Describe active power and what is its SI unit.
Activve power does the work for the system providing the motion, torque, heat or anything else required. Measured in kilowatts kW.
Describe reactive power and what is its SI unit.
Reactive power doesn’t do useful work but simply sustains the electromagnetic field. Meaured in kilo-volt-amperes-reactive, kVAr.
Describe apparent power and what is its SI unit?
Working power and reactive power together make up apparent power. Meaured in kilovolt-amperes, kVA.
What is power factor?
It is the ratio of real power to total apparent power and it indicates how efficiently electrical power is converted into useful work. The ideal is 1 or unity. Less than this means extra power is required to perform the task.
List 3 reasons for a less than 1 power factor?
Reactive power, which uses power to maintain magnetic fields and it adds extra burden on the supply system. Large phase difference between voltage and current, common inductive loads like transformers and motors, rectifiers and inverters that distor waveform sources and high harmonic content.
How can power factor be improved?
It can be improved by connecting capacitors in parallel to the motor or lighting circuits to compensate for the lagging current created by the inductive loads. Static pfc can be applied at each individual motor by connecting the correcting capacitors to the motor starter.
What is another equation for power factor?
cosine (angle of V - angle of I)
What causes a large reactive power in a system and list some examples?
Inductive loads which include transformers, induction motors, induction generators and high intensity discharge lighting.
In relation to a right angled triangle, what side does active, reactive and total power resemble? What angle in the triangle is used?
Total power is the hypotenuse side, active is the horizontal or x-axis side and reactive is the vertical or y-axis side. The angle used is the one between the active and total power, opposite to reactive power.
List 3 reasons as to why improving power factor is important.
Reduction of electricity bills, environmental benefit because of less greenhouse gas emissions, extra kVA available from existing supply, reduction of heat losses in distribution equipment, reduction of voltage drop in long cables and extended equipment life.
Where should you study power factor correction calculations?
In your notes!
