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- Calculate Lock Rotor Current.
- Calculate Motor Starting Current.
- Calculate Motor Full Load Current.
- Calculate Non-time Delay/Time Delay fuse Size.
- Calculate Circuit Breaker Size.
- Calculate Overload Relay setting.
- Calculate Type of Contactor.
- Calculate Size of Main Contactor.
- Calculate Size of Star Contactor.
- Calculate Size of Delta Contactor.
- Standard Arrangement of Main and Auxiliary Contactor.
Calculating the size of a Direct-On-Line (DOL) starter and a Star Delta starter involves determining the appropriate ratings and components for motor control in an electrical system. These calculations are crucial for efficient motor operation and protection. Below are the steps to calculate the size of both types of motor starters:
For a Direct-On-Line (DOL) Starter:
Motor Power (P): Determine the power rating (in kW) of the motor that you intend to start. This can often be found on the motor nameplate.
Voltage (V): Note the supply voltage (in volts) available for the motor. It should match the motor's voltage rating.
Full Load Current (FLC): Find the motor's full load current (in amperes) from the nameplate data.
Locked Rotor Current (LRC): Identify the motor's locked rotor current. This is the initial current surge when the motor starts, which is typically several times the full load current.
Calculate the Size of DOL Starter: The size of the DOL starter depends on the FLC and LRC of the motor. Ensure that the DOL starter is rated to handle both the continuous FLC and the initial inrush current (LRC). The DOL starter should also be rated for the same voltage as the motor.
For a Star Delta Starter:
Motor Power (P): As with the DOL starter, determine the power rating (in kW) of the motor.
Voltage (V): Note the supply voltage (in volts) available for the motor, matching the motor's voltage rating.
Full Load Current (FLC): Find the motor's full load current (in amperes) from the nameplate data.
Locked Rotor Current (LRC): Identify the motor's locked rotor current. This is crucial for sizing the contactors and overload relays in the star-delta starter.
Calculate the Size of Star Delta Starter: The size of the star-delta starter depends on the FLC and LRC of the motor. Additionally, you need to consider the switching capacity of the contactors and the setting range of the overload relays. The starter should be rated for the same voltage as the motor and capable of handling both the continuous FLC and the initial inrush current (LRC).
Star-Delta Transition Time: Calculate the time duration for which the motor remains in the star configuration before transitioning to delta. This transition time should be suitable for the motor and load requirements.
Remember to consult the manufacturer's specifications for the DOL or star-delta starter components to ensure they meet the calculated values and standards. Proper sizing and selection of motor starters are essential for safe and efficient motor operation, as well as for preventing overheating and damage to the motor and electrical system. If in doubt, seek assistance from a qualified electrical engineer or technician.
