Surge Protection

A surge is a transient electrical fluctuation that happens in a fraction of a second and can cause serious damage to electronic and electro mechanical equipment.

Surges can be caused by lightning strikes and local power utility company ‘spikes’ which can enter your business or home through the electrical system, for example cable television or telephone wiring, and attack any electrical equipment attached to them.

TOPOLOGIES

Many people believe the most important issue is power loss or blackouts, yet the truth is that the majority of power faults are caused by power surges or noise transients.

Power surges and noise transients are caused by:
  • Lightning strikes
  • Substation switching
  • ariable speed drives
  • Electric motors

    • These can be destructive to electronic equipment. There are two ways to provide protection:

    Surge diversion

    Surge diverters are single-stage, shunt connected devices which are generally used for point-of-entry (main switchboard) protection. They provide coarse protection that is suitable for the protection of non sensitive equipment.

    Surge power filters

    Since surge filters are connected in series, they must be suitably rated to carry the amount of electrical current that your equipment is using.NPS provide a range of surge filters with load ratings from as low as 3 Amp (typically used to protect a computer or a PLC) all the way up to 2000 Amp (typically used to protect an entire installation.

    The cost and size of surge filters changes depending upon the load current rating. To achieve effective and economical power line surge protection, NPS recommend a staged approach with a surge diverter installed at the main switchboard to provide coarse protection for all equipment and surge filters installed downstream to protect critical equipment.

    By only protecting critical equipment with surge filters the overall size and cost of the protection is minimised. Equipment is considered to be critical if it is sensitive to surge (ie it contains a microprocessor or other sensitive solid-state electronics) and the cost of downtime of the equipment is unacceptably high or the equipment is relatively expensive to replace.

    SURGE PROTECTION AND UPS

    A UPS is designed to handle the ‘tail end’ of a major surge in the surge protection circuitry in the UPS, not the whole surge itself.

    If additional protection is not fitted, the surge protection components inside the UPS are unlikely to last very long. All surge filters are designed to last for at least 5–10 years and depending on the location will last longer. However if a large direct lightning strike or sustained over-voltage condition will destroy any small filter, but the filter is designed to ‘self sacrifice’ in order to protect the equipment it is connected to.

    The main purpose of a UPS is to provide backup power in the event of mains failure. Most UPS also provide some means to adjust the mains voltage in order to keep it within reasonable limits. (AVR or Line interactive) When the UPS can no longer keep the voltage with tolerance, it switches to battery.

    So, unless the UPS is running from batteries, the equipment powered from it is simply connected to the mains supply and any noise or surges will flow through the UPS to the equipment. In the case of an On-Line UPS, the load is not connected to the incoming power therefore the equipment should be protected.

    The input to the UPS itself is not protected, therefore the UPS itself needs surge protection. Generally most UPS include some form of protection to protect the UPS itself from surges. As stated above, a UPS is designed to take the ‘tail end’ of a surge, therefore the surge components are designed with a limited life span.

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