Significance:

Part 5: 

Article describing trends and desirable performance features in the development of power quality 

monitoring instruments.

One of the few 1963-vintage surge counters built for the General Electric survey (see the file “Res&Ind 

Surges” in Part 3), still in existence and now safeguarded on a shelf, as referred to in the preamble of 

this article, is still operational. See the file “Surge Counter” Part 5 for a description of this low-cost 

counter.

n the edge of a shelf, high above my workstation, sits one of my favorite 

power quality monitors-an impulse recorder built years ago by Fran~ois 

Martzloff.The instrument shows its age: its zip-type power cord is cracked 

and frayed, the last date on its log label is March 21,1968, and its only display is an 

electromechanical counter. Recently, I plugged the monitor into a 1980s vintage 

Schaffner disturbance generator. When I pushed the generator's trigger, the mechanical counter clicked politely, recording its first impulse in 34 years. What a wonderfully reliable monitor! Future PQ monitors need that kind of reliability, but they 

also need functionality well beyond yesterday's and today's capabilities (see Photo 

I, on page 1 4).The following discussion addresses the current state of PQ monitoring and identifies areas that require further development. 

When power disturbances interrupt 

facility operations, engineers need sophisticated monitoring tools- to get the 

facility up and running as quickly as 

possible. In the following sections, I'll 

discuss the current state of affairs and 

the near-term outlooks for the most 

important aspects of power quality 

monitoring. As you'll see, the journey 

to advanced PQ monitoring systems is 

far from complete. 

Clarity 

Although many peopls receive PQ 

monitoring data, they still don't understand power. I was reminded of this 

point recently when a highly skilled 

engineer and power systems designer 

asked me, "What's a swell?" 

It's even worse outside the engineering field. Most large-scale decisions are made by executives who 

don't know how a light switch works, 

let alone the consequences of a 50% 

sag for 12 cycles. We can be dismayed 

by this fact or, more practically, we can 

accept it and make sure that the outputs of our power quality instruments 

are at least acceptable to nonspecialists. This means having automated systems that can convert raw data into 

information that compares past and 

present events and intelligently solves 

problems. In addition, the systems need 

to express this data in basic terms. 

The nearfuture. The range of problems suitable for analysis will expand 

rapidly. Reports will describe specific 

causes and solutions -based on power 

quality data-in simpler terms. Reports 

with neutral recommelidations (i.e., 

"don't do anything") will become more 

common because most suspected power quality problems are not PQ problems at all. 

Completeness 

If engineers only monitor and record the 

data they think they'll need, they may 

miss the data that's actually required. 

For years, industry experts thought it 

was enough to record the depth and 

duration of sags, until they found out 

that information in rms time plots could 

determine the cause of a sag. It took 

several more years of recording rms 

time plots to find out that information 

in point-on waves could ascertain the 

likely effects of a sag. 

I don't know what will come next, 

but I do know it's important to keep 

raw voltage and current waveforms, 

especially in research projects. These 

voltage and current waveforms will 

undoubtedly yield more information. 

The near future. The industry 

will witness abrupt, nonincremental 

changes in what it considers necessary data, similar to the text-to-graphics change in the rrai,d 1980s. 

Robustness 

Power quality monitors need to function well in nasty environments. Their 

very reason for existence is to record 

what happens when other electronic equipment fails. But equipment 

doesn't fail just because of a lapse 

in power quality. It also fails because 

of temperature extremes, vibrations, 

mechanical shocks, huge magnetic 

fields, radio interference, voltage 

swells, and electric impulses. 

Manufacturers must construct 

PQ monitors that sneer at these violent disruptions. Unfortunately, the 

monitors produced by inexperienced 

POWER QUAUTY JULY 2092 13 . ,. .fa .=.A 
Yhoto I. One oj the newest power qualzty monztors szts atop a 

GE lightning strike recorderfrom the 1920s. The tiny, low-cost 

PQl power quality relay, which is embedded inside larger 

systems, detects impulses, sags, and swells. It has I6 interna- Photo 2. Power quality monitors are expected to survive and 

tional depth-duration standards built-in. 

manufacturers just aren't tough enough, and they fail at the same time 

as' the equipment they're monitoring. 

