IEEE Std 1584-2018 – A Journey in Understanding the Anatomy of an Arc

Welcome, everyone. This is the EPower webinar series. My name is Jim Chastain. I'm your host for today. And, we're very fortunate to have with us an esteemed gentleman who has a very exceedingly nice resume in the field of, arc flash. Doctor Li received his bachelor and a master's degree in electrical engineering from National Taiwan University in Taipei, Taiwan in nineteen seventy eight and nineteen eighty, respectively. In nineteen eighty five, he received a PhD from the University of Texas at Arlington in electrical engineering. Also in nineteen eighty five, he joined the University of Texas at Arlington where he's currently a professor of electrical engineering department and director of the Energy Systems Research Center. Over the course of more than ten years beginning in the year two thousand four, a multimillion dollar research project sponsored by IEEE and NFPA involved a series of over eighteen hundred arc flash tests performed in high voltage laboratories. And it was doctor Li who led this research project, which evolved into the IEEE fifteen eighty four model. We are fortunate to welcome to our podium doctor Wei Jin Lee. Good morning, good afternoon, or good day, everybody. And, I'm very happy to share with you on the IEEE STD fifteen a four twenty eighteen, the guide for perform a crash hazard calculation. And then I tried to basically, okay, give some background information because I know since that this, webinar is the host by, and I believe everybody understand how to run the calculation. So on that part, I will skip that part and try to give you some behind the scene that the the activity. And then so, hopefully, that give you a better idea, better understanding on how the the the model was developed. And, as we know that electrical incident represent a relatively small percentage of the work related incident. However, they are disproportionate battle. And in the case of the burns, may result in extended hospitalization and the rehabilitations. So if you according to Richter, electrical related fatality is the number five leading cause of death in the workplace. And when you look at the crash point the from the crash point of view, that the actual boy fifteen eighty four and the NFPA seventy e have been developed to protect the safety of the workers. And, from the approach point of view, NFPA seventy e tried to use a tabularized one. However, from the attribute point fifteen eighty four point of view, since we are engineer. So a lot of time, we try to do a more quantitative result and, give you the formula to do the calculation or the estimations. So when you talk about arc flash in the in the regular setup, in the electrical installation, you all have enough insulation level, so it will not create any leakage current or any pass between two conductors. And, however, in some case, okay, we sometime we call it a screwdriver alert and somebody during the work, and then they drop the tool, they create a sum show circuit. So once the show circuit happen, then that bounce into that, it's going to create a lot of heat, and the the heat will then ionize the air. So on that way, that will basically create the breakdown of the air. So the airbrush is basically from this way here. Once the ionized air, then even the two bounce away, then the current continues. And for this one here, it will be a sudden release of the heat. And, basically, a lot of time, if you if you have ever experienced, I hope it doesn't, okay, it it's going to create a big pump, and it's also sudden release of the energy. And on that one, that can basically, okay, cause an injury or even create a fatal of the worker even in nearby. And, of course, on this one here, when you talk about the arc flash, arc flash, if it is a short circuit, then since r equal to zero, so there's no energy release. So from the arc point of view, there's a bit there's a resistance between the two conductors. So that I square r produce the energy that can basically release millions of joules in one incident. And for this one here, this is basically I know most of you have seen this this, basically, this video clip, and it's the u it's from the YouTube. And then you can see in one moment, everything seems seems normal. And, however, all of a sudden, that basically okay. Well, on this one here is more like, they are wrecking wrecking the circuit breaker and the misalignment on the circuit breaker that caused the short circuit and then caused the caused a crash. And, so the first edition of the fifteen eighty four was published in two thousand two. So at that time, that we only have two models. Okay. One is the basically, you can see here, this is a electrode over there. This is a vertical electrode and the inside the inside the box. And then these are the carrometer that basically try to measure the the insulin energy. And then the other configuration is the vertical electrode in the air in the open air. So on that calculation point of view, that is a very relatively simple configuration. Everybody can when you look at the in the in the field and when you look at the configure look at the setup, you can identify what kinds of configurations. So at that time, it's basically we only we only identify or provide the formula for two two configurations. And right after the publication, people people basically criticize, say, okay. Well, this doesn't re did not represent the whole configuration. So in two thousand four, as the Jim mentioned, okay, in two thousand four, they formed a committee between the NFPA and IEEE. They say, okay. Well, let's put two organization together and then try to develop the a common the, basically, the model that can be used for both organization. And, for this one year, with about ten ten years effort, I was invited into the the student the the, basically, the collaborative research project. We call it algebraic n f p a Afresh Phenomena Collaborative Research Project in two thousand eight. And, after ten years effort in twenty eighteen, that fifteen eighty four was published. So that is, basically, in the fifteen eighty four because the it was a a little bit rushed. And then so in two thousand two, they