110. Idea: VFDs and Applications to Use Them Transcript

Chase: 00:00

A soft starter can only ramp the device up to it’s rated speed, whereas the VFD can run it the motor at any speed under the right scenarios. And it can do it continuously without overheating it and provide the motor with an optimal amount of torque at just about any of those speeds. 

Chris: 00:16

Welcome to EECO Asks Why. A podcast that dives into industrial manufacturing topics and spotlights the heroes that keep America running. I’m your host, Chris Grainger, and on this podcast, we do not cover it’s features and benefits on products that come to market. Instead, we focused 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 back to EECO Asks Why. We’re very excited for this episode to be digging into the topic of what is the variable frequency drive and what should I consider on my applications. Joining us today, we have mr. Chase Boehlke from Siemens. Has a lot of experience in this field.

Looking forward to digging into this topic with Chase, really appreciate you again, Chase for taking the time to sit down and talk with us and for our listeners, you bring so much value every time you get, you come on our show. So let’s just start off with basic explanation of what is a variable frequency drive.

Chase: 01:19

Thanks to you guys for having me today. It’s always fun. I enjoy doing these. What is a variable frequency drive? My job is, is basically a VFD specialist. So that’s my favorite kind of question. Yeah,   There’s three types of basic ways that we run a motor.

The first one would be a starter and that’s just basically you get your line protection, a contact or an overload device, and then you’ve got a soft start, which slowly ramps the load up. And has its own overload protection built in, but it still needs a line protection device. And then you’ve got a VFD. The main difference between a soft starter and a VFD is the fact that the VFD can vary the frequency continuously.

A soft starter can only ramp the device up to it’s rated speed, whereas the VFD can run it the motor at any speed under the right scenarios. And it can do it continuously without overheating it and provide the motor with an optimal amount of torque at just about any of those speeds. 

Chris: 02:17

Very good. Very good. Thank you for that breakdown. We hear a lot of times to terms and we’re trying to specify a drive. This comes up all the time. Constant torque. Variable torque. Can you explain the differences for our listeners out there so that they can make the right decisions here? 

Chase: 02:33

Absolutely. it’s, it’s actually a really easy term once, you know what it is. So variable, torquing, constant torque to the most common industry standard terms. Think of a variable torque load as a fan or a pump. And when I say pump, only a centrifugal pump. I’m not talking about positive displacement pumps or dosing or metering pumps. Those are different, and we’re not going to go down that rabbit hole right now, but for centrifical pumps and fans.

What happens is when you spin a fan, think of a fan spinning really slowly. I could probably walk up to a fan. That’s being run with a 100 horsepower motor hang off of the fan blades and the is going to turn right. And that’s because I’m overcoming, some, given inertia, some low amounts of friction with the bearings, things like that.

The fan will turn. But it’s easy to turn because there’s really no load on the fan. I’m not pushing a bunch of air as soon as I start turning that fan. And the same goes with the pump. You can walk up to a pump and usually make the pumps spin very slowly with your hand. That take that same hundred horsepower motor.

That’s lifting up some three or 400 ton block off the ground. I don’t know about you. I’m not weightlifter, I’m not picking up a 300 pound block by myself. My point is that a constant torque load, like a 300 pound block sitting on the ground? That load is always there. To move it at any speed whatsoever, I need to overcome that 300 pound force. 

So that’s the main difference. A constant torque means there’s always torque required to move that load. A variable torque like a fan or a pump means that load increases the faster it spins. 

Chris: 04:13

So knowing that, how does that impact the selection of the drive for an application?

Chase: 04:21

That’s the perfect follow-up question. So what we do in industry is we have different kinds of Drives. In Siemens, we call it low overload and high overload. Some of the manufacturers refer to at the same kinds of things, normal and heavy or something of that nature. What we’re really doing is we’re just increasing the drive size by one.

Okay. A motor can suffer through two, three, even 400% torque sometimes without a problem, it takes it time to overheat and get hot. Drives on the other hand, have IGBTs on their output and they get hot very quickly. 

What you need to do is oversize the drive based on load. If it’s a fan or a pump, it’s conceivable that the motor’s probably not going to go over its full load amps and very often, and if it does, it’s not going to be very much so you could use what we call a low overload drive.

So if you have a 15 horsepower motor, we would spec you have 15 horsepower drive and then give you in general, 110% for 60 seconds, right? For a high overload situation, like a conveyor. Anything where you’re lifting things and things like that. You may pick out what we call a high overload drive, and that one’s going to give you 150% over current for 60 seconds.

