Surge protection made easy
We invest thousands of dollars in state-of-the-art electronic
equipment and insure it against theft and damage. But when it comes to
protection against damage caused by overvoltage surges we’re sometimes
unaware of what is available.
The causes of surges are many and varied. By far the most common
cause is through switching operations in the network. Surge damage
caused by lightning strikes also occurs frequently.
Computers are one of the most relied on tools of the trade and the
information stored in them can be irreplaceable if lost. Fax machines,
photocopiers and valuable printing equipment all need protection from
the hazards of lightning strikes. Overvoltage peaks lasting only some
millionths of a second, can cause the failure of a semiconductor module
and destroy the whole system.
Protection is gained by connecting all possible conductive paths to
earth at the instant the overvoltage appears within the installation and
thereby breaking up the otherwise harmful surge.
It can be difficult to know which parameters are important when
selecting surge protection equipment. The following information has been
prepared to help you.
The Safe Protection Concept
Test Wave Forms
Test wave forms are used to emulate real life transients from which
surge protection devices are designed. Below in yellow shows the
transient a spark gap product must endure during a direct lightning
strike. Below in green shows the transient a varistor must endure during
a switching transient or an indirect lightning strike.
Power Range Arresters
As a first protective measure, a barrier is necessary to keep the
lightning current out of the system.
Spark Gaps respond to the lightning current impulse of 10/350µS at
the required level and break it to a current impulse of 8/20µS tolerable
for subsequent Surge Protection Devices.
When using Spark Gaps in the power supply system, the mains follow on
current must be safely extinguished after discharging a current impulse.
As a second protective measure,
the remaining current impulse (approx. 8/20µS) is discharged and limited
to a voltage level compatible with the system.
A varistor (non-linear resistor) is ideal for this task. Modern metal
oxide varistors are distinguished by their fast response time and low
residual voltage (voltage protection level).
What does 20kA (8/20µS) mean?
20kA is the impulse current.
8/20µS. The first value (8) is the rise time (from 10% to 90% of peak).
The second value (20) is the duration for the test transient to decrease
to half its peak value.
Surge Protection Devices
Electrical equipment will be vulnerable if exposed to voltages
greater than 1.5kV, particularly with sensitive electronic equipment at
voltages greater than 800V.
Clipsal Surge Protection Devices work to reduce overvoltages to
figures less than 800V.
To do this most effectively, there are three methods of combating
the likelihood of this danger to equipment occurring.
Method of Protection
Method 1 (Lightning Current)
Spark Gap Arresters are heavy-duty devices that work on a similar
principle to a car spark plug. (i.e., when energy is large enough it
jumps the gap to earth.)
These devices can handle high currents similar to direct lightning
strikes, however leave a relative high residual voltage less than 4kV.
(Not suitable for equipment protection, but reduces energy to a
manageable level.)
Method 2 (Overvoltage)
The most common and inexpensive first line of defence against a power
surge is a Metal Oxide Varistor (MOV).
Clipsal Overvoltage Arresters have a discharge capacity of 20kA
(8/20µS).
The component that protects electrical equipment from overvoltages will
withstand this current impulse at least 20 times, non destructively and
without changes to its characteristic.
These devices will give voltage protection less than 1 to 1.5kV
(8/20µS), and are used in locations that are exposed to indirect
lightning strikes and switching transients.
Method 3 (Overvoltage Filtering)
Mains Filters provide additional overvoltage protection to protect
sensitive electronic equipment.
The Clipsal Mains Filters are used in conjunction with overvoltage
protection by providing additional filtering to slow down the rate of
rise of voltage spill and reduce let through voltage to less than 800V.
Power range surge arresters
950/4 High Capacity 4 Pole Arrester
- Combined overvoltage and current arrester (spark gap, inductor
and metal oxide varistor)
- DIN mounted 6.5 modules wide
- Surge current 65kA (4/10) 4 pole
- Maximum pre-fuse 100A gl
Benefits
- Fast and easy installation
- Provides lightning current and overvoltage protection (lightning
protection)
Limitations
- Visual indication when overloaded and replacement required
- Must replace whole unit (higher material cost)
- Care taken during installation due to blow out path
970 Overvoltage Arrester (Metal Oxide Varistor)
- 275V, 20kA 1 pole DIN 1 module wide
- Maximum pre-fuse 125A gl
- First line of protection against overvoltages
Benefits
- Fast and easy installation
- Provides overvoltage protection
Limitations
- Does not protect from a direct lightning strike
- Visual indication when overloaded and replacement required
- Must disconnect wiring to remove
970RM Overvoltage Arrester (Metal Oxide Varistor)
- 275V, 20kA 1 pole DIN 1 module wide
- Maximum pre-fuse 125A gl
- First line of protection against overvoltages
Benefits
- Fast and easy installation
- Provides overvoltage protection
- Removable modules allow quick replacement without the need to
disconnect wiring
Limitations
- Does not protect against a direct lightning strike
- Visual indication when overloaded and replacement required
|
