• A 1-minute voltage sag/dip video
• Sag immunity testing: 1-phase vs 3-phase?
• Price increase in June - PSL's Industrial Power Corruptor
• Power quality instruments: 61000-4-30 Class A certification
• 4-terminal resistors
• Energy conservation in the semiconductor industry
• Which way are the harmonics flowing?
• Low-cost "Voltage Performance Monitor" (Ideal)
• Upcoming Power Quality visits world-wide

Voltage sags (or dips) are a big problem for industrial customers, and I'm often asked why electric companies don't just fix the problem. The question has been asked enough times that I made a 1-minute video to explain. This question tends to come up during my world-wide travels, so I avoided using English in the video.

If you find this video useful, please feel free to make copies, or distribute it in any way you like. Also, if there are other power quality topics that you'd like me to address in a 1-minute video, please let me know: Alex@PowerStandards.com, and I will see what I can do.

Voltage sags/dips - a 1-minute video (20 MB)

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All the voltage sag immunity standards (SEMI F47, IEC 61000-4-34, IEC 61000-4-11) require testing your 3-phase equipment with voltage sags that affect one phase-to-neutral pair, or one phase-to-phase pair.

Why not sag all three phases at the same time?

First, it's important to recognize that a sag (or a dip - "sag" is American English, and "dip" is British English) is a voltage, so you must talk about two conductors. Anybody who talks about "a dip on Phase A" isn't being clear: they might mean a dip between Phase A and neutral, or Phase A and earth, or Phase A and Phase B, or...? That's why the standards are so careful to say that you test one pair of phase-to-neutral conductors at a time, then one pair of phase-to-phase conductors at a time.

Still, why not require testing on three phase-to-neutral voltage simultaneously? The answer is that voltage dip immunity standards are economic compromises. It's easy to make any piece of equipment immune to all possible voltage dips - but only if you can spend lots and lots of money. The standards recognize that sags affecting one pair of phases are fairly common, and sags that affect all three pairs of phases are rare; and that it's fairly cheap to protect against one pair of phase dips, while it's expensive to protect against dips that affect all three pairs of phases.

• Roughly 85% of dips affect primarily one phase-to-neutral pair, or one phase-to-phase pair. For dip immunity purposes, this statistic must be measured at the equipment terminals, not at substations.
• The cost of voltage dip immunity is roughly proportional to the energy that must be stored.
• To survive a one-phase-to-neutral dip (or even two-phase-to-neutral dip), or one-phase-to-phase dip, you only must store enough energy to support the equipment until the non-sagged phase comes around - about 10 milliseconds worst case, no matter how long the dip lasts. In contrast, to survive a rare dip that affects all three phase-to-phase pairs, you must store enough energy to last until the end of the dip, perhaps 200 milliseconds or longer. That costs 20 times as much, and protects you against a rare event. Is it worth the extra money?
• Finally, if you do decide to protect against dips that affect all the conductor pairs, you're going to install a three-phase UPS or its capacitor-based equivalent. Once you do that, why bother testing?

Learn more about 3-phase dips with my FREE Power Quality Teaching Toy program

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We've held the price steady on the world's most popular voltage sag generator, PSL's Industrial Power Corruptor®, for two years now, but the price must increase in June 2007. All orders received before 30 June will be accepted at the present (lower) prices. If you have a purchase pending, now would be a good time to push it through.

The Industrial Power Corruptor takes in clean single-phase and three-phase power, and adds voltage dips and swells. Rated at up to 200 amps per phase (1000 amps peak), the Industrial Power Corruptor is widely used for testing and certifying industrial equipment in North America, Asia, and Europe. It is fully compliant with SEMI F47, IEC 61000-4-11, and IEC 61000-4-34.

The price on PSL's Industrial Power Corruptor® will increase in June 2007

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Here at Power Standards Lab over the last few months, Alec, Thomas, Takashi, and I have been testing and certifying new PQ instruments from around the world for IEC 61000-4-30 Class A compliance.

It is a fascinating process. IEC -4-30 has been written so that any two instruments that comply with Class A will produce the same answer when connected to the same signal.

Sounds simple, right? It's not.

We have developed a huge library of test waveforms to verify that the instruments we're testing actually comply. Most don't. However, many of the better manufacturers have been able to adjust their firmware (or sometimes their documentation) to attain PSL certification.

We have been particularly suprised at the number of instruments that claim to be "Class A" that aren't. Our suggestion: if you're paying for Class A, look for a PSL Certificate. As far as we know, we are the only lab in the world that is doing full Class A testing.

Testing an instrument for Class A compliance at PSL

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I receive many questions about precision currents for calibrating power quality meters. Ultimately, all practical current calibrators rely on a precision voltage source, and a precision resistor.

Engineers generally understand precision voltage sources, but high-current precision resistors can be complicated. Unlike ordinary resistors that have two terminals, high precision low-value calibration resistors have four terminals.

You can find a complete explanation of how 4-terminal resistors work here, using PSL's calibration lab as an example. (I'm proud that Wikipedia's discussion of resistors uses this explanation as an "External Link"!)

Using 4-terminal resistors for calibration at PSL

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Along with some of our long-term clients, we're launching a project on energy conservation in the semiconductor manufacturing industry. I think there's a lot of room for improvement. But I'm optimistic; the industry is quick to adopt new technologies, and we've learned that other industries often follow the path that has been identified in the semiconductor industry. Maybe we can improve the world, at least a little.

If you're interested in participating, or finding out more, please send me an e-mail at Alex@PowerStandards.com.

Semiconductor manufacturing energy conservation - a new project at PSL

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We're wrapping up an interesting project on harmonic flow.

Working along with Bill Moncrief and Mack Grady, PSL's Matthew Muh and I have been investigating various ways of measuring harmonic direction flow for last two years.

It's not an easy question; to begin with, harmonic voltages and currents are sinusoidal so they flow equally in both directions. But it's more complicated than that: it's not always clear what we're trying to measure (the direction to the source? the "badness" of a particular customer? the most likely solution?), and the measurements are difficult. In fact, we've had to develop a new instrument just to make sufficiently precise harmonic measurements.

The project is funded by CEATI, with sponsorship from Electricite de France, Hydro Quebec, Manitoba Hydro, PSE&G, and others. If you would like more information about this project, please contact CEATI's Jerry Lepka jlepka@ceatech.ca.

PSL's Matthew Muh investigating harmonic direction flow

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If you're looking for an inexpensive, single-phase power quality instrument, take a look at the new Voltage Performance Monitor from Ideal Industries. It's a clever design that just won the "product of the month" award from Electrical Construction & Maintenance Magazine.

The hand-sized instrument captures and time-stamps voltage sags, voltage swells, high-frequency impulses, and voltage THD. It has a series of snap-on mains plugs so it works anywhere in the world. Best of all, no computer is necessary: everything shows up on the meter's screen. For a low-cost instrument, it's very well designed.

(Full disclosure: PSL participated in the development of this instrument, so our enthusiasm may be a little biased. Still, we're enthusiastic!)

An interesting PQ instrument: the Voltage Performance Monitor from Ideal Industries

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