Kohler RSB Series - Source Sensing; Sequence of Operation

TP-6487 8/0714 Section 2 Operation
2.3 Source Sensing
The transfer switch controller monitors the utility power
source voltage and initiates the transfer sequence if the
source voltage falls below the voltage dropout setting.
Retransfer is initiated when the utility source rises above
the voltage pickup settings and remains stable for at
least 6 minutes. See Figure 2-3.
Source Sensing
Single-phase voltage sensing, both sources ±5%
Line-line frequency sensing, standby source ±2%
Undervoltage dropout 80%
Undervoltage pickup 85%
Voltage dropout time 0.5 sec
Underfrequency dropout 90%
Underfrequency pickup 96%
Frequency dropout time 1sec.
Figure 2-3 Source Sensing
2.4 Sequence of Operation
Figure 2-4 illustrates the transfer sequence when the
normal source fails and Figure 2-5 illustrates the
sequence when it returns. Time delays before load
transfer prevent nuisance transfers during brief power
interruptions.
Total transfer time depends on the generator set engine
cranking time and other factors. Events such as the
failure of the generator set to start can change the
sequence of operation.
If the standby source fails and the normal source is not
available, the transfer switch controller powers down
until one of the sources returns.
Transfer will not occur if one of the source circuit
breakers opens on a fault.
The time delay option board allows time delay
adjustments. See Section 4.1.
Transfer time delay from normal to
standby source (3 sec.) *
* The time delay option board allows adjustment of these
time delays. See Section 4.1.
Engine start time delay (3 sec) *
Normal power source voltage falls below
80% of nominal
Undervoltage dropout time delay,
0.5 seconds (fixed)
Load shed circuit breakers open
Load control contact opens
Generator set engine crank and start
Command to transfer to the standby source
Figure 2-4 ATS Sequence of Operation, Transfer to
Standby
Retransfer from standby to normal time delay
(5 min.) *
Command to transfer to the normal source
Time delay engine cooldown (5 min.) *
Engine start signal removed
Normal power source voltage rises above
85% of nominal
* The time delay option board allows adjustment of these
time delays. See Section 4.1.
Load control contact closes
Load shed circuit breakers close
Figure 2-5 ATS Sequence of Operation, Retransfer
to Normal