Testing of Distribution TransformerDistribution Transformer Principle of Transformer Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 2 Principle of transformer action A current flowing through a coil produces a magnetic field around the coil. The magnetic field strength H, required to produce a magnetic field of flux density B, is proportional to the current flowing in the coil. 3 Principle of transformer action A transformer is a static piece of apparatus used for transferring power from one circuit to another at a different voltage, but without change in frequency. It can raise or lower the voltage with a corresponding decrease or increase of current. 4 Distribution Transformer Principle of transformer actions Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 5 T BUSHING BREATHER TAP SWITCH L.T BUSHING RADIATOR HV / LV WINDING OIL BOTTOM VALVE 6 .Construction of Transformer CONSERVATOR TANK EXPLOSION VENT H. Construction of Transformer DELTA / STAR n R r HV LV . Y y ETH B b 7 . 6/25/2015 Distribution Transformer 8 . 6/25/2015 Core and Coil Assembly 9 . Distribution Transformer Principle of transformer actions Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 10 . 7 VECTOR GROUP : Dyn11 TYPE OF COOLING : ONAN IMPEDANCE VOLTS : 5 % 11 . Vector group & Impedance volts play an important roll for calculating test values.2 ) Amps FREQUENCY : 50 HZ TAPPING : No.HV/LV current.Transformer Name Plate Details . of Taps :. MAKE : ( XYZ ) KVA : (315) NO LOAD VOLTS HV / LV ( 11000 / 415 ) Volts FULL LOAD AMPS.5 / 438. Size of transformer. HV / LV ( 16.Before any testing study of name plate details is must. The HV/LV voltage . Name plate of Distribution transformer-Sample 12 . Distribution Transformer Principle of transformer actions Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 13 . Routine Test Generally routine test is carried out at stores where we received New / Recovered transformers from manufacturer and site. Insulation Resistance Test Continuity test Ratio test (Voltage / Turns ratio) Short circuit test (Short circuit current) Open circuit test (Magnetizing current ) Magnetic balance test Vector Group test Oil test 14 . Following Test are perform as routine test. = _____ M 15 . It gives us the status of insulation of HV winding and LV winding with respect to earth and between the winding. HV WDG. TO EARTH = _____ M HV WDG.TO LV WDG.Insulation Resistance Test (IR VALUE) Insulation resistance test to be carried out by 1 / 2. TO EARTH = _____ M LV WDG.5 / 5 KV manual or motor driven megger. Insulation resistance measurement between LV winding and earth Insulation resistance measurement between HV winding and earth TR BODY TR BODY LV R R N HV Y Y B 0 M MEGGER B 0 M MEGGER 16 . Insulation resistance measurement between LV winding and HV winding TR BODY LV R R HV N Y Y B B 0 M MEGGER 17 . K) 18 .K ) VALUE = INFINITY ( CONTINUITY NOT O.Continuity Test CONTINUITY TEST CARRIED OUT BY MEGGER OR AVO METER TO CHECK ANY OPEN CIRCUIT FAULT IN THE HV & LV WINDING OF THE TRANSFORMER. HV SIDE n r LV SIDE R RY = _____ YB = _____ BR = _____ y rn = _____ yn = _____ Y b bn = _____ B VALUE = ZERO ( CONTINUITY O. Continuity test for HV winding Continuity test for LV winding TR BODY TR BODY LV R R N HV Y Y B B 0 M 0 M MEGGER MEGGER 19 . The % Error of the voltage ratio is not more that +/. 20 .0.5 % as per the IS 2026 and IEC 60076 • Apparatus: 3 phase supply -415V (Applied to HV side) Clip on meter for measuring voltage at LV side.Voltage ratio test • Objective: To check that the ratio of voltages ( in 3-phase transformers. line to line voltages) is as per designed value in all tap position. VBN).Voltage ratio test Procedure: • Apply 3 phase 415V supply on HV side and LV side voltage is to be measured. Tap position Vrn Vyn Vbn Vry Vyb Vbr 1 2 3 4 5 6 7 21 . VYN. • Output voltage will be measure between phase & neutral (VRN. Ratio will be changed in respect to tap positions. TR BODY LV R R N HV Y Y B B VOLT-METER ICTP Voltage ratio test 400v AC supply 22 . Voltage ratio test HV side 415V applied LV side voltage measurement Tap switch position 23 . Shorting Link (For passing full load current).Short circuit test • Objective: To determine the Short Circuit impedance voltage. 24 . To determine the Load losses of the transformer Short circuit loss = I2R Loss + stray loss • Apparatus: Voltage injection set (Applied on HV side) Clip on meter (Measuring current at LV side). Short circuit test • Procedure: LV side will be shorted through shorting link. Load loss and impedance voltage measured on power analyser. 25 . This Load loss measured at Room temperature Converted this loss into 75 Degree C and it should be within the specified limit. Unbalance current should not be more than 2% of full load current. Unbalance current and phase to phase current measure with the help of Clip on meter. Applied the 3 phase voltage on HV side and increased the voltage till the full load current passed through the transformer. Short circuit test TR BODY LV R R HV Y B ICTP 400v AC supply N Y B Load loss at 75 Degree C = Load loss at RT (A+75) / (A+RT) Here RT= Room Temperature A= 235 for CU wound A= 225 for Al wound 26 . No load loss = hysteresis loss + eddy current loss • Apparatus: Voltage injection set (Applied on LV side) Clip on meter for measuring no load current at LV side. 27 .Open circuit test • Objective: To know the Excitation losses and currents of Transformer when excited at rated kV at rated Hz To determine the No load losses(Core loss) of the transformer To check healthiness of winding and stampings. The energy required to change the orientation of the magnetic grains in the direction of the magnetic field is lost in the form of heat.Hysteresis Loss when a magnetic field is applied all the grains of the magnetic material will orient in the direction of magnetizing force. 