TESTING AND COMMISIONING THE POWER TRANSFORMER DET 310

TESTING AND COMMISIONING THE POWER TRANSFORMER DET 310 CHAPTER 4 THE POWER TRANSFORMER

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 3. 1 INTRODUCTION Substation transformers can range from the size of a garbage can to the size of a small house; they can be equipped with a wide array of gauges, bushings, and other types of auxiliary equipment.

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 2 TRANSFORMER NAME PLATE The transformer nameplate contains most of the Important information that will be needed in the field. The nameplate should never be removed from the Transformer and should always be kept clean and legible.

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 CONTINUE- a) SERIAL NUMBER i) WEIGHT b) CLASS j) DIMENSION c) KVA RATING k) TAP CHANGER d) VOLTAGE RATING e) WINDING f) VEKTOR GROUPING g) PERCENTAGE IMPEDANCE h) INSULATING FLUIDS

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 2. 1 TRANSFORMER CLASS ONAN - Oil natural air natural ONAF - Oil natural air force (use fan) OFAF - Oil force air force ( use oil pump and fan) OFWF -Oil force water force (use oil pump and water cooling) ODAF – Oil force and air force Example Transformer Rating: 1000 KVA 550 C ONAN, which stands for the capability to supply 1000 KVA with a temperature rise of 550 degres celcius with normal oil circulation (no fans or pumps).

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Hermetically sealed ONAN Conservator Type OFAF

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 2. 2 VA RATING Every transformer has a maximum output current that it can deliver at its standard output voltage. This VA rating (KVA or MVA for large power transformers) is dependent on the ambient temperature or cooling provided. Exceeding the VA rating will cause overheating of the core and windings and subsequent damage

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Continue. The capacity of a power transformer is defined by full load power, in k. VA it can produce. Where S = Full load Power Uph= rated voltage at no load (V) Iph = rated output current (A) For Star Connection: I phase= Phase Voltage=

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING 4. 2. 3 VOLTAGE RATING DET 310 Transformer rated voltage is usually specified by the voltage ratio Example: 11/0. 415 k. V ; Primary rated Voltage : 11 k. V Secondary rated Voltage: 0. 415 k. V 4. 2. 4 WINDING EXAMPLE: PRIMARY : DELTA SECONDARY: STAR 4. 2. 5 VEKTOR GROUP The vector groups denotes the way the transformers windings are connected:

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Continue: Example: Dy 11 D= HV delta winding y= low voltage star winding 11=clock face (30 degrees lead) with reference to the HV 12 o’clock

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Continue: Winding falls into three main types: star, delta, and zigzag Can be categorised into four groups Group 1: 0 degress phase shift: Yy 0, Dd 0, Dz 0, Zd 0 Group 2: 1800 deg phase shift: Yy 6, Dd 6, Zd 6, Dz 6 Group 3: -30 deg phase shift: Dy 1, Yd 1, Yz 1, Zy 1 Group 4: +30 deg phaseshift: Dy 11, Yd 11, Yz 11, Zy 11

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING 4. 2. 6: IMPEDANCE DET 310 The impedance of transformers is express in percentage values to Enable fault level calculations to be carried out Example: 11/0. 416 k. V Impedance: 4. 75% Fault level:

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 2. 7 TRANSFORMER OIL Act as an insulation and thermal transfer agent Mineral hydrocarbon oil to BS 148 Sometimes synthetic liquids, called askarels (pyroclor) are used instead of oil as they are non-inflammable and non-explosive but very expensive

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING 4. 2. 8 TAP CHANGER DET 310

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 TAP CHANGER FUNCTION: ALLOWS THE NOMINAL VOLTAGE TO ADJUSTED TYPICALLY 2. 5% AND 5% ABOVE AND BELOW NOMINAL VOLTAGE EXAMPLE: 11 k. V 5 taps Tap 1: 5% below: 10. 45 V Tap 2: 2. 5 % below 10. 725 V Tap 3: Nominal Tap : 11 k. V Tap 4: 2. 5 % above: 11. 275 k. V Tap 5: 5% above: 11. 5 k. V

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 3 TRANSFORMER OIL 4. 3. 1 OIL DETERIORATION a) Oxidisation of Oilb) - Oil reacts with oxygen to form a hydrocarbon sludge c) - The sludge is deposited on the winding tank walls d) - Causing heat to develop. e) - Sludge may also block the cooling ducts. f) - Oxidisation will results in formation of hydrocarbon and acid g) - Causing corrosion of the various metals within the transformers

