Generator Transformer PRESENTED BY PROF VG PATEL TRANSFORMER
Generator Transformer PRESENTED BY PROF. VG PATEL
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER Generator step-up transformers (GSU): Generator step-up transformers (GSU) are the critical link between the power station and the transmission network, often operated day and night at full load. They must be built to withstand extreme thermal loading without ageing prematurely. GSU take the voltage from the generator voltage level up to the suitable transmission voltage level. These transformers are located in a power station and are built as single-phase or three-phase units. There are two (2) basic technologies for designing and manufacturing: core and shell. With shell-formed transformers, the primary and secondary are on one leg and surrounded by the core. With a core-formed transformer, cylindrical legs windings cover the core legs. Monday, March 8, 2021 VG PATEL 2
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER This is the main power transformer employed in the power plant. It steps up the voltage from 11 k. V to 66 k. V or 132 k. V and also from 21 k. V to 220 k. V or 400 k. V and delivers the power. Stepping up the voltage reduces the transmission losses which occur during the power transmission to long distances. The rating of this transformer (MVA rating) will be almost equal to the alternator or generator rating. The average loads are nearer to full load and these are designed in such a way that maximum efficiency at full load condition. Monday, March 8, 2021 VG PATEL 3
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER The generator transformer is the first essential component for energy transmission, allowing energy supplied by the generator to be transferred to the network at the required voltage. It is static device which steps up or step down the alternate current voltages and it is working on the principle of mutual induction. The main function of the generator transformer is to transfer electric power from one circuit (LV) to another (HV). Monday, March 8, 2021 VG PATEL 4
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER The transformers which are directly connected with generator to step up the generated voltage is called generator transformer. It is not always necessary that generating transformer is in 3 single windings. If depends up on the MVA rating of generator. Main reason for using 3 single winding transformer for large MVA is if we use 3 winding transformer it will become too bulky. And it will be very difficult to carry it from its manufacturing place to main site. Our in case of any damage, from SS to place of repair. Monday, March 8, 2021 VG PATEL 5
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER The reason behind using delta star transformer as a generator transformer and not star transformer is. . In delta connection, the line voltage is equal to the phase (single phase to ground) voltage. In star connection, the line voltage is 'root(3) times the phase voltage'. Therefore, if we use delta star connection, with a smaller voltage we can get much higher voltage on the secondary side. The insulation will be less stressed in case of a delta star winding since a smaller voltage is imposed on the phase windings. Monday, March 8, 2021 VG PATEL 6
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER In star - star connection, the primary will draw magnetizing currents having 3 rd and 5 th harmonics. If neutral is not provided, the harmonics currents cannot flow and therefore the flux will not be sinusoidal and voltage will be distorted. This can be overcome by connecting the neutral of the primary with the generator neutral or by earthing it. However, even if it done and still third harmonics are present in alternator voltage, they will appear on the secondary side. In case of delta - star connection the delta connected winding always allows a path for third harmonic currents to circulate and as a result there is no distortion. Monday, March 8, 2021 VG PATEL 7
TRANSFORMER ENCYCLOPAEDIA GENERATOR TRANSFORMER The generator transformer is used to connect the generator whose voltage is probably maintained within ± 5% of nominal, to a 400 k. V system which normally may vary independently by ± 5% and up to +10% for up to 15 minutes. This cannot be achieved without the ability to change taps on load. However, in addition to the requirement of the generator to produce megawatts, there may also be a requirement to generate or absorb VARs, according to the system conditions, which will vary due to several factors, for example time of day, system conditions and required power transfer. Monday, March 8, 2021 VG PATEL 8
TRANSFORMER ENCYCLOPAEDIA OPEN FORUM Monday, March 8, 2021 9
TRANSFORMER ENCYCLOPAEDIA THANQ Monday, March 8, 2021 10
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