Home Page Products Page Service Projects Contact Support

Power Factor - Frequently asked Question -

What is power factor?
Power factor is the ratio between active power (KW) and total power (KVA). Active power does work and reactive power produces an electro-magnetic field for inductive loads.
PF(%) = KW ÷ KVA x 100
What are harmonics?
Harmonics are multiples of the fundamental frequency distortions found in electrical power, subjected to continuous disturbances. In a 50 Hz electrical system 250 Hz is the 5th harmonic, 350 Hz is the 7th harmonic, and so on. Harmonics are created by the use of non-linear devices such as UPS systems, solid state variable speed motor drives, rectifiers, welders, arc furnaces, fluorescent ballasts and personal computers. Individual harmonic frequencies will vary in amplitude and phase angle, depending on the harmonic source.
What is harmonic resonance?
When a capacitor bank is added to a power system, it is effectively connected in parallel with the system's impedance, which is primarily inductive. As far as the harmonic source is concerned, it sees a capacitor in parallel with an inductor. Since the capacitive and inductive reactance are frequency dependent, there is a frequency at which these two parameters will be equal. This frequency is called the system's natural resonant frequency. At this frequency, the system's impedance appears to the harmonic source to be very large, therefore, a harmonic current at the resonant frequency flowing through this impedance will result in a very large harmonic voltage.
Why tuning for the 5th harmonic?
The 5th harmonic is generally considered to be the most offending. It is important that the tuned frequency for the 5th harmonic, be at least at the 4.7th harmonic (235 Hz). Tuning slightly below the offending harmonic will accommodate for standard tolerances in the manufacturing process, but remove the largest offending portion of the 5th harmonic. Parallel resonance will occur around the 4th harmonic, at a much lower amplitude and in an area that does no harm to the capacitors or system. Many other systems are designed at the 4.08th harmonic to help extend the life of the capacitors. This tuning frequency does not remove the majority of the 5th, 7th, etc. harmonic from the system. Nokia capacitors do not need this safety factor.
How to solve harmonic resonance?
The solution can be accomplished by:

1. Adding or subtracting capacitance from the system to move the parallel resonance frequency to one that is not deleterious.
2. Adding tuned harmonic suppression reactors in series with the capacitor to prevent resonance.
3. Altering the size of the non-linear devices.

What are some indications of harmonic resonance?
Some indications are overheating, frequent circuit breaker tripping, unexplained fuse operation, capacitor failures, electronic equipment malfunction, flicking lights and telephone interference.
What are the benefits of power factor improvement?
  • Less total plant KVA for the same KW working power
  • More KW working power for the same KVA demand
  • Improved voltage regulation due to reduced line voltage drop
  • Reduction in size of transformers, cables and switchgear in new installations
  • Reduced power losses in distribution systems

What are the factors that affect your electric utility billing?
1. Energy Charge:
  • Number of kilowatt-hours used during the billing period
  • Number of kilovolt amperes (KVA) used during the billing period
2. Demand Charge: This type of charge compensates the utility for the capital investment required to serve the facility's peak load. Demand charges may be a large portion of the total electric bill, as much as 75%. Demand charges can be reduced by reducing energy peaks, reducing KVA and improving power factor.
3. Power Factor Penalty Charge: This is a rate structure charge imposed to encourage the industrial, commercial and institutional user to improve power factor. With many of the electric utilities, penalty billing is imposed when the power factor (PF) drops below 95%. In most cases, the least expensive, most efficient and most reliable method to reduce this charge (improve PF) is by adding properly designed fixed or automatic power factor correction capacitor systems.
At present it is in the Bylaws (available from your local Electrical Authority) and it seems that it will be implemented in the near future.
What types of equipment cause low or poor power factor?
Lightly loaded or varying load inductive equipment such as: HVAC systems, induction furnaces, molding equipment, presses, etc.
What do power factor capacitors do to improve power factor?
Power factor correction capacitors supply the necessary reactive portion of power (KVAR) for inductive devices. Because the capacitors supply this necessary power, the electric utility does not have to supply it, resulting in reduced generating costs for the utility.
Where is the most efficient location for power factor capacitors?
The location that provides maximum benefits of power factor correction is at the load. Capacitors work from the point of installation back to the generating source. Individual motor correction is not always practical, sometimes it is more practical to connect larger capacitors on the distribution bus or install an automatic system at the incoming service along with fixed capacitors at the load.
What kind of savings can I realize by installing power factor correction capacitors?
Every application and installation is different. However, in those areas of the country where the electric utilities have a penalty based rate structure, power factor correction capacitors and systems can generate a one year or less payback. Consult our Savings and Application Guide for details on how potential savings can be calculated.

