ML20043F663

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Training Material for E-111 Emergency Diesel Generator Course, Chapter 10 (3-16), Emergency Diesel Generator Control and Monitoring
ML20043F663
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Issue date: 02/12/2020
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Office of the Chief Human Capital Officer, Woodard Corp
To:
Gary Callaway
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Emergency Diesel Generator EDG Control and Monitoring 10.0 EMERGENCY DIESEL GENERATOR systems and components are also required CONTROL AND MONITORING in order to start, run, and stop the diesel engine. It is essential that the engine be This chapter describes the control and monitored by the control system which can monitoring of the diesel generator as applies shut down the engine and generator in the to the nuclear plant application. event that there is a problem or failure in the unit. The purpose of this chapter is to tie Learning Objectives together the control and monitoring of the engine. The governor primarily controls the As a result of this lesson, you will be able to: speed of the unit. The EDG generator, its exciter system and the voltage regulation

1. Describe the functions of the control system were discussed in Chapter 9. The system in starting, running, and shutting voltage regulator controls generator output down the diesel engine. voltage by controlling generator excitation current. The generator output requirements
2. Describe the various parameters to be are dependent on the generator load.

monitored in order to ensure proper operation of the engine and generator. In addition to these very important controls, the engine must be started when required

3. Explain how the engine controls sense and stopped when not needed. The engine essential engine parameters and control must also be stopped when there is a these in operation of the engine. problem that continued operation would result in destruction of the engine and/or
4. Identify the key components of the generator. For that reason, the engine and engine protection system and state the generator operating parameters must be purpose or describe the function of each. monitored by the overall control system, and the proper steps taken when a problem is
5. Recognize various control components encountered.

of this system, how they are put together, and the various ways they could fail. Local control panels in the EDG room contain all of the instrumentation, meters,

6. Recognize signs of component controls, alarms, shut-down trips, and deterioration, impending failure, or actual lockout needed by the local operators.

failure. They can monitor EDG parameters, manually startup, increase speed,

7. Explain generator loading onto the synchronize with the grid, load onto the grid, engine. separate from the grid, operate the EDG at any speed, and shut it down. Controls 10.1 EDG Control Systems enable the operator to conduct technical specification surveillance tests. A local Chapter 8 discussed the governing system remote switch will provide the main control and its components necessary for proper room with the ability to monitor, control, and operation of the diesel engine. Other operate the EDG including synchronizing Rev 3/16 10-1 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring and loading onto the grid to conduct A generic plant FSAR assumes that specific surveillance tests. The local control panel protective features will be incorporated into has an extensive array of meters, indicator the emergency diesel generator control lights, and alarms, while the main control scheme. The following trips are provided to room has only those of highest importance. protect the EDG units at all times (not bypassed for ESF):

The local control panel has a keyed lockout switch which will prevent operating the EDG 1. Engine Over-speed from any input signals. This is for operator 2. Generator Differential Protection safety, when work is being done on the EDG system. NOTE: When locked out, the EDG NOTE: Additional trips may be permitted is 'unavailable' for emergency service and but only if coincident logic is provided, the the time duration for that condition is limited sensors are individually alarmed, and each by the plant's operating procedures. one can be individually tested.

10.2 EDG Protection Systems Lubricating oil at proper pressure and in sufficient quantity is provided by an engine-Some engine and / or generator parameters driven gear pump. Without proper require engine shutdown whenever a lubrication, engine wear surfaces problem is encountered in that area, even if deteriorate rapidly which can lead to the unit is running in emergency mode. component and engine failure. Since there Others are permitted to shut down the is little time until the unit would have ceased engine in test mode but not shut it down if in operation from its own internal deterioration, the emergency mode. Still others are simply and a redundant EDG is provided, there is monitored and an alarm given. Some items no justifiable reason for operating a diesel are monitored and displayed for operator generator without proper lubricating oil information, but are not alarmed nor will they pressure. Two independent indications of shut down the EDG. In this and following low lube oil pressure are required, with the sections we will discuss the parameters coincident logic previously discussed.

monitored and how their inputs are processed by generic protection systems. Similar reasoning applies to inclusion of generator time (voltage restrained) over-Emergency diesel generators are designed current protection. Operation of the diesel to start and operate automatically. During generator with a multi-phase fault on the periodic testing and surveillance, plant switchgear bus could quickly result in operators are assigned to the EDG to destruction of the generator. Since the monitor and control its operation. However, generator cannot maintain bus voltage during actual emergency conditions, under these conditions, there is no substantial time may pass before an justification for allowing this to occur when a operator would be on station with the EDG. redundant diesel generator is available.

