ML20043F658
| ML20043F658 | |
| Person / Time | |
|---|---|
| Issue date: | 02/12/2020 |
| From: | Office of the Chief Human Capital Officer, Woodard Corp |
| To: | |
| Gary Callaway | |
| Shared Package | |
| ML20043F634 | List:
|
| References | |
| Download: ML20043F658 (28) | |
Text
Emergency Diesel Generator Diesel Engine Starting Systems 7.0 DIESEL ENGINE STARTING facilities must be capable of achieving a SYSTEMS minimum voltage and frequency upon initiation of a "start" signal. Both conditions This chapter presents the requirements for must be achieved within an acceptable time starting a diesel engine for an EDG in a frame that meets the plants Technical nuclear plant and the equipment and Specifications.
systems required to accomplish it.
Typical specifications involve the engine Learning Objectives starting from keepwarm conditions and accelerating to a minimum, self-sustaining As a result of this lesson, you will be able to: rotational speed (RPM). Simultaneously, the generator must establish the required
- 1. Describe the requirements for starting an voltage and frequency all within the time Emergency Diesel Generator in a limits specified. An example of a set of nuclear plant application. typical EDG specifications is given below:
- 2. Identify the components and describe
- 60 Hz + 1.2 Hz the operation of a direct air injection, com-pressed air diesel engine starting
- Rated Voltage (4000 + 320 volts) system.
- < 10 seconds
- 3. Identify the components and describe the operation of an air motor type, com- 7.2 Starting Characteristics pressed air diesel engine starting system. By reviewing the operational characteristics of the diesel engine, we can gain a better
- 4. Identify the components and describe understanding of what is required of the the operation of a typical starting air starting system.
supply system used in a nuclear plant application. 7.2.1 Admission of Air
- 5. Identify the components and describe A fresh charge of air must enter the cylinder the operation of an electric diesel engine during the intake event to provide the starting system for a nuclear application oxygen required to support combustion of diesel engine. the fuel. This is accomplished by either of two ways. For a 4-stroke cycle engine, this 7.1 Technical Specification Starting is accomplished by the downward motion of Requirements the piston during the intake stroke. For a 2-stroke cycle engine, the pumping action of In accordance with the applicable regulatory the engine-driven blower (either positive requirements, emergency diesel generators displacement or centrifugal) delivers the air specified for use as emergency onsite charge to the cylinders.
power supplies at commercial nuclear Rev 3/16 7-1 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems 7.2.2 Compression of Air Charge function of the compression pressure minus any pressure lost past the piston rings and Once the cylinder has been charged with valves and any heat lost to the incoming air fresh air, the rapid upward or inward charge or relatively cool internal movement of the piston compresses the air components of the engine. Assuming the charge, increasing its temperature to a point engine is mechanically sound, the higher than that required to ignite the fuel. compression, and therefore ignition temperature, becomes a function of the 7.2.3 Injection of Fuel engine compression ratio, valve or port timing, and cranking speed.
With the piston near to top or inner most point of its stroke, fuel is injected into the The single most important element in heated air charge where combustion occurs attaining the compression pressure, and and power is delivered to the crankshaft. As therefore the air charge temperature the cylinders begin to fire, the engine required for ignition of the fuel, is the achieves self-sustained operation. cranking or rotational speed of the engine during the starting sequence. Figure 7-1 For the three activities listed to occur, the depicts a typical relationship between the engine crankshaft must be rotated by an cranking speed (RPM) and the compression external source of power. The engine pressure (PSIG) achieved for a high speed starting system stores energy either as diesel engine. Several factors contribute to compressed air in the systems air receivers this relationship:
(the term commonly used for compressed air tanks), or as chemical energy in the
- The more rapid the rate of compression designated storage batteries. is, the higher the pressure and temperature of the air charge.
Upon initiation of a start signal, the stored energy is converted into the mechanical
- Rapid compression allows less time for energy needed to rotate the engine pressure to be lost past the piston rings components. and valves.
7.2.4 Compression Characteristics
- At higher cranking speeds, less time is available for the heat of compression to Charging the cylinder with air and injecting be lost to relatively cool metal surfaces the fuel at the proper time are basic that surround the combustion space.
functions of crankshaft rotation. Crankshaft rotation also causes the air charge to be 7.3 Starting System Capability compressed; however, the rotation alone does not ensure the air charge will reach the In addition to the engine start criteria listed temperature needed to ignite the fuel in section 7.2, the EDG starting system must injected into the cylinder. have capacity and redundancy that are commensurate with the safety function of The actual air temperature achieved is a the unit.
