Three-Phase Power Factor Correction Flashcards
What does it mean when power factor is unity?
All of the power supplied by the system does useful work.
What are the two main reasons for maintaining a high power factor?
Reduced energy costs and an increased system capacity (boost to efficiency).
Would a power company charge you more for running at a low power factor?
Yes they would probably charge more based on the low pf.
What is a major benefit of placing corrective devices near the “corrected” lagging devices?
The line current up to that point will be reduced, reducing line loss/drop.
What are the two main methods of power factor correction?
- Installing capacitors or cap banks;
- Running a synchronous motor at a leading pf.
What is a synchronous condenser?
A synchronous motor without a load attached to the shaft.
What is a possibility in an overcorrected circuit?
Damage to the motor or equipment.
How would you size a cap bank to bring power factor to unity.
It would be as large as the sum of all inductive reactive power.
What are the main differences in a wye or delta connected cap bank?
Voltage is lower in wye (reduced size);
Line current is larger in delta (bigger wires);
Reactive power is larger in delta (3 x larger).
What is the typical range of power factor after correction?
0.9 to unity.
Why must capacitors have a means to discharge their stored charge?
Because they present a large shock hazard.
What precautions must be taken when discharging a cap bank through the motor windings, when installed on the load side of a controller? What else must be considered in this installation?
A large discharge current can damage the windings, always follow manufacturers reccomendations;
The reduced line currents will affect overload sizing.
