GE Industrial Solutions ZBTE Series - Manual (Page 16)

91 R -1000 Page 14 Zenith ZTE/ZBTE Series Operation & Maintenance Manual
Sequence of Operation
Automatic transfer switches transition from one source
to a second source in three different ways: standard
(also referred to as open), delayed and closed transition.
Delayed transition switches have an intermediary mid-
point location where the switch is not connected to either
source when transferring to the non-preferred source
after a preferred source failure. For closed transition, both
sources are connected momentarily. Timers are utilized
to insure that sources are stable before transferring or
to prevent a hurried, ultimately unnecessary transfer
when the apparently failed source was actually not in
a state of failure.
When transferring with two good sources (either a
retransfer back to Source 1 or a system test transfer),
closed transition switches are momentarily connected
to both sources for a period of less than 100 ms. The
controller prevents transfer until Source 2 is in electrical
synchronism with the utility.
Sequence of Operation for
Bypass/Isolation Transfer Switch
An automatic transfer switch equipped with a bypass/
isolation switch provides the ability to withdraw the
automatic transfer switch for testing and/or maintenance
purposes without interrupting the served load. The bypass
manual switch is the upper power panel while the
automatic switch is housed in the lower panel (see
Mimic Bus and Indicator Lights Schematic in Figure 15).
Operation of the unit is quick and convenient, requiring
only one operator and less than one minute to complete.
Instructions are mounted on the front of each isolation
switch door along with a mimic panel providing indication
of power source availability and bypass/ATS switch
positions.
The manual bypass switch is normally open on both
sources with the ATS feeding the system load. During
operation, the bypass switch is closed, paralleling the
ATS contacts which then allows withdrawal of the ATS to
the TEST or ISOLATE position. Mechanical and electrical
interlocks are included to prevent cross-sourcing or
bypassing to a dead source.
In the TEST position, the ATS is disconnected from the
load (which is instead powered through the bypass
panel). However, control power is available to the ATS
to permit operational testing through the control panel
of the transfer switch while removed from Source 1
and Source 2.
In the ISOLATE position, the ATS is completely withdrawn
and may be removed from the enclosure, if desired, for
maintenance.
After the isolation operation, if the bypass is closed into
Source 1 and this source happens to fail, an auxiliary
contact on the bypass control will automatically start
the alternate generator source (Source 2). The manual
handle of the bypass may then be operated to transfer
the load to Source 2. Interlocks guard against inadvertent
manual connection to an opposite source if the ATS is in
the circuit. Also, the reconnection of the ATS is prevented
via interlocks if the source positions don’t match.
Comparative sequences of operation for bypass/isolation
transfer switch as a function of rated amperage are
shown in Figure 16.
Figure 15
Bypass/Isolation
Transfer Switch
Mimic Bus and
Indicator Lights
Schematic
WARNING
While the bypass switch is out of the AUTO position/mode, the
ATS is INHIBITED from automatic operation. Make certain the
ATS is left in automatic after completion of any service.
!