alternating current machines 2

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Learning outcome 2

Motor protection

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Over temperature protection

If the temperature of the insulation is exceeded, it starts to degrade and will eventually fail.

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The most common and effective protection is thermal overload devices.

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Primary resistance starter

TOL device

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Typical TOL with adjustable settings.

Adjustable electronic protection device with overload, phase failure and asymmetry protection.

NUE046 L/O 2 jh 7/05 9Insulation damage due to overload in 2 phases.

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Rotor damage due to locked rotor condition.

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Common problems.

• Asymmetry – voltage and phases not correct

• Single phasing - loss of a phase• Overloading• Moisture• Foreign matter in motor –sand etc• Frequency fluctuation• Voltage fluctuation

P 240 section 10.10