Case Studies

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Fluke Corporation
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PO Box 1186, 5602 BD
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ax (9
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©2005 Fluke Corporation. All rights reserved.
Printed in U.S.A. 1/2005 2398469 A-US-N Rev A
In modern power systems,
transients are present all the
time, some small and some
large. Switching of inductive
loads, lightning strikes and
transmission system switching
can all generate huge voltage
spikes. These transient voltage
spikes last as long as 100
microseconds and can be
extremely dangerous.
More commonly, when an
inductive load such as a motor
or a transformer is switched on
or off, it generates a voltage
spike sometimes called a “kick-
back spike.” Given the layout of
this particular system, facilities
suspected a startup-inrush
current of some kind was caus-
ing the breaker trip.
They selected the Inrush
Currents function on the
analyzer and reviewed the
current levels for all the loads
managed by the emergency
power system
. The technic
ians
did see an inrush event. The
inrush magnitude was within
the equipment spec
ifications ...
but why was the inrush event
occurring when the system was
already operational?
For some reason, the elevator
system wasn
’t sensing the
power fault condition. So, every
time emergency power was
reapplied, the elevator system
started to perform a normal
start-up — and that much
inrush and start-up current on
top of normal operations
exceeded the rating of the
power emergency protection
circuit breaker.
Solution:
A simple adjustment to the
elevator power fault sensing
circuit allowed the new system
to properly perform the individ-
ual elevator car power failure
procedure. In the process, facili-
ties verified the protection
circuit breaker settings and
adjusted them back to the
proper set points.
Given our tendency to get
jobs done as fast as possible,
some testing procedures can
easily get overlooked. Even if
new or upgraded equipment
appears to perform basic opera-
tions, it doesn’t elimate the
need for comprehensive accept-
ance testing. If the original
installers had performed the
emergency system test them-
selves, they would ha
ve spotted
the problem sooner and had a
much happier customer.
Then, they selected the
V
olts/Amps/Hertz feature from
the menu. The power quality
analyzer immediately began
recording voltage and current
on all three phases. Then, one
technician conducted a genera-
tor test. As predicted, the
breaker tripped.
Looking at the trended
Volts/ Amps/Hertz data, the
technicians could see where
the breaker tripped, but they
didn’t see any event data that
would have caused it. This
problem was too fast for regular
readings.
2 Fluke Corporation Power Quality Case Study: Elevator trips emergency generator breaker
The team switched to the
analyzer’s Transients function,
so they could see transients as
fast as 5 microseconds, started
recording and conducted the
generator test. When the
breaker tripped this time, a
transient was clearly evident.
All three phase voltages go to zero until the
circuit breaker is reset.
Sample screen.