Please help analyze the problems that have occurred during the operation of this rectified power supply system
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The old chlor-alkali plant commissioned Phase 1 with a capacity of 6,000 t/a of chlor-alkali in 1991, Phase 2 with a capacity of 20,000 t/a in 1996, and Phase 3 with another 20,000 t/a capacity in 2003. The three rectification systems operate independently, with the following load allocations: 54 metal anode electrolyzers of types 1 and 8, and the rectifier transformers are 3,000 KVA three-phase bridge parallel connections in the same phase； 2. 58 units of type 16 metal anode electrolytic cells, with rectifier transformers of 63,000 KVA in a three-phase five-column configuration connected in inverse parallel within the same phase ； 3. 58 units of type 16 metal-expansion anode electrolytic cells; the rectifier transformers are 73,000 KVA in structure, with a double reverse-star configuration and balance reactors connected in phase in parallel ； The supply bus voltage is 35 KV; three sets of power systems operate in parallel on the same bus, and all rectifier units are of the 6-pulse type. The 35KV power supply bus system is equipped with one set of 6000KVAR and one set of 3000KVAR reactive power compensation units, respectively, for voltage compensation and improvement of the power factor in the bus system. Since the 3 rectifier systems were put into operation at different times, and harmonic effects were not taken into account comprehensively in the early stages of the project, plus the power sources operated in parallel on the same bus, for the third phase of the project, the harmonic issue was addressed by setting the phase of the three-phase five-column rectifier transformer in phase two at an angle of 30 degrees offset; in phase three, the primary side of the rectifier transformer was modified to have a delta-connected double wye configuration with balance reactors. Since the rectifier transformers of the 3 systems have different structures, please help analyze the issues that arise between the rectifier equipment and the power grid system during the operation of the rectifier power supply system
In terms of transformer capacity, the capacity of Phase 1 is 3000 KVA, which is relatively low compared to Phases 2 and 3; therefore, it can be disregarded. In the second and third stages, the primary phase shift of the rectifier transformers is 30 degrees, resulting in an asymmetric 12-pulse waveform; the harmonics transmitted into the power grid system are mainly of the 11th and 13th orders. Therefore, the harmonics that may exceed the limit during operation are the 11th and 13th harmonics. Based on our operational experience, excessive harmonics can cause the capacitor compensation device to frequently experience fuse burnout and capacitor breakdown.
Could an expert tell me how to do it?
Based on my many years of experience in engineering, I believe that for this type of load, shifting the phases of the transformers by 30 degrees is merely a theoretical approach. The reason for this is quite simple: the loads on the two transformers usually do not occur at the same time. Using filter capacitors for static compensation can only solve 60% of the problem; the true solution lies in adopting a dynamic compensation approach (TCR + FC)!