TRF testingPOWER TRANSFORMER1Insulation Resistance MeasurementProcedurea.For LT systems, use only 500V or 1000V Megger.b.For MV & HV systems, use 2500V or 5000V Megger.c.Remove Earth from Transformer neutral.d.Measure as per table below.CircuitMegger UsedMV & HV1U - E5kV2U - E5kV1U - 2U5kV2Winding Resistance MeasurementCircuitTap NoResistance 1U-1NAll Taps1V-1N1W-1N2U-2N2V-2N2W-2N3Magnetic Current TestApplied VoltageMeasured Current1U-1V1U1V-1W1V1W-1U1W1U-1N, 1V-1N,1W-1N1N4Magnetic Balance TestApplied VoltageMeasured Voltage1U1N1V1N1W1N1U1N1V1N1W1N2U2N2V2N2W2N415----415----415-Applied VoltageMeasured Voltage1U1V1V1W1W1U1U1V1V1W1W1U2U2V2V2W2W2U415----415----415-5Vector Group Confirmation.Dyn1Conditions:1-1U and 2u should be shorted.2-Apply 415V to 1U,1V&1W3-Satisfy the following conditions.1U1W = 1U2n + 1W2n1W2w = 1W2V1V2v < 1V2wDyn113-Satisfy the following conditions.1U1V = 1U2n + 1V2n1V2w = 1V2v1W2w < 1W2v5Vector Group Confirmation.Ynd13-Satisfy the following conditions.1U1N = 1U2v + 2v1N1W2v = 1V2v1V2v < 1V2wYNyn03-Satisfy the following conditions.1W2w = 1V2v1W2n = 1V2n1U1N = 1U2n + 1N2n6Short Circuit Test and Differential Stability.7REF Stability Test8Cooler Circuits9Temperature Indicators Calibration10Auxilliary Protection Circuits

1U1V1W1N2U2V2W2N1U1V1W1N2U2V2W2NWINDING RESISTANCE METERI I I I I1 P1 P2 I21U1V1W1N2U2V2W2NmA415 V ACmAmAmA1U1V1W1N2U2V2W2N415 V ACMeasured voltage1U1V1W2W2U2V1U2U1V1W2V2W2n1U1V1W2W2U2V2U1U1V1W2W2V2n1U1V1W2W2V2U1N1U1V1W2W2V2U1U1V1W2W2V2U1N2n1U1V1W2W2V2U2n1N

Short circuit6Short Circuit Test and Differential Stability.Stable Condition.Diff RelayP1S1300/1 AS2S1S2S1P2S2B-PhY-PhR-PhP1S1500/1 AS1S2S1S2S2P2Example:Short Circuit Current Calculation.Rating : 100MVAHVLVVoltage220 kV132kVCurrent262.43 A437.40 A% of Impedance (%Z)= 8.05%HV MVA = LV MVA = 100MVA3 x 220000 x I1 = 3 x 123000 x I2 = 100,000,0003 x 220000 x I1 = 100,000,000I1 = 100,000,000 / (3 x 220000)I1 = 262.43A3 x 123000 x I2 = 100,000,000I2 = 100,000,000 / (3 x 132000)I2 = 437.40A%Zv =8.05%= 220kV x % of impedance= 220000 x (8.05/100)%Zv = 17,710 VIf We may apply 415 V to HV sideHV I primary = (415 x 262.43) / 17710HV I primary = 6.15 AHV sec = 6.15 / 300HV sec = 0.0205ALV I primary = (415 x 437.4) / 17710LV I primary = 10.25 ALV sec = 10.25 / 500LV sec = 0.0205 AUnstable ConditionS1S2S1S2S1S2S1S1S2S1S2S2

Apply 3-Ph AC VoltageN R Y BTemporary ShortIdApply 3-Ph AC VoltageTemporary ShortIdIdIdIdId

REF7REF Stability Testi)Stable Condition.RYBP1S1S1S1P2S2S2S2S2S1NP2P1P2P1nS2S1P1S1S1S1P2S2S2S2rybii)Unstable Condition (Type 1)S1S1S1S2S2S2S2S1S2S1S1S1S1S2S2S2iii)Unstable Condition (Type 2)S1S1S1S2S2S2S2S1S2S1S1S1S1S2S2S2

Apply 3-Ph ACFaultHV REFLV REFSHORTApply 3-Ph ACSHORTLV REFHV REFLV REFHV REFLOADING TRANSFORMERLOADING TRANSFORMER