40 0 225KB
Prepared by Manoj N
RET670 TESTING PROCEDURE Differential Protection(87) – High impedence protection
During Testing By pass all Series connected resistors and Parallel connected Metrosil for Safety purpose. U > Alarm Pick up current = Set Voltage / Set resistance value = 15V / 1000Ω = 0.015 A.
U > Trip Pick up current = Set Voltage / Set resistance value = 75V / 1000Ω = 0.075 A.
Measurements AD Phase
Alarm
Alarm Delay
Channel
Pick-up val. [A]
Drop-off val. [V]
R
AI01 AI02
0.016 0.015
0.014
Y B
AI03
0.015
0.014
AI01-03
0.016
RYB
0.014 0.014
AD
inj. val. [A]
meas. val. [s] 5.033
0.030
5.030 5.028
B
0.030
5.059
Phase
Trip
Trip Delay
Channel
Pick-up val. [A]
Drop-off val. [A]
R
AI01 AI02
0.076 0.076
0.073
Y
AI03
0.076
0.074
AI01-03
0.075
0.074
RYB
0.074
inj. val. [A]
meas. Val. [ms] 30.40
0.150
28.90 31.40
0.150
30.20
Differential Protection(87) – Low impedence protection
Pick up 3φ = diff setting * (Full load current / CT Ratio ) Pickup 1φ = diff setting * (Full load current / CT Ratio) * 1.5
Bias Characteristics:
Curve can be obtained as follows
Using the parameter setting idmin, endsection1,2 slope section 2,3 the curve can be obtained. 1.Bias can be checked by Omicron, 2.Bias can also be checked by Manually by injecting in times of Trafo Nominal current on both side with 180° shift, vary any one angle till trip, I Diff can be calculated using
ϕ I diff = 2 ⋅ iinj ⋅ sin 2
Where, iinj = Injected Current, Φ = Operated angle.
Blocking of Differential protection: 1. Harmonic Restraint(2nd & 5th Harmonic) Harmonics is nothing but Multiples of Frequency Second harmonic: Inject the full load current as per the calculation + inject >10 % of the full load current with set 100 hz frequency(2*50 hz) → NO TRIP. Inject the full load current as per the calculation + inject 25 % of the full load current with set 250 hz frequency(5*50 hz) → NO TRIP. Inject the full load current as per the calculation + inject