Good morning. First, I would like to introduce myself. My name is Richard Wolff, VP of Business Development at JST Power Equipment located in Carlstadt, New Jersey.
Today, I'll be speaking about cast epoxy resin transformers for medium voltage applications. Here are my objectives today. I'll start with a brief talk on transformer evolution, followed by a discussion on dry type transformers.
I will follow this with a company introduction and include commentary on our installation base for cast resin transformers. Then we will conclude with a question and answer session. When we speak of transformer evolution, we will confine our discussion to medium voltage power transformers.
We begin with oil fill. Because of their ability to use an insulating fluid to cool the transformer during operation, oil-filled transformers were almost exclusively used in medium voltage power applications. However, due to environmental factors and the high maintenance required for oil-filled, it became desirous to use dry-type transformers where possible.
When developing dry-type transformers, there was a continuous effort to increase the mechanical robustness and as well as the dielectric properties of the insulation system. The sequence of dry type transformer development progressed with these improvements in mind. Starting with the open wound construction, dry type transformers were immersed in varnish and baked in ovens to cure the varnish. Later processes were developed that would provide for a forced displacement of air trapped between the transformer windings with varnish. Vacuum Pressured Impregnation or VPI is one such process.
Vacuum Pressure Encapsulation or VPE includes several additional dip processes to offer better protection against the elements. Encapsulated transformers are simply open wound, dipped and baked or VPI transformers that are encapsulated with a protective insulating coating such as epoxy. Cast coil transformers have the transformer windings solidly cast in epoxy resin. This is accomplished by placing the transformer windings in a mold and molding the windings in epoxy while placed in a vacuum casting chamber.
We will now contrast some of the features associated with dry type transformers. Starting with VPI and VPE, we find these to be more environmentally friendly than oil-filled and less costly than cast coil. Disadvantages, however, can be seen in their performance.
Weaker dielectric properties result in relatively lower BIL ratings and a higher level of partial discharge. They also run hotter and are not as reliable in harsh environments. Cascoil on the other hand is an environmentally friendly transformer and offers better performance characteristics when compared to those with varnish insulation systems.
Good dielectric properties yield bil ratings to 200 kilovolts and typical partial discharge is below 10 picocoulombs. They run cooler than those with varnish insulation systems but hotter than oil filled. For example, Oil filled will typically perform to a 60°C temperature rise, cast coil to an 80°C temperature rise, and VPI or VPE to a 150°C temperature rise.
Cast coil additionally offers superior mechanical strength and performs well in harsh environments. The main disadvantage is they come with a typically hard higher price tag. Considering some of the attributes just mentioned for the different transformer types, we see that certain applications favor use of one type of transformer over the other.
We list here some general guidelines for applications respective of the different transformers and under each transformer type we restate some of their positive and negative attributes. Oil fields are well suited for outdoor applications in areas that are less populated and not prone to natural disasters. There should also be easy access for maintenance.
VPI and VPE are suited for indoor applications where the performance requirements are not as critical. Cast coil can provide a very good combination of electrical and mechanical factors that lend themselves to both indoor and outdoor applications in densely populated areas as well as the ability to operate in harsh environments. Now I would like to shift our focus and specifically talk about cast resin transformers.
Shown here is a core and coil assembly along with a cross section of the molded coil. As you see the transformer windings are originally bound in epoxy resin. This core and coil assembly has both a high and low voltage coil for each phase.
These coils are coaxially arranged around the steel core and both are vacuum cast. I mentioned before that cast resin transformers have a higher price tag than other transformers. So why use them? To reiterate some of the positive attributes, there is higher reliability and performance with cast and they are superior with respect to safety and impact on the environment. But one thing I did not mention is that they actually have a lower cost of ownership than liquid filled.
In the next few slides we will expand on some of these attributes. When you see that each set of coils is rigidly cast in a solid block of epoxy, It should be easy to understand that this structure is less prone to the effects of contaminants, moisture, and other particulates than the transformers with a varnish insulation system. Design life is typically specced to be 25 years, but actual design life is usually well beyond that.
