are used for back up purpose.

13. Slide 13
SETTING DEFINITE TIME OVERCURRENT
RELAYS
Definite time over current relays have
adjustable over current elements. When an
element picks up, it energizes a built in time
element which initiates a tripping signal after
elapse of set time. In definite time over
current Relays, we have to set,
The over current element for its pick up
value, the high set element for its pick up
value along with the time delays required.
The instantaneous element pick up
value for the current is to be selected
whereas time setting is instantaneous.

14. Slide 14
7SJ602 SETTING POSSIBILITIES
OVERCURRENT RELAY 7SJ602
PHASE FAULTS EARTH FAULTS
STAGE I> DEFINITE TIME DEFINITE TIME
OR OR
IDMTL IDMTL
STAGE I>> DEFINITE TIME DEFINITE TIME
OR OR
INSTANTANEOUS INSTANTANEOUS
STAGE I>>> INSTANTANEOUS - - - - - - - - - - - -

15. Slide 15
OVERCURRENT RELAY SETTINGS

16. Slide 16
OVERCURRENT RELAY SETTINGS
The relay at the far end B is set with shortest
operating time. The Relay on upstream which
is at end A has to be time graded against
relay at end B with a minimum time difference
of 200-300mSec for numerical relays and of
400-500mSec for electro-mechanical relays.
The relay at end B is required to be set with
the minimum operating time IDMTL mode and
to be set for TMS of 0.1or 0.05 Time Dial
whichever setting is available. The relay at
end A has to be set accordingly.

17. Slide 17
SETTING OF OVER CURRENT RELAYS

18. Slide 18
OVERCURRENT RELAY SETTINGS
In the previous diagram, the relay at far end (D) is
set with shortest operating time. Relays on the
upstream are to be time graded against the next
down stream relay in steps of 0.2 Secs.
Definite time characteristic is selected where
Source Impedance is quite larger compared to the
line impedance. This means small current
variation between near and far end faults.
The inverse mode is selected where fault current
is much less at the far end of the line than at the
local end.
(Selection also depends on the utility preference looking into their
operational requirements.)

19. Slide 19
7SJ602 SETTING CALCULATIONS FOR
AUTOTRANSFORMER 3x200 MVA 500KV
3 × 200 MVA Auto-transformer HV Winding Circuit
Time Over Current Relay Type: 7SJ6021-5EB20-1FA0
CT Ratio : N = 3250/1
Rated power: S = 600MVA
Rated voltage: (at minimum tap) U = 472.5KV
Required Settings:
Plug Setting
Characteristic to be selected
Time Multiplier Setting (TMS)
High Set Element Settings, I >>
Instantaneous Element Setting, I >>>
Plug Setting:
Autotransformer HV winding rated current IN = S ÷ ( 3 × U ) IN = 733A
Allowed overloading = 5%
Relay's resetting ratio = Drop off ÷ Pick up R = 0.95
Relay's setting current = (IN + IN ) ÷ R Is = 810A
Corresponding secondary current = Is ÷ N = 0.25A

20. Slide 20
7SJ602 SETTING CALCULATIONS FOR
AUTOTRANSFORMER 3x200 MVA 500KV
Characteristic to be selected:
Normal Inverse Characteristic is selected according to the NTDC System practice.
Usually for inductive loads, inverse time characteristics are selected.
For line feeders, definite time characteristics are suggested.
Time Multiplier Setting:
Fault current at HV Connection of autotransformer IF =11548A
Multiples of Fault Current (PSM) = IF ÷ Is =14.25
As per IEC Normal Inverse characteristic =0.14÷{(14.25)0.02-1}
Operating time at TMS = 1 A =2.565 sec.
For selectivity as backup, tripping time chosen B =1.200 sec.
Required time multiplier setting, = B ÷ A TMS = 0.47
High Set Element setting = to be blocked
Instantaneous setting (Ipick up = 5 × IN ) =5.00 I/In
Settings recommended:
Over current plug setting =0.25 I/In
TMS setting =0.47
Characteristic = Normal Inverse
Instantaneous setting (Ipick up = 5 × IN ) =5.00 I/In
High Set Element Settings, I >> IE >> = Blocked

