Fluke 1577, 1743, 1744, 1760, 1760TR Service Guide

PART FOUR

of a predictive

maintenance series

Applying power quality
measurements to
predictive maintenance

You may already be using pre­dictive maintenance (PdM)
techniques on your motors and
drives. But how often do you
inspect the power to your equip
ment? By adding basic power
quality measurements to produc
tion equipment maintenanc
procedures you can head off
unexpected failures in both
production equipment and your
power system.

Cost savings

Insurance claims data in the
NFPA 70B maintenance standard
shows that roughly half of the
cost associated with electrical
failures could be prevented by
regular maintenance. A study
published in IEEE 493-1997 says
that a poorly maintained system
can attribute 49 % of its failures
to lack of maintenance.

To determine the cost of a
failure, it helps to consider three
key categories:

ross marg

ome (g

ost inc

L

•

due to dow

Cost of labor to troubleshoot,

•

patch, clean up, repair and

restart

Cost of damaged equipment

•

and materials, including

repairs, replac

scrapped material
To calculate power quality

costs and potential savings
at your facility, reference the
online calculator at
www.fluke.com/pqcalculator.

ntime

ements and

-

-

e

in)

Application Note

e 1.

Figur

limit and then the effect of the corrective action.

This maintenanc

e control chart tracking voltage unbalance shows a Nov-03 reading above the 2.5 %

For more information on Fluke Predictive

Maintenance Products and Services go to

www.fluke.com/pdm

Integrating power quality
into PdM

Unlike a comprehensive electrical
system survey, predictive mainte­nance power quality focuses on a
small set of measurements that
can predict power distribution or
critical load failures. By checking
the power quality at critical
loads, you see the effect of the
electrical system up to the load.
Your predictive maintenance
inspection route probably already
includes any motors, generators,
pumps, A/C units, fans, gear­boxes, or chillers on site.

Measurement Guidelines

Voltage Measurements Phase-to-Neutral Voltages

Voltage Sags Phase to Neutral Sag Count
Voltage Harmonics Phase Voltage THD
Current Measurements Phase Currents
Voltage Unbalance Negative Sequence, Zero Sequence

Table 1. Basic power measurements for 3-phase Wye equipment

Voltage stability, harmonic
distortion, and unbalance are
good indicators of load and distri­bution system health and can be
taken and recorded quickly with
little incremental labor. Current
measurements can identify
changes in the way the load is
drawing. All of these measure­ments can be taken without
halting operations and generate
numbers that can easily be
entered into maintenance soft­ware and plotted over time.

For each measurement point or
piece of equipment, determine
what limit should trigger c
tive action. Limits should be set

elow the point of failure,

well b

Neutral-to-Ground Voltages

orrec-

and as time goes on limits may be
“tightened” or “loosened” by ana­lyzing historical data. The appro­priate limits depend somewhat on
the ability of your loads to deal
with power variation. But for most
equipment, your maintenance
team can devise a set of default,
“house limits” based on industry
standards and experience.

The cost of three-phase power
analyzers is lower now than ever
and it should only take roughly 15
minutes to take the readings dis­cussed in this article. (Storing volt­age sag data will add more time,

e it requires picking up the

sinc
data after a day or so.)

Voltage

Good voltage level and stability
are fundamental requirements for
reliable equipment operation.

Running loads at overly high

•

or low voltages causes reliabil­ity problems and failures.
Verify that line voltage is
within 10 % of the nameplate
rating.
As connections in your system

•

deteriorate, the rising imped­ance will cause “insulation
resistance drops” in voltage.

2 Fluke Corporation Applying power quality measurements to predictive maintenance

Added loads, espec
with high inrush, will also
cause voltage decline over
time. The loads farthest from

vice entrance or trans-

the ser
former will show the lowest
voltage.

eutral to ground voltage tells

N

•

you how heavily your system
is loaded and helps you track
harmonic current
ground voltage higher than
3 % should trigger further
investigation.

ially those

. Neutral to

Figure 2. Recording all phase voltages and neutral to ground voltage
is a good start for a PQ analysis of critical equipment and overall
distribution system health.