Search Results for – "TRANSFORMERS"

Sequence Impedance and Networks of Transformers

Sequence Impedance and Networks of Transformers: Sequence Impedance and Networks of Transformers – It is well known that almost all present day installations have three-phase transformers since they entail lower initial cost, have smaller space require­ments and higher efficiency. The positive sequence series impedance of a transformer equals its leakage impedance. Since a transformer is […]

Phase Shift in Star Delta Transformers

Phase Shift in Star Delta Transformers: Phase Shift in Star Delta Transformers – Positive and negative sequence voltages and currents undergo a phase shift in passing through a star-delta transformer which depends upon the labelling of terminals. Before considering this phase shift, we need to discuss the standard polarity marking of a single-phase transformer as […]

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 […]

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 […]

Three Phase Transformers

Three Phase Transformers In generation, transformation, transmission and utilization of electric energy it can be shown that it is economical to use the three-phase system rather than the single-phase. For three-phase transformation, three single-phase transformers are needed. Two arrangements are possible: a bank of three single-phase transformers or a single three-phase transformer with the primary […]

Excitation Phenomenon in Transformers

Excitation Phenomenon in Transformers It was stated in Sec. 3.3 that the no-load current in a transformer is nonsinusoidal. The basic cause for this phenomenon, which lies in hysteresis and saturation non­linearities of the core material, will now be investigated; this can only be accomplished graphically. Assume that the voltage v1 applied to the transformer […]

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