Facts on Power Factor Conditioning – Part II

The Role of the Capacitor in the Electrical Power System

A capacitor is a device that stores energy in the electric field established between a pair of conductors on which equal but opposite electric charges have been induced. Historically,
capacitors have taken the form of a pair of thin metal plates, whether flat or tightly coiled up in a cylinder (like a sushi roll), but every multi-conductor geometry exhibits the phenomenon of capacitance. The capacitance of a traditional flat-plate capacitor and, resultantly, the amount of energy that can be stored in the capacitor–is proportional to the surface area of the conducting plate and inversely proportional to the distance between the plates. It is also proportional to the permittivity of the dielectric substance that separates the plates, whether vacuum, air, or specially engineered materials chosen for their high electrical permittivity. In a direct-current (DC) circuit, a capacitor acts like an open circuit: no current flows through it, though the potential difference initially induced between its conductors can serve as an exponentially decaying energy source for the circuit. In an alternating-current (AC) circuit, a capacitor cyclically stores and releases energy at twice the frequency of the forcing source.

Power Factor Correction

ABET-2201 brings the advantages of the power factor correction capacitor to household use. Figure 1 shows a typical connection of the ABET unit in a household. This unit is usually connected to the breaker panel where the electricity is distributed to different locations in the house. As mentioned above, the current passing through the current coil of the Energy-meter installed by the power distributor to monitor power consumption is the algebraic aggregate of the individual resistive, inductive, and capacitive currents flowing in different loads of the household, as shown in Fig. 1. Since the currents flowing in inductive and capacitive loads are half a cycle out of phase, it is possible to make their sum zero at any particular time by adjusting their magnitudes, consequently reducing the total current magnitude flowing through the Energy meter.

Fig. 1. An example ABET-2201 installation in a typical household.

Figure 2 (a) illustrates the instantaneous supply voltage, and currents in resistive, inductive, capacitive loads. It can be clearly seen that while the current in the resistive load is in phase with the supply voltage (? = 0o), the current through the inductive load lags the supply voltage by a quarter of a cycle (? = -90o), and the current through the capacitive load leads the supply voltage by a quarter of a cycle (? = +90o). Figure 2 (b) displays the instantaneous supply voltage and the total current with and without the ABET-2201 capacitive load. Figure 3 is an exploded view of a section of Fig. 2 (b) showing clearly the reduction of the phase angle between the supply voltage and the total current when ABET-2201 is connected to the system, thus improving the power factor and consequently, reducing the total current magnitude. Due to the reduction in the total current, the power loss (I2 total x R1) in the resistance R1, between the wattage meter and the ABET- 2201, which varies from house to house, is also reduced. This is the instantaneous power saving that is achieved by installing the ABET-2201. It is important to note that i) the resistance R1 will depend on the locations of the Energy-meter and ABET-2201, and ii) the power saving is proportional to the square of the reduction in the current brought about by the ABET-2201. Figure 4 presents average voltage, current, power, and power factor measured over a period of one hour in an actual household. It is clearly observed that the power consumption is reduced along with the improved power factor and reduced current.

Fig. 2. (a) Instantaneous voltage and current waveforms of individual components, (b) Instantaneous voltage and total current waveforms before and after ABET-2201.

Fig. 3. Phase angle reduction (power factor correction) with the addition of ABET-2201 to the system. (Circled part of Fig. 2(b) zoomed in.)

Fig. 4. Measurement results of average voltage, current, power and power factor in a household.