Emergency Diesel Generator Diesel Engine Controls and Governing

8.0 DIESEL ENGINE CONTROLS AND allowing operators to achieve and maintain
GOVERNING a safe shutdown condition.

This chapter presents the principles of the EDGs consist of two physically and
governing system which controls the power functionally related components. The
output by the engine. It is the electrical driven component, the electric generator,
demand on the generator that sets the load produces the power required to safely
demand on the engine. The governor operate plant systems in the event of a loss
controls the fuel to the engine to establish of the plant primary power sources. The
the speed of the engine, and thereby the driving component, the diesel engine,
frequency of the generator. converts energy supplied in the form of fuel
oil into mechanical energy. During opera-
Learning Objectives tion of the EDG, the power (voltage and
current) produced by the generator is
As a result of this lesson, you will be able to: regulated by the generator excitation
system.
1. Describe the functional relationship
between the engine control governor As discussed in Chapter 4, the power
and the fuel injection system. output of the diesel engine, and
consequently the power input to the
2. Explain how the engine control governor generator, is controlled by regulating the
senses changes in the generator load or quantity of fuel delivered to the engine
demand and compensates by regulating cylinders. In turn, the regulation of the fuel
the fuel delivery to the diesel engine. is controlled by the engine control
governor.
3. Describe the primary components of the
governing systems used on diesel The relationship between the generator
generator set engines used in nuclear output frequency and the engine speed is
applications. expressed by the formula:

4. Explain how the terms isochronous and F=N P / 120

droop apply to the diesel generator set
engines used in nuclear applications. Where F is frequency, N is the engine
speed in RPM, and P is the number of
8.1 Control Fundamentals poles on the generator. A 900 rpm engine
requires an 8-pole generator to produce 60
8.1.1 Diesel Engine to Generator Hz power. For 60 Hz, use the following:
Relationship N = 7200/P (therefore, P = 7200/N)

In the application of Emergency Diesel 8.1.2 Governor Principles

Generators (EDGs), the primary objective
is to provide the electricity needed to Chapter 4 discussed the very basic
operate the plant safety-related systems, principles of the governing of the engine

Rev 1/11 8-1 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

through a system that controls the amount If the diesel generator is operating all alone
of fuel delivered to the engine cylinders on an electrical system and is not in any
through the control of the fuel injection way connected to other generators, it is
equipment on the engine. This section will most desirable to have the generator
expand upon the governing system aspect maintain its frequency (speed) regardless
of the engine control system. The of the load it is carrying. In other words, it
governing system monitors the speed should be 'isochronous.' However, if that
and/or load on the unit and regulates the same unit were put on a system with other
fuel injection system to attempt to hold the generators, and particularly if there were
speed or load on the unit constant. We will many other generators and a very large
explain how this is done in a number of system (infinite bus), there is a potential
different systems that are used on diesel problem. If the new unit’s frequency
engines in nuclear plant applications. (speed) is even a small amount higher than
the system frequency, the new unit will
8.1.2.1 Isochronous-Droop Relationship attempt to bring the system up to its
frequency. The only way it can do this is to
Every governing system and governor type attempt to carry the whole system load.
has to contend with a problem of the This would result in the new unit being
control of a generator when it is connected overloaded, and could damage it.
into a large system with other generators.
A very large system is often referred to as If the new unit’s frequency (speed) is just a
an 'infinite bus' or 'the grid.' Some means little lower than the system frequency, the
must be provided to allow control of a system will attempt to bring the new unit up
single machine while paralleled with other to the system frequency. The only way the
machines. system can do this is to drive the new unit
or in other words, to motorize the generator
Two terms have come into usage for in order to bring the unit up to the system
describing the requirements of control in a frequency. Since the unit will now be
governing system. The first is running at a speed that is above its
'isochronous;' the other is 'droop.' The governor speed setting, the governor will
word 'isochronous' can be broken into two back off the fuel and the unit will simply
parts – 'iso' meaning 'equal' and 'chronous' operate as a motorized unit. This is not
relating to 'time.' As applied to an engine, harmful to the generator nor the engine
isochronous means that each revolution of providing that fuel flow is maintained to the
the engine takes an equal time, or in other fuel injection components such that they
words, the speed is constant. 'Droop' are lubricated. The term 'reverse power' is
indicates that something is falling off or applied to this condition, and it will be
drooping. As applied to a generator set, it discussed further in Chapter 10,
means that as load is applied the speed "Emergency Diesel Generator Control and
falls off or diminishes. The following Monitoring."
explains how these terms are applied to the
diesel generator and why droop is required. Droop in a governing system is defined as
the change in speed the unit makes in

Rev 1/11 8-2 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

going from 100% load to no load. By the unit's subsequent recovery time).
definition, it is the difference between the
no-load speed and the rated speed, divided If the unit were operating alone (on an
by the rated speed, all times 100 to obtain isolated system) with droop, then the
the percent change. operator would dial in the desired speed.
As the unit were loaded, the speed would
drop. To compensate for the speed drop,
the operator would have to continuously
adjust the speed reference up in order to
One means of determining the droop is to
arrive at the rated speed at 100% load.
run the unit at 100% load with the speed
adjusted to 60 hertz. Trip the load breaker
Two lines are shown on the chart going
open, and the unit will end up at a higher
through 100% load and rated speed (60 hz)
speed. This is the no-load speed. Apply
- one for 3% droop (solid line) and one for
the formula above to compute the percent
5% droop (dashed line). Note that the
droop.
speed reference is now at 61.8 Hz and 63
Hz respectively for the 3% and 5%
To prevent the unit from being either
conditions.
overloaded or motorized, droop is
introduced into the governing system. As
Since the operator cannot change the
the engine is loaded, the speed/frequency
system speed, his only means of loading
tends to drop off (droop). Since the unit is
the unit against the system-maintained
locked into the grid, it cannot change
speed is to change the speed reference
speed, but that is what the droop in the
setting. Another solid line for 3% droop
governor would attempt to do.
shows the setting for 50% load. This is
what is done when a unit is synchronized to
To best explain how droop is used in the
the system in order to manage the loading
system, refer to Figure 8-1. In this
of the unit. After synchronizing the unit and
diagram, the right ordinate axis represents
closing its breaker, the operator must
the grid frequency. The left ordinate is the
adjust the speed reference input (through
reference speed input (the point to which
the motor operated potentiometer or other
the operator wants the unit to run). The
means) to have the unit take on load or to
abscissa is the percent loading and goes to
decrease the load.
110% in as much as most EDG units will
have an 'overload' rating.
Once the unit is on the system and loaded
to the desired load, the unit will not change
If the unit is running in ‘isochronous’, the
load unless the operator changes the
right and left ordinate values are the same
speed reference input. However, if the
with the load line being flat and having no
system frequency were to change by a
slope (parallel to the base of the graph).
small amount, the load would also change
The operator sets the unit at the desired
by some small amount as shown by the two
speed and the unit operates at that speed
lines close to, and parallel with, the 60
for all loads (with only short durations of off
hertz isochronous line.
speed during the actual load change and

