Fluke 434 Series Ii Application Note 2435490

: Fluke Fluke-434-Series-Ii-Application-Note-808976 fluke-434-series-ii-application-note-808976 fluke pdf

Open the PDF directly: View PDF .
Page Count: 6

There are hundreds of power quality measurements you can take

on electrical systems and equipment. These instructions focus on

four predictive maintenance (PdM) measurements and two power

consumption measurements that can help you uncover hidden

costs, protect equipment from damaging conditions, reduce

unscheduled downtime and improve system performance.

What is it? In a balanced 3-phase system, the

phase voltages should be equal or very close to

equal. Unbalance is a measurement of the inequal-

ity of the phase voltages.

What does it do? Voltage unbalance can cause

3-phase motors and other 3-phase loads to

experience poor performance or premature failure

because of the following:

•Mechanical stresses in motors due to lower

than normal torque output.

•Higher than normal current in motors and

3-phase rectifiers.

•Unbalance current will flow in neutral

conductors in 3-phase wye systems.

simple ways to

reduce costs

with a Fluke 434 Power Quality Analyzer

6

PdM Measurement #1: Voltage Unbalance

How much does an incident cost? The major

costs are associated with motor replacement (labor

+ equipment) and lost income due to circuit protec-

tion trips.

Example Calculation

Assume the cost to replace a 50 hp motor each

year is $5000 including labor.

Assume 4 hours of downtime per year with

income loss of $6000 per hour.

Total Cost: $5000 + (4 x $6000)

= $29,000 annually

What to check? Inputs to motors, VFDs, UPSs1.

How much is ok? The EN50160 power quality

standard requires voltage unbalance, as a ratio of

negative to positive sequence components, to be

less than 2 % at the point of common coupling.

NEMA specs call for less than 5 % for motor loads.

Consult user manuals for other equipment.

How do I measure it with the Fluke 430

Series Power Quality Analyzer?

1. Connect the voltage leads of the analyzer.

2. Configure the analyzer for the appropriate

3-phase power system: delta or wye.

3. Select “Unbalance” from the main menu.

1VFD: Variable Frequency Drive; UPS: Uninterruptible Power Supply

Vneg is the ratio of negative to positive sequence voltage and Vzero is

the ratio of zero to positive sequence voltage. They are both indications

of voltage unbalance.

For more information on Fluke Predictive

Maintenance Products and Services go to

www.fluke.com/pdm

PdM Measurement #2: Total Harmonic Distortion

What is it? Total Harmonic Distortion (THD) is the

sum of the contributions of all harmonics. Harmonic

distortion is a normal consequence of a power sys-

tem supplying electronic loads such as computers,

business machines, electronic lighting ballasts, and

control systems.

What does it do? Harmonic distortion can cause:

•High current to flow in neutral conductors.

•Motors and transformers to run hot, shortening

their lives.

•Increased susceptibility to voltage sags,

potentially causing spurious resets.

•Reduced efficiency of transformer — or, a larger

unit is required to accommodate harmonics.

•Audible noise.

How much does an incident cost? The major

costs are associated with shortened life of motors

and transformers. If the equipment is part of pro-

duction systems, income may be affected as well.

Example Calculation

Assume the cost to replace a 100 KVA

transformer is $7000 including labor each year.

Assume 8 hours of downtime each year with

income loss of $6000 per hour.

Total Cost: $5000 + (8 x $6000)

= $29,000 annually

What to check? Motors, transformers and neutral

conductors serving electronic loads.

How much is ok? Voltage distortion (THD)

should be investigated if it is over 5 % on any

phase. Some current distortion (THD) is normal on

any part of the system serving electronic loads.

Monitor current levels and temperature at trans-

formers to be sure that they are not overstressed.

Neutral current should not exceed the capacity of

the neutral conductor.

How do I measure with the Fluke 430

Series Power Quality Analyzer?

1. Connect the voltage and current leads of the

analyzer.

2. Configure the analyzer for the appropriate

3-phase power system: delta or wye.

3. Select “Harmonics” from the main menu.

Voltage THD should be investigated if it is higher than 5 % on any phase.

PdM Measurement #3: Increasing Phase Current

What is it? As insulation deteriorates it begins to

leak. Loads will draw slightly higher current as

they age and they may send some of this leakage

current into the grounding system. Faults within

the equipment may also cause high ground current.