Mechanical strength is superior to all other types of transformers. and outperforms them with their ability to withstand an electrical fault without damage. Also, cast resin transformers will not encounter problems associated with the restriction of fluids.
As testimony to our claim that cast resin is safer and better for the environment, we have seen use in some of the most pristine environments. We have provided cast resin transformers to projects at over a dozen North American universities and college campuses. There are no flammable liquids or other chemicals that can be considered a hazard to the environment. This greatly simplifies the efforts required for waste disposal during decommissioning. In addition, in many cases, cast resin transformers have been chosen as the replacement for some of the older oil-filled transformers with PCBs.
While the purchase price of buying a better performing, highly reliable, and environmentally safe transformer may be a bit more costly up front, these costs can be made up over the long run as a result of the installation and cost of ownership benefits associated with cast resin transformers. Site preparation is greatly simplified by negating the need for catch basings needed for liquid-filled transformers. You can also save on real estate by close coupling to switchgear. Maintenance is significantly reduced and is a matter of keeping the transformer clean.
The lower losses when compared to other dry type transformers help save on energy costs. Lastly, decommissioning costs are much less than liquid filled with respect to waste disposal. Earlier, I presented an applications guide pointing out that cast resin transformers are well suited for indoor and outdoor applications that can be situated in densely populated urban areas or those with harsh environments where the extra degree of protection afforded by cast is welcomed. With this in mind, it can be easily understood why cast resin transformers have made their way into the applications shown here.
Urban development places an importance on environmental factors and consists of subways, hospitals, airports, and large office buildings. Commercial development, where reliability and performance in harsh environments is a must. These consist of factories, processing plants, and data centers where reliability is crucial. Electrical power generation also places importance on reliability, so it is no wonder why cast resin transformers are commonly used for the excitation and isolation transformer.
Wind energy which is one of the most competitive industries, is becoming one of the largest applications for cast resin transformers. Now that we have contrasted the differences associated with epoxy cast transformers and what applications they are suited for, we turn our attention to how these are made. Shown here is our facility located in Carlstead, New Jersey, which function as a North American and European headquarters.
The facility consists of 25,000 square feet and houses an area for doing assembly, design, and routine testing, as well as warehousing. Behind our North American operations stands four large-scale factories which produce the major components for the company's cast resin transformer product line. Those four factories are shown here. all being located throughout China.
With a market over 10 times the size of the North American market, China is the largest user of epoxy cast transformers on a worldwide basis. In the late 1990s, China changed their building code such that any building with public access required the deployment of cast resin transformers. From a company perspective, JST expanded from a single location to those four factories which you see here before you.
This effort in expansion included equipping the factories with the most modern equipment imported from around the world. Today, a capability stands second to none with respect to producing cast epoxy resin transformers. We will now take a look at the processes involved. There are four major processes, coil winding, casting, core cutting and stacking, then final assembly and test.
We start with coil winding. What is not shown here is the preparation of the conductors. Prior to coil winding, except for the case of a conducting foil sheet, which is typically used in low voltage windings, the wire is wrapped with an exorptive crepe paper.
Epoxy is drawn into the paper during casting, helping to ensure a void-free casting. Coils are wound on a mandrel while paying strict attention to Tension, the number of turns, which is a complete revolution, and location of any taps that are required. In turn, the wound coils are fit to a mold for the vacuum casting process. Oops! Casting.
Well, we got our presentations mixed up. This one is from a presentation for those that do. maintenance on cast resin transformers.
There we go. The other kind of casting. Vacuum casting chambers are loaded with molds that contain the wound coil from the previous process. Air is evacuated from the chambers by an oil diffusion pump. While under vacuum conditions, the epoxy resin and hardener are injected into the mold.
A static mixing technique is used by JST. This technique is basically opposite of batch mixing and is more of a metered mixing where both resin and hardener are mixed at the time of injection into the mold. While equipment to do this is more costly, dividends are paid in achieving a more uniform cure rate and a higher degree of integrity in the casting. Sophisticated controls are used throughout the entire process. The final cure operation is done by removing the molds from the casting chamber and loading these into large ovens.