Rev 3/16 7-2 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems 7.3.1 System Capacity 7.3.3 Energy Storage System Each starting system must have an energy storage capacity sufficient to support a The energy required for starting the EDG is specific number of start attempts prior to stored as compressed air in designated air reaching a low energy level (e.g. low air receivers or as chemical energy stored in a pressure, low battery voltage). For battery bank. In either system, a minimum example, a starting air system may be energy level must be maintained at all times required to perform two consecutive start for the unit to be considered operable.
attempts before reaching a specified low pressure of 150 psig. With the compressed air systems, the receivers must be kept above a minimum The generic nuclear application starting air pressure. This is accomplished by air system also provides control air for diesel compressors which automatically recharge engine controls and instrumentation during the system when the low pressure limit is standby and during operation. The control reached. For electric powered systems, the air portion of the Starting Air System will be batteries are maintained at a voltage above discussed in Chapter 10, "Emergency the minimum electrical storage capacity by Diesel Generator Control and Monitoring." the battery charging systems. The electric system will be discussed in greater detail 7.3.2 System Redundancy later in this chapter.
To preclude a single failure, which could 7.4 Starting Air Systems prevent the engine from starting, each unit is required to be equipped with two parallel, There are two types of compressed air non-connected redundant starting systems. starting systems used in nuclear plant Each system must be capable of starting the applications: the direct air injection system EDG in the event of a failure in the other shown in Figure 7-2A and the air motor system. system shown in Figure 7-2B. In both systems, air is stored under pressure in air In some specifications, the requirement was receiver tanks. Quick opening solenoid-to attempt to start the engine on one system operated air admission valves prevent air and then go to the second (redundant) from reaching the engine until actuated by system if the engine failed to start. This an engine start signal.
philosophy wastes time and probably results in a failed start in that the unit would not be 7.4.1 Direct Air Injection Systems up to rated speed in the required time.
This system is also often referred to as the All of the systems furnished to date use both 'air over piston' or the 'cylinder air start' systems simultaneously (in tandem) such system.
that if one system failed, the other system would automatically start the unit with only With the direct air injection system (Figure an extended time probable, but not a failure 7-2A), air under pressure is applied to the to start. inlet of the Starting Air Admission Valve and Rev 3/16 7-3 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems to the Starting Air Solenoid Valve. With no The Solenoid Valve then closes, allowing start signal present, both valves remain the Air Admission Valve to close. Air then closed. Upon receiving a "start" signal, the vents from the Starting Air Distributor and Solenoid Valve opens, directing air to the Air Starting Air Header. This allows the spring-Admission Valve pilot section, causing the loaded Starting Air Check Valves to close main valve to open. and returns the engine starting air system to the standby mode.
Downstream of the Air Admission Valve, the air flow is split. The major portion of the air 7.4.1.1 Starting Air Admission Valves is passed to the Starting Air Header. A small portion of the air is also directed to the Figure 7-3 shows a typical pilot-operated, Starting Air Distributor. Air from the Starting poppet type Starting Admission Valve. The Air Header enters each of the Starting Air Solenoid Valve is generally mounded Check Valves. Starting Air Check Valves, directly to the Admission Valve. In other where used, are mounted in each of the applications, the Solenoid Valve may be engine cylinder heads. For the Fairbanks- mounted remotely to the Admission Valve Morse Opposed Piston engine, the starting and connected by pipe or tubing.
air check valves mount through the wall of the cylinder liner. The design of these In the standby mode, the spring-loaded valves is such that they will remain closed valve poppet is held in the closed position by until acted upon by a pilot signal from the the force of the spring. Air from the air Starting Air Distributor. receiver enters the valve as shown. The design of the valve poppet is such that the The Starting Air Distributor, driven by the air pressure acting against the poppet is engines camshaft or accessory drive gear balanced by the equal areas of the valve train, provides a pilot air signal in proper poppet. The force of the spring is sufficient sequence to each of the Starting Air Check to keep the valve closed. A portion of the air Valves. At the appropriate time, usually a entering the valve (pilot air) is directed to the few degrees past Top Dead Center (TDC), inlet of the Solenoid Valve. In standby, the the pilot air signal is applied to each Starting Solenoid Valve is also closed (not Air Check Valve, causing it to open. Starting energized).