Once on station, the operator needs only to Three separate measurements of over-monitor the engine operating conditions and current are provided with coincident logic to take the required logs. initiate a diesel generator trip.

Rev 3/16 10-2 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Over-speed protection is provided by a 10.3.1.1 Jacket Water Temperature gear-driven auxiliary mechanical / hydraulic governor and/or centrifugal switch A key monitoring point is the temperature of mechanism as described in Chapter 8, the jacket cooling water as it leaves the Section 8.4. engine. The engine manufacturer has set a recommended maximum temperature, In addition, the following trips are typically generally less than 200oF for low pressure provided to protect the EDG units during systems on EDGs, which should not be routine surveillance testing or runs made exceeded during normal operation.

following maintenance, but not during an emergency demand: Jacket water temperatures which climb above the recommended operational point

1. Jacket water high temperature for the engine are normally an indication of
2. Jacket water low level in expansion tank a problem developing. In some instances,
3. Jacket water low pressure the water or air sink temperature to which
4. Crankcase high pressure the unit rejects its excess heat may be too
5. Lube oil high temperature high to remove enough heat from the
6. Room fire alarm cooling system. Under such conditions,
7. Others may be included at plants option. reductions in engine load are recommended to reduce the heat load on the engine.

These trips are automatically bypassed in the event of an accident condition. The Under Engineered Safety Feature (ESF) design includes the capability for testing the actuation conditions, the temperature of the status and operability of the bypass circuit. jacket cooling water becomes secondary to Alarms of abnormal values of bypassed providing the needed power for plant parameters are in the control room. shutdown. At this point, any trips associated with jacket water overheating are bypassed, 10.3 Engine Parameter Monitoring and only an alarm is given.

10.3.1 Temperature Monitoring Other temperature sensors or transmitters may be located in the cooling system at a Generally, temperatures which are too high variety of points; however, the primary point are detrimental to engine operation. High for generic engine temperature monitoring is temperature can weaken the engine internal the "Jacket Water Temperature Out."

components, reduce clearances, and cause a chemical breakdown of the lubricating oil. 10.3.1.2 Lubrication Oil Temperature Monitors or sensors are installed at various As with the jacket cooling water, excessive locations in the engine to detect excessive temperature of the lubricating oil can lead to temperature and respond with an alarm. If engine damage and failure. As discussed in allowed to go unchecked, these Chapter 5, the lubrication system not only temperatures would eventually lead to provides lubrication for the engine damage or engine failure. components, it also serves a cooling Rev 3/16 10-3 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring function by removing excess heat from specified value (e.g. 228oF), the engine various points in the engine not cooled by should be shut down to assess the problem.

the jacket water system.

10.3.2 Pressure Monitoring In addition, chemical failure (break-down, of the lubricating oil) will occur if it is not Depending on the specific pressure being adequately cooled. This leads to reduced oil monitored, an alarm or trip may be initiated viscosity. Reduced oil viscosity will by a pressure either too high or too low.

ultimately result in metal-to-metal contact, friction, excessive wear, component 10.3.2.1 Lubricating Oil Pressure damage, and possible engine failure.

