Question

What is the approximate capacitor in kVAR to be added to 3.7 kW/5 hp 1440 RPM agriculture pump motor for power factor improvement from 0.75 lag to near 0.95 lag?
1. 2 kVAR
2. 2.5 micro farad
3. 3.7 kVAR
4. 5 kVAR

Answer 1

Correct Answer - Option 1 : 2 kVAR

Power factor:

• The overall power factor is defined as the cosine of the angle between the phase voltage and phase current. 
• In AC circuits, the power factor is also defined as the ratio of the real power flowing to the load to the apparent power in the circuit. 
  Hence power factor can be defined as watts to volt-amperes.
• It is also defined as the ratio of resistance to the impedance of the circuit.
• So that by increasing resistance, the power factor can be increased. But due to power losses practically it is not used.
• Typically capacitor is used for power factor improvement purposes.

 

The kVAR need to supply to improve the load power factor 

Q = PL (tan ϕ₁ – tan ϕ₂) 

Calculation:

Given that

PL = 3.7 kW

cos ϕ1 = 0.75, cos ϕ2 = 0.95

tan ϕ₁ =0.88, tan ϕ₂ = 0.328 

The kVAR need to supply by the synchronous motor to improve the load power factor to 0.95 is

Q = PL (tan ϕ1 – tan ϕ2) 

= 3.7 (0.88 - 0.328)

= 2 kVA