Fixed capacitor banks for transformer.

ask for datasheet

Hello Guest,

Most applications do not have fixed capacitor banks, but use electronic PF correction, which cuts in or out the necessary capacitors as required, to maintain the correct PF.

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Kind Regards....

Normally, you would be correcting the load that is connected to the transformer. In order to calculate the capacitance, you need to determine what the load is.

You can then apply static correction to each motor, or bulk correction at the point of supply.

Correction should not be applied to a transformer that is lightly loaded, as this can cause resonance between the transformer leakage reactance, and the capacitors.

For more information, see http://www.LMPhotonics.com/pwrfact.htm

Best regards,

Mark Empson.

Power factor correction is a complex process to be carried out depending on load conditions.It is normally carried out in three stages and not to be entirely corrected centrally and by a simple formula. The three stages are individual compensation , group compensation and central compensation.

First consideration is that there should be PF correction at the load centre itself depending on the type of load. if you have induction furnace as load The PF will be very low and PF correctors have to be provided along with the Induction furnace panel to avoid KVAR loss. Similarly if your load is purely resistance load as resistance furnace then the PF will be very close to unity. For a load of large Induction motors capacitors are to be connected for PF correction along with motor control panel depending on the available data of motor.

The second stage is to correct the PF at the central electrical distribution panel after carefully statistical study of the power system in respect of KVA , KVAR and PF with the help of special instruments designed for load management.Here capacitance banks of smaller units can be switched on if operators are available or with the help of automatic pf correction panels stage by stage switching can be done.

The third stage of PF correction is to be made at substation along with LT switching control panel where it is advisable to provide APFC ( Automatic Power Factor Corrector )panel where condensers will be switched on and off in stages depending on the actual PF value of the system( from time to time) depending on the load current. When there is no load condition the transformer will remain highly inductive and the CT, and controller will remain in effective for automatic correction. So while designing a portion of capacitors are kept as fixed and rest kept for auto control in stages. A proper load study of KVA,KW,PF and KVAR is needed to arrive at the actual requirement of capacitance. It is not a simple calculation. Can see an example of a study result

Refer to fig.below It is the study conducted for a specific plant before designing the APFC panel for variation of system power factor during the working time without the power factor correction .The average PF is around 0.65 only.

So you can get your own answer for design after proper study.

Hello V.I.Abraham

Your "diagram" is perhaps a good one, unfortunately it is blank, or sometimes blank grey, except a small square at top left, with a red dot inside, indicating the graphic was not accepted by the CR4 software, for some reason.

If you save the diagram to your own PC, rename it, then upload it from your own computer in a new Post, visibility of the diagram may prove OK.

Cheers, and Kind Regards....

Hi Sparkstation,

The graph is very clearly visible ( opening from CR4) in my computer. I do not know why it is not properly opening on your computer, there may be some software mismatch problem. It is a simple graph of actual PF variation plotted in a case study ( time vs PF).Nothing very special , simple graph. It is reproduced only to show , how PF varies and why automatic correction is required and why proper study is required.

Hello again V.I.Abraham

I have checked the graphic: C:/Documents and Settings/DELL/My Documents/Electrical Energy Audit at an Indane (LPG) Bottling Plant - A Case Study - An Article from Suresh Kumar K_S_files/fig45.gif.

This has been "uploaded" from your own computer, and the reason it cannot be viewed by others, is that you uploaded with a link to the full file location in your own personal computer.

The graphic comes from http://sureshks.netfirms.com/article/aud1/aud.htm and because others will have the same problem, I place the chart here.

Kind Regards....

Hello,

You are correct this graph is from that enerrgy audit report.

Regards

what is the present Power factor and to what value u want to correct it?

Dear Friend,

You have to provide the following.

1. What are the Speeds of the motors connected. Lesser the speed, lower will be the P.F.

2. What is the minimum Power Factor to be maintained - this may be governed by local regulations.

3. What is the present power factor and what is desired.?

Based on the above we can calculate capacitor bank. Generally it for 3 phase, 420 Volts motor it will be 40% on H.P of the motor, if 0.8 PF is decided.

Capacitor to be connected as close as possible to the motor.

DHAYANANDHAN