During engine operation, it is important to Temperature sensors are normally located maintain the proper lubricating oil pressure.

in the lubrication oil sump or in the exit piping Loss of sufficient pressure could lead to an from the sump. Specific locations within the insufficient flow of lube oil to key engine engine experience lubricating oil components. A severe loss of lubricating oil temperatures greater than those in the oil pressure will quickly result in engine failure.

sump, but these locations cannot be monitored easily or accurately. A lubricating oil pressure sensor or switch is normally connected to the main lube oil Typical high lubricating oil temperatures header. It monitors the lube oil pressure would be in the 180oF to 220oF range, being supplied to the majority of the engine depending on the design of the engine. As components.

with high jacket water temperature, high lube oil temperature trips would be It may be desirable to monitor lubricating oil bypassed during ESF conditions. Under pressure at selected locations other than the such emergency conditions, the engine main oil header. For example, oil pressure becomes sacrificial. is often monitored at the inlet to the engine turbocharger. A decrease in pressure at this 10.3.1.3 Main Bearing Temperature location may not be indicated by a sensor at the main oil header. A low pressure On some large engines, it is desirable to indication at the turbocharger inlet would monitor directly the temperature of the generally initiate alarm and not necessarily engine main bearings. Direct measurement engine trip.

here will indicate to plant operators the potential failure of an engine main bearing. 10.3.2.2 Engine Crankcase Pressure A temperature probe is shown on Figure 5- The general rule for large diesel engines is 17 in Chapter 5 (Lube Oil System). It is to maintain the crankcase at a slight placed in close proximity to all or selected vacuum. This reduces the chance for engine main bearing shells. Output circuitry crankcase explosions by preventing the provides for indication alarm and trip. buildup of potentially explosive hot oil Should the bearing temperature exceed the vapors.

Rev 3/16 10-4 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Crankcase pressure is monitored by a 10.4 Summary of Trips and Alarms diaphragm-type pressure switch, similar to the one shown in Figure 5-16 (Chapter 5). The following tabulation summarizes the Separate, spring-loaded explosion relief trips and alarms most often provided for doors (panels) are often provided. In the monitoring the diesel engine and its event of an explosion they pop open generator in nuclear applications. Consult automatically to relieve crankcase pressure FSAR for specific plant requirements:

then immediately shut to prevent the entrance of air, which could result in another 10.4.1 Shutdown-Trips with Alarms crankcase explosion, or fire.

Emergency Mode - Mandatory Trips 10.3.3 Engine Over-speed

  • Engine Over-speed Large diesel engines typically have some
  • Generator Differential Fault type of over-speed sensing device that acts independently of the governor, to shut down Trips allowed with Coincident Logic the unit before it reaches a speed at which (Typical-possible) engine damage is likely. It functions in any operating mode, including an emergency
  • Lube Oil Pressure Low-Low run. See 8.7 (Chapter 8) for discussion of
  • Jacket Water Temperature High-High over-speed trip mechanisms.
  • Crankcase Pressure - High
  • Generator Current - High 10.3.4 Vibration Trips
  • Generator Under Voltage-Low Excessive engine vibration can be the warning sign of an impending catastrophic Test Mode (Typical): The two Mandatory failure or simply an imbalance in power Trips listed above for Emergency Mode, between the engines cylinders. In either plus the following:

case, the condition requires evaluation and corrective action.

  • Lube Oil Temperature - High Vibration monitors sense axial (length-wise)
  • Crankcase Pressure - High and lateral (side-to-side) movement or
  • Jacket Water Temperature - High vibration and generate the appropriate alarm or trip as required. These monitors
  • Jacket Water Pressure - Low consist of spring- loaded weights (masses)
  • Fuel Oil Pressure - Low which respond to the amplitude and
  • Combustion Air (Manifold) Temp - High frequency of the vibration. Should the
  • Generator Over-current imbalance become severe enough, the
  • Generator Reverse Power weight becomes displaced against a spring,
  • Generator Loss of Field generating the alarm or trip signal.

Generally, vibration monitors must be manually reset after a trip has occurred. 10.4.2 Alarms - Any Mode - Any Time Rev 3/16 10-5 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring ENGINE PARAMETERS ** Input to generator lockout-86 Trip - Shuts down engine or trips gen breaker, in test.

