Star delta starter power circuit wiring diagram
The star-delta starting diagram must make it possible to wire a control cabinet connected to a three-phase asynchronous motor.
The diagram derives from the knowledge of the coupling at the level of the terminal board and from the purely electrotechnical study of star-delta starting.
The requirements for drawing up a scheme are as follows:
The delta coupling must correspond to the mains voltage,
The starting of the engine must be done in two stages,
First step: coupling of the star windings and energization,
Second step: removal of star coupling, immediately followed by delta coupling.
Analysis of start-up operation
At start-up the motor is star-connected. The voltage applied to a phase is reduced, i.e. U divide by the square root of three.
The current absorbed (proportional to the voltage applied) is 1/3 of that which the motor would absorb if it started directly in delta. The value of the current peak generally reaches twice the nominal current.
The starting torque (proportional to the square of the voltage applied) and the maximum star torque are reduced to 1/3 of the values obtained in direct starting. The value of the starting torque generally reaches 0.5 times the nominal torque.
Break (star-delta passage):
The passage time between the two couplings must be very short.
Triangle coupling:
A second inrush of current occurs; it is a function of the duration of the star coupling and can reach the peak value of direct starting. This peak of short duration comes from the fact that the electromotive forces which remain at the stator during the delta coupling are not in phase opposition with the line voltages.
Star delta starter power circuit wiring diagram
The star-delta starting diagram must make it possible to wire a control cabinet connected to a three-phase asynchronous motor.
The diagram derives from the knowledge of the coupling at the level of the terminal board and from the purely electrotechnical study of star-delta starting.
The requirements for drawing up a scheme are as follows:
The delta coupling must correspond to the mains voltage,
The starting of the engine must be done in two stages,
First step: coupling of the star windings and energization,
Second step: removal of star coupling, immediately followed by delta coupling.
Analysis of start-up operation
At start-up the motor is star-connected. The voltage applied to a phase is reduced, i.e. U divide by the square root of three.
The current absorbed (proportional to the voltage applied) is 1/3 of that which the motor would absorb if it started directly in delta. The value of the current peak generally reaches twice the nominal current.
The starting torque (proportional to the square of the voltage applied) and the maximum star torque are reduced to 1/3 of the values obtained in direct starting. The value of the starting torque generally reaches 0.5 times the nominal torque.
Break (star-delta passage):
The passage time between the two couplings must be very short.
Triangle coupling:
A second inrush of current occurs; it is a function of the duration of the star coupling and can reach the peak value of direct starting. This peak of short duration comes from the fact that the electromotive forces which remain at the stator during the delta coupling are not in phase opposition with the line voltages.
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