Direct On Line
The starting equipment consists of only a main contractor and thermal or electronic overload relay. The following characteristics would usually be found with DOL starting:
- Starting Current for the motor would normally be between 6 to 7 times the rated motor current
- Potential peaks of 9 or 10 times the rated current exist in some cases
- Very High Starting Torque which exceeds what is necessary for most applications.
- High torque causes unnecessary stresses on the motor couplings and the application
- Can cause belts to slip which can generate high noise levels during starting
- Not suitable for applications requiring varying speed
Star Delta Starter
This is a starting method that reduces the starting current and starting torque. The device normally consists of three contactors, an overload relay and a timer for setting the time in the star-position.
The following characteristics would usually be found with DOL starting:
- The motor must be delta connected during a normal run
- The starting current is about 30 % of the starting current during direct on line start
- The starting torque is reduced to about 25 % of the torque available at a D.O.L start
- Reduces stress on the motor couplings and the application
- Not suitable for heavily loaded applications at start up due to reduced
- Increased panel size due to extra cabling, controls and contactors
- Can have large current peaks if application is heavily loaded at switch over to Delta
- Not suitable for applications requiring varying speed
Soft Starter Control
A Soft Starter has different characteristics to other starting methods. Thyristors in the main circuit allow the motor voltage to be regulated during the start process thus allowing for more control of the Current and torque. The following characteristics would usually be found with Soft Starter Control:
- Reduced Starting Current compared to DOL starting
- Adjustable Torque Characteristics
- Relatively Compact in size
- Inexpensive method of providing motor control
- Removes need for additional Overload relay with some models
- Controlled and smooth start can be expected
- Controlled and smooth stop can be expected
- Built in bypass removes need for additional contactor like older installations
Variable Speed Drive Control
A Variable Speed Drive(VSD) is also known as a Variable Frequency Drive(VFD) or frequency converter or just a Drive. The VSD consists primarily of two parts, one which converts AC (50 or 60 Hz) to DC and the second part which converts the DC back to AC, but now with a variable frequency of 0-320 Hz. The following characteristics would usually be found with VSD Control:
- Speed Control of the motor which is needed for a lot of process applications
- Energy Savings can be achieved when not running motor at full speed
- Controlled Start/Stop reducing strain on motor couplings and application
- Fully programmable to manage the most complicated of Application requirements
- Communications to BMS systems via Profibus, Modbus etc. available
- Built in protections to protect the motor such as Motor O/L, Thermistor Input, Earth Fault detections, Input Phase Supervision etc.
- Simple Direction Change possible without need for swapping phases via contactors
- Fault Logs and Operational data all held within memory