After the final cure, the coils are cooled and removed from the molds. Cores are made from sheets of electrical grade silica steel which need to be cut to shape and stacked together to form the core lamination. The core is constructed from a series of step-lap layers, each layer having a specified width.
In addition, each layer is cut with a mitered section corresponding to the location where it will be joined with another lamination to form a right angled section. This step-lap miter construction offers better performance for audible noise and reduces electrical core losses. The steel sheets are stacked in such a way as to simulate a circular cross-section.
This is accomplished by an automated process that varies the strip width during stacking. In fact, both strip width and strip length are controlled for each layer to yield the step-lap construction of appropriate cross-section. Once the layers are cut and stacked, It is assembled into a trident structure and painted with a protective paint. The trident structure and the upper yoke will be staged for final assembly.
When I speak of final assembly, I should clarify and state that we are looking at the core and coil assembly. There is another level of assembly where the core and coil assembly itself is assembled into an enclosure and that is what undergoes final test. To better illustrate cast epoxy resin transformers, we have limited the photos shown here to the core and coil assembly only. In this process, we marry the casted coils to the Trident structure mentioned previously. Both high voltage and low voltage castings are lowered onto one of the three core legs.
Once this has been completed, the upper yoke is assembled and secured. with the upper core clamp. Assembly of the upper yoke is a manual operation associated with interleaving the steel sheets of the upper yoke with those of the core legs.
Once complete, the upper yoke is painted with the same protective paint as the trident structure. The core and coil assembly will now be finished with the appropriate bus work and connections and prepared for assembly into the enclosure. At this point, the completed transformer is now ready for test.
In some cases, the complete core and coil assembly will be sent to our Carlston, New Jersey location for final assembly into the enclosure and final test. In any case, once final testing has been complete, the transformers are ready to be deployed into their intended application. Shown here is a list. to exemplify a few of the installations for JST transformers.
It can be seen that these installations are a representative of the types of applications the cast resin transformers are well suited for in that they require transformers that are reliable, perform well, and in some cases harsh environments. While there are many installations throughout the world, The list here is confined to US installations with the audience in mind. When we think of applications that demand reliability, we can look no further than data centers and hospitals. Ability to perform in harsh environments is represented by manufacturing and processing plants, as well as the subway projects, which also demand some of the strictest performance requirements. The urban aspect can be seen from the representative cities listed here, New York, Chicago, and Philadelphia.
However, there is probably no better example of a large city infrastructure project than that which follows. When the new Freedom Tower was constructed at One World Trade Center in New York City, cast epoxy resin transformers were specified in many of the applications. as commonly seen in such large-scale, high-profile infrastructure projects.
During the initial construction, JST cast resin transformers were used for the temporary power and the transportation hub substation. Other applications in this project benefiting from the deployment of JST transformers included the chiller plant which provided cooling for a multitude of users, the World Trade Center Memorial, and the PATH Subway Hall Rectifier Transformer. To summarize, cast epoxy resin transformers provide better reliability, better performance, lower ownership cost, and is better for the environment. They are well suited for indoor and outdoor applications in densely populated urban areas and harsh environments. JST Power Equipment uses the most modern production equipment combined with extensive experience to manufacture cast epoxy resin transformers which are deployed throughout the world.
And last but certainly not least, I'd like to thank you for your interest. and taking the time out of your busy morning to be here with me today for this session on cast resin transformers and now i will open it up for your questions thank you okay um let me read our first question how does the cost of the cast resin transformers compare with other types of transformers um okay um i guess in in general um it's it's kind of a tough question to answer because there's so many different variations so let me just try and answer it as generally as i can oil filled and a lot of that depends on the type of oil that's used there's some oil that's more environmentally friendly than others and i think it costs a little bit more but in general i think uh for the original purchase price it could be anywhere from a 10, I'm sorry, 15 to 20% difference in price. And again, that depends on a lot of things, but that's just a general guideline.
