Transcript

Introduction

Hi everyone, welcome to today’s Ask a Pro session. I’m Scott Windsor, the lead software engineer at PMI, and I’m joined today by our president, Chris Mullins. Today we’re gonna be talking about voltage sag analysis in PQ Canvass.

In this presentation, we’re going to cover industry standard IEEE standard 1668-2017, industry standard SEMI F47-0706, and how to perform a voltage sag analysis using those standards in PQ Canvass. Let’s dive into it.

IEEE Standard 1668-2017

For industry standard IEEE standard 1668-2017, it’s also known as the Recommended Practice for Voltage Sag and Short Interruption Ride-Through Testing for End Use Electrical Equipment Rated Less Than 1000 Volts, a real short title.

It provides some standardized framework for assessing and improving equipment resilience to voltage sags, defines test protocols for equipment performance under voltage sags and short interruptions, and it applies to low-voltage systems under 1000 volts for single-phase, two-phase, and three-phase systems.

It characterizes sags by magnitude, duration, and phase relationships, and it sets realistic test points using real-world data, such as equipment must withstand 50% voltage sags for .2 seconds without a failure.

The key here is it’s under 1000 volts, so that means the secondary transformers. This is not a medium voltage or primary side type of standard, so it’s meant for customer secondary, the transformer, and this is really a recommended practice for testing sag immunity for customer equipment.

So really it’s not a utility standard per se, but it’s one the utilities should be very familiar with because if utilities are meeting the sag limits that are in 1668, which derive directly from the SEMI F47 limits, if utilities are meeting those limits with their sags, then it’s reasonable to expect customer equipment to be compatible with that sag environment.

And if it’s not, if you have a customer that has equipment that’s misoperating and yet your sags are all within 1668 or SEMI F47, then you have a legitimate kind of pushback to explain, well, your sags are within industry limits, it’s impossible to get rid of sags completely, and your equipment is overly sensitive. They should have their equipment vendor verify that it was tested 1668, there may be power conditioning equipment that will bring it into compliance with 1668, and this standard is how you would test for that, so that the customer can be assured their equipment will work in the environment they’re sent.

SEMI F47-0706

SEMI F47-0706 is published by the Semiconductor Equipment and Materials International. It standardizes sag classification, outlines some testing procedures for sag simulation and performance evaluation, and defines test protocols for assessing voltage sag immunity, especially in semiconductor processing equipment. It’s covering low-voltage systems—single-phase, two-phase, three-phase equipment.

It specifies sag magnitude and duration based on real-world data. It hearkens back to the 50% voltage sags for .2 seconds without a failure, same standard as the other one. This can aid utilities and also aids manufacturers in designing reliable equipment and helps identify things like sag-prone areas in fabs for semiconductor fabrication.

By meeting the standards requirements, semiconductor manufacturers, equipment suppliers, and facility managers can achieve higher operational reliability and possibly enhance their market competitiveness. The IEEE standard derives from this one.

The goal was to have 1668 have the limits in there exactly match F47. There were some typos and unintentional differences that are being actually ironed out in the upcoming 1668 new edition, so it’ll be exactly the same as what’s specified in F47.

SEMI F47 was originated in the semiconductor manufacturing arena where it’s extremely expensive for a semiconductor fab plant to go down because of a sag. They were extremely focused on making sure that didn’t happen to their equipment because it costs them millions of dollars per hour or day or something extremely expensive, so they wrote their own standard for this.

Originally the focus was on semiconductor manufacturing equipment, that’s where the SEMI comes from, but it’s been more widely adopted as a guideline for a lot of other industrial equipment. Even though technically it’s for semiconductor equipment, it’s used generally as a benchmark for other industrial equipment as to what’s reasonable effort to put in for sag immunity, how much ride-through they need in their power supplies, how much bulk capacitance to ride through certain levels of sags.

Voltage Sag Analysis in PQ Canvass

Next we’re gonna show how you can perform voltage sag analysis in our PQ Canvass cloud software. For any of you who don’t know, PQ Canvass is our subscription-based cloud software for power quality analysis.

The voltage sag analysis in PQ Canvass targets detection of short-duration reductions in RMS voltage, typically lasting from a half cycle up to a minute, classified by magnitude and duration as prescribed in both the standards we just talked about. Every sag event is logged with a timestamp, retained voltage, duration, and inception angle.

