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 […]

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. […]

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 […]

Basic Relays

Basic Relays: Most of the Basic Relays used in the power system operate by virtue of the current and/or voltage supplied by current and voltage transformers connected in various combinations to the system element that is to be protected. Through the individual or relative changes in these two quantities, faults signal their presence, type and […]

Protective Relay

Protective Relay: A Protective Relay is a device that detects the fault and initiates the operation of the circuit breaker to isolate the defective element from the rest of the system. The Protective Relay detect the abnormal conditions in the electrical circuits by constantly measuring the electrical quantities which are different under normal and fault […]

Switchgear Components in Circuit Breakers

Switchgear Components in Circuit Breakers: The following are some important components common to Switchgear Components in Circuit Breakers : Bushings Circuit breaker contacts Instrument transformers Bus-bars and conductors 1. Bushings: When a high voltage conductor passes through a metal sheet or frame which is at earth potential, the necessary insulation is provided in the form of […]

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