Popular science丨Diesel generator set self-starting device and maintenance method thereof

The generator set commonly used in the data center can start autonomously and output excellent power to replace the mains power supply equipment when the mains power is interrupted, and its self-starting device is an important operating mechanism. In response to readers' inquiries, this article introduces its operation process and maintenance points.

Generator sets consisting of synchronous generators (diesel, gasoline, gas) engines, control cabinets, etc., are installed in large numbers in data centers as backup power sources for mains. They complement each other with their connected UPS, which can not only rely on UPS to reverse the DC power of the battery pack into AC supply load equipment when the mains power is interrupted, but also provide continuous work for UPS by the generator set when the battery capacity of the mains power is not enough for a long time, so as to ensure the power safety of the non-power-off equipment in the data center. The generator set can automatically run and generate qualified power at any time from the usual standby state, and these key conversion processes are completed by the automatic start device.
First, the operation process of the self-starting device
The self-starting device of the generator set is mainly composed of automatic transfer switch (ATS), generator set control cabinet, DC starting motor, battery pack and charger.
The ATS consists of two electric transfer switches and a programmable controller (PLC) or microprocessor as the controller, and is the heart of the self-starting device. In the application of the data center, the parameters such as the upper and lower limits of the variable range of the input voltage and frequency of the UPS used, as well as the time of the delay operation of the switching switch, are preset in the ATS controller. The intelligent controller monitors the voltage and frequency of the mains or generator set entering the ATS in real time, and if it exceeds the pre-set limit, it is judged to be abnormal power, and an alarm is issued and the switching program is entered. The two electric transfer switches in the ATS control the mains access and generator access respectively, and their actions are completely controlled by the controller, and follow the basic rules of disconnecting one switch and then closing the other switch and eliminating simultaneous closing, and execute each pre-set instruction step by step. Although various brands of ATS have their own characteristics, their working principles, program logic, and preset delay parameters are similar.
Second, the maintenance summary of the self-starting device
The self-starting device is the key mechanism for whether the generator set can start. Familiarity with how they work and how they work can help you improve the efficiency of your operations. For the medium and high-power generator sets commonly used in data centers, there are some key points to pay attention to in maintenance practice for reference:
1. The mains power is directly connected to the ATS, and the high-voltage spikes that rush into the power grid when lightning occurs may damage the power sampling sensors and controllers. Therefore, the ATS cabinet and the input distribution cabinet connected to it must be protected against lightning.
2. The signal line connecting the ATS cabinet and the generator set control cabinet shall be a cable with a cross-sectional area of more than 2 square millimeters and a shielding layer to reduce the loss of control pulse signal and the interference of electromagnetic field.
3. Two 12V100~200AH lead-acid batteries are commonly used in series to form a 24V battery pack to start the engine of the generator set. In addition, the battery pack is also the power supply for the genset control cabinet and the ATS controller, and its performance is critical. The change of the internal resistance of the battery is a sign of consideration, and generally more than 15mΩ is no longer suitable for starting the battery, because the instantaneous starting current is too large.
4. When the mains power is normal, the charger of the generator set control cabinet charges the battery pack, and the voltmeter on the panel indicates about 27V, indicating that it is in the state of floating charge. When the mains power is interrupted, the generator set starts to supply power, and the silicon rectifier charging generator and its voltage regulator come with the unit to charge the battery pack. At this time, you should check whether the indication value of the voltmeter is normal and stable. Otherwise, it needs to be carefully inspected during maintenance.
5. The DC drive motors on both sides of the engine flywheel automatically stretch out and mesh with the outer gear ring of the flywheel when starting, driving the crankshaft and flywheel to rotate. It will automatically disengage after a successful engine start. When the engine starts weakly, it may be caused by too much sludge or inadequate meshing of the outer gear ring of the flywheel. After successful starting, if the drive gear of the drive motor is not in place, it will emit noise. It should be stopped for inspection.
6. For the generator set in standby state, no matter when and where, as long as the start command is received, it should be started immediately and the rated power should be issued. This is a fundamental requirement for O&M. The second instruction only successfully started the generator set, indicating that there are still maintenance deficiencies in its oil circuit, steam circuit, circuit and other links. The chances of a successful third launch are slim. The cause should be identified for further maintenance work.
7. ATS mostly has automatic test function, this mode of operation is according to the user's preset parameters, at the specified time to run the command to start the generator set. After the unit runs smoothly and outputs the rated power, the ATS controller commands to disconnect the mains side switch and then turn on the generator set switch, and the load becomes the power supply work of the generator set. After 15~30 minutes of operation, the controller commands the generator set switch to be disconnected, and the mains switch is closed, which becomes the mains power supply. Then command the generator set to stop. The automatic test process is not only a comprehensive inspection of the software and hardware of the ATS related devices, but also a test of the functional components of the automatic starting device of the generator set. Running automated test programs every 10 days and a half months is part of O&M.