  • Fuel Oil Level-Day Tank-Low
  • Starting Air Pressure-Low 10.4.3 Monitored Items
  • Start Failure Most items above are monitored, meaning
  • Intercooler Water Temperature-High their value is displayed on a gauge board or
  • Jacket Water Keep Warm Temp-Low control panel, and alarmed. The following
  • Jacket Water Pressure-Low items are monitored but are NOT ALARMED.
  • Jacket Water Level-Low
  • Cylinder exhaust temperatures with
  • Lube Oil Stainer Differential-High pre/post turbo temperatures.
  • Engine Speed (RPM)
  • Hours of operation (Hour meter)
  • Rocker Arm LO Pressure-Low
  • Engine Main Bearing Temperatures
  • Rocker Arm LO Lever-Abnormal
  • Generator Field Amps and Volts
  • Engine Vibration-High
  • Generator Phase Currents and Voltage
  • Loss of Control Power
  • Switch not in Auto
  • Generator Bearing Temperature
  • Engine Lockout Tripped (86DG)
  • Generator Frequency (Hertz)
  • Engine Ready to Load 10.4.3.1 Typical Monitored Item Values GENERATOR PARAMETERS ENGINE TEMPERATURES:
  • Generator Current-High (Over-Current)**

Individual Cylinder Temps 600-1200oF

  • Generator Field Current-High (Over Pre-Turbo Exhaust Temps 500-1300oF Excitation)

Cooling (Jacket) Water- out 140-195oF

  • Generator Field Current Low Cooling Water Delta T 8-10oF
  • Generator Ground Fault **

Lube Oil Temp - out 160-215oF

  • Generator Stator Temperature-High Lube Oil Delta T 20-50oF (one phase)

Inlet Manifold (post intercooler) 110-150oF

  • Generator Voltage-High / Low (over-Voltage)**

ENGINE PRESSURES:

  • Generator Frequency-Low/High (Under Frequency) Lube Oil to Engine/Header 30-80 psig
  • Generator Bearing Temperature-High Water Pump(s) outlet 20-50 psig
  • Generator Reverse Power ** Fuel Oil Pressure to header 20-30 psig
  • Generator Neutral Over-Voltage Blower Scavenged 4-8" H2O
  • Generator Lockout (86G Trip) Turbocharged @ rated load 15-30 psig Rev 3/16 10-6 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring 10.5 Typical Engine Control Circuitry An Emergency Start contact in the control room (or elsewhere) initiates a fast start by Engine control circuits can be conveniently picking up the ESS relay shown in Figure broken down into four functions: starting, 10-1. Picking up the ESS relay will in turn speed monitoring, stopping, and shutdown pick up the 4 relay. The 4 relay picks up the on fault. For this discussion, Figures 10-1 Air Start Solenoid Valves (ASV), which through 10-3 show those segments of the cranks the engine for starting. Note that the circuits and are explained below. ESS relay will cause a start whether the control switch is in the Remote or Local 10.5.1 Starting Circuit position, but not the Maintenance position.

Note also that a 4 contact in series with the Figure 10-1 shows a typical start circuit for ESS contact latches in the 4 relay. The TD2 the EDG. The circuit includes a relay CP1, relay is a timing relay set for 7 seconds. It is which monitors power on this portion of the in parallel with the 4 relay.

circuit. There is a similar relay (CP2 and CP3) in the circuits shown on 10-2 and 10-3 When the engine starts and accelerates, that monitor the power in those sections of first the LSR relay will pick up and then the the circuits. A contact on each of these HSR relay will pick up at their respective relays goes to an annunciator window to speed set points. The 4 relay and the ASV alarm if power is lost. Figure 10-1 also solenoid will be de-energized to complete shows the EDG Main Control switch on the the starting process. (The speed monitoring local control panel in the EDG room, used to circuit is shown on Figure 10-2.)

select the control mode of operation of the EDG. When the switch is in the 'REMOTE' If the engine does not start or get up to the position (thrown to the left), the unit can be LSR speed by the time TD2 has timed out started from the control room or other (7 seconds), the SFR (start failure) relay will remote location. When in the 'LOCAL' (mid) be picked up, and this will cause the 4, TD2 position, the unit can be started from the relays and ASV air start valve to drop out, local panel (but not from the control room). terminating the start attempt. An alarm is When the switch is in the 'MAINTENANCE' given when the SFR relay picks up. It is (right) position, the engine can be started possible to have a near miss. That is, the only by the operator at the local panel. This engine is slow to accelerate such that the position precludes EDG start if it is down for TD2 times out, but the engine goes ahead maintenance, when starting the engine and ultimately reaches the governed speed.

could cause damage to the engine or injury In this case, a start failure alarm will sound, to personnel. but can be ignored. The SFR relay is manually reset by the Engine Reset push The engine is routinely started by operating button.

a manual pushbutton switch located on the electrical switchboard in the control room or Note that this circuit very often is duplicated by either of two pushbutton switches on the such that there is a redundancy in the EDG local control panel, as permitted by the starting circuits and either circuit will start EDGs main control switch position. the unit.