And what that does that gives you a truckload more torque to give to the motor for a length and amount of time. And that’s good for high starting and things like that. 

Chris: 05:48

Very good. Very good. Now you mentioned something. Oh, I want to go back to real quick. IGBT for our listeners. Can you just break down that acronym for us?

Chase: 05:58

So IGBT stands for insulated gate bipolar transistor. It’s the most common type of transistor in a low voltage variable frequency drive used today. They’re very, very efficient and they’re basically just transistors. Okay. So transistors are very good at switching current, but they can also get hot if they’re not properly cooled. Just like your computer CPU.

It gets very hot. If it doesn’t have its adequate cooling and it does it in a hurry. Whereas the big motor takes a long time to overheat. If it’s over, it’s continuous current. 

Chris: 06:29

Right. So that kind of leads me into to a question chase when it comes to sizing a drive. Cause you mentioned that the IGBT, they get hot. Dives put off a lot more heat than a typical starter or soft start application.

So that has to be taken in consideration. So when I go about sizing them, how do I exactly do that in a, in certain applications? Is it changed based off the constant or variable torque applications? Do I always upsize one that’s a 10 horsepower to always go to a 15 horsepower drive, for instance. Just can you give us some basic rules of thumb when it comes to sizing my VFD?

Chase: 07:06

Yeah. So when you want to size a VFD, the most important thing, anybody should ask you, number one, every single time or a soft start or starter, no matter what it is, the very most important thing that we want is the motor name plate information. And we want a really good photo. The motor name, plate information is critical to sizing your drive.

Okay. And there’s some other things too, but let’s talk about the motor name plate first. So on a three horsepower motor name plate, you’re probably going to see it say something like 460 volts. You need to make sure the drive matches that, 300 to 480 volt input. You’re going to want to make sure that it has the right amount of current.

Okay. So three horsepower motor, let’s say 4.3 amps is what it’s going to pull. So I need to make sure that if I’m doing a fan or a pump, I have at least a three horsepower drive. And that would probably provide you with 4.8 amps or something like that. 

Right? If it was heavy duty, we’d go to the next size up. But there’s other things that need to be taken into consideration. If you look at the NEC it only covers four pole motors. And so a lot of specialty scenarios are not considered. As you increase a motor pole count, okay. So if I have a six pole motor pulling 12 or running at 1200 RPMs or an eight pole motor running at 900 RPMs, those motors will inherently pull more current with the exact same amount of horsepower. 

And so it’s very important to understand that because then the drive may not be big enough for your application, right? So that’s what the name is so important. Other things to consider are other specialty motors, severe duty motors.

I’ve also seen very big vertical pump application motors where the service factor is more than one. Now most motors, if you guys don’t know what service factor is, service factor means it’s a motor his ability to run above its name, plate current for some set amount of time. Okay. So if I have a service factor of 1.15, and I have 10 amps, that means I can pull 11.5 amps from that motor for some amount of time without damaging the unit.

Most of those service factors go down to a 1.0 service factor when you’re running them with a drive, but not all of them. And so it’s very important to find out from the manufacturer of that motor, is that service factor, does it go down to a 1.0, when you’re running it with a VFD? Most cases. Yes. But if it’s not, I’ve actually seen somebody where they said that 500 horsepower drive and somebody had to buy a second drive because of the service factor.

So that’s really the main thing we want to look at. So service factor, full load amps to the motor pull counts, but like I said, the absolute, most important thing, please get us a picture of the name plate, and that’s what we can size just about anything from that. 

One other special consideration is lead length. There’s something called cable charging current. So if I had like a one horsepower motor running, two, 300 feet, that cable can chew up an ampere, two of current in a small drive, all of a sudden you’re driving may not even be able to turn that motor. 

Chris: 10:04

Good point. Good point. Absolutely. So I really appreciate how you walked us through some of those different areas. I had, the cable length is something that hadn’t came up in a while. I haven’t considered that. So really thank you there. How about applications where, we don’t want to use a VFD, is there, are there any applications out there that you just say, huh? That’s probably not the best application for a variable frequency drive here.

Chase: 10:29

I’m a VFD specialist, so I always want to use a drive. No, there’s, there’s a couple situations. If you always want to run the exact same speed, no matter what, and don’t waste your money. I don’t want to waste anybody’s money. I’m not trying to oversell anyone. If you have a pump, it always needs to run into given speed.

