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Power Factor Controller - Few Topics


Tech77

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Hi !

 

I am in the process of validation of APFC controllers for a power factor correction system and bit new to the subject also.I am going thru' some of the controller like ENTES RG-12B series / Mikro's PFR & Novar.After studying product catalog , i have few topics to have a discussion / query.

 

1. I have seen setting of target cos phi is up to 0.8 LEAD besides 0.8 lag.

 

When & why that Target cos phi : "Lead" would be required ?generally we know that when

cos phi is required to improve to cos phi :1.00 from say 0.8 lag..then when will be the case where it is required to improve up to 0.8 lead ( e.g )

 

2. The Capacitor switching is done basically by 3 methods what i found out

 

a. Rotational / Circular switching

b. Linear switching

c. Intelligent switching.

 

Rotational switching is that equal steps ( as per cap power ratio setting ) would be switched in /out circular fashion such way that first IN capacitor will be the first capacitor OUT when req. to be disconnected.

 

Linear switching : In this the Last capacitor IN would be the first capacitor that will be switch OUT when req...... NOVAR 300 follows this linear mode. ( First in Last Out principle)

But in ENTES , they say that in linear mode ....the first or oldest capacitor IN will be the first capacitor req. to be switch OFF or OUT...here it is First IN First OUT.

 

Hope this switching scheme is standard one ..then why it's different in 1 case.

 

In Intelligent switching ,i believe it doesn't switch based on any sequence.It sees the req. KVAr and appropriate Capacitors which can supply the req. kVAr.And then switches those.

 

 

3. Is it that the controller starts switching when ever

Kvar req = Present reactive power - (Px tan (Arcos(target Cos phi)) is

greater then the present kVAr or any %of Capcitor also needs to be seen ..How this exactly ?

 

Looking forward to get some hints...

 

 

Thanks & Regards,

 

Tech77

 

 

 

 

 

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Hello Tech77

 

Re your questions.

 

1. The normal target PF would always be inductive and usually between 0.95 and 0.98. I am not sure why you would ever select a target that is capacitive.

 

2. The advantage of first in first out, is that there is a better balance of operating time with the capacitors used. Last in first out means that the first in accumulates the highest operating hours and fails earliest.

 

Using different values for the banks and intelligent switching can give much closer control of the power factor.

 

3. The control algorithm varies between controllers.

 

PLEASE NOTE :

Power factor is the ratio of KW : KVAR and is a combination of both displacement power factor and distortion power factor.

Capacitive correction only corrects displacement power factor. It is becoming more common for true power factor to be the issue, in which case the harmonic currents need to be corrected as well.

 

Best regards,

Mark.

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