Heat Treat Radio #128: Silicon Carbide Without Transformers: How Is That Possible?

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In this episode of Heat Treat Radio, Tony Busch of Control Concepts, Christina Clowes of I Squared R, and Dr. Stephen Feldbauer of Abbott Furnace Company join host Doug Glenn to discuss a new transformer-free approach to electrically heated furnaces. The group walks through how SCR power controllers paired directly with silicon carbide heating elements can reduce system cost, simplify design, and improve control accuracy. They also explore the global adoption of zero-cross technology and its growing relevance in North America.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.

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The following transcript has been edited for your reading enjoyment.

Introduction (0:45)

Doug Glenn: We’re going to be talking about a relatively new combination of two fairly well-known technologies that will help some people save money. Those two technologies are SCR power controllers and silicon carbide heating elements. It’s actually kind of a little case study. If you’ve got an electrically heated furnace, this would be one you’ll want to stay and hear.

Our first guest is Tony Busch from Control Concepts. Tony Busch is the North American sales manager for Control Concepts. Next is Christina Clowes, the vice president over at I²R Elements Company. Our final guest is Dr. Stephen Feldbauer, the director of research and development at Abbott Furnace Company.

A Furnace with a New Configuration (1:45)

Doug Glenn: To get a sense of this furnace that we’re talking about, can you describe the situation and this new configuration of power controls for the heating elements?

Steve Feldbauer: What I can say is that this was a new piece of equipment to replace an old technology for a new facility.

Okay, so they were going to move to a new facility and they said, “Hey, we don’t want this old stuff. Let’s look at just buying a new furnace for this application.”

This is for the casting industry. The molds go into the furnace and traverse through; the furnace preheats them so that operators can then pull them out and fill them with metal. So it’s a continuous furnace for mold preheating application for the casting industry.

It was exciting! We had an electrically heated furnace, and then began talking with Tony and Christina. Control Concepts had this concept, no pun intended: Traditionally, design of an electrically heated furnace above a certain temperature (1850 degrees), we use silicon carbide heating elements and — due to resistance changes over time — we have to put transformers in there that allow us to keep upping the voltage and maintain heating capability. Control Concepts said, “Hey, we can take innovate technology and save some money, make things a little easier, and get rid of the transformers.”

And we really had a great outcome.

Doug Glenn: This is a foundry industry application, the preheating of molds, and this is a continuous furnace. You guys, Abbott, obviously won that bid to supply that furnace. I’m sure it was a competitive situation, so congratulations.

Traditional SCR and Silicon Carbide Heating Element Configuration (4:40)

Doug Glenn: So Tony, one of the great features of this Abbott furnace that helped them win this order was this relatively new configuration of the power supplies. as Steve was saying. Tell us a little bit more about the SCRs and the silicon carbide heating elements.

Tony Busch: I think it’s important to understand where we came from and where we are now with this new technology.

In the past, at least in North America, silicon carbide heating elements produce a high temperature, a high current. To help that happen and so you do not have a big, thick gauge wires, a transformer would be added to the design very close to the furnace. This reduces the conductor size. That transformer often was a multi-tap transformer. From a SCR power controller standpoint, you would be controlling the power on the primary side of the transformer, let’s say 480 volt stepping down into 60-70, whatever volts are required for the application. To use a transformer with a power controller, you need phase angle power control.

This is how it has been done in the past with phase angle firing varying every half cycle into the primary of a transformer.

The New Setup (06:09)

Doug Glenn: What is the new configuration?

Tony Busch: With the new scheme, we are removing the transformer. Now you have an SCR power controller firing directly into the silicon carbide heating elements.

To do this, you will have to have slightly bigger power controllers, but you’re completely eliminating the transformer and you’re going directly into it. To take it a step further, we use a special firing mode called Fast Zero Cross. This mode satisfies the heating elements.

We are maintaining a very smooth watt density output to the heating elements. You can control it and the power feedback if you need to, which is essentially your unit of measure to control the power, which can be in KW versus voltage or current.

Doug Glenn: That’s on the power side. Control side of things. That’s basically the new arrangement: removal of the transformer; direct feed into the heating element, with some advantages. Christina, how about the heating element? Can you tell us a little bit about the heating element in this situation?

Christina Clowes: This is not a unique heating element in this particular case, because the same heating element configuration probably would’ve been used even if you were using a multi-tap transformer based system.