Rev 1/11 8-3 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

8.1.3 Governor Classifications of both the load and speed of the governor
system. A view of a typical electric-
8.1.3.1 By Design and Construction hydraulic actuator is shown in Figure 8-4.
The actuator is the interface between the
Mechanical governors: In mechanical electrical portion of the governing system
governors, the output or controlling force is and the engine (mechanical portion). An
created by centrifugal force acting on a set example of this scheme is shown in Figure
of rotating weights. Because the weight 8-5.
assemblies are relatively small, the output
force is not sufficient to control the injection An electric control valve is connected to an
pumps on large engines. Mechanical armature in an electromagnetic field. An
governors are limited to use on small and electric control box sends a signal to the
automobile type diesel engines. A simple field which positions the armature and,
diagram for a mechanical governor is therefore, the control valve to regulate the
shown in Figure 8-2. fuel delivery. When operating in the
electric mode, the electric control overrides
Hydraulic Governors: With hydraulic the mechanical hydraulic control. In this
governors, the rotating weight assemblies way, the diesel engine operates in
connect to a control valve rather than response to the demand on the emergency
directly to the fuel control racks. The generator.
control valve directs hydraulic fluid to or
away from a power piston. The power Detail of the governor actuator and the
piston, in response to the hydraulic fluid, electric governor are explained in more
controls the fuel racks and therefore the detail later in this chapter.
engine power or speed. In this way, a
greater force is available to move the fuel 8.1.4 Principles of Operation
racks on medium and large size diesel
engines. A simple diagram for a hydraulic The following three sections discuss the
governor is shown in Figure 8-3 basic principles of governor operation.

Electric-Hydraulic Governors: The 8.1.4.1 Flyweight Assembly

electric-hydraulic governors normally
utilized in nuclear service have a governor Virtually all governors are equipped with a
actuator with two sections–a mechanical rotating flyweight assembly as shown in
hydraulic backup governor and an electric Figure 8-2. Two or four individual
governor. If the electric governor were to flyweights are mounted on the rotating
fail, it is possible to run the unit on the ballhead. The ballhead is driven by the
mechanical hydraulic backup governor engine through a drive gear assembly. The
under manual control. In normal operation, speed of the ballhead is directly
the mechanical hydraulic backup governor proportional to the engine speed.
is set at a speed above the rated speed,
and the electric governor is used to control As the ballhead rotates, centrifugal force
the unit. The electric governor has control acts on the flyweights forcing them

Rev 1/11 8-4 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

outward. The amount of force exerted on the output control stay in the same position.
the weights is a direct function of the But, the only way to maintain that position
engine speed. The higher the engine is to have the engine operating at a lower
speed, the higher the force exerted on the speed. Therefore, there is always droop in
flyweights. The speeder spring is installed this system.
to counteract the force of the flyweights.
8.1.4.2 Hydraulic Controls
With mechanical governors, the flyweights
connect to a control sleeve which in turn With the hydraulic governor, the fly-weights
connects to the injector fuel control racks. connect to a hydraulic control or spool type
With the engine operating at a constant valve as shown in Figure 8-3. Hydraulic oil
speed and load, the force on the flyweights is supplied to the control valve by a small
is exactly balanced by the force of the gear pump mounted in the base of the
speeder spring. governor. A power piston is hydraulically
connected to the fuel control racks. A
If the load demand on the engine is spring acts on the power piston to oppose
increased, the engine tends to slow down. the hydraulic force. The bottom of the
As the engine slows, the force of the control valve sleeve is open to the oil sump
speeder spring overcomes the force of the in the bottom of the governor housing.
flyweights and the control sleeve lowers.
Lowering of the control sleeve causes the At a constant speed and load, the control
fuel control racks to increase fuel delivery valve is positioned to block the ports in the
and therefore the power developed by the valve sleeve which creates a hydraulic lock
engine. With the increase in engine power, to the underside of the power piston.
the engine returns to the desired rpm, and
the forces of the speeder spring and An increase in load causes the engine to
flyweights again balance. slow down. The flyweights move in when
the levered force exerted by the flyweights
If the load demand on the engine is falls below the force exerted by the speeder
reduced, the engine speed tends to spring. This action lowers the control valve
increase. The increased speed increases which directs the oil pressure supplied by
the force exerted by the flyweights which the gear pump through the sleeve to the
now overcome the force of the speeder underside of the power piston. Upward
spring, raising the control sleeve. This motion of the power piston moves the fuel
movement of the control sleeve reduces racks to increase fuel delivery and return
the fuel delivery and the engine power to the engine to its steady state rpm. As this
cause the engine to return to its steady happens, the control valve raises to again
state rpm. take the neutral or blocking position.

There is in this mechanical scheme an The hydraulic governor acts as a

inherent droop. The only way that the mechanic/hydraulic amplifier. A small
increase in fuel necessary to support an mechanical input can produce an output
increase in load is maintained is to have force, created by hydraulic pressure,

