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Вариант 2. 1. Read and translate the text in a written form. Maintenance of A.C. Motors. A.C. Motors may run for extremely long periods witho
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Вариант 2.
1. Read and translate the text in a written form.
Maintenance of A.C. Motors.
A.C. Motors may run for extremely long periods without repairs. If the bearings are properly lubricated and air passages are kept clear, then most of the A.C. Motors do not have failure problems, as the motors have no commutators which cause motor failure. There are few motors which have commutators, such as universal motor, repulsion motors in single phase system.
Squirrel Cage Induction Motor:
Overheating and shock may damage the squirrel cage rotor, which may cause fractures in bars in the slots and end ring connections and joint in the rotor cage. Satisfactory operation of motor is difficult with fractured rotor cage and end rings. In large motors the bars are bolted or wedged in slots and can be tightened readily if these become loose. Loose coils can be detected with the help of growler. If it is not possible to disassemble the motor, connect an ammeter in series with one phase and apply 25% of full voltage to one of the stator phase winding and turn the rotor slowly by hand. If the ammeter reading varies in excess of 3%, it can be assumed that there is loose bar in rotor.
Wound Rotor Motors:
Working principle is same as 3 phase sq. cage rotor induction motor, having better torque and speed. Wound rotor may have low speed with starter resistance cut off from rotor circuit. If there are no openings in control and starter circuit, the rotor coils should be tested for continuity. Growler test may reveal open are short circuit in the coils. There is also possibility of brushes sticking in the holder or brushes may not have sufficient tension (sparking and overheating at contact area).
Growler is an electromagnet having 110 V /240 V supply voltage and suitably shaped for testing armature/ rotor, by placing the growler core (or rotary growler for testing stator winding) and slowly moving on/in it shorted or broken coils can be detected by noting the change in the humming noise of the growler.
Техническое обслуживание асинхронных двигателей
Асинхронные двигатели могут работать в течение очень долгого периода времени, не нуждаясь в ремонте. Если подшипники смазаны должным образом, а вентиляционные каналы чистые, то большинство асинхронных двигателей не имеют проблем, так как в двигателях нет коммутаторов, которые вызывают отказ двигателя. Есть несколько двигателей, которые имеют коммутаторы, такие как универсальный двигатель, отталкивающие двигатели в однофазной системе.
Асинхронный короткозамкнутый двигатель:
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