Selection of Power Distribution Main Transformer in 110kV Substation Design

power distribution Main Transformer

The substation is an important part of the power system, and the selection of the substation main transformer is very important.

The capacity and number of the main transformer affect the form of the main wiring and the structure of the power distribution device.

The transmission power value and the matching between the transformer and the system are the main factors influencing the selection of the transformer.

In addition, the choice of the main transformer has a great influence on the reliability of the power supply and subsequent expansion.

Pad-mounted Transformer

We can provide you single phase and three phase pad mounted transformer

Dry-type Transformer

Type:Cast resin; Rated Capacity: Up to 25MVA; Rated Voltage: Up to 36KV;

Pole Transformer

TypeCSP type Frequency: 50/60Hz; Rated Power: 5~167kva

Dry-type Transformer

Frequency: 50/60Hz Rated voltage:10kv, 20kv,30kv Rated Power: 400~2500kva

The Ultimate FAQ Guide

Principles to be Followed in The Selection of Main Transformers in Substations

(1) 110KV substations are generally equipped with 2 main transformers. 220KV, 550kvd substation is equipped with 3~4 transformers.

(2)The substation is equipped with more than two main transformers. It is required that when one transformer is out of service, other transformers must complete more than 60% of the load of the substation. And other main transformers should ensure the power supply of primary and secondary loads.

(3)When choosing substations with three voltage levels, the main transformer generally chooses a three-winding transformer.

(4) For transformers connected to two types of 110kV and above neutral point directly grounded systems, autotransformers are generally preferred.

5) For substations that transmit electricity to densely populated areas, dual-winding transformers can be used.

Selection of 500kV Main Transformer in Hydropower Station

Determination of The Number of 110kV Main Transformers

When the substation needs to supply agricultural electricity.

Due to seasonal fluctuations in agricultural electricity consumption, two large-capacity main transformers are required in the initial stage of the substation.

The two main transformers are to ensure that when one is repaired, the other can guarantee power supply.

With the future economic development, another transformer can be put in.

What are the main neutral grounding methods of power systems?

Determination of 110kV Main Transformer Capacity

The selection of the main transformer capacity should refer to the 10 to 20-year load development of the substation.

For the suburban substation, the main transformer should be combined with the urban planning.

This substation to be built is located in the suburbs.

Due to the development of the city’s economy, it is recommended to choose a large-capacity transformer.

Selection and Capacity Calculation of Transformers Used in Substations

In a specific case, determine the transformer capacity:

(1) When one transformer in the substation stops running, the other transformer can guarantee 60% of the total load, that is:


(2) The operation of a single transformer must meet the power supply needs of the primary and secondary loads.

The first and second load is 15+10+0.63+0.42+0.78=26.83MVA

Therefore, the capacity of the transformer is at least 62.241MVA.

110kV Transformer Type Determination

Choice of the number of phases

The selection of the main transformer needs to consider factors such as reliability and transportation conditions.

When not restricted by transportation conditions, three-phase transformers are used in power plant substations of 330kV and below.

At the same time, due to the high price of single-phase transformers, choose three-phase transformers are used.

A Complete Guide to Three-Phase Distribution Transformers

Winding form

There are mainly two windings and three windings in the form of windings.

When choosing the winding form of the transformer, priority is given to the three-winding transformer. Because of the cost-effectiveness and high efficiency of the three-winding transformer.

If the substation needs to go deep into the load center, a dual-winding transformer can be used. Especially when the transformer has a high-voltage to low-voltage power supply condition.

Where winding transformers are usually used

  • A substation needs to be equipped with two types of step-up winding transformers. They can power users.
  • The main form of the step-down substation with 3 voltage levels. High voltage supplies power to medium voltage and low voltage. High voltage and medium voltage supply power to low voltage.
  • In the hub substation, two systems of different voltage levels need to be connected to each other.
  • In a wye-wye-connected transformer, a delta-connected third winding is required. The substation to be built has three voltage levels of 110kV, 35kV, and 10kV, so a three-winding transformer is proposed.

Preventive measures for tripping of three-side switch of 110kV main transformer

Choice of common type and autotransformer

Autotransformer is a kind of multi-winding transformer. The characteristic is that the two windings are connected in electromagnetic and circuit.

Therefore, The autotransformer uses electromagnetic connections to complete a part of it to transmit power. The other part uses the circuit connection.

The size of the electromagnetic transmission power determines the size, weight, core cross-sectional area, and loss of the transformer.

Therefore, compared with the ordinary transformers of the same capacity and the same voltage level, the economic benefits of the autotransformer are significant.

Due to the simple and economical structure of the autotransformer, it is widely used in the 110kV and above neutral point directly grounded system.

The replacement of ordinary transformers by autotransformers has become a development trend. Therefore, consider the selection of autotransformers.

Neutral grounding method

The grounding method of the neutral point of the power grid determines the grounding method of the neutral point of the main transformer.

The main transformer selected for the substation to be built is an auto-coupling three-winding transformer.

Link at the center point in the main transformer. The 110kv side adopts the direct grounding method. 35KV and 10KV adopt non-grounding mode.

Concluding Remarks

The choice of transformer is related to the success of the design of the substation to be built. Its choice must not only meet the requirements of the short-term load but also take the long-term into account.

The choice of transformers should be given sufficient attention.

Custom Distribution Main Transformer

If you need to purchase a main transformer for your substation, Daelim can provide you with a quote. Daelim has multiple series of main transformers. At the same time, Daelim can also design and produce the main transformers you require. Daelim has a main transformer design and production team with 15 years of experience.

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