Rev 1/11 8-5 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

sufficient to control the fuel racks with a with the control valve in the blocking
higher degree of sensitivity than is possible position.
with a mechanical governor.
An electronic governor control box (EGA)
Because there is no longer a direct monitors the output of the generator for
relationship between the power piston both load and frequency. The control box
position and the control valve position, this generates a signal which is applied to the
system eliminates the ‘droop’ inherent in field coil in the governor actuator housing.
the strictly mechanical governor. An increase in load demand or decrease in
speed causes the control box to generate a
8.1.4.3 Electric Controls signal which lowers the armature magnet
and control valve. Oil pressure is now
Within actuators used on EDGs in nuclear directed to the underside of the power
power plants, there is both a mechanical- piston, raising the power piston and
hydraulic governor and an electrical- increasing the fuel delivery. The engine
hydraulic section that is operated from the returns to its steady state mode, and the
electrical governor control unit. There are control valve is returned to the blocking
two different systems being applied to position.
these EDGs. One system is an older
obsolete system referred to as the EGA With a decrease in load demand and/or
control. The newer unit is the 2301A increase in speed, the control box raises
control. In this section, we will discuss the the armature magnet and control valve.
actuators used in both systems. The oil under the power piston is now
drained to the governor sump, and the
8.1.4.3.1 EGA Actuators (Figure 8-5A) spring pushes the power piston down. This
reduces the fuel delivery and engine power
Depending upon the size of the engine, the to return the engine to its steady state
EGA actuator will be either the EGB-10C condition.
(used on the FME OP engines and ALCO
units), the EGB-35C, or the EGB-50C Actually, there is a small bias voltage put
(used on the FME Pielstick engine units). out by the control box when the control
The numerical value following the EGB valve is centered (in the blocking position).
signifies the maximum work effort (in foot This is to cause the electric governor
pounds) that the actuator can produce in section to go to the full fuel position in the
moving the engine fuel controls. event that the electric control box fails.
This causes the actuator to go to the
In addition to the backup hydraulic mechanical hydraulic actuator higher speed
governor with its control valve, the electric- setting until normal operator action is taken
hydraulic governors uses a second control to reduce the speed setting to the desired
valve connected to an armature magnet in control point. Only one of the governor
a variable electro-magnetic field as shown actuator sections may be in control at one
in Figure 8.5A. A set of centering springs time; otherwise, governor instability can
are used to center the armature in the field result.

Rev 1/11 8-6 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

8.1.4.3.2 2301A Actuators (Figure 8-5B) 2301A control causes the electric governor
section to go to the full output position.
Depending upon the size of the engine, the This causes the actuator to go to the
2301A actuator will be either the EGB-13P mechanical hydraulic actuator higher speed
(used on the FME OP engines and ALCO setting until normal operator action is taken
units), the EGB-32P or the EGB-50P (used to reduce the speed setting to the desired
on the FME Pielstick engine units). The 'P' control point.
suffix indicates a proportional actuator
system. Only one of the governor actuator sections
may be in control at one time; otherwise,
The actuators used with the 2301A governor instability can result.
governing system are proportional systems.
That is, the governor output is proportional 8.1.5 Nuclear Application Governors
to the electrical input from the 2301A
control. On the EGA actuator, the output Diesel engines used to supply Class 1E
was only as required to close the actual power to electrical load at nuclear power
speed to commanded speed loop. plants require very precise control to
ensure proper operation under emergency
In addition to the backup hydraulic conditions. Governors specific to nuclear
governor with its control valve, the electric- applications will be covered in detail below.
hydraulic governors use a second control
valve connected to an armature magnet in 8.1.5.1 Types of Governors in Nuclear
a variable electro-magnetic field as shown Service
in Figure 8.5B. However, in addition to the
centering springs is a lever system that Mechanical-Hydraulic Governing - For
biases the transducer in proportion (in units equipped with only the mechanical-
relation) to the position of the electrical hydraulic governor such as the UG8, the
portion power piston. This causes a feed governor functions in response to a speed
back into the 2301A control such that it sensing flyweight assembly. Changes in
knows about how much fuel is going into engine load/demand tend to cause a
the engine for a given load and speed change in the engine’s operating speed
condition. The output signal from the (RPM). The flyweight assembly, in
2301A control therefore becomes response to changes in the engine speed,
proportional to the load on the unit and the increases or decreases the fuel delivery to
fuel requirement to support that load or maintain the desired speed through the
speed. hydraulic servo system.

Other than that difference, the remainder of These units are predominantly the earlier
the 2301A actuator works essentially the units supplied to the nuclear industry. Most
same as the EGA actuator, as described of the later units use the Electric Load
above. Sensing governing systems.

A failure of the electrical signal from the

Rev 1/11 8-7 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Electric Speed and Load Sensing - When mechanical backup governor set high, the
the electric governor is used, both speed electric governor then controls. Should the
sensing and load sensing are provided and electric governor fail, the mechanical
controlled by the electric control box backup governor will automatically take
through a signal in the electric section of over control, but at the higher speed
the governor actuator. The control box setting. It is necessary to manually adjust
senses the engine speed by either the backup governor to get back to the
converting the generator voltage signal to a normal speed setting. If the mechanical
voltage proportional to the frequency or by backup governor is set at the same speed
means of a speed sensor (magnetic as the electric governor, the two systems
pickup) mounted on the engine near the could fight each other and instability would
flywheel or other gear that operates in occur. The mechanical backup governor is
proportion to the engine’s speed. Load is normally set to operate at about 63 hertz in
sensed by having both the current and order to provide latitude for operation of the
voltage at the generator output measured electric governor.
through current and potential transformers.
A section within the control box converts 8.2 Engine Governor Operation
these input signals to a voltage proportional
to the real load (KW) on the generator. There are several types and models of
governors used to control EDG operation in
When the unit is operated in parallel with nuclear plant applications. Since they all
the power grid, droop is introduced into the operate on the same basic principles, we
control box. The droop may be adjusted will concentrate our discussion on the
from 0 (isochronous) to about 10% by Woodward series EG Governor Actuator
means of the "droop" potentiometer. When and the EGA control box. Some more
paralleled, some droop must be present to recent units have the Woodward 2301A
provide for load sharing. When the unit is control box and some units are now being
run alone, the droop function may be converted to the 2301A system because of
switched off (governor switched to obsolescence of the EGA control box. The
isochronous). differences will be explained later.