Automatic PFC and Harmonic Solutions

Benefits of Power Factor Improvement
Description
Automatic power factor correction systems are designed to automatically turn power factor correction capacitors on or off to maintain a desired target power factor under varying load conditions on the low voltage distribution systems of industrial, institutional, and commercial facilities.

Applications
Automatic systems, rather than fixed capacitors, should be applied where the following conditions occur:

  • Electric utility rates include KVA demand billing or a power factor penalty clause, or
  • The facility is experiencing KVA capacity problems causing overheating of system components resulting in increased operating costs and KW usage, or
  • The facility is not able to maintain a desired power factor window, especially when extreme fluctuating loads are present, or
  • Sustained leading power factor problems are experienced when the electric distribution system is lightly loaded.

Benefits of Power Factor Improvement

Simplified Power Factor Capacitor Applications
The automatic power factor correction equipment featured in this catalog monitors the system power factor to maintain the desired target power factor. The only information required to correctly size the equipment to the electrical distribution system is the monthly maximum KVAR, based on the last twelve month's usage.

Reduced Insulation Costs
Automatic equipment eliminates the need to install smaller capacitor units and associated switching devices on the electrical distribution system, thus eliminating additional installation costs.

Enhanced System Reliability
PFC Engineering automatic equipment is application specific to provide many years of trouble free operation. Design features that ensure a long service life follow.

  • Significant reduction of capacitor inrush current that causes early contact failures and misoperation of sensitive electronic equipment is virtually eliminated. This is primarily due to the addition of engineered air core inductors. Tests have verified that property designed air core inductors will substantially reduce contact wear and capacitor switching transients. In addition, individual capacitor stages are switched onto and off of the circuit by a non-sequential rotational principle. This means the capacitor stage that was switched off last will not be the first stage to be switched on. Each capacitor stage operates for equal periods to ensure even wear.
  • The power factor controller utilizes switching time delay and loss-of-voltage dropout features. The time delay protects the capacitors from over voltage by allowing the capacitor discharge network to drain the capacitor voltage before the capacitor is re-energized. The loss-of-voltage dropout disconnects all capacitors if a power failure occurs. After power is restored, the automatic equipment will energize the capacitors, one step at a time, until the desired power factor is again achieved.
  • Micro-processor based Power Factor Controller measures the reactive current on every passage of the voltage through zero.  Measures the active [Iw] and reactive [Ib] currents separately and mathematically calculates Power Factor from these values ensuring accuracy down to about 0% Power Factor. Automatically switches capacitors as required by the plant load to maintain a desired Power Factor. Target Power Factor range programmable from .80 inductive to .95 capacitive. Capacitors switched in a non-sequential rotation or sequential stepping arrangement [selectable]. Programmable stage ratios to allow for larger capacitor banks. Programmable Harmonic voltage and current alarm, programmable failure to meet Power Factor alarm, loss of voltage alarm, and loss of current alarm.
  • Automatic C/k calculation
  • Automatic Phase Rotation Identification and CT location
  • Auto / Manual Operation
  • Programmable switching time delay
  • Programmable Capacitor Discharge Time
  • Sequential or Non-sequential stage switching
  • Loss of Mains system voltage Alarm
  • Failure to Meet Power Factor Alarm
  • Harmonic Over voltage Alarm
  • Harmonic Over current Alarm
  • Automatic Program Lockout
  • Current Transformer direct ratio input
  • C/k input - manual over ride
  • Control Transformer Voltage ratio setting
  • Controller shut down due to System voltage loss
  • Controller shut down due to low or loss of current signal
  • Removal of failed capacitor stages from usage
  • Programmable maintenance shut down
  • Suitably rated current limiting fuses are utilized, providing additional protection from faults that would have to be cleared by upstream protective devices if each capacitor module did not include current limiting fusing.
  • State-of-the-art, low loss, self clearing capacitors are utilized in every automatic system. Each capacitor cell is protected with an internal pressure sensitive interrupter providing additional protection for the system.

All capacitors comply with IEC specification 831 part one and two.