The nearfuture. Experienced manufacturers have the test equipment and 

the staff to duplicate and solve the 

problems that PQ monitors have to 

deal with (i-e., sags, swells, high frequency impulses, etc.), including those 

in corrosive, vibrating, or even hazardous locations (see Photo 2). 

Conciseness 

The big challenge with PQ instruments 

is deciding what data to keep. Too 

much data can be as useless as too little 

data. A 16-bit instrument that monitors 3-phase voltages and currents and 

performs 2 MHz sampling accumulates 24 MB of data per second, or a 

little over 2 terabytes of data per day. 

That's more than anyone can reasonably store, even in the near future. Most 

of that data is dull and uneventful as 

perfect sine waves slew up and down 

in regular patterns. Either you toss out 

most of the data, trying to come up 

with algorithms that correctly identify 

the interesting parts, or you compress 

the data and try to keep the most useful information. 

Typical compression algorithms include rms measurements that can be 

further compressed with minimud 

prosper in dzficult environments. 

average/maximum values, resulting 

in typical compression ratios of a billion-to-one. Of course, this directly 

conflicts with the completeness requirement previously addressed. In addition, there are some bad compression 

algorithms, such as 15-minute averages, that engineers must avoid. 

The nearfuture. New compression 

and selection algorithms will lead to 

incremental improvements. Algorithms that compare present waveforms to prior waveforms can quickly 

pick up any changes in quality. In addition, wavelets may be used to pick 

out interesting disturbances and describe their key characteristics. 

Other averaging techniques, such as 

peak-sense-equivalent, may supplement the rms values that reflect the 

way resistors respond to waveforms. 

(Peak-sense equivalent is a technique 

that produces values that represent the 

way electronic loads react to voltage 

waveforms.) 

Correlation 

There's a big difference between a 

voltage sag in an empty building and 

one in a semiconductor plant. The latter will cost someone a lot of money. 

By some respectable definitions, an 

event isn't a "power quality" event unless a load is disturbed. Some even argue that disrupted equipment-not 

power quality events-should trigger 

PQ monitors. It makes sense, then, to 

record the effects of a power quality 

disturbance as well as the disturbance 

itself. If the equipment is operating 

perfectly, then there's not much pain 

in discarding power quality data. 

The near future. Look for rapid improvements in this area. Work is just 

beginning, and it has a great potential 

for economic return. (See the sidebar, 

on page 18. ) 

Communication 

In most instances, obtaining real-time, 

onsite power quality data is a challenge. When something goes wrong 

with the power, the monitor is usually 

located in a grimy factory, tucked underneath an airplane's landing gear, 

or deep inside a peanut-sorting machine. Engineers need the data to appear immediately in an office, on a 

pager, or even at a consultant's lab 

half way around the world. 

The near future. Internet use will 

increase, but firewalls continue to restrict the easy flow of data. More 

power quality data will be "piggybacked" on other communication 

channels, such as meter-reading and 

e-diagnostics channels. 

Continued on page 17 
Continued from page 14 

Correctness 

Sometimes engineers measure the 

wrong thing. For example, they 

might measure the electric power 

when, in actuality, sabotage, humidity, or trucks striking the loading dock are to blame. They also 

might measure in the wrong location, such as downstream from a 

UPS or on the wrong phase. 

I remember one case in a peanut-processing facility. Sensitive 

loads failed only when the huge 

sorting machine was running. The 

problem related to power quality 

only indirectly. The sorting machine vibrated the whole building 

and shook loose the connections on 

the circuit breakers. 

At another site, a minicomputer 

failed at the same time each day. A 

power monitor revealed nothing. It 

turned out that the computer operator would sit at the computer at that 

time each day, smoking a cigar. The 

smoke from the cigar corrupted the 

read head on the hard drive. 

A fish processing plant in Canada 

serves as a final example. An intermittent computer failure was traced to 

pulsed radiation from an arcing bug 

zapper. A power quality monitor was 

actually useful because it recorded the 

pulses even though it wasn't connected 

to the power line. 