The best way to check insulation is by periodically

checking equipment with an insulation tester. But

you can also check equipment while it’s in service

by monitoring all of the currents (phase, neutral

and ground) to make sure none of these is increas-

ing significantly over time.

What does it do?

•Excessive phase currents can further damage

insulation and overheat the load, resulting in a

shortened life of the load.

•Over-current will cause protection devices to

trip, resulting in unscheduled downtime.

•Excessive ground current can create unsafe volt-

ages on metal chassis, cabinets, and conduit.

How much does an incident cost? Costs come

from premature motor failure and lost income due

to over-current protection devices tripping.

Example Calculation

Assuming the failure of a pump motor each

year costs $7000 to replace and causes a

$2,500,000 per year continuous process to be

shut down for 10 hours. Assume it takes two

people 6 hours to clean and restart the process

at $50 per hour each.

Lost income = 10 hours*($2,500,000 / (365

days/year * 24 hrs/ day)) = $2853

Motor replacement = $7000

Clean and restart = $600

Total Cost $10,453 annually

What to check? Any critical load, but especially

motors, VFDs and transformers.

How much is ok? The nameplate rating of the

load should never be exceeded. If you track the

phase current being drawn by a load over the

months or years, you should be able to get a sense

whether the current is changing.

How do I measure with the Fluke 430

Series Power Quality Analyzer?

1. Connect the voltage and current leads of the

analyzer.

2. Configure the analyzer for the appropriate

3-phase power system: delta or wye.

3. Select “Volt/Amp/Hertz” from the main menu.

4. Press “Save Screen” to record measurements for

comparison with future readings.

5. Monitor phase current regularly for changes.

Troubleshoot further if amps rms readings increase dramatically, or show an

increasing trend, between maintenance intervals.

Deep, frequent voltage sags can cause trouble, especially with industrial controls and computers.

PdM Measurement #4: Voltage Sags

What are they? Voltage sags are momentary

reductions in rms voltage for 1 cycle to 2 minutes.

Loads may be added without notifying plant man-

agement, and these loads may draw down system

voltage, especially if they draw high inrush cur-

rents. Also, as electrical systems age, the impedance

of the system may increase, making the system

more prone to voltage sags.

What do they do? Voltage sags can cause:

•Spurious resets on electronic equipment such as

computers or controllers.

•Sags on one or two phases of 3-phase loads

causing the other phase(s) to draw higher cur-

rent in an attempt to compensate. This may trip

overcurrent protection.

How much does an incident cost? The main

cost factors are lost income due to computer reset,

control system reset, VFD trip, and shortened life of

backup power system‘s UPS due to frequent cycling.

Example Calculation

Assume a voltage sag causes a VFD on a con-

veyor system to trip offline at least once a year.

No income is permanently lost, but 10 hourly

workers have to work 4 hours to make ship-

ments at $30/hour, which includes overtime.

Added Labor = 10 people * 4 hours * $30/hr

= $1200 annually

What to check? Motors, VFDs, UPSs, panels or

PDUs* serving computer equipment or industrial

controls.

How much is ok? Most loads will operate at

90 % of nominal voltage. The ITIC curve suggests

that single-phase computer equipment loads should

be able to ride through drops to 80 % of nominal

for 10 s and 70 % of nominal for 0.5 s.

How do I measure with the Fluke 430

Series Power Quality Analyzer?

1. Connect the voltage and current leads of the

analyzer.

2. Configure the analyzer for the appropriate

3-phase power system: delta or wye.

3. Select “Dips and Swells” from the main menu.

4. Monitor power over time.

5. View either as a trend display or event list.

*PDU: Power Distribution Unit

Power Measurement #1: Peak Demand

With the demand interval set correctly, the Fluke 430 Series will plot one

average demand reading for each demand interval. Your peak demand will be

the highest of these readings.

What is it? Utilities monitor the amount of power

a facility consumes and several times an hour they

calculate the average demand for that interval.

Peak demand is the highest average demand dur-

ing all of the intervals in a billing cycle.

What does it do? Utilities charge based on peak

demand because they have to maintain infrastruc-

ture large enough to supply power at peak levels.

Commercial and industrial customers can manage

the high cost of peak demand rates by staggering

load cycles to reduce total draw at any one time.

How much does an incident cost? This

depends on the rate schedule of the utility. It may

be higher during summer months and certain times

of day.

