130. Idea – Variable Frequency Drive Startup: What should I know? Transcript
I would say the most important thing is take your time. Everybody’s very busy these days, but when you’re starting up a drive, just remember what you’re sitting in front of. You’re sitting in front of something that could be potentially very dangerous. It’s got a lot of power and you have the ability to ruin a lot of things. If you tell it to do the wrong thing. So at all times just relax. I would just say, take your time. No matter who’s looking over your shoulder. You should never rush.
Welcome to EECO Asks Why a podcast that dives into industrial manufacturing topics, spotlights the heroes that keep America running. I’m your host, Chris Grainger. And on this podcast, we do not cover the latest features and benefits on products that come to market, instead, we focus on advice and insight from the top minds of industry because people and ideas will be how America remains number one in manufacturing in the world.
Welcome to this episode of EECO Asks Why. Today we’re going to be digging into the topic of what do we need to understand about a variable frequency drive and start-up. So today we have with us, Mr. Chase Boehlke from Siemens. I’m very excited to have Chase back for those who listen, he’s been on several episodes and Chase is going to be digging into this topic with us. So Chase welcome hope you’re having a great day.
I am. I hope you are too.
Absolutely. So we’re looking at EECO Asks Why. So why is commissioning a VFD important?
That’s a really good question. When you are starting up a motor with a starter, it’s pretty simple, right? You make sure that you have the proper line protection and you make sure that you have the proper overload. And if it’s one of those little dial overloads, you make sure it’s in the right spot and you call it a day as long as it doesn’t lockdown, or there’s no mechanical problems it’s going to run and it’s going to be fine.
Soft starts can be pretty simple too. Maybe a couple of settings you set up, maybe a few more if you want do some network control and things like that, but usually, they’re pretty simplistic. A VFD largely depends on what you’re doing. If it’s a simple fan or a pump startup shouldn’t take very long and sometimes it can take 10, 15 minutes and you can be done.
But in more advanced applications, if we’re trying to do load sharing or we’ve got multiple axes working together or we’re doing camming or gearing. There’s so many things that you have to set up to make sure that everything works properly especially when you’re doing very specific things.
And that means that your fundamentals have to be set. Absolutely correct. All the motor followed amps and things like that, but the VFD has to be set up properly so that it runs your effort application properly.
Very good. So when we get started, what wiring should we verify prior to any startup here?
Oh, man, the answer to that is everything. If you’re the guy that’s going to start the drive up, you should also be the guy that’s looking at the wiring. I, And I stand firm on that. There have been several times I’ve seen where somebody came up to commission the drive. And then somebody had accidentally wired the 460-volt input to the output of the drive, and then they put power on the drive and the drive blows up.
And then it’s a who done an issue and whose fault is it? And obviously, nobody wants that to happen. So there’s never anything wrong with double checking and triple checking connections to make sure things are set up. So I would say very first, make sure the line and the load wires are actually set up in the right places.
If you’re hooking up a brake resistor, make sure that you’ll hook it directly up to the DC bus wires, there’s usually, depending on your manufacturer, a switching screw and either a ground screw or a positive screw, depending on how it’s set up. So never hook up a true resistor without a chopper on it directly to the DC bus. That’s another thing.
IO wiring, common mistakes that are often seen. Multiple drives will have multiple grounds. Your analogs may have their own ground because they need to be isolated. You may have five IO points that have one ground. You may have another three IO points that have a separate ground, and that helps you isolate things in noisy environments.
So if you are trying to wire multiple inputs and inputs, zero through three words and input four doesn’t work, make sure that your grounds are actually all tied together for whatever supply you’re using, whether it be the internal power supply of the product or a separate 24 volts source.
Well, it sounds like you’re just in general grounding. You’ve mentioned that several times. That sounds is a pretty key area that needs to be verified during this start-up.
Oh yeah. There are so many different kinds of power structures in the US. Wise, Deltas, Stinger Legs there’s just so many different kinds of power in the United States.
