Protection & Measuring Devices of power transformer.

How power transformer Protected

i) Oil Conservator Tank

a) The Conservator tank shall have adequate capacity between highest and lowest visible levels to
meet the requirement of expansion of the total cold oil volume in the transformer and cooling equipment.
 b) The conservator tank shall be bolted into position so that it  can be remove for cleaning  purposes.
c) The conservator shall be fitted with magnetic oil level gauge with low level electrically insulated
alarm contact.
 d) Plain conservator fitted with silica gel breather.

 ii) Pressure Relief Device.

The pressure relief device provided shall be of sufficient size for rapid release of any pressure that may  be generated in the tank and which may result in damage of the equipment. The device shall operate at a static pressure of less than the hydraulic test pressure of transformer tank. It shall be mounted direct on the tank. A pair of electrically insulated contract shall be provided for alarm and tripping.

iii) Buchholz Relay

 A double float type Buchholz relay shall be provided., Any gas evolved in the transformer shall collect in this relay. The relay shall be provided with a test cock suitable for a flexible pipe connection for checking its operation. A copper tube shall be connected from the gas collector to a valve located about 1200 mm above ground level to facilitate sampling with the transformer in service. The device shall be provided with two electrically independent potential free contracts, one for alarm on gas accumulation and the other for tripping on sudden rise of pressure, 

iv) Temperature Indicator

a) Oil Temperature Indicator (OTI) The transformers shall be provided with a mercury contact type thermometer with 150 mm dial for top oil temperature indication. The thermometer shall have adjustable, electrically independent potential free alarm and trip contacts. Maximum reading pointer and resetting device shall be mounted in the

local control panel. A temperature sensing element suitably located in a pocket on top oil shall be furnished. This shall be connected to the OTI by means of capillary tubing. Accuracy class of OTI shall be ± 1% or better. One No electrical contact capable of operating at 5 A ac at 230 volt supply.
b) Winding Temperature indicator(WTI)

A device for measuring the hot spot temperature of the winding shall be provided. It shall comprise the following.
i) Temperature sensing element.
ii) Image Coil.
iii) Mercury contacts.
iv) Auxiliary CTS, If required to match the image coil, shall be furnished and mounted in the local control panel.
v) 150mm dial local indicating instrument with maximum reading
pointer mounted in local panel and with adjustable electrically independent ungrounded contacts, besides that required for control of cooling equipment, one for high winding temperature alarm and on for trip.
vi) Calibration device.
vii) Two number electrical contact each capable of operating at 5 A ac at 230 Volt supply.

                                                                                                       Source-REC Technical Specification
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