air, under pressure, is admitted directly into the engine cylinder. This air pressure When a "start" signal is generated, it is rapidly pushes each piston downward in applied to the Solenoid Valve. This signal succession. As each piston is later moving energizes the solenoid coil. The magnetic upward, the air charge is compressed in field created lifts the valve plunger, opening preparation for injection of the fuel. the valve. Pilot air is then directed through the signal port (orifice) to the top of the pilot As the engine achieves self-sustained piston (part of the valve poppet). The force operational speed, a signal from the control of the air pressure applied to the pilot piston system shuts off the starting air supply. This exceeds the force of the spring holding the is usually controlled by a speed sensing poppet in the closed position. This device monitoring the engine speed (RPM). differential force causes the valve poppet to Rev 3/16 7-4 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems move downward, opening the valve. Air cam or vent position by the force of the from the air receiver passes freely through spring as shown in Figure 7-5. This the valve and on to the Starting Air Header prevents the spool valve from contacting the and Starting Air Distributor. timing cam during normal engine operation or standby.
Loss of a "start" signal closes the Solenoid Valve, which vents air from the pilot piston. When a 'start' signal is generated, the air Spring force causes the valve poppet to admission valve opens supplying high close returning to a standby mode. pressure starting air to the internal passages of the distributor housing. This air pressure 7.4.1.2 Starting Air Distributor forces the spool valves downward into contact with the timing cam as shown in Since the Starting Air Check Valves must Figure 7-6. In the high cam position, the open at a specific time relative to the spool valve is held in the vent position, and position of the piston in the cylinder, a no pilot air signal is applies to the associated Starting Air Distributor is needed and Starting Air Check Valve.
provided. The Starting Air Distributor, which is timed from the engine camshaft(s) or Rotation of the timing cam will eventually other portion of the engine gear train, directs align the low portion of the cam with the a pilot signal to each Start Air Check Valve, spool valve as shown in Figure 7-7. The when the piston is slightly after top dead pressure of the starting air from the internal center and maintains that signal until the passages of the distributor housing will keep movement of the piston reaches the spool valve in contact with the timing approximately 120 after top dead center. A o cam. The spool valve moves downward typical Start Air Distributor is shown in blocking the vent port and connecting the Figure 7-4. Starting Air Check Valve port. Starting air pressure is then applied to the pilot piston of The Starting Air Distributor consists of a the associated Start Air Check Valve, series of spool valve assemblies, one for opening the valve and allowing starting air to each Starting Air Check Valve. One enter the engine cylinder. When the timing assembly for each cylinder is mounted in a cam has moved beyond a spool valve common housing. The timing cam, timed to position, the spool valve is returned to the the engine, causes each spool valve to vent position and the air signal is removed direct pilot air pressure to or vent the from the Starting Air Check Valve.
pressure from each of the Starting Air Check Valves. Operation of the spool valve With cessation of the 'start' signal, the Air assemblies is shown in Figures 7-5 through Admission Valve closes allowing the air to 7-7. vent from the Starting Air Distributor internal passages. This loss of air pressure allows With the starting air admission valve closed, the force of the spring to lift the spool valves no air is applied to the Starting Air off the timing cam. All of the spool valves Distributor. With no air pressure present, will be returned to the off/vent position, and the distributor spool valves are held in the off the starting process will be terminated.
Rev 3/16 7-5 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems 7.4.1.3 Starting Air Check Valves pilot air signal, which is applied to the pilot piston, overcomes the spring force holding In the start mode, air from the Starting Air the valve closed. This opens the Starting Air Header is delivered to each of the Starting Check Valve allowing starting air to enter the Air Check Valves mounted in the engine engine cylinder.
