Application of the hottest PLC in platform emergen

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Application of PLC in platform emergency generator set I. Introduction since the birth of the world's first IC in 1959, microelectronic technology has developed at a high speed, and integrated circuit, printed circuit board, programmable logic device and other technologies have been gradually applied to intelligent instruments and automatic control. Due to the wide variety, large volume, long design cycle and high cost of integrated circuit (IC) system chips; The cross and overlap of wiring between components on the printed circuit board (PCB) not only complicates the process, but also increases the distributed capacitance of the electrical wiring, increases the load on the front circuit, and increases the interference of the system. At the same time, the multi solder joints of PCB and the connection holes of double-sided wiring lead to the decline of the reliability of the system; Programmable logic controller (PLC) is a new and universal automatic control device based on microprocessor, which integrates computer technology and communication technology. It has the advantages of simple structure, superior performance, high reliability, flexible and universal, easy programming, convenient use and so on. In recent years, it has been widely used in industrial automatic control, electromechanical integration, transformation of traditional industries and so on

PLC control for emergency generator set has many advantages. It is mainly controlled by software, which saves the hardware development work, and there are few peripheral circuits, which greatly improves the reliability and anti-interference ability of the system; Because of its simple and easy programmable function, it can change the control requirements of the system without changing the external hardware wiring of the system, and greatly improve the "flexibility" of the system

II. Main design functions

offshore drilling platforms are generally equipped with separate power stations. In the production process, if the main station suddenly loses power due to failure, and there is no standby power supply to continue to supply power, it is likely to cause accidents. In case of emergency, the emergency power station shall at least be able to supply power to the following equipment:

1, radio communication and navigation signal light equipment

2. Lighting in important areas, such as escape exits, central control room, radio room, etc

3. Fire and toxic gas alarm device

4. Wellhead blowout preventer

5. Emergency fire pump and bilge pump

the prime mover of the emergency power station generally adopts a diesel engine with an independent cooling and oil supply system, and is equipped with a self starting device to ensure that it can be started within seconds after the main station loses power. The emergency power is usually a part of the main power. Under normal circumstances, these electrical equipment are powered by the main distribution board, but only by the emergency generator set in case of emergency, Therefore, an electrical interlock is set between the main switch of the emergency generator on the emergency distribution board and the switch that the main switch supplies power to the emergency distribution board to ensure safety. See Figure 1 for the distribution system of Shengli 7 platform:

under normal power supply, K13 is closed to make the emergency load and emergency lighting circuit work normally as part of the normal circuit. Under normal power loss, kt1-kt4 and K13 knife switches jump off, and Ke is closed to send power to the emergency load and emergency lighting after the emergency generator eg is started. As a platform emergency power supply, the emergency generator set shall have the following basic requirements:

1. Automatic startup

when the normal power supply fails (power failure), the unit can automatically start, automatically speed up and automatically switch on to supply power to the emergency load

2. Automatic shutdown

when the normal power supply is restored and it is judged to be normal, control the switch to complete the automatic switching from emergency power to normal power, and then control the unit to slow down to idle speed and stop

3. Automatic protection

during the operation of the unit, if the oil pressure is too low (less than 0.3mp), the cooling water temperature is too high (greater than 95 ℃), and the voltage is abnormal, the unit will be shut down in an emergency, and an audible and visual alarm signal will be sent at the same time. If the water temperature is too high (greater than 90 ℃), the oil temperature is too high. Then sound and light alarm signals will be sent to remind maintenance personnel to intervene

4. Three start function

the unit has three start functions. If the first start is unsuccessful, it will be started again after a 10 second delay. If the second start is unsuccessful, it will be started for the third time after a delay. As long as one of the three starts is successful, it will run down according to the preset program; If the startup fails for three consecutive times, it will be deemed as startup failure, and an audible and visual alarm signal will be sent (it can also control the startup of another unit at the same time)

5. Automatically maintain the quasi start state

the unit can automatically maintain the quasi start state. At this time, the automatic periodic pre oil supply system of the unit, the automatic heating system of oil and water, and the automatic charging device of the battery are put into operation

6. It has two operation modes: manual and automatic

III. hardware design of control system

for offshore petroleum equipment built in China, 135 series diesel units are mostly used for emergency power supply. The following is an example to use PLC to control the self starting of diesel engines

circuit design is shown in Figure 2:

2. Circuit analysis

Design Description: there are "manual/automatic" selection knobs on the control panel, "stop/idle/or print and paste spoon chopsticks signs (see Appendix A for details)" rated speed "selection knobs," start "," close "and" open "buttons. Motor a drives cam switch ZK to rotate with three positions ABC, corresponding to three positions of stop/idle/rated speed respectively, That is, the three positions of the throttle. Speed relay, voltage detection, water temperature and oil pressure are all external switch signals

original state: the diesel engine profile is mainly delivered, the throttle lever control motor is in the "shutdown" state, the cam switch a is closed, and both B and C are disconnected

one time starting process: after normal power loss, after 5 seconds of confirmation, the throttle controller acts, motor a rotates forward to pull the throttle to the "low speed" position, at the same time, the cam switch ZK acts to disconnect a, close B, and start motor B for 4 seconds, such as diesel engine 2 Partial rotation (generally used for butterfly valve, ball valve, plug valve and other valves that can be opened and closed only by rotating 90 degrees) is ignited. When the speed rises to rotation, the sensor acts, and motor a acts again to pull the throttle to "full speed". At this time, cams B and a are disconnected, C and C are closed, the generator starts to generate power, and after the voltage is normal, the main switch Ke is closed to supply power to the load

three startup processes: if the first startup is unsuccessful, the speed relay is still in its original position. It is controlled by the timer inside the PLC to start again. Taking 10 seconds as a cycle, the three startup time is about 30 seconds, and the alarm is output after 32 seconds.

startup failure and diesel unit shutdown: after the startup failure, the system process is 50 seconds later, the motor a is controlled to reverse, and the oil

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