21. Slide 21
7SJ602 SETTING CALCULATIONS FOR
AUTOTRANSFORMER 3x200 MVA 500KV
3 × 200 MVA Auto-transformer HV Winding Circuit
Earth Fault Time Over Current Relay Type: 7SJ6021-5EB20-1FA0
CT Ratio : N = 3250/1
Rated power: S = 600MVA
Rated voltage: (at minimum tap) U = 472.5KV
Required Settings:
Plug Setting
Characteristic to be selected
Time Multiplier Setting (TMS)
High Set Element Settings, IE >>
Instantaneous Element Setting, IE >>>
Plug Setting:
Autotransformer HV winding rated current IN = S ÷ 3 × U ) IN = 733A
Minimum fault current considered as percentage of rated current = 5%
(for purpose of pick up of relay)
Relay's resetting ratio = Drop off ÷ Pick up R = 0.95
Relay's setting current = ( )×(IN ÷ R) =.05x733 ÷.95=38.57 or Is = 39A
Corresponding secondary current = Is ÷ N = 0.01A

22. Slide 22
7SJ602 SETTING CALCULATIONS FOR
AUTOTRANSFORMER 3x200 MVA 500KV
Characteristic to be selected:
Normal Inverse Characteristic is selected according to the NTDC System practice.
Usually for inductive loads, inverse time characteristics are selected and
For line feeders, definite time characteristics are suggested.
Time Multiplier Setting:
Fault current at HV Connection of autotransformer IF =1469A
Multiples of Fault Current (PSM) = IF ÷ Is =38.07
As per IEC Normal Inverse characteristic =0.14÷{(38.07)0.02-1}
Operating time at TMS = 1 A =1.854 sec.
For selectivity as backup, tripping time chosen B =1.100 sec.
Required time multiplier setting, = B ÷ A TMS = 0.59
High Set Element Setting = to be blocked
Instantaneous setting (Ipick up = 5 × IN ) =5.00 I/In
Settings recommended:
Over current plug setting =0.01 I/In
TMS setting =0.59
Characteristic = Normal Inverse
Instantaneous setting (Ipick up = 5 × IN ) =5.00 I/In
High Set Element Settings, I >> IE >> = Blocked

23. Slide 23
OVER CURRENT RELAY SETTINGS FOR 11KV
FEEDER
11 kV Outgoing Panel
CT Ratio = 400/5 = 80 Relay 7SJ602 O/C Settings
Calculations
Load Current = 360 A
Relay Nominal Current = 5A
___________________________________________________________________________
Settings Required
1) Characteristic to be chosen
2) Plug Setting
3) Time Multiplier Setting TMS
4) High Set elements settings I >> IE >>
5) Instantaneous element setting I >>>
___________________________________________________________________________
PHASE FAULT: Ip > (Pick Up)
1) Characteristic = Normal Inverse (IEC)
2) Plug Setting
Considering Full Load Current. = 360 A
Permissible over loading = 10 %
Relays Resetting ratio = Drop off/Pick up = 0.95
Relay setting current = 360x1.1 = 417 A
.95
Secondary Current = 417 = 5.2 A
80
Selected Pick Up Setting = 1.04
3) Time Multiplier Setting
Assuming fault current = 1350 A (an hypothetical value)
Multiple of Fault Current (PSM) = 1350 = 3.23
417

24. Slide 24
OVER CURRENT RELAY SETTINGS FOR 11KV
FEEDER (continues)
Operating time as per
IEC NI Characteristics = 0.14 = 0.14 = 5.24
(3.23 0.02
– 1) 0.0267
Time required for Relay Operation is = 300 mSec ( Normally site requirements should be
considered. )
Therefore: TMS = _0.3_ = 0.057
5.24
PHASE FAULT: Ip >> (High Set)
1) Characteristic = Definite Time _
2) Plug Setting
Considering 4.0 times the Pick up Current.
Secondary Current = 1668 = 20.85 A
80(ct ratio)
Selected Pick Up Setting = 20.85/ 5 =4.17
3) Time Setting
= 0.1 s (to be chosen by the engineer as per requirement)
PHASE FAULT: Ip>>> (Instantaneous)
1) Characteristic = Instantaneous
2) Plug Setting
Considering 5.0 times the Pick up Current.
Secondary Current = 417x5 = 26.05 A
80
Selected Pick Up Setting = 26.05/5 = 5.2
(or we can calculate from I pick up which will be 1.04 x 5 = 5.20)
(Please note that the fault current is to be calculated based on fault calculation study on HT side
and considering the secondary impedance of the Transformer installed )