Running the Report

This is a recording up in our PQ Canvass software, and when you’re on the recording page, right now this says beta feature, but we’re releasing this publicly, I believe this week. So you’ll click on Analytics, and you can see we have several other reports which we have already one webinar out about one of these and then another upcoming, but we’re gonna click on the Voltage Sags and configure it.

This one’s already been run so I’m not gonna touch any of these settings, but you might change some of these settings depending upon your specific requirements or investigation. And then we’re gonna click Run.

While that’s running, it’ll take just a few seconds here, PQ Canvass uses RMS current data in this report to determine if sags are caused by external factors or maybe on-site issues like a motor start. Those on-site sags can be addressed with load sequencing or ride through devices, while the external sags might require utility investigations.

Report Overview and Sag Classification

This starts with a kind of similar review of what the recording was, some of the parameters of the recording, a summary of the sags, and gives you some details of the sags. 1668 goes into a lot of detail on sag classification and measuring the angle of inception and the other parameters in case you need to know how long the sag lasted.

Every sag that’s been captured with a waveform capture is analyzed, so you have the exact sag duration, the retained voltage, and what did the voltage go down to.

CMF 47 Plot

Then we have the CMF 47 plot. Again, the CMF 47 thresholds are meant to be exactly the same as 1668, so this works for both. These little diamonds represent the three sags that are in this file, and these are all in the acceptable range.

If it’s above the blue line, that means that the magnitude and duration is above the CMF 47 limit and customer equipment should be able to ride through that without any problem. If we had any of these red diamonds below that blue line, in the white area, then that’s a possible incompatibility. That means the sag may cause trouble with equipment.

Voltage and Current Correlation

Here we have a strip chart of minimum voltage to match current. This can be helpful in determining where the sags were in time in relation to other types of voltage fluctuations. If you’re going to analyze whether the customer load caused the sag or if the sag goes upstream, then you wanna look at the relationship between voltage and current.

If the current spikes at the same time as the sag, that sort of correlation can help determine where’s the source of that sag. If there’s a sag happening somewhere, that means somewhere there’s current flow causing that voltage drop, and one of the first questions is, is the customer causing their own sags or are they coming from the utility?

Many utilities take the stance that if a customer is causing the sags and they’re secondary with their own loads, then it doesn’t really matter if it exceeds the limits or not. The customer is causing their own sag, it’s not causing trouble for anyone else and it’s not on the primary side. The solution typically is load sequencing or soft starters on motors or even a variable frequency drive to reduce that inrush current. Or, in some cases, a reasonable amount of current may cause an abnormally large sag if there’s a poor connection, like a corroded connection or a bad splice, that may be on the utility side. So some of those details are helpful, that are in the report.

Waveform Captures and Sag Details

Here we have the sags broken down. Here we see the waveform capture or we see the raw sine waves, and the sag portion is outlined in red, or shaded in red. The bottom plot is the sliding RMS graph, so the software is taking the sine waves, applying a one cycle RMS calculation, and slides that window one sample at a time to produce a continuous RMS graph here.

So here we’re looking at RMS values and we can see the sag and see the return voltage, which isn’t the same level as the starting voltage. This is a load start, and this red shaded portion is the duration of the sag.

Then here is the chart that shows us the duration in milliseconds, the retained voltage, what did the voltage go to in terms of a percent or per unit basis of the nominal. That’s given for each sag that’s in this recording. So if there’s a particular sag, especially if it’s in violation, you might want to focus in detail on these.

Observations and Conclusions

In this recording, each of the sags was in compliance, and then there’ll be an observation. This is drawing some patterns from the sags here. There’s only three sags in this file so there’s not a lot of patterns to conclude from, but there’ll be some observations in the end of the report to help give you some guidance on how often these sags are happening or if there’s any patterns to that sag.

So this is somewhat of a clean bill of health. The sag environment here at this location is compatible with the levels that are given in CMF 47 and 1668, so if customer equipment is misoperating due to these sags, the utility has justification for saying, “Well, our sags are within industry standards and the equipment is overly sensitive.”

That equipment needs some power conditioning, maybe some ride through ability depending on what’s dropping out, because it’s not practical to mitigate the sags better than this, and it’s almost impossible for a utility.

Closing

Well, thank you for those insights, Chris. That just about does it. Be sure to check out any of these links for additional information. As always, thanks to everyone for tuning in and have a great rest of your day.