28
The experimental work is conducted on three 4 pole motors, a 10 hp motor, a 50 hp motor,
and a 75 hp motor. However, before any of the testing began, a device that is capable of
producing momentary service interruptions for these size motors is constructed. Next, the
preliminary experimental work is performed and finally, a comprehensive data set is
collected.
3.1 POWER DISTURBANCE GENERATOR
In order to conduct a comprehensive experimental study on the transients developed during a
momentary service interruption, a point on wave interruption generator is needed. Portable
power disturbance generators are available commercially, but are expensive and are limited
to 200A continuous, 600-700A peak and 480V and below [30][31]. Other non-commercial
designs are available in the literature, but can not be used the motor testing in this study
because of insufficient ratings or operation specifications [32][33][34][35][36]. A simple
electromagnetic contactor can not be used because of the inconsistent drop-out and pick-up
time. A custom built solid state device is therefore needed. This section presents the basic
design of the custom built power disturbance generator that is capable of producing
momentary service interruptions. Detailed design and operation information can be found in
Appendix B.
3.1.1 Block Diagram
Figure 21 shows a block diagram of the solid-state POW controller. The bold lines represent
the three-phase, 480V
rms
power circuit and the remaining lines represent the control circuit.
The control circuit is powered by a 5V
dc
power supply. The actual switching of each phase
of the power circuit is performed by a single fiber optic controlled Integrated Gate
Commutated Thyristor (IGCT).
Chapter 3
Experimental Based Stress Assessment of Single
Motors