cylinder heads. In the Fairbanks-Morse Opposed Piston engine, the Starting Air The pressure of the starting air entering the Check Valves mount through the wall of the engine cylinder is applied to the top of the cylinder liner adjacent to the fuel injection engines piston forcing the piston downward nozzle. A typical Starting Air Check Valve is and causing rotation of the crankshaft. This shown in Figures 7-8 and 7-9. rotation subsequently causes upward motion of other engine pistons. As each The air start check valve assembly includes engine piston moves upward on the a poppet type valve which is located in a compression stroke, the air in that cylinder precision bore cast body or housing. A is compressed to achieve the temperature spring applied to the upper end of the valve required for ignition.
keeps the valve in the closed position. The design of the valve including the balance Rotation of the crankshaft also causes piston is such that the starting air entering rotation of the timing cam for the Starting Air the valve body is balanced. Starting air Distributor (see Figure 7-4). As the engines pressure acting against the valve is piston nears the bottom of its stroke, the balanced by the air pressure acting against Starting Air Distributor closes the associated the equal area of the balance piston. The valve port and vents the pilot air signal from force of the spring is sufficient to hold the the Starting Air Check Valve. This allows valve in the closed position. A pilot inside the spring to return the valve to the closed the piston cap rests against the tip of the position. As this occurs, other Starting Air valve. Check Valves are receiving the pilot signal which results in a continuous rotation of the Initiation of a start signal opens the Air engine until engine start is achieved or the Admission Valve allowing air to enter the start signal ceases.
housing as shown. The balanced design of the valve maintains it in the closed position The Starting Air Check Valves have to until a pilot air signal is applied to the pilot remain closed during normal engine piston. operation. If a Starting Air Check Valve should leak or fail to close, the combustion As mentioned previously, air from the gases from the cylinder will leak out of the Starting Air Admission Valve is directed to Starting Air Check Valve and it will become the Starting Air Distributor as well as the extremely hot (possibly glowing), and may Starting Air Header. The Starting Air further seize. It is important to occasionally Distributor is timed to direct a pilot signal to check the Starting Air Check Valves and the the Starting Air Check Valve, when the associated Starting Air Supply Header to piston for the cylinder involved is just past determine that none of the valves are top dead center. The force supplied by the leaking.
Rev 3/16 7-6 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems 7.4.2 Starting Air Motor System volume between the rotor and housing increases.
In the air motor system, shown in Figure 7-2B, engine rotation is accomplished by a The pressure differential between the air rotary vane or piston type air motor which inlet and the exhaust (atmospheric engages with a ring gear mounted to the pressure) creates the torque necessary for periphery of the engine flywheel. During a the rotor to rotate. As the starting air start sequence, the drive mechanism of the reaches the exhaust port, it is exhausted to starting air motor engages with the flywheel the atmosphere as pressurized air continues ring gear. Air entering the starting air motor to enter the inlet.
then causes rotation of the engine crankshaft. The power and rotary motion of the rotor is transmitted through shafts and in some Upon completion of the start sequence, the applications, through gears to the starter air is shut off and vented. This allows the drive gear which is engaged with the starting air motor to disengage from the flywheel ring gear. The subsequent rotation flywheel gear. of the engine flywheel and crankshaft is used to generate the engine start.
7.4.2.1 Starting Air Admission Valve 7.4.2.3 Start Drive Gear - Bendix The Starting Air Admission Valve used with the air motor system is similar to that used As the starting air motor in required only in the direct injection system. Notice in intermittently, a drive mechanism is Figure 7-2B that the solenoid valve is not provided which will engage and disengage connected directly to the Air Admission the starter from the flywheel ring gear as Valve but feeds the pilot signal through the needed. A starter drive gear, often referred drive mechanism of the Starting Air Motor. to as a Bendix, is shown in Figure 7-11.
With this configuration, the Starting Air Motor drive fully engages with the flywheel The starter drive mechanism that is shown ring gear prior to achieving rotation of the mounts either directly to the rotor shaft or to Starting Air Motor. an output shaft via a set of reduction gears.
Where used, the reduction gears allow the 7.4.2.2 Vane Type Air Motors rotor to rotate at a high RPM while increasing the overall output torque. A drive A typical vane type Starting Air Motor is gear is provided which will mesh with the shown in Figure 7-10. It consists of a rotor teeth of the ring gear on the flywheel.
mounted off center within a cylindrical housing. A set of sliding vanes radiate When the starting motor is not required to outward from the rotor to make contact with rotate the crankshaft, the drive gear the bore of the housing. As air enters the assembly is spring loaded in the disengaged inlet of the housing, the pressure is applied position. A drive piston is provided to to the sliding vanes as shown, causing the engage the drive gear with the flywheel ring rotor to rotate. Air continues to enter as the gear during the start sequence.
