# How to Choose a Substation Transformer?

With the development of society and economy and the continuous increase of power energy demand, the power load continues to increase.

As important power equipment for substation operation, transformers used in substation stations have a very important role and influence on its normal substation operation.

Therefore, research on the selection and capacity calculation of transformers for substation stations has a very important role and significance for ensuring the reasonable selection, design, and application of transformers for substation stations and ensuring the stable operation of substations.

Selection of Power Distribution Main Transformer in 110kV Substation Design

## Load Calculation of Substation Transformer

Under normal circumstances, the calculation, determination, selection, and application of the load size of the transformer according to the operating conditions of the substation is an important part of its design and selection of the transformer.

In the calculation and selection of a load of transformers used in substation stations, the continuous operation and regular short-term operation of the power equipment and load conditions in the operation of the substation should be reflected in the transformer load calculation.

In addition, for infrequent short-term operation or occasional, infrequent intermittent operation of equipment and its power load conditions, it is not necessary to consider in the calculation.

Finally, in the calculation and selection of the load of transformers used in substation stations, the calculation is usually carried out by converting the rated power of the load of the electrical equipment of the substation into the rated power of the load of the transformer.

In the calculation process, the load conversion factor for the electrical equipment of the substation is generally set to 0.85. However, 1 is used as the conversion calculation factor for the calculation and application of the conversion calculation of the electric heating load and the lighting equipment load in the substation system.

According to the above analysis of the relevant situation of the calculation of the transformer load used in the substation station, in the actual calculation and selection design, it is necessary to effectively classify the load of the electrical equipment of the substation to realize the conversion analysis of the specific load size, so as to avoid the calculation result and the actual load. The error between the two will affect the selection of the transformer load for the substation.

In addition, in the division of different types of electrical equipment and line loads, it is necessary to note that continuous load requires a single continuous load operation time of more than 2 hours, while short-term loads require a single continuous load operation time of more than 10 minutes. Within 2h. Intermittent load means that each time the load is operated to no-load or stopped state for repeated periodic work operation, the time of a single cycle should be within 10min;

The load used for frequent operation mostly refers to the situation that needs to be used every day, and the load used for infrequent operation refers to the load situation that does not operate under normal conditions and only operates under certain circumstances such as overhaul or accident.

## Selection and Calculation of The Capacity of Substation Transformers

Under normal circumstances, in the selection and calculation analysis of the transformer capacity for substation stations, the capacity and load conditions of various power equipment in the substation are calculated to determine the situation, which does not include the fire load, and the capacity and load are compensated. The capacity is the main basis for selecting and designing the capacity of transformers used in substation stations.

For example, formula (1) is the formula for selecting and calculating the capacity of transformers used in substation stations. In this formula, S is the capacity range of transformers used in substation stations, generally expressed in kVA, and K1 represents the power load conversion of transformers used in substation stations.

In general, the coefficient value is usually set to 0.85; in addition, P1, P2, and P3 respectively represent the sum of the power, electric heating, and lighting system load of the power equipment used in the substation station, and the unit is expressed in kW. S≥K1·P1+P2+P3 (1)

How To Choose The 10kv Transformer Capacity Grade

## Transformer Type and Impedance Analysis of Substation Station

In the operation of the substation, the main purpose of the selection and application of station transformers is to ensure that the output voltages of the station transformers and backup transformers in the substation connected to the grid are consistent, so as to provide a guarantee for the safe and stable operation of the power system.

Combined with the current transformer types used in power system substation stations, Dyn and Yyn connection types are the main ones. And the zero-sequence impedance of the transformer of the first connection type is much lower than that of the second connection type.

Among them, the single-phase short-circuit current in the operation of the transformer will increase and change, and the difference between the three-phase short-circuit current and the three-phase short-circuit current will be significantly reduced.

This means that in the station transformer system using the first connection type, the protection action sensitivity of the system protection equipment under the problem of single-phase short-circuit faults is greatly improved, and at the same time, the system protection equipment and the circuit feeder line cross-section selection and coordination are greater.

In addition, the simplified setting and application of the system protection structure and form can also be realized, without the need for separate settings and application of single-phase short-circuit protection. In the high-voltage side, overcurrent protection of the power system and the low-voltage side single-phase short-circuit protection, both have more advantages.

Dyn type connection transformer equipment, its internal delta winding arrangement creates a current path for the third harmonic current or zero sequences current in the transformer connection line, and at the same time makes the phase voltage in the line closer to the sine wave The voltage change form has a more prominent effect and effect on the improvement of the line voltage waveform quality.

In addition, in this type of connection type transformer equipment, if there is a three-phase load imbalance on the low-voltage side of the transformer connection line, the floating displacement of the low-voltage side neutral point in the transformer equipment will not change, thereby supplying power to the grid. The stability of it has a greater guarantee.

Therefore, in actual design and application, D, yn type connection transformers are the main choice for substation station transformers.

In addition, the impedance calculation of the D, yn type connecting transformer in the operation of the substation is generally determined based on the current-carrying capacity of the low-voltage electrical appliances in the substation system under short-circuit faults. According to this situation, the impedance of the transformer is used in the substation station. In the selection and design applications, ordinary transformers designed with standard impedance are generally used as transformer equipment for substation stations for selection and application.

Take a transformer for a 220kv substation station as an example. The transformer is a dry-type transformer with forced air cooling and a protective enclosure.

After determining its technical parameters, including the operating frequency of the transformer, no-load current, insulation grade, withstand voltage, connection method, operating environment, etc., the capacity of the transformer can be calculated according to the comprehensive situation of each load in the substation Determine, and select the application in the design of the substation.

Power Transformer and Distribution Transformer

## Conclusion

In short, the research on the selection and capacity calculation of transformers used in substation stations has a certain reference value and significance for its selection and application in actual design. It can promote the reasonable selection and application of substation equipment, and ensure the safety of the power system. Stable and reliable operation.

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