We have a very I’ll call it, we have a very diverse power grid. Let’s say that. So we’re just going to talk about two really common ones. Well, three. We have your standard grounded system, right? Now to be very clear. I’m not talking about the fact that you put a drive on the panel. You grounded the panel to a ground rod in the ground right next to it.
That’s not the kind of ground that we’re talking about. That’s important to have good grounding and good bonding, but also what I’m talking about here is the incoming power supply grounded as well? If your incoming power supplies floating, then you have no idea. So what you need to do is make sure that the power supply is grounded and that you have 277 volts to ground.
If it’s not a grounded power supply, you may not have 277 volts to ground. You could have 350. You could have 230. The point is that you don’t know. And if you set up the drive to be grounded, the drive expects to be grounded. And if it’s not, then you can ruin the product very quickly.
There are different capacitors in there. There are bus capacitors, there’s line-to-line capacitors for noise cancellation. There’s a lot of different things in there that need to be set up properly so that the drive doesn’t have a failure. We treat high resistance grounds, which are often found in places that do a lot of welding.
We treat those like an ungrounded power supply because of a high resistance ground. There are some applications where we have ships and other things which are ungrounded as well. So you have to be careful of those because you can very easily emanate noise around too when you have a floating power supply.
The best kind of power system is always a grounded power system. Now a lot of our drives can run grounded or ungrounded, and that’s a great thing that Siemens offers. You should always check the manufacturer to make sure what type of system it can run on, whether it’s a, grounded system, isolated system or a high resistance ground, you should always check that and make sure the manufacturer’s product can actually be used on the type of system that you’re connecting into, because there’s just so many of them that talk about.
Well, thank you. Thank you, Chase for walking us through that. Definitely some key points you brought up there from the grounding needs. Let’s put our hard hat on and go out to the plant virtually if you will, what tools, but we need to bring when we’re doing a startup commissioning and we’re the guy or girl who is in charge of getting that drive ready to do the startup, what equipment do they need to bring to to be able to complete that?
Typically if the drive’s already installed, hopefully the IO has been checked out, but again, as I say, you always want to check it, double-check it. You’re the first guy or girl that’s going to be there. Make sure that you check it too, right? The biggest thing, like I said, incoming and outgoing power, if you make sure that’s okay usually everything else will eventually fall in place.
Your standard set of screwdrivers. If they’re insulated, they’re going to be working hot. You did to make sure you have all the proper protective equipment. Me personally, I would much rather have an operator panel on the door and not even come close to the product because we always talk about what’s the most important thing with starting up or commissioning a drive it’s safety, and the most dangerous time to turn a drive on is the very first time it gets turned on. Now that’s my opinion. But the very first time it gets turned on. That’s the very first time it’s ever worked. So I don’t know if everything went well. I like to shut the panel and be nowhere near it when it gets turned on.
Now after that, then we can go start things up and do what we need to, but, safety is number one. One thing to consider also I like to have a regular fluke meter or whatever meter that you have, but I’ve always trusted my fluke meters. Test your meter before you test it on a derive, make sure that your meter is actually in proper working order.
If you’re going to shut down the drive and work on it, those DC bus capacitors get really big. And when you shut down a drive and you need to check something or work on it, those DC bus capacitors can stay alive for minutes and be several hundred volts. So it’s always very important to make sure that it’s safe to work on before you go touching things.
But having said that. Verify your connections. Good set of screwdrivers. A good fluke meter or a meter that you trust. Please do not bring in that Harbor Freight meter that comes free when you buy something. We’re dealing with seven, 800 volts here sometimes it’s gotta be a good appropriate meter, but yeah those are the main tools that I would say that I would bring.
Now let’s say we have all that stuff taken care of and we’re ready to pre-commission the drive prior to, applying power. Can you walk us through some of those items? What we need to consider or definitely take advantage of? You really camped out on safety and I’m so glad you did it cause EECO Asks Why were really trying to increase safety across the board, but go along with this, the pre-commissioning items. Can you kind of walk us through that?