Rev 3/16 10-7 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring 10.5.2 Speed Monitoring and Stop relay contact picks up and opens the circuit Circuits to the coil of the 5' relay. This terminates the stopping process and automatically Figure 10-2 shows the speed monitoring resets the circuit.

and stop circuitry. The speed control portion operates as follows. When the engine There is also a Normal Shutdown push achieves 125 rpm, the LSR relay is picked button in series with a normally closed ESS up. When the engine achieves 800 rpm relay contact for putting a stop signal into the (900 rpm rated speed), and the HSR relay is 5 relay. However, in this case, the signal is picked up along with the TD3 relay (a time ignored if there is an emergency start delayed relay set for 7 seconds). The signal present (ESS picked up).

electronic speed switch is connected to a signal generator mounted on the engine that There is also an SDR relay contact in the feeds in a signal of the engines speed circuit to shut down the engine in case of a (RPM). Many of the speed switches also fault in the system. The fault monitoring have a tachometer output to a meter on the circuits are shown in Figure 10-3.

engine gauge panel or in the control room so that the operator can monitor the 10.5.3 Fault Monitoring Circuits engines speed.

Figure 10-3 shows the typical fault The stopping portion of this circuitry follows. monitoring circuits. The EOS (engine It consists of an 'Emergency Shutdown' overspeed switch) is mounted on the push buttons that can be used to stop the engine. The 86T is the generator fault relay engine at any time whether there is an in the generator control panel. These emergency start signal present or not. Note switches are active at all times and will that the Emergency Stop switches are in cause the SDR (shutdown relay) to activate series such that both must be pushed to when either of them closes.

initiate a stop. In this way, an accidental push on just one switch will not initiate a The OPL1, OPL2, OPL3 are switches stop. This switch picks up the 5 and 5A (coincident logic) that monitor the Lube Oil relays. The 5 is an instantaneous relay, a Pressure at the engine Lube Oil Header.

contact of which picks up the SDS shutdown CCP is the Crankcase Pressure Switch.

solenoid. This solenoid may be in the CTHS is the Coolant Temperature High governor or may be part of the engine Shutdown Switch. OTHS is the Oil control system. Picking up SDS causes the Temperature Shutdown Switch. Note that fuel system to go to minimum fuel, and the CTHS and OTHS are active at all times.

engine will shut down. The 5 relay also Note that the OPL1, OPL2, OPL3, and CCP latches itself in the circuit. switches will activate only when their associated relays (OP1, OP2, OP3, and Because it takes some time for the engine to CPR) and TD3 have timed out (7 seconds roll to a stop, the signal to SDS must be after the engine has achieved 800 rpm or maintained for a time. This is the purpose of higher). The purpose of TD3 is to give the 5A relay. After 120 seconds, the 5A opportunity for the engine to establish lube Rev 3/16 10-8 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring oil and crankcase pressures before 10.5.5 Digital Instrumentation and monitoring starts. Also, a 5 relay contact in Control that circuit precludes getting these alarms when the engine is being shut down. The preceding presentations were of analog type instrumentation control and monitoring Note also that there is a series of OP1, OP2, systems. It takes very few relays to set up OP3 contacts in the shutdown logic of the the control system for a diesel engine. This SDR (Shutdown) relay. It takes closure of at control could be accomplished by some least two of these relay contacts to get a loss digital components. Instrumentation can be of lube oil pressure signal to the SDR relay, provided in digital format also. For this thus the coincident logic matrix. Also note presentation, digital instrumentation and the ESS normally closed contact in the control is broken down into three categories:

bottom line into the SDR relay coil. If there discrete devices, control devices, and is an emergency start signal present (ESS computer systems.

