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9400016-J0 Rev E
CXPS-E3
User Guide
4.11 600A LVD override
4.11.1 Introduction
Contactors are mechanical switches, which connect and disconnect high current power sources and electrical
load, for example between rectifiers and batteries or loads in a power system. The CXPS-E3 600A takes
advantage of the higher efficiency and smaller form factor of a latching contactor, along with heavier bus work,
to enable a much higher current rating than the original CXPS-E3 in the same physical volume. For example,
when combined with the 3.0kW rectifier it has a rating of 625A compared to 450A for the CXPS-E3 with 2.4kW
rectifiers. To safely and reliably control the latching contactor, the CXPS-E3 600A has a different LVD interface
board than the original CXPS-E3. While the original CXPS-E3 had an LVD Override Board, which enabled
service to force the LVD on even if the controller was removed, the CXPS-E3 600A has an LVD Control Interface
(LCI) which buffers the L-ADIO control signals for the higher coil current and enables manual operation.
Traditionally the Telecom industry has used non-latching contactors which have a simple operation: when
power is provided to the contactor it closes and maintains closure (connecting two points electrically); if power
is removed the contactor automatically opens. The advantage of these contactors is that if power is lost to the
contactor they simply open, so called fail-safe operation, but the disadvantages are continuous heat losses in
driving the coil closed and higher losses in the electrical contacts.
A latching contactor has a strong permanent magnet capable of holding the contacts closed and only a short
pulse of current is needed to close it initially. Because coil operation is only temporary a much higher current
can be allowed without concern of overheating, and this allows the closing force to be higher. The result is
lower electrical losses in both the actuating coil and the load connections, overall providing a more compact and
efficient design. The added complexity makes these contactors a little more expensive, but the more significant
difference is that if power fails they do not automatically open. Depending on the application this might be viewed
as an advantage or disadvantage; the inherent fail-safe operation is lost, but it is also less likely to unexpectedly
drop a load by opening due to controller failure.
4.11.2 Normal operation
Standard function
In an CXPS-E3 600A system, the latching contactor is used as a low voltage battery disconnect (LVBD) between
a bulk feed input and the main bus where the load breakers connect. During normal operation the LVBD is
closed, the battery bank is connected to the main bus, and the batteries are charging. The user will have to set
a minimum voltage threshold, below which the batteries might be damaged if discharged. The user will also
have to set a reconnection voltage above which the batteries should reconnect to the main bus. As per standard
practice the reconnect voltage is above the battery open circuit voltage so it will not reconnect until AC power
returns. From this state the Cordex HP will use two control relays on the L-ADIO to control the contactor state as
described.
Upon AC power failure, the batteries discharge to support the critical load. If the main voltage falls below the
threshold where the batteries may be permanently damaged, the Cordex HP controller opens the latching LVBD
by energizing a relay on the L-ADIO, which is connected to the Latching Interface board. When the LVBD opens
the batteries disconnect, and within a few seconds the Cordex HP controller loses power and turns off and the
control relay on the L-ADIO is disabled.
Upon return of AC power if the batteries are disconnected, the rectifiers turn on and provide power to the load.
Once the main bus voltage exceeds the reconnect threshold, the Cordex HP controller closes the LVBD by
energizing a relay on the L-ADIO (different than the one that is used to open the contactor). This connects the
batteries to the main bus and returns the system to a normal operating state.
Fault recovery and alarms
The Cordex HP controller monitors the state of the LVBD through a digital input on the L-ADIO board. If the
controller detects that the LVBD state is not as expected (closed when expected to be open or open when
expected to be closed), it attempts to correct this by energizing the appropriate control relays. For example, if a
service person opens the contactor using the manual controls (refer to “Service Operation”) then the controller
