Transcript
Introduction
Thank you for joining us. I’m Charlie True. I’m one of the hardware engineers here at PMI, and this white paper goes over some of the steps and settings you can use for analyzing motor startups and their effects on electricity feeding them. While this paper specifically utilized the Bolt for generating the recordings used throughout the paper, the information can be applied to most all the recorders we offer here at PMI.
Why Investigate Motor Startups
Investigating motor startups can be quite helpful in determining not only how a motor is performing in the specific area, but if it’s causing issues in other areas that are fed by the same lines. A good scenario where one could investigate would be when the motor starts up, the lights flicker. A good scenario where this occurs is someone powering a portable air compressor on a branch circuit that has both the outlets and lights on the same circuit.
Another scenario that would warrant an investigation would be if when your motor starts up, the overload protection for the motor’s tripping. Analyzing this event with the power quality recorder helps give insight to if the trip is caused by a true overload event or if it was simply some transient currents causing the issue.
Recorder Settings
Motor startups are quick events and can be very hard to capture, so you want to make sure you have your settings right. Using PMIView, which is available on Windows or iOS, you are able to create and save a custom template that can be used as a basis for motor startup recording.
In PMIView, you would go to the templates tab seen here in figure two, click on that, and you’ll be presented with a general-purpose overview of the template. On the left of the screen, you can see different areas of the template we’re able to configure, with these being the strip charts, waveforms, events, flicker, abnormal voltage, and then finally, the miscellaneous tab.
The general tab here, you’re able to enable overwrite for your strip charts, you set your recording interval, you can set your waveform captures, periodically capture, to disable that, your voltage and current thresholds, as well as your hookup and your current range. Going into these different tabs, you’re able to, on a more granular level, change all your settings.
For instance, on strip charts, you want to enable overriding as well as set up a short interval for this recording. Typically, one cycle to one second is best for startup events.
Waveform Triggers
On the waveform triggers tab, we’ll be able to set when and how the waveform capture occurs during the motor startup. Default settings in the general-purpose template are a good starting point, but it’s typically best to trigger off the current. To do this, you set your threshold just over the full load amperage of the motor, i.e. if you have 100 amp rated motor, you’d set the trigger to about 150 amps.
Events will be set up to reflect the needs of the particular motor you’re recording, such as your voltages and other current types. The miscellaneous tab lets you see what channels you want enabled, as well as gives another area to check your current range and hookup type to make sure they are correct for the specific entity.
Hooking Up the Recorder
Hooking up the recorder for the motor start-up is similar to hooking up the PQ recorder for any other PQ investigations. You do channel one to phase one, channel two to phase two, et cetera. It is important to note, however, to ensure the recorder is hooked up close to the motor, but still on the line side of the motor control devices. If the recorder gets installed on the low side of the motor control devices, the recorder will not be powered on or recording when the startup occurs.
A good practice for generating the recording is to start up the motor, allow it to run for a couple minutes before shutting it down, and repeat this a couple times to get several waveforms generated. That way, you have more than one to evaluate. If the motor’s load is variable, it is recommended to repeat the process under all loads.
Analyzing Recordings in PQ Canvas
Once we have a recording, we can upload it to PQ Canvas to evaluate it. Figure three, seen here, shows an overview of one of the recordings used for this white paper and reveals three distinct inrush events indicating motor startups. By taking a closer look, such as if we look at figure four here, we can see a peak inrush current of approximately 325 amps before tapering off to a running 10 amp current level.
Looking at the waveform captures themselves versus recording overview allows us to get a closer look at what the waveform is doing during the startup event. Looking here at figure five, which shows a high inrush current for a short period of time before tapering off to the running current. Then, we can also see that correlated with this inrush current, we have a slight voltage drop that recovers as soon as the motor tapers off into the running current.
If we look at the RMS view in PQ Canvas of this waveform capture, we can see a little bit easier what exactly is happening values-wise. For instance, we’re going from roughly 123.5 volts online to about 111.5 during the startup, and then we climb back up to the 123.5 before the startup for a decent recovery.
Event Change Table
Figure seven, we offer an event change table in PQ Canvas as well, and this is useful if you want quick numbers-based units without digging into the waveforms themselves. In this example of an event change table report, we can say it displayed a triggered event of 10 cycles that occurred on both channels one and two.
The minimum voltage, seen here, is 109.6 volts, and the maximum was 118.5 volts, with a current being minimum during this event as 28 amps, maximum as 132 amps. Two extra columns here on the right that are available in the event change table is the pre-cycle reading as well as a post-cycle reading. The pre-cycle reading here was shown at zero amps, and then afterward, the post-cycle reading, we’re seeing eight amps, which would help indicate that this is in fact a good motor startup, as we had no current before, high current during the event, and then lower current afterwards.
Three-Phase Motor Startup Example
If we go to figure eight, we show a three-phase motor startup that, when commenced, channel one and two both dropped significantly on their voltages, with channel two dropping the lowest. It went from a resting 245 volts to 120 volts during motor. This drop resulted in an increased ramp-up time for the motor, causing a longer period of that high current draw.
This is something that you would not normally be able to see utilizing just a straight multimeter to monitor your lines coming in, and it’s a great way to indicate we need to look into what’s causing this large drop in voltage during motor startup.
Using Merlin for Automated Analysis
These are a couple of tools that we offer in order to manually look over your motor startup recordings and waveforms. One of our newest products, Merlin, allows you to do this automatedly. The easiest way to do it is when you go into your recording overview, you’ll see a little Merlin hat at the top. You’ll be able to click on that and enable Merlin to run through your recording and analyze it for you.
It is important to note that if you’re planning on Merlin analyzing your recording, it can only go down to a one-second interval. It is not compatible with one-cycle intervals at this time.
The nice thing about Merlin is that once it’s gone over, we can see here in figure nine the overview dashboard of everything it found. It goes through and checks for flare, harmonic sag, swells, looks at your waveforms, analyzes your strip charts, and kind of gives you an at-a-glance cursory overlook of what’s going on. Looking at this overview here, there’s not a whole lot that looks to be of concern.
Merlin Waveform Analysis
To get a deeper dive into things such as your waveforms, you would click on the Waveform tab, and you’d be presented with the waveform overview seen here in figure 10. This one shows that we have a one-waveform capture that I looked at, and it shows that voltage dropped from about 123 volts down to roughly 111, 112 volts, or 233 milliseconds, coinciding with a large inrush current. Because the voltage recovered so quickly, instead of this being considered a sag, it is considered a rapid voltage change.
It also found that looking at the waveform, Merlin was able to tell that there’s no significant impulsive oscillatory transients in the instantaneous waveforms, and the THD remains low before and after the startup event.
The nice thing about utilizing Merlin is that you are able to set it off to analyze your recording while you are doing other items, such as setting up the recorder to go out in the field for another event, or having to deal with any other kind of power quality things you might need to analyze.
Conclusion
Analyzing startups does provide critical insight into how motors in our facility are operating and how they could be affecting other equipment. Utilizing one of the many recorders that we offer here at PMI, such as the Bolt that was used in this paper, allows the user to generate recordings to analyze and help make informed decisions on how to handle these PQ issues that crop up with motors. When coupling these recordings with Merlin, you’re able to get these insights quicker, easier than ever before, in a fraction of the time.
