How to choose a transformer? How to determine the reasonable capacity of the transformer?

How to choose a transformer? How to determine the reasonable capacity of the transformer?

First of all, it is necessary to investigate the power supply voltage of the place where the electricity is used, the actual electricity load of the user and the conditions of the location, and then refer to the technical data marked on the transformer nameplate to select one by one. Generally, the transformer capacity, voltage, current and environmental conditions should be considered comprehensively. Among them, the capacity selection The capacity of the transformer should be selected according to the capacity, nature and use time of the user's electrical equipment to determine the required load.

During normal operation, the power load of the transformer should be about 75-90% of the rated capacity of the transformer. When it is measured that the actual load of the transformer is less than 50% during operation, a small-capacity transformer should be replaced, and if it is greater than the rated capacity of the transformer, a large transformer should be replaced immediately.

At the same time, when selecting a transformer, the voltage value of the primary coil of the transformer is determined according to the line power supply, and the voltage value of the secondary coil is selected according to the electrical equipment. It is best to choose a low-voltage three-phase four-wire system for power supply. This can provide power and lighting electricity at the same time.

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 starting current of the motor is 4 to 7 times larger than that during sinking operation).

Why can't the transformer run on overload?

Overload operation refers to the operation of the transformer exceeding the current value specified on the nameplate.

Under special circumstances, the short-term overload operation of the transformer should not exceed 30% of the rated load (in winter), and it should not exceed 15% in summer.

What kinds of tests should the transformer do during operation?

In order to ensure the normal operation of the transformer, the following tests should be carried out frequently:

(1), temperature test. Whether the transformer is running normally or not, the temperature is very important. The regulations stipulate that the upper oil temperature shall not exceed 85C (that is, the temperature rise is 55C). Generally, transformers are equipped with special temperature measuring devices.

(2), load measurement. In order to improve the utilization rate of the transformer and reduce the loss of electric energy, in the operation of the transformer, it is necessary to measure the power supply capacity that the transformer can really bear. The measurement work is usually carried out during the peak period of electricity consumption in each season, and is directly measured with a clamp-on ammeter. The current value should be 70-80% of the rated current of the transformer. If it exceeds, it means overload and should be adjusted immediately.

(3) Voltage measurement. Regulations require that the range of voltage variation should be within ±5% of the rated voltage. If it exceeds this range, taps should be used to adjust the voltage to the specified range. Generally, a voltmeter is used to measure the terminal voltage of the secondary coil and the terminal voltage of the terminal user.

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