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 […]

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. […]

Choice of Transformer Connections

Choice of Transformer Connections: 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 large […]

Three Phase Transformer

Three Phase Transformer: 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 Transformer, 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 […]

Variable Frequency Transformer

Variable Frequency Transformer So far we have considered transformers which operate at fixed frequency (50 Hz). Their purpose is to transform electric power from one voltage level to another; their performance measures being high efficiency and low voltage regulation. Small transformers (usually iron-cored) are used for coupling purposes in electronic circuits for communication, measurement and […]

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 […]

Voltage Regulation Formula

Voltage Regulation Formula: Voltage Regulation Formula – Constant voltage is the requirement of most domestic, commercial and industrial loads. It is, therefore, necessary that the output voltage of a transformer must stay within narrow limits as the load and its power factor vary. This requirement is more stringent in distribution transformers as these directly feed […]

Efficiency and Voltage Regulation

Efficiency and Voltage Regulation Power and distribution transformers are designed to operate under conditions of constant rms voltage and frequency and so the efficiency and voltage regulation are of prime importance. Efficiency The rated capacity of a transformer is defined as the product of rated voltage and full load current on the output side. The […]