TOPIC TITLE TRANSFORMERS 2 a Name the types of onload tap c

TOPIC TITLE : TRANSFORMERS

2.

(a) Name the types of on-load tap changer.

(b) Which is the most commonly used and why?

Solution

OLTC

provision of taps in a transformer in order to control the voltage is called tap cahnging.in a transformer tapching can be done in two situations

off load conditions- tap positions are changed by taking transformer out of the circuit and reconnecting it back to the circuit.it is cost effective but interrupt the power suppy.hence genrally on load tap changing transformer method is used for voltage control

ON LOAD TAP CAHNGING TRANSFORMER-

in this method tap changing is done without disconnecting load current,hence maintainig the continuity of power supply. OLTC is comparetively costly hence oltc are classified on the following basis-

1-on the basis of tap changers

2-scheme used for tap canging

on the basis of tap changing-

there are two type of tap changers-

a) Mechanical tap changer- by using tap selector switch mechanicaly tapping is done

b) thyristor tap changer-tap changing is done by using thyristorsas a tap changer. its complicated, costly, automated but efficient method .this type of tap changer is used in modern transformer

ON THE BASIS OF SCHEME USED FOR TAP CHANGING-

OLTC ARE KEPT AT HIGH VOLTAGE SIDE BECAUSE THE MAGNITUDE OF CURRENT IS LESS SO THAT INTENSITY OF ARCING IS LESS DUE TO TAP POSITION CHANGING

REACTOR METHOD- in this method auxillary reactor is used for tap changing which provides an alternate path  for load current to flow.

PARALLEL WINDING METHOD-in this method primary winding is spillited into two parallel circuit each having taps two circuit breaker also required for the parallel circuit breaker which increases the cost of system

B) in genral aumatic tap changing that is thyristor tap changer is preffered over mechanical ,as it is operated by motors,which respond to relay set to hold the voltage at the prescibed level providing an additional discharge path for load current through reactor so that circuit allow the change to be made without interrupting the supply

BOOSTER TRANSFORMER IS ALSO PROVIDED SUPPLY BY A SOURCE TARNSFORMER HAVING OLTC ARRANGEMENT