Transients – Their Impact on the Power Quality Industry

Years ago, transients were thought to be non-existent figments of the imagination of persons who sold unnecessary protection for an imaginary problem. The education and experience of the last several years have clearly demonstrated that transients are anything but imaginary. With many industries moving toward automated information and reporting function systems and automated material handling systems, transients are a relevant and ever present problem. Once the destructive transient problem is understood, solutions may be sought and implement.

Power companies have little or no control over transients induced by lightning or high power switching at substation levels. Currents from a direct or indirect strike may be induced or directly enter conductors of a suspended cable or a buried cable. Either way, the surge will propagate in the form of a traveling wave bi-directionally on the cable from the point of origin.

A major automotive manufacturer realized first hand the effects of lightning strike casualty potential. According to the automotive manufacturer’s research laboratory personnel, several months after the installation of transient voltage surge suppression (TVSS) devices, lightning struck the substation, which was located on the roof of their Atlanta I.C. Assembly plant. This substation powered the automated assembly robots in the auto body area. The substation literally exploded and created a hole in the roof that was large enough for a man to walk through. The 480-volt raceway that powered the equipment was vaporized and the swing plugs were welded together. The only thing that stood between disaster and the expensive computerized robots were the TVSS devices. The TVSS devices functioned properly and shielded robots from lightning induced transient activity. The only robot damaged was the one, which was bolted to the beam directly supporting the substation. Operations resumed in short order. Had TVSS devices not been installed, that event alone could have had a primary cost of over $250,000.00. Secondary costs would have been exorbitant, as total operation shutdown for repairs, replacement and reprogramming would have been necessary. Immeasurable lost opportunity would have been suffered as well.

Internally generated transients result from switching within the facility. Any time the flow of electricity is altered; such as in the simple act of turning a motor or light on and off, transient activity can result in what is known as inductive kick. An excellent example of this phenomenon can be seen in the following illustration. At a site survey monitored by General Electric Houston Lab personnel, transient activity was generated when a four-foot, two-bulb, fluorescent fixture was turned off. Twenty four damaging transients in excess of 1200 volts occurred. When a TVSS device was installed, the site was again monitored and transient activity was virtually eliminated.

For years, the burden of the manufacturer and TVSS industry engineers was to convince a population, uninformed in this specific field, that transients were something other than harmless. In recent years, the challenge to the TVSS industry has become that of assisting the TVSS consumer in determining:

1. If TVSS devices are a viable solution to their particular power quality problem, either by using TVSS devices alone or in conjunction with other power quality equipment, and;
2. Which TVSS designs are most suitable for the specific application? Suitability of TVSS design is not a reference to brand or manufacturer choice, but rather refers to the circuit topology and function itself, e.g. parallel versus series design, threshold versus sine wave tracking devices, and electrical system compatibility issues and specific levels of performance deemed acceptable.

With today’s sophisticated equipment, it is essential that TVSS devices be manufactured to application requirements. It should be noted that TVSS devices are also referred to by many and specifically in international circles as SPDs or Surge Protective Devices. For purposes of this paper, the acronym TVSS will be used.

An understanding of the equipment being protected, the surge environment, and specific protection needs, becomes necessary when applying TVSS. The maxim, one size fits all, is not appropriate for the application of TVSS devices. For example, when considering data line applications, one must consider that the data is transmitted at various voltage levels, as well as data rate, frequency, digital or analog equipment considerations.

Test procedure parameters and test equipment must be included in the specification data. Today, we have the benefit of well-established industry standards and guidelines to which we test. Specifically, ANSI/IEEE C62.41-1991 and C62.45-1992. By controlling and defining the voltage, current, waveform rise and decay time, surge polarity, phase angle, and applied power status, test results can be well documented and utilized for application suitability analysis. Utilizing industry-accepted or an NRTL (Nationally Recognized Testing Laboratory) lab certified test equipment is required as well. It is important to remember when conducting these tests that changing any of the control items shown above, can and will affect the outcome of the testing conducted and therefore, when comparing models, testing similarity should be considered. For example, one may test two units (same model) at 6 kV and get completely different numbers because the impulse current has been changed.

Another factor to consider specifically when testing parallel design suppression devices is lead length. Lead length may be defined as the length of conductor from the unit under test to the test equipment connection point. On a parallel design unit, lead length will significantly affect the results both in the test laboratory and more importantly, in the actual field application.

In order for consumers to make a TVSS unit selection, the consumer needs to consider the safety agency listings those products bear and manufacturer qualifications. Look for the UL 1449 listing which is Underwriter Laboratories, Inc. standard for transient voltage surge suppression. ISO 9001 Quality System registration gives the consumer assurance that the manufacturer doe indeed operate a quality system, which is in compliance with this international quality system standard and is audited by a reputable quality system registrar such as DNV, UL or BSI.

As Dr. Wei-Jen Lee, of the University of Texas at Arlington, has pointed out, in the absence of certain data, one may find manufacturer’s specification data difficult to understand. NEMA has also addressed this issue in their LS-1 Standard which offers recommended data inclusions for a manufacturer’s specification sheet.

The consequences of transient activity on unprotected automation equipment in the grain elevator, auto, aircraft or any industry can be devastating, resulting in immediate equipment destruction or cumulative damage. Selection of transient voltage surge suppression devices should be the result of an intelligent informed decision process, based upon an understanding of the system to be protected and an understanding of the manufacturer’s specification data and qualifications.