Where is a 33 kv Distribution Transformer Used for?

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33kv distribution transformer is the well used power transformer in the electric transmission.

Daelim provide 33KV mini substation transformer, three phase pad mount transformer, dry type transformer and also single phase pad mount transformer comply with USA IEEE standards, Canada CSA standards, Australia AS standards. 

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

Oil immersed transformer

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

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Design selection of the 33kv distribution transformer

The power transformer, as an important electrical equipment of the substation, its power loss accounts for 20%~50% of the loss of the whole power system. 

The reasonable selection of the power transformer is crucial to energy saving and loss reduction, and is the focus of energy saving and loss reduction of the substation.


Selection of the capacity of 33 kv distribution transformer

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The power loss of the transformer changes with the change of the load. 

For small and medium capacity transformers, the load is 50%~60% of their rated capacity. This area is generally called the economic operation area of the transformer. 

In contrast, the power transformer is less efficient and increases its own loss at full load.The efficiency drops more with a small power factor. 

By calculation, the efficiency of a 2500kVA transformer decreases by 0.69% when the power factor is 0.6; even if the power factor reaches 0.8, the efficiency should decrease by 0.52%.

From the point of view of energy saving and loss reduction. Choosing the main transformer capacity according to the economic operation area of the transformer can achieve the minimum loss of the main transformer. 

Obviously, this method of choosing the power transformer capacity will make the power transformer capacity greater 30%~40% than the comprehensive load of the substation, although increasing the investment of the main transformer, but from the long-term energy saving benefit it works.

Learn more about 3 Phase Transformer Power Transformer Manufacturer Daelim

 Selection of 33KV distribution transformer quantity

The load of the substation generally fluctuates greatly. In order to make the power transformer work reliably in the economic operation area as far as possible, no less than two power transformers (power transformer N ≥2) should be set up。

And the possibility of parallel operation is considered, so as to determine the operation mode of the power transformer and the substation with hand joint load concentration according to the load situation.

If the load change is large and the capacity ratio is small, we can adopt the operation mode of mother and child changes, and the mother and child changes capacity ratio is 1:0.476 and 1: 0.625.

It is not advisable to use only a single power transformer for operation in the substation.

First, when the power load changes, the load rate is difficult to meet the requirements, the transformer can not operate in the economic operation area; 

Second, once the main transformer maintenance, will cause a large area of power failure, causing passive power supply service.

Selection of the model of 33kv distribution transformer

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Substation design should be s9 or s11 series power transformers, because they use new technology, new craftwork, new materials.

Compared with the same grade of old models, has the advantages of less loss, small size, small quality. 

S9 series can save power by 9kw·h per kva than SL7 series; S11-M.R power transformer off-load loss drop 30%, on-load loss drop 70% compared with S9 series.

You may interested in 15kva transformer Tips

Select the three-winding transformer reasonably

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The use of three-winding transformer can reduce the transformer power loss by nearly 30%.

Now the models and specifications of small and medium capacity three-winding transformer are relatively complete, and there is a lot of choice, reasonable selection can reduce the investment and reduce the loss.

Know more about 25 kv oil immersed transformer  DAELIM

Use of on-load power transformer

In substations with large voltage change with load, on-load regulating power transformer should be adopted to ensure stable voltage output.

For terminal substations transformer with large voltage fluctuation, in order to improve the terminal voltage quality, a power capacitor can be installed at the incoming end line of the substation for reactive power compensation to reduce voltage loss and reduce voltage fluctuation.

Try for free Where is a 33 kv Distribution Transformer Used for?

Reasonable compensation for reactive power of 33 kv power transformer

Increasing the power factor can reduce the power transformer loss, improve the utilization efficiency, also can reduce the voltage loss and line power loss.

It is estimated that when the power factor increases from 0.7 to 0.95, the transformer can reduce the winding loss by 4.6W/KVA. The line loss can be reduced by about 45%.

At present, in the reactive power compensation technology, the parallel power capacitor compensation technology is widely used.

The key is the choice of compensation point and compensation capacity. If the selection and configuration are not appropriate, the overcompensation will be counterproductive.

Therefore, in the design of the substation, it is necessary to investigate the comprehensive load structure of the substation, such as the continuous production shift of large enterprises, power capacity, power factor, electricity characteristics, etc., after statistical analysis to determine the compensation type of the substation.

Generally speaking, the combination of centralized compensation and decentralized compensation, decentralized compensation and local compensation, power supply enterprise compensation and user compensation should be adopted. 

The centralized compensation capacity of the substation is generally decentralized compensated on the distribution line so that the main transformer power factor reaches 0.8. Then increase from the centralized compensation to 0.9 for calculation.

To compensate the reactive power, the control method should be correctly selected according to the compensation requirements and operating conditions of the substation, considering not only the energy saving and loss reduction effect, but also the voltage regulation control.

