低压电动机的起动计算和校验

Start ing Calculation and Calibration of Low-voltage Motor

介绍低压电动机起动计算和校验步骤,强调进行电动机起动计算前,一定要先进行电动机回路电压降和保护灵敏系数验算。运用基尔霍夫第一、第二定律进行电气计算,通过不计电阻影响和计电阻影响两种情况下的低压电动机起动计算与校验实例,对比分析两种情况计算结果,验证工程设计中在不计电阻影响情况下进行低压电动机起动计算的合理性。同时指出低压电动机采用降压起动,大多数情况不是因为起动时的母线电压降或电动机端电压不满足要求,而是为了满足短路保护灵敏系数要求、减小导线截面、减小应急发电机容量。

The starting calculation and calibration procedures for low-voltage motor are introduced. It is emphasized that the checking calculations for motor circuit voltage drop and short circuit protection sensitivity coefficient must be carried out before the starting calculation of motor. Using the Kirchhoff＇s first and second law for electrical calculation, through the calculations for low-voltage motor with and without considerations of resistance influences and comparison between the calculation results of the two conditions,the reasonability of starting calculation for low-voltage motor without consideration of resistance influence in engineering design is verified. Meanwhile, it is pointed out the reason that reduced voltage starting is adopted for low-voltage motor is not the voltage drop of busbar or the terminal voltage of motor when starting do not meet the requirements in most cases, but to satisfy the requirement for sensitivity ratio of shortcircuit protection, reduce the cross- section of conductor,and decrease the capacity of emergency generator.