If you have a conveyor, it always is running at a given speed and it doesn’t matter if you start at hard, it that’s fine. You don’t need to use a drive. Yeah. If you want to drive, that’s great. We think it’s wonderful. We’re happy to sell them to you, but that’s a great scenario where if you’re trying to save a couple of bucks, don’t put a driver on something that doesn’t need it.

Another thing is if you can’t provide the adequate environment, okay. In some scenarios, let’s just say, if you have a hot  environment, or really dirty or caustic environment. And you can’t take that drive out of that environment. It’s not going to last. You’ve got circuit boards in the drive.

You have to have adequate cooling for a drive. And a lot of the times you can put that unit inside of a panel and take care of that. Or there are some, wall-mounted products that can handle that sort of thing. But if you can’t provide the proper environment and you’re going to have constant failures, then it’s either time to look at moving that drive to a different location.

Because you can run cables along distance in general, or maybe consider an alternative to that product. You can’t move it. 

Chris: 11:50

Right. Bottom line is we want to find applications that you can use to drive on, right? 

Chase: 11:55

Absolutely. That’s right. I’ll put a drive in the coffee maker. I don’t care. 

Chris: 11:58

There you go. There you go. Now let’s talk about protection, for a minute from an overload source circuit standpoint. How does that scheme look for vFD? What should we consider? Is there anything different than a typical motor application for a VFD? 

Chase: 12:13

So just like in the beginning of the podcast, we always want to talk line protection and line protection you should always go to the manufacturer’s documentation and figure out what types are available to be used and the maximum amount of size for that breaker. You can always put a certain amount size on there and you’re okay with it. You can actually downsize it depending on if you know what your load is.

Where you want to look at that is the NEC article four 30. And that’s where the protection is like outside of the panel, or if you’re going to do inside of a panel. Usually we’re going to look at UL 508-A, but again, like I said, it’s usually done by the manufacturer in their documentation.

And that’s what you want to look at. So Siemens provides a wide range of protective devices. All the way from non semiconductor fuses to types of motor circuit protectors and type combination, motor controllers. One thing to watch out for is UL 508 C was withdrawn by UL in February of 2020.

And so now everybody’s looking to go and move to UL. 61 800 dash five dash one because it provides a safer product and we already adhere to those guidelines. It’s a great thing. It gives you flexibility for panel builders so they can pick out their separate device. The last thing for protection is, again, we talked about this just a minute ago, but, make sure your overload is done properly, and make sure your over temperature protection is taken care of so that the drive doesn’t overheat, 

Chris: 13:42

Right? Absolutely. Okay. Now how about control? When we talk about control for VFD, there are multiple different ways to obviously make a drive run, but what do you typically see out there as being a standard, if you will, from a control standpoint? 

Chase: 14:00

Yeah. So the main control standards we have are either going to be hardwire control where we’re running 24 volt or 120 volt inputs to the drive with push buttons, something like that. So the operator can walk right up to the drive or the panel and push the push buttons, make it go. Sometimes it’s rare, but sometimes people will actually operate directly from the operator panel.

That’s usually what we would call like hand mode or something like that. The other option is network control. All of our VFDs for this point, and most of our soft starts actually have a network control options. So the most common today I would say is ethernet. There’s several protocols under ethernet. We support PROFINET and several other ethernet and protocols as do other manufacturers. But network control is probably the easiest. That’s where you’ve got that PLC talking to that drive and ethernet can run a very long distance. It’s very reliable. But we would usually consider that auto.

And the reason I bring that up is because sometimes people want, what’s called a hand-off auto switch on the front of a panel. And most typically auto is going to be either a network control or an analog signal going directly to the drive. And there’s an off button for the middle. And then there’s also a hand button.

And when you put it in hand mode, it will usually operate off of maybe an analog potentially amateur on the front and those hard wire iOS. 

Chris: 15:19

Gotcha. And we definitely promote the networker, smart devices  and drives, we do a lot with that in our labs and  

Chase: 15:27

You just get so much more with network control. 

Chris: 15:29

Absolutely. Absolutely. Just it 

Chase: 15:31

opens a cost thing, you know 

Chris: 15:33

yeah. and then you have, was it. One, one cable to run to, to make all these things happen. When I, when he specify drive, I know a lot of people, they see things like line reactors, load reactors, resistors filters.

What does all that mean? What I mean, are there any, we could go on probably for days about each one of those topics, but just, maybe a high level overview of, Hey, when do I need to start thinking about line reactor or load reactor, resistors, things like that. Could you help our listeners with that?