Oh, sure. Safety first, verify your connections, verify your safety. Once the unit is powered up, that’s when we want to do a start-up on the drive.
So usually what I like to do is I like to have my computer and some software. We don’t charge for our software, so it’s good to start up your basic drives. I always like to bring my laptop. Battery fully charged. I always try to another thing to add to the tools. I always try to bring an extension cord because to be honest, you never know when power is going to be close or far.
And it’s always good to have that, but that’s when I start to like work through the parameters, we go through setting things up. Once I set up all those parameters then we’ll do a bump test on the motor to make sure it’s actually operating in the right direction because there’s so many machines out there that can be damaged by actually just moving it in the wrong direction to start with.
Sometimes you have to tune the motor and when you tune the motor, then you also have to be careful because if it tunes and it tunes in the wrong direction, you can wreck things too. So I like to have an e-stop ready to go or something set up.
At that point we’re going to load tests, the motor. I want to make sure that it runs smoothly, that I don’t see any major current spikes that the equipment doesn’t sound awful. There’s no bearing screeching, things are, as they should be. Ben several times where the brake wasn’t properly hooked up and we were trying to drive the motor against the brake. So make sure the brake is actually operating properly.
Sometimes that drive will turn the motor, even with a holding brake on there. And it doesn’t sound great, but you’re like, okay, it’s moving, but if you look at it, it’s pulling like 200% current, right? So that’s something to look at as well. Once everything’s running and not screeching and making good noise and we can go about tuning and fine-tuning everything.
How about you mentioned parameters. Are there any critical parameters that, that you definitely want to check and ensure prior to your basic operation and startup?
Yeah so a lot of the parameters we have in our products, for instance, we have a good startup menu, right? And a good startup menu is essential to starting up a product because not everybody has a computer to go start up the drive.
And to be honest, not everybody wants a computer to start with a drive. For instance, we have a SINAMICS G120X drive and it’s for fans and pumps and we do the entire startup right on the faceplate of the product. So it walks you through as any good drive. Should it walks you through all the parameters to set up.
So for instance, some of the parameters to set up are going to be your control mode. Do you want to set this thing up in volts per Hertz mode, right? Where it just gives the voltage and a frequency. And the current pulls is the current at pulls. Or do you want to set up in vector where I can limit torque and do advanced speed control and have speed loop PID and things like that?
Do I want to run it in a torque mode for an unwind, right? I just want to maintain attention and I really don’t care how fast it goes. So the control mode of the product, how you want to run the drive is very critical. The motor data is paramount. If you put in, it seems we offer a four to one mismatch on our general-purpose drives, right?
So I can put a 10 horsepower drive, theoretically and a two and a half horsepower motor. It’s a pretty wide range, which is great, but you also have to be careful that you put the proper data into the drive. If I don’t tell that drive that I’ve got 4.3 full load amps on my motor, the drive doesn’t know it.
And the problem with that is if you try to run this motor, the drive has no idea that the motor sitting there grinding against bearings, burning away the drive is big enough to supply the load. And it came with the default of a 10-horsepower overload. Meanwhile, I have a three-horsepower motor on there that’s baking away and the drive knows none of it.
So it’s very important to set your motor data, especially the full load amps. Another thing is you also want to set the RPMs of the motor to exactly what the nameplates says, okay? A lot of drives have what’s called a slip regulation in them. So it’s looking at how much current is going out to the drive and a lot of other things, depending on the control mode.
And it’s trying to ascertain how fast that motor is actually going. So the more slip that means the heavier, the motor is loaded. And the only way the drive can figure that out is if you put 1,725 RPMs in there, like the nameplate says, instead of just saying 1800. If you just put an 1800, the drive has no idea.
