How to choose a transformer? How to determine the reasonable capacity of a transformer?
First of all, we need to investigate the power supply voltage of the place where electricity is used, the actual power load of the user and the conditions of the place where it is located, and then select one by one according to the technical data marked on the transformer nameplate. Generally, the capacity, voltage, current and environmental conditions of the transformer should be considered comprehensively. Among them, the capacity selection The required load should be determined according to the capacity, nature and usage time of the user's electrical equipment, so as to select the transformer capacity.
During normal operation, the electrical load the transformer should bear is about 75 to 90% of the rated capacity of the transformer. When the actual load of the transformer is measured to be less than 50% during operation, the small-capacity transformer should be replaced. If the load is greater than the rated capacity of the transformer, the large-capacity transformer should be replaced immediately.
At the same time, when selecting a transformer, determine the voltage value of the primary coil of the transformer based on the line power supply, and select the voltage value of the secondary coil based on the electrical equipment. It is best to choose a low-voltage three-phase four-wire power supply. This can provide both power and lighting electricity at the same time.
When selecting the current, attention should be paid to whether the load can meet the requirements of the motor when it starts (because the starting current of the motor is 4 to 7 times larger than that of sinking operation).
Why can't transformers be overloaded?
Overload operation means that the current value specified on the nameplate is exceeded when the transformer is running.
Under special circumstances, the overload operation of the transformer in a short period of time cannot exceed 30% of the rated load (winter), and it must not exceed 15% in summer.
What kind of tests should be done on the transformer during operation?
In order to ensure that the transformer can operate normally, the following tests should be carried out frequently:
(1) Temperature test. Whether the transformer is operating normally or not and whether the temperature is high or low are 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, the power supply capacity that the transformer can truly bear must be measured during the operation of the transformer. The measurement work is usually carried out during the peak period of electricity consumption in each season, and is measured directly with a clamp ammeter. The current value should be 70 to 80% of the rated current of the transformer. If it exceeds, it indicates overload and should be adjusted immediately.
(3) Voltage measurement. Regulations require that the voltage variation range 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 secondary coil terminal voltage and the terminal voltage of the end user respectively.
