April 2007 Variable Voltage Made Easy
SPECIAL NOTICE: Please check each course for verification of approval before purchasing. This test is based on the article, Variable Voltage Made Easy and counts as 3 contact hours (0.3 CEU) of elevator-industry continuing-education credit. Most courses are approved by NAEC for CET/CAT and NAESAI for QEI and in the following states: Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Maryland, Mississippi, Missouri, Montana, Oklahoma, Pennsylvania, Vermont, Virginia, Washington, West Virginia, Wisconsin. Learning Objectives - After reading this article, you should have learned about:
- the theory of variable-voltage control applied to elevators using the Ward-Leonard system
- methods of obtaining control of acceleration, deceleration and leveling
- how to circumvent residual currents
- the best way to obtain smooth control of elevator motion
- the use of damping-field and shunt-field motor control
- the design and operation of a self-excited generator
- the methods designed to prevent the hoist motor from pulling through the brake
- what happens when motor load and slip increase
- resistance and Star-Delta methods of AC-motor starting
- troubleshooting noises in the driving motor on a motor-generator set
- causes of sparking in generators and hoist motors
- how to check a DC machine or motor-generator set for electrical neutral
- how to trace various variable-voltage problems to parts of the system
- how to determine the synchronous speed of a motor
- determining the causes and finding remedies for rough stops
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