398-76083-0 Tohatsu ACTUATOR, NEUTRAL SWITCH

Definitions
Derating - The reduction of engine horsepower in response to an abnormal operating conditionRamped loading - An increase of the engine load over a period of timeRamped unloading - A decrease of the engine load over a period of timeContinuous rated output - The maximum allowable continuous engine operating speed or loadBase load - This is the continuous, controlled engine operating speed or load that is set by the operator. The range of the base load can be adjusted from a minimum up to the continuous rated output. The base load can be adjusted at any time. This includes operation during an alarm condition. The operator can reduce the base load if the engine cannot provide full power without operating in an alarm condition.Types of Derating
Different abnormal operating conditions have different potentials for causing damage. Some conditions can cause greater damage than other conditions. The potential abnormal operating conditions are classified by these three Types: 1, 2 and 3.Type 1 alarm conditions have complete priority over Type 2 and Type 3 conditions.Table 1 shows the types of derating, the parameters (abnormal operating conditions), and the setpoints which initiate the derating. The setpoint for derating the operation is equal to the setpoint of the alarm for each parameter.
Table 1
Derating for 3600 Series Generator Set Engines (Heavy Fuel Oil)
Type of Derating Parameter Setpoint
1 High exhaust port temperature deviation Difference of 50 °C (122 °F) from the average
1 High driveline torsional vibration Woodward 721 setpoint
2 High ACOC water temperature (inlet) 38 °C (100 °F)
2 High inlet manifold air temperature 70 °C (158 °F)
2 High inlet manifold air pressure 269 kPa (39 psi)
2 High lube oil temperature 92 °C (198 °F)
2 High jacket water outlet temperature 103 °C (217 °F)
2 Low sea water pressure (inlet) 172 kPa (25 psi)
2 High turbocharger speed 32,000 rpm
2 High generator stator temperature 155 °C (311 °F)
3 Lube oil centrifuge (alarm) No lube oil centrifuge Common Terminology and Procedures
The following terminology and general procedures are common to all three types of derating:
Operating parameters are monitored by a programmable logic control. The programmable logic control is located in the cabinet of the generator set control panel.
Sensors detect the operating parameters. The sensors communicate the information to the programmable logic control via a serial network connection.
The programmable logic control controls the loading and the unloading of the engine. The programmable logic control also monitors these processes.
When the operation is automatically derated, ramped unloading occurs. When the operation is restored, ramped loading occurs.
The rates for ramped loading and unloading are preset.
The programmable logic control limits the time of low load operation. Even if no derating is active, only 15 minutes of operation are allowed at 40 percent or less of the continuous rated output. An alarm lamp for "Low Load Operation" illuminates during the 15 minutes. This notifies the operator that the load must be increased. If the 15 minutes elapse without an increase of the load, automatic unloading is initiated. This is followed by a cooldown and a shutdown.
When the engine output is derated, the minimum allowable operation is 40 percent of the continuous rated output. The engine output will not be reduced to less than 40 percent unless the operation is being shut down.
When the operation is automatically derated, a "DERATE OPERATION" lamp illuminates continuously. If the alarm condition is corrected, the "DERATE OPERATION" lamp flashes. This notifies the operator that the operation is satisfactory and normal operation may resume.
The operator may use a "DERATE RESTORE" push button in order to resume base load operation after an alarm condition has been cleared. The "DERATE RESTORE" push button affects operation only if an acceptable “restore from derate” condition exists.
“Automatic Derate/Restore” operation only occurs when the controls for loading are in the "AUTOMATIC" mode.
If the abnormal operating condition recurs after restoration, the process of deration is restarted. The process is restarted if any of the conditions occur.
If the process of deration shuts down the engine, the "DERATE OPERATION" lamp and the alarm condition are active until the operator resets the control panel.Type 1 Derating
Illustration 1 represents the possible effects of a Type 1 derating.
Illustration 1 g00487374
(Y) Percent of continuous rated output
(X) Time in minutes The following Steps can occur as a result of a Type 1 derating. The Steps explain the process that is represented in Illustration 1.
Upon detection of a Type 1 alarm condition (1), operation is automatically reduced to 50 percent of continuous rated output. The "DERATE OPERATION" alarm lamp illuminates continuously. If an alarm occurs because of driveline torsional vibration, the electronic actuator initiates the process of deration. A contact within the Woodward 721 closes. This signals the derating to the programmable logic control.If an alarm occurs because of the exhaust port temperature deviation, the programmable logic control automatically initiates the process of deration.The derating is intended to allow the operating parameters to “stabilize” within acceptable limits.Note: It is unlikely that an operator will be able to correct a Type 1 alarm condition within the time that is allowed.
After the derating (2), five minutes are allowed for the operator to correct the condition. If the condition is corrected within the five minutes (3), a 15 minute “restore” timer is activated. The engine must run satisfactorily for 15 minutes before the base load can be restored. If the engine runs satisfactorily for those 15 minutes, the operator can restore base load operation (4).If an alarm condition occurs during the 15 minutes, the corresponding strategy is initiated.
If the condition is not corrected within the five minutes (3), another derating occurs. This is followed by another allowance of five minutes.
If the load is reduced to 40 percent of continuous rated output, the "Low Load Operation" lamp illuminates continuously. The engine will be allowed to operate for another five minutes. If the alarm condition is not cleared, the engine is automatically unloaded. A cooldown and a shutdown (5) also occurs.