单项选择题
A.higher than that of copper B.lower than that of copper C.equal to that of copper D.reached when the conductor it is protecting becomes "white hot"
The most common source of excitation for synchronous mo...
单项选择题The most common source of excitation for synchronous motors is a/an （）.
A.low voltage battery B.motor attenuator set C.DC exciter generator D.AC supply
Before reassembling any machinery, you should （）.A.repl...
单项选择题Before reassembling any machinery, you should （）.
A.replace all bearings regardless of length of service B.apply a heavy coat of oil to all mating surfaces C.clean any corroded surfaces and file all burrs smooth D.coat all parts with alemite grease
Ammeters and voltmeters used in sinusoidal AC power sys...
单项选择题Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured?（）
A.Peak value B.Root-mean-square value C.Average value D.Maximum value
