Disadvantages of Low Power Factor

The three phase line current I_L = P / ( √ 3 ) V_L Cos Ф

As the power factor is low, the load current is high and vice versa. The low value of power factor affects following ways.

Transformer

• The kW capacity demand of the transformer decreases due to lower power factor.

       kW = kVA Cos Ф

Line loss

• As the power factor decreases, the line losses increase. 
• This will increase heating of conductor as well as insulation and decreases line efficiency. 
• Higher losses adversely decrease the life of insulation.

Transmission line

• The load current carries by the line increases due to decrease in the power factor for a fixed amount of power transmitted.  
•  As the current density of the conductor is constant, cross sectional area of the conductor increases in order to carry large amount of current.

       Current density δ = I / a ( amp / mm²)

• This will result in volume of conductor material increases which result in capital cost of conductor increases.

Generator

• The kW capacity of the generator decreases due to lower power factor.
• The generator copper losses are increases which further decreases the efficiency.

Voltage regulation

• There is large voltage drop in the transmission line as well as winding of transformer and alternator due to low power factor. 
• Higher the voltage drop, poor voltage regulation and vice versa.

Cost of switch gear equipment

• The rating of switch gear equipment increases due to poor power factor therefore the cost of switch gear equipment increases.

Reactive power compensating device

• As the power factor ( Cos Ф ) decreases, the Sin Ф increases. 
• This will result in increase of reactive power. 
• There will be reactive power compensating devices necessary in order to reduce reactive power of the line.

       kVAr = kW Sin Ф ( r = Stands for reactive power )
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