To understand power factor, visualize a horse pulling a railroad car down a railroad track. Because the railroad ties are uneven, the horse must pull the car from the side of the track. The horse is essentially pulling the railroad car at an angle to the direction of the cart’s travel. The power required to move the car down the track is the working or real power. The effort of the horse is the total or apparent power. Because of the angle of the horse’s pull, not all of the horse’s effort is used to move the car down the track. The car will not move sideways; therefore, the sideways pull of the horse is wasted effort, which represents non-working or reactive power.
To move this analogy into reality, consider a motor that is powered on, but is not currently performing any work. While the motor runs, reactive power is used to maintain an electro-magnetic field so the motor is ready to work when necessary. Again, this reactive component is non-working and therefore inefficient.
Additionally, reactive power is created when there is a difference between the amount of current drawn and used. For instance, light bulbs and resistance heaters draw current exactly synchronized and proportional to voltage. However, most other equipment draws current with a time lag (phase shift) or distortion (harmonics). As a result, it takes more current to deliver the actual power to run the equipment.
Power Factor Penalties
Throughout the United States and the world, utilities are putting financial penalties on facilities whose power factor is lower than 95%. Utilities want to encourage clients to improve power factor, as it will increase the generation capacity.
In addition to the penalty on your utility bill, low power factor has a negative impact on your internal distribution system. Uncorrected power factor will cause power losses in your distribution system. Additionally, you might experience voltage drops as power losses increase, and excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment.
Power Factor Correction
There are several ways to correct your power factor. The most inexpensive way is to minimize operation of idling or lightly loaded motors. Additionally, avoid operation of equipment above its rated voltage to ensure power quality. You should operate all motors near their rated capacity to gain the most efficient power factor. In addition to these procedural changes, you can install capacitors in the AC circuit to decrease the magnitude of reactive power.
Capacitors
Capacitors store reactive power (measured in kVArs) caused by inductance and release energy opposing the reactive energy caused by the inductor. The presence of both inductance and capacitance in the same circuit results in a continuous alternating transfer of energy between the capacitor and the inductor, thereby reducing the current flow from the generator to the circuit.
When the circuit is balanced, all energy released by the inductor is absorbed by the capacitor. In the horse and railcar analogy, this is equivalent to decreasing the angle the horse is pulling on the railcar by leading the horse closer to the center of the railroad track. Since the side pull is minimized, less total effort is required from the horse to do the same amount of work.
Trizec Hahn Property Management
Service
Power Factor Correction Implementation
Challenge
- Needed to correct power factor to avoid paying a penalty at three separate properties
- Renaissance Tower
- Galleria Towers
- Plaza of the Americas
Solution
- Provided extensive engineering studies to determine the best capacitor system for each location
- Designed and installed capacitor systems