What is the rating of transformer used in 33 kV distribution transformer?

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The rating value of the transformer is mainly as follows:

Rated capacity: Rated capacity refers to the rated at the power of the transformer, with the unit using VA or kVA. 

Due to the high efficiency of the transformer energy transfer process, the capacity design of the original and auxiliary side winding is usually equal.
Rated Voltage: rated original, secondary side voltage U1N and U2N.
Original side rated voltage U1N refers to the voltage to be added to the original side of the transformer under rated operation.

The secondary side rated voltage U2N refers to the no-load voltage of the secondary side when the original side plus the rated voltage, and the unit use is V or kV.

The rated voltage of the three-phase transformer means the line voltage.

Rated Current:  The current I1N and I2N calculated by the rated capacity and rated voltage is called rated current, in A or KA.

The rated current of the three-phase transformer means the line current.

Rated frequency F:  The frequency of the original side of the transformer plus the AC voltage during the rated operation. China, Australia and a lot of European countries standard industrial frequency is 50Hz. Canada, the USA and a lot of American countries frequency is 60HZ.

In addition, the transformer nameplate is also marked with: rated temperature rise θN, rated ηN, etc.

How is a transformer sized or rated?

First to investigate the local power voltage, the actual power load and local conditions, and then refer to the transformer nameplate of technical data selected one by one, generally from the transformer capacity, voltage, current and environmental conditions, 

the capacity selection should be based on the user of electricity equipment capacity, nature and use time to determine the required load, in order to choose the transformer capacity.

During normal operation, the power load of the transformer shall be about 75~90% of the rated capacity of the transformer.

When the actual load of the transformer is less than 50% during operation, the small capacity transformer should be replaced. 

If the rated capacity is greater than the transformer, the large transformer should be replaced immediately.

At the same time, in choosing the transformer according to the line power supply to determine the primary coil voltage value of the transformer, 

according to choose the voltage value of the secondary coil according to the electrical equipment, it is best to choose the low-voltage three-phase four-wire power supply.

This provides both power electricity and lighting electricity.

For the selection of current, it should be noted that the load can meet the requirements of the motor when the motor starts (because the motor starting current is 4~7 times larger than when the sinking operation).

What is the transformer specification?

There are a lot of models and specifications of different transformer type. 

Transformer’s specifications of transformer, meanwhile the power transformer is also different. 

Our common transformer such as resin cast dry transformer, its model is “SCB22-1500KVA/11KV/0.415KV”, so for this dry transformer that S means the transformer is a three-phase dry type transformer.

And C means that the transformer winding is resin cast formed solid, not oil filled, that is, dry transformer. B is represented by foil winding.

The representation of the 10 is a design serial number, also called a technical serial number.

The 2500KVA indicates the rated capacity of a power electric transformer (2500 kVA). 34.5 KV means a primary rated voltage, and 0.415KV means a secondary rated voltage.

The widely use model of power transformer in our life, it usually has symbols indicating phase number, cooling type, tap change mode, winding line core materials, as well as indicating the transformer capacity, rated voltage and winding connection type. 

For example, the model is named as SFSZ9-31500 / 110 power transformer, it explain as below: S, means three-phase, and F represents air cooling, Second S represents three winding, Z is load regulating, 9 is the design serial number. 31500 is a transformer rated capacity of 31500kVA, 110 represents the primary side rated voltage of 110kV.

According to the models and specifications of the transformer, if it is distinguish based on the voltage class of the transformer, then the transformer model can be divided into 1000KV power transformer, 750KV power transformer, 500KV power transformer, 330KV power transformer, 220KV power transformer, 110KV power transformr, 66KV substation transformer, 35KV mini substation transformer, 20KV distribution transformer, 10KV distribution transformer, 6KV distribution transformer, etc.

Try for free information about the Some tips about 225 kva transformer

Which type of transformer is used in 33kv substation?

The 33 kV substation is the most basic transmission and distribution unit in the county power grid. Its design work is a wide range of areas involving the system engineering. 

The 33kV substation is the most basic power transmission and distribution unit in the county power grid. Its design work involves a wide range of systems engineering.

The transformers used in 33kV substations are usually step-down transformers. Generally, it is a three-phase transformer, but it does not mean that the transformer in the substation can only use three-phase. Three single-phase three-winding transformers can form a three-phase transformer, which has the function of three-phase.

Both Oil immersed transformer and dry type transformer 33kV station can be used in 33kV substation.

Mini substation transformers or pad mounted transformers are generally used in 33kV skid-mounted substations. Many of Dalin’s customers in Australia and North America use these types of transformers.

Keep on reading The Ultimate Guide to 300 kVA Pad Mounted Transformer

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About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. If you have problems when you are looking for the equipment, what you need to do is tell us.