Conditions necessary for two transformers to operate in parallel

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Conditions necessary for two transformers to operate in parallel Font: Small Medium Large | Print Published: 2009-2-07 21:15 Author: boyandey Source: China Electric Power Research Network For two transformers to operate in parallel, the following conditions must be met: (1) The voltage ratio must be the same, with the maximum difference not exceeding ±0.5%. (2) The wiring groups are the same. (3) The percent impedances must be equal, with the maximum difference not exceeding ±10%. If the voltage ratio difference is too large, circulating currents will be generated during parallel operation, affecting the transformer’s output. If the wiring groups are different, it will cause a short circuit or a large circulating current. For example, when transformers with single-winding and double-winding configurations (such as one △/Y-11 and one Y/Y-12) are connected in parallel, the circulating current can damage the transformers. If the percentage impedance difference is too large, the load on the transformers operating in parallel cannot be distributed reasonably according to their capacity ratios; the transformer with the lower impedance carries a larger load, which also affects its output capacity. Furthermore, based on operational experience, the capacity ratio of two transformers operating in parallel should not exceed 3:1. Font: Small Medium Large | Print Published: 2009-2-07 21:15 Author: boyandey Source: China Electric Power Research Network For two transformers to operate in parallel, the following conditions must be met: (1) The voltage ratio must be the same, with the maximum difference not exceeding ±0.5%. (2) The wiring groups are the same. (3) The percent impedances must be equal, with the maximum difference not exceeding ±10%. If the voltage ratio difference is too large, circulating currents will be generated during parallel operation, affecting the transformer’s output. If the wiring groups are different, it will cause a short circuit or a large circulating current. For example, when transformers with single-winding and double-winding configurations (such as one △/Y-11 and one Y/Y-12) are connected in parallel, the circulating current can damage the transformers. If the percentage impedance difference is too large, the load on the transformers operating in parallel cannot be distributed reasonably according to their capacity ratios; the transformer with the lower impedance carries a larger load, which also affects its output capacity. Furthermore, based on operational experience, the capacity ratio of two transformers operating in parallel should not exceed 3:1.