【单选题】一台SN=5600kVA,UN/U2N=6000/330V,Yd联结的三相变压器,其空载损耗p0=18kW,短路损耗pkN=56kW。当负载的功率因数cosφ2=0.85(滞后)保持不变,变压器的效率达到最大值时,变压器一次侧输入电流为( )。
【简答题】如图,交流信号源的电动势 E= 100 V,内阻 R 0= 8 00 W ,负载为扬声器,其等效电阻为 R L = 8 W 。要求( 1)当RL折算到原边的等效电阻, 求变压器的匝数比和信号源输出的功率;(2)当将负载直接与信号源联接时,信号源输出多大功率。
【简答题】We'd better hurry ____ the store closes soon.
【单选题】听力原文:M: We'd better hurry or we'll be late. W: I know we are in a hurry, but the speed limit on this freeway is 65 miles per hour. What are the man and the woman doing?
C.
Packing their luggage.
【简答题】当变压器的输出功率为0时,其效率为0。当输出功率增大到一定值时,其效率又下降?效率最大的条件?
【判断题】对互换性的要求是:装配前不必挑选:装配时不必调整修配;装配后可满足预定的性能要求。
【单选题】We'd better hurry it is getting dark.