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China Aerospace Science and Technology Corporation Subsidiary Shanghai Xinli Machinery Factory
Shanghai Xinli Machinery Factory is affiliated to Shanghai Aerospace Administration of China Aerospace Science and Technology Corporation, and is a large and medium-sized state-owned enterprise that produces forging machine tools. The factory is one of few manufacturers engaged in the research, development and production of precision CNC and ordinary bending machines and shears in China. It is also one of the most excellent enterprises in the production of forging equipment in China.
The company's production equipment is mainly electrical components such as motors, cutting machines, punches, and inverters. The current harmonic content is large on the site. the harmonics cause capacitor breakdown, bulging, liquid leakage and other phenomena. As shown in the figure below, the capacitor is seriously damaged and can no longer work normally even affect the normal operation of the power system .
show capacitor breakdown, explosion and liquid leakage.
Site survey and testing
We learned that the company’s system current harmonic is mostly the 3rd and 5th harmonics by our company’s technical staff. And the original capacitor cabinet compensation adopts equal-capacity group switching. This distribution method is unreasonable and the compensation accuracy is not fine enough, resulting in compensation that can only be compensated in integer multiples of 25kvar. The positive reactive power compensation has defects.
On-site feedback
In addition to the accident power distribution room, the reactive power compensation cabinets in the other power distribution rooms are equipped with reactors that the reactance rate is 14%. In addition, the company’s production equipment includes large motors, frequency dividers, electric arc furnaces, welding machines and other devices that are prone to generate harmonics. It have rectifier and inverter circuits, so the quality of the system power grid is poor. Considering that in three-phase balanced system, even harmonics can be offset. Therefore, this scheme does not consider even harmonics. We analyze the odd harmonics: the harmonic current content rate is very high, which belongs to serious harmonic pollution and is very harmful to electrical equipment!
Failure analysis
Combined with the on-site pictures and the data provided by the harmonic tester, we can know:
① Capacitor breakdown: Capacitor breakdown is abnormal damage with high harmonics. Capacitors bear long-term over-voltage, over-current, overload, and the insulation performance is reduced. It is easy to break down. It will only leak when it is slight, and it will happen when it is serious. The short circuit exploded.
② The original reactive power compensation cabinet of the company adopts 25Kvar equal capacity configuration. The method is single, and it can only compensate integer multiples of 25kvar, which easily leads to insufficient compensation accuracy.
Technical solutions
Based on the original reactive power compensation cabinet foundation and on-site measured harmonic data, the harmonics are mainly the 3rd and 5th harmonics. Therefore, an anti-harmonic reactor with a reactance rate of 14% is added to make it have an anti-harmonic function. It can suppress system harmonic amplification and effectively protect power capacitors.
Based on the above analysis, the following specific solutions are proposed for the explosion of components in the reactive power compensation cabinet:
① Replace the capacitor. Due to the existence of short circuit, explosion, harmonics, etc. The inside of capacitor may be damaged or in a critical state. It is recommended to replace it, otherwise it is prone to failure.
② Increase the anti-harmonic reactor. The reactance rate is 14%.
③ Remove the original capacitors in the cabinet, clean up the internal garbage, add horizontal and vertical beams, install capacitors at the bottom, and install reactors at the top. All internal cables need to be replaced. Replace the original 4mm2 with 10mm2 cables to improve safety.
④ Replace the original capacitor with the following configuration:
| Compensation capacity | Number of compensation channels | |
| 1 | 10Kvar | 2 |
| 2 | 20Kvar | 1 |
| 3 | 25Kvar | 1 |
| 4 | 35Kvar | 2 |
| 5 | 40Kvar | 4 |
According to the above figure, the compensation capacity is rich and diversified, which can compensate 10kvar, 20kvar, 30kvar, 40kvar. The compensation accuracy is higher!
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