TRANSFORMERS

Voltage and Current Transformers

Voltage and Current Transformers Voltage and Current Transformers – These transformers are designed to meet the specific need of measurement and instrumentation systems, which accept voltages in the range of 0-120 V and currents upto 5 A. Power system voltages can be as high as 750 kV and currents upto several tens of kA. Their […]

Tap Changing Transformer

Tap Changing Transformer Tap Changing Transformer -Voltage variation in power systems is a normal phenomenon owing to the rapid growth of industries and distribution network. System voltage control is therefore essential for: Adjustment of consumers’ terminal voltage within prescribed limits. Control of real and reactive power flow in the network. Periodical adjustment (1-10%) to check […]

Phase Conversion

Phase Conversion Three/Two-phase Conversion (Scott Connection) Phase conversion from three to two phase is needed in special cases, such as in supplying 2-phase electric arc furnaces. The concept of 3/2-phase conversion follows from the voltage phasor diagram of balanced 3-phase supply shown in Fig. 3.61(b). If the point Mmidway on VBC could be located, then […]

Three Winding Transformers

Three Winding Transformers Three Winding Transformers may be built with a third winding, called the tertiary, in addition to the primary and secondary. Various purposes which dictate the use of a tertiary winding are enumerated below: To supply the substation auxiliaries at a voltage different from those of the primary and secondary windings. Static capacitors […]

Parallel Operation of Transformers

Parallel Operation of Transformers When the load outgrows the capacity of an existing transformer, it may be economical to install another one in parallel with it rather than replacing it with a single larger unit. Also, sometimes in a new installation, two units in parallel, though more expensive, may be preferred over a single unit […]

Back-to-Back Test on Three-phase Transformers

Back–to–Back Test on Three–phase Transformers Fig. 3.52(a) shows the connection arrangement for the back-to-back test on two identical 3-phase transformers. The two secondaries must be connected in phase opposition and in proper phase sequence. The auxiliary transformer for circulating¬†full-load current is included in the circuit of the two secondaries; it could also be¬†included in the […]

Three-phase Bank of Single-phase Transformers

Three-phase Bank of Single-phase Transformers Delta/delta connection The supply voltage provides only sinusoidal magnetizing current so that core flux is flat-topped; but the third-harmonic emfs induced (cophasal) cause circulating currents in deltas restoring the flux to almost sinusoidal. The third-harmonic voltages are very small as the transformer offers low impedance to third-harmonic currents. Star/delta and […]

Choice of Transformer Connections Star/star

Choice of Transformer Connections Star/star This is economical for small HV transformers as it minimizes the turns/phase and winding insulation. A neutral connection is possible. However, the Y/Y connection is rarely used* because of difficulties associated with the exciting current. Delta/delta This suits large LV transformers as it needs more turns/phase of smaller section. A […]

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