Electric Governor Backup - In most It should be realized that Woodward

applications of the electric governor, the Governor Company has obsoleted the EGA
governor actuator mounted on the engine control and the Motor Operated
includes a backup mechanical-hydraulic Potentiometer speed setting units. They
governor. In order that this mechanical will no longer supply nor repair older units.
backup governor not interfere with the Therefore, the 2301A has become the only
operation of the electric governor, it is unit now qualified for Nuclear Service. A
intentionally set to operate at a speed program is underway to replace EGA
higher than the normal speed of the unit. controls with the 2301A control. This
The lever system in the actuator forms a conversion/replacement program is
low pass OR gate such that the lowest discussed later in this Chapter.
speed input controls the unit. With the

Rev 1/11 8-8 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

8.2.1 Woodward EG Governor Actuator reservoir and pump which supplies the
hydraulic pressure needed to operate the
The Woodward EG-B Governor Actuator, fuel control assemblies. Hydraulically, the
shown if Figure 8-5, is the mechanical EGB actuators consists of three distinct but
portion of the electric governor system. interconnected sections.
The “B” in the designation indicates that the
actuator includes the mechanical-hydraulic Mechanical Backup Section - A
backup section/function. A number mechanical-hydraulic (flyweight type)
following the “B” indicates the work effort governor functions to control the engine
rating of the actuator in foot-pounds of speed when the engine is operated at
torque at stall. speeds other than near rated speed or in
the event the electric governor control has
When the actuator is provided with the failed.
backup section, it is normally termed as a
‘reverse acting’ actuator. That is, the signal The mechanical Backup Section is the
from the control to the actuator is inverse to same for both the EGA system and the
the difference in the speed error detected 2301A system.
by the control box. The reason for this
inversion is to cause the actuator to go to Electric Transducer Section - The second
the mechanical backup governor should the governor is the actuator portion which
electrical signal from the control box works in conjunction with the Electric
disappear/fail. Control Box (EGA or 2301A control). When
the actuator is used with the Electric
The actuator consists of two separate but Control Box (EGA or 2301A Control), the
interconnected governors; the mechanical actual monitoring and governing takes
backup section and the electric transducer place in the control box.
section. The mechanical-hydraulic
governor section controls engine speed When the Electric Transducer Section is in
when the mechanical backup governor is in control, the Mechanical Power Piston would
control (set lower than the electric be in its full upward position (fixed) and the
governor). When the electric governor is in electrical power piston is then free to move
control (set lower than the mechanical and control the input to the hydraulic
backup governor and receiving a signal amplifier.
from the electric control), the mechanical
section goes to the full output position so The second section of the actuator consists
that the end of its floating lever becomes of the electric transducer wherein the signal
fixed. from the electric control box is used to
position the electric pilot valve in that
The actuator, mounted vertically to the section. When there is no signal from the
engine governor drive assembly, is driven electric control, the electric power piston
directly from the engine gear train which goes to its full output position, and its end
allows it to sense engine speed. The of the floating lever becomes fixed. To
actuator unit incorporates its own oil insure this happens upon failure of the EGA

Rev 1/11 8-9 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

electric control box signal, the center of the Rotation of the pump gears draws a suction
electric pilot valve is intentionally offset. on the oil reservoir, and the oil is
This causes the EGA control box to put out discharged to the accumulator section.
a small signal in order to hold the electric
pilot valve in the centered (blocked) The accumulator provides a reservoir of oil
position. This EGA bias voltage is usually under pressure while also acting as a
set at between 0.5 and 1.0 volts. The full pressure relief/regulating valve. Oil
swing of the EGA electric control box signal pressure from the pumps acts against the
is from -6 to +6 volts. force of the accumulator springs. As the
pistons pass the bypass port, excess oil
In the case of the 2301A system, the pressure is vented back to the sump.
voltage to the actuator is proportional to the Normal oil flow continues on to the top side
inverse of the fuel required to regulate the of the relay servo piston and on to the relay
engine speed, and there would normally be valve plunger and bushing. The relay
a voltage on the transducer coil. In the servo piston connects to and controls the
event that the 2301A control box fails, the piston of the terminal output shaft of the
voltage would go to zero (the full output actuator.
condition) and the actuator would go to the
mechanical backup section control. The relay valve plunger, which is controlled
by the loading piston, controls oil flow to the
Hydraulic Amplifier Section - The third underside of the relay servo valve. When
section is the hydraulic amplifier section the engine is operating in a steady state
which provides the output force needed to condition, the control land of the relay valve
operate the fuel controls on the engine. plunger just blocks the port to the
Again, the Hydraulic Amplifier Section is underside of the relay servo piston. This
the same for both the EGA system and the creates a hydraulic lock which prevent oil
2301A system. pressure, acting against the top of the relay
servo piston, from forcing the piston
The three sections are connected through a downward.
loading piston which functions to position
the terminal output shaft of the actuator in When there is a change in engine speed or
response to changes in either of the first generator load, the loading piston will move
two sections. as a result of the action of the mechanical-
hydraulic or electric governor, depending
The hydraulic amplifier section, shown in on which is in control. This movement of
Figure 8-5, consists of an oil sump, oil the loading piston causes the relay valve
pump, accumulator assembly (pressure plunger to raise or lower.
storage and regulation), relay valve
assembly, relay piston and linkage to the When there is an increase in generator
terminal shaft. load or a decrease in engine speed, the
loading piston will rise. This will, through
The governor drive shaft causes rotation of the linkage shown, cause the relay valve
the oil pump and the relay valve bushing. plunger to drop, directing oil pressure to the

Rev 1/11 8-10 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

underside of the relay servo piston. Since the armature magnet and pilot valve
the bottom of the relay servo piston has a plunger to move up or down in response to
larger area than the top, the larger force of changes in the generator speed/load.
the oil acting on the bottom of the piston
will cause it to move upward. This upward With the unit operating at a steady state
movement is carried through the terminal condition, a small signal is present in the
shaft to the fuel control linkage causing the transducer and magnet. As such, the pilot
fuel delivery to the engine to increase. valve and plunger are centered, blocking
the port and creating a hydraulic lock below
During a decrease in generator load or the electric governor power piston. A
increase in engine speed, the loading change in the generator load or speed
piston is forced down, raising the relay causes the signal to be change by the EGA
valve plunger and relieving oil pressure control box, which will move the pilot valve
from the underside of the relay servo plunger up or down.
piston. The reduced pressure on the
underside of the relay servo piston causes An increase in load or decrease in speed
a net downward force on the piston. The on the generator will result in a signal from
piston is forced down, reducing fuel the EGA control box causing the armature
delivery to the engine. to move down. This motion allows oil to be
directed to the underside of the electric
The relay beam, intermediate shaft, and power piston. The increased pressure on
bearing transfer the movement of the relay the underside of the power piston will
servo piston back to the relay plunger cause it to rise, raising the loading piston.
valve. This returns the relay plunger valve This action, as discussed earlier, results in
to the blocking or steady state position. the relay valve plunger directing oil to the
underside of the relay servo piston, which
8.2.1.2 Electric Governor Section - EGA causes the terminal shaft to move the fuel
control assemblies (racks) to the increased
The electric governor section controls the fuel position required to re-establish rated
position of the loading piston (as shown in speed.
Figure 8-5A) and ultimately the relay servo
piston and terminal output shaft by With a decrease in load or increase in
controlling the movement of the electric speed of the generator, the EGA control
governor power piston. box will provide a signal to the transducer
and magnet causing the pilot valve plunger
The control element of the electric governor to move up. This upward motion of the
section is the pilot valve plunger which is pilot valve plunger vents oil from the
attached to an armature magnet. A underside of the electric governor power
centering spring suspends the armature piston. As the electric governor power
magnet and pilot valve in a transducer and piston moves down, it causes the loading
magnet. The transducer and magnet is piston to move down, which raises the relay
electrically connected to the EGA control valve plunger. Upward movement of the
box. A signal from the control box causes relay valve plunger vents oil from the

