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Advanced On-load Tap-changer (OLTC)

The on-load tap changer (OLTC) is used to change the tapping connection of the transformer winding to change the voltage ratio while the transformer is still in service without interrupting the load [1][2]. An on-load tap-changer gear comprises two major components, the tap selector and the diverter switch. The tap selector selects the tapping and its electrical contacts are designed to carry the rated current of the transformer but not to make or break this current. The diverter switch, however, needs to be designed to carry, make and break the load current in circuits previously selected by the tap selector. During the operation of diverter switch the transition resistors bridge the tap in use and the tap next to be used, thereby limiting the circulating current due to the inter-tap voltage[3].


On-load tap changing transformers are widely used for voltage regulation and also as phase-shifting Transformers[4].


[1] Albrecht, H. C. Transformer Tap Changing Under Load. Transactions of the American Institute of Electrical Engineers. Volume: XLIV. Page(s): 581 - 586 . Jan. 1925.
[2] Douglas. M. Getson. On-load Tap Changers. Document updated: 2002-11-06. ABB
[3] Dawei Gao, Qingchun Lu, Jishou Luo. A New Scheme for On-load Tap-changer of Transformers. International Conference on Power System Technology, 2002. Proceedings. Vol.2 Page(s): 1016 - 1020. Dec. 2002
[4] On-Load Tap-Changers for Power Transformers A Technical Digest. MR Publication. URL: http://www.reinhausen.com/XparoDownload.ashx?raid=2188

Key Technology Area: 
Advanced Components

Sample Vendors:
Name Product description Submitted on Submitted by Affiliation Contact information
ABB 09/30/10
AREVA 09/30/10
GE 09/30/10
Siemens 09/30/10
TOSHIBA 09/30/10


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