Static Correction Of Screw Refrigeration Compressors
#1
Posted 23 November 2006 - 08:09 PM
All help appreciated.
Kens
#2
Posted 23 November 2006 - 08:28 PM
For static correction, you should correct 80% of the magnetising current of the motor.
The magnetising current is constant, load independent so there wil not be any resonance issues at line frequency.
The only variation in reactive current drawn by the motor is due to the load current and the leakage reactance. This is generaly very small relative to the magnetising current.
If you require to correct to 0.95 or better using static correction, this can be a problem as you may well correct to better than 80% of the magnetising current and this can cause resonance issues at ramp down.
I always recommend that a separate contactor is employed for the capacitor control when using static correction. This will diconnect the capacitors from the motor and eliminate resonsance issues during motor shut down.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#3
Posted 23 November 2006 - 09:00 PM
Thanks
Kens
#4
Posted 24 November 2006 - 02:46 AM
If you have accurate data on the motor, you can use my electrical calcs software to give you a good recommendation using method 2. - you need to know full load and half load efficiencies and power factors.
Other alternative is to use a suitable meter and measure the VARs at the lowest load you can achieve.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
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