Chase: 16:06

Absolutely. So a line reactor does two main things and it’s the most common. I jokingly say to my customers, you know, it’s the, would you like fries with that of drives, right? A line rector that’s two things. It resists change in current. It resists very fast changes in current. So if you get spikes from the outside world, including but not limited to lightening strikes, not saying that a line reactorwould protect against the lightning strike.

Nothing really does that, but surges and swells and voltage and current and things like that can be reduced by having a line reactor. So that helps protect the product. And some of the Siemens drives that we have actually have what we call a link choke inside of the drive. And the advantage of that is that you don’t have to use a line reactor.

So it just depends on the manufacturer. The other thing that line reactor does is it can reduce harmonics. Harmonics are something that every drive puts out for the most part. You want to try and limit those, especially on six pulse drives, which are the most common kind of drive. So line reactor, you can reduce that, harmonic level in the plant.

Now that harmonic levels are usually lowered by any other devices in the plant that are more linear, but it’s something that you want to watch out for. 

As far as load reactors go, you don’t always want to throw a load reactor on a drive. I know some people that want to throw a load reactor on everything, but what you’re doing is you’re artificially lowering the voltage to that motor.

So you’re going to get less power out of the motor too. So we only want to use load reactors essential, and load reactors are going to limit reflected wave. What they’re doing is they’re slowing that rise time of that transistor firing. And so it lets you run a longer cable distance.

So in addition to load reactors, load rectors are usually just, a bunch of wild copper around an iron bar, right? They’re inductors. There’s also things like DVDT filters. So they’ve got other elements in them to help limit things. And if he wants to run an extremely long distance, then we actually can use something like a sine wave filter or things like that. And you can get those products from EECO. 

There’s also break resistors. So I love to joke about break resistors. When I have a lot of energy or we have something like a flywheel or a large load that we can’t stop. Meaning if I pulled the disconnect to the drive, is that load just going to keep going?

Is it like a train or a flywheel? Is it going to keep going? If I don’t hit the brakes, like a car, right? So that’s kinetic energy. So if I need to stop that load quickly, what am I going to do? I have a lot of energy and I need to put it somewhere. So a brake resistor is literally nothing more than a gigantic toaster.

Literally exactly what it is. So when the driver tries to slow down that load, all that energy starts coming back to the drive and the drive has to say, what am I going to do with this? Now it, Siemens has several options where you can just push the energy back to the line. But if you’re only going to do it once in a while, or only under an e-stop condition, and it’s not worth spending the extra money to have a regenerative product, a lot of drive manufacturers we’ll let you attach a brake resistor to their product, and that we’ll just use that kinetic energy to heat up the resistor. So that’s a brake resistor. 

And filters is a very difficult term. Filter depends on who’s saying what a filter is. So some people call a line reactor or a filter because technically it is a filter. Siemens refers to filters as something like an EMC filter. So the switching of the IGBTs, we’re trying to filter that out. So when somebody says filter, I would say, you need to find out what exactly are they trying to filter? It could be the filter on the cleanliness of the drive. It could be an EMC filter. It could be align reactor. But those are some of the main things that we, the main terms that we hear and when we use them. 

Chris: 19:50

Well, I’ll tell you, I’ll never, look up a brake resistor again, and ever be able to look at that and not think toaster. So thank you for that.

That was great. Really loved how you walked through each one of those for our listeners. Hopefully that, that really connected a lot of dots out there. So yeah. I know one question that we see come up from time to time, can a  drive control more than one motor. And if so, how? 

Chase: 20:17

Absolutely. There are limitations though. Okay. So we would call that a multi motor installation. For instance, let’s say that a customer wants to have 10 motors and they want to attach them on one drive because all those motors need to spin roughly the same speed, but they’re not physically attached to each other, they’re, they can be, it just depends on so many scenarios.

But if they want to do a multi motor application, that means that they’re going to have multiple motors connected to the drive at one time. And one thing you need to watch out, there’s a couple things you need to watch out for. You always want to use what we call a high overload drive. So whatever the motor full load amps all adds up to, let’s say it adds up to a hundred full load amps.

We want to make sure that we use a overrated device for that 100 amps, right? Heavy hi overload drive. That’s the first thing. The second thing is you want to make sure that you are counting how much cable footage you have. Not every drive can handle 1400 feet of cable, right? So if I have 20 5horsepower motors, and they’re all running a hundred feet out, that drive may not be able to handle that strictly from the cable charging and the impedance and all the other properties the cabling, right?

So you have to watch out for that as well. And the third thing to watch out for is that each individual motor, after a certain horsepower, and this is defined by NEC, each motor is going to have its own individual overload. Remember earlier how I said that each drive has an overload built into the product?