Rev 1/11 8-11 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

underside of the relay servo piston causing normally slightly higher than the speed
it to move down. This downward setting used for the electric governor to
movement rotates the terminal output shaft prevent the two sections from acting
to the reduced fuel position required to re- against each other.
establish rated speed.
The pilot valve plunger of the mechanical-
Operational stability is achieved by a hydraulic governor is connected to the
negative feedback to the compensating flyweight assembly. This section also
land of the pilot valve plunger through the includes a buffer system consisting of a
buffer system. Oil from the governor oil buffer piston, needle valve, and
pump is directed to the top of the compensation land as was used with the
compensating land of the pilot valve electric governor. The desired engine
plunger and to the left side of the buffer speed (RPM) is established by setting the
piston. The right side of the buffer piston is force applied by the speeder spring which
connected to the underside of the acts to oppose the motion of the flyweight
compensating land of the pilot valve assembly.
plunger. This pressure creates sufficient
force to move the pilot valve plunger up, With the engine operating at the desired
returning it to the steady state blocking speed, the centrifugal force acting on the
condition. Movement of the power piston fly-weights exactly balances the force
ceases, and the engine accepts the applied by the speeder spring. This
increased load on the generator. The equilibrium condition holds the pilot valve
sensitivity of the buffer system is plunger in the blocking position, locking the
determined by the setting of the needle mechanical governor power piston and the
valve, which functions as an orifice loading piston in the steady state condition.
between the two sides of the buffer piston
and compensating land. Should the mechanical load on the engine
increase, the engine tends to slow down.
8.2.1.3 Mechanical-Hydraulic Governor This reduces the centrifugal force of the
flyweights acting against the speeder
Figure 8-5 shows the mechanical-hydraulic spring of the valve. The force of the
governor section, combined with the speeder spring overcomes the centrifugal
electric governor and the amplifier sections. force and the pilot valve plunger lowers.
The mechanical-hydraulic governor section Oil pressure is then applied to the of the
functions only when the electric governor buffer piston moving it to the right. This
control box is not functioning or when the displaces the oil on the right of the buffer
mechanical speed setting is below the piston, applying its pressure to the
electric control speed setting. When the underside of the mechanical governor
mechanical-hydraulic governor is in use, power piston. The power piston moves
the electric governor section is hydraulically upward, repositioning the loading piston,
locked with the electric governor power thereby increasing the fuel delivery to the
piston fully extended (fixed). The engine.
mechanical-hydraulic governor setting is

Rev 1/11 8-12 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

The pressure differential created is also the unit were connected to a grid without
applied, via the needle valve, to the speed droop, that unit would attempt to
compensating land of the pilot plunger. lead the entire grid. This would lead to
This moves the pilot valve plunger upward. unstable operation and possible damage to
At the same time, the upward movement of the generator and/or engine. See the
the mechanical governor power piston acts discussion earlier on the definition and use
to move the speed adjusting/speed droop of speed droop.
floating lever upward, reducing the force
applied by the speeder spring on the Operationally, speed droop is a function of
flyweight assembly. This allows the pilot the position of the mechanical-hydraulic
valve plunger to return to the steady state power piston. Movement of the power
blocking position. piston causes a proportional movement of
the speed adjusting/ speed droop floating
8.2.1.4 Actuator Dial Settings lever which reduces the force on the
speeder spring on the flyweight assembly.
The mechanical linkage, as shown on the Setting of the Speed Droop knob moves
left side of Figure 8-5, is connected to the the adjusting pin (fulcrum point) which
three adjustment knobs on the face of the changes the lever ratio between the
governor (see Figure 8-4). These mechanical governor power piston and the
adjustment knobs allow for setting specific speeder spring.
operating parameters for the mechanical-
hydraulic section of the governor. With the speed droop set at 0%, the full-
load speed and the no-load speed would
The "Speed Setting" knob is connected to be the same. This condition, called
the speed adjust lever through a screw isochronous, is satisfactory when the unit is
shaft and clutch. This allows the operator powering its own isolated bus. A speed
to manually set the desired no-load engine droop of about 3 to 5% would be
speed by adjusting the force of the speeder appropriate for units connected to the grid
spring. In the nuclear application, this knob for surveillance or post-maintenance
is normally set at the 'high speed stop' testing.
position.
In the nuclear application, this function is
The "Speed Droop" knob only effects to not used as the system in under control of
speed droop of the mechanical backup the electric governor. To ensure proper
governor section of the Actuator. Electrical operation of the electric governor, it is
Droop is set in the Control Box. recommended that the mechanical speed
droop knob be set at ‘zero’.
The term "Speed Droop" refers to the
difference in engine speed between no- The "Load Limit" knob connect through a
load and full load operation. It is a key load limit lever to the pivot lever. The pivot
factor when operating two or more units in lever limits the upward travel of the
parallel or when operating connected to an intermediate lever regardless of the
infinite bus (electrical grid). For example, if position of the loading piston and output