Rev 3/16 7-7 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems To prevent over-speeding of the starting air 7.4.3 Supplemental Components motor as the engine begins to fire, an overrunning clutch is incorporated between In order to meet the "fast start" requirements the drive gear and the rotor shaft. This of diesel engines in nuclear applications, it clutch mechanism engages the rotor shaft is necessary to move the fuel racks to the with the drive gear when the starting motor full fuel position as soon as possible. The is driving the engine flywheel. As the engine following two devices are employed to work RPM increases, the speed of the drive gear with the starting air system to bypass the is greater than that of the rotor shaft. At this governor and give the cylinders full fuel point, the clutch mechanism releases the during the start sequence.
drive gear from the rotor shaft, thereby disengaging the starter.. The drive gear can 7.4.3.1 Governor Boost Cylinder continue to rotate with the engine flywheel without transmitting that high speed to the A governor boost cylinder, as shown in starting motor rotor assembly. Figure 7-12, is mounted to the side and below the level of the governor housing. It 7.4.2.4 Starting Motor Operation is hydraulically connected to both the governor oil sump and to the governor When a start signal is received, the power piston housing.
solenoid valve opens (see Figure 7-2B) directing air pressure to the drive piston port The boost cylinder is simply a pneumatic-in the starter housing as shown in Figure 7- hydraulic cylinder with a spring loaded
- 11. This air pressure moves the drive piston piston. As the force of the spring moves the causing the starter drive gear to engage with piston down, oil is drawn from the governor the engine flywheel ring gear. This piston oil sump through the inlet check valve to fill movement also opens an outlet port which the volume above the piston. The volume directs pilot air pressure to the pilot port of below the piston is connected to the starting the starting air admission valve causing it to air header.
open.
When a start signal is generated, air under With the air admission valve open, full pressure from the starting air header or starting air pressure is directed to the inlet of supply pipe to the air start motor enters the starting air motor causing it to rotate, below the piston forcing it upward sharply.
driving the flywheel ring gear and rotating This discharges the oil above the piston past the engine crankshaft. When the start the outlet check valve to the governor power signal is turned off by the control system, the piston. This increased oil pressure quickly solenoid valve closes blocking air flow to the moves the fuel control linkage to the full fuel starter drive piston, which disengages the position ensuring a rapid engine start and drive gear and blocks the air flow to the air acceleration.
admission valve. Loss of the pilot signal to the pilot piston of the air admission valve The oil supplied by the boost cylinder bleeds allows the valve to close, returning the start off through the internal passages of the system to the standby mode. governor as the governor takes over Rev 3/16 7-8 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems operation of the fuel control linkage. The 7.4.4 Starting Air Supply System outlet check valve prevents governor oil pressure from entering the boost cylinder. Regardless of the type of starting air system Closure of the starting air admission valve used, sufficient air pressure and volume drops air pressure from the boost cylinder must be available at all times to ensure and the spring again moves the piston engine start capability. The air to support downward, refilling the space above the engine starting is automatically maintained piston with oil from the governor oil sump. in ASME Class 3 air receivers located near the engine. It is the starting air supply On the actuators used with the electronic system which maintains the air pressure and governing systems (to be discussed in volume in these receivers. A typical starting Chapter 8), the boost oil does not actually lift air supply system is shown in Figure 7-13.
the power piston but charges portions of the Starting air piping is ASME Class 3 and hydraulic circuit with oil which allows the designed for seismic loading.
governor to take control earlier than would be the case without the boost oil. 7.4.4.1 Air Receivers 7.4.3.2 Shuttle Valve Compressed air receivers are cylindrical pressure vessels whose design and When only one boost cylinder is used, a construction is governed by the shuttle valve is installed to maintain the requirements of the ASME Boiler and redundancy and separation required by Pressure Vessel Code, Construction of nuclear specifications. Unfired Pressure Vessels. The generic plant air receivers are designed to conform Under normal conditions, the shuttle valve to the requirements of ASME Code, Section takes a center position directing air from III for Class 3 components.