Also important to put in things like the service factor and how many RPMs the motor is. So the driver understands how fast it should be going. If you have an encoder, obviously encoders are paramount. If you put it in the wrong encoder counts or you don’t put them in at all, then the drive has no idea if the motor is moving or not, because it’s counting on that.
Another thing you want to look at is brake resistors. If you are using a brake resistor, it’s going to need to know how powerful that brake resistor is. What’s the continuous amount of power that the resistor can handle and what’s the peak amount of power that the resistor can handle? A lot of situations, we just use a brake resistor to stop a load in an emergency stop.
And so we can size it kind of like a traditional starter is on a car. We don’t fire the starter a lot in the car. We fire it once when we get in the car in the morning, maybe another time an hour later, but the starter isn’t just sitting there cranking away. So, If you actually tried to start your car for 30, 40 seconds, that started can get very hot and overheat.
Well, It’s the same with a brake resistor. You can use a very small break resistor to stop a pretty decent size load, but you can only do it once for so many minutes or some amount of time. So it’s very important that you set that up in the drives so the drive knows how hot the resistor is getting.
And many of these resistors also have an over temp circuit, which you absolutely need to have wired into the drive. A lot of customers, wire it up to what we call an external fault input. And so the drive will actually coast to a stop if the brake resistor, overheats, rather than trying to brake the load because it thinks something is wrong.
The last thing you want to do when you’re resistor is overheating is try to e-brake to a stop, which just makes it worse. And there’s other guidelines to follow through that, but one of the things I like to set up is, your XL times, your decel times, is that acceleration/deceleration be managed to the drive or is it being managed through a PLC and what are you doing with your DC bus management?
And what I mean by that is if I am trying to stop a load and it can’t stop quick enough, am I going to extend out my decel time or is decel time-critical and I would rather have it fault?
Our drives have a really cool option that I really like. And it’s if you have a high inertial load and you were to lose power, you can set this option in our DC bus management and basically it will use the motors, inertia, and power to keep the drive alive through a brownout situation or a blackout situation. And it’s really cool. Those are other parameters that we have that you need to really take a look at when you’re setting these things up.
Very good information that you provided right there. And then the slip regulation. That was one that stood out to me that I really hadn’t thought about a lot in the past. Now, when you get the basic parameters set up on a startup, typically you move into the auto-tuning and can you, and walk us through, what is auto-tuning and why is that important for our listeners?
So there’s different kinds of tuning that a motor has. Siemens calls it motor ID, but basically it’s all the same. It’s all motor tuning, but there’s a couple of different kinds of tuning that you need to be aware of. So there’s, what’s called a standstill tune, which to be honest, most typical standard applications, fans, pumps, compressors, conveyors, those kinds of things without a feedback device, like an encoder are going to be absolutely fine with use using what we call a standstill tune or a standstill motor ID. It just sits there. It goes out. It looks at the motor. It tries to ascertain a couple of properties about the motor. And then the drive knows how to modulate the output to the motor in the best way possible without burning things up.
If you want to do very good speed regulation or very good torque regulation, things like that are going to be doing positioning. It’s very important that the motor has a very good relationship with the drive. And so what we do is we have what’s called a rotate tune. So in the rotate tune, it can actually look at it a ton more parameters that we’re not going to do right now, but it looks at a ton more things behind the scenes of that motor and drive relationship and the cable length and things like that to make sure that it’s controlling the motor in the best way possible, but that’s the tune that happens between the drive and the motor.
So at that point, you’re trying to ascertain your torque loop and that’s very important. And you’re also trying to maintain the best relationship. The second kind of tuning is your application tune. So if I’m trying to do very good speed regulation, or if I’m trying to run in, what’s called a vector mode where the drive is actually trying to run in the most accurate speed possible. And behind the scenes, that’s actually trying to figure out where the rotor position is and where to fire everything next to maintain the closest, exact speed, rather than just volts per Hertz motor where at hands out a voltage and a frequency, very cool stuff.
