16 Main Parts of Electrical power Transformer-Electronicsinfos

 Construction of Electrical Transformer

A transformer consists of different parts that play an important role in working. The different parts are

1. core
2. Steel tank
3. Windings
4. Conservator
5. Breather
6. Thermometer
7. pressure relief pipes
8. Valves
9. Buchholz Relay
10. Bushings
11. Tap changing switch
12. Oil gauge
13. Radiator
14. Cooling fans
15. Oil pumps
16. Transformer insulation

core

Every transformer contains laminated steel sheets. The purpose of laminated steel sheets is to reduce the eddy current losses and provide a regular magnetic path. we also process heat treatment on the steel sheets. The result of heat treatment is an increase in the permeability of magnetic material. The permeability and hysteresis losses are inverse relations that's why we process heat treatment on the steel sheets to increase the permeability. each sheet of the core is laminated by an insulating medium. The thickness of sheets at 50c/s is 0.35mm and at 25c/s is 0.5mm.

In standard practice, a single-phase transformer core consists of 2 legs and a three-phase transformer core is consist of 3 legs. The core is constructed circular and rectangular depending on the capacity of the transformer. This laminated core is also tight with the help of bolts.

Steel tank

The steel tank is constructed with steel material in a box form. The windings, core and other auxiliary components are put in the steel tank to protect from mechanical strikes and environmental conditions. This tank is filled with insulating oil or mineral oil that provides insulation and cooling.

Windings

A single-phase transformer consists of one primary and secondary winding and a three-phase transformer consists of three primary windings and three secondary windings. These winding are connected in proper sequence. The sequence of windings in the core is first we wind low voltage winding and then wind high voltage winding. both windings are insulated from each other. The windings are also constructed in the form of a disc and helical coil springs. The form of windings depends on the capacity of a transformer either constructed in square form or continuous disc wound form. To increase the mechanical strength of windings we varnish with the heat-bonded.

Conservator

A conservator is a small tank which is used on the upper side of the main tank. this type of tank is normally cylindrical. conservator and main tank are connected to each other with the help of a pipe. A Buchholz relay is also used between the conservator tank and the main tank if the size of the transformer is above 1MVA. The main function of a conservator is 

1. When oil is heated and expended it provides a space.
2. It reduced the oxidation to reduce the oil surface area.

because we know the expansion co-efficient of oil is high the level of oil also increases and decreases.

Breather

A breather is a device that is used to in and out of the air in the transformer. when oil is expanding due to heat the air is out from the tank and when oil is compressed the air is in from the environment. One side of the breather is connected to the conservator tank. the breather contains silica gel in a box. When air is entered into the tank the moisture content is present in the air that disturbs the insulation of winding so we use silica gel for this purpose .silica gel absorbed all moisture content in the air and sends dry air to the transformer. Due to the absorption of moisture, the colour of silica gel is changed from blue to pink then needs to be changed.

Thermometer  

If the transformer rating is above 50Kva, we use a Thermometer to analyse the internal temperature of the transformer or oil. when the temperature exceeds the predetermined value or threshold value the signal is generated and the transformer is trip. we use a dial-type thermometer in the transformer. The dial-type thermometer is connected to the sensor that senses the temperature of transformer oil. The threshold temperature of the oil is 105 Degrees.

pressure relief pipes

pressure relief pipe is mounted on the main tank of the transformed. it is a curved pipe that protects from excessive pressure. When Decomposition is started in the transformer high pressure is generated and pressure relief pipes are used to withdraw this high pressure and protect the transformer from bursting. The structure of the pressure relief vent consists of adjusting the spring and bellows that sense the high pressure and operate mechanically shaft.

Valves

There are different valves used in the transformer to fill the oil, Drain the oil, Filter the oil and sample of oil.

Buchholz Relay

Buchholz is a gas-operating relay that is used to protect the transformer from bursting. It's connected between the main tank and the conservator. it s consists of two floats. one float is operated in an emergency situation and connected to the trip circuit. The other float is generate an alarm signal. when the oil level is low or another internal fault appears in the transformer the gases are produced due to the decomposition of insulating material. Due to the lightweight of the gas, it moved to the upper side and operates the Buchholz relay float. This float is connected to the alarm circuit and trips the circuit.

Bushings

Bushings are used to withdraw the terminals from the transformer to protect against short-circuiting. The material of bushings is porcelain and oil-filled capacitor type. There are two types of busing one for L.T and another one for H.T side. To protect from lightning The arching horns are used on the upper and lower sides of bushings. There are two types of bushings w.r.t construction one is Sealed condenser type oil filled bushing that voltage ratings are 34.5 kV and plain bushings that voltage rating is 25kv.

Tap changing switch

There are two types of Tap changing Switch 

1. Offload Switch
2. On load Switch

Offload Switch

The offload switch is used to change the voltage ratio of the winding in the transformer. When primary voltages are high we need a high number of turns and when voltage is low the low number of turns is used in the transformer. This whole process is done in the off-circuit because when we change the turns ratio the arc is produced in the windings so we need to shut down the transformer to operate the offload switch. In a small transformer, the internally operated switch is used and for a large transformer, the external switch is used in the transformer.

On load Switch

Resistor-type and reactor-type tap changers consist of oil switches and vacuum switches. Resistor-type selector switches are used in the power distribution transformer. these windings are connected by the star and delta. In the star connection, the voltage ratings are between 66kv to 30MVA and in the delta connection, the voltage rating is between 66Kv to 40MVA. we also used an autotransformer with voltage ratings up to 132kv.

Oil gauge

Oil gauges are used to measure the level of the oil. oil gauge is normally a dial-type in which a pointer is used to indicate the level of transformer oil. the one advantage of dial type is we can easily measure the level of oil. oil gauge is used in the medium level of the transformer.

Radiator

Radiators are used if transformer ratings are above 50KVA. Radiators are used with the main tank of the transformer. This consists of pipes and tubes that increase the surface area of the tank. Radiators are used for the cooling purpose of transformer oil. this method is also called ONAN(Oil natural and Air natural).

Cooling fans

Cooling fans are used in the ratings of 1MVA to 26MVA. These are used with the radiator to increase the efficiency of the radiator. This model is also called ONAF(Oil Natural And air forced). There are some specific temperatures on the contacts.

Oil pumps

if transformer ratings are above the 26MVA The oil pumps are also used with cooling fans and radiator. oil pumps are used too fast for the circulation of oil. This type of mode is called OFAF(Oil forced and air forced).

Transformer insulation

Mineral oil is used in the transformer for insulation protection. This oil provides cooling also in the transformer. we also used SF6 as an insulating media.

If we used an SF6 the overall weight is also reduced in the transformer. The chemical property of SF6 is fireproof.

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