Location of capacitors to reduce losses
There is a good reason for selecting the above case study. The reduction of losses was possible, since the PFC capacitors were located close to the motor terminals.
In many large industrial sites, the PFC capacitors are installed close to the utility supply point. In such cases, the objective of installing the PFC capacitor is to meet the power factor requirement enforced by the utilities. This is done by the utility in the following ways:
- By specifying the power factor requirement at the supply point as a part of supply conditions.
- By providing a tariff incentive in the form of maximum demand charges based on kVA / MVA demand instead of kW / MW demand.
Most designers of industrial power systems associate the power factor correction with utility requirements and maximum demand charges. Hence, it is common to install the PFC capacitors close to the supply point. This is often the most convenient location for installing the PFC capacitors.
The installation of PFC capacitor close to the supply point has minimal effect on the reduction of power loss in the system.
The location of PFC capacitor close to the load is the best option. If this is not feasible, then as a compromise, PFC capacitors can be located at the substation switchroom close to the loads. This results in the following benefits:
- Reduces the reactive power flow in the distribution system, which in turn reduces the power loss (I2R loss) in the distribution system. This helps to reduce the electricity costs as illustrated in the above case study.
- Reduced reactive power flows will reduce the voltage drops in the distribution system. This will help to improve the voltage levels in the system and provides better voltage support during motor start conditions. This will also help to avoid mysterious under-voltage trips in the system!
- Location of PFC close to the load helps to reduce the current flows in the distribution system. In other words, the distribution feeders and substation transformer capacity can be better utilised. For example, by judicious choice of transformer taps and PFC capacitors, it is possible to supply up to 20% more load by the same transformer.
Include PFC capacitors at the planning stage
Quite often, there is a tendency to avoid planning for PFC capacitors at the project planning stage, especially when the emphasis is on reducing initial project costs. In such cases, the PFC capacitors are included only to meet the utility requirements.
It is important to conduct the power loss studies during the project planning stage. As illustrated in the above case study, judicious location of PFC capacitors will reduce power losses. In addition, they will also help to reduce the equipment ratings. Hence, the power system studies must be conducted for optimum sizing and location of PFC capacitors. These studies should be included in the project feasibility report to illustrate the economic benefits of PFC capacitors.
If there are project financial constraints, then at the minimum, PFC capacitors should be included in general arrangement (GA) drawings. This will enable the installation of PFC capacitors at a future date. Quite often, it may not be feasible to install capacitors at optimal locations at a future date unless a provision is made at the project planning stage.