both headers to the underside of the boost cylinder piston. However, should a failure of Their specific size (volume) is a function of one of the redundant systems occur, the air the size of the engine they are required to pressure from the operational side causes start and the number and duration of start the shuttle valve to shift blocking off the attempts specified by the FSAR. The failed side and directing air from the generic FSAR requirement is to have air operational side to the boost cylinder. storage capability to provide two (2) consecutive diesel engine starts. The two 7.4.3.3 Other Fuel Rack Boost Systems (2) start capability is required to assure that the engine can help mitigate the Some engines such as the Colt Pielstick consequences of design basis events (e.g.
engine line include fuel rack boost cylinders LOCA). A number of the later plants and shuttle valves that are part of the engine specified capacity for five (5) start attempts, fuel rack control system. These units do not a starting attempt generally taking more air use the governor boost cylinder system as than a successful start. NOTE: If either described above. starting air receiver is inoperable on one diesel, then the diesel is inoperable.
Rev 3/16 7-9 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems 7.4.4.2 Air Compressors 7.4.4.3 Pressure Switches Starting air compressors are normally of the Operation of the compressor is controlled by reciprocating (piston) type. They are usually a pressure switch located on the air multiple-stage, multi-cylinder types with receiver. Set at a specified "cut-in" cylinders configured in a V or W. They pressure, the switch starts the compressor may be either air cooled or water cooled. when the pressure becomes lower than the set pressure and allows the compressor to Compressor capacity is based upon the run until the receiver is at or slightly above amount of time required to recharge the the desire operating pressure. As the air receiver from a specified (cut-in) pressure to pressure reaches the operating pressure, the desired operational pressure. the pressure switch opens the circuit, Compressor capacity may be determined stopping (unloading) the compressor.
using the following formula:
7.4.4.4. Pressure Relief Valves
( 2 ) ( 1 ) To protect the system from over-
= pressurization, pressure relief valves are 15 installed near the discharge of the Where: compressor and on the starting air receiver.
The safety valve near the compressor D = Compressor capacity, cubic feet of discharge is normally set at 115% of the free air per minute rated operating pressure. The safety valve installed on the air receiver is normally set at V = Volume of the Receiver, cubic feet 110% of rated pressure.
P1 = Cut-in Pressure, absolute (PSIA) 7.4.4.5 Aftercoolers P2 = Desired operating pressure, As air is compressed, its temperature absolute (PSIA) increases substantially. This reduces the T = Recharging time, in minutes density of the air being discharged from the The generic starting air compressors are compressor. To compensate for this designed to deliver 40 SCFM at 250 psig. condition, aftercoolers are installed They require Class 1E power and are downstream of the compressors. Either air indirectly tested by diesel start tests. cooled or water cooled, these aftercoolers cool the air to100oF prior to its entering the If two compressors are inoperable on one air dryer. Air-cooled units often use force diesel, then the diesel is inoperable. draft fans to increase their cooling capacity.
In some specifications, the air compressors 7.4.4.6 Air Dryers were sized such that the tanks had to be charged from atmospheric pressure to high Air taken from the atmosphere contains a cut-out pressure within 30 minutes. certain amount of moisture (humidity). Air-Rev 3/16 7-10 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems operated equipment including starting air cylinders and position engine fuel racks motors and various valves may become during starting. Control air continues to damaged or degraded if exposed to excess pressurize the run/shutdown cylinders to moisture in the compressed air. Moisture support EDG operation. Solenoid valves may be carried by the air into the air control the air flow during start and run receivers. This moisture may condense and sequences. The solenoids are powered collect in the receiver causing localized from a Class 1E DC power supply. If the corrosion. This corrosion could lead to control air solenoid valves are inoperable, weakening of the receiver and failure of the then the EDG is inoperable.
components. Moisture carried by the air past the receiver into the system can 7.5 Electric Starting Systems damage the starting air system components and / or restrict air flow through small orifices Electric starting systems utilize direct and passages. current (DC) motors which engage with a ring gear on the engine flywheel as with the Air dryers usually use a combination of starting air motor system. A set of batteries desiccant and temperature reduction are installed to provide the necessary (refrigerants) to remove unwanted moisture electric energy needed to operate the from the compressed air. As the air passes motors.
through the desiccant tower, the pellets of desiccant absorb and hold the moisture. 7.5.1 Electric Starting Motor Periodically, heated air is passed backwards through the desiccant tower to dry out the A typical electric starting motor is shown in desiccant pellets preparing them for further Figure 7-16. The main structural use. components of the assembly are the field frame, lever housing, and nose housing.
