维修电工初级问答(Maintenance electrician primary quiz)

维修电工初级问答（Maintenance electrician primary quiz）1. Why the low voltage winding of the transformer is inside, while the high voltage winding is outside?

A: the arrangement of transformer high and low voltage winding is determined by many factors. But for most transformers, the low pressure winding is placed in the high voltage winding. This is mainly about insulation. Theoretically, no matter how the high - voltage winding or low - voltage winding is arranged, it can become a transformer. But because the core of the transformer is grounded, because the low voltage winding is close to the core, it is easy to do from the insulation Angle. If the high voltage winding is close to the core, the voltage of the high voltage winding is high and the insulation requirement is required. This not only increases the volume of the winding, but also wastes the insulation material.

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Moreover, as a result of the transformer voltage regulation is to rely on change of the high voltage winding tap, namely change the number of turns, so the high voltage winding is placed in the low voltage winding outside, lead more easily also.

How does the three-phase asynchronous motor rotate?

Answer: after the three-phase alternating current flow into the three-phase stator winding, the stator cavity to produce a rotating magnetic rotation before often stationary rotor conductors under the effect of rotating magnetic field, the equivalent of the rotor conductors relative to cut magnetic

lines, which produced the induced current in the rotor conductors (electromagnetic induction principle). These conductors of the induction current occur in the production field (the effect of the current, the electromagnetic force). Because the inner conductor of the rotor is always arranged symmetrically, the electromagnetic force generated on the conductor is the opposite direction, forming an electromagnetic torque and turning the rotor. Since the current in the rotor conductor is generated by the stator rotating magnetic field induction, it is also known as induction motor. It is also known as the asynchronous motor because the rotor speed is always lower than that of the stator rotating magnetic field.

3. Why doesn't the transformer make the direct current transformer?

Answer: transformer can change voltage condition is that the original edge to ac electric potential to produce alternating magnetic flux, alternating magnetic flux will generate induced potential, at the edge of the deputy the size of the induction electric potential is proportional to the change rate of flux. When the transformer is in direct current, the current size and direction are the same, and there is no alternating magnetic flux in the iron core, which means that the magnetic flux is constant and the flux rate is zero. Therefore, the induction potential is also zero. At this point, the total dc voltage is added to the winding with a small resistance, causing the current to be very large, causing an approximate short circuit.

The alternating current is changed alternately. When the