# ENHANCED NUMERICAL BREAKER FAILURE PROTECTION by harikumaru

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```									   ENHANCED NUMERICAL
BREAKER FAILURE PROTECTION

1
OVER VIEW

•   INTRODUCTION
•   CHALLENGES FOR CURRENT-BASED BF
DETECTION
•   FAST CURRENT-BASED BF DETECTION
•   ILLUSTRATION OF THE ALGORITHM OPERATION
•   TEST RESULT FOR THE FAST RESET OVERCURRENT
ALGORITHM
•   REFERENCES

2
INTRODUCTION

Breaker Failure protection is designed to operate when the protective
relaying scheme initiates a CB trip and that breaker does not correctly
interrupt the fault

Breaker Failure can be caused by

- Failure to trip
- Failure to clear
- Contact flash over

CBs are monitored locally by breaker failure (BF) relays and in the case of
a failure of a given CB to interrupt the fault current the associated BF relay
opens all surrounding breakers to clear the fault

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CONTD…

 The total BF trip time is the sum of the main protection operating
time,trip time of the main breaker, reset/response time of the BF
function, and the trip times of backup breakers.

 In the case of remote breakers, teleprotection time is added as well
to account for the time required to send and receive the direct transfer
trip command.

This seminar presents a novel current-based BF detector based on
differentiating between an alternating pattern of a true fault current, and
a decaying pattern of a subsidence current.

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RELAY - SAMPLE CURRENT WAVE FORM

Fig 1. Sample current wave form with subsidence

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CHALLENGES FOR CURRENT-BASED BF
DETECTION
• In a CT, when the primary current is interrupted CT is driven closer to
its saturation point, a subsidence current produced their secondary
circuits

• The decaying subsidence current contains a wide           spectrum of
frequencies including nominal system frequency

• Magnitude estimators of a protective relay—by design—measure in
that near-nominal frequency band and, therefore, will see a small
portion of the decaying current with system frequency current.

• It takes an extended period of time for any magnitude estimator to
ramp down from fault level to a low level to a low reset threshold
value

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FAST CURRENT-BASED BF
DETECTION
• In order to differentiate between the alternating and decaying
patterns, we look at the current through a pair of orthogonal
filters.

• In this particular application we use a half-wave sine and cosine filters
with the windows of 1/8th of a power cycle
(   NH = 8 samples while sampling at                samples/cycle )‫‏‬
N1  64


hs cs s  


0.
k 5
   
n
i             
   

   a
1
N       H



   

 
h c c

.

c c o         k 5

0

s             
   

   b
1
 H



N
  
 ... H
1 ...
..
k ....N
c09 4 c7..d
1 0
s . 8  . ..1
c 1..(
0 . .. )
. 8. .
8. ..
0. .
.
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CONTD…………..

• The filter is performed by

i h is
s
                 i i......2
h.. .. .(
c.. .. )
c



.
.
. . .. .

Where   i   S   – sine component of current

ic– time derivative
• Under clean sine wave, the trajectory is a perfect circle with
the point making one full revolution in each power cycle.

8
•         When the primary current is cleared and the subsidence
current is created, the trajectory changes dramatically. It   stops
rotating,and starts moving toward the origin of the         plane

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•        The angles of subsidence trajectory are always around 110–
120º for positive polarity and (-80) – (-70)º for negative polarity.

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• The characteristics of subsidence trajectories can be explained by
the equation

RSTp = (ic < Δ) & (is > - Δ)& (is > -Co.ic-Δ) --------(3a)‫‏‬

RSTN = (ic > - Δ) & (is < Δ)& (is < -Co.ic+Δ)---------(3b)‫‏‬

Δ‫‏=‏‬Over‫‏‬current‫‏‬Threshold‫‏‏‏‏‬

Co(Factory constant)=1

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• A subsidence current resembles an exponential function and its
derivative is an exponential function as well as proportional to
time constant of decay

t
...a
iT... )
s 0 ...4
i....
0. . .
e . .
. . .
.
. .(
.

T


t
 00 b
c i 1 4
1
i d i)
 e (
s  T 
t
d  1
10

i c  1c
is 
  4
   ()
T
01

ω1= Radian system frequency
To = Decaying time constant of subsidence current
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• To strengthen the algorithm a supervisory flag is created

RSTsup-1 = (   ic < max(C1 is ; Δ)) -------------(5)‫‏‬

C1 =0.75

• During current reversals the trajectory may shift in the direction
opposite the natural direction of rotation.

RSTsup-2 = (   ic < max(C2 iMAG ; Δ)) -------------(6)‫‏‬

C2 =0.75
iMAG = standard full cycle amplitude.

RSTRaw =(RSTp or RSTN ) & RSTsup-1 & RSTsup-2 -----(7)‫‏‬

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ILLUSTRATION OF THE ALGORITHM OPERATION

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ILLUSTRATION OF THE ALGORITHM OPERATION

15
TEST RESULT FOR THE FAST RESET OVERCURRENT
ALGORITHM

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CONCLUSION

• The fast reset algorithm for current-based BF detector is very simple,
fast and robust

• The algorithm can be further enhanced by recognizing that
when the current vector stops rotating and starts decaying due
to subsidence.This reversal of the angular speed can be used to
strengthen and speed up the algorithm.

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REFERENCES

[1]  IEEE Guide for Breaker Failure Protection of Power Circuit
Breakers,IEEE Standards. C37.119–2005.

[2] U. D. Annakkage and P. G. McLaren, “A current transformer model
based on the Jiles-Atherton theory of ferromagnetic hysteresis,” IEEE
Transactions on Power Delivery, volume. 15, no. 1, pp. 57–61,
January. 2000.

[3] N. T. Stringer and D.Waser, “An innovative method of providing total
breaker failure protection,” IEEE Transactions on. Industrial Application,
volume. 32, no. 5, pp. 1011–1016, September. 1996.

[4] H. J. Altuve, M. J. Thompson, and J. Mooney, “Advances in breaker
failure protection,” presented at the 33rd Western Protective Relay
Conference., Spokane, WA, 2006.

[5] AFC Cable Systems Cable Catalog, 2006. [Online]. Available: www.
afcweb.com.

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THANK YOU

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