187787508 Over Current Earth Fault Setting Calculations

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Slide 1

6

th

Comprehensive Protection Training Program

at Pearl Continental L

AHORE in 2012

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Slide 2

SIEMENS

LECTURE ON

OVER CURRENT & EARTH FAULT RELAY

SETTING CALCULATIONS

AT

PEARL CONTINENTAL HOTEL

LAHORE

ON 04-09-2012

BY

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Slide 3

RELAY SET T I N G CALCU LATI ON S

A guide for the calculations of the Relay

Settings for:

Over current and Earth fault Relays

a) Definite Time Relays

b) Inverse Time Relays

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Slide 4

RELAY SETTING CALCULATIONS

1. Enlist the technical data required

in network study and

calculations of relay settings.

2. Ask from client\consultant

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 consultant\client 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

client\consultant\contractor.

10. Upload the parameters in the relays

according to the calculations

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Slide 5

RELAY SETTING CALCULATIONS

Please note that

- Minimum generation is considered for

relay setting calculations. (pick up,trip)

&

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Slide 6

PAKISTAN

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

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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

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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

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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

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-Slide 15

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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

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Slide 17

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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.

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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 I_N = S ÷ ( 3 × U ) I_N = 733A

Allowed overloading = 5% Relay's resetting ratio = Drop off

÷

Pick up R = 0.95

Relay's setting current = (I_N + I_N )

÷

R Is = 810A

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Slide 20

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 I_F=11548A

Multiples of Fault Current (PSM) = I_F ÷ I_s =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 × I_N ) =5.00 I/In

Settings recommended:

Over current plug setting =0.25 I/I_n

TMS setting =0.47

Characteristic = Normal Inverse

Instantaneous setting (Ipick up = 5 × I_N ) =5.00 I/I_n

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Slide 21

7SJ602 SETTING CALCULATIONS FOR

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 I_N = S

÷

3 × U ) I_N = 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 = ( )×(I_N

÷

R) =.05x733

÷.95=

38.57

or

Is = 39A

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Slide 22

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 I_F=1469A

Multiples of Fault Current (PSM) = I_F ÷ I_s =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 × I_N ) =5.00 I/In

Settings recommended:

Over current plug setting =0.01 I/I_n

TMS setting =0.59

Characteristic = Normal Inverse

Instantaneous setting (Ipick up = 5 × I_N ) =5.00 I/I_n

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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

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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)

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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

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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

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Slide 27

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Slide 28

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Slide 29

Protection Co ordination of inverse time relays &

Disc emulation

Disc e m ulat ion e vok e s a dropout proc e ss, w hic h be gins a fte r de ene rgiza t ion. T his Proc e ss c orre sponds t o the bac k t urn of a Fe rra ris Disc . I n c a se se ve ra l fa ults o-c o-c ur suo-co-c e ssive ly, it is e nsure d t ha t due t o t he ine rt ia of the Fe rra ris Disc , t he

h-ist ory is t ak e n into c onside ra t ion.

Conside r t he ma in ove r c urre nt re la y of e lec t ro m e c ha nic a l t ype a nd t he fe e der re la y of nume rica l t ype . T he re a re c hanc es t ha t t he

M a in re la y ma y opera t e unne ce ssa rily on repe at e d fe e de r fa ult . T o avoid t his Disc e mula t ion fe a ture is int roduc e d.

T he Disc e mulat ion fea t ure

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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

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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 t

_L

(I/ I

_L

)

2

- 1

where

t is tripping time

I is over load current

I

_L

parameterized threshold value

t

_L

parameterized time multiplier

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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.

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Slide 33

CONCEPT OF I/I

N

I

_N

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 I

_N

---4.0 I

_N

If I

_N

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 I

_N

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/ I

_N

from 0.1 to 4.0(10% to 400%)

This statement is independent of amps. We have to always look at

I/I

_N

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