Transformer Tap Changing
A tap changer is a device fitted to power transformers for regulation of the output voltage to required levels.When load is constant its ok but whenever load is not constant its varying with the requirement. Hence, Transformer Tap Changing is necessary.
By tap changer we can varying voltage as per require voltage of load. Voltage regulation of the secondary voltage of transformer can be over came by using tap changer at secondary side.
When transformer is loaded with the constant primary voltage. Its secondary voltage changes because of its internal resistance and reactance of conductors.
Voltage control in system is done by the altering voltage transformation ratio by providing tappings on the high voltage winding.Tap changing is done when transformer is disconnected from the supply.
There are two types of tap-changers,
- ON load tap changer
- OFF load tap changer
OFF Load tap changer :-
Arrangement of off load tap changer is shown in fig,
In this type of changers generally 2.5% to 5 % tapping arr provided on the transformer winding for regulating the voltage. This is made by off load tap changer at high voltage side. for the changing of tap its necessary to disconnect the supply by circuit breaker. this type is used when tap changing required for very long time.
ON load tap changer:-
Arrangement of ON load tap changer is shown in fig,
The tappings of ON load tap changer is can be changed without disconnect supply voltage from the circuit.
Motor drive unit is used for the operations of tap changer. Its operated by manually in Case of emergency and by remote control during normal conditions. durimg the tap changing high short circuit current will flowing. By using the pair of resistors we can limit that high current.
Tappings are provided on the high voltage side.because of following reasons ,
- High voltage side current rating is low ,hence during the tap changing no sparks occur between the two terminals.
- The Low voltage winding is placed on the inside nearer to the core while High voltage winding is placed on the outside.
- Fine voltage regulations can be obtained, because no of turn in high voltage winding is large.
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