Is Replacing a 25 kVAr Unit with Two 12.5 kVAr Units More Efficient?

In summary, the power factor correction unit for a building needs maintenance and the service report recommends replacing the existing 25 kVAr unit with 2 x 12.5 kVAr units. This is based on the analysis of interval data, which shows that at most, there is only 30 kVAr required at peak demand and often only 12.5 kVAr. The decision to switch to smaller capacitor banks depends on how the energy supplier bills for Power Factor, as some may charge for capacitive PF while others do not. If there is a charge for capacitive PF, the cost of the new arrangement should be compared to the cost of doing nothing. If there is no charge for capacitive PF, the change
  • #1
AbdullahS
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TL;DR Summary
Advice needed on Power Factor Correction Unit upgrade
Hi all,

The power factor correction unit for one of the buildings that I am working on needs maintenance. The service report recommends replacing the existing 25 kVAr unit with 2 x 12.5 kVAr units as "the demand on your site according to the data supplied shows us that at most there is only 30kVAr required at peak demand and quite often only requires 12.5kVAr".

This has been recommended after the analysis of interval data. The following graph shows the KVAr at the site for a period of 3 months.

1581896853254.png


Could you please advice if replacing the larger bank with two 2 smaller capacitor banks justified? If so, what is the reason? Shouldn't the old one do the job even when the kVAr requirement is low?

A bit of background about myself:
I am a mechanical engineer who is working in sustainability industry. I do have basic knowledge of reactive power but not detailed enough to answer questions such as these.

Thanks in advance.

Regards,
Abdullah
 
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  • #2
Whether the change is a good economic decision (or not) depends primarily on how your energy supplier bills for Power Factor. In the simplest case, Power Factor correction systems add capacitance to 'offset' the inductive character of most loads. A 'too large' correction will leave your power factor 'too capacitive.' 2 smaller systems would allow closer to ideal (net zero) correction for a range of loads. As I understand it, some utilities charge for capacitive PF, and some don't - if yours does bill for capacitive PF, you'll need to compare the 'do nothing' cost to the cost of the new arrangement. If they don't bill for capacitive PF, you probably can't (economically) justify the change.
 
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Likes berkeman
  • #3
Thanks @Dullard!
 
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Related to Is Replacing a 25 kVAr Unit with Two 12.5 kVAr Units More Efficient?

What is a Power Factor Correction Unit?

A Power Factor Correction Unit (PFCU) is an electrical device that is used to improve the power factor of an electrical system. It works by correcting the phase difference between the voltage and current in an AC circuit, resulting in a more efficient use of electrical energy.

Why is power factor important?

Power factor is important because it affects the efficiency and cost of an electrical system. A low power factor means that the system is not using electrical energy efficiently, resulting in higher electricity bills and potential damage to equipment.

How does a Power Factor Correction Unit work?

A PFCU works by using capacitors to store and release electrical energy, which helps to balance the power factor in an AC circuit. It measures the power factor and adjusts the amount of capacitance needed to improve it.

What are the benefits of using a Power Factor Correction Unit?

Using a PFCU can result in several benefits, including improved energy efficiency, reduced electricity bills, and increased lifespan of electrical equipment. It can also help to reduce voltage drops and improve the overall stability of an electrical system.

Do all electrical systems need a Power Factor Correction Unit?

No, not all electrical systems need a PFCU. It depends on the power factor of the system. If the power factor is below 0.95, it is recommended to install a PFCU to improve efficiency and reduce costs. However, if the power factor is already above 0.95, a PFCU may not be necessary.

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