What is are the Type of Temperature Indicator of Transformer?

What is are the Type of  Temperature Indicator of Transformer?

Temperature Indicator Definition

A temperature indicator in transformers is defined as a precision device used for protection, temperature indication, and cooling control.

Construction of Temperature Indicator of Transformer

These indicators are provided with a sensing bulb. This sensing bulb is placed in a pocket on the roof of transformer tank. The pocket is filled with transformer oil. The bulb is connected to the instrument housing by means of flexible connecting tubing consisting of two capillary tubes. One capillary tube is connected to the operating bellow of the instrument and other to a compensating bellow. Compensating bellow compensates variation of ambient temperature. The pointer is fixed with a steel carriage on which normally four mercury switches are mounted. The make and break temperature of these mercury switches can be adjusted separately. One mercury switch is use to operate cooling fans, one mercury switch is used to switch on oil pumps, one mercury switch is for high temperature alarm and last switch is used to inter trip the transformer in extremely high temperature condition.

Types of Temperature Indicator of Transformer

• Oil temperature indicator (OTI)

• Winding temperature indicator (WTI)

• Remote temperature indicator (RTI)

Oil Temperature Indicator (OTI)

OTI measures the top oil temperature using a sensing bulb and liquid expansion to drive a pointer indicating temperature.

Operating Principle of Oil Temperature Indicator

This device measures top oil temperature with the help of sensing bulb immersed in the pocket by using liquid expansion in the bulb through a capillary line to operating mechanism. A link and lever mechanism amplifies this movement to the disc carrying pointer and mercury switches. When volume of the liquid in operating mechanism changes, the bellow attached to end of capillary tube expands and contracts. This movement of bellow is transmitted to the pointer in temperature indicator of transformer through a lever linkage mechanism.

Winding Temperature Indicator (WTI)

WTI measures winding temperatures using a sensing bulb heated by a coil, reflecting the current through the transformer winding.

Operating Principle of Oil Temperature Indicator

The basic operating principle of WTI is same as OTI.

Remote Temperature Indicator (RTI)

RTI uses a potentiometer as a transmitter to relay temperature data to a remote repeater.