Rev 1/11 8-13 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

nut. The intermediate lever, working The Load sensor receives voltage and
through the bearing and relay beam, current signals from each of the three
establishes the maximum fuel position of phases of the generator output and uses
the relay servo piston and the terminal these signals to calculate the total electrical
shaft. When classified as operable, the (KW) output of the generator. This
load limit knob on a nuclear application calculated total load is converted to a DC
EDG would be set at the “max fuel” voltage through a bridge of rectifiers and is
position. It should be noted that the ‘Load fed into the summing junction if the system
Limit” is always active, whether the unit is is set up for droop or load sharing
on the mechanical-hydraulic governor or operation. This section includes a
the electric governor. It does not limit just potentiometer that allows this watts
the operation of the mechanical-hydraulic transducer to be calibrated to the specific
governor section. In the nuclear unit rating, etc. Another potentiometer
application, this knob is normally set at allows the amount of droop desired to be
'Max Fuel' position. set into the system if the unit is in the droop
mode of operation.
8.2.2 EGA Control Box
Another input is from a potentiometer or
The EGA Box, as pictured in Figure 8-6, is another electrical/electronic device that
an the electrical part of an electro- sets the level of the load or speed at which
mechanical servo system programmed to the unit is to run. This is called the speed
maintain a preset engine speed and load reference.
sharing level in proportion to the capacity of
the unit being controlled. For the purpose 8.2.2.2 Control Section
of study, we will consider the EGA as
having three sections, as illustrated in the The control section consists of a set of
block diagram shown in Figure 8-8 - EGA differential amplifiers and power amplifiers.
Control Block Diagram. An input signal is fed into these from the
summing junction.
8.2.2.1 Input Section
The speed reference section supplies a
The input section consists of a load sensor regulated DC voltage to the speed setting
(watts transducer), a resistor box, a speed potentiometer (which is mounted outside
sensor, and a power supply section. the EGA Control Box). The output of this
During operation, the speed sensor potentiometer is adjustable by the operator
receives a signal from one phase of the or by automatic control, and the output
generator output via potential transformers (proportional to the desired speed) is also
and converts it to a DC voltage proportional put into the summing junction. The
to the speed of the engine. This voltage is voltages from the speed setting
then fed into the amplifier portion of the potentiometer and the speed transducer
circuit at the summing junction. This is (mentioned above) are the same value but
called the speed transducer. they are of opposite polarity so that the
resulting voltage at the summing junction is

Rev 1/11 8-14 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

zero when the engine is at the desired the neutral or blocking position.
speed.
Under conditions of increasing load, the
The droop switch controls the load sensor output signal for the amplifier is applied to
output in both the droop and isochronous the coils of the transducer and magnet.
modes. In the isochronous mode, the The polarity of the signal causes the
output of the load sensors is fed to the armature to move downward, increasing
summing junction only if the unit is set up the fuel delivery to the engine. When the
for isochronous load sharing with other engine reaches the desired operating
units on the same isolated bus. In the conditions, the signal ceases and the pilot
droop mode, however, the output of the valve plunger returns to the steady state
load sensor is fed to the droop control and position.
then into the summing junction. The droop
control is used to adjust the percent droop With a decrease in load or increase in
(1 to 10%) by applying a variable portion of engine speed, the polarity of the signal is
the load sensor output to the summing reversed. The armature now moves
junction. upward, allowing the oil pressure under the
electric power piston to return to the sump.
The summing junction calculates the This lowers the loading piston, leading to a
algebraic sum of the input signals from the reduction in fuel delivery to the engine.
load sensor, the speed sensor, and the
speed setting potentiometer. This summed 8.3 The 2301A Governing System
signal becomes the input signal to the
amplifier section. The 2301A Governing System is of slightly
more recent development. With the
Operational stability is achieved by obsolescence of the EGA system, it is the
regulating the rate of change of the best logical replacement for the EGA
actuator from one level to another during system. See the comments in the section
load or speed changes. This dampens out below on the conversion of the EGA
transients and oscillations in the control of system to the 2301A system.
the engine.
8.3.1 2301A Actuator
8.2.2.3 EGA Output to Actuator
The actuator used with the 2301A control
The output of the EGA Control Box is fed to system looks identical to the EGA actuator
the actuator. The magnitude and polarity of on the outside except for the nameplate.
the signal determines the movement of the The actuator type number ends with the
armature and pilot valve plunger. letter 'C' for compensated and with a the
letter 'P' for proportional actuator. The
During steady state conditions, the differences inside are not great. The
armature is centered in the transducer and mechanical-hydraulic section is identical as
magnet. With only the bias voltage applied is the amplifier section. The only difference
to the coils, the pilot valve plunger takes is in the electric section. The 2301A

Rev 1/11 8-15 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

compensated actuator does not have the EDG, the input voltage it typically 125VDC.
buffer section and the needle valve
because the compensation is all done Like the EGA, there are terminals for the
electronically in the control box. For the signal going to the actuator. There are also
proportional actuator, the transducer has a terminals for input of the speed reference
system of levers that feed the electric signal, either from a motor operated
power piston position back to the potentiometer (like the EGA control) or from
transducer to bias it in a position between a Digital Reference Unit (DRU) or other
its centering springs that are proportional to voltage reference signal.
power output.
Unlike the EGA, the 2301A requires a
On the actuators with backup sections, the speed signal supplied from a Magnetic
transducer and 2301A are set up for Pickup (MPU). This pickup is usually
reverse action operation. That is, the mounted next to a gear (such as the
voltage to the actuator is low for increased flywheel or coupling ring) with a speed
fuel and higher for idle or no fuel. input proportional to the engine’s speed.
Figure 8-11 shows a typical Magnetic Pick
In all other respects and settings, the (MPU) unit. This is an assembly of a fine
2301A actuator is the same as the EGA coil of wire wound over a permanent
actuator. The same dials and settings are magnet, housed within a magnetic material
used. body. Any metallic (particularly magnetic)
material that passes by the tip of the pick
8.3.2 2301A Control Box will influence the magnetic field and cause
the MPU to put out a pulse. It is used to
The 2301A control box is shown in Figures count the teeth of a gear to establish the
8-7 and 8-9. This control has the same speed of the engine.
basic connections as the EGA control. It
has load sensor connections from the Like the EGA, the 2301A can be used in
generator terminals through potential and isochronous mode or in droop mode. In the
current transformers so that the KW load case of the 2301A, only one switch contact
on the unit can be measured. This is used is necessary to control the operating mode.
primarily to set the droop mode as the
voltage connections are not used for the 8.3.3 Speed Reference Input
governor power supply or for sensing the
unit speed. Figure 8-10 shows the external The speed reference (the speed at which
connections to be made to the 2301A the operator wants the unit to run) can be
control box. input from a number of sources. To make
the system as flexible as possible, including
It is necessary to provide power to operate changing speed setting rapidly and
the governor, and this can be either from a automatically, the Digital Reference Unit
DC supply at 20 to 40 volts, or an AC or DC (DRU) is preferred. Figure 8-14 shows the
supply at 88 to 132 volts for AC input, or 90 DRU unit and its inputs and connections
to 145 volts for a DC supply. For Nuclear are shown on Figure 8-15.

