Effects of low power factor

Effects of low power factor

Phase angle lagging / leading:- AC (Alternating current) voltage or current is continuously varying in magnitude and direction with respect to time. Its instantenious magnitude varies according to sine function of angle from 0 to 360 degree or 0 to 2π radian. Voltage value is increases from 0 volt to maximum positive value Emax volt and then decreases back to 0 volt in positive half cycle. In negative half cycle voltage decreases from 0 volt to maximum negative value -Emax volt and then  increases to  0 volt. These are known as positive half cycle and negative half cycle. One positive half cycle and one negative half cycle makes a complete cycle. The alternating voltage cycles are repeated continuously. The number of cycles per second is known as frequency of supply. For 50 hz supply there are 50 cycles per second that means supply voltage will change its direction 50 times in a second. For one cycle it takes 1/50 second ie 20 mili second known as time period of ac cycle denoted by capital letter T. A cycle consist of one positive and one nrgative half cover 0 to 360 degree angle. 0 degree of this cycle is consider as reference point for angle measurement. For example in three phase system three alternating voltage are present whose staring point is 120 degree apart from each other. If we consider red phase as first phase then yellow phase 0 degree point is 120 degree after the red phase 0 degree starting poing. Similarly blue phase 0 degree point is 120 degree after the yellow phase 0 degree point. Again red phase will come after 120 degree of blue phase and this continue endlessly. This 120 degree is known as phase difference. As in this case yellow phase voltage come 120 degree after red phase it said like this  the yellow phase is 120 degree lagging red phase. Or red phase is leading yellow phase by 120 degree. The word leading means before and lagging means after.

Types of load :- there are mainly three types of load. Resistive load, inductive load and capacitive load.

Resistive load:-When  ac voltage is applied to a resistive load such as filament bulb the current flowing through resistance is in same page with voltage, means the 0 degree starting point of current is at the same 0 degree point of voltage. This is said as current is in phase with voltage. The power factor is cosine of angle between voltage vector and current vector (ac quantities are represented as vector)
Power factor = cos(0)
Power factor =1
So in resistive load power factor is always 1.

Inductive load:- Inductance always oppose to change of flow of current. Due to this property when ac voltage is applied to an inductive load ac current is start flowing through it but the current is some degree (say for example 30 degree) lagging the aoplied voltage. Now power factor is cosine of angle
Power factor = cos(30)
Power factor = .866
So here we say power factor is .866 lagging.

Capacitive load:- When ac supply is applied to a capacitive load the current flowing in pure capacitor is 90 degree leading with voltage. Hence the power factor is cos(90) = 0  leading.

Conclusion:- in resistive load power factor is always 1 also said unity power factor. In pure inductor power factor is 0 lagging. But inductor is always having some resistance so that power factor lies between 0 to less than 1 lagging. in case of capacitor power factor if 0 leading.

Power in ac circuit:- The power in ac circuit is product of voltage and component of current in phase with voltage. So if applied voltage is V and current flowing in circuit is I and the angle between voltage and current is phi. Then

Power = V x I x Cos(phi)
The equation show that cos(phi) is a multiplying  factor in power calculation, that,s why it is known as power factor.

Effect of power low factor:- It is clear from equation that if power factor is low then more current is required for the same load. Therefore any load which is running at low power factor will draw more current from power supply system.

Disadvantage of lower power factor

1 conductor size is line need to be of higher size as per increased demand of load current.
2 All switchgear sizes are to be of higher size.
3 Transformer will supply less power as compared to they could supply at good power factor.

Due to all these problems power supply authorities are always insists for improving power factor for industrial consumers,