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1、Electrical MachineryParallel Operation of Transformer3.3.1 Parallel Operation of TransformerAdvantage of parallel operation:(1)the reliability of power supplying is improved.(2)Adjust the number of transfers in parallel operation according the size of load to improve the work efficiency.(3)the reser
2、ve capacity can be reduced,and the new transformer can be installed by stages as power consumption increases to reduce initial investment.LoadUABUABUabUabTransformer ITransformer II3.3.1 Ideal parallel operation condition of transformer(1)For the transformers,their rated voltages of the primary side
3、 and the secondary side are respectively equal,so the transformation ratios are equal.(3)Per unit value of short-circuit impedance for transformers(short-circuit voltage)are equal,so short circuit impedance angles are equal.(2)The vector group symbols of the transformers are same;3.3.2 Parallel oper
4、ation when transformation ratios are unequalEnsure ring current not exceed the rated current by 10%when it is no-load operation.Transformation ratios are different,k k 3.3.3 Parallel operation when the vector group symbols are different Parallel operation are prohibited for the transformers whose ve
5、ctor group symbols are different.I:Y,d11II:Y,y0of and are same,but their phases are different.The sum of voltages in the circuit of the secondary side isnt equal to zero,then the big ring current will be produced 3.3.4 Parallel operation when per nit value of short circuit impedance and short circui
6、t impedance angle are equalSimplified equivalent circuit when its parallel operationIn the same way,The size of the load borne by the transformer is inversely proportional to the per unit value of short-circuit impedance.3.3.4 Parallel operation when per unit values of short-circuit impedance are un
7、equalShort-circuit impedance angles should be equal when the transformers are in parallel operation:In order to make the short circuit impedance angles same:The phases of current for the two transformers should be same,Then the sum of the output capacities is equal to the capacity actually attained
8、by the load.If the impedance angles are unequal,the current phases of the transformers arent same.Generally,the difference between the rated capacities of the transformers in parallel operation is bigger,the utilization ratio of the equipment is lower.Therefore,capacity ratio is required not to exceed 3:1.THANKS FOR WATCHING!