Rudolf Simon Compatibiliteitsmodus

CT Requirements of Distance RelaysExample MiCOM P43x range

Rudolf Simon, Dr.-Ing.Product Manager

Schneider Electric Energy – Frankfurt / Germany

Agenda

Impact of CT saturation on distance measurementeasu e e

Determination of relays CT requirements

CT sizing based on application data

Schneider Electric 2- AFS/M-F – Rudolf Simon – November 2011

Impact of CT saturation on distance measurement

CT saturation causes measurement errorsExample based on Fourier Filtering:Example based on Fourier Filtering:Fundamental current magnitude measurement value is too small⇒ impedance gets bigger

St ti I>> / Z<300

⇒ Starting I>> / Z< - may pick up delayed or - falsely reset temporarily

50

100

150

200

250

i''p(t) in Ais(t) in A

Fourier -150

-100

-50

0

50

0 10 20 30 40 50 60 70 80 90 100

t / [ms]

s( )

Fourier t / [ms]

80

100

120

Impact depends 20

40

60

80

Ip in AIs in A


p pon methods ! 0

20

0 10 20 30 40 50 60 70 80 90 100t / [ms]

Impact of CT saturation on distance measurement

● CT saturation causes measurement errors

Xfault impedanceduring transient

saturation

Using Fourier Filtering:● Fundamental current magnitude measurement value is too small

⇒ impedance gets bigger⇒ Starting I>>/Z< may pick up delayed

initial loadimpedance

steady-state fault impedance

⇒ g y p p yor falsely reset temporarily

● Fundamental current is phase-shifted anti-clockwise, further lagging to voltage

R

p

zone 1⇒ impedance gets turned clockwise ⇒ reactance becomes bigger

(in extreme situations, directional decision would be endangered ?)

I d t t i di t l i t i t t t i i⇒ Impedance may not get immediately into instantaneous tripping zone ⇒ Distance protection tends to underreach (= lack of dependability).

Effect depends on zone characteristic and impedance calculation method(s)● Effect depends on zone characteristic and impedance calculation method(s).

● Transient CT saturation causes transient measurement errors, effective for about 2 x Tp only


effective for about 2 x Tp only.

Agenda





Determination of relays CT requirementsCT dimensioning factorCT dimensioning factor

CT dimensioning formulae:⇒ Secondary accuracy limiting voltage

(≠ Kneepoint voltage)(= Ealreq per IEC 60044 or 61869)

⇒ or Rated CT accuracy limit factor

To avoid saturation, dimensioning factor has to be

But saturation is acceptable …

CT dimensioning factor depends on application and device.


g p ppDetermination by manufacturer!

Determination of relays CT requirementsTest system modelTest system model

A B C

DISTDIST

A B CA B C

DIST


Determination of relays CT requirementsImpact of CT modelImpact of CT model

BAccurate CT model

H

B

+ CT model simplification requires less calculation b d id h

Neglecting Hysteresis B

bandwidth.

B t d l ig g y

H

B - But model inaccuracy results in determination of higher CT requirements

Linearised characteristic B

HS

BS

H

B

( ) nS

S InLRAN

NAN

B

2

12

22

22

1

2

21⋅⋅⋅+⋅⋅

⋅=

⋅Ψ

= ωω


nS InRL

TlNH 1

2

2

2

2

1 211⋅⋅⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛+⋅⋅=

ωω

Determination of relays CT requirementsTestsequenceTestsequence

Parameters: Test series● Un Nominal voltage (ref.)● Isc Short-circuit current (ref.)● α Fault location (% X1) Test cycle

D t i ti f CT di i i

Test series= Variation of all parameters

( )● SIR Source impedance ratio● F Type of fault● ϕ Point on waveTest process

= Determination of CT dimensioning for a given set of parameters

ϕ● TP Primary system time constant● rL0, rS0, xL0, xS0

ratio of zero- to positive-sequence I di id l t t

= Reduction of dimensioning factor, until incorrect protection operation occurs in at least 1 out of 10 repetitions

line (source) resistance (reactance) ● TS CT secondary side time const.● XS/RS Burden quality

Individual test= shot test and comparison of actual with ideal operation


Determination of relays CT requirementsResultResult

25

30

α = 95%

15

20

K

10

15Kemp

α = 85%

α = 90%

0

5

00 20 40 60 80 100 120 140 160

Xp/Rp


Agenda





CT sizing based on application dataGeneral check pointsGeneral check points

1: Check correct backward decision (security case)2: Check correct forward decision (dependability case)3: Check at Zone 1 reach limit (dependability case)4: Check Zone 2 operation at line end (security case)4: Check Zone 2 operation at line end (security case)

Source: CIGRE B5-02 Co-ordination of Relays and Conventional CTs (draft)Equivalent to IEC 60255-121 (CD) considerations


Equivalent to IEC 60255 121 (CD) considerations

CT sizing based on application dataRecommendationRecommendation

Usually, it is sufficient to determine the required dimensioning based on the maximum short-circuit current for faults at the zone 1 end reach. The instantaneous zone 1 operation then isThe instantaneous zone 1 operation then is ensured acc. to the permitted tolerances mentioned on previous slide.

For close up faults in backward direction it is essential to take the correct directionalFor close up faults in backward direction it is essential to take the correct directional decision. This is secured even with minimum CT dimensioning factor (per curve (3) on previous slide), if the short-circuit current is less than twice the maximum short-circuit current at zone 1 reach end. Otherwise, with bigger short-circuit currents for faults in backward direction, a second calculation of the required dimensioning factor needs to be done, using that fault current and the (possibly different) primary system time constant for that fault scenario.

It is generally recommended to use CTs of accuracy class 5P


g y y(or equivalent).

CT sizing based on application dataConsideration of Auto ReclosingConsideration of Auto-Reclosing

Example 1-shot unsuccessful AR

⇒ Additional dimensioning factor to consider⇒ magnetization of CT core due to current flow during initial fault (duration = t‘)⇒ magnetization of CT core due to current flow during initial fault (duration = t )

⇒ de-magnetization of CT core during dead time(small TS advatangeous ⇒ linearized TPZ core)



Yo r e perienceYour experience … ??????


Make the most ofMake the most of your energy™

Documents

Rudolf Simon Compatibiliteitsmodus