Tips & News - April 2012

TIPS NEWS &

Reduce System Losses It should also be noted that all HV surge arresters, by design, dissipate power from the grid when operating at normal system voltage levels. For the gapped SiC arrester, the continuous power loss is a result of high resistive current flowing through the arresters grading resistors. MOV gapless surge arresters do not require this resistive grading structure. Comparison tests have confirmed thatMOV arresters consume less continuous watts from the grid than comparably rated gapped-SiC arresters. This energy saving feature is consistent with the government’s mandate for utilities to reduce energy losses on the grid. As an example, replacement of a single early

It redirects the surge to ground and, in doing so, limits the exposure of the equipment’s insulation to acceptable voltage levels. MOVs: Improved Protective Margin and Higher Energy Capability While the gapped SiC arresters provided state-of-the art protection when manufactured, recent testing has confirmed that the MOV gapless arresters, manufactured since the mid-1970s, actually provide improved performance characteristics. The most important improvement provided by gapless MOV surge arresters is their inherently lower protective levels, critical to extending service

. . . replacement of a single early 1960s vintage 120-kV rated gapped SiC arrester with a similarly rated MOV gapless arrester would result in an annual energy savings of more than 1000-kWh.

life of aging, possibly degraded, electrical insulation of power equipment that has been in service for many years. Replacement of gapped SiC arresters with gapless MOV surge arresters is a simple, cost effective way of extending the service life of expensive, aging equipment and, at the same time, minimizing unplanned power outages. For example, replacement of a gapped SiC by a new gapless MOV surge arrester on an older 69-kV transformer would be less than 2% of the cost of transformer replacement. Similarly, for an older 345-kV station, arrester replacement would be less than 1% of the cost of replacing the transformer. Gapless MOV surge arresters also have higher energy absorbing capability, minimizing the chance of failure, when discharging an over voltage surge. Laboratory testing indicates that HV MOV gapless arresters have an energy discharge capability approaching twice that of comparably rated gapped, SiC arresters.

1960s vintage 120-kV rated gapped SiC arrester with a similarly rated MOV gapless arrester would result in an annual energy savings of more than 1000-kWh. It is estimated that a large quantity of gapped SiC high voltage surge arresters may still be installed on utility power systems. Some utilities understand the benefits of gapless MOV arresters versus old style gapped SiC arresters and have initiated replacement programs. Others have little or no information on these 30-50 year old surge arresters. To address this concern, the NEMA 8LA Surge Arrester Section has developed a web site http:// www.nemaarresters.com/, targeted to provide information on gapped SiC arresters, including an identification guide and detailed discussions of arrester replacement considerations.

www.hubbellpowersystems.com

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