103
Two step definite and inverse time-
delayed residual
overcurrent protection (TEF1 and TEF2)
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The directional/nondirectional residual current functions are intended for solidly
earthed multiphase systems. The function has two measurement steps, one low current
step with definite or inverse-time-delay and one high current step with definite time-
delay.
For TEF1 input I4 is used to measure I
N
and for TEF2 I5 is used. Except from this the
two functions are identical. References will therefore only be made to TEF1 in the fol-
lowing description, but they also apply for TEF2.
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In case of single-phase earth-faults, the primary fault resistance varies with the network
conditions, the type of fault and location of the fault. In many cases, the fault resistance
is much higher than the resistance that can be covered by an impedance-measuring dis-
tance protections. This can be the case with a phase to earth fault to a tower with large
tower footing resistance.
Earth faults with high fault resistance can be discovered by measuring the residual cur-
rent
I
N
=I
L1
+I
L2
(Equation 49)
The inrush current can cause unwanted tripping of the earth-fault overcurrent relay
when energizing a directly earthed power transformer. The earth-fault overcurrent pro-
tection is therefore provided with second harmonic restraint, which blocks the operation
if the residual current (I
N
) contains 20% or more of the second harmonic component.
In some cases, it is possible to improve the selectivity by adding a settable minimum
operate current (I
N
>Low) and a minimum operate time (tMinInv) to the inverse char-
acteristic. These functions are included in the earth-fault protection modules.
To minimize the operate time, in case of closing the circuit breaker to a fault, the resid-
ual overcurrent protection module is provided with a switch-onto-fault logic, which can
be activated at breaker closure. The tripping time will temporarily be reduced to 300 ms.
Содержание REO 517
Страница 10: ... RQWHQWV ...
Страница 16: ...6 Introduction to the application manual KDSWHU QWURGXFWLRQ ...
Страница 64: ...54 Blocking of signals during test KDSWHU RPPRQ IXQFWLRQV ...
Страница 88: ...78 Scheme communication logic ZCOM KDSWHU LQH LPSHGDQFH ...
Страница 100: ...90 Time delayed phase and residual overcurrent protection TOC1 KDSWHU XUUHQW Equation 36 Iset IsSEC I1b 100 ...
Страница 146: ...136 Unbalance protection for capacitor banks TOCC KDSWHU XUUHQW ...
Страница 166: ...156 Dead line detection DLD KDSWHU 3RZHU V VWHP VXSHUYLVLRQ ...
Страница 171: ...161 About this chapter KDSWHU RQWURO KDSWHU RQWURO ERXW WKLV FKDSWHU This chapter describes the control functions ...
Страница 293: ...283 About this chapter KDSWHU RJLF KDSWHU RJLF ERXW WKLV FKDSWHU This chapter describes the logic functions ...
Страница 378: ...368 Monitoring of DC analog measurements KDSWHU 0RQLWRULQJ ...
Страница 379: ...369 About this chapter KDSWHU 0HWHULQJ KDSWHU 0HWHULQJ ERXW WKLV FKDSWHU This chapter describes the metering functions ...
Страница 384: ...374 Pulse counter logic PC KDSWHU 0HWHULQJ ...
Страница 412: ...402 Serial communication modules SCM KDSWHU DWD FRPPXQLFDWLRQ ...
Страница 440: ...430 LED indication module KDSWHU DUGZDUH PRGXOHV ...