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Solving Common Power Quality Issues

Key Points
  • Transients and voltage sags are power quality issues that can disrupt or damage electronic equipment.
  • Surge suppressors and a variety of other equipment can help provide protection against transients.
  • UPS equipment and dynamic sag correctors can protect your equipment from voltage sags.

Many facilities experience power quality problems. Transients and voltage sags are two of the most common. They can disrupt or damage critical electronic equipment. A number of solutions are available to help protect your facility.

A short take on power transients

lightning_stockxchng.jpgTransients are brief voltage spikes originating outside your facility. Causes include lightning, utility capacitor switching, neighboring plants or work areas that start or stop large equipment, such as motors or presses.

Spikes can also originate from inside your facility. When large motors, relays and other inductive devices are shut down, the voltage that was flowing must be absorbed into surrounding wires and other devices.

Capacitor switching before the meter can cause voltage transients, too. When power factor correction capacitors are switched on, line voltage falls, followed by a sudden rise. This process repeats until the system settles down within one half-cycle. After the initial voltage drop, there is an oscillation caused by interaction between the capacitor bank and system inductance. Disruptive transients can travel through the grid and create problems for motors, process controls and other electronic devices.

A number of devices are available to protect your facility and its critical equipment:

  • Surge protection devices (SPDs) can be used for lower-voltage transient attenuation. It clamps the line voltage to a specific value and conducts any excess impulse energy to ground.
  • Zero threshold surge suppressors (ZTSS) shunts transient energy away from sensitive equipment.
  • Surge suppressor panels, receptacles and power strips use solid-state metal oxide varistors (MOVs) as the suppression element.

The lowdown on voltage sags

A sag is a reduction in voltage (typically at least 10 percent) that doesn't hang around for long. They usually last for less than a second, although they can go on for up to a minute or two.

Sags can originate on either side of your electric meter, and their exact source is often difficult to pin down. Frequently, they're caused by equipment within your facility; a bunch of motors starting at the same time, for example. Outside, wind or trees falling on power lines can also produce sags. The source doesn't have to be close by. A voltage sag on a power grid can impact facilities within a 100-mile radius.

A power quality monitor is the most commonly used tool for detecting voltage sags. Simple monitors measure and record power as it enters your facility. More sophisticated models use software to track voltage sags and other power quality disturbances.

How do you protect your facility from voltage sags? First, fix the problem causing the sag and then focus on upgrading your equipment to ensure that it's more capable of riding out voltage issues. Specify and purchase electrical equipment that's more tolerant of voltage variations.

Next, take steps to compensate for sags when they do occur. Install uninterruptible power supply (UPS) devices on critical electronic equipment. A UPS constantly conditions power, including correcting voltage sags. Dynamic sag correctors are another option. They regulate voltage as the incoming primary voltage changes, riding through sags down to 50 percent.

By taking the time to understand how power quality issues can affect your critical equipment, you can take steps to protect your facility, which will save money and reduce downtime.

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