Introduction
In this session we are gonna discuss about some protective devices and accessories ie used in transformers
1.Double-float Buchholz relay
For sudden pressure rise and gas detection in oil-immersed transformer tanks with conservator. Installed in the connecting pipe between tank and conservator and responding to internal arcing faults and slow decomposition of insulating materials. Additionally, backup function of oil alarm. The relay is actuated either by pressure waves or gas accumulation, or by loss of oil below the relay level. Seperate contacts are installed for alarm and tripping.
In case of a gas accumulation alarm, gas samples can be drawn directly at the relay with a small chemical testing kit. Discolouring of two liquids indicates either arcing byproducts or insulation decomposition products in the oil. No change in colour indicates an air bubble.
2.Dial-type contact thermometer
Indicates actual top-oil temperature via capillary tube. Sensor mounted in well in tank cover. Up to four separately adjustable alarm contacts and one maximum pointer are available. Installed to be readable from the ground.
With the addition of a CT-fed thermal replica circuit, the simulated hot-spot winding temperature of one or more phases can be indicated on identical thermometers. These instruments can also be used to control forced cooling equipment
3.Magnetic oil-level indicator
The float position inside of the conservator is transmitted magnetically through the tank wall to the indicator to preserve the tank sealing standard device without contacts; devices supplied with limit (position) switches for high- and low-level alarm are available. Readable from the ground.
4.Protective device for hermetically sealed transformers (TUMETIC)
For use on hermetically sealed TUMETIC distribution transformers. Gives alarm upon loss of oil and gas accumulation. Mounted directly at the (permanently sealed) filler pipe of these transformers.
5.Pressure relief device
Relieves abnormally high internal pressure shock waves. Easily visible operation pointer and alarm contact. Reseals positively after operation and continues to function without operator action.
6.Dehydrating breather
A dehydrating breather removes most of the moisture from the air which is drawn into the conservator as the transformer cools down. The absence of moisture in the air largely eliminates any reduction in the breakdown strength of the insulation and prevents any buildup of condensation in the conservator. Therefore, the dehydrating
breather contributes to safe and reliable operation of the transformer.
7.Bushing current transformer
Up to three ring-type current transformers per phase can be installed in power transformers on the upper and lower voltage side. These multiratio CTs are supplied in all common accuracy and burden ratings for metering and protection. Their secondary terminals are brought out to short circuiting-type terminal blocks in watertight terminal boxes.
Additional accessories
Besides the standard accessories and protective devices there are additional items available, especially for large power transformers. They will be offered and installed on request.
Examples are:
■ Fiber-optic temperature measurements
■ Permanent gas-in-oil analysis
■ Permanent water-content measurement
■ Sudden pressure rise relay, etc.
Also read
What is Instrument Transformers?
What is Linear Variable Differential Transformers(LVDT)
