Transients - Utility

The most spectacular cause of transients originates from lightning. Lightning is, in effect, a discharge of stored electricity in clouds. This discharge may occur between two points in the clouds, or between a cloud and the earth. Quite often, lightning strikes something projecting up from the earth such as a telephone pole. If this happens, then the lightning's energy is dumped into the power lines. Transients generated from direct strikes have the greatest potential for harm -- both for the utility and the customer.

But lightning does not have to strike the power lines to cause spikes. A strike in the vicinity of the lines can induce enough energy in them to cause a significant transient with a lot of punch to it.

Lightning is not the only source of impulses on the utility side of things. Whenever large, reactive loads such as power factor correction capacitors are turned on they also generate a transient. This transient, although less powerful than a lightning strike, still transmits enough energy to disrupt the integrity of data transmissions.

The same is true when load transfer switching is done at the substation level. Adding or removing a large bulk of the load will oftentimes create transients that can travel far enough on the lines to enter facilities.

If transients coming in from outside a facility are determined to be the problem, there are several possible solutions.

For lightning, there's no substitute for a quality lightning arrestor system. A system should include proper earth connection - not necessarily connection to the building's ground system. Conduction path clearances must be maintained to ensure no energy couples into facility wiring.

Where lightning is common, add to the arrestor system a transient voltage suppressor system, or TVSSs, at the service entrance. Always remember that poor installation of these systems negates their effectiveness.

It is likely that even with these systems enough transient energy will still reach equipment to disrupt communications and corrupt data. TVSSs or other technologies such as transformer based power conditioners, placed at panels or at the point of concern, can prevent the costly side-effects of transients.

If the problem is traced to switching transients, the lightning arrestors are not needed. Use of large and small scale TVSS systems reduces the magnitude of spikes within a business.

However, transient reduction may not be enough. The levels of impulses still allowed through a TVSS device could still be a problem. When this is an issue, then other mitigation devices are needed. Technologies such as computer-grade power conditioners and ferroresonant line conditioners have proven effective over the years in eliminating spikes.

Don't forget about back-door hits as well. Make sure all devices interconnected are protected so no spike can get onto the data lines and enter equipment through them.