Picked up), then the shutdown relays to the right of that contact are not active (will not 10.5.5.1 Discrete Devices give a signal to pick up the SDR relay). This is the bypass trip function. This category would include instruments that could be provided in an analog or digital Upon being actuated, the SDR relay will format-that is the display of the value could cause a shutdown by picking up the 5 relay be in numbers / letters or by a pointer or as shown earlier. Also, the SDR relay is needle pointing to a value. Almost all analog latched in on its own contact. It is necessary instruments such as pressure gauges, to manually reset the SDR circuit when the temperature gauges, volt meters, fault has been cleared. ammeters, watt meters, tachometers, and so forth can be provided with a digital Other parameters could also be included readout of the value. In most cases, there is here providing they have a coincident logic a transducer (piezoelectric crystal) that matrix, similar to the one shown for lube oil operates under pressure or force or pressure monitoring. These could include differential temperature or motion to put out Jacket Water Temp -High, Crankcase a small voltage. This voltage is amplified Pressure-High, High Vibrations, etc. and converted to a digitized output by means of scaling the parameter as a 10.5.4 Summary number of words or bits. These are further processed to show a moving LED line or These circuits presented are typical. There actually put out as a alphanumerical are actually many variations, but the reading.

purposes are very much the same as those presented. There may be many more inputs Digital instruments have an advantage in to the monitoring, control, and shutdown that they are generally easy to read.

circuits. The alarm circuits usually go However, there are cases where an analog directly into the annunciator and are not meter is better for a particular situation. For covered in detail. instance, the electric governor output Rev 3/16 10-9 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring voltage to the engine-mounted actuator Very often the PLC can be connected to must be monitored using an analog meter. other computers so that the data within the This is essential because of the need to PLC can be forwarded to or received from know how the voltage is changing rather other PLCs or remote computers. Monitors than an exact value of the voltage. on such computers can display tables of Monitoring the voltage oscillations and their values, system or process diagrams, alarm rate and magnitude of change is essential status, and so forth.

for making proper governor adjustments.

Most digital meters have a sampling time A word of caution is in order. When a (1 sample per second, for example) in order computer system is connected to the PLC for the display to be stable, without dither on that is controlling the EDG, special the smallest digit. When monitoring a provisions must be made to guard against voltage that is changing, the digital meter the computer, computer viruses, and output appears to jump all over the place. unauthorized entry into the system being able to influence the PLC. In other words, Discrete devices typically can be calibrated the PLC should be in control, with data going for accuracy, but cannot be programmed or primarily from the PLC to the computer for adjusted over a broad range. Their monitoring purposes.

programming and operation are fixed by design. PLCs generally are programmable through a computer connection or a hand held 10.5.5.2 Programmable Control programming device. The programming is Devices generally in ladder logic and may be printed out for record purposes, or for circuit A computer can be programmed to receive operation analysis when theres a problem.

and analyze data from a control or High class PLCs may also contain PID loop monitoring system. When a computer is capability so they can control operating used, it has to have input and output parameters such as water temperature, air modules associated with it to convert field manifold temperature or pressure, etc.

data into digital data of some sort. Digital data may be in the form of bit changes per As in all computer systems, the problems second (or millisecond) or converted to a found in such systems are typically with the level by dividing the input into bits according transducers that bring information into the to a voltage or milliamp level. A better computer / PLC or put out commands to the approach to digital control is to use a devices in the systems. The second place dedicated computer system, usually to look is at the input / output modules of the referred to as a PLC (Programmable Logic PLC. A lot of time can be consumed in Control). Most of these have input and trouble shooting by thinking that the problem output modules that form a part of the PLC. is in the computer or PLC or its programming Their inputs can be digital (1 or 0, on or off), when its a bad input from a transducer or a binary level, or analog to digital conversion bad input/output module. Back up parts and as well as digital to analog conversion a good electronic technician are essential modules. for trouble-shooting these systems.