But to do that, it also needs to know how much load you have, how heavy is the load, how much inertia is on the load. So that has called the speed loop tuning, right? So that’s where we have the drive go out, run the motor, look at the application, see how hard it is for the motor to get the load up to speed.
See your hard it is for it to break the motor. And then we can get an idea of how tightly we can run that speed loop in the drive. And then there’s one more loop that sometimes we tune called a positioning loop and that’s the top loop. And if I’m going to be going back and forth and I want this thing to snap back and forth, then I would run a position loop as well. And then the drive will sit there and it’ll spin things back and forth and try to look at the response of how everything works. So there’s three main loops, but the most common one is just the drive to motor relationship
Right now. Should that be done every time you do a VFD to a motor, or if you swap out a motor, should you redo that auto-tune?
Absolutely. Every single time you ever want to put a drive and motor together, I would always recommend that you run a standstill motor ID on your motor. Maybe not the rotate, maybe not the speed, nothing like that, depending on your application, but always, always, always, especially if you’re gonna replace it power structure, because remember you’re putting different transistors into the scenario.
They could be different transistors. They’re a different manufacturer. They’re a different date. They could operate differently. It could be a different series unit or a different hardware set internally. These things actually matter. Or if you change out the motor, it could be the same motor by the same manufacturer, or it could be a different efficiency class.
Let’s be honest if your plant goes down and you lose a three-horsepower motor, you’re going to put whatever three-horsepower motor you’ve got on there. So it’s important to go back, look at the slip RPMs, look at the FLA of the motor, put in the exact correct parameters and the drive, and just go through basic tune again.
Absolutely. Yeah, that’s a good point. That was something that I would always have heard. It’s want to make sure we kind of went over that for our listeners. It’s definitely go back through, do that autotune. A lot of times we do find it’s difficult to do the rotational one, but the, because usually the motors are coupled, but like you said, the stationary is definitely highly recommended it. So let’s move to drive faults. What are some of the most common drive faults that you see out there?
So the most, common faults I get are, some of them are actually pretty common. And actually, I just remembered one of the things that I wanted to tell you guys about, when you’re checking a drive, you want to make sure that everything’s connected.
We had talked about that. I actually had a customer one time where we went to start up a drive is a very big drive and they had not actually wired or put down the big lugs between the output of the drive and one of the output contactors and the lugs were sitting about three millimeters from the load contacts. So had they arced, it could have been a really bad situation. So just keep that in mind.
But the most common false, the very first thing I see all the time, DC bus under voltage. Doesn’t matter who the manufacturer is you’re probably going to see that fault on a daily basis if you’re going to look at drives and that’s not necessarily a bad thing, DC bus under voltage just means that the drive went under voltage, which is the exact kind of fault that you get if you shut the power off.
Don’t panic. If you see DC bus under voltage, it could just mean that the power got cycled recently on the product. Now it could mean other things, right? If you actually lost a phase and you’re running overload, because a lot of drives will actually run on two phases instead of three, and they can run it at a reduced capacity.
But if it gets loaded down too much, you may get too much DC bus ripple, or it may show an under-voltage. So it’s important to take that into account if you do actually have a problem. As long as we were talking about DC bus under voltage, there’s also DC bus overvoltage, there’s a couple things that typically cause this.
DC bus overvoltage is usually caused by too much energy being fed back to the drive. I have too much low or too much inertia that I try and just, or too much kinetic energy that I’m trying to stop. Where’s the energy going to go? It’s going to come back to the drive. If the resistor overheats it can’t push it out any further. Or if it’s too much power coming back into the drive and it can’t handle it at all. Those are the kinds of situations that will give you a DC bus over-voltage.
I actually also had a customer have a DC bus over-voltage because they had tuned the motor speed loop to hot. And when we went in to the DC bus, we saw a DC bus ripple that was so heavy. It actually was causing false trips on the DC bus and we had to back down tuning and it was fine.
