Information about RET 670 transformer protection - testing procedure

Published on October 17, 2016

Author: davidroy39

Source: slideshare.net

2. Ø Differential Protection(87) – Low impedence protection Pick up 3f = diff setting * (Full load current / CT Ratio ) Pickup 1f = diff setting * (Full load current / CT Ratio) * 1.5

3. 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 ÷ ø ö ç è æ ××= 2 sin2 j injdiff iI Where, inji = Injected Current, Φ = Operated angle. Blocking of Differential protection: 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 – according to country standards)→ NO TRIP. Inject the full load current as per the calculation + inject <10 % of the full load current with set 100 hz frequency(2*50 hz - according to country standards) → TRIP. Fifth harmonic: Inject the full load current as per the calculation + inject >25 % of the full load current with set 250 hz frequency(5*50 hz - according to country standards) → NO TRIP.

4. Inject the full load current as per the calculation + inject <25 % of the full load current with set 250 hz frequency(5*50 hz - according to country standards) → TRIP. Open CT detection. ü The OPEN CT Algorithm will only detect an OPEN CT if the load on the power transformer is from 10% to 110% of the rated load current. ü The search of OPEN CT starts after 60 seconds since the bias current enters the 10-110% range. OPEN CT DETECTION→ Block Diff Protn.. Cross Blocking 2nd or 5th Harmonic Restraint in R ph → Block Diff Protn in Y & B phases. 2nd or 5th Harmonic Restraint in Y ph → Block Diff Protn in R & B phases. 2nd or 5th Harmonic Restraint in B ph → Block Diff Protn in R & Y phases.

5. ØTHERMAL OVERLOAD PROTECTION(49) We need to test this in 2 methods 1. Without Cooling 2. With Cooling Trip Lockout will be connected to Trip matrix.so once after cool down to allowable temp we can energise the transformer. *) Calculation of nominal value: TTrip = ((IRef*IBase/IRef)*(ITrip/10000))2 *100 = ((100*100/100)*(100/10000))2 *100 = 121% TStart = TTrip*Start injection/100 = 121%*50%/100 = 60.5% t = 150 ln (((52 – (60.5 – 0)/100) / ((52 –(121-0)/100))) = 226.01s

6. Trip temperature (with cooling) T=150min Current Delay Phase Sensors Injected. val. [A] nom. val. [s]* meas. val. [s] R AI01 226.20 Y AI02 5*0.58=2.9 226.01 225.90 B AI03 225.70 Trip temperature (without cooling) T=360min Current Delay Phase Sensors Injected. val. [A] nom. val. [s]* meas. Val. [s] R AI01 292.10 Y AI02 6.74*0.43=2.9 293.16 291.40 B AI03 291.3 ØOVER EXCITATION PROTECTION(24) No current compensation is used.

7. Tailor made curve Over excitation is based on Voltage of LV side of transformer any two phase is enough to measure based on setting in general setting. ØTAPCHANGER OVER CURRENT BLOCKING This is an over current used to inihibit the operation of Tapchanger. When we have current threshold higher than the set value, tap changer operation is blocked.

8. RET 521 Configuration sample First read the parameter setting from relay, then go to settings - setting Group-n - transformer differential Then go to basic function settings, operation-0n, Idmin (means minimum operating differential current) - when 20% of differential current flow through relay than relay will trip (settings will be changed according to customer specifications, I2/I1 ratio - second harmonic setting, I5/I1 ratio – fifth harmonic Block setting should be kept as ON for harmonic blocking

9. Enter the transformer name plate details, Sr1- MVA rating, Ir1-rated current of HV winding, Ir2- rated MV winding current, Ir3-rated LV winding current,Ur1,Ur2,Ur3 - rated voltage of HV,MV,LV windings If you want to use tap changer inputs for relays, the number of taps has to be specified here.

10. If you want to use Time overcurrent protection, the settings has to be done here. Go to configuration, then Analog input modules in order to configure the relay according to the schematic diagram

11. Here 10 analogue channels are provided Channel1–R phase current of HV, channel 2, 3 –Y, B of HV Winding side, channel 4,5,6 - R,Y,B current of MV Winding, channel 7,8,9-R,Y,B of LV winding, channel -10 is for voltage Enter the CT ratio and mention the star point for all channels

12. BIAS TEST PROCEDURE: Apply equal value of current in a-SIDE (HV SIDE) & b-SIDE (LV SIDE). a-SIDE (HV SIDE ) input energizing quantity (current) is increased slowly until relay contact operates. Actual Differential Current = Vector sum of both current Bias Current = (Magnitude sum of currents) / 2 Theoretical Differential current = 0.2+0.2 XIb (for slope=20%) =0.2 +0.2 X 1.5 +(Ib-1.5) X 0.8 (for slope=80%) SECOND HARMONIC TEST PROCEDURE: Current 0.2 A at 100 Hz is to be applied in A-PHASE and relay is found to be in the non- operated condition. Apply current with frequency 50 Hz in phase with 100Hz current in A-PHASE and increase slowly until relay contact closes. Record 50 Hz current. REF TEST PROCEDURE: Input energizing quantity (current) is increased slowly until relay contact operates DTOC FUNCTION TEST PROCEDURE: Input energizing quantity (current) is increased slowly until relay contact operates V < > (UNDER/OVER VOLTAGE) FUNCTION TEST PROCEDURE: Apply AC voltage (110V) and increase the voltage for over voltage or decrease the voltage for under voltage function till the function assigned contact closes f < > (UNDER/OVER FREQUENCY) FUNCTION TEST PROCEDURE: Apply AC phase voltage (110V) with rated frequency and increase or decrease the frequency till the function assigned contact closes DTOC FUNCTION TEST PROCEDURE: Apply two times setting current in each phase till the function assigned closes and note down relay operating time. PHASE FAULT IDMT TIME PROCEDURE: Apply more than setting current in each phase till the function assigned contact closes and note down relay operating time. EARTH FAULT IDMT TIME PROCEDURE: Apply more than setting current in one phase till the function assigned contact closes and note down relay operating time. V < > (UNDER/OVER VOLTAGE) FUNCTION TEST PROCEDURE: Apply Rated AC voltage and increase the voltage to 1.1 times of setting voltage for over voltage or decrease the voltage to 0.9 times of setting voltage for under voltage function till the function assigned contact closes and note down the relay operating time. f < > (UNDER/OVER FREQUENCY) FUNCTION TEST PROCEDURE: Apply AC voltage (110V), 50Hz, change the frequency from 50Hz to 45Hz.Measure the operating time between change of frequency to contact closing. Apply AC voltage (110V), 50Hz, change the frequency from 50Hz to 55Hz. Measure the operating Time between change of frequency to contact closing

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