A distribution transformer is used to step down the 11 kv a.c. supply to 230/440 volts a.c. and are available in different KVA rating depending upon the requirement of the consumers. The main parts of a distribution transformer are explained
a) Primary Winding: The primary winding of a distribution transformer is connected in delta as shown in figure. There are three different windings and is circular wound. These are placed on the three different limbs of the transformer core. The size of primary winding wire used is thinner than secondary winding but having larger number of turns.
b) Secondary Winding: The secondary winding of a distribution transformer is connected in star as shown in figure. There are three different windings and is circular wound. These are placed on the three different limbs of the transformercore. The size of winding wire used is thicker than primary winding but having lesser number of turns.
c) Transformer Oil: The transformer oil is used to transfer the heat generated due to copper losses in the winding as well as in the transformer core due to eddy currents and hysteresis. Due to passage of time, the transformer oil loses its dielectric strength due to absorption of moisture through the breather. The solid impurities present in the oil also reduce its dielectric strength. A good
remedy is to filter and dehydrate the transformer oil with a special technique and machine, known as “Transformer oil Filtration Machine” to increase its dielectric strength.
d) Conservator: It is used as reservoir mounted on the top of the transformer.It is connected to the transformer through the buchhol’s relay.This relay is only used in large capacity transformers. An oil level indicator is provided to observe the oil level in the reservoir. The oil level can be maintained by adding more dry oil in the conservator. It provides a reserve space for the expended oil due to increase in temperature of the winding and core. When the temperature is reduced the expended oil starts contracting and goes back to the transformer tank and hence it acts as a reservoir.
e ) Breather: As the name indicates, it is used for providing breathing passage for the transformer. The air present in the empty conservator is forced to escape to the atmosphere through the breather, when the oil level in the conservator increases due to increase in temperature and vice versa. This air is escaped to atmosphere through a box containing silica gel in the form of crystals. The colour of fresh or fully activated gel gets changed from blue to bright pink as it absorbs the moisture. It absorbs the moisture from the atmosphere, when the transformer oil starts contracting or during inward rush of air. This pink deactivated silica gel is removed from the breather and baked in a baking oven for reactivation. After reactivation its colour will again converted into blue.
f) Oil Drain Point: It is used to drain the transformer oil in a container when it becomes necessary to drain all the oil from the tank for visual inspection or repair and maintenance of winding. Sometimes we have to replace the transformer oil when the dielectric strength gets reduced. A screwed cap and valve is also provided on the out let, for opening and closing the drain point.
g) Cooling Tubes: As the name indicates, these tubes are used to cool down the temperature of the transformer oil. The shape, size and number of tubes depend upon the KVA rating of the transformer. In small capacity transformers cooling is provided by natural convention of heat generated, through the cooling tubes but in large capacity transformers the fans are provided for forced air-cooling.
h) Oil Level Indicator: The oil level indicator is used to indicate the minimum oil level in the reservoir. The level may be top up by adding new or dehydrated transformer oil.
i) Earth point: The earth point is used to connect the neutral wire and body of the transformer to ground potential. It is mandatory from safety point of view.
j) Explosion Vent: When there is sudden increase in oil level due to any external or internal faults, the oil level in the reservoir will increase sharply. Although the buchhol’s relay is provided to meet such type of eventualities or emergencies but in the event of failure of all other protections the safety plug will burst and oil is allowed to flow out through the explosion vent.
k) Tap Changer: The tap changer is used to increase or decrease the a.c. out put voltage of the transformer depending upon the requirement and conditions.It is always connected in the low current winding so that minimum arc is produced, while changing the voltage tapings. We can change the tapings with or without load. In small rating transformer it can be operated manually where as the large capacity transformers are motor operated through remote instrumentation.
a) Primary Winding: The primary winding of a distribution transformer is connected in delta as shown in figure. There are three different windings and is circular wound. These are placed on the three different limbs of the transformer core. The size of primary winding wire used is thinner than secondary winding but having larger number of turns.
b) Secondary Winding: The secondary winding of a distribution transformer is connected in star as shown in figure. There are three different windings and is circular wound. These are placed on the three different limbs of the transformercore. The size of winding wire used is thicker than primary winding but having lesser number of turns.
c) Transformer Oil: The transformer oil is used to transfer the heat generated due to copper losses in the winding as well as in the transformer core due to eddy currents and hysteresis. Due to passage of time, the transformer oil loses its dielectric strength due to absorption of moisture through the breather. The solid impurities present in the oil also reduce its dielectric strength. A good
remedy is to filter and dehydrate the transformer oil with a special technique and machine, known as “Transformer oil Filtration Machine” to increase its dielectric strength.
d) Conservator: It is used as reservoir mounted on the top of the transformer.It is connected to the transformer through the buchhol’s relay.This relay is only used in large capacity transformers. An oil level indicator is provided to observe the oil level in the reservoir. The oil level can be maintained by adding more dry oil in the conservator. It provides a reserve space for the expended oil due to increase in temperature of the winding and core. When the temperature is reduced the expended oil starts contracting and goes back to the transformer tank and hence it acts as a reservoir.
e ) Breather: As the name indicates, it is used for providing breathing passage for the transformer. The air present in the empty conservator is forced to escape to the atmosphere through the breather, when the oil level in the conservator increases due to increase in temperature and vice versa. This air is escaped to atmosphere through a box containing silica gel in the form of crystals. The colour of fresh or fully activated gel gets changed from blue to bright pink as it absorbs the moisture. It absorbs the moisture from the atmosphere, when the transformer oil starts contracting or during inward rush of air. This pink deactivated silica gel is removed from the breather and baked in a baking oven for reactivation. After reactivation its colour will again converted into blue.
f) Oil Drain Point: It is used to drain the transformer oil in a container when it becomes necessary to drain all the oil from the tank for visual inspection or repair and maintenance of winding. Sometimes we have to replace the transformer oil when the dielectric strength gets reduced. A screwed cap and valve is also provided on the out let, for opening and closing the drain point.
g) Cooling Tubes: As the name indicates, these tubes are used to cool down the temperature of the transformer oil. The shape, size and number of tubes depend upon the KVA rating of the transformer. In small capacity transformers cooling is provided by natural convention of heat generated, through the cooling tubes but in large capacity transformers the fans are provided for forced air-cooling.
h) Oil Level Indicator: The oil level indicator is used to indicate the minimum oil level in the reservoir. The level may be top up by adding new or dehydrated transformer oil.
i) Earth point: The earth point is used to connect the neutral wire and body of the transformer to ground potential. It is mandatory from safety point of view.
j) Explosion Vent: When there is sudden increase in oil level due to any external or internal faults, the oil level in the reservoir will increase sharply. Although the buchhol’s relay is provided to meet such type of eventualities or emergencies but in the event of failure of all other protections the safety plug will burst and oil is allowed to flow out through the explosion vent.
k) Tap Changer: The tap changer is used to increase or decrease the a.c. out put voltage of the transformer depending upon the requirement and conditions.It is always connected in the low current winding so that minimum arc is produced, while changing the voltage tapings. We can change the tapings with or without load. In small rating transformer it can be operated manually where as the large capacity transformers are motor operated through remote instrumentation.
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