Harmonics -Softstarter 1

[power2020]

Dear Folks,
Pl. clear the doubt on softstarters. Does soft-starter for motor generate harmonics, if it operates at full output voltage (no voltage reducing condition)and without by-pass contactors?
Advanced thanks..

 

[Marke]

Hello power2020

Soft starters reduce the voltage during start by phase controlled SCRs in series with each phase applied to themotor, or each winding of the motor. This does cause harmonics during start and during soft stop.
During run, provided that there is no energy saving algorithm in operation, the soft starter does not produce harmonics. If an energy saving algorithm is in operation, the voltage to the motor can be reduced by the SCRs and at this time, harmonics are produced.
The harmonics produced by soft starters are primarily low order odd harmonics due to the symmetric operation of the SCRs and the inductive nature of the motor.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[power2020]

Dear Marke,

So, Softstarter will act like a back-to-back doides during running and no harmonics will be generated if there is no energy saving algorithm. Thanks for your information.
How energy saving algrorithm works for soft-starter without frequency control (v/f control)?

 

[Marke]

The energy saving algorithm was developed by Frank Nola of NASA back in the 1970's on small single phase motor applications. The principle is to reduce the voltage applied to the motor when it is operating at reduced efficiency and thereby reduce the iron losses in the motor.
This has been commercialized by a number of manufacturers and claims have been made that it will save vast amounts of energy. The reality is that with three phase motors, the efficiencies are already high, the iron loss is small and the energy savings are very small relative to the rating of the motor,and only achieved when the shaft load of the motor is very low. There are few truely viable applications that provide reasonable payback periods.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[power2020]

Thanks Marke for information.
In addition, could you pl. clarify that what is the fault current contribution of Softstarter drives and VFD if there is a fault on line side?
Advanced Thanks...

 

[Marke]

Hello power2020

The fault current contribution with a soft starter is up to the same as a full voltage starter.
The fault current of a standard VFD is 0, and a regenerative (active front end VFD) is current limited by the drive to less than 150% of the drive rating.

Best regards,

Mark Empson

http://www.lmphotonics.com