Onan MEP-003A - Page 60

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CHAPTER 6
MAINTENANCE OF CONTROL SYSTEM
Section I. DESCRIPTION AND FUNCTION
6-1 . DC CONTROL SYSTEM . 6-3 . VOLTAGE REGULATOR .
Refer to the Operator and Organizational
Maintenance Manual for the description and function
of the dc
control system
.
Excitation
current
is
controlled
through
the
static
type
automatic
voltage
regulator
. The
voltage
regu
lator
continuously
compares the
output
voltage
of
the
synchronous
generator
with
a stable
reference
volt
age
. The
difference
between
the
two
voltages con
stitutes
an
error
signal
which
indicates
an
output
voltage
that
is
higher
or
lower
than
the
generator
set
point
. This
error
signal
is
amplified
and
used
to
control
the
direct
current
output
of
the
voltage
regu
lator
which
is
applied
to
the
control
windings
of
the
current
- voltage
transformers
.
6-2
. AC
INSTRUMENTATION
SYSTEM
.
Refer to the Operator and Organizational
Maintenance Manual for description and function of
the ac
instrumentation
system
.
Section II . MAINTENANCE
6-4
.
CONTROL
CUBICLE
.
a . Wiring Harness .
( 3 )
Percent
Current
Meter
( M4
) ( 17 , figure
6-3
) .
Connect
an
ac
test
ammeter
in series
with
the
% rated
current
meter
. Operate
Generator
Set
with
a single
phase
load
. Continue
adding
load
to
set
until
meter
reads
0.75
amps
. Meter
( M4
) should
read
100
% + 2 % .
Replace
meter
if
necessary
.
( 1 ) Remove . Disconnect wires of wiring harness
from all components . Remove clamp attaching harness
to control panel and remove harness .
( 2 ) Repair . Table 6-1 lists the wire number ,
gauge , color , length and terminal lugs for each wire
in the harness . Repair consists of replacing wires as
required .
( 4 ) AC Voltmeter ( M5 ) ( 18 , figure 6-3 ) . Attach
test ac voltmeter in parallel ( across terminals ) with
panel ac voltmeter ( M5 ). Operate Generator Set and
compare readings of the two meters . Panel voltmeter
must be accurate to $ 2.5 % , except between 115 and
125 volts , accuracy must be £ 3 volts and between
200 and 250 volts , accuracy must be + 5 volts . If panel
meter does not meet these requirements , replace
meter
.
( 3) Installation . Install harness by connecting
wires to components per figure 6-1 . Attach harness to
control panel
with
clamp
.
c
.
Meters
(
remove
).
b .
Meters
( on
equipment test
).
( 1 ) Frequency Meter ( M3 ) ( 16 , figure 6-3 ) . Tag
and disconnect two leads from meter . Remove three
screws , lockwashers , and nuts attaching meter to
panel and remove meter .
( 1 ) Frequency
Meter
( M3 ) ( 16 , figure
6-3
) . Con
nect
a frequency
meter
of known
accuracy
to single
phase
output
terminals
of load
terminal
board
. Make
certain
reconnection
switch
is in proper
position
for
single
phase
output
. Operate
Generator
Set
and
check
readings
of panel
meter
( M3
) against
test
frequency
meter
. If panel
meter
does
not
give
the
same
reading
as the
test
meter
, test
transducer
as given
in ( 2 ) below
.
( 2 ) Frequency Transducer ( A3 ) ( 56 , figure 6-3 ) .
Test transducer using the same procedure as for
testing frequency meter . If transducer does not give
oper meter reading , replace the transducer and / or
the meter .
( 2 ) Frequency Transducer ( A3 ) ( 56 , figure 6-3 ) .
Tag and disconnect four leads to frequency transducer .
Remove four screws ( 54 ) and nuts ( 55 ) attaching
transducer to back of control cubicle and remove
transducer .
( 3 ) Percent Current Meter ( M4 ) ( 17 , figure 6-3 ) .
Tag and disconnect two leads from meter . Remove
three screws , lockwashers , and nuts attaching meter
to control panel and remove meter .
Change
4
6-1