Rev 1/11 8-16 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

The DRU allows one to set an idle speed, a Woodward Governor Company has stated
maximum speed, and set point speed. The that they will no longer supply the EGA
set point speed would normally be the rated Control Box, nor will they attempt to repair
speed of the unit. The operator can also older units. They have also obsoleted the
raise and lower the speed for manual MOP, as the only source of the variable
control of the speed during engine resistors (potentiometers) previously used
maintenance or for loading the unit once is to buy them from foreign sources.
synchronized to the offsite power system.
In addition, the EGA governor requires
The DRU has two possible ramp rates such output power from the EDG generator to
that on one ramp rate, the rate of changing operate. It will not function to control the
the speed can be slow so that operators engine. The mechanical governor must be
feel comfortable when making speed or adjusted down to the desired speed. This
load adjustments. By closing a contact, a makes the EDG unit inoperable since it
fast ramp rate can be selected for use in cannot respond to an accident signal to
getting the unit up to rated speed rapidly in establish rated speed and voltage. For
the event a “start” signal is received while these reasons, many owners are replacing
the unit is at idle or some other the EGA with the 2301A governing system.
intermediate speed condition. On units
converted to date, much flexibility is evident The 2301A governor control receives its
as systems have been developed to meet speed input from a magnetic pickup
different operation/plant desires for control. mounted near the flywheel or other gear
that runs in proportion to the engine’s
Some earlier 2301A applications used the speed. Therefore, the 2301A system can
same Motor Operated Potentiometer that control the engine speed at other than
the EGA system used. With the rated speed conditions.
obsolescence of the MOPs, the DRU also
becomes a viable replacement for the MOP In conjunction with the use of a Digital
on both the earlier 2301A systems and on Reference Unit (DRU - in place of the
the EGA systems. Motor Operated Potentiometer previously
supplied with the EGA system), the unit can
Figure 8-12 shows a typical 125VDC Motor be set up to run at a lower speed (idle at
Operated Potentiometer, with its internal 300 rpm, for instance), and yet it can
circuitry shown in Figure 8-13. respond to an emergency signal and be at
rated speed within 10 seconds.
8.4 Governor System Change Out
8.4.1 Advantages and Disadvantages
The EGA governor system components,
particularly the EGA control box, have The EGA did have some advantages but
become obsolete. Some of the electronic also disadvantages compared to the
components are no longer available, and 2301A, and vise versa, as listed below.
using new components would require a
wholesale redesign of EGA circuit boards.

Rev 1/11 8-17 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

EGA Advantages: along with fast loading of the generator

• Powered from Generator Voltage - self stress the engine and the generator.
sufficient
The NRC authorized plants to make slow
EGA Disadvantages: starts by Generic Letter 84-15. However,
• No governing until Generator is at units with the EGA governing system
voltage cannot make a slow start on the electric
- for Power Supply governor. It is necessary to use the
- for Speed Sensing mechanical back-up governor (on the
• Will not operate at reduced speed actuator). In this state, the unit CANNOT
• Part of compensation is hydraulic within respond to an emergency start signal. The
the actuator, subject to oil temperature unit is effectively 'inoperable' when on the
and condition mechanical governor.

2301A Advantages: The 2301A governor, when applied with the

• Control at all conditions (not dependent DRU, can be operated at idle speed under
on generator voltage) electronic governor control and CAN
• In conjunction with DRU, can respond to immediately go to rated speed (within 5
emergency signal while shutdown or at seconds) upon receipt of an emergency
idle. signal.
• All compensation is electronic - tuned
for best performance. 8.4.3 Governor Conversions:
• Can control at idle or rated speed
The following plants have made governor
equally well
conversions:
Detroit Edison - 4 OP units
2301 Disadvantages:
Beaver Valley - 2 PC units
• Requires external power supply to
Snupps-Callaway - 2 PC units
operate (125VDC)
Snupps-Wolf Creek - 2 PC units
• Requires Magnetic Pickup (MPU) for
PSNH - Seabrook - 2 PC units
speed input (MPU’s are very reliable)
Calvert Cliffs - 3 OP units
• Requires gear wheel on engine/
VC Summer - 2 PC units
generator.
Duane Arnold - 1 of 2 OP units (Nov)

Most failures, on either system, result in

The following other plants are
operation on backup governor at a higher
contemplating governor conversions:
speed.
Alabama-Farley - 2 OP amd 3 PC units
Millstone III - 2 PC units
8.4.2 Fast Start Problem
PECO-Limerick & Peach Bottom – OP's
Indian Point - 3 ALCO units.
A ten-second start sequence is equivalent
to 35 to 50 hours of engine operation at
8.5 Other Possible Governor Systems
rated load. Fast starts ultimately reduce
the life and reliability of the unit. Fast stars

