SKF AWAIV-12, Руководство пользователя

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Motivation for surge testing
Motors are subjected to high-energy, high-voltage transients in everyday operating
environments. These transient pulses can damage the insulation in the motor and—given
enough time—cause a catastrophic failure with the motor. High-energy, high-voltage
transients are typically caused by:
• Motor start-up current coupled with contact bounce in the MCC
• Lightning strikes in the power system
• Inverter drive transients
• Line surges caused by tripped motors or transformers elsewhere in the power
system
One of the primary functions of a tester is to simulate real-world transient voltages likely to
be encountered by the motor without the high energy typical of real-world transients. Such
spikes are a significant aging factor for the end turn insulation of an electric motor.
Contact bounce
Oddly enough, one of the major sources for the high-energy transients is the MCC, a device
that is supposed to protect the motor. When the breaker contacts close in the MCC during
startup, they will often “bounce” or chatter; this means that the high inrush current is being
made and breaking several times. As a result of interrupting the current, an inductive “kick
back” voltage spike develops. Large inrush currents along with the high inductance of
electric motors are what give these “kick back” voltage spikes their high energy.
Lightning strikes
Lightning strikes often hit power systems or grids. Although a great amount of effort is made
to protect grids from lightning damage, high-voltage transients caused by strikes can still
reach motors.
Inverter transients
Variable speed drives or pulse width modulated drives are based on switching currents very
quickly in such a manner that the motor runs at a preset speed. The switching of the current,
combined with the obvious fact that the motor is an inductor, results in the motor drive
electronics generating high-speed transients. These transients impress on the motor where
they can slowly degrade the insulation in the motor windings.
Line surges
The stored energy in a motor or transformer must dissipate when that motor or transformer
trips offline from its power system. Either the device absorbs the energy or the energy
pushes out onto the power system where other transformers or motors absorb the energy.
Often, large transient voltage spikes are generated when this energy is released on a power
system. Such spikes can easily damage motors, especially if the motor has weakened
insulation.
128 SKF Static Motor Analyzer—Baker AWA-IV User Manual
Motor testing theory and reference