Rev 3/16 10-10 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring 10.5.5.3 Restricted Programmability 10.6 Engine-Generator Responses Devices There are a few important characteristics of This would include devices such as the the engine and generator which influence Woodward 2301D and 723 governing their responses to a change in loading on systems, including the Digital Reference the EDG. They are as follows:

Unit (DRU) referred to in Chapter 8. These devices have limited programmability and 1. The governor controls and/or responds are only programmable by a special to the change in KW loading. The engine programming module or software package. does not respond to changes in KVAR Once adjustments are made and the loading except as that subtly effects the programmer is removed, the operating generator efficiency.

parameters can only be changed by again connecting the programmer. In the case of 2. The voltage-regulator and exciter control the DRU, and 2301D, there are adjustments and/or respond to changes in the KVA made via potentiometers and some internal on the system, that being made up of switches. The programming is thus limited both the KW and KVAR loading.

to these certain adjustments. These devices typically do not involve 'software' 3. The KVAR loading on an isolated system per se. Some use EEPROMS that (not in parallel) is a result of the nature of remember the programming once the the load on the unit. If the unit is carrying programmer is removed. primarily motor loads, the power factor will be less than 1, and there will be 10.5.5.4 Programming (Source) Code KVAR load. A strictly resistive load results in KW only - no KVAR (unity PLCs and computers may have power factor). Loaded induction motors, programming that can be printed out or the type commonly used to drive heavy manipulated via a programming system loads such as the large pumps used for (programmer) or by special software. Very core cooling, typically result in a power often, the most deeply imbedded code is factor of about 85% (0.85).

considered proprietary and cannot be viewed or manipulated by the system It is important to understand what happens operator. Thats the case with Woodward when a load is applied to the diesel digital governors and other controls. While generator set, particularly if large motors are internal constants can be adjusted via the started. Figures 10-4 and 10-5 show a trace programmer, the whole code is not visible. of the speed (Hz) and voltage during the This restriction is to protect property rights starting of a large motor. Before a load is and also to ensure that some unknowing applied, the governor is giving the engine person cannot make changes to the code just enough fuel to maintain speed at the that would cause the equipment to existing load. The exciter system is giving malfunction, thus putting the supplier under the generator field just enough current to jeopardy for loss of function, property maintain the voltage at the existing electrical damage, or injury or loss of life. load. The system is in balance.

Rev 3/16 10-11 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring As the motor load is applied, it requires a motors speed-torque curve it accelerates, large inrush of current into the systems. including a peak in the KW curve as the Typically, motor inrush starting current motor pulls into synchronism with the (sometimes referred to as locked rotor system. The bottom of the Figure shows the current or SKVAstarting KVA) may range motor KW curve and resulting load change.

between 5 and 8 times the motors normal Because of voltage dip, there was some full load current. This inrush of current softening of the effect on KW the engine causes the EDG voltage to drop since the sees at the beginning of the motor start.

exciter system is only applying enough excitation to sustain the prior existing loads. The frequency trace on the Figure 10-5 The voltage regulator senses the voltage dip curve begins to show deceleration as the and immediately begins to increase the field motor load is applied. The governor takes current. However, due to the magnetic time to recognize a speed and / or load inertia within the generator, it takes about change and can then begin to change the 0.01 to 0.03 seconds for the generator to fuel to the engine. It also takes time for the begin to utilize the new field current. electrical signal from the control box to have Therefore, the voltage dips to an extent that an effect on the hydraulic circuits in the is proportion to the new load applied (SKVA) actuator, and it takes time for the actuator to and the generators overall characteristics move the fuel racks on the engine (because (the reactances). of the momentum of the fuel linkage). Once the fuel to the engine has changed, there is When the generator receives the additional still a one-cycle time delay. Engine field current, it begins to recover to rated cylinders receive fuel only one time during volts. As the motor accelerates, it continues their cycle. On a 2-cycle engine, that is one to draw a high current until the point it pulls revolution. On a 4-cycle engine, it takes two in to 'synchronism' with the generator. At revolutions for all of the cylinders to receive this point, the motor current drops rapidly to a new ration of fuel. The general rule is that the motor load current. Because the motor only half of the cylinders of an engine that current was still high during the acceleration, fire in one revolution will receive fuel on that but now quickly drops down to a more revolution. So, there is a delay in the normal current, the voltage regulator takes engines response to a new fuel setting.

time to sense the need for less excitation current which causes voltage overshoot. All of these delays add up to about 0.2 to 0.4 The voltage trace on Figure 10-4 shows the seconds on a 2-cycle engine and 0.3 to 0.5 voltage dip and the over-shoot aligned with seconds on a 4-cycle engine. This is shown the motor speed curve. on the graphs as 'System Dead Time.'

