Do Power Conditioning Devices Save Energy?

By Jim Grossman - Rocky Mountain Power

Key Points
• Surge protection devices operate so infrequently the energy savings are negligible.
• Your energy consumption (kWh) and energy charge will not change when capacitors are used to improve power factor.
• If the power quality at the targeted end-use application is currently good, a power conditioner will likely not have much of an impact in reducing energy use.

The primary purpose of power conditioning devices, such as transient voltage surge protection devices (SPD) or capacitors to improve power factor, is to protect equipment. Recently, there have been several SPD and capacitor manufacturers that are also pushing the energy savings aspect of power quality. There are claims of energy savings in the 20 percent range from some of these manufacturers, which is a significant savings. The purchaser of SPDs, capacitors or other power conditioning equipment needs to understand the basis for these energy savings claims before raising an expectation for similar performance.

An SPD is a faster-acting transient device that can be used for lower-voltage transient attenuation. It acts by clamping the line voltage to a specific value and then conducting any excess impulse energy to the safety ground, regardless of frequency. The energy shunting capability of an SPD is expressed by its short circuit current rating which determines the amount of energy the device can handle. SPD devices can be economical solutions for protecting personal computers and other lower energy use equipment, dedicated to the specific purpose of isolating harmonics and other low voltage transients. However, they operate so infrequently that energy savings are negligible.

Power factor is the ratio of real current over total current, or the ratio of real power (kW) over apparent power (kVA). Rocky Mountain Power must supply more power to account for the losses incurred due to excessive inductance. If the useful power that the energy user consumes is described as "working power," "active power," or "real power" (kW), then the component of lost power is sometimes referred to as "reactive power," or kilovolt amps reactive (kVAR). The total amount of power that the electric utility has to supply to the customer is called "apparent power," and is given in kVA.

From a current perspective, part of the total current is reactive current, which creates the magnetic field but does not do useful work. Real power and real current do useful work. So, the reactive current is not really flowing through the circuit and creating I²R losses; it is bound up in the magnetic field, if you will. It can be confusing but the following picture helps to illustrate:

Adding capacitors improves power factor and removes reactive power. The real power (kW) to the motors does not change (blue color), but the reactive portion (red color) is removed from the utility input. Your energy consumption (kWh) and energy charge will not change, but power factor penalty charges will be reduced or eliminated.

Power conditioners are often combinations of transient voltage surge suppressors, noise filters, capacitors and isolation transformers or voltage regulators. The product specifications vary according to the intended purpose at the customer location. The right combination of mitigation devices is coordinated to lessen the vulnerability of the electrical equipment that is being protected.

When evaluating marketing statements from power conditioning device manufacturers and testimonials from their end users, be aware that the energy savings are dependent on the power quality for a specific application. In addition, power quality is affected by harmonics, most of which are generated internally within an energy user's facility by motor drives, switches, older lighting ballasts and other non-linear electrical equipment. If the end user does not have a preponderance of this type of equipment, the energy savings benefit of power conditioning devices will likely be minimal. The bottom line is that if the power quality at the targeted end use application is currently good, the power conditioner will likely not have much of an impact in reducing energy use.