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 3. 2 Thermal Decomposition of Oil - Heating of a Transformer will results of thermal decomposition - Will lead to breakdown of oil insulation - Prolonged operation above 98 deg reduces transformers life 4. 3. 3 Contamination - Particularly from moisture which enters through transformer breather

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 4 Oil System for Large Transformer a) The conservator b) - Oil reservoir and expansion vessel c) - Exhaust through breathing device-usually fitted with d) silica gel or drycol refrigeration dryer type e) b) Explosion Vent f) g) h) i) j) - Consists of a thin and relatively weak diaphragm -Under internal fault, the excess pressure in the tanks burst into explosion vent to release the pressure - Under normal circumstances, seals the transformer from the atmosphere

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 CONSERVATOR TANK BREATHER

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 RELIEVE VALVE

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 5 THE BUCHOLZ A mechanical relay connected through pipe and situated between main tank and conservator tank of a transformer. Only certain k. VA transformer need to be installed with one, normally above 1 MVA. It will be connected to the trip coil of the circuit breaker controlling the transformer or the installation

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Continue Principles of operation: Electrical faults cause violent generation of gases, which flows to the highest point, namely the conservator. This gases will Trapped inside the Bucholz compartment causing the level of oil to reduce thus causing the relay to initiate.

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 continue”: Buchholz relay can be triggered by three operation 1) Air from atmosphere while filling the transformer oil 2) Mechanical failure 3) Insulation breakdown from oil 4) Winding insulation breakdown Gas formed usually consists of hydrogen, Acetylene and carbon monoxide.

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Continue: 1) If the gas only contained less then 2% carbon monoxide, only breakdown in oil occurs. 2) If the gas contained more then 20%, the fault are due to both breakdown of oil and insulation

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 6 COMMISSIONING TESTS 4. 6. 1 DATA COLLECTION - manufacture and date of manufacturer - serial Number - rating-normal and assisted - nominal voltages - full load current at nominal tap - percentage impedance - vektor group - tap changer type, range and no of tap

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 6. 2 General check and Inspection -Coordinating Gaps -Labelling -Earth Connections -Breathers -Valves in operational position -Tightness of fastening -Insulators undamaged and clean -No oil leaks -Correct oil levels in conservators

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 6. 3 Insulation Tests 1. Check Insulation between low voltage winding to earth with 1 k. V IR tester 2. Check Insulation between high voltage winding to earth with 5 k. V IR tester. 3. Check Insulation between HV and LV winding with 5 k. V IR tester Duration of all are one minutes

Insulation Test 1 kv and 5 k. V: Power Transformer Hv Side Lv Side E Bacaan 100 M, ohms keatas ARB

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 6. 4 Polarization Index Test. Carry out IR test between Low Voltage to Earth with 1 k. V IR tester Carry out IR test between HV to Earth with 5 k. V IR tester Carry out IR test between HV to LV with 5 k. V IR tester Duration of test is 10 minutes Divide the value obtained with value for 1 min test Polarization Index = R 10/R 1

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Between Insulation Resistance (MΩ) PI Accepted value Not less than 1. 2 1 Minute 10 Minute Primary & Earth 4000 MΩ 7000 MΩ 1. 75 Secondary & Earth 3500 MΩ 8000 MΩ 2. 29 Primary & Secondary 5100 MΩ 10000 MΩ 2. 00

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 6. 5 Ratio Test 1) Inject 415 V three phase supply to HV side of transformer with the LV side open circuited. 2)Measure the HV side and LV side voltage and calculate the ratio. Compare the ratio with the name plate value and ensure that the ratio is within the tolerance. 3)Repeat for all transformer taps.

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 Primary Voltage AB: 200 BC: 200 CA: 200 Secondary output voltage Tap No Voltage an bn cn 4. 32 1 11550 4. 43 2 11275 4. 54 3 11000 4. 66 4 10725 4. 78 5 10450 Example: a) At tap changer no 1: VAB = 200 V (Delta) Therefore the ratio is correct.

INSUALTION TEST OF ELECTRICAL EQUIPMENT TESTING AND COMMISIONING DET 310 4. 6. 7 Impedance test: Positive sequence impedance 1) Inject three phase supply to HV side of transformer with LV side short circuited as shown below. 2)With the transformer at nominal tap, measure and record the current and voltage at HV side. 3) Calculate the percentage impedance as given below: % Impedance Where Vm = measured voltage Im = measured current Vr = rated voltage Ir = rated current Compare the results with declared value on the nameplate. Repeat the above for transformer at lowest and highest tap positions.