Power Transformer Complete Accessories

1. Cooling Unit (Radiators, Cooling Fans & Oil Pumps)

As the name says, a function of the cooling unit of the Power Transformer is to cool down Transformer oil. When the Power transformer is in service, the temperature of the Transformer oil rises. Hence it is essential to keep the oil temperature down for smooth running of the Power Transformer.

2. Conservator Tank & Air Cell

whenever we see a transformer, we notice a cylindrical tank mounted a little higher than the transformer. This tank is called an oil conservator tank. The main function of a conservator is to store extra oil of the transformer and provide space for transformer breathing. This extra oil compensates for oil drained in case of small oil leakage or seepage from the transformer tank, and hence keeps the insulation strength of the transformer unaltered. In the absence of an oil conservator, oil leakage will cause low oil levels in turrets of the bushing, since bushing turrets are the uppermost part of the transformer. This leads to degradation of the insulation level of turrets which is undesirable. Hence in such cases, since the conservator is at a higher altitude than the transformer tank and bushing turrets, the oil level will get down in the conservator only, keeping the insulation level of turrets intact. Thus it also provides some extra time for transformer oil refilling. Because without a conservator, leakage will cause a low oil level in the main tank itself causing an emergency. Whereas low oil levels in the oil conservator can be refilled at a suitable time but the earliest. This avoids an emergency in an electrical substation.

Also there is another layer of protection, which is aircell. Aircell is made of Nitrile Rubber. Since air gets accumulated in air cell, there is no direct contact between breathed in air and transformer oil. Hence this avoid any possible moisture ingress or contamination of transformer oil. Which consequently increases transformer life.

3. Silica Gel Breather

Silica gel breathers are used in Power Transformers for the breathing process. Silica gel is the most commonly used desiccant means hygroscopic drying agent.  Silica gel absorbs water. This is the main property due to which silica gel is used as a drying agent. When transformer oil temperature drops, oil contracts and oil level in conservator goes down. So to compensate for this contracted volume of oil, atmospheric air gets inside the air cell through a breather and it air cell expands, compensating contracted oil volume. When the transformer oil temperature increases, the oil expands, and the oil level in the conservator goes down. To accommodate this extra volume of oil, expanded oil pushes the air cell up, and the air cell gets contracted, pushing air out through breathers. This process of air in and out through a breather is called transformer breathing. Here the air which gets inside of air cell passes through silica gel breathers. This silica has the property of absorbing water. Also, there is an oil cap at the bottom of the breather which catches any other contaminations in the air. Hence the air that goes into air cell is dry and free of contamination.

4. PRV/PRD - Pressure Relief Valve

 PRV/PRD installed on transformer tank, called as Pressure Relief Valve/Device. As name says, this device provides a passageway, for oil to release the pressure, developed inside transformer. Hence it protects transformer from developing a very high pressure inside Transformer Tank.

5. MOLG - Magnetic Oil Level Gauge

MOLG – Magnetic Oil Level Gauge. Function of MOLG is to measure and indicate Transformer Oil Level. MOLG also has N-O N-C contact. Using these contacts Alarm and Trip commands are given by MOLG to the Transformer Protection system. This helps to monitor the transformer oil level.

6. POLG - Prismatic Oil Level Gauge

POLG – Prismatic Oil Level Gauge. This is also a Transformer oil level indicator. The main difference between MOLG & POLG is that MOLG can give Alarm and Trip commands to the transformer protection system, whereas POLG dos not have such provisions. POLG is used just for Transformer oil indication.

7. Buchholz Relay

The Function of the Buchholz Relay is to identify the incipient internal faults of the power transformer. This helps to avoid any major failure of the transformer, since the fault is detected in its early stage due to the Buchholz Relay. Using its N-O & N-C contacts Buchholz Relay sends Alarm and Trip Signals to the Protection system of Power Transformer, depending upon severity of faults.

8. Marshalling box

Marshaling Box is nothing but the common junction point for OTI and WTI housing. Also, Cooling fans and pumps controls, wiring of Buchholz relay, PRV, OSR, MOLG and other important monitoring and protection system is housed in the TB mounted in the Marshalling box.

9. OTI - Oil Temperature Indicator
WTI - Winding Temperature Indicator

As the name says, OTI & WTI are used for Transformer Oil Temperature Indication and Winding Temperature Indication respectively. Similarly, OTI & WTI have N-O & N-C contacts used for Alarm and Trip command purposes. 

10. OSR - Oil Surge Relay

OSR – Oil Surge Relay is used for identification of Oil surges in OLTC oil Compartment. OSR is mounted on the pipe connecting OLTC oil compartment & Oil Conservator. In case of Oil surge OSR give trip command to the Transformer protection system.

11. OLTC DM box - On Load Tap Changer Drive Mechanism

OLTC DM has an electric motor and gear assembly which operated OLTC. In the case of an AVR i.e. Automatic Voltage Regulator. DM box and accordingly it changes the tap to the desired position automatically depending upon high voltage or low voltage levels. In Case of non AVR system. OLTC taps can be changed by giving raise or lower manually, by using the respective push button.

12. Air release plug

Air Release Plug is used to release the trapped air during oil filling. This air gets trapped inside the pockets of the Transformer tank and Radiator due to the profile of the Transformer Tank & Radiator. These are generally made of Brass material.

13. Gate Valve

Gate Valves are used for Oil flow control of the Power Transformer such as Oil Filling, Oil draining, oil filtering, and flushing. With Gate Valve, oil flow can be controlled manually by rotating its handle.

14. Butterfly Valves

Butterfly Valves are used for coupling Radiators to the Transformer Tank. Butterfly Valve in an open condition allows only one-directional oil flow. Unlike Gate Valve, Butterfly Valve does not provide flow control. Once opened it allows complete flow in one direction. These are used in places where the backflow of the oil is not desired.

15. Rollers

These rollers are fitted on the base of Transformer tank. And these rollers are mounted on the rails. This makes the movement, fixation and installation of the transformer easy. Bi-directional type of rollers can be locked in the required direction by bolting the roller mounting pad welded on the tank base.

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