During the system dead time, nothing is In the meantime, the engine detects a really happening except that the engine is change in the KW from the motor start. As decelerating at a rate proportional to the the motor starts, it has to develop a torque new load just applied and the inertia of the to cause it to accelerate. This torque reflects engine and generator. If full load is applied, itself onto the engine as a change in KW the rate of the deceleration will be twice that through the generator. The KW mimics the for half load.

Rev 3/16 10-12 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring As soon as the cylinders receive their for BMEP in Paragraph 2.3.2.3 (Chapter 2):

additional fuel required to pick up the added load, the engine begins to accelerate to return to rated speed. The engines rate of =

396,000 recovery is proportional to its total output load capability and the total of all the loads it is required to pick up and accelerate. This You can see it contains a speed term. If the includes overcoming and increasing the engine speed drops, the BHP also drops for inertia of the entire rotating engine and the same amount of fuel (BMEP). If the fuel generator components. Therefore, it can pumps bump up against the engines take considerable time to recover the maximum fuel stop, the engine is limited in frequency, especially if the engine is heavily BHP and that is affected by the speed.

loaded by the time it is recovering. Therefore, the last of the recovery curve may be fuel / speed limited.

There are some other things that also affect the engines ability to recover. If the engine If the speed drops far enough and the is highly turbocharged, it may also lack air generator is capable of maintaining the KW as well as fuel during the recovery process. load (KW is dependent entirely on the This is shown in the upper section of Figure system load and voltage), the engine may 10-5. If the new load is small, the engine not be capable of putting out enough probably has enough air to immediately horsepower to overcome the KW loading begin to recover at the end of the system from the generator. In this case, the engine dead time. This is shown by the dashed line. will continue to decelerate to a point the If the load is large, then the engine may not power at that frequency may not be useful.

have the required air to burn the fuel, even though the governor has made a correction The bottom of Figure 10-5 shows a typical to fuel. In this case, the engine is slow to situation wherein the motor load is large and recover. There may be more frequency dip the load already on the unit is considerable.

after the end of the system dead time as In this case, the frequency dip mimics the shown by the solid line. inverse of the motor KW curve and recovery does not begin until the motor has pulled in.

Immediately after the dead time, the engine If this is a very large motor and is slow to is shown continuing to decelerate. During accelerate, it may be difficult for the engine this time, the engine is putting out more to recover the frequency in a short time, as exhaust energy which begins to accelerate shown.

the turbochargers that will begin to provide more air flow. As more air is provided, the It is important to realize that the situations engine begins to accelerate more quickly, as described are very dynamic in character and shown. If the frequency dip was great vary greatly from plant to plant and situation enough, there may develop a point at which to situation. They are presented here only there is enough air but now not enough fuel to provide a feel for the complexity of or speed. Brake horsepower (BHP) can be response and operation of EDGs when they expressed as follows, derived from the formula suddenly have to pick up very large loads.

Rev 3/16 10-13 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring It is not possible in most nuclear plants to actually run a LOCA or LOOP condition with all of the associated equipment operating as it would in the actual circumstance of the real situation. Very often, computer programs are used to analyze what will happen and what frequency and voltage excursions may be expected when the plant scenario is to be changed or a change is anticipated. These programs are only effective if all of the inputs can be verified and all assumptions are relevant. Even then, they have to be taken with a grain of salt in as much as it is not possible in most computer programs to account for all of the possible effects.

Rev 3/16 10-14 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Figure 10-1 Starting Circuitry Rev 3/16 10-15 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Figure 10-2 Speed Monitoring and Stop Circuitry Rev 3/16 10-16 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Figure 10-3 Fault Shutdown and Monitoring Circuits Rev 3/16 10-17 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Figure 10-4 Motor Starting Load Rev 3/16 10-18 of 19 USNRC HRTD

Emergency Diesel Generator EDG Control and Monitoring Figure 10-5 Typical Loading Situation Rev 3/16 10-19 of 19 USNRC HRTD

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