12 replies to this topic

[tenbu]

Dear All

I need some technical advice. Suppose I have an electrical system witha power factor of 0.65 lagging. The system will be something like I have a Medium Voltage circuit breaker (11kV/6.66kV FROM Supply Authority).This is connected to a step down transformer where I get about 400V and then I have a Low Voltage circuit breaker then the load. What are the power factor correction measures for such a power factor? Secondly where can I install the power factor correction equipment at Medium Voltage cct breaker or low voltage cct breaker. I would be most obliged if you may include the reason for your choice. I am a baby to this stuff am reading as much as I can .

Thank you

[AB2005]

What are the power factor correction measures for such a power factor

Sorry your first question is not cleared what you want to ask.

where can I install the power factor correction equipment at Medium Voltage cct breaker or low voltage cct breaker

Every kind of load which have coil (transformers, motors, ballasts etc) needs reactive power. When you connect the primary side of traffo with supply, it also needs reactive power but it is not our duty to connect medium voltage capacitors for providing this reactive power, it is the responsibility of power distribution companies. But the distribution companies force to user to maintain there power factor at secondary side of traffo. That’s why we have to install a PFC system. Usually we connect the capacitors at main bus bar of low voltage power distribution board. This type of correction is called “Bulk Correction”.

[tenbu]

Sorry your first question is not cleared what you want to ask.


For my first question what I mean is what implementations can I do to get 0.65 as close to 1 as possible? Isn't that is the whole point of power factor correction?

[tenbu]

Just to say my second question still holds because I guess you are saying that the Medium Voltage side is the Power Distribution Company's responsibilty because I said the input is from the power suppl authority however the Supply authority's MV switchgear is also duplicated at the client's side such that I have a Consumer's MV switchgear and this is my responsibility. So we are back to square one.

[marke]

Hello tenbu

Welcome to the forum.

Firstly, have you read the information on power factor correction at http://www.LMPhotonics.com/pwrfact.htm and Power Factor?

Secondly, why are you interested in adding power factor?

Thirdly, Who owns the transformer and where is your power metered?

The answers to these questions may help us to give you a more meaningful answer.

Best regards,

[tenbu]

Hello tenbu

Welcome to the forum.

Firstly, have you read the information on power factor correction at http://www.LMPhotonics.com/pwrfact.htm and Power Factor?

Secondly, why are you interested in adding power factor?

Thirdly, Who owns the transformer and where is your power metered?

The answers to these questions may help us to give you a more meaningful answer.

Best regards,

Thank you Marke for those questions will answer them as best as I can. On the part where you say why am interested in adding power factor well it seems to be a requirement of the Supply Authority that we take power factor correction measures and we do stand to gain isn't if our real power is close to apparent power. By the way I have read the information on power factor correction from LMPhotonics site.
The transformer is on the consumer's side which makes it ours. As for where the power is metered have to check for that, how does this matter though?
I hope this will help. Thank you for the advise that wasn't my intention (to be a pest i.e.).

Regards
Tenbu

[tenbu]

The power metering is on the low voltage side.Wanted to attach a diagram of what I have but can't see how I can do it.I will just try to explain myself.Its two lines with a setup that I described earlier on that is MV CCT BREAKER transformer LV cct breaker power metering then load.On the low voltage side there is a connector line running between these lines kind of like a switch really then well feed into the load.I hope you get it.

[marke]

Hello Tenbu

OK if the major reason is to satisfy the power board, then there is no point in applying the correction upstream of their metering as they will not see any improvement that you make. This essentially answers the question in regard to MV or LV correction. If the metering is on the LV side, then you must apply the pf correction on the LV side on the load side of the metering. The metering must measure the load current and the power factor correction current or it will not register.

Best regards,

[tenbu]

Hello Marke

Thank you for that input, as much as it appears like the reason for the power factor correction is to satisfy the power board its not so. We are looking for a cost effective solution. As of the moment we are paying for the real power to the factory kW/h and for the kVA meant for the factory. Aren't there any advantages and disadvantages in tems of analysing the costs, cutting back on the payments have to make now for real and apparent power when looking at either placing the PFC at the MV or LV side.

Best Regards
Tenbu

[marke]

Hello tenbu

If you are paying for KWHs and also for KVA, then to reduce your payment, you need to reduce the KVA. This can be done by correcting the power factor.
If you apply the power factor correction on the supply side of the metering, the KVA measured will not change so you will still pay the same amount.
If you apply the power factor correction on the load side of the metering, then the reduction in KVA will be measured and your payments will reduce.

Best regards,

[tenbu]

Hie Marke

Thanks a million for that response I just could not get it from anyone. If I may ask this is for my understanding it will probably sound stupid but how come the power metering utility wont register the kVA if its done upstream.

[marke]

Hello tenbu

how come the power metering utility wont register the kVA if its done upstream

When you add power factor correction, you do not reduce the current flowing into the motor. The voltage across the motor terminals is the same (or possibly a little higher) so the current is essentially the same, however the current in the supply, upstream of the power factor correction, is the sum of both the motor current and the capacitor current. The reactive current into the motor lags the voltage and the current into the capacitor leads the voltage. The inductive current and the capacitive current are 180 degrees out of phase and cancel out, so the current in the supply is reduced.
One way of looking at it is to consider that the current into the motor remains the same, but the reactive current is supplied by the capacitor rather than the supply.

Best regards,

[tenbu]

Hello tenbuWhen you add power factor correction, you do not reduce the current flowing into the motor. The voltage across the motor terminals is the same (or possibly a little higher) so the current is essentially the same, however the current in the supply, upstream of the power factor correction, is the sum of both the motor current and the capacitor current. The reactive current into the motor lags the voltage and the current into the capacitor leads the voltage. The inductive current and the capacitive current are 180 degrees out of phase and cancel out, so the current in the supply is reduced.One way of looking at it is to consider that the current into the motor remains the same, but the reactive current is supplied by the capacitor rather than the supply.Best regards,

Hello MarkeOk, I 'm at the moment just trying to get the explanation into my head. Oh saw the part where I can attach my diagram and please just take a look at it if you can.What you will see is the setup we have that I have been trying to describe hope I wasn't far off. If you get new ideas on the design of the PFC I would be happy to know of them. And the question of harmonic filtering when installing PFC what considerations need to be taken into account. Are they any calculations that can be done to come up with the suitable harmonic filtering? Let me try digging it up from the net.RegardsTendai

Attached Files

•  diag_for_pfc.doc   27.5KB   8 downloads
•  diag_for_pfc.doc   27.5KB   3 downloads