Power Transformer & Distribution Transformer

Distribution Transformer & Power transformer:

Based on the service of the transformers in power systems may be divided into two categories. These are

  • Distribution transformers
  • Power transformer

Distribution Transformers:

The Word in the distributions transformer’s “distribution” means the equipment distributing something.  Distribution Transformers are, upto a size of about 500kVA in rural areas and up to 5 MVA in industrial area, used to step down the transmission voltage to a standard service typically 440 Volts in India, 120 Volts in US. They are kept in operations all the 24 hours in a day irrespective of the load i.e You can load it 100 % or you can keep the transformer in no load condition. In rural area, Distribution transformer will be installed with GOS (Gang Operating Switch). These switches are used to power shedding to manage the power demand. In India, For usage of power in all agriculture purpose is free. But Government allows only 12 hours in a day. Hence they (Government authorities) open one of the phase out of three phase like that. Hence the distribution transformer still in two phase charge condition.  Energy lost in iron losses throughout the day while the copper losses account for loss in energy when the transformer loaded. Therefore, The manufacture designs the transformer with low iron loss, i.e to have high efficiency at lower load than full Load. In other words, they should be designed to have maximum efficiency at a load much lower than full load. Owing to low iron loss, the distribution transformers have a good all day efficiency.

Distribution Transformer
Distribution Transformer


Distribution transformers should have a good voltage regulation and therefore they should be designed for a small value of leakage reactance. The distribution transformer is a responsible for delivering power to the end user (power consumers). It is a part of a certain area’s power distribution. In a system, The number of quantity of the distribution Transformer is Greater than the quantity of power transformer. At the same time, the Power rating of the power transformer is always greater than the sum of all distribution transformers power rating.

Power transformer:

Power transformers are delivering power to the another equipment such as distribution transformer, Transmission lines, distribution lines, HVDC lines etc. We cannot consume the power transformer’s output. Power transformer is doing both step up process and step down process. Here step down means it gives required input voltage to the distribution transformer. Example: if you want 440 Volts from 110 kV line means we use one power transformer for reducing the voltage from 110kV to 11kV or any and another distribution transformer 11kV to 440 Volts. The power rating of the power transformer is greater than 500 kVA and are used in generating end of a power transmission line for stepping up or stepping Power Transformers. They have a rating abo ions and substations at each down the voltage. Actually the power rating of the power transformer is in the order of MVA.

Power transformers
Power transformers


They are generally preferred to operate during full load condition, at least 5% of the load to be maintained. During light load condition these transformers are kept in disconnected position, because of the transformer gives poor efficiency at light load conditions. Therefore, power transformers should be designed to give maximum efficiency at or near the full load. Power transformers are designed to have considerably greater leakage reactance than is permissible in distribution transformers as in the case of power transformers inherent voltage regulation is less important than the current limiting effect of the higher leakage reactance. Power transformers are surrounded lot of protection relay units. Power transformer are more sensitive and needs to be monitored and maintained carefully.

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