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
- Variable 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 devicesw hich 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.
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.
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.