The key to the operation here is the very rapid switching of full sine waves through the heating elements, where you’re proportioning the “on-to-off” cycles, electrical cycles, so rapidly that the heating element does not have time to respond to the very high instantaneous loadings during each “on” cycle.

For example, in the U.S., typically you are looking at a power supply that’s at 60 hertz, 60 cycles per second. One electrical cycle is one 60^th per second, or 16.66 milliseconds. In that case, if you were regulating the outputs from the heating elements to 50%, you would have one cycle on, followed by one cycle off, and that being repeated continually.

The heating element during that one cycle, that 16.66 milliseconds, does not have enough time to respond firmly to that very high loading. As a result, the RMS voltage, the natural average voltage over time, governs the load into the heating elements. So, you can design around systems based on 480 volts but regulate the RMS output on the controller to whatever the heating element needs to generate the amount of power that’s needed by the process.

The control is the key to this operation.

Doug Glenn: Is it possible to use a standard or any type of heating element or do you need a special silicon carbide type?

Christina Clowes: It is not a special silicon carbide. We designed this particular application around the needs of the process, the operating temperature, the specific loading required for the process. But it is a different control methodology that’s really the key.

New Technology for North American (10:22)

Doug Glenn: While this technology is somewhat new in North America, it is actually not new on a global context. Can you address this?

Christina Clowes: In Europe, this kind of zero-cross base system has been commonplace for quite some years; also in Asia. The difference in North America is, I think, tradition, more than anything else. People have been used to using phase angle control for silicon carbide heating elements. That’s kind of where this technology grew out from, and people have stuck with that because it works. But this new technology though gives an opportunity to save money and space, while achieving the same result.

Doug Glenn: So for the North American market, this is somewhat new. But it is a proven technology. It’s not a new technology that we are still trying to get our hands around. It’s been done globally, which is an important point.

Cost Savings for the Customer (11:45)

Doug Glenn: With respect to cost savings for the customer, can you describe the capital expenditures, operating costs, and even maintenance costs?

Steve Feldbauer: We know that by eliminating the transformer, there’s the substantial costings. The SCR is doing the change in the voltage and controlling and eliminating that need for the transformer.

By eliminating that piece of equipment, you’re seeing upwards of anywhere between a 50 to 75% cost savings per heating zone. That’s a big number. There’s a wide range in that cost savings depending on the size of the heating zone, the size of the furnace, and the number of heating zones. That is a substantial saving.

In addition, the customer sees savings in shipping costs. In this case, removing the transformer reduced the size of the furnace by 2,100 pounds. That goes directly into your shipping cost.

Customers also see a lot less downtime because every time that you would want to change the tap in a traditional furnace, you have to power the furnace down, which interrupts production. There’s a knowledge base needed to know when and how to change the tap. But with this new technology, the furnace just continually operates.

There is also space savings. That transformer takes up space, which limits where we can put in things. For example, for the last line on a continuous furnace with a belt, the placement of the belt is dictated by where we put the transformers because the transformers typically go up underneath the hot box. Without the transformer, we now have flexibility and design.

So, we save in a number of different areas.

Maintenance of the SCR (14:24)

Doug Glenn: Maintenance wise, are the SCRs easier to maintain?

Steve Feldbauer: There is not much maintenance required for the SCRs. Once you put them in and they are set up, our customers really do not have to touch them unless they have to replace them. As far as tuning them and similar maintenance, there’s really not a lot that goes into them. Especially since now, you’re also not changing voltages. There’s not a lot of variability in the system. It’s set up and it just sits there and controls itself.

Advantages for the Customer (17:45)

Doug Glenn: What are the advantages for the customer?

Steve Feldbauer: There are many advantages in terms of cost, maintenance, and the ease in usage. There’s also less training, because you’re not teaching someone when or how to change a tap. This is a marked change in how you look at electrical furnace control in North America. This is something that is widely used throughout the rest of the world, so it’s not a new technology, but it’s new and innovative to North America. If you can optimize and streamline the process, why wouldn’t you?

Upgraded Features: Digitization and Data (18:58)

Doug Glenn: I also understand there are upgraded features because you’ve moved to an SCR and into a digital world with being able to get data back out of the furnace and understand the operation of the system because of the digitalization of it. Do you want to address that?

