Three-Source Systems; Three Source Engine Start Mode; Preferred Source Toggle; Three Source System Test And Exercise - Kohler MPAC 1500 Manual

5.15 Three-Source Systems

A three-source system provides the means to connect a
utility and two generators to a single load.
Figure 5-27. Two generators and two transfer switches
are required.
Note: The second transfer switch (ATS2) requires an
external battery supply module (EBSM) to
provide power to the controller.
During normal operation, the utility source supplies the
load with power. In the event of a utility failure, generator
set G1 or G2 will supply the load as described in
Sections 5.15.1 and 5.15.2.

5.15.1 Three Source Engine Start Mode

There are two modes of operation for three-source
engine start. Select Mode 1 or Mode 2 on ATS2 as
needed for the application.
Mode 1
In mode 1 there will be an attempt to start only the
preferred source generator. If the preferred source does
not achieve voltage and frequency within a fail to acquire
time period, the standby engine start contact will close.
The fail to acquire will be indicated. If the standby
source subsequently fails to achieve voltage and
frequency, a separate fail to acquire standby will be
indicated.
Mode 2
In mode 2 both generators receive a start signal
simultaneously. The ATS2 will transfer to the first
generator set to reach proper voltage and frequency. If
the first source to reach available status is the preferred
source, the engine start signal to the standby source will
open immediately. If the standby source is the first to
reach available status, the contactor will transfer to the
standby position. When the preferred source generator
output reaches available status, the controller will
transfer to the preferred source and open the engine
start contacts to the standby generator (after the
cooldown delay has elapsed).

5.15.2 Preferred Source Toggle

The preferred source toggle function alternates
between the two generator sets each time the
three-source function is activated. If G1 is the preferred
source during the first run, then G2 will be preferred
during the next run. The preferred source selection will
continue to alternate between G1 and G2 for each
subsequent run.
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5.15.3 Three Source System Test and
Exercise
See
Unloaded Test
Unloaded testing is possible at each transfer switch.
Initiating the unloaded test function at ATS1 starts and
runs the preferred generator set attached to ATS2.
Initiating the unloaded test function at ATS2 starts and
runs the standby generator set.
Loaded Test
Loaded testing is also allowed at each transfer switch.
Loaded testing of the standby generator set is only
possible during a loaded test from ATS1 because the
standby generator can only be connected to the load
when ATS1 is connected to emergency. To initiate a
loaded test of the standby generator set, first use ATS1
to start a loaded test of the preferred source generator
set. Then use ATS2 to start a loaded test of the standby
generator set.
Unloaded Exercise
The exercise program in ATS2 controls the operation of
each generator. The exercise function does not require
interaction with ATS1. If the utility is lost during an
unloaded exercise event, the event is canceled and the
load is transferred to the preferred generator set.
Loaded Exercise
The exercise program in ATS2 controls the operation of
each generator. The loaded exercise event requires
synchronization with a loaded exercise from ATS1.
Program the ATS1 exercise to start before the ATS2
exercise. Set the ATS2 exercise to end before the ATS1
exercise ends. If the utility is lost during a loaded
exercise event, the event is canceled and the load is
transferred to the preferred generator set.

5.15.4 Three-Source System Setup

See Figure 5-27 and Figure 5-28 for connections during
the following steps.
1. Connect the power sources to the transfer
switches as described below. Refer to the transfer
switch operation/installation manual or specification
sheet for cable sizes.
connections.
a. Connect the utility power source to the normal
side of ATS1.
b. Connect the load to the load side of ATS1.
See Figure 5-27 for
Section 5 Setup 87