Example Calculation

Assume your normal demand is about 600 kW,

but three HVAC chillers come on at once and

your demand hits 750 kW at 4 p.m. on a

Wednesday in July.

Assume the utility demand charge is $100

per kW.

(750 kW - 600 kW) * $100.00 = $15,000 in

potential savings for July

What to check?

•Find out what demand interval the utility

uses — 15 minutes is common.

•Measure demand over time at the service

entrance.

•Look for significant loads operating concurrently

and use demand measurement to verify read-

ings for the individual loads.

How much is OK?

There are no safety or regulatory limits other than

what the facility can afford.

How do I measure it with the 430 Series

Power Quality Analyzer?

1. Connect the voltage and current leads of the

analyzer.

2. Configure the analyzer for the appropriate 3-

phase power system: delta or wye.

3. Set the demand interval to correspond to the

one specified by your power utility. Press Setup,

Function Pref (F3). Select “Power & Energy” from

the Select Function menu. Arrow down past the

bottom of the screen until “Demand int” is high-

lighted.

4. Select “Power & Energy” from the main menu

and monitor the power for as long as necessary.

5. Use the trend display to see the peak demand.

The cursor will help you see the demand at any

time during the recording.

Power Consumption

Commercial and industrial power consumers are charged for

power consumption based on multiple variables including energy

(kWh), peak demand (kW), and power factor. Power quality ana-

lyzers can help manage utility bills by determining which loads

have a significant effect on peak demand and power factor.

Power Measurement #2: Power Factor or Reactive Demand

What is it? Power factor compares the real power

(watts) being consumed to the apparent power

(Volts-Amps) of the load. A purely resistive load

would have a power factor of 1.0.

What does it do?

The power available to perform work is called real

power (kW). Inductive loads such as motors, trans-

formers, and high-intensity lighting introduce reac-

tive power (kVARs) into a power system. The

system capacity is rated by the apparent power

(kVA) which must be large enough to accommodate

both the real power (kW) and reactive power

(kVAR). Since reactive power requires system

capacity, but performs no work, utilities and plants

try to keep net kVARs low. High reactive power

translates to low power factor.

•Utilities may charge higher rates or penalties for

low power factor or high VARs.

•System capacity restrictions cause voltage drops

and overheating.

•Inductive VARs can be corrected by applying

capacitors or active conditioners.

What to check?

•See if your utility rate plan imposes a charge

for reactive demand or power factor.

•Find out how the utility measures power

factor or VARs. For example, are they looking

at peak intervals or averages?

•Identify loads that are causing lagging reactive

power and develop a strategy for power factor

correction.

How much is OK?

To avoid paying higher utility fees, power factor

should be higher than .97. Capacitors may be

applied on individual loads, at a confluence of

several, or at the service entrance to improve

power factor.

Note: This varies. Some utilities charge a rate for every percentage

point between .85 and .97. Some charge a rate based on the number

of VARs you use. Some don’t charge at all.

How much does an incident cost?

Example Calculation

Assume the utility adds 1% of demand charge

for each 0.01 below PF of 0.97.

Assume your PF averages 0.86 each month and

your demand charge is $7000.

(0.97-0.86) * 100% = 11%

(11% x $7000) x 12 months = $9,240

avoidable annual cost

How do I measure it with the 430 Series

Power Quality Analyzer?

Start at the service entrance, where the utility

takes its data, and then check individual loads or

transformers.

1. Connect the voltage and current leads of the

analyzer.

2. Configure the analyzer for the appropriate

3-phase power system: delta or wye.

3. Set the demand interval to correspond to the one

specified by your power utility. Press Setup,

Function Pref (F3). Select “Power & Energy” from

the Select Function menu. Arrow down past the

bottom of the screen until “Demand int” is high-

lighted.

4. Select “Power & Energy” from the main menu

and monitor the power.

Measuring the lowest power factor for a

demand interval: Press F4 Trend and then

press F1 to toggle through the parameters until PF

is displayed.

Measuring average power factor: Take the

ratio of kWh/kVAh to get the average PF over the

recording period. In the example shown below,

2.267/2.309 = 0.9818.

Measuring kVARh:

Whether your utility charges on total power factor(PF) or total kVARh

you can see it on this screen.

Cursors can help you record the lowest (PF) over a recording session.

©2005 Fluke Corporation. All rights reserved.

Printed in U.S.A. 3/2005 2435490 A-US-N Rev A