Case Studies

Fluke.Keeping your world
up and running.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. [phone] or
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In Europe/M-East/Africa (31 40) 2 675 200 or
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In Canada (800)-36-FLUKE or
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From other countries [phone] or
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Web access: http://www.fluke.com/
©2003 Fluke Corporation. All rights reserved.
Printed in U.S.A. 8/2003 2103520 A-ENG-N Rev A
Theory and analysis
Machine tool applications need
high torque at low speeds, and
dc motor/drive configurations
serve this need well. Thus,
machine tools commonly have
dc motors and drives. The input
rectifier circuit in a dc drive is
designed to provide variable
amounts of current to meet the
torque and speed requirements
of the motor. A commonly used
circuit configuration uses silicon
controlled rectifiers (SCRs) to
provide the variable current.
The SCR circuit produces
commutating spikes as one
rectifier is turned off before the
next rectifier is turned on. In
this case, the spikes generated
when the lathe was operating
were large enough to disrupt
the traffic light.
Solution
The engineer ordered a new
transformer and separate feeder
connection for the traffic light.
This new configuration
provided enough isolation to
keep things running normally.
Measurements
The engineer connected his
43B to the machine shop’s
service entrance, line-to-line
with “Transient Capture” mode
activated. The 43B recorded
large voltage spikes whenever
the lathe was operating. See
Fig. 2.
Fig. 2 Voltage spikes from a dc adjustable
speed drive
2 Fluke Corporation Power Quality Case Study: Malfunctioning traffic light