Facts on Power Factor Conditioning – Part III

Motor Inrush Current

When the power switch is turned on, a stationary motor acts as short circuit causing a much higher than normal current to flow. As time passes the magnetic field builds up and the motor starts to rotate and reaches steady state rpm and the current drops down to normal values. This high current is called “inrush current” which has minimal impact on the total power consumption of the motor but may adversely affect motor lifetime by stressing out its wiring. The magnitude of this current is a function of the motor horsepower and design characteristics. Our experiments have shown that adding ABET-2201 has reduced the peak inrush current of the tested motor by about 5%. Also, when the motor was under full load, the unit has reduced the inrush current time about 15%.

Fig. 5. Motor inrush current with and without ABET-2201 capacitor unit at 1.6 lbf-in dynamo-meter load.

Voltage Sags

The current i, and the voltage V, in a capacitor C, is related to each other by the following equation,

where dV dt is the time rate of change of the voltage across the capacitor. Therefore, the voltage across the capacitor cannot change instantaneously (i.e., dt = 0) because it will then need an infinite amount of current to do so. As a consequence, whenever the capacitor is subjected to a sudden voltage surge or sag, the capacitor tends to reduce it to certain extent depending on its size. This behavior of capacitors have lead to applications where these are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal voltage and current fluctuations from the primary power source to provide a “clean” power supply for signal or control circuits. Such effects in capacitors can also be interpreted to act as a local reserve for the DC power source, to smooth out fluctuations by charging and discharging each cycle. Figure 6 presents the effects of ABET-2201 capacitor on voltage sag due to an induction motor switching in a household.

Fig. 6. The effects of ABET-2201 capacitor on voltage sag due to an induction motor switching in a household.

Harmonics and Temperature

Harmonic distortion is the deviation in the waveform of the supply voltage from its ideal sinusoidal waveform due to inclusion of higher frequency components in addition to the
fundamental frequency. The major adverse effect of the harmonics is heating of induction motors and transformers in the household leading to reduced lifetime of the motor. It has been known that a reduction of 10 oC in the operating temperature of a motor essentially doubles its lifetime. The ABET-2201 in conjunction with the resistance of the household wiring forms a low-pass filter which prohibits higher frequency components from the incoming supply into household loads. Consequently, motors are subjected to less heating as illustrated in Fig. 7.

Fig. 7. The effect of ABET-2201 capacitor on the temperature of a motor running under dynamo-meter load.

The power distribution panel installed by distributor

The distributor of electrical energy installs a power distribution panel outside a household so that their personnel can monitor the total energy consumed by the household by reading the Energy meter installed in the panel. Two wires with 220 V across them are brought in from the locality supply grid into the distribution panel. All loads in the house which run on 220 V are connected across these two wires. Loads which run on 120 V are connected across one of these two wires and the ground terminal which is fabricated in each household by inserting a solid copper rod deep into the soil. All 120 V loads are divided into two circuits, each consisting of one the above mentioned two wires and the ground terminal. Figure 8 shows these two different configurations.

Fig. 8. Distribution panel configurations in a household

Conclusion

An attempt has been made to elucidate the principle of operation of the ABET-2201 Power Conditioning Unit in offering significant benefits in the areas of reduced power usage, decreased motor temperature, improved power factor, reduced inrush current and suppression of voltage sags. Investigations are being continued to understand and explain other effects that may have implications on the ABET-2201 such as i) Harmonics generated in the household loads, ii) Impact of the unit to the distribution system during non-peak hours (i.e., nights).