Power Factor Correction

Utilities

Utilities must manage the reactive power required to operate the grid and to compensate for poor power factor caused by their customers. Power factor correction within the grid may occur at a central substation and spread out over the utility power distribution system. Utilities must compensate for loads that are too inductive as well as loads that are too capacitive.

Correction within the grid must also take into account the correction made at a utility feeder powering a commercial or industrial plant as well as how much correction is made within power-consuming equipment itself. Most power electronic-based equipment appears a capacitive, causing a shift in the current as it leads the voltage. Electronic switching within equipment power supplies causes harmonic currents to be drawing from the customer’s electrical system. If the customer cannot provide enough or all of the harmonic currents, the remainder must come from the utility.

Utilities invest a lot of money in engineering and equipment to ensure reactive power is managed. The management of reactive power at any point on the grid or inside the customer’s facility wastes energy and generates heat.

Electrotek’s expert engineers can conduct power factor correction studies along with harmonics evaluations regarding PFC concerns on the power distribution system. Electrotek can conduct in-depth PQ monitoring at selected points on the grid to gather PQ data critical to modeling and simulating various systems and problems. Electrotek’s expertise also involves determining the most appropriate solutions to utility PFC problems.

Architecture & Engineering Firm

The design and upgrade of industrial plants involves upgrading traditional existing plant equipment to modern power electronic-based (non-linear) loads. Typically, the plant electrical system is also upgraded to power the new loads. However, in some cases the system is not upgraded and left to support the new loads. The electrical engineering may involve the design of a new power factor correction (PFC) system or the upgrade of an existing one.

Power factor correction capacitors can be a very economical means for many industrial customers to reduce demand charges and power factor penalties.  With appropriate controls, the systems are designed to maintain a desired power factor over a wide range of load variations. Despite the benefits that can be realized using power factor correction capacitors, there are a number of concerns that should be evaluated when the capacitors are required during an industrial plant project. The most important of these concerns fall in two basic categories:

Harmonic distortion concerns:

  • Resonance conditions resulting in excessive distortion levels.
  • IEEE Standard 519-1992 and IEEE Standard 519-2014 compliance.

Transient overvoltage concerns:

  • Magnified transients at lower voltage buses, and within customer facilities.
  • Nuisance tripping of end-use power electronic equipment, such as variable frequency drives (VFDs), electronic battery chargers, etc.

Electrotek Concepts® has developed a comprehensive approach for computer simulation and analysis of utility capacitor switching events. We use the Electromagnetic Transients Program—Revised Version (EMTP-RV) and PSCAD® to simulate electromagnetic, electromechanical, and control systems transients in multi-phase power systems.

Equipment Manufacturers

Some equipment manufacturers (i.e., industrial plants) have power factor correction (PFC) capacitor banks on their plant property—internal and external to their facility. Some PFC capacitors are static (i.e., not switched), and some are dynamic—switched IN and OUT of the feeder as needed to maintain a high power factor. PFC capacitors have a component life and will eventually fail with age. Specific PQ phenomena can shorten their useful life. 

If a plant experiences load changes as production requirements change or as sections of the plant are shutdown or added, engineering changes to an existing PFC system may be needed to ensure PFC is optimally maintained. Modifications to an existing PFC system may be needed if harmonic currents flowing through the capacitors are found to be high or if the voltage has to much harmonic distortion. If voltage distortion is too high and has the right spectral characteristics, power electronics-based equipment used in the plant may experience malfunction or failure.

Failures may also occur because of increased ambient temperatures and poor ventilation around the capacitors. If a customer experiences an increase in power factor penalty charges or catastrophic failure of one or more capacitors, a PFC system inspection should be conducted. Such an inspection will require detailed PQ monitoring, so PFC operating conditions and performance metrics can be documented and analyzed.

Electrotek’s expert engineers will conduct in-depth PQ monitoring at different points on the PFC system. High harmonic currents will be detected along with transient voltages. Capacitor and/or air temperature around the capacitors can be detected with one single Dranetz monitor. Remote PQ monitoring can be carried out with minimal investment. Remote monitoring allows Electrotek to have 24-hour access to each Dranetz monitor, so appropriate monitoring changes might be made.

End Users

End users who operate commercial and industrial facilities with no manufacturing can also have power factor correction (PFC) problems. Facilities with a lot of power electronics-based equipment per square foot will demand significant harmonic currents, compromising their total true power factor (TPF) at the point-of-common-coupling (PCC).

Although almost all power electronics-based equipment utilizes automatic PFC (APFC) technology to compensate for distorted AC input current and correct for poor power factor, some harmonic currents are still demanded from the customer facility. Most input AC total harmonic distortion (ITHD) levels for electronic equipment range from 10 to 20%, well under the limit of about 30% published by the IEEE and IEC. Most PFC levels range between 0.95 and 0.99. Many facilities incorporate the use of static or dynamic PFC as a part of their facility power system. If not, they rely on the utility to provide the remaining reactive power required to operate their electronic loads.

However, end users may find themselves with higher ITHD levels and lower PFC levels than recommended levels published in standards. End users that operate static PFC systems may require Electrotek expert engineers to help them retune that system or convert to a dynamic PFC system, if load levels significantly change.

Regardless of the PFC requirement, Electrotek expert engineers will conduct in-depth PQ monitoring at different points on the facility’s electrical system. High harmonic currents will be detected along with transient voltages. Capacitor and/or air temperature around the capacitors can be detected with one single Dranetz monitor. Remote PQ monitoring can be carried out with minimal investment. Remote monitoring allows Electrotek to have 24-hour access to each Dranetz monitor, so appropriate monitoring changes might be made. This provides PQ data necessary for Electrotek to model and simulate the system and identify viable solutions to PFC problems.