they the model is based on about three hundred test. For the fifteen April two thousand eighteen, we have I have run more than two thousand test. But, some of the test that that we we say, okay. It doesn't sustain. It did not sustain. So the useful information is about eighteen fifty test. And, fifteen eighty four only provide two configuration, but, for the the two thousand two model only provided two configuration, and the two thousand eighteen, we extended to five configurations. So on this one here, when you when you look at this one here, okay, this guide, we provide the model into an analytical process to enable calculation of the predicted thermal instant energy, arc flash boundary, and the acting current. For this one here okay. So every model has a limitation. So on this one here, we basically recover the two zero eight to fifteen kV, and, it's a three phase AC current AC system. So on this one, the purpose of this one, this, guide is try to have a qualified person to analyze the power system for the purpose of calculating the IE and, that is basically that employee could expect during the operating or maintenance work if something happened. Okay? So that is basically that also provides some information for the owner to basically help providing appropriate protection. And, for this one here, as I have mentioned, this is only for three phase. So it doesn't cover the single phase AC system. And then we basically just provide it because the okay. Well, you can extract it from the three phase. And then in the fifteen eighty four two thousand eighteen, they also provide some guidance to okay to for possible application on the single phase. And it doesn't go with the DC either. Okay? So it doesn't cover the personal protection equipment, the PPE side, because sometimes when you try to determine the PPE in addition to the arc brush, you have some other considerations. So it's basically the the recommendation for the PPE is not in the in this one here. And then this the other one is the one big difference between two thousand two and the two thousand eighteen. Is in the two thousand two, they say, okay. Well, if the two hundred two two hundred forty volt below and the the one hundred twenty five kVA the transformer, then that arc is unlikely to sustain. However, when I did the test a separate test to try to identify this issue, then we see in some case, that we do we did see the sustainable arc during the during the test. So I run a more than one time test in one of the lab. And then so this one here is actually at the time that the when I when I run it, it's we just go down to about twenty five hundred amps. And then in the working group, they feel, okay. Well, from the safe side, more conservative side, they put the two thousand amps. So they say, okay. Well, it's, it's possible, but less likely in the three phase system, operate two hundred forty volt, nominal or less, and the variable short circuit current of two thousand amps. And, when they can put the two thou two two hundred forty volt over there, it's basically from if you if you think about it, it's basically on the high side of the two zero eight one twenty. And, also, all the single phase the basically okay. The three phase, the one twenty two zero eight system, and then you price the five percent over there. So if you look at the range over there, this is the two thousand eighteen. It pretty much match the two thousand two, the range. Okay? From point five to one zero six amps well, for voltage below six hundred volts. And then from the six hundred volts to fifth fifteen kV, it's point two to sixty five k a. So for this one here, the big difference between the two thousand eighteen and the two thousand two is that if you if you pay attention on the two thousand two model, on the one thousand minus and one thousand plus, you are using the two formula, and they have a discontinuity result. Okay? They come out with a different result. For this one here, it's a it's a basically okay. Well, there's no no gap between the comp comp calculation even those we look at it as the six hundred volt on the basically, on both side. So but the the result is continuous. And then, of course, the since this is the for the low voltage to have a sustainable arc, then the gap will be a little bit smaller. Okay? So when I when I run the test, it will basically follow the UER standard, AANI standard. And then for the high voltage, we use the the BIL as a as a as a reference. And, for the in the two thousand two model, it doesn't consider the the enclosure size. And, for the two thousand eighteen, we do consider in enclosure size. Here, we put in a forty nine, and, actually, you basically run-in the forty nine and fifty that bay they are about the same. And then, also, you have a five configuration. We call it the VCP. It's a vertical electrode in the cubic box. Okay? And then we at that time, during the test, we use the cubic box. So we basically just name it as the cubic box. It's a metal enclosure, and then VCBB is the vertical electrode in the metal enclosure and with barrier. HCB is the horizontal inside the metal enclosure, and then VOA is the vertical open air. HOA is the horizontal open air. So on this one here, you can see here when you when you look at it, okay, the basically, for this configuration and this is the vertical one. And, if I if I okay. So if I put in this one here, you can see, okay, that the plasma is basically go downward. And, so this is one of the configuration in the two thousand two. Then if you come into here, it's a basic this is a horizontal configuration. So if you look at the this one here, we we basically assume this is the worker standing at here, and then you you you can see the difference between the vertical and the horizontal. Horizontal, the trajectory of plasma basically prior to toward to the the worker directory, and, this is much serious situation. Okay? So this is the basically, we tried to for this version of the vermin, we tried to basically look at it. Okay. What is the what is the configuration? And then, normally, you're going to see much severe situation like this one. And then during your your calculation, you you you will realize, okay, from the vertical the