Every electric machine needs active power (kW) and reactive power (kvar) to operate. The power rating of the installation in kVA is the combination of both:

(kVA)² = (kW)² + (kvar)².

The Power Factor has been defined as the ratio of active power (kW) to apparent power (kVA).

Power Factor = (kW) / (kVA).

The objective of Reactive Energy management is improvement of Power Factor, or “Power Factor Correction”.

The principle of ʺPower Factor Correctionʺ (or ʺReactive Energy compensationʺ) is to generate the reactive power close to the load, so that the supply source could be relieved. when connected with the loads, Capacitors banks are most commonly used in electrical network to supply reactive energy.

Figure 1

What is Power Factor?

Power factor (p.f.) is the relationship between working (active) power and total power consumed (apparent power). Essentially, power factor is a measurement of how effectively electrical power is being used. The higher the power factor, the more effectively electrical power is being used.

A distribution system’s operating power is composed of two parts: Active (working) power and reactive (non-working magnetizing) power. The active power performs the useful work… the reactive power does not. It’s only function is to develop magnetic fields required by inductive devices.

Generally, power factor decreases (angle Φ increases) with increased motor load. This geometric relationship of apparent power to active power is traditionally expressed by the right triangle (Fig 2) relationship of:

Cos Φ = P. F. = kW/kVA

Figure 2

Why improve low power factor?

Low p.f. simply means poor utilization efficiency. Cos Φ varies between 0 and 1, hence a value between 0.9 and 1.0 is considered good power factor and essentially means that metered power and used power are almost equal. From a consumer’s perspective, it simply means you are using what you paid for, with minimal wastage. When p.f. is low, the utility must provide the non-productive reactive power in addition to productive active power. For the utility that means larger generators, transformers, conductors and other system devices that pushes up their own capital expenditures and operating costs, which they simply pass on to industrial users in the form of power factor penalties. Hence, improved power factor helps avoid those penalties.

Benefits of reactive energy management:

Optimized management of reactive energy brings economic and technical advantages.

Savings on the electricity bill:

Eliminating penalties on reactive energy and decreasing kVA demand.

Reducing power losses generated in the transformers and conductors of the installation.

• Increasing available power:

A high-power factor optimizes an electrical installation by allowing better use of the components. The power available at the secondary of a MV/LV transformer can therefore be increased by fitting power factor correction equipment on the low voltage side.

• Reducing installation size:

Installing power factor correction equipment allows conductor cross-section to be reduced, since less current is absorbed by the compensated installation for the same active power.

• Reducing voltage drops in the installation:

Installing capacitors allows voltage drops to be reduced upstream of the point where the power factor correction device is connected. This prevents overloading of the network and reduces harmonics, so that you will not have to overrate your installation.

Options and solutions:

We are at Eletra Electric providing the three main options for PFC are as follows:

• Individual capacitor units: One capacitor unit for each inductive load (in most cases a motor)
• Banks of capacitor units:  Several capacitors grouped in an enclosure that is connected at a central point in the distribution system. Fixed capacitor banks comprise multiple capacitors racked in a common enclosure with no switching while automatic capacitor banks, also called “cap banks” have capacitors in a common enclosure with contactor or thyristor (SCR) witched by a controller.
• Combination of above: Where individual capacitors are installed on the larger inductive loads and banks are installed on main feeders or switchboards, etc.

Figure 3

The selection of Power Factor Correction equipment can follow a 4-step process:

• Calculation of the required reactive energy.
• Selection of the compensation mode:
• Central, for the complete installation
• By sector
• For individual loads, such as large motors.
• Selection of the compensation type:
• Fixed, by connection of a fixed-value capacitor bank;
• Automatic, by connection of a different number of steps, allowing
• adjustment of the reactive energy to the required value;
• Dynamic, for compensation of highly fluctuating loads.
• Allowance for operating conditions and harmonics.

Figure 4

Typical wiring diagram (detuned)

References:

1. Power Factor Correction – Power Quality – Catalogue 2022 – Low Voltage Power Factor – Correction Components – Schneider Electric
2. Low Voltage Products – Power factor improvement – Application guide – ABB