Kohler Generator Sets 20--2800 kW - Manual (Page 47)

TP-5700 7/93 35 Section 7 Electrical Requirements
Section 7 Electrical Requirements
Before installing the generator set, provide for electrical
connections through conduit to the transfer switch and
other accessories for the generator set. Carefully install
the selected generator set accessories. Route wiring to
the generator set through flexible connections. Comply
with all applicable codes when installing a wiring
system.
AC circuit protection. All AC circuits must include
circuit breaker or fuse protection.
Select a circuit
breaker for up to 125% of the rated generator set output
current. The circuit breaker must open all ungrounded
connectors.
The circuit breaker or fuse must be
mounted within 7.6 m (25 feet) of the alternator output
terminals.
7.1 Batteries
Batteries should be located in a clean, dry area. Position
them so that the caps are readily accessible for checking
the electrolyte level. Keep batteries out of areas subject
to high temperatures. Locate them close to the set to
keep cables short and thus insure maximum output.
Several types of battery racks are used throughout the
product line—be sure to refer to the submittal drawings
for your unit. Figure 7-1 shows a typical battery system.
Starting batteries are usually lead-acid type sized
according
to the engine manufacturer’s
recommendation for a particular ambient temperature
and required cranking time. Recommended cranking
periods are specified in NFPA 110. It allows a single
45-second cranking cycle for generator sets below
20 kW. For larger models, three 15-second crank cycles
separated by 15-second rests are required. The battery
industry rating standard most commonly used to specify
batteries is the cold-cranking ampere rating. Refer to the
unit’s specification sheet for battery cold-cranking
ampere rating.
Nickel cadmium batteries are sometimes used for
standby generator sets because of their long life
(20 years). This is offset by their high initial cost, larger
space
requirements, and special charging
requirements. Conventional lead-acid batteries have
proven satisfactory for the majority of generator set
applications.
Batteries are charged by engine-driven, battery
charging alternators whenever the generator set
operates. These systems are normally capable of
charge rates of 30 amperes or more and can restore the
charge used in a normal cranking cycle within a short
period of operation. When the engine is not operating, a
very low charge rate from an AC-powered battery
charger is sufficient to maintain the batteries fully
charged. These chargers may be automatic or manual
with a high charge rate of 2 amperes and a trickle charge
rate up to 300 milliamperes. They can be separate,
self-contained units or built into the automatic transfer
switch. Due to the low maximum charge rate, they are
not well suited to restoring fully discharged batteries.
Automatic float chargers with high charge rates of
10 amperes or more are available if full recovery
capability independent of the engine-driven charging
system is required.
The most common reason for the failure of an
emergency generator set to start when needed is
starting battery failure. Two common causes of battery
failure are: a manual charge rate set too low to maintain
the battery, or a manual chase rate set too high, which
results in loss of battery electrolyte. For this reason,
automatic float chargers, which vary the charge rate in
response
to battery condition, are strongly
recommended over manual types.
For large engines using two starters, either one bank of
batteries and chargers for both starters, or separate
battery systems may be used. The latter system is
preferable since it reduces the chance of one
component’s
failure making the entire system
inoperative.
Battery cables. A UL-2200 listed generator set
requires battery cables with positive (+) lead boots.
Factory-supplied and optional battery cables include
positive (+) lead boots. When battery cables are not
factory-supplied, source battery cables with positive (+)
lead boots for UL-2200 compliance.
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2
4
3
TP-5700-7
1. Battery cables
2. Battery secured in mounting rack
3. End view
4. Generator set skid
Figure 7-1 Typical Battery System, Side View