Transients - External

The most spectacular cause of transients is lightning. Lightning is a discharge of stored electricity in clouds. This discharge may occur between two points in the clouds, or between a cloud and the earth. Lightning often strikes objects projecting up from the earth, such as utility poles. If this happens, the lightning's energy is dumped into the power lines. Transients generated from direct strikes are potentially most harm harmful -- both for the utility and the customer.

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

Lightning is not the only source of impulses on the utility side of things. Whenever large, reactive loads are turned on they also generate transients. These transients, although less powerful than a lightning strike, still cause problems. Keep in mind that the larger the facility, the more likely it is to have capacitor banks.

The same kinds of transient problems exist when utilities and customers do load transfer switching. Adding or removing a large bulk of the load will often create significant transients.

At the least, transient energy disrupts the normal activity inside equipment. This leads to such things as lock-ups and restarts.

If the problem is external transients, there are several possible solutions.

For lightning, the only solution is a quality lightning arrestor system. This should include proper earth connection - not necessarily a connection to the building's ground system. Conduction path clearances must be maintained to ensure that no energy gets into facility wiring.

Where lightning is common, add a transient voltage suppressor system, or TVSS, 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 operation. 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 large and small scale TVSS systems to reduce the magnitude of spikes within a facility.

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, other mitigation devices are needed. Technologies such as computer-grade power conditioners and ferroresonant line conditioners are effective in eliminating spikes.

Don't forget about back-door hits. Make sure all interconnected devices are protected so that no spike can get onto the data lines.