between the hydraulic actuator and the turbine is free
The load pulse signal is initially maximum and
from binding or lost motions. If the linkage is proper,
gradually decreases to zero. Figure 9-11 represents load
check the voltage regulator for proper operation. If
pulse signals in response to load changes. The signal is
these checks do not reveal the cause of the speed
of the proper polarity to set the steam valve in the right
variation, the governor is probably faulty.
direction to compensate for the change. The output
signal is applied to the summing point in the EG-M
In troubleshooting the governor system, first check
control box (fig. 9-7).
the voltage across the input to the hydraulic actuator.
This should be done with the system running on speed
PARALLEL OPERATION WITH OTHER EG
and set for single operation. If the voltage is not correct
GOVERNOR SYSTEMS.-- When the load signal box
(+0.5 volt dc to -0.5 volt dc) and cannot be set within
is used with other EG governor systems, the operation
range by the centering screw in the actuator, or if the
is the same as for single operation (fig. 9-10) except for
voltage fluctuates more than +0.25 volt dc and cannot
a closed circuit breaker (not shown). The closed circuit
be stilled by the GAIN ADJ. or the STAB. ADJ., the
breaker connects the paralleling lines. This enables the
control box may be defective.
load signal box to provide the same signal information
to the control box of all the parallel units.
To bench test the control box, disconnect it from the
PARALLEL OPERATION WITH DIS-
load signal box. Use a three-phase power supply instead
SIMILAR TYPE GOVERNOR SYSTEMS.-- For
of the normal supply. Instead of the speed signal, apply
operation with dissimilar type governor systems,
a frequency oscillator output signal set to the rated speed
the droop switch must be turned on (down position
frequency of the PMG (fig. 9-7). Use a resistive load
in fig. 9-10). This shorts out the paralleling lines so
instead of the actuator. If an oscillator is not available,
that the parallel units are effectively not connected
you can manually control the turbine-generator set to
to the load signal box. The signal to the control box
provide the PMG signal.
is fed by the DROOP ADJ. potentiometer. This
The converter section is working properly if, after
adjustment compensates for differences in
removing the amplifier section, the voltage at the
generator ratings and the reactive load carried by
collector of Q2 (fig. 9-7) is correct (6 volts dc at rated
them.
speed). If this is correct, place the amplifier back in the
circuit. The voltage across the resistive load
MAINTENANCE
should be about zero volts. If not, the amplifier section
is faulty.
Governor faults are usually revealed in turbine
speed variations. However, a check of the system is
If the trouble is a change in unit steady-state speed
necessary since not all speed variations are caused by a
as the load is changed, check the voltage across the
faulty governor.
actuator input under different load conditions. If the
volt age is the same at both loads, the control box may
Check first to determine that the changes are not a
be defective. If the voltages differ by more than 0.2 volt
transient result of load changes. If the load is constant,
dc, the actuator is probably faulty,
hold an inspection to see that the operating linkage
The source of most troubles in the hydraulic
actuator or valve operator is dirty oil. Grit and other
impurities may be introduced into the system with the
oil or may form when the oil begins to break down
(oxidize) or become sludge. The moving parts within
the actuator and valve operator are continually
lubricated by the oil within the units. Thus, grit and
other impurities can cause excessive wear of valves,
pistons, and plunger. This can cause these parts to stick
or freeze in their bores.
For the remainder of this chapter, we will discuss
the EGB-2P governor/actuator and the 2301 load and
Figure 9-11.--Comparison of load pulse signals to load
speed-sensing control, which are used to form another
system.
changes.
9-14
