Power Pollution Management 101

03/26/2003 |

Learn to Manage Power Events in Your Facility

Power Pollution Primer

Most people recognize power pollution by assorted symptoms, which we classify as “events.”

  • Power Outages. Power outages are most easily recognized as “lights out,” or an absence of power for more than 20 milliseconds.
  • Undervoltage. Voltage is lower than 90 percent of nominal for more than 10 seconds.
  • Overvoltage. Voltage is higher than 110 percent of nominal for more than ½ second.
  • Voltage Sag. Voltage is lower than 80 percent of nominal for less than 10 seconds.
  • Voltage Swell. Voltage is higher than 120 percent of nominal for less than ½ second.
  • Surges. Also known as voltage spikes/transient voltage surges. Voltage is very high for short durations of less than 0.003 seconds (3 milliseconds).
  • Harmonics. Distortion of either the fundamental voltage or current waveform.

Managing electrical infrastructure power pollution is easy, but you have to be proactive. Everyone involved in the ownership, design, and construction of the building must be thinking alike from the start.

Power Outages. This is an inevitable power problem facing all of us. Managing it is as simple as making good decisions in the very beginning of the design phase. Talk to your utility supplier. What is the outage history for the area? What were the causes? What are they doing to be proactive in eliminating potential outage causes? For example, something as simple as a good tree-trimming program can save you many future headaches.

If the critical loads (life safety and security systems) cannot handle a 10-second break in power, an uninterruptible power supply (UPS) system is needed. If they can handle a 10-second break, it’s possible that the only thing required is a standby engine-generator with 10-second auto start. If possible, plan for installation of either a UPS or an engine-generator at the start.

Harmonics. Harmonics are everywhere, but only because we let them into our building’s electrical infrastructure. The utility company should be supplying a relatively clean sinusoidal voltage source. Sometimes your potential neighbors can be a great source of harmonic power pollution.

Other times, you are your own worst enemy. The easiest way to manage harmonic power pollution is to not install harmonic-polluting equipment inside your facility.

If you put in a new UPS system, variable speed drive, elevator, etc., be careful; it could be an old design. Even though it may perform its intended function, it can also cause problems for the facility’s electrical infrastructure.

All equipment going into a new building should be specified to be power factor corrected (PFC), have an input power factor of 1.0, and less than five-percent input harmonic current distortion.

Undervoltage. These conditions (brown outs) are usually caused by overload of the electrical infrastructure, either at the utility level or at the building level.

Overvoltage. These are usually caused by poor voltage regulation by the utility, improper switching of capacitor banks, or even improperly tapped transformers.

Voltage Sag. These are most common and are caused by utility line faults (birds, squirrels, falling branches, ice storms). Another source is equipment in the building that requires very high starting currents (motors, HVAC units, elevators, etc.).

Here again, modern power electronics can help you manage this type of pollution. Specify a “soft start circuit” for cyclic equipment.

Voltage Swell. These can be caused by utility faults; usually, utility-generated sags and swells go hand-in-hand. However, they can also be caused by large variable speed drives with “regenerative braking.”

Surges. This is probably another of the most recognized power pollution problems. The causes: utility faults, circuit breaker operation, power factor capacitor switching, and everyone’s favorite – lightning.

Assess your potential risks and take proactive steps to eliminate power pollution before it disrupts your facility. Manage your electrical infrastructure power pollution before it manages you.

Al Warner is world wide applications engineering manager of remote monitoring at West Kingston, RI-based American Power Conversion Corp. (www.apcc.com).

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