Traditional star-delta engine starting
Due to their simplicity, robustness and cost effectiveness, squirrel cage motors are the industry's preferred choice. On starting, they develop currents up to about 8 times the rated current and the high starting torque associated with them.
Traditional Star-Delta engine starting method used in practice (photo credit: teslacomponents.com.au)
The high starting currents often lead to unwanted voltage drops in the supply network and the high starting torque puts the mechanical elements under considerable stress.
Therefore, power companies determine limit values for motor starting currents in relation to rated operating currents. The permissible values vary from network to network and depend on its load capacity.
As far as mechanics are concerned, methods are needed to reduce the starting torque. Different starters and methods can be used to reduce currents and torque, but in the following passages only the traditional star-delta method used in practice is explained in more detail.
Normal star-delta starters
Improved Star-Delta Starters
Star-Delta Starters with Uninterrupted Switching (Closed Transition)
1. Normal star-delta starters
To allow the motor to start, the motor windings are star configured according to the supply voltage. The voltage applied to the various windings of the motor is therefore reduced by a factor of 1 / √3 = 0.58 this connection represents approximately 30% of the delta values.
The starting current is reduced to one third of the direct starting current, i.e. generally 2
.
2.5 Ie.
Due to the reduced starting torque, the star-delta connection is suitable for drives with a high inertia mass, but a low resistance torque or one that only increases with increased speed.
It is preferably used for applications in which the motor is only put under load after starting, for example for presses, centrifuges, pumps, fans, etc.
Traditional star-delta engine starting
Due to their simplicity, robustness and cost effectiveness, squirrel cage motors are the industry's preferred choice. On starting, they develop currents up to about 8 times the rated current and the high starting torque associated with them.
Traditional Star-Delta engine starting method used in practice (photo credit: teslacomponents.com.au)
The high starting currents often lead to unwanted voltage drops in the supply network and the high starting torque puts the mechanical elements under considerable stress.
Therefore, power companies determine limit values for motor starting currents in relation to rated operating currents. The permissible values vary from network to network and depend on its load capacity.
As far as mechanics are concerned, methods are needed to reduce the starting torque. Different starters and methods can be used to reduce currents and torque, but in the following passages only the traditional star-delta method used in practice is explained in more detail.
Normal star-delta starters
Improved Star-Delta Starters
Star-Delta Starters with Uninterrupted Switching (Closed Transition)
1. Normal star-delta starters
To allow the motor to start, the motor windings are star configured according to the supply voltage. The voltage applied to the various windings of the motor is therefore reduced by a factor of 1 / √3 = 0.58 this connection represents approximately 30% of the delta values.
The starting current is reduced to one third of the direct starting current, i.e. generally 2
.
2.5 Ie.
Due to the reduced starting torque, the star-delta connection is suitable for drives with a high inertia mass, but a low resistance torque or one that only increases with increased speed.
It is preferably used for applications in which the motor is only put under load after starting, for example for presses, centrifuges, pumps, fans, etc.
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