The combination of these two methods Field windings, anchored to the field frame, removes most of the moisture from the produce a strong magnetic field when compressed air prior to its reaching the energized. The armature with its receiver. A drain valve is normally provide commutator forms the rotary component of at the lowest point of each air receiver, to the motor. The starter drive mechanism or provide a convenient means of removing Bendix including an overrunning clutch any liquid that accumulates. All of these similar to the one used on the vane type air measures protect both the receivers and the motor is mounted to the armature shaft and air-operated components of the system. is enclosed by the nose housing.
7.4.5 Control Air A solenoid switch, mounted to the field frame, serves two functions. First, it Control air, supplied from the engine starting provides a means for positive engagement air system, utilizes an air filter pressure- of the drive gear with the flywheel ring gear.
reducing valve and volume control tank. In Secondly, it acts as a switch to make the a generic system, control air aligns a pilot connection between the batteries and the valve to pressurize engine run/shutdown field windings and motor brush assembly.
Rev 3/16 7-11 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Initiation of a start signal electrically It is recommended that a separate set of connects the solenoid switch to the batteries be supplied for engine starting.
batteries. Energizing the windings of the The station battery (typically 125VDC) solenoid switch creates a magnetic field should not be used for engine starting, as which pulls the plunge into the core of the running down that set of batteries would switch. That causes the shift lever to pivot impact critical monitoring-control functions forcing the drive gear to mesh with the and also preclude the engine running.
flywheel ring gear.
As the plunger makes contact with the switch rod, the contact plate is forced against the motor contacts. This then makes the electrical connection between the batteries and the field windings and armature. Once the field windings are energized, the motor begins to rotate the engine crankshaft starting the engine.
Loss of the start signal de-energizes the solenoid switch allowing the spring force to disengage the drive gear from the flywheel ring gear. The solenoid switch also breaks the circuit between the batteries and field windings and armature. At this point, the motor is disengaged and de-energized.
7.5.2 Batteries Starting system batteries are of the lead acid type. Each cell of the battery produces about two volts. In series, starting system batteries produce 24 or more volts depending on the design specifications of the licensee.
Battery chargers constantly monitor and maintain the batteries in a fully charged condition. Periodic inspection and testing of the batteries is required to ensure that the batteries are kept fully charged and that they have the capacity (rate of chemical energy conversion) to provide the power necessary for an engine start.
Rev 3/16 7-12 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-1 Cranking Speed vs Compression Pressure Rev 3/16 7-13 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-2 Starting Air Systems Rev 3/16 7-14 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-3 Starting Air Valve (Solenoid Activated)
Rev 3/16 7-15 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-4 Starting Air Distributor (FM OP Engine)
Rev 3/16 7-16 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems 7-7 Spool Valve Low Cam 7-6 Spool Valve High Cam Figure 7-5 Spool Valve Off Cam Rev 3/16 7-17 of 28 USNRC HRTD
Rev 3/16 Emergency Diesel Generator 7-18 of 28 Figure 7-8 Starting Air Check Valve - Open Figure 7-9 Starting Air Check Valve - Closed USNRC HRTD Diesel Engine Starting Systems
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-10 Vane Type Starting Air Motor Rev 3/16 7-19 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-11 Bendix Drive Assembly Rev 3/16 7-20 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-12 Governor Boost Cylinder (Woodward Governor Co.)
Rev 3/16 7-21 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-13 Starting Air Supply System Rev 3/16 7-22 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-14 Typical Components Direct Air-Over-Piston Starting System Rev 3/16 7-23 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-15 Typical Direct Air-Over-Piston Starting System Rev 3/16 7-24 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-16 Electric Starting Motor System (with Bendix)
Rev 3/16 7-25 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems Figure 7-17 Air Start Check Valve Rev 3/16 7-26 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems HANDS-ON SESSION 7
- Air-start check valve
- Starting distributor 7.0 DIRECT AIR INJECTION SYSTEM
- Governor boost cylinder Purpose 7.1.1 Air Start Distributor The purpose of this session is to The air start distributor consists of a number complement Chapters 3 and 7. of valve assemblies, usually one for each cylinder of the engine. There is a cam, Learning Objectives driven by the engine at engine speed. This cam has a flat which is located such that for Upon completion of this lesson you will be a particular cylinder, the flat allows the valve able to understand: for that cylinder to open at a point just past top dead center (or inner dead center) for
- How the direct air-over-piston starting that cylinder on its power stroke.