Rev 1/11 8-18 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Over the last few years, governor suppliers and affect governor stability.
have developed a number of other types of
governing equipment. Most of these A voltage reducing scheme could be used,
involve digitizing the governor control but with the 125VDC power supply having
algorithms used. One such governor to operate between 90 and 140VDC, there
system provided by Woodward Governor is a problem with stability in that type of
Company would be the 2301D, a digital supply - they are hard to regulate when
version of the 2301A (an analog system). both the input voltage and the load current
can change that drastically.
Another is the 700 series, specifically the
723PLUS units. There are a number of For generator applications, the 723 series
reasons that these particular units are not comes in two parts – the 723 unit to control
appropriate for use in nuclear power plant the speed and the DSLC (Digital
applications. These governor packages Synchronizer and Load Control) unit for
have many, many features that make them input of the generator parameters in order
ideal for specific application requirements to have the system operating in the droop
that are not appropriate for nuclear plants. mode for surveillance testing. Or, the 723
unit would need a GLC (Generator Loading
Both the 2301D and the 723 series can be Control) in order to simulate a load control
provided with dual dynamics that allow the signal. The combination of these units
same governor, by closure of switch/relay requires much more space in the generator
contacts, to operate a diesel fuel burning control panel than the 2301A or the 2301D.
unit or a gaseous fueled or dual fuel unit to The 723 series would not be applicable as
be managed equally well. The gas engines a retrofit for the obsoleted EGA system
must have a much slower responding (whereas the 2301A or D will generally fit in
governor in that mode in order to keep the the space vacated by the EGA
air to fuel ratio under tight control. Such is components).
not applicable to straight diesel engines in
nuclear service. Nuclear power plant governor applications
are really quite simple: to provide good
Another problem with using these units in stability and the ability to respond rapidly to
nuclear service is that their power supplies sudden and large load changes (such as
are limited to 18 to 40VDC, while most starting large pump motors) and to provide
nuclear plant station battery power systems a means of controlling the loading on the
are at 125VDC. To apply these units to unit during monthly surveillance testing.
nuclear service would require that either The 2301A can operate just as well for
one of the following be provided: these simple tasks as the more
• A separate battery power supply, or sophisticated digital units. The primary
• An inverter type power supply, to limitation for large load pickup is not the
decrease the voltage for the power to governor, which always acts fast enough,
these governors. This type of power but the engine itself. (Refer to the
supply generally introduces reliability discussion at the end of Chapter 10.)
problems, and their output can be noisy

Rev 1/11 8-19 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

8.6 Governor-Linkage Relationship full/rated load position is somewhat less

than the overload position as shown.
Regardless of the type of governor used, Typically, the governor linkage is set up to
there has to be a relationship between the use about 60 to 70% of the governor travel
governor output and the fuel injection in getting the engine from idle to full rated
system components–the fuel racks. This is fuel as shown.
normally provided by some sort of linkage
consisting of levers and links. Most 8.7 Engine Overspeed Governor/Trip
governors used in nuclear plant EDGs have
a rotary output, referred to as a 'terminal Mechanically, diesel engines must operate
shaft.' Some may have a linear output and within a specific speed (RPM) range. In
require a 'J' bar linkage system. Figure 8- order to maintain the proper frequency,
16 shows the relationship normally set up EDGs have a set RPM which is maintained
between a governor with a rotary output (45 by the engine control governor. Should the
degrees of rotation typical of the EGB governor fail to maintain the proper engine
actuator) and the engine fuel requirements. speed or should there be a failure in the
fuel injection system which prevents control
On this diagram, note that the linkage of the engine, the engine could increase in
relationship established certain key speed to an unsafe level.
conditions to allow for engine operation
under a number of conditions as described Such overspeed conditions, which could
below. When the governor is at the result in severe engine and/or generator
minimum (no) fuel position, the engine damage and fire hazards to operating
must also be at the 'no fuel' condition; personnel, are not uncommon with diesel
otherwise, the governor may not be able to engines. To prevent such a condition, a
shut the engine down. In fact, the governor redundant speed monitoring or overspeed
is usually set up such that there is a slightly device is required.
negative fuel rack position when the
governor is at minimum fuel just to ensure The overspeed device may be a separate
that the governor can shut down the governor driven by the engine gear train, or
engine. Many governors contain a it may be a separate overspeed trip
shutdown solenoid that when operated, mechanism such as that shown in Figure 8-
puts the governor terminal shaft at 17.
minimum fuel in order to shut down the
engine from a remote location. The overspeed trip shown in Figure 8-15 is
mounted directly to the end of the engine
The engine requires some fuel to operate camshaft. Since camshaft speed is either
when it is idling. The typical position is as equal to or one half the engine crankshaft
shown on the diagram. The engine also speed, this is an ideal location for such a
has to occasionally run at an overload. device. The trip shaft and trip pawl are
Therefore, the linkage must ensure that the mounted directly to the engine while the
governor can move the fuel racks to at flyweight and spring assembly rotate with
least that position plus some margin. The the engine camshaft.

Rev 1/11 8-20 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

During normal operation, the force of the

spring is sufficient to keep the flyweight
clear of the trip pawl. During an overspeed
condition, the centrifugal force acting on the
flyweight is sufficient to overcome the force
of the spring. This allows the flyweight to
move outward. The flyweight makes
contact with the trip pawl, unlatching it from
the trip shaft. The trip shaft, which is spring
loaded, rotates as shown to activate the trip
mechanisms, which by its spring force,
returns all of the injectors to the no-fuel
position. With no fuel going to the engine
cylinders, the engine coasts to a stop. If
the engine is still loaded, it stops rapidly.
With this system, fuel to the engine is
shutoff in less than one engine revolution.

An engine overspeeding is one of the two

conditions that are allowed to shut the
engine down. Overspeed trips are normally
set to activate at 110 to 115% of the
engine’s rated speed. The overspeed trip
or overspeed governor normally is required
to be reset manually. The engine
overspeed is active under all engine
operating conditions and modes.

Rev 1/11 8-21 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-1 Droop-Isochronous Relationship

Rev 1/11 8-22 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-2 Basic Mechanical Governor

Rev 1/11 8-23 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-3 Basic Governor with Hydraulic Power Piston

Rev 1/11 8-24 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-4 Electronic Governor Hydraulic Actuator

Rev 1/11 8-25 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-5 EGB-10C Actuator Schematic

Rev 1/11 8-26 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-6 EGA Governor Control Box

Rev 1/11 8-27 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-7 2310A Control Panel

Rev 1/11 8-28 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-8 EGA Control Block Diagram

Rev 1/11 8-29 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-9 2391A Governor Control Box

Rev 1/11 8-30 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-10 2301A Control Block Diagram

Rev 1/11 8-31 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-11 Typical Magnet Pickup

Rev 1/11 8-32 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-12 MOP for 125VDC Motor

Rev 1/11 8-33 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-13 Schematic of MOP Unit

Rev 1/11 8-34 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-14 Digital Reference Unit (DRU)

Rev 1/11 8-35 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-15 DRU Connections

Rev 1/11 8-36 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-16 Relationship Between Governor Output & Fuel Control (Rack)

Rev 1/11 8-37 of 38 USNRC HRTD

Emergency Diesel Generator Diesel Engine Controls and Governing

Figure 8-17 Overspeed Trip (Governor) Mechanism

Rev 1/11 8-38 of 38 USNRC HRTD