Page 227 - IPD Product Catalog V17

Lightning & Surge Protection

LIGHTNING & SURGE PROTECTION

Overview
1 1
Spikes, surges, and transients are common terms for overvoltage events that can reach tens of thousands of volts with rapid durations of
a few microseconds. The combination of a high peak value and a rapid rate of rise of voltage can cause damage and major issues to the
connected equipment.

The Australian Standard on Lightning Protection, AS 1768, provides a risk analysis against the threat of lightning, along with information of
ways these over voltages can enter a building.
There are many causes of transient over voltages, natural phenomenon such as lightning is the most destructive and popularly named cause,
however transient over voltages can also be generated by utility grid switching, local circuit breaker switching, motor starting and stopping,
other load switching etc. Research has shown up to 70-85% of transient over voltages can be generated within an installation, meaning only
15-30% coming from external sources.

Test waveforms and SPD type specifications

AS 1768 refers to IEC standards and these define some current waveforms for the classification of surge protection devices
(SPDs) according to discharge capacity. Comparing the 8/20 and 10/350 waveforms with the same peak value as shown in the
diagrams, the energy of the 10/350 wave is much higher. (The numbers define the waveshape according to time to rise to 90%
of peak value/time to decay to 50% of peak value, i.e. 10/350 equals 10μs rise to 90% peaks and 350 μs decay to 50% of
the peak).
SPDs are classified in terms of ‘Types’ and ‘Test Classes’ in the IEC standard.

Type 1 SPD’s are tested with an 10/350 waveform (Class I test) known as the maximum impulse value I , which provides a
imp
simulation of a direct or nearby lightning strike.
Type 2 SPDs are tested for a nominal discharge current I with an 8/20 waveform, which requires 15 test cycles at the I rating.
n n
This provides a simulation of a distant lightning strike, utility grid switching, load switching etc.
Previously, Type 2 SPDs were tested for a maximum discharge current I with an 8/20 waveform (Class II test), however this
max
test criteria has been removed from the latest edition of IEC 61643.
Type 2 I values are now considered an optional parameter and is shown in product data for clarity.
max
Type 1+2 SPDs are tested with both a 10/350 waveform (Class 1) and with an 8/20 (Class II) waveform.

Additional test waveforms are also available for Type 3 SPDs.

10/350 μs 8/20 μs

1300 556 601 | ipd.com.au | V17-R05 227