For VPI, I would say you're looking at about a 10% difference. And when I say differences, those are all lower cost. Remember, cast is generally more affordable.
a little bit more. However, I can say this, depending on some units, when you look at things that come out of our factory, where there's a lot of economies of scales, I've even seen some cases where the price tag with VPI was right in line and pretty close to oil filled as well. So it depends on a lot, but in general, um, that's what i would say for oil filled you're looking at an initial price tag that's about 15 to 20 percent less than cast and for vpi around 10 maybe that percentage is even a little bit lower than 10. we have our next question is there any difference in temperature ratings of the cast resin transformers when compared to vpi transformers the answer is yes there is And I'll explain that in a sec. I just want to point out something we mentioned in one of the other slides, which was the temperature rise.
What's really key is the temperature rise of the transformers are designed such that you have headroom between that and the temperature rating for the insulation systems. In fact, the more headroom there is, When operating, you basically extend the life of the transformer. So having said that, if you remember back, I think we said for oil field, the typical specified rise is 60 degrees C, and that is typical. For cast, we said the typical spec is 80 degrees C.
What I didn't mention, I'll mention now, there is another value that people do select. It's an option offered. It's 115 degrees C, temperature rise. And the reason they select that, it obviously runs a little bit hotter. So it's a lower cost option for people.
With the rating of cast resin transformers on insulation, somewhere they are, there is enough headroom. So they select that option and save some upfront cost. And then the rise for a VPI transformer was 150 degrees C.
So that's the typical rises that are spec'd and pretty much what you can achieve. And when you compare that to the ratings, what you typically see in dry type, there's two insulation classes that you will see for cast. You'll see class H, which is 180 degree insulation system, and class F.
which is 150. Pretty much in the US, I'd say almost 90% of the specs I see are all class H, 180 degree insulation system. And that enables you to select the 115 degree rise option that gives you a little bit of a lower cost up front. With 80 degree, you have a lot of flexibility. plenty of headroom with a 180 degree insulation system. When I say headroom, you have to remember that you're taking the rise, but you need to add whatever the maximum ambient is, plus there's allowance for the hotspot.
And probably now's a good time to point out that the hotspot for cast resin transformers is a lot lower than it is for the VPI. I think the IEEE ANSI standard If you're not able to measure it, it gives you an allowance of 30 degrees C for the hot spot. And we typically see less than half of that for cast.
But we do use in our calculations 30 degrees C, the guard banded. So having said that, 150 degrees C, class F, and 180 degrees C. class h are what you see for class um for cast for vpi um most of your varnish systems are rated class r which is 220 degrees c and basically you're going to need that uh with 150 degree rise so that's basically it that's uh pretty much the difference in in the ratings but like i said the key factor is when you operate it the headroom that you do have because that has all to do with the life expectancy of a transformer.
Okay, we have our next question. You mentioned that the cast epoxy resin offers better dielectric properties than VPI and VPE transformers. Can you describe in what way?
Yes, yes, that I can. And I'm just thinking back. we presented a slide when we talked about the dielectric properties. And I think the two biggest areas, the specifications where you see the largest departure in performance are with partial discharge, PD, or corona, however you like, and basic impulse level, BIL. Basically, let me stick with PD first.
with the cast and because of the pressures you're able to realize in the vacuum casting chambers and the way they're able to get the epoxy to absorb into the the crepe paper that's used with covering the wire when you wind these coils you're able to get a casting that's void free. There's absolutely nowhere, anything else that gets trapped between those windings, where it's a bit more difficult to achieve with VPI. And so the discharge you see is basically with the internal windings, there's a lot less discharge by nature of the structure of cast epoxy resin transformers than there is with VPI. And that's a good point because one of the things that you see with the VPE and actually taking a varnish transformer and encapsulating it in epoxy, and that's done to give you the same level of protection against moisture and particulates in the air.
and all the things in a harsh environment that would drive you to use a cast epoxy resin transformer they encapsulate and encapsulate in epoxy but you still have the same internal winding structure and you'll never get the levels of discharge as you would with a cast epoxy resin transformer. The other area is BIL, and that just is really with the dielectric strength. And typically your BIL is a rating that's based on the voltage class, so you could be 1. 2kb up to 34.5 kb and in general if you look at what you're able to achieve with a cast versus a vpi you're anywhere from 30 plus higher with a basic impulse level than you are with the vpi as a as a maximum typically and i know we've done some things a little bit higher but what we typically will entertain are specs for 34.5 class kv class transformers with the 200 kb bil rating and i think that's extremely difficult if not impossible all together with with vpi but But in general, I think for BIL that's what you see, maybe about 30% to maybe even as high as, more than 50% increase in BIL and it all depends on the voltage class.
