AC Cables
Copyright © 2011 Eaton Corporation. All Rights Reserved.
IPN 997-00012-82B May 2011
35
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 (8/20μs 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
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.
Secondary transient protection for 3P+N+PE system:
Phase-to-neutral metal oxide varistors (MOVs) with a voltage rating to suit the supply
voltage, capable of withstanding temporary over-voltages
A neutral-to-earth spark gap (gas discharge tube)
Surge decoupling coils
Secondary transient protection for 3P+PE system:
Phase-to-neutral metal oxide varistors (MOVs) with a voltage rating to suit the supply
voltage, capable of withstanding temporary over-voltages
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.
