AC Cables
Copyright © 2008-2009 Eaton Corporation. All Rights Reserved.
IPN 997-00012-71B July 2009
29
Primary Transient Protection
Primary transient protection must be considered at all sites. Eaton recommends, primary
transient protection on the incoming ac supply either at the main ac switchboard or sub-
switchboard.
In the absence of sufficient information, primary transient protective devices with a
minimum repeat strike rating of 100kA (8/20
μ
s wave shape) are recommended.
In addition, primary transient protection must be coordinated with downstream secondary
transient protection via suitably rated surge decoupling coils. These should have been
specified as part of the transient protection plan for the site. If no surge decoupling coils were
specified, then air-core 15
μ
H surge decoupling coils are suitable.
Secondary Transient Protection
Secondary transient protection (downstream from the primary transient protection) must be
present at all sites to protect the dc power system from transients.
This will protect the power system from a limited number of repeated 15kA transients
(8/20µs wave shape).
Secondary transient protection typically consist of:
•
Phase-to-neutral metal oxide varistors (MOVs) with a voltage rating of 440V, capable of
withstanding temporary over-voltages
•
A neutral-to-earth spark gap (gas discharge tube)
•
Surge decoupling coils
This secondary transient protection must be installed in the ac switchboard that supplies the
dc power system.
Carefully consider the residual voltage seen by the dc power system (maximum 6kV) and the
decoupling between the transient protection system and the dc power system. Transients
must be limited to less than 2kA.
Tertiary Transient Protection
Eaton rectifiers are fitted with low-level transient protection. This is designed to protect the
rectifiers from voltage spikes generated during operation of the upstream transient protection
system. Do not install rectifiers without adequate upstream surge protection.
