Where to install power factor correction capacitors?
Global compensation
(see Fig. L13)
| Where a load is continuous and stable, global compensation can be applied |
Principle
The capacitor bank is connected to the busbars of the main LV distribution board for the installation, and remains in service during the period of normal load.
Advantages
The global type of compensation:
- Reduces the tariff penalties for excessive consumption of kvars
- Reduces the apparent power kVA demand, on which standing charges are usually based
- Relieves the supply transformer, which is then able to accept more load if necessary
Comments
Reactive current still flows in all conductors of cables leaving (i.e. downstream of) the main LV distribution board
- For the above reason, the sizing of these cables, and power losses in them, are not improved by the global mode of compensation.
Fig. L13: Global compensation
Compensation by sector
(see Fig. L14)
| Compensation by sector is recommended when the installation is extensive, and where the load/time patterns differ from one part of the installation to another |
Principle
Capacitor banks are connected to busbars of each local distribution board, as shown in Figure L14.
A significant part of the installation benefits from this arrangement, notably the feeder cables from the main distribution board to each of the local distribution boards at which the compensation measures are applied.
Advantages
The compensation by sector:
- Reduces the tariff penalties for excessive consumption of kvars
- Reduces the apparent power kVA demand, on which standing charges are usually based
- Relieves the supply transformer, which is then able to accept more load if necessary
- The size of the cables supplying the local distribution boards may be reduced, or will have additional capacity for possible load increases
- Losses in the same cables will be reduced
Comments
Reactive current still flows in all cables downstream of the local distribution boards
- For the above reason, the sizing of these cables, and the power losses in them, are not improved by compensation by sector
- Where large changes in loads occur, there is always a risk of overcompensation and consequent overvoltage problems
Fig. L14: Compensation by sector
Individual compensation
| Individual compensation should be considered when the power of motor is significant with respect to power of the installation |
Principle
Capacitors are connected directly to the terminals of inductive circuit (notably motors, see further in Clause 7). Individual compensation should be considered when the power of the motor is significant with respect to the declared power requirement (kVA) of the installation.
The kvar rating of the capacitor bank is in the order of 25% of the kW rating of the motor. Complementary compensation at the origin of the installation (transformer) may also be beneficial.
Advantages
Individual compensation:
- Reduces the tariff penalties for excessive consumption of kvars
- Reduces the apparent power kVA demand
- Reduces the size of all cables as well as the cable losses
Comments
- Significant reactive currents no longer exist in the installation