25. Slide 25
EARTH FAULT SETTINGS FOR 11KV FEEDER
Relay 7SJ602 E/F Settings
Calculations
EARTH FAULT: Ie> (Pick Up)
CHARACTERISTIC SELECTED = NORMAL INVERSE (IEC)
Plug Setting
Considering NTDC practice to set the E/F element pick up at 20% of ct
sec. rated current. = 0.2 x 5 = 1 (effective value in amps = 80 Amps)
(Utilities normally select earth fault element pick up from 10% to 20%. At
lower pick up values, sensitivity increases and stability reduces. At
higher pick up, the sensitivity is reduced but stability is increased.
Normally time of operation is set equal to phase operation time.)
Time Multiplier Setting
Assuming single phase to ground fault current = 650 Amps
Multiple of Fault Current = 650 = 7.71
84.2
Operating time as per
IEC NI Characteristics = 0.14 = 0.14 = 3.365
(7.71 0.02
– 1) 0.0416

26. Slide 26
EARTH FAULT SETTINGS FOR 11KV FEEDER
Time required for Relay
Operation is = 0.3 Sec ( to be selected considering site
conditions)
Therefore: TMS = 0.3 = 0.089
3.365
EARTH FAULT: Ie>> (Instantaneous element setting)
1) Characteristic = Instantaneous
2) Plug Setting
Considering fault Current = 650A
= 650 = 8.125
80
Pick Up Setting for instantaneous element = 8.125/5=1.625
(It is to be noted that settings are selected keeping in view
the site conditions and past experience. No hard and fast
rules can be chalked out. These examples are to show the
procedure only. )

27. Slide 27
Thank you for your Attention

28. Slide 28
CONSTRUCTION OF ELECTRO-
MECHANICAL RELAYS

29. Slide 29
Protection Co ordination of inverse time relays &
Disc emulation
Disc emulation evokes a dropout process,
which begins after de energization. This
Process corresponds to the back turn of
a Ferraris Disc. In case several faults o-
ccur successively, it is ensured that due
to the inertia of the Ferraris Disc, the h-
istory is taken into consideration.
Consider the main over current relay of electro mechanical type and
the feeder relay of numerical type. There are chances that the
Main relay may operate unnecessarily on repeated feeder fault.
To avoid this Disc emulation feature is introduced.
The Disc emulation feature
Offers its advantages when the grading co ordination chart of
the time over current protection is combined with other devices
(elect. Mech or induction base) connected to the system.

30. Slide 30
SLAVE POINTER AND MEAN
VALUES
Slave pointer and Mean values is
basically a measuring technique to
measure the Maximum , Minimum and
average values of waveform. The
waveform can be of current or voltage.

31. Slide 31
THERMAL OVER LOAD PROTECTION
The thermal Over load protection prevents the protected object (
cables, motors and transformers etc) from damage caused by
thermal over loading. This protection operates independent on the
time over current and unbalanced load protection. It can work with
memory or without memory.
OVER LOAD PROTECTION WITHOUT MEMORY
If the overload protection without memory is selected, the tripping
time is calculated according to a formula. When the current in any
phase exceeds threshold value, timer picks up. Trip command is
given after the time has elapsed. This method is easy in handling.
t= 35x tL
(I/ IL )2 - 1
where
t is tripping time
I is over load current
IL parameterized threshold value
tL parameterized time multiplier
(tripping time with 6 times the
threshold value IL)

32. Slide 32
THERMAL OVER LOAD PROTECTION
OVER LOAD PROTECTION WITH MEMORY
The unit computes the temperature rise according to a
thermal single body model (thermal replica). This method
requires some knowledge of the protected object, its
ambient context and its cooling temperature etc.
This method is used when the object is to be operated at
the limit of its performance.

33. Slide 33
CONCEPT OF I/IN
IN is the rated current of the relay and also the secondary current
of the Current Transformer. They should match with each other so
that correct setting and pick up values could be selected.
Example: In the 7SJ602 relay, the phase current pick up I range
has been defined as 0.1 IN ------4.0 IN
If IN is 1 amp then it is easy to understand that the pick up range
will be from 0.1 amp to 4.0 amp
However if IN is 5 amp then the pick up range will be from 0.5 to 20
amps
To make it simpler we can write the above pick up range as
I/ IN from 0.1 to 4.0(10% to 400%)
This statement is independent of amps. We have to always look at
I/IN and set the relay from 0.1 to 4.0
Assume ct 100/1,relay rated current 1, the relay pick up set at 1
means relay will pick up at 100 Amps in primary
And if we assume ct of 100/5, relay rated current 5, the relay pick
up set at 1 means that relay will pick up at 100 Amps
(ct 100/5 relay 1 amp- relay pick up setting possible 2 to 80 Amp)
(100/5 means 20 relay can be set 20 x 0.1-4.0 i.e. 2-80 Amps)