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Firstly to investigate the electrical parts of the supply voltage and the user's actual load and the local conditions, then refer to the transformer nameplate marked technical data one by one, generally from the transformer capacity, voltage, current and environmental conditions, in which the capacity selection should be determined according to the user with the electrical equipment capacity, nature and time required to load, in order to choose the transformer capacity.
During normal operation, the transformer should bear the electricity load of transformer rated capacity of 75 ~ 90%. In the operation of the transformer can be measured by the actual bearing load of 50 to less than%, should be replaced with small capacity transformer, such as transformer rated capacity greater than the large transformer should be replaced immediately.
At the same time, in the selection of the transformer primary coil voltage line power transformer according to the decided value according to the voltage of secondary coil of the electric equipment, the best choice for low voltage three-phase four wire power supply. This can also provide power and electricity for lighting.
For the current selection should be paid attention to in the motor starting load can meet the requirement of the electric motor (because the motor starting current should be 4 to 7 times larger than the sinking operation).