Applications and selection criteria
3RW44 soft starters are an alternative for star-delta starters and frequency converters.
Their major benefits are smooth starting and stopping, uninterrupted changeover without current peaks that would stress the power supply, and their compact dimensions.
Numerous drives which previously could only be operated with frequency converters can be changed over to soft starter operation using the 3RW44 soft starter, as long as no speed control, no particularly high starting torque or no startup with close to nominal current is required.
Applications
Possible applications include:
• Conveyor belts
• Powered roller conveyors
• Compressors
• Ventilators, fans
• Pumps
• Hydraulic pumps
• Stirrers
• Centrifugal machines
• Milling machines
• Mills
• Crushers
• Disk saws/ribbon saws
Advantages
Conveyor belts and systems:
• Jerk-free starting
• Jerk-free braking
Centrifugal pumps, reciprocating pumps:
• Water hammering is avoided
• Increased service life of the tubing
Stirrers, mixers:
• Reduced starting current
Fan
• Reduced stress on transmissions and V-belts
Friday, January 30, 2009
Operating Mode of the SIRIUS 3RW44 Electronic Soft Starter
The 3RW44 soft starter has two anti parallel thyristors in each of the phases.
There is one thyristor for the positive and one thyristor for the negative half wave.
Using phase angle control and various control methods, the R.M.S. value of the motor voltage is increased from a definable start voltage or start torque to the motor rated voltage within a selectable starting time.
The motor current acts proportional to the voltage applied to the motor. Thus, the starting current is reduced by the factor of the voltage that is applied to the motor. The torque behaves quadratically in relation to the voltage applied to the motor.
The starting torque is thus reduced quadratically based on the voltage applied to the motor.
The following graphs illustrate the behavior of the starting current and torque of auto 3-phase asynchronous motor in combination with a soft starter
Starting
This means that because the electronic soft starter controls the motor voltage during motor start-up, it simultaneously controls the ingoing starting current and the starting torque generated in the motor.
The same principle is also used during the stopping process. The effect is that the torque generated in the motor is slowly reduced, thus enabling soft stopping of the application
During this process, the frequency remains constant and corresponds to the network frequency, contrary to the frequency-controlled starting and stopping of a frequency converter.
Upon completion of motor start-up, the thyristors are fully utilized, resulting in the complete network voltage being applied to the motor terminals. Since no motor voltage control is required during operation, the thyristors are bridged by integrated bypass contacts. This reduces the waste heat developing during continuous operation which is caused by power loss of the thyristor. Therefore, the area around the switching devices heats up less.
The following graph illustrates the mode of operation of the 3RW44 soft starter
There is one thyristor for the positive and one thyristor for the negative half wave.
Using phase angle control and various control methods, the R.M.S. value of the motor voltage is increased from a definable start voltage or start torque to the motor rated voltage within a selectable starting time.
The motor current acts proportional to the voltage applied to the motor. Thus, the starting current is reduced by the factor of the voltage that is applied to the motor. The torque behaves quadratically in relation to the voltage applied to the motor.
The starting torque is thus reduced quadratically based on the voltage applied to the motor.
The following graphs illustrate the behavior of the starting current and torque of auto 3-phase asynchronous motor in combination with a soft starter
Starting
This means that because the electronic soft starter controls the motor voltage during motor start-up, it simultaneously controls the ingoing starting current and the starting torque generated in the motor.
The same principle is also used during the stopping process. The effect is that the torque generated in the motor is slowly reduced, thus enabling soft stopping of the application
During this process, the frequency remains constant and corresponds to the network frequency, contrary to the frequency-controlled starting and stopping of a frequency converter.
Upon completion of motor start-up, the thyristors are fully utilized, resulting in the complete network voltage being applied to the motor terminals. Since no motor voltage control is required during operation, the thyristors are bridged by integrated bypass contacts. This reduces the waste heat developing during continuous operation which is caused by power loss of the thyristor. Therefore, the area around the switching devices heats up less.
The following graph illustrates the mode of operation of the 3RW44 soft starter
Physical Basics of the 3-phase Asynchronous Motor and Mode of Operation of the Soft Starter
3-phase Asynchronous Motor
Applications of the 3-phase asynchronous motor
Thanks to their robust and simple design and low-maintenance operation, 3- phase asynchronous motors are used in large numbers in commercial applications, trade and industry.
Problem
If switched on directly, the typical current and torque behavior of the 3-phase asynchronous motor may negatively influence the feeding supply network and the load machine during start-up.
Starting current
3-phase asynchronous motors have a high direct starting current I(starting).
Depending on the motor version, this current may be 3 times to 15 times the size of the rated operating current. A typical value is 7 to 8 times the size of the motor rated current.
Disadvantage
This results in the following disadvantage
• Higher load on the electrical supply network. This means that the supply network must be dimensioned for this higher output during motor start-up.
Start torque
The start torque and the stalling torque can usually be assumed to be between 2 and 4 times the rated torque. For the load machine, this means that the starting and acceleration forces in relation to rated operation result in increased mechanical load on the machine and the conveyed material.
Disadvantages
This results in the following disadvantages
• Higher load on mechanical parts of the machine
• Higher costs because of application wear and maintenance
The current and torque behavior during start-up can be optimally adapted to the requirement of the application using the SIRIUS 3RW44 electronic soft starter
Solution The current and torque behavior during start-up can be optimally adapted to the requirement of the application using the SIRIUS 3RW44 electronic soft starter.
Applications of the 3-phase asynchronous motor
Thanks to their robust and simple design and low-maintenance operation, 3- phase asynchronous motors are used in large numbers in commercial applications, trade and industry.
Problem
If switched on directly, the typical current and torque behavior of the 3-phase asynchronous motor may negatively influence the feeding supply network and the load machine during start-up.
Starting current
3-phase asynchronous motors have a high direct starting current I(starting).
Depending on the motor version, this current may be 3 times to 15 times the size of the rated operating current. A typical value is 7 to 8 times the size of the motor rated current.
Disadvantage
This results in the following disadvantage
• Higher load on the electrical supply network. This means that the supply network must be dimensioned for this higher output during motor start-up.
Start torque
The start torque and the stalling torque can usually be assumed to be between 2 and 4 times the rated torque. For the load machine, this means that the starting and acceleration forces in relation to rated operation result in increased mechanical load on the machine and the conveyed material.
Disadvantages
This results in the following disadvantages
• Higher load on mechanical parts of the machine
• Higher costs because of application wear and maintenance
The current and torque behavior during start-up can be optimally adapted to the requirement of the application using the SIRIUS 3RW44 electronic soft starter
Solution The current and torque behavior during start-up can be optimally adapted to the requirement of the application using the SIRIUS 3RW44 electronic soft starter.
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