It can only watch how much current is going out of the drive. So if there’s one motor, you’re fine, but it’s kinda like a breaker in your house. If I have three vacuum cleaners, running off a one breaker, I have no idea which one is pulling too much current, which one’s about to burn out.

So that’s why we say with the NEC, all the motors, they have to have individual overloads based on certain sizes, but those are the main things to watch out. And then one other thing I almost forgot,  several modes that you can run a drive in, full vector control with encoder feedback and vector control without a sensor, where it watches just the flux current. In a multimodal scenario in most applications, the only way that you’re going to be able to run several induction motors off of one drive.

And I say induction because there’s other specialty applications that we’re not going to get into today. But if you’re running several induction motors off a variable frequency drive, you’re going to want to set that drive to straight volts for Hertz mode. And what that means is the drive’s going to give out a frequency.

It’s going to give it a voltage. And as long as it doesn’t go over a certain amount of current, it’s going to be happy. So it’s very important that you don’t set your drive to vector mode. 

Chris: 22:59

Right. Very good. Now I’ve heard this come up before too, Chase, and may just, we don’t have to go deep here, but I think since we’re talking about running more than one motor at one time off of one drive, sometimes that could get confused. Heard people talk about coordinated drive systems. Could you just give a high level overview of what a, of a coordinated drive system would be? 

Chase: 23:23

Yeah. A coordinated drive system is where you’re going to have typically a main master drive or a master access. And that can be a virtual access that doesn’t have to be real, but you’re going to have some master that’s running at a given speed or given position, and then several other devices will be running off of that masters signal.

Okay. So if you think of something like a printing press or something like that, where I’ve got, 10, 12, 20, 30 different motors, and they’re all running it in a synchronous speed at a different ratio for instance. So you’ve got one motor that has to run at 1800. You’ve got another one that runs at 900 and then I’ve got a slitter that comes across every amount of time.

That’s a coordinated drive system. So one drive speed or position dependent upon another drive speed or position or a virtual accesses speed or position. So when we say coordinated drive system, typically there’s only one motor per drive, but all of those drives and motors are talking to each other. And typically there’s either a servo controller handling that, or there’s a PLC or in some cases, both.

Chris: 24:27

Very good. Very good. Thank you for that. I think that helped a lot. Kind painting that  picture of that one access and everything keeping up there. So really appreciate it. Chase, you have a lot of experience in this field. You work in a lot of industry. You’ve seen tons of different applications.

We try to help here on EECO Asks Why, our listeners think through and learn from others, if you will. And sometimes that may me learning from people’s mistakes or just stories in general. From your experience, do you have any typical or maybe atypical stories or applications that would help our listeners avoid in the future when they’re trying to apply drives in their plants?

Chase: 25:09

Oh yeah. When somebody says, Oh, it’s just a five horsepower motor. That’s a flag, right? Whenever anybody just says, Oh, it’s just a five horsepower or don’t worry about it. Because in that scenario, I don’t know if its a servo motor. I don’t know if its an induction motor. I don’t know what drive to apply to it.

I don’t know what network control on an, on a size at anything like that. And so the customer is usually in a panic or trying to get something they may be down and it’s important to get the right information. And if you just throw something at them, that may be a good five horsepower drive. It may not be the right product.

And then you can get yourself into trouble. Whenever there is a down situation. It is very important to get the right product to somebody, but it’s even more important to get the right product the first time. They’re there over my time, about 18, 19 years of doing this, I’ve seen several scenarios where, somebody shipped something out and myself included.

We got something to the customer and it turned out to be the wrong application, right? Oversizing or undersizing the drive is another thing. You can damage motors. Setting up the draft properly is very important. Take your time, no matter what the scenario is, rushing leads to problems. And I have to tell myself that tons of times a day.

So I think that’s the one biggest lesson that I learned over time, just to make sure that it’s the right product, take your time, get the information you need and things will usually go smoothly after that. 

Chris: 26:34

That’s great. That’s great advice. And working with partners like you Chase with Siemens and the many different partners we have at EECO. That’s, that’s the key, take your time. If we’re asking questions, it’s usually you try to avoid a mistake right into make our heroes do look like a hero at the end of the day. Chase, I really appreciate you taking the time with us today. Here on EECO Asks Why I really think this brought a lot of value.

A lot of knowledge out there and I’m sure it will resonate with our listeners. So thank you so much again. 

Chase: 27:06

Thank you guys. I really appreciate it. And, Oh, we’re always glad to be available. It’s been great. Thanks for bringing me on.