
Current Variation In Line Side And Load Side Of Soft Starters
#1
Posted 01 March 2014 - 04:46 PM
#2
Posted 01 March 2014 - 08:39 PM
hello amb2000
The current drawn by a motor comprises a resistive component and an inductive component.
The resistive component is in phase with the voltage and the inductive component is 90 degrees behind the voltage.
The current measured is the vector sum of both the resistive and inductive currents.
Power factor correction uses capacitors to draw capacitive current which leads the voltage.
The capacitive current is 180 degrees out of phase with the inductive current and can be used to cancel the inductive current.
With power factor correction installed, the current into the motor is the resistive current and the inductive current. There is no change resulting from the addition of the pf correction.
The current drawn from the supply is the current into the motor plus the capacitive current.
If the capacitive current is equal to the inductive current, the inductive current is cancelled from the supply, so the net current is reduced.
This is the whole role of pf correction.
Best regards
Mark
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 02 March 2014 - 08:08 AM
Hi amb2000;
Can you please share the drawing of your system for better understanding?
"Don't assume any thing, always check/ask and clear yourself".
#4
Posted 02 March 2014 - 10:13 AM
Can you please provide your mail ID, I will sent it thru it or kindly advise how to share here
Abhilash
#5
Posted 03 March 2014 - 04:25 AM
hello amb2000
The current drawn by a motor comprises a resistive component and an inductive component.
The resistive component is in phase with the voltage and the inductive component is 90 degrees behind the voltage.
The current measured is the vector sum of both the resistive and inductive currents.
Power factor correction uses capacitors to draw capacitive current which leads the voltage.
The capacitive current is 180 degrees out of phase with the inductive current and can be used to cancel the inductive current.
With power factor correction installed, the current into the motor is the resistive current and the inductive current. There is no change resulting from the addition of the pf correction.
The current drawn from the supply is the current into the motor plus the capacitive current.
If the capacitive current is equal to the inductive current, the inductive current is cancelled from the supply, so the net current is reduced.
This is the whole role of pf correction.
Best regards
Mark
Hello Mark,
Thanks for your kind support, Just need to check with you few things,
1) Is there any possibility of making both the currents the same. How we can reduce the current in the Outgoing side of Soft Starter as we cannot connect the capacitors in the Outgoing side.
2) Is this the same scenario in all the circuits where ever SoftStarters and Drives are coming along with Capacitor banks.
3) Can I advise my customer, our system is working perfectly and there is no problem to worry in this regard.
Please reply me
Abhilash
#6
Posted 03 March 2014 - 04:37 AM
Very easy. Just prepare the drawing, get its image and attach with your post.
"Don't assume any thing, always check/ask and clear yourself".
#7
Posted 03 March 2014 - 04:56 AM
Hello Abhilash
1) If you measure the current at the actual input and output of the soft starter, you will find that they are equal. The current is only reduced on the line side of the PFC connection.
2) Any system that has power factor correction will (should) show a reduced current on the line side of the power factor correction connection point.
In the case of VFDs, you do not apply power factor correction capacitors because the displacement power factor is already better than 0.95 The true power factor will typically be much less because the harmonic power factor is less than 0.95
3) Definitely!!
Best regards,
Mark
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
#8
Posted 03 March 2014 - 06:53 AM
Dear Mark,
Kindly note for above Point 1 , I would like to share the single line diagram for more clarity. Please go through this and advise, Soft Starter Line side and the Capacitor bank connection points are the same here. Then why there is difference in current in both Ammeters.
Can you please check.
Abhilash
#9
Posted 08 March 2014 - 07:51 AM
Hello amb2000
There is no any diagram attached with your post.
"Don't assume any thing, always check/ask and clear yourself".
0 user(s) are reading this topic
0 members, 0 guests, 0 anonymous users