Discussion on UPS power supply reliability of larg

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Discussion on the reliability of UPS power supply of large thermal power units

large thermal power units have a high degree of automation, and the thermal microcomputer control system and other safety control devices have high requirements for the continuity of working power supply, so it is necessary to configure AC uninterruptible power supply (UPS). UPS power supply is very important to the safe and stable operation of the unit. How to improve the reliability of UPS is a problem often considered by field engineers and technicians

the author takes Panshan Power Generation Co., Ltd. (hereinafter referred to as Panshan Power) 2 × Taking the UPS system of 600 MW units as an example, this paper discusses many problems existing in the design, product quality, maintenance and management of UPS for large thermal power units, and puts forward some suggestions for improvement

1 system profile

three UPS produced by Swiss gutor company with the same capacity are installed in the power panel, forming an n+1 configuration scheme. That is, a single UPS is configured for a single unit. At the same time, a public standby ups with the same capacity is configured for two or more units. The ups model is pew/220-en, and the capacity is 80 kV · a

during normal operation of UPS system, three input power supplies are required: main power supply, bypass power supply and DC power supply. There are four operation modes: normal operation mode of main power supply, DC power operation mode, bypass operation mode and backup operation mode

normally, the load is provided by the rectifier and inverter of the system through the rapid development of the main power supply and LED technology. When the main power supply fails, it will be automatically powered by DC power supply through inverter. In case of inverter or DC power failure, ups will automatically convert to bypass power supply through static switch. During UPS maintenance, the bypass power supply can directly supply power to the load by giving full play to the efficiency of measurement data through the manual bypass switch that is on first and then off. During normal operation, the bypass power supply of ups of unit 3 and 4 is provided by standby ups. When the standby UPS fails or is overhauled, the bypass power supply is provided by the security section B of unit 3 (called the backup bypass power supply), as shown in Figure 1

2 the main advantages and disadvantages of the system

2.1 the UPS system does not have its own battery

the auxiliary power system has a perfect DC system and a large capacity battery pack. The ups load has been considered in the calculation of battery capacity, which can ensure that the AC power supply continues to supply power to the load for more than 0.5 h in case of power failure, so the UPS system does not need to bring its own battery with a large capacity. This not only reduces the cost of equipment, but also reduces the cost of overhaul, operation and maintenance of the battery to complete the fatigue test function

2.2 cooperation between inverter and auxiliary DC system

the rated input voltage of the inverter of the UPS is 220 V DC. When ensuring the output data, the allowable range of input voltage is -15% ~ +20%; When the performance is guaranteed, the allowable range of input voltage is ± 25%. According to the regulations, the allowable voltage fluctuation range of the DC power system of the power plant is 87.5% - 112.5%, and the parameter calculation and equipment selection of the DC system are also carried out according to this. This voltage range can be guaranteed within the normal operation and the allowable accident discharge time. Therefore, the DC input voltage of the inverter fully adapts to this range and leaves a certain margin. At the same time, in order to avoid battery discharge during normal operation, the output voltage of the rectifier is higher than the upper limit of the DC system voltage fluctuation, and diodes are added to prevent the rectifier from charging the battery

2.3 the bypass power supply is equipped with isolation transformer and voltage stabilizing transformer

considering that the auxiliary power voltage is generally high, and the frequent startup of electrical equipment will inevitably affect the voltage quality, a voltage regulator is added to improve the voltage quality of the bypass power supply. At the same time, the 380 V power supply system for the plant is a neutral grounding system, and DCS, DEH and other thermal loads do not want to share the grounding point with the electrical, so an isolation transformer is installed to prevent the two systems from generating electrical connection

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