Let says, there is a small Multipurpose Hall with the total loads as per tabulated below and you are being assigned to design the power factor correction.
Before designing the power factor correction, you should know what’s the purpose in correcting the power factor and how to do the correction of power factor?
The Theories
Looking into the description of the load, the biggest loads are contributed by the mechanical equipments which are pumps and motors.
Bear in mind that pumps and motors are the inductive loads. These inductive loads will increase the value of the Reactive Power (KVAR). The Power Triangle below illustrated the relationship between the KW, KVA and KVAR.
From the power triangle above, the power factor are derives as per below formula;
In order to obtain an efficient systems;
a) The power factor should reach to 1.
b) The angle θ should reach to 0.
c) The capacitive load needs to be added in the system.
Why Power Factor Needs To Be Improved?
Money is the major reason. By improving the power factor, you’ll actually can:
a) Reduce the Maximum Demand and electricity bill
Higher KVAR will lower the power factor. Meaning that, more power or Maximum Demand (KW) is needed to counter the increase of the inductive load (KVAR). The more power that being consumed, the more utility bill that needs to be pay.
b) Avoiding the power factor penalty
The utility provider will impose the power factor penalty should the power factor in your system falls below their minimum power factor value.
c) Increase system capacity
Let say, 1000KVA transformer @ 80% power factor will produce 800KW of power. If we increase the power factor to 90%, that same transformer can deliver 900KW of power. The increase KW will generate more load can be added to the systems thus increasing the system capacity.
d) Reduce system loses and voltage drop level
The more power consume, the more heat will dissipate in the systems. This heat is actually the electrical loses in your power system and it will increase the voltage drop level.
Ok... we go to the basic formula of three phase power;
For the power factor of 0.8, the current that required will be 17.4A. If you increase the power factor to 0.9, the required current is only 15.5A. Based on this current comparison, the lower power factor will increase the value of current in the systems. Due to this increase in current, more heat will generates along the feeder cable thus increase the electrical loses in the system.
Now, you already knew the theories and the reason behind the power factor correction. The next question is how to design the power factor correction.
HOW TO DESIGN THE POWER FACTOR CORRECTION?
First and foremost, in order to reduce the inductive load (KVAR) (some people called correction of power factor) in the system is by adding the capacitive load in your system. This is due to the capacitive load is inversely proportional to the inductive load.
Let says your initial Power Factor (PF) = Cos Ө1 = 0.7
Final Power Factor (PF) = Cos Ө2 = 0.85 (Based on your final required value)
Therefore; Ө1= Cos-1 (0.7) = 45.57°
Ө2= Cos-1 (0.85) = 31.79°
KW = Maximum Demand = 78.63kW
Vector Diagram (Final)
The added KVAR will be based on the below formula:
KVAR (Added) = KW (Tan Ө1 - Tan Ө2)
= 78.63 [Tan (45.57) – Tan (31.79)]
= 78.63 [(1.02) – (0.62)]
= 31.45 KVAR
Conclusion
The design KVAR should be more that the calculated KVAR. Therefore, the added KVAR shall be based on 35KVAR.
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