Fact Sheet

GE
Energy
ALTERREX* excitation systems were supplied with large
steam-turbine generators that shipped between 1965 and 1992.
The system consisted of a second AC generator, commonly
referred to as the Alterrex alternator, attached to the main unit
shaft via a rigid coupling. The output of the Alterrex was then
rectified by a set of fixed diode-based rectifier bridges installed
in the Alterrex alternator “doghouse.” The system utilized a
dedicated loop from the unit stator water-cooling system to cool
the individual diode bridges. The bridges consisted of 12 or
24 press-pack diode modules delivering high performance
and reliability in an efficient form factor made possible by the
liquid cooling.
The Problem
Unfortunately, the non-conductive de-ionized water used by the
stator is corrosive. The corrosive nature of the cooling water and
years of continuous high velocity flow are the root-cause of most
of today’s maintenance problems. Specific maintenance issues
associated with the system cooling components include: thin
walling/erosion of the copper pipe used for supply lines and
manifolds; fitting erosion; braze leaks; Teflon (black) tubing
cracks; O-ring hardening; gate valve corrosion; and copper
migration within Teflon
®
(white) tubes. Aging electrical components
are also driving increased maintenance, as diode indicating lights
used for diagnostics fail more often than the diodes, causing
false failure indications and wasted maintenance time.
The Solution
After more than a 30-year average service life and advances in
material technologies, the original diode bridges can be replaced
with a modern power conversion system. GE has custom-
designed a new EX2100 Rectifier Bridge for a one-for-one
replacement of the original rectifier and mounting in the original
cubicle. The new diode bridge is available with a range of on-
and off-site services to ensure the right level of services to meet
plant personnel, budget and outage limitations.
ALTERREX
*
Rectifier Replacement
fact sheet