Generac Power Systems 53187 - Manual (Page 26)

SECTION 1.5
INTRODUCTION TO TROUBLESHOOTING
Rotor Rotational Speed
L
"NP" series generators are equipped w ith a 4-pole
Rotor. That is, the Rotor has tw o south m agnetic poles
and tw o north m agnetic poles. A 4-pole Rotor m ust be
operated at 1800 rpm to obtain a 60 Hertz AC output
frequency. The follow ing form ulas apply w hen calculat­
ing frequency, rpm and num ber of Rotor poles:
Hertz = RPM X No. of Rotor Poles
2 x 6 0
RPM = 2 X 60 X Hertz
No. of =
Poles
No. of Rotor Poles
2 X 60 X Hertz
RPM
Voltage and Frequency
The generator's solid state Voltage Regulator w ill
m aintain an AC output voltage that is at a fixed ratio to
frequency. For exam ple, at a frequency of 60 Hertz, AC
output voltage w ill be m aintained at about 120/240 volts
(plus or m inus 2%). Should frequency drop to 30 Hertz,
voltage w ill decrease proportionally to about 60/120
volts.
For generators rated 120/240 volts, the engine gover­
nor should be set to m aintain a NO-LOAD frequency of
about 60.5-63.5 Hertz. The Voltage Regulator should
then be set to m aintain a voltage of about 121-127 volts
(line-to-neutral); or 242-254 volts (line-to-line).
Stator AC Connection Systems
1-PHASE, DUAL W INDING TYPE:
Som e NP/IM series generators have dual AC
pow er w indings (Figure 3). Each w inding supplies a
120 volts AC output. W hen the tw o w indings are con­
nected in series (Figure 4), a 240 volts AC output
results.
W hen installed, the unit m ay have ben connected to
supply a dual voltage output (120 and/or 240 volts). This
is show n In Figure 4. A 3-w ire connection system Is
used. Stator leads No. 11 and 44 form the tw o "hot"
leads; the Junction of stator leads 22 and 33 form the
"Neutral" lead. Notice the "Neutral" line is grounded.
A second alternative Is to connect the w iring to supply
120 volts AC only (Figure 5). W hen this connectior
m ethod Is used, a jum per w ire m ust be connected
betw een the tw o m ain circuit breakers (CB1 and CB2),
as show n.
PART 1
THE REVOLVING FIELD AC GENERATOR
Figure 3. The Dual Stator AC Pow er W indings
nnrowi fWtrCPi
,, 22 33 44
)CB. ‘f CBzS
/
T2
(WHnE)
-120 V.----------------^ ■ 120V.-
T1
(RED)
■ 24-3V.
T3
(BLACK)
Figure 4. Connected for Dual Voltage AC Output
11
22 33 1------------------------------------
L 1
44 ------
K —
1
T
T3
T2
r
1
(BLACK)
(WHITE)
T1
(RED)
I«----------------- 120 V.---------------- P
^----------------- -------------120V.--------------------------------- -------»
Figure 5. Connected for 120 Volts AC Output
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