ELECTRO-HYDRAULIC GOVERNING SYSTEM
(CLASS I, PRECISE SETS ONLY)
a. The electro-hydraulic governing system is a
speed (frequency) sensing
stem used to maintain
prime mover speed constant and therefore generator
output frequency, during periods of unchanging
load and when load additions or deletions occur.
b . The system consists of a control unit, load
measuring unit and hydraulic throttle actuating unit.
c. The control unit inputs are the generator output
voltage, and a dc voltage (0-9. 8 Vdc) proportional to
the generator load, supplied by the load measuring
The generator voltage input is applied to a
frequency sensing network and reference voltage
network, The differ ential output of these two net-
works determines the control current of two mag-
netic amplifiers whose outputs drive separate coils
of the hydraulic actuators pilot valve. The actuator
pilot valve positions the actuator power piston which
is connected to the input arm of the fuel injection
pump. The actuators hydraulic system is comprised
of a reservoir, engine driven pump (300-320 psi, 2
gpm), cooler and filter.
d. Any deviation of engine speed, reflected as a
change in frequency at the input of the governor, pro-
duces a change in the magnitude and direction of mag-
netic amplifier control field current. This change in
ccntrol field current will increase the strength of one
coil of the pilot valve while decreasing the strength of
The resultant difference repositions the
pilot valve in turn repositioning the power piston which
changes the output of the fuel injection pump, chang-
ing engine speed and consequently restoring generator
frequency to its nominal value.
The load measuring units (LMU) input to the
governor control provides for automatic load sharing
when two or more sets are operated in parallel.
Each set is equipped with an LMU.
f. If the load added to the system is not equally
divided, the LMU inputs to their respective govern-
ors will differ. The resulting difference acting
through additional windings of each sets governor
(which are all connected in parallel) will reposition
each sets actuator power piston such that fuel flow
in the more heavily loaded set is decreased while
that of the lightly loaded set is increased. Since the
power input of each prime mover has been readjusted,
equal division of true power (Kw) occurs with no
deviation in frequency of any set.
The following procedures are to be performed in the
generator set unless otherwise specified.
a. If the FL - NL or NL - FL transient exceeds
1-1/2 percent of rated speed and/or does not re -
establish stable engine operating conditions within
one second, realign the control unit in accordance
with paragraph 7-8 .
Also follow this procedure
if the engine speed hunts. If the set cannot be
stabilized, check sockets A and B of plug P-21
(refer to Operator and Organizational Maintenance
Manual) for 24 Vdc (A is positive).
b. If the engine speed increases to above nominal
operating speed, check sockets A and B of P-17 for
120 Vat. If it is missing, troubleshoot the generator
set wiring. (Refer to Operator and Organizational
Maintenance Manual). If it is present, check the
resistance of the frequency adjusting circuit con-
sisting of R4 (250 ohms) rheostat R1 frequency adjust
(500 ohms) and R5 (250 ohms) fixed resistor.
Refer to Operator and Organizational Maintenance
Measure the total circuit resistance
across N and T of harness plug P17. The circuit
resistance should be 1000 ohms (5 percent tolerance).
After testing for correct total resistance, test the
operation of the frequency adjust rheostat by
connecting an ohmmeter across pins M and T and re-
volving the frequency adjust rheostat through
its entire travel. The resistance should vary from
750 ohms to 250 ohms. Repeat this procedure
using the ohmmeter across pins M and N of the
If the problem persists, check sockets
A and B of plug P-21 for 24 Vdc (A is positive).
If the engine speed remains below the nominal
operating speed, adjust R1. If there is no improve-
ment, check the resistance of the frequency adjust
circuit. Disconnect P-17 and check the resistance
of the frequency adjust circuit consisting
of R4 (250 ohms) fixed resistor, R1
frequency adjust rheostat (500 ohms) and R5
(250 ohms, 5 percent) fixed resistor. Refer to
Operator and Organizational Maintenance Manual.
Measure the total circuit resistance across N and T
of harness plug P17.
The circuit resistance should
be 1000 ohms (5 percent tolerance). After testing
for correct total resistance, test the operation of the
frequency adjust potentiometer by connecting an
ohmmeter across pins M and T and revolving the
frequency adjust potentiometer through its entire
travel. The resistance should vary from 750 ohms
to 250 ohms.
Repeat this procedure using the
ohmmeter across pins M and N of the harness plug.
Disconnect actuator electrical connector before
making this measurement. Push actuator piston all
the way down and adjust engine speed with manual
throttle. If this value resistance is measured, check
sockets A and B at plug P-21 for 24 Vdc (A is positive).
d. If the set is operating at a constant load and
voltage and during an eight-hour period the change
in ambient temperature does not exceed 60°F, the
set frequency should not drift beyond 1/2 of one
percent of rated frequency. The above requirement
assumes that the set temperatures were stabilized