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What is Power Factor Correction?

The power factor is a measure of how effectively electrical power is being used by a device or system. It is the ratio of real power (measured in watts) to apparent power (measured in volt-amperes).

When considering Power factor correction (PFC) this can be determined by the following information.

Qc can be determined from the formula Qc = P (tan φ – tan φ’), which is deduced from the diagram. The parameters φ and tan φ can be obtained from billing data or direct installation measurement.


Power Factor Correction


This is a very simplistic view of PFC, and it can involve far greater detail, especially when you get into the building or specify a capacitor bank and reactive power compensation panel, this is a whole specialised field within electrical engineering, and I do not profess to be an expert at all.

In simple terms these types of devices are best left to experts in the field, although many Electrical engineers may have installed them, they often have no idea about the Design element or the intricacies of how they work, dozens of parameters need to be considered, and, as systems change these systems need to evolve as well, and be adjusted.

Often buildings have work or refurbishment carried out but little or no thought is given to any adjustment now needed for this vital piece of equipment, although many of them have an automatic control via a power factor regulator, this can only compensate so far, these systems need to be checked maintained and monitored throughout their lives, correctly balanced systems save money and cost.

If I remember correctly EN 61921:2017 is the latest guide on how to build these safely, there is always another guide or standard we need to look at, BS 7671 is not the end of it by any means.

A small extract from within this standard is the following: –

  1. access to the elements within the capacitor bank should be arranged so that there is no issue or problem to replace the elements in case of failure.
  2. The degree of protection depends on the place of the installation of a capacitor bank. If the capacitor bank is to place in the same place as the main switch gear or utility room next to it, IP 20 is enough but due consideration should be given to the environmental conditions within this environment.
  3. The construction of these devices – in a device for reactive power compensation, particularly sections can be determined, by placing them in separate partitions all within the same cubicle.
  4. Identification – each capacitor bank must have a nameplate, which contains information about and identification numbers, date of manufacture, and rated power in [kVar], the rated voltage in[V]. Min and Max ambient temperature, index of protection, and short-circuit strength in [A]

This is just a very small snapshot of what is required to build these units.

It is also very important to ensure the thermal conditions are met this I believe can be found under IEC 60831-2 where minimum and maximum operating temperatures are clearly laid out.

How often do I go into a mains room only to find air vents blocked by combustible materials, storage boxes, plastic or capacitor banks covered in 10mm of dust as they have never been looked at from the day they went in? This is not only a fire hazard, but the detrimental effect on the systems could mean they’re not working and therefore serving no benefit to the building or to the customer, and all the while the customer is unaware, that they are paying increased energy costs.

The issue of cooling is very important, these units degrade if they get improper thermal conditions and are exposed to overheating and their life expectancy degrades.

To mitigate this, we need to follow a few rules that reduce unwanted effects.

  1. The distance between the inlet and outlet should be as far apart as possible to provide maximum airflow.
  2. The dimension of the inlet should be at least 10% bigger than the outlet.
  3. Avoid airflow in zigzag or right-angle lines ensuring the inlet and outlets are opposite each other.
  4. In many cases. Forced airflow is needed to be placed at the bottom of these cubicles to keep a constant cold airflow into this type of switchgear to reduce overheating and thermal degradation.
  5. The real airflow should be considered since theoretical airflow can be higher in terms of the counter pressure effect.

In general terms, we can assume that the power loss of the power capacitors (including wires discharge resistors and contactors) is approximately 7W per/KBA are four (capacitor and reactor)

Therefore, according to the following formula, as an example: –

D = 0.3 times PS[m3/h]

D=0.3 x (200 x 7) = 420 [m3/h]

Where: –

D = minimal efficiency of ventilators

PS = total power loss OD capacitor circuit

This will give you the size of the cabinet that you need to use for the given situation you are trying to achieve.

I’ve only summarised a few points in this complex type of system, so that the reader may begin to understand in a small way the complexities involved in this sort of system design.

I have therefore only given a small outline of what is involved in producing one of these systems, when looking at all the regulations and rules required EN 61921:2017’s 42 pages long and IEC 60831-2 is 22 pages in their present forms so as you can see, I’ve only extracted a very small amount.

The money that can be saved by ensuring that your electrical systems PFC were correctly designed thereby reducing costs in energy use if they are maintained properly and updated, is vital in the design and maintenance of any electrical system and your company’s bottom line, especially with the cost of electricity at present, so speak to professionals who deal with this every day and get them to ensure that your current PFC is fit for purpose.