Next question is, are the use of epoxy transformers limited at all when considering various applications? That's a good question. And the answer is yes.
In fact, dry type transformers are limited in the way you're able to apply those. In that, typically, you will not see the use of dry type transformers in high voltage applications beyond 34.5 kV. Pretty much used in medium voltage applications. And really it's the current that's the limiting factor. You get to levels of current that are just so high that there's really no way to cool the conductor effectively.
It has to be a liquid, which is a lot better at taking away the heat. A liquid's a good medium to take away the heat versus air. And so there are limitations on air cooling and air cooled transformers, which dry type transformers are.
Having said that, I know when I look at power ratings, we've made some up to 40 MVA, but it was perfect in that. the way the the voltages and currents worked out that you you were able to keep the the current within the limitation so it could cool effectively without damaging the dielectric but anyway um that's yeah that's one application i would think is um you cannot go uh with epoxy or vpi for that matter um in in high voltage applications it's pretty much medium voltum applications. The other limitation I would say for for cast is basically cost. I think there's just some general applications where you don't really need the performance, it's not in a harsh environment, reliability is not an issue and at that point you'd probably want to consider VPI because it's just the will come with a little bit of a cost savings than if you expect a CAS. So I say that would be another limitation is basically in areas where you don't need the performance or the things that CAS have to offer, then you really that would limit the use of CAS because I don't think you'd want to pay the extra for something you didn't need.
Okay, the next question is, what is the useful life of the cast resin transformer? That's a tough one to answer. I could answer, I could see what I see. Specified a lot. I see 20 and 25 years specified quite a bit.
Not even sure how that number came to be, but I could tell you we have things operating out in the field that have been operating longer than that. The key to it goes back to what I think is the operating conditions. Also, maintenance has a lot to do with it.
While cast requires little maintenance, especially when compared to liquid-filled, it still has to be maintained. And now is probably a good time to mention it. Really, one of the things, and however often you need to build it into the maintenance cycle, it really depends on the environment you're going to use the cast resin transformer in.
And as I said, it's designed to perform in harsh environments, but in the maintenance cycle, it should be subject to regular cleaning. It's not maintenance-free. And in environments where there's a lot of particulate matter, and especially if it could basically end up on the surface of the coils, that should be wiped down periodically, because as debris starts to build up, it will electrify and which is discharge and over over time if you operate it without cleaning it when the debris does discharge it will start to attack your insulation system so if you do clean it on a regular maintenance schedule and that is really dependent on some applications I seen some cases where they've used cast where the things just stayed as clean as could be forever um but i've seen others where they get dirty fairly quickly so uh again the the maintenance has to be a little bit more frequent there and it needs to be clean um but that's one thing uh having said that um if you remember back when we answered the question on temperature rating you um there was uh I pointed out that there was headroom and when you operated a transformer much lower than the headroom you got more life out of it and uh basically when they rate insulation system that's pretty much what what it's all about um arbitrarily they picked the arbitrary time for the insulation system rating they said it's 40 000 hours and basically they use that to come up with the temperature rating but really what it boils down to is um there's if if you look at the theory there's a relationship between temperature and time with respect to the way the insulation system will decay or it's it's it's really a chemical rate equation And so if you operate the transformer well below that rating, or there's a lot of headroom, you're going to be able to get life well beyond, as I said, we have them out in the field well beyond 20 years and 25 years. So I don't think there's a real exact answer to that, but I can tell you this, that we do see 20 and 25 years specified quite a bit.
And I would say if you haven't retired by then, for something you were involved with, it's worth checking them because I expect it could go a lot longer.