Tony Busch: By having a digital SCR power controller, you can connect up to your network, whether it’s Ethernet IP or Modbus TCP. You are able to collect all of that data. From that data, you are able to do things such as monitor the KW per hour. If you’re starting your process, and you want to know how much power was consumed during that particular time period, you can reset your KW per hour. Then you can find out how much you consumed when you are done and evaluate your efficiencies. All of that is recorded within the power controller. It’s essentially an industrial grade power meter built in.

Also, now that you are directly coupled with the silicon carbide heating elements, you have a very accurate load resistance monitoring capability. You are able to analyze the resistance and determine the health of your silicon carbide heating elements.

You can also plot a resistance curve. So you would know that if tolerance drifts 10, 20, 30%, you may be looking at a predictive maintenance situation where you look at your heating elements at some point and monitor the load currents. For a three-phase setup, if you notice that one of the phases is unbalanced, you may want to evaluate and determine the cause. You are able to be alerted without manually getting in there with a multimeter and doing your own research.

Christina Clowes: Compared to phase angle firing, which has been historically the most commonly used in North America, switching to a zero-cross system, a full sine wave based system, the SCRs turn on and off at zero volts potential.

As a result, that doesn’t produce any transient spikes that create a harmonic overlay, so there’s no electrical noise being generated. Utility companies do penalize their customers for generating electrical noise on their supplies.

In addition, because you have false sine waves, you have unity power factor, essentially. There’s no poor apparent power factor, which you have with a phase angle firing because you’re chopping the sine wave and conducting only part of the sine wave.

When you have purely resistive load, in the case of a Star Bar element, there’s no reactance, inductance, or capacitance. But because of the way that a phase angle SCR fires, it appears that there’s a power factor and people pay for energy that they are not consuming. This is more efficient way of driving an element system with a better handle over the energy that you’re consuming.

Doug Glenn: Is it more difficult to engineer these systems?

Christina Clowes: The exciting or interesting part is introducing new technology to people that actually helps them and provides real benefits. The total cost of the system is simplified and reduced, which makes it far more attractive for Star Bar-based systems to be sold into applications.

Doug Glenn: Right, right. Okay. Tony, how about you? What was interesting and challenging?

Tony Busch: Sure, yes. Christina touched on it a little bit. It would be that power factor in harmonics — being able to show the ability and not be penalized from your utilities for power factor and potential harmonics. Those questions come up, you know, pretty much anytime you’re using an electric furnace and SCR power controllers, but it’s much more easy to demonstrate to customers that you’re not going to see any of those issues. And I’ve seen our electric bill. When you’re running phase angle, you get these big old penalties that come up on there. It’s nice to be to pass that savings onto the customers with this new application.

Doug Glenn: Yeah. Yeah, that’s interesting. And Steve, I saved you for last because you were the ones that really had to interface with the customer. What was interesting or challenging for you guys?

Steve Feldbauer: I’ll tell you what, it was exciting for us to be able to provide new technology — new to North America — that number one makes it simpler for the customer to use.

You know, one of the challenges is always trying to teach people, “when do I need to change a tap or is there really some other problem?” Well, this eliminates that. Now we’re helping them to be able to operate the furnace more efficiently. And, you know, they don’t require all of the training.

We’re also able to pass on some cost savings because we aren’t buying that transformer. We’re able to have some leeway internally for design and construction. So all the way around, it’s a win-win, right? For the customer, for us, and for the industry, in general. Because now we’re able to move the heating technology forward.

Sustainability Benefits of the SCR Power Controller (26:31)

Doug Glenn: Yeah. I probably should have asked this question before, but there’s always a lot of talk about sustainability and greenness. Are there advantages here on this system?

Steve Feldbauer: Tony, you want to talk about it? I’m sure you can address the harmonics and different things that actually help out.

Tony Busch: Most definitely. From a power controller standpoint, the efficiency is right around 99.9%; you’re not really getting any losses through the power controller. And now you’re talking about being full wave firing, so you’re not trimming back that sine wave, you’re eliminating all those other harmonics. You should see a benefit from all of your equipment, if they ever experience that as well as, and your utility bill, not seeing that power factor.

Doug Glenn: Yeah. So basically I guess that’s it. The simple answer is if you’re reducing your energy bill, then obviously we’re using less energy and that’s probably less of a carbon footprint depending on where your electricity’s coming from. Well guys, thanks very much. This is a very interesting, great partnership between the three companies, obviously for the benefit of customers. Appreciate you working for the benefit of a customer and for spending a little bit of time with us here today.

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