It seems most answers are ommiting the essential
function/characteristic(ON LOAD).I have a vague idea may be
someone will add.
It is my understating that with this tap changer you can
change winding tap position without breaking/swithing off
the load.This is achieved by the MAKE BEFORE BREAK
mechanism in the tap switch.
Hope someone will add.
Dear Dnyaneshwar, Please mote that 1)In HV transformers the LV winding is nearer to core and the HV winding is away from Core There fore it is easy for taking the taps .2) The current in HV being lower the switching current in OLTC is low.
Please note. 3)The RTCC means the Remote Tap Change Control Cubical This is installed in Control Room so that the Taps of the Transformer which is installed in Switch Yard can be changed from the Control room only. 4)The RTCC if provided with AVRCR then the taps are changed automatically by sensing the LV voltage. The AVRCR means AUTOMATIC VOLTAGE CORRECTION RELAY. 5) In bigger transformers say Voltage class 220 KV and above the OLTC tap connections are provided on LV side due to the insulation levels of high voltages at the switch.
OLTC is On load Tap Changer to maintain constant voltage at
secondary side according to change in load. Tappings are
provided on HV winding as this winding is outer on the core.
So less insulation will be required. By changing taps on HV
side, we can monitor voltage at secondary side. Basically,
this tapping is provided on HV side because there is high
fluctuation of voltage on HV side (i.e. from supply
company). Tap changing process is done by RTCC (i.e. Remote
Tap Changer Controller). This is installed in HT panel of
transformer. RTCC sends signal to LCP (local control panel)
which is in turn motor rotates it rotor as per signal
received from RTCC. It is generally used for higher capacity