TP-6126 8/02
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Section 4 Operation
Section 4 Operation
4.1 Introduction
This section contains descriptions and flowcharts for
typical transfer switch operating sequences.
This
section also describes faults and provides other
information related to the controller operation.
On systems not equipped with the preferred source
selector switch, the preferred source is the source
connected to the Normal side of the power switching
device. The source connected to the Emergency side of
the contactor is the standby source.
4.2 Sequence of Operation
4.2.1
Automatic Operation, Open- and
Programmed-Transition Switches
Typical ATS operation in utility-to-generator set mode is
divided into two sequences:
D
Failure of the Normal (preferred) power source
and the resulting load transfer to the Emergency
(standby) source.
D
Restoration of the preferred power source
and the
resulting load transfer back to the preferred source.
Events such as the failure of the generator set to start
can change the sequence of operation.
If the emergency source fails and the normal source is
not available, the transfer switch controller powers down
until one of the sources returns.
Figure 4-1 Illustrates the transfer sequence when the
normal source fails, and Figure 4-2 illustrates the
sequence when it returns.
Figure 4-3 shows the
operation of the user interface LEDs during loss and
restoration of the normal source.
Time Delays.
Time delays before load transfer prevent
nuisance transfers during brief power interruptions. The
voltage and frequency debounce time delays prevent
nuisance transfers caused by brief spikes and dips in the
power supply. See Section 3.5 for the default settings
for the time delays and debounce times.
Loss of Phase.
If the system detects a loss of phase in
the connected source, it attempts to transfer to an
alternate source. The system considers a phase lost if
its phase is 45 degrees from the rotation setting. The
controller logs loss of phase events in the event history.
Programmed-Transition Switches.
Programmed
transition switches provide an OFF position during
transfer between two sources. The adjustable time off
period allows residual voltages in the load circuits to
decay before connecting to the second source. During
the off period, the ATS main contacts are open and
neither source powers the load.
The off-to-standby and off-to-preferred time delays
control
the
length
of
the
off
period
for
programmed-transition switches. The time delays are
factory-set to the defaults shown in Figure 3-13. The
time delays can be changed using the optional Setup
Program.
The End Time Delay Button and Remote Bypass
command do not override the off-to-standby and
off-to-preferred time delays.
Time delay preferred-to-standby
Transfer to OFF position
(programmed-transition only)
Transfer to emergency (standby) source
Time delay off-to-standby
(programmed-transition only)
Post-transfer load control (as programmed*)
* See the Setup Program Operation Manual.
Normal (preferred) power source fails
Time delay engine start
Figure 4-1
ATS Sequence of Operation, Transfer to
Emergency (standby source)
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