Distribution Transformers with OLTC

On load tap changer (OLTC) is used with higher capacity transformers where HT side voltage variation is frequent and a nearly constant LT voltage is required. OLTC is coupled with the transformer itself. Multiple tapings from HV windings are brought to the OLTC chamber and connected to fixed contacts. Moving contacts rotates with the help of rotating mechanism usually a Geneva mechanism having a spindle. The spindle can be rotated manually as well as electrically with a motor. Motor is connected in such a way that it can rotate in both the directions such as to rotate the OLTC moving contacts clockwise and anti clockwise. Two push buttons are fitted on the LCP (lowcontrol panel) to rotate the motor and hence the OLTC contacts. This movement of contacts thus controls the output LV voltage of the transformer. So rotating of the OLTC contacts with spindle or push button in this way is manual process. In case this process of rotating the OLTC contacts and hence controlling the LV side voltage is to be done automatically then a RTCC (remote tap changer controller) is installed with the transformer ht panel. The RTCC panel which has sensors which sense the output voltage and accordingly sends signal to LCP and LCP in turns rotates the motor as per signal received from the RTCC.

GTB Distribution Transformer with OLTC
Distribution Transformer with OLTC


OLTC Transformers are used in :-

1.) Chemical plant, Bottling plant.
2.) Paper mills, Sugar mills, Rolling mills, Steel mills.
3.) Industries which rely heavily on automation, where electronic cards, PLC and VFDs are used in operations and actuation.


Unless or otherwise specified, the transformers will be connected as per Vector Group reference DYn 11 in accordance with International practice.

The core used is best quality cold rolled grain oriented and laser processed silicon steel sheet. They provide low iron loss, low noise, and compact size and have the best performance for high efficiency transformers.

We use high quality conductor of copper aluminium in our products. Round or rectangular copper/aluminium wires ribbed with thermally upgraded insulting paper are applied in oil immersed transformers. The winding have a compact size, excellent heat transmission, low load loss, high lighting impulse resistivity and outstanding anti-short- circuit strength.

Our oil-immersed transformers are insulated by electrical grade insulated press board and thermally upgrade insulating Kraft paper.

Tapings + 5% to -15% in steps of 1.25% or as per customer’s requirement.

Dehydrated EHV-Grade transformers oil as per IS 355 (1993) with latest amendments is used for proper insulation and cooling after testing for all the parameters viz a viz resistivity, tan delta, BDV, neutralization, flash point etc.

HV/LV Bushings: The quality porcelain bushings are used on the high voltage terminals/low voltage terminals. Optional bushing wells, inserts and elbows are available upon request. High voltage cables are inserted directly and show no live parts outside.

The accessories include an oil filling hole, oil drain valve, safety valve, standard thermometer, oil level gauge, skid wheel, jacking pad, breather, earthling terminal


Buchholz relay, cooling fan, HV & LV cable box, cable duct, bus bar duct, dial-type thermometer, oil level gauge, on-load type tap changer, protective fuse and lightening arresters are available upon customer’s request at extra cost.