system operates including its components and their location on the When the valve in the air start distributor engine. opens, its causes the air start check valve on that cylinder to also open, thus allowing 7.1 Air Start System and Its Components starting air to enter the engine cylinder at a considerable pressure. The air between the Utilizing the OP, ALCO, and Pielstick engine pistons forces the pistons apart. This force cutaways, the instructor will conduct a drives the connecting rods that power the Hands-on presentation to identify the crankshafts, which causes them to rotate.
location of the air starting system and its Reference Figures 7-4 through 7-7.
components. Starting air will be traced from its input to the Air Admission Valve and to all In the air start distributor on the Opposed of its output locations including: Piston engine, air is admitted to the distributor when the engine start signal
- The main Starting Air Header and its flow causes the air start solenoid valve to open.
to each cylinders Air Start Check Valve The air pressure inside the air start distributor causes the individual cylinder
- The Starting Air Distributor with its lines valves to push in against the cam surface.
to the pilot valve on each cylinders Air When there is no air pressure present, Start Check Valve springs in each valve cause the valves to be
- The line to the Governor Boost Cylinder forced outward, away from the cam. Thus, when there is no air pressure, there is no The instructor will discuss each application contact between the valves and the cam and of starting air to these components and no wear occurs on the parts.
show cutaways of the components.
When the cam rotates to the point that the
- Multi-port air admission valve flat is located at an individual valve, the Rev 3/16 7-27 of 28 USNRC HRTD
Emergency Diesel Generator Diesel Engine Starting Systems valve moves further toward the cam. Ports pressure, usually at about 250 psig, to the in the housing are opened to allow pilot air valves. As each air start distributor valve is pressure to be transmitted to the air start opened by the air start distributor, air check valves in the associated cylinder. The pressure from the distributor causes the pilot air opens air start check valve which individual air start check valve to open in admits air from the starting air manifold sequence.
header into the cylinder. When the cam continues to turn, the flat passes that valve When the air start pressure/supply is on, and the valve is rammed to the closed indicating the engine is to be started, position, venting the air signal from the pressure enters the air start check valve cylinder air check valve and shutting off the from the starting air header. The valve is of air into that cylinder. the balanced pressure design, and this header pressure will not cause the valve to This happens to each cylinder in the firing open on its own. The spring ensures that order sequence of the engine until the the valve will not open from the header engine is started. When the engine reaches pressure. A pilot piston is operated by the a self-sustaining speed of about 125 to 150 air start distributor air pressure, which rpm, a speed sensing mechanism shuts off causes the pilot piston to overcome the starting air to the distributor and header. spring pressure and allow the air start check valve to open.
The instructor will demonstrate the operation of the air start distributor by The instructor will show a sectioned air start applying air pressure to the inlet fitting and check valve and will also demonstrate its then will demonstrate the operation of the operation by applying pressure to the pilot individual cylinder valves by turning the piston.
cam.
It is very important that the air start check The air start distributor on some early model valve seal tightly when it is closed because OP engines was mounted on the front of the the valve is subject to the pressures and upper crankshaft as shown on Figure 2-37 temperatures inside the cylinder during (Chapter 2). The display model has this normal operation. If the valve were to leak, configuration. On all 12-cylinder and later it would allow pressure and heat to build up model OP engines, the air start distributor is in the air start header, which is not made to mounted on the opposite control side of the operate at such conditions. During normal engine (opposite the governor) on the front operation of the engine, it is a good idea to end or the engine. occasionally feel the air start check valves.
If they are hot, then they may be leaking and One air start check valve for each cylinder is they should be removed from the engine mounted at the center of the cylinder liner on and replaced or rebuilt.
the opposite control side (OCS). See Figure 7-17 for a cutaway view of the valve. There is an air header that connects to each air start check valve and supplies starting air Rev 3/16 7-28 of 28 USNRC HRTD