An automobile factory is powered by two 110kV buses, one of which is powered by a dedicated line, which operates in open-loop mode and runs in two sections at 10kV. From the primary equipment wiring diagram, we can see that there are current quality control devices in both sections of the 10 kV bus. The field engineers feedback that the current quality of the factory meets the requirements of the national standard, and the problem of harmonic interference has been well suppressed. It does not affect the normal operation of the factory and does not cause pollution to the power grid.
Due to the failure of the on-site monitoring instrument, the detailed waveform data were not obtained. According to the feedback of the field engineers, there were two voltage sags or short interruptions in 2017, some of the on-site production equipment stopped unplanned, and it took time and effort to start again, seriously affecting the production task index and bringing significant economic losses to the enterprise.
Power quality issues:
Taking the painting workshop as an example, the on-site load is analyzed. According to the feedback of the field engineers, the equipment that affects the production recovery time after the voltage sag or short-term interruption accident are electrophoretic drying furnace, sealant robot, control system and so on. The recovery time of this kind of equipment is long after shutdown, which seriously affects the recovery time of production.
Sensitive electrical equipment includes digital control equipment, computer equipment, AC contactor equipment, motor equipment, frequency conversion servo controller speed regulation equipment, lighting equipment and protection equipment and so on.
The main cause of voltage sag is caused by short circuit fault in power supply system and internal equipment of users. Excessive and severe weather conditions, such as lightning, strong wind, blizzard and hail, are often directly related to the occurrence of voltage sag. Voltage sag accidents can be caused by the decrease of electrical characteristics caused by insulation aging and pollution, electric shock caused by animals and branches, and man-made short circuit faults in related construction and transportation activities. In addition, the starting of large motor, transformer power-on or load switching will cause voltage sag.
Power quality governance:
Through the analysis of the power quality of the automobile painting workshop, the current quality control measures have been taken in the whole plant, and the harmonics have been reasonably suppressed. The main reasons affecting the continuous production of the factory are voltage sag and short-term interruption.
The park uses 110kV double-circuit power supply, power switching time load requirements of the national standard, reasonable distribution line planning, no high energy consumption and heavy load enterprises, preventive test inspection in place, the line has added effective lightning protection measures, such measures have controlled the number of failures to a minimum. The factory equipment has been put into operation, it is not feasible to improve the anti-disturbance ability of electrical equipment in full-load production, and there is no electrical equipment that can meet the on-site demand in the market at present.
Based on the above, in order to solve the problems and losses caused by voltage sag and short-term interruption, it is necessary to control the voltage sag and short-term interruption of the electrical equipment in the painting workshop. It can be divided into two schemes: changing the power supply mode and installing mitigation equipment. The first scheme is to add one set of management equipment locally or multiple sets of management equipment according to the production function area in the factory, change the power supply mode of sensitive electrical equipment, and adopt AC / DC redundant power supply to improve power supply reliability to solve the problem of unplanned parking or to quickly resume production. The second scheme is to install mitigation equipment on the equipment.