28 . This loss is called hysteresis loss. In another cycle this grains will orient in opposite direction in the direction of magnetizing force. 29 . Insulation between laminations: Oxide coating is provided for CRGO laminations to reduce eddy current losses. Lamination Cores are used: By using thin laminations the core thickness is reduced so eddy current losses are reduced. This induced emf will cause small circulating current s called eddy currents.Eddy current Loss Eddy Current Loss: When an alternating magnetic flux is applied to the iron core small emf will be induced due to change in flux linkage. So CRGO steel laminations are used as a core material. In order to reduce the Eddy Current loss: Use of Material having high electrical resistivity: By using superior grain orientation CRGO steel will have higher electrical resistivity. Eddy current flowing through the material causes I2R losses in the material. Thus eddy current loss can be reduced. No load current should not be more than 3% of full load current. Note: Nobody can go closer to HV side because it is subject to 11KV. No load current measured by clip on meter and no load loss measured by power analyzer.Open circuit test Procedure: Rated voltage applied on LT side of distribution transformer for energizing transformer. 30 . TR BODY LV R R N HV Y B Open circuit test Y B ICTP 400v AC supply 31 . Star Rating of Transformer(BEE) Rating KVA 1 star 2 star Max Max Losses Max Losses Losses at at 50% at 100% 50% (Watts) (Watts) (Watts) 3 star 4 star 5 star Max Losses at 100% (Watts) Max Losses at 50% (Watts) Max Losses at 100% (Watts) Max Losses at 50% (Watts) Max Losses at 100% (Watts) Max Losses at 50% (Watts) Max Losses at 100% (Watts) 16 200 555 165 520 150 480 135 440 120 400 25 290 785 235 740 210 695 190 635 175 595 63 490 1415 430 1335 380 1250 340 1140 300 1050 100 700 2020 610 1910 520 1800 475 1650 435 1500 160 1000 2800 880 2550 770 2200 670 1950 570 1700 200 1130 3300 1010 3000 890 2700 780 2300 670 2100 32 . BEE Star Labeling 33 . 2 515 2750 630 33.6 300 1600 315 16.4 222.5 800 4700 990 52 1377 1250 6200 34 .5 438.1 876.Full load current and loss of different rating transformers KVA HV (Amp) LV (Amp) NO LOADLOSS ( Watts) LOAD LOSS (Watts) 160 8. Division should 65:35 between central and the other extreme limb if one of the extreme limbs is excited and is 50:50 for central limb excitation rn yn bn rn= 240 240 156 84 yn= 240 120 240 120 bn =240 84 156 240 35 .Magnetic Balance Test: Applied 240V on LV side and voltage measured on respective LV terminals as under. 36 . 37 .5mm.Break down voltage test of Oil • Transformer oil is used insulation as well as cooling purpose. • BDV tester ranging from 0100KV used for test. • Gap between two electrodes must be maintain 2. • BDV of new insulating oil Should be more than 60KV. 03 for new insulating oil. 38 .(mgKOH/gm) • Acidity must be less than 0.Acidity test of Oil • In this test we will measure the value of free carbonic and non-carbonic acid in oil and this will be measured with the help of acidity testing kit. Distribution Transformer Principle of transformer actions Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 39 . This type of test required some specific testing instruments and testing facilities. even through some of the test carryout at site also. Winding resistance test Vector group test Separate source voltage test Temperature rise test Induced overvoltage test 40 .Factory Test In addition to routine test some more test are carryout at factory. Distribution Transformer Principle of transformer actions Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 41 . this type of test required some special testing instrument and testing facility. Impulse Voltage Test .18.Type Test Over and above routine test some important test are carried out at factory or laboratory like ERDA & CPRI.4 KA for 3 sec Partial discharge test 42 .95KVp Short circuit withstand test . Distribution Transformer Principle of transformer actions Construction of Transformer Transformer Name plate details Routine Test Factory test Type Test Transformer failure and causes 43 . • Lack of installation checks. • Seepage of water in oil. • Faulty operation of tap changer switch. • Prolonged Over loading. • Single Phase loading.Failure & Causes • Insufficient Oil level. • Unbalanced loading. 44 . • Prolonged Short Circuit. • Faulty Termination (Improper sized lugs etc) • Power Theft. Insufficient cooling ducts in the winding. Bad Quality of raw material. transformer is removed and replaced with new/repaired one without removing the cause of failure which results in immediate or short time failure. Burr /sharp edges to the winding conductor. Burr to the lamination blades Improper brazing of joints. After failure .Failure & Causes • Faulty design • Poor Workmanship • • • Improper formation of core. Transit damaged transformers. 45 . Improper core bolt insulation. Bad insulation covering. Incomplete drying. 46 . 6/25/2015 47 . 6/25/2015 48 . 49 . 50 . 51 . Thank You .