There’s a couple of things that can cause that. Over-temperature. Now there’s a couple different kinds of overtemperature faults. The first one would be if the drive is overtemperature the very first thing that you look at, what’s the very first thing that always fails on a drive. It’s almost always the fans, right? In an over-temperature fault.
So go back, look at the fans, lay your eyes on them, get your flashlight out is the heat sink clean? Are the fans able to spin? I was at another customer’s plant and they had used a push-through design where the heat sink sticks out the back of the enclosure and it works for about six months and they kept getting an over-temperature fault and somebody kept going out there and just hitting the fault reset button.
So they burned up a drive in three months. And it was improperly applied because this plant had a lot of dust and sediment and everything flying around. The fans and the heat sink got clogged. They were behind the back of the enclosure so nobody could see it. And the drive burnt out. So that’s another thing is the drive getting over-temperature? And that could happen if air conditioner faults too. If a drive is over-temperature, there’s usually a pretty darn good reason why it happened.
The other one would be overcurrent. So there’s several different types of overcurrent faults. One could be if the motor is over current and there’s a couple of reasons that could happen. Obviously, if we have, going back to that situation, maybe a bad bearing now the motor’s getting overloaded. The drive is going to stop it because it sees it’s pulling more than a certain amount of current or a certain amount of time. It’ll stop that load. And it’ll tell you the motors over current, or it’s over-temperature because the motor can be over temperature too.
But if the drives over current, that could mean that your motor is blocked, which is typically a separate fault for us, but if you can’t get it going or anything like that, you could see a blocked motor, but overcurrent, it could mean that the drive is stuck in over current because the most we’re getting locked down.
Face-to-face faults if you ever see a ground fault please trust the drive. If we ever see a ground fault, that is a very good reason to stop what you’re doing and reevaluate. I had a customer one time. There were four, 200 horsepower air handlers up on a roof. And three of them worked flawlessly and the startup was easy. It took 10 minutes a drive. It was one of those beautiful calls I went on. And then I got a call a week later, and it said, your drive is terrible. It’s getting ground falls and we keep resetting it, but it keeps happening.
Long story short, we went out on the roof and we find out that last drive and motor combination had been wired up there was no glass tape on the motor. There was none of the proper stuff. It was literally just wound with some electrical tape and after a week. And if you guys that do a lot of HVAC stuff, know, these things vibrate pretty decently. After about a week, it had pushed and vibrated through all the electrical tape. And one of the phases was arching to the motor. So that’s a real good situation where somebody could have gotten hurt. The drive could have blown up, or we could have had a pretty catastrophic failure. So please the drive says ground fault, trust it, get a Megohmeter, meg it out. And don’t forget to disconnect the drive because if you meg a drive, you’ll blow the drive up.
But it’s also a good idea to get a big Megohmeter and actually test the cable, going to the drive as well, because it’s just as likely that the cable could be bad if the motor’s bad or the cable could be bad or the motor could be bad.
Exactly. Thank you for walking us through some of those common areas, Chase. That was great. Just to kind of wrap us up here. Do you have any parting tips or advice for our listeners when it comes to anyone is tasked, was commissioning and starting up a drive?
Yeah, I would say the most important thing is take your time. With today being the way it is, everybody’s got 80,000 things to do. Everybody’s trying to get this done and get that done. And it is important.
Everybody’s very busy these days, but when you’re starting up a drive, just remember what you’re sitting in front of. You’re sitting in front of something that could be potentially very dangerous. It’s got a lot of power and you have the ability to ruin a lot of things. If you tell it to do the wrong thing. So at all times just relax. I would just say, take your time. No matter who’s looking over your shoulder. You should never rush. That’s the number one thing I would say.
Absolutely. Absolutely. That’s great advice. And Chase, you really brought a ton of value to our listeners today. So we thank you for your time, for your knowledge. We hope that this will help our listeners as they get tasked with starting up a VFD to do it safely. And we’re just, again, thank you again, Chase for all your time today.
Thank you guys very much. Appreciate being part of your show.