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4. CONNECTION OF LOAD
4.1 Input power
[Attended operations]
If select the motor with improper capacity, it is possible to fail in starting the motor.
Decide the capacity of motor as per followings:
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According to load type, purpose, start mode, quantity, loading factor, features of generator, and
type of auto voltage regulator, the starting power is different.
Upon starting motor, its current is 5-8 times of rated current. The rapid rise of starting current
causes instant overload of generator. Then voltage of generator falls down rapidly. Therefore
sometimes it is difficult to start the motor.
It is recommended to discuss with manufacturer upon decision of capacity.
●
User can calculate the capacity simply with below formulas.
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Input power of squirrel-cage asynchronous motor (kVA)
Input power (kVA)= Rated power of motor (kW)
Motor efficiency x Power factor
Power factor of motor: 0.8 Motor efficiency: 0.8
Input power (kVA)=1.56x rated power of motor (kW)
○
Direct-starting squirrel-cage asynchronous motor (with knife switch)
Generator capacity = 2x input power of motor
○
Direct-starting squirrel-cage motor (with contactor)
Generator capacity = 3x input power of motor
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Star/ triangular-starting squirrel-cage motor
Generator capacity = 1.2~1.5x input power of motor
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It is required to balance the load if more than one AC electric welder is used.
Therefore user shall distribute phases equally as per following:
Attended operation:
Input power of each welder shall be 1/3 below the output power of generator.
Over-load may cause motor damage.
Start the starter with no load, and never start the starter with load.
Start the bigger power starter first and then the smaller power starter.
