Case Studies

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This story features a regional

wastewater treatment plant on

the shores of Puget Sound,

Washington. An award-winning

facility serving six cities, the

plant processes an average of

.1 million gallons of waste-

water daily, with a daily

capac

ity of up to 28.7 million

gallons

Most water treatment facili-

ties use the same basic

proc

esses, but this one has

been continuously updated

since it opened in 1984, includ-

ing high-intensity U

V light and

soon, a new Class “A” biosolids

ying fac

ility.

Application Note

Clean power delivers

clean water

From the Fluke Digital Library @ www.fluke.com/library

Measuring tools: Fluke 434 Power

Quality Analyzer

Features: Power factor, harmonics

Power

Quality

Case

Study

In this particular case, main-

tenance electrical specialist

Mark Newport was in the

process of installing new elec-

tronic power factor correction

units at multiple motor control

centers (MCCs) to improve

power quality, protect equip-

ment and reduce costs.

However, since corrective

measures can often introduce

new power quality problems

into the system, he used a

handheld Fluke 434 three-

phase Power Quality Analyzer

to make sure their efforts were

successful.

stem details

The treatment plant relies on

hundreds of motors, some as

large as 500 hp. A SCADA

ontrol system is interfaced to

the M

Cs, as well as valves,

actuators, sensors, and power

monitors. It also allows instant

isibility into the system at

numerous stations.

If the plant went down for

any reason, such as a regional

power outage, sewage would

continue to flow through the

plant and though the sedimen-

tation tanks, but it would be

discharged into Puget Sound

without full treatment.

To prevent this from ever

happening, the plant electrical

system has several levels of

redundancy. It’s served by dual

utility feeds from two substa

tions. Generally the load is

shared between the two feeds,

but either feed can handle the

whole facility through a tie-

breaker system

. A 1.25 MW

generator on an automatic

transfer switch can take over

within 8 seconds, if both utility

feeds fail

. Small, single-phase

uninterrupted power supplies

(UPS) maintain the elements of

the redundant control system

while the generator starts and

synchs.

Summary of content (4 pages)

PAGE 1
Clean power delivers clean water Application Note Power Quality Case Study In this particular case, maintenance electrical specialist Mark Newport was in the process of installing new electronic power factor correction units at multiple motor control Features: Power factor, harmonics centers (MCCs) to improve power quality, protect equipment and reduce costs.
PAGE 2
Power correction The power correction systems were being installed primarily to correct power factor. The same conductors were used to feed both adjustable-speed motor drives (ASDs) and across the line motor starters. The ASDs are non-linear loads and draw harmonic currents, especially at the fifth harmonic. Power factor capacitors present a lower impedance to higher frequencies, than to the 60 Hz fundamental. So a system with harmonic currents can cause overcurrent in correction capacitors.
PAGE 3
Before and after Before After The power correction system lived up to expectations. Six screens from the power quality analyzer tell the whole story. The change in current is a real testimony to the impact of power factor correction. By correcting the power factor the rms current drawn by the MCC was reduced by 27 %. You can see what happens in the power Figure 2 and 3: Power usage The Fluke 434 shows the power usage of the MCC with and without the power conditioner. measurements.
PAGE 4
Why correct harmonics? 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 system 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.