Application Notes

EAP-030033

Why does phase difference occur? What is power factor?

The phase angle of the current in reference to the voltage changes depending upon the characteristic of the load. Electric current phase angle does not change if the load is a pure resistor (0 degree phase difference). However, it advances by 90 degrees if the load is the pure capacitor. On the other hand, it lags by 90 degree if the load is the pure inductor. Therefore, the phase difference changes depending upon the resistance, the capacitance and the inductance that the load has.

Power factor is cosine of the phase difference between voltage and current. It is a proportion of the apparent power, voltage and current that effectively becomes power. The lower a power factor, the higher the required electric power supply; therefore an electrical facility becomes larger. Generally, a power factor lower than 85% is considered a low power factor. M-System Model LPF or LTPF Power Factor Transducer is useful to manage the power factor. Typical power factors of electric devices are as follow:

Devices	Power Factor	Devices	Power Factor
Incandescent bulb	100%	Three-phase induction meter	70 - 85%
Electric heater	100%	Fan	65 - 85%
Electric stove	100%	Fluorescent light	60 - 70%
Iron	100%	Motor (sewing machine)	50 - 80%
Color TV	90 - 95%	AC welding machine	30 - 40%
Stereo	0 - 95%