Power Factor Correction
Power factor is a measure of how effectively your equipment converts electric current from BC Hydro's system to useful power output, such as heat, light or mechanical motion. Low power factor costs you money.
There are two kinds of power:
- Usable power called kilowatts (kW)
- Reactive power called kilovar (kVar)
The ratio of your usable power consumption to your reactive power consumption determines your power factor. Some electrical equipment, such as motors and transformers, require both types of power. Power factor gets smaller as reactive power increases in comparison to usable power.
The train analogy diagram helps explain how it works.
When your power factor drops below 90%, a power factor surcharge is applied to cover the cost of supplying additional reactive power. The surcharge chart shows how your charges are calculated.
Low power factor is usually caused by devices, such as motors and transformers, which use a magnetic field to function. Some of the incoming current used to create the magnetic field leads to reactive power consumption, measured in kilovar-hours (kVarh). The ratio of your kWh consumption to your kVarh consumption determines your power factor each month.
There are corrective devices to solve power factor problems. Speak to a qualified electrician to find out how to take it to the next step.
Benefits of power factor correction
By optimizing your energy use you can:
- Reduce electricity costs by eliminating power factor surcharges
- Enhance equipment operation by improving voltage
- Improve energy efficiency
- Reduce line losses
- Delay costly upgrades
- Free up transformer and distribution system capacity
Power factor corrective devices
1. Capacitors
Power factor correction capacitors are the most common method of correcting power factor. They can be:
- Installed at various locations on your electrical system
- Switched on by large loads such as electric motors
2. Controlling capacitors
A controller provides automatic switching of capacitor units and maintains the power factor level under any changes in operation or load.
3. Adjusting existing capacitors
Existing capacitors may be correctly sized but incorrectly controlled, leading to poor overall power factor. Blown protection fuses on capacitors take the capacitor off-line.
Looking at the condition and control of existing capacitors and fuses, especially after a shutdown, may solve some power factor problems.
4. Installing the right size motor
Oversizing motors without proper power factor correction is a leading cause of low power factor. One of the most effective means of improving power factor is by installing correctly sized motors for the job. This will also reduce energy consumption and your total energy bill.
5. Power quality effects
Harmonics, a power quality phenomenon, may be generated by some electrical equipment such as:
- Adjustable speed drives
- Switched power supplies
- Electric smelters
These installations require carefully designed power factor capacitors or in some cases harmonic filters to avoid amplifying harmonics which may damage components of your electrical system. The presence of harmonics in your electrical system points to a power quality problem.
Surcharge chart
Calculating your surcharge
You are billed for the usable power and a surcharge is applied to cover the cost of supplying the reactive power whenever the power factor drops below 90%. Capacitors are used to increase power factor to above 90%.
To measure the amount of reactive power used, your business is equipped with a kVARh (kilovar-hour) meter. This meter enables the power factor of your electrical system to be calculated.
Calculating your surcharge
| Power Factor | Surcharge |
| Less than 100% but 90% or more | Nil |
| Less than 90% but 88% or more | 2% |
| Less than 88% but 85% or more | 4% |
| Less than 85% but 80% or more | 9% |
| Less than 80% but 75% or more | 16% |
| Less than 75% but 70% or more | 24% |
| Less than 70% but 65% or more | 34% |
| Less than 65% but 60% or more | 44% |
| Less than 60% but 55% or more | 57% |
| Less than 55% but 50% or more 72% | 72% |
| Less than 50% | 80% |
Example:
If your total charges are $1,398.05 per month ($1,393.90 usage charge + $4.15 basic charge) and your power factor is 77% then your surcharge, from the above table, is 16% of the total charges or $223.68.
These details are shown on your BC Hydro bill.
Train Analogy Diagram
Imagine a locomotive pulling a boxcar on a parallel train track with a chain. The tension in the chain is higher due to the sideways component of pull but the work done in moving the boxcar is exactly the same as if the locomotive was directly in front of the boxcar requiring a much lower chain tension.
The increased tension in the chain when pulling from the side is analogous to the increased current necessary to supply the reactive power in an electrical circuit. The chain has a limited capacity for tension before it will break just as electrical wires have a limited capacity to carry current before failing. By increasing power factor (putting the locomotive in front of the boxcar) capacity is freed up in the electrical system (the chain has more spare tension before reaching the breaking point).
For more technical details download the Power Factor guide [PDF 1 Mb].
Last Modified: May 9, 2009