Even when electric power is the 

culprit, it's possible to measure the 

wrong parameter. For example, total 

hamonic distortion for current measurements is a useless parameter because it uses the amount of fundamental current as a reference, and the 

amount of fundamental current wanders up and down dramatically. 

The near future. We need to broaden the vision of PQ specialists. Field 

engineers who solve real-world problems know that power quality is only 

one of many mysterious, hard-toduplicate issues. Practical, hands-on 

reports explaining how suspected 

problems were solved (even if they 

weren't power quality problems in the 

end) would be helpful. 

Consistency 

Two power quality monitors connected 

to the same wires should record the 

same results, but they usually don't. 

This is a real problem for enforcing 

power quality contracts. Perfectly accurate instruments, with perfectly correct algorithms, can produce wildly 

different readings. 

For example, true rms meters can 

differ on their averaging interval. Remember, the "m" in rms stands for 

"mean," and nobody knows if that average should be 1 cycle, 1 second, or 

15 minutes. 

The near future. Some standards 

are beginning to address this issue. 
Productivity Monitoring 

Managers don't spend money to 

measure power qualiiy; they spend 

money to kq their manufaduring 

processes running. Here's an interesting example from a textile mill. 

Vdtage sags don't matter at this location, but broken threads do. As it 

turns out, some voltage sags- but 

not all-cause broken threads. 

In addition to monitoring AC 

voltages and currents, this particular monitoring system also monitors 

motor speeds, tensions, temperatures, and other parameters. 

The upper graph shows a traditional presentation of the voltages 

and currents during a sag. Experts 

transmitted these waveforms 

through the Web for analysis. Note 

the huge increase in current at the 

end of the sag-typical behavior for 

electronic power supplies. Although 

these graphs are %meaningful to 

power quality engineers, they mean 

nothing to the people who matter: 

the managers of this factory. 

The lower graph shows the process parameters recorded by the 

power quality monitor during the 

sag. The arrow points to an overshoot in the tension-control backup 

signal, a real problem to the factory managers, and one they know 

how to fix. 

The key here is getting the right 

data, in the right form, to the right 

-301 I I I 1 

14:3693.05 14:3&33.10 t&36..33.15 14:36.33.20 204:36:33.25 t4:3633.30 14:36:33.35 14:36:33.4 

CHAVdts - CHB Volts - CHCVolts - CHD Volts 

CHAAmps - CHBAmps - CHC Amps - CHD Amps 

Fig. 1. The voltages and currents during a sag at a textile mill. 

Fig. 2. The process signals reconied by a PQ monitor at a textile mill. 

people. The power engineers need the the process parameters to solve 

voltages and currents to identify their theirs. A power quality monitor should 

problem, and the factory managers need record both. 

For instance, IEC 61000-4-30 specifies quite precisely how engineers 

should measure voltage sags, dips, and 

swells, which is good news in a way. 

But standards that specify how to do a 

task, instead of specifying the required 

result, always end up discouraging innovation. As a result, the industry must 

do some careful balancing. 

sive accessory buried inside productive devices, and one that communicates 

through the device's data channel. 

The near future. Look for accessory-type power quality monitors at 

costs that are one to two orders of magnitude lower than traditional monitors 

and embedded in larger systems. 

cost 

By the time you need a monitor, the 

problem has already happened. The 

only solution is to have lots of low-cost 

monitors in place before a problem 

shows up. This implies that the ideal 

PQ monitor is more like an inexpenConclusion 

To date, no power quality monitor 

meets the goals of clarity, completeness, robustness, conciseness, correlation, communication, correctness, consistency, and cost. Indeed, it may not 

be possible because some of the goals 

contradict each other. 

Your challenge, as a user, is to figure out why you need to monitor and 

what you plan to do with the results. 

Next, review the goals outlined in this 

article and select the most important 

ones for your application. The chances 

are good that you'll find an available 

power quality monitor that meets your 

needs. Chances are even better that, in 

the near future, improved power quality monitors will meet needs that you 

didn't even know you had. Po 

Alex McEachem is the president of Power Standards Laboratory in Emeryville, 

Calif. You can reach him at alex@power 

standards.com or through his Web site, 

www.alex.mceachem.com. 

18 POWER QUALITY JULY 2002