Calculation Of Circulating Current Losses In Stator Bars For Large Synchronous Compensator

The synchronous compensator has good reactive power adjustment capability and is widely used in ultra-high voltage power grids.The stator bars are the basic link of the electromagnetic conversion in the synchronous compensator,and its design occupies an important position in the design of the synchronous compensator.In order to reduce the eddy current losses,the stator bars usually use multiple strands in parallel and short-circuited at the ends.The parallel strands generate uneven induction electromotive force in the uneven leakage magnetic field of stator.It forms a loop current and additional circulating current losses between the parallel strands,which causes the varied temperature rise in the strands and directly harms the insulation life of synchronous compensator.In this paper,taking a 300 Mvar synchronous compensator as an example,the leakage magnetic field and circulating current losses of the stator bars for the synchronous compensator are studied.The field-circuit coupling calculation models of the synchronous compensator under different operating conditions are established,the two-dimensional magnetic field distribution of the synchronous compensator under the different operating conditions and the leakage magnetic field in the slot of the stator bars for the synchronous compensator under the rated operating conditions are calculated.The influence of the magnetic saturation phenomenon in the slot leakage magnetic field of the stator bars is discussed.Aiming at the problem of calculating and optimizing the circulating current losses for the synchronous compensator,an improved strand loop method including an explicit calculation method for the slot leakage reactance of the stator bars is proposed.Based on the interpolation method to accurately simulate the transposition path of the strands in the slot,the calculation formula for the slot leakage reactance of the synchronous compensator with less than 540 degree transposition and less than540 degree void transposition strands.The numerical method is used to calculate the strand currents and circulating current losses of the 540 degree transposition stator bars.Comparing the calculation results with the calculation results of the improved strand loop method,the accuracy of the improved strand loop method is verified.The explicit calculation method of slot leakage reactance for strands with less than 540 degree transposition and less than 540 degree void transposition and firefly algorithm are combined into two transposition optimization algorithms for circulation current losses.Taking the circulation current losses of the single-slot stator bars as the optimization target,the insufficient transposition angle of the upper and lower strands and the position of the void transposition section are optimized variables.The stator bars is optimized to obtain the best transposition type corresponding to the two transposition methods,which effectively reduces the circulating current losses.