Effective Power Factor Correction Using Synchronous Motors

Power factor and power factor correction are familiar electrical terms, but just in case they are new to you, let’s do a quick review. As it relates to electrical energy, power factor is the ratio of working power to apparent power. Working power (kW) is the electrical energy you need to do useful things, namely, run production equipment. Apparent power (kVA) is the electrical energy your utility company must supply in order to deliver the working power you need.

These two energy values aren’t the same thing, and they aren’t necessarily equal. Another type of energy present within the electrical system, reactive power (kVAR) counteracts working power (kW), causing it to be used less efficiently. In practice, the more kVAR you have in your system, the more apparent power (kVA) your utility must provide to supply the working power (kW) you need to run equipment.

F igure 1—Less kVAR, Better Power Factor
Figure 1—Less kVAR, Better Power Factor

As mentioned, power factor is the ratio of kW to kVA. The closer these values are to a 1:1 ratio, the closer you are to an ideal power factor of 1.0 and efficient power usage.

Conversely, the more kVAR your system has, the greater the ratio between kW and kVA (0.90:1, 0.85:1, etc.) and the poorer the power factor.

F igure 2—More kVAR, Poorer Power Factor
Figure 2—More kVAR, Poorer Power Factor

Your utility tracks the kW you use and the kVA it must supply, and from this, it can calculate your power factor. If your power factor is below a certain level (e.g., 95%, or 0.95), the utility probably charges you a power factor penalty fee. Depending on your facility, this monthly penalty can be substantial. The good news is that power factor can be corrected to improve your kW-to-kVA ratio, which, in turn, can reduce your kW load and eliminate your power factor penalty fees.

When companies consider power factor correction, they typically think in terms of adding capacitor banks to decrease kVAR. Often, however, another excellent source of power factor correction is already installed within their plants: the synchronous motors running their processes. If your facility has synchronous motors, you may presently have all the equipment you need for better power factor and lower monthly electric costs!

Unlike induction motors that are by nature reactive, or “lagging,” synchronous motors can be set to operate in a “leading” mode that enables them to perform essentially the same function as capacitor banks, creating capacitive energy to counteract system kVARs and permit more efficient kW usage. For the production facility with (a) power factor problems and (b) synchronous motors on hand, this approach is an excellent alternative. But before you start adjusting synchronous motor settings, following are seven guidelines you should keep in mind to ensure a better, more effective project outcome.

  • Complete a power quality analysis of your electrical system—Power quality analysis helps identify any harmonic, transient, and grounding issues that could impact power factor correction results. It also helps reconcile your facility’s power factor ratio with the one reported by your electric utility.
  • Check your motor types—This is more than just verifying induction motors vs. synchronous motors. Some synchronous motors can be adjusted to no more than a 1.0 (unity) power factor mode, while others can be adjusted to a leading mode of 0.80 or more. For power factor correction, you need synchronous motors that can be set to a leading mode.
  • Evaluate motor loading—If synchronous motors are under a full load, they may not be able to run in the leading mode, even if they have that capability. Remember, the lead is where the power factor correction is. To put motors in the lead, you may need to do some load shifting.
  • Examine the motor controller—This involves determining how difficult it is to adjust the controllers in order to place the motors in the lead. If the process is too complicated, you may need to consider other options.
  • Verify the magnitude of the power factor correction need—Setting your synchronous motors in the lead may reduce—but not eliminate—your power factor problem. For a total solution, you may also need to consider stationary, static, or climatic power factor correction equipment along with the synchronous motor adjustments.
  • Perform preventive maintenance (PM) prior to adjusting the motors—Preventive maintenance ensures the motors and related equipment are in peak condition and operating correctly so that if a problem occurs after the adjustments are made, the equipment will shut down properly to protect itself.
  • Meter motor operations—After synchronous motors have been placed in the lead, they need to be monitored to ensure they are performing as expected. If your electrical system doesn’t have the built-in metering capabilities for this, setting up a temporary metering installation is a wise investment.

In many cases, placing synchronous motors in the lead solves power factor problems without adding equipment to the system. It also eliminates related issues such as increased maintenance and decreased reliability. Additionally, when you factor ina typically better ROI than that of installing capacitors, the synchronous motor option is worth considering.

In many cases, placing synchronous motors in the lead solves power factor problems without adding equipment to the system. It also eliminates related issues such as increased maintenance and decreased reliability. Additionally, when you factor ina typically better ROI than that of installing capacitors, the synchronous motor option is worth considering.

But synchronous motor adjustments aren’t something you do as an isolated event. By following a few practical tips before and during motor adjustments, you’ll ensure this solution is as effective as it can be to deliver the power factor correction results you’re expecting.

For more information on how you can implement effective power factor correction using synchronous motors, contact D.L. Steiner, Inc.