RET670 Transformer Testing Guide [PDF]

Zitiervorschau

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