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Difference between Power Transformer and Distribution Transformer
Power transformers and Distribution transformers are extensively used in power systems for stepping up and down the voltage level for various applications such as transmission and distribution. Read through this article to find out the major differences between power transformers and distribution transformers and how they function.
What is a Transformer?
A Transformer is a static electrical machine which changes the level of voltage and current in a circuit without changing the frequency of the supply. Transformers works on the principle of electromagnetic induction.
Based on the design, operation, purpose of use, transformers are classified into different types such as auto-transformer, current transformer, potential transformer, power transformer, distribution transformer, etc. The use of all these types of transformers is same, i.e., step-up or step-down the level of voltage and current without changing in the power and frequency of the supply. But, this article is about power transformers and distribution transformers and the main differences between them.
What is a Distribution Transformer?
An electrical transformer which is employed in the power system near the load points for stepping-down the high voltage to the safest rated utilisation voltage is known as distribution transformer. Therefore, the distribution transformer is a step-down transformer which reduces the supply voltage to the voltage level demanded by the consumer’s load (both 1-phase and 3-phase).
In actual practice, the voltage ratings of the distribution transformers are 11 kV, 6.6 kV, 3.3 kV, 440 V, 120 V and 110 V. Distribution transformers are designed in such a way that they have maximum efficiency at 60% to 70% of load.
What is a Power Transformer?
An electrical transformer having very high MVA rating and is used to transmit high electric power at high voltage level through the power lines to the distribution centres is known as power transformer.
Generally, a power transformer is rated over 200 MVA with voltage rating of 33 kV, 66 kV, 132 kV, 220 kV, 440 kV, and so on. The power transformer are mainly used for increasing the low voltage level (at generating end) to a high voltage level for the transmission purpose. The power transformers are designed in such a way that they have maximum efficiency at or near the full load.
Differences between Power Transformer and Distribution Transformer
The following table highlights the key differences between power transformers and distribution transformers −
| Point of Comparison | Distribution Transformer | Power Transformer |
|---|---|---|
| Definition | A distribution transformer is the one which is employed for reducing the high voltage to a low voltage level suitable for the distribution and utilisation. | Power transformer is the type of transformer which have high power handling capacity with the high voltage ratings and used in the transmission section of the power system. |
| Purpose | Distribution transformer is used to step down (reduce) the high voltage to the low voltage for supplying consumer’s load. | Power transformer are used to increase the level of voltage to a high value for transmission of the electric power over the long distances. |
| Location | Distribution transformer are installed on the poles near the load centres (consumer’s end). | Power transformers are installed at the generating station and transmission substations, i.e. they are installed in the transmission section of the power system. |
| Function | In actual practice, the distribution transformers only step-down (reduce) the voltage level. | Power transformers are mostly used for stepping up (increase) the voltage level, but step down is also possible. |
| Power rating | For distribution transformers, power rating is less than 200 MVA. | The power rating of power transformers is greater than 200 MVA. |
| Voltage rating | The usual voltage ratings of distribution transformer are 11 kV, 6.6 kV, 3.3 kV, 440 V, 220 V, 110 V, etc. | The voltage ratings of power transformer are 33 kV, 66 kV, 132 kV, 220 kV, 440 kV, and above. |
| Winding configuration | For a distribution transformer, the primary winding is connected in delta while the secondary winding is connected in star to provide neutral point for single-phase purpose. | For a power transformer, both the primary and secondary windings are connected in delta. However, in some special cases (like generating transformer) the primary is connected in star with neutral earthed and the secondary is delta connected. |
| Number of primary and secondary | A distribution transformer has single primary winding and the secondary winding may be single or tapped (i.e. two or more). | Power transformer has single primary winding and single secondary winding. |
| Size | A distribution transformer is smaller in size. | Power transformer has relatively larger size. |
| Operating period | Distribution transformers operate during load and no-load periods. | Power transformers operate only during the load periods. |
| Operation during light loads | Distribution transformers remain connected during light load periods. Thus, these transformers operate at light loads during major part of the day. | Power transformers are disconnected during the light load periods. |
| Load fluctuations | Distribution transformers are designed to withstand high load fluctuations. | Power transformers are subjected to low load fluctuations. |
| Flux density in core | Distribution transformer has lower flux density. | Power transformer has high flux density. |
| Operating conditions | Distribution transformers always operate at a load less the rated full load. | Power transformers always operate at full load. |
| Maximum efficiency | Distribution transformers are designed to give maximum efficiency at 60 to 70% of the rated load. | Power transformers have maximum efficiency at full load. |
| Leakage reactance | Distribution transformers are designed with small leakage reactance. | Power transformers are designed with high leakage reactance. |
| Voltage regulation | Distribution transformers are used to supply the consumer’s load so they have good voltage regulation. | In case of power transformers, the voltage regulation is not an important parameter. |
| Applications | Distribution transformers are used to distribution electrical power to the consumers. | Power transformers are employed for step-up and step-down (rarely) in generating stations, receiving stations, substations, etc. |
Conclusion
From the above discussion, it can be seen that there are various differences between power transformers and distribution transformers. The knowledge of these differences can help an individual in selecting either of them as per the exact requirements.
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