Presentation on theme: "Unit Transformer Unit transformer are step up transformer which is connected to generating house & step up voltage from 15kV voltage to 132 voltage level."— Presentation transcript:
2 Unit TransformerUnit transformer are step up transformer which is connected to generating house & step up voltage from 15kV voltage to 132 voltage level as requirement or line design parameter.It is just like transformer but connected to unit of the generating house that's why we called it unit transformers.Transformers used in three-phase systems may consist of a bank of three single-phase transformers or a single three-phase transformer which is wound on a common magnetic core.In Tongi power plant they use three single phase transformer which make a bank and produce three phase supply.Fig: Unit Transformer used in Tongi plant
3 Cont. Main transformer specifications: Application standard IEC 60076 Rated parametersType DFZ-55000/132W2 TH (single-phase composite type) transformer)Cooling type ONAN/ONAF (75%/100%)Frequency HzImpedance voltage %Rated power ×550000kVARated voltage /√3×(1±8×1.25%)/15kVWiring Ynd1Insulation level LI650AC275-LI650AC275/LI105AC45Rated current / A
5 Current TransformerCurrent transformers are used for reducing/stepping down a.c. current from higher value to lower value for measurement /protection/control.Typical secondary current of CTs are 5A or 1A r.m.sThere are two classes of current transformer:Measuring current transformerProtective current transformerFig: Current Transformer used in Tongi plant
6 Cont..Here is difference between the protection CT and metering CT in operating conditions…The CT using for protection will have to carry the fault currents which are 10 times the normal full load current.The CT used for metering will have to carry only full load current
9 Voltage transformerVoltage transformers are use for measurement and protection. It stepping down the voltage for the purpose of protection, measurement and control.The primary of voltage transformer is connected directly to power circuit between phase and ground depending upon rated voltage and application.Typical secondary voltage of VTs are 110V or 100V.Fig: Voltage transformer used in Tongi plant
13 The trip circuit When a fault occurs in the protected circuit, the relay(2) connected to the CT an PTactuates and closes its contacts(6). Current flows from thebattery (5) in the trip circuit (4).As the trip coil of the circuitbreaker(3) is energized, the circuitbreaker operating mechanism isactuated and it operates for theopening operation.