Surge Suppression Takes the Bite out of Transients

Posted by admin | Posted in Power Quality Products | Posted on 22-07-2009

(Excerpts taken from the Plant Engineering article “Surge Suppression Takes the Bite out of Transients” written by Carey Mossop, Eaton Electrical’s product line manager for TVSS. Download the full article PDF from top right column above)

Voltage transients are just one of those things you may not give a lot of thought to until they’ve done their worst. Taking preventive measures will put transients in their place and allow you to rest easier. An effective program can even have a positive impact on the bottom line. In fact, one particular deployment of transient voltage surge suppressors brought 80% annual savings in equipment repair costs while helping maintain smooth operations.

Outside threats and those from within
A voltage transient is a high-rising, short-lived voltage on one or more phases of a system. Transients can reach 20,000 V or more. While they last but two milliseconds or less, the damage they can cause can be considerable and long term.

Transients are generally thought of as being threats from outside the facility. While many do arise from outside sources (most particularly lightning, but also distribution system short circuits, load switching and capacitor switching), in truth, 80% originate within the facility.

Internal transients can be caused by virtually any load turning on or off; by the starting and stopping of motors; by photocopiers, arc welders, florescent lighting and even light dimmers.

Transients are a bigger threat today than ever before. The potential danger of transients occurring lies not only in ac power systems but with all conductors. A communications network, for example, must also be protected. Today’s power systems are increasingly challenged by the ubiquity of electronics and microprocessor-based equipment. Microprocessors are getting ever smaller, faster and more sensitive and they require clean power. Non-electronic loads may operate without disturbance in an environment with low to medium transients; devices such as electric motors, incandescent lighting and resistive heating loads typically take longer to be damaged by medium and low-level voltage transients.

But electronics – particularly microprocessors – operate at much lower voltage levels and are therefore far more susceptible to transient damage. Microprocessor-based loads often share circuits with transient-generating equipment such as switching power supplies, lighting panels and non-linear demand loads.

Identifying a transient problem
Since transient voltages occur very quickly – typically lasting 50 nanoseconds to 2 milliseconds – they can’t be captured by most conventional meters found on electrical distribution equipment or most standard voltage and current meters. High-speed power-quality meters and oscilloscopes are able to capture transient activity, but these devices can cost tens of thousands of dollars each and are therefore often economically impractical.

But it doesn’t necessarily take tens of thousands of dollars to find a transient problem. There are often tell-tale signs that voltage transients are negatively affecting the electrical system and equipment. They include:

– Equipment damage
– Insulation breakdown on electrical conductors
– Premature aging of electrical and electronic equipment
– Process interruption
– Data loss and data transfer-rate reduction.

Transients also can affect logic signals in electronic equipment, in that noise can be interpreted as legitimate signals, resulting in operating errors and downtime.

Unfortunately, many users chalk these damages up to ‘unavoidable business costs’ or to ‘normal maintenance expenses.’ In fact, these damaging effects can be easily and cost-effectively downgraded to manageable transient voltage surge events, saving time and money and avoiding data loss.

Transient voltage surge suppressors are the answer. The bottom-line objective of a TVSS is to prevent damage, disruption and degradation to electrical and electronic equipment. TVSSs serve as pressure relief valves, shunting a harmful surge current to ground under a surge condition. Most surge suppressors use metal oxide varistors, which are primarily composed of zinc oxide grains, as the common building block for surge diversion.

Under normal operating voltages, a TVSS is virtually invisible to the electrical system. It may draw a few mA of current to power-monitoring circuits, but otherwise doesn’t affect the electrical distribution system. When a high voltage level on the electrical system appears due to a voltage transient, the suppressor kicks into action and changes state to a very low impedance. When in this overvoltage state, the TVSS bears the brunt of the harmful transient, shunting tens of thousands of Amperes to ground.

A high-quality, modern surge suppressor can take multiple surge events over its lifetime. Many surge suppressors have been tested in high-power laboratories in accelerated lifetime testing and have been shown to survive thousands of transients of 20 kV, 10 kA. When properly applied and sized, a TVSS should have a useful life of more than 30 years. TVSSs are available in a variety of voltages and sizes, measured in kA of surge current.

Turn to a proven manufacturer
A comprehensive transient voltage protection solution reduces equipment damage, decreases maintenance costs and improves system uptime and in so doing realizes savings in operational costs. TVSSs can be installed for total facility protection – from powerful motors to sophisticated lighting controls and sensitive computer-based controllers.

Protection begins at the incoming power panels and extends to system distribution centers, panel breakers, points of use and even to individual equipment. These solutions take into account the fact that every TVSS application must respond to a number of particulars – including the sensitivity of the equipment, the criticality of the process being protected and the location of conductors and electrical distribution equipment. TVSS solutions are available in varying kA ratings, filtering options and more, meeting the requirements of each specific application.

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