Induction motors are widely used in industry. They have lots of advantages however they inherit a problem of high starting current. As compared to full load current, the starting current is 6 to 10 times higher. This high inrush of current can damage the motor windings and other parts. High inrush current can also affect the source. Therefore it is required to limit the high starting current in induction motor. There are lots of methods for smooth starting of induction motors. Each one has its own advantages and disadvantages. Some of them are
- Star delta starting method
- Auto-Transformer method
- Rotor resistance method
- Primary resistance starter
In this article we will discuss the primary resistance starter with detail and also learn how to implement it in PLC. Motor starters are among of the basic PLC applications.
Operating principle of primary resistance motor starter
Primary resistance starting method is based on the reduced starting voltage concept. This method introduces the resistance in series with the stator windings of squirrel cage induction motor. Voltage drop occurs in the added resistors during starting which provides reduced voltage across the stator windings. With the reduced voltage, the starting current is lower than it would be if the motor is started on full line voltage. After a preset delay, the resistance unit is shunted out of the circuit and the motor continues to run on line voltage.
Primary resistance starter arrangement
Above figure shows the primary resistor starter arrangement. It consists of a main contactor and a second contactor labelled as S2. Resistors are connected with each phase of stator winding in series to reduce voltage. The value of these starting resistors can be determined by the method explained in the article
By pass switches are connected in parallel to with the starting resistors which are controlled by S2 contactor.
Working
The motor is started by closing the main contactor. This supplies power to the motor through series starting resistance. The contactor S2 is open thus the current has to pass through the resistors resulting in voltage drop. Due to voltage drop in these resistors, the motor gets reduced voltage.
A timer is installed with a preset time delay. When the delay is over, the contactor S2 is closed closing the parallel switches.
As it can be seen in the above figure that closing the S2 bypass all the resistors. As a result full line voltage is applied to the motor windings.
PLC Applications: PLC program for primary resistance starter
Following figure shows the PLC program for Primary resistance motor starter
Induction motors are widely used in industry. They have lots of advantages however they inherit a problem of high starting current. As compared to full load current, the starting current is 6 to 10 times higher. This high inrush of current can damage the motor windings and other parts. High inrush current can also affect the source. Therefore it is required to limit the high starting current in induction motor. There are lots of methods for smooth starting of induction motors. Each one has its own advantages and disadvantages. Some of them are
- Star delta starting method
- Auto-Transformer method
- Rotor resistance method
- Primary resistance starter
In this article we will discuss the primary resistance starter with detail and also learn how to implement it in PLC. Motor starters are among of the basic PLC applications.
Operating principle of primary resistance motor starter
Primary resistance starting method is based on the reduced starting voltage concept. This method introduces the resistance in series with the stator windings of squirrel cage induction motor. Voltage drop occurs in the added resistors during starting which provides reduced voltage across the stator windings. With the reduced voltage, the starting current is lower than it would be if the motor is started on full line voltage. After a preset delay, the resistance unit is shunted out of the circuit and the motor continues to run on line voltage.
Primary resistance starter arrangement
Above figure shows the primary resistor starter arrangement. It consists of a main contactor and a second contactor labelled as S2. Resistors are connected with each phase of stator winding in series to reduce voltage. The value of these starting resistors can be determined by the method explained in the article
By pass switches are connected in parallel to with the starting resistors which are controlled by S2 contactor.
Working
The motor is started by closing the main contactor. This supplies power to the motor through series starting resistance. The contactor S2 is open thus the current has to pass through the resistors resulting in voltage drop. Due to voltage drop in these resistors, the motor gets reduced voltage.
A timer is installed with a preset time delay. When the delay is over, the contactor S2 is closed closing the parallel switches.
As it can be seen in the above figure that closing the S2 bypass all the resistors. As a result full line voltage is applied to the motor windings.
PLC Applications: PLC program for primary resistance starter
Following figure shows the PLC program for Primary resistance motor starter
Induction motors are widely used in industry. They have lots of advantages however they inherit a problem of high starting current. As compared to full load current, the starting current is 6 to 10 times higher. This high inrush of current can damage the motor windings and other parts. High inrush current can also affect the source. Therefore it is required to limit the high starting current in induction motor. There are lots of methods for smooth starting of induction motors. Each one has its own advantages and disadvantages. Some of them are- Star delta starting method
- Auto-Transformer method
- Rotor resistance method
- Primary resistance starter
In this article we will discuss the primary resistance starter with detail and also learn how to implement it in PLC. Motor starters are among of the basic PLC applications.
Operating principle of primary resistance motor starter
Primary resistance starting method is based on the reduced starting voltage concept. This method introduces the resistance in series with the stator windings of squirrel cage induction motor. Voltage drop occurs in the added resistors during starting which provides reduced voltage across the stator windings. With the reduced voltage, the starting current is lower than it would be if the motor is started on full line voltage. After a preset delay, the resistance unit is shunted out of the circuit and the motor continues to run on line voltage.
Primary resistance starter arrangement
Above figure shows the primary resistor starter arrangement. It consists of a main contactor and a second contactor labelled as S2. Resistors are connected with each phase of stator winding in series to reduce voltage. The value of these starting resistors can be determined by the method explained in the article
By pass switches are connected in parallel to with the starting resistors which are controlled by S2 contactor.
Working
The motor is started by closing the main contactor. This supplies power to the motor through series starting resistance. The contactor S2 is open thus the current has to pass through the resistors resulting in voltage drop. Due to voltage drop in these resistors, the motor gets reduced voltage.
A timer is installed with a preset time delay. When the delay is over, the contactor S2 is closed closing the parallel switches.
As it can be seen in the above figure that closing the S2 bypass all the resistors. As a result full line voltage is applied to the motor windings.
PLC Applications: PLC program for primary resistance starter
Following figure shows the PLC program for Primary resistance motor starter
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