basically, vertical configuration and horizontal configuration. Horizontal configuration, the protection boundary, it's a little bit shorter than the vertical configuration. This is because when the when the plasma flow over there, okay, and then hot air is going to go up quicker. So when you move the major point further away, then the the thermal, the degradation that basically they drop because of hot air blow up, and then so it doesn't touch the the sensor. So on that way, from the calculation point of view, that horizontal one, horizontal configuration, even though it's at the shorter distance, they have a higher instant energy. However, their protection boundary will be short the the with with shorter distance. And for this one here, this is the VCBB configuration over there, and, you can see okay. Well, it's, this is the fourteen one four four point one six kV and with sixty three k. And, one thing that I have to mention is okay. If you look at it, there you're going to see a a metal droplet here. And, from the measurement point of view, metal droplet, we won't be able to measure the major droplet. It's a hot spot. So this is another thing that you have to you have to consider. And, of course, when you try to look at the fracture study procedure, everybody know that. Okay. I'm basically, you understand the configuration and, obtain the parameter calculation of circuit current. Okay. And then estimate argent current. From the argent current, you estimate argent duration. And, of course, the when you use the EZ power, they basically help you do all this because they have a table of the fuse curve or a relay curve. So you can estimate the act duration, and then you try to determine the working distance. Normally, the is, arc initiation point to the to the worker's chest area, the the distance. Then we consider that one is the working distance, and then you try to estimate that instant energy, and then you try to calculate protection boundary. And then, of course, the protection boundary, you will base on the one point two caliper centimeter square. That is the from the STOW curve. So for the the difference between the two thousand two and the two thousand eighteen on the fifteen eighty four is the we have three additional configuration. So on that way, the people always ask, okay. How can I determine which configuration to use? Alright? So here, I give an example here. It's basically from the basic physics. We call it the right hand rule. So you can see here, this is f. This is the b is the flux, and the I is the current direction. So here is your current here. And the b is basically created by this one. The current for inside the inside the conductor is going to create. So based on based on your right hand rule, you you can see, okay, the the b flux direction here and then create the interaction with this one. So the f coming to here. So you you when I show you the first vertical configuration over there, the plasma trajectory is go downwards. This is the big basically, you are using the right hand rule. And, for this one here, this is on MCC, and, we basically initiate the port at this point. When you initiate this the port at this point, this is more on the v VCB or VOA, depends on the the enclosure size. And, you can see here that the trajectory is going downward. For the same equipment, if I have a four if I basically initiate, arching fault at this point, which is at this point here, then it become a horizontal. So you can see here that basically come into the horizontal. Alright? So when you try to determine the configuration, then you try to first thing you have to do is determine why at what point you think the arc flash will happen. Okay? And then that determine the trajectory of the plasma, and then you determine the the configuration over there. So here is the basically, you can see, okay, this is the the break mark over there that basically show you how the how the arc flash, the trajectory, the plasma trajectory that flow in during the incident. And, so on this one here, as I have mentioned, I'm going to give you some background information. Okay. So this is the measurement equipment on the airbrush test. And, so the first one is the basic of course, you have to collect the data. So the data acquisition system and the thermal management system. So at the beginning that, we we used the offshore product, and then it's basically a USB connection. So it basically, according to the spec, it was pretty good. They the sampling rate is more than two hundred k, and then they give you a end of eight end of channel. Well, unfortunately, the on this one here, you did not have enough isolation. So, also, this one, it will be in inside the lab, and then you don't you don't you don't want to stay in the lab. So we basically use a use a USB extender and then use the USB to the CAT five. So they will we will be able to measure the basic correct data three hundred feet away. And, yeah, it was basically work for the one eighty volt testing, and, unfortunately, it was destroyed that, for the in the higher voltage test. Because you can see here, okay, on the on this on the measurement side, That here, you are using the carrometer over here, and the carrometer is the thermocouple, and the front end is a copper. So the plasma basically touch the surface of the calorimeter, and then that touch the high voltage. So insulation become very important one. And, also, the the thermocouple output is on the millivolt. This is this one here, okay, four hundred eighty volt, that's the minimum. The two hundred two zero eight is the minimum. Then then aside, it can go to the fifteen kV. So on this way here, since some small difference, it's going to go back and then destroy destroy the the circuit by itself. So this yep. The during the test, the second test, it was out. So I went back and then come back and come up my own design. Alright? So on this way here, this is the basically, okay, the carrometer here, and then you have a thermocouple go through an a conditioner. So that basically convert the convert into a voltage and then go through the isolation here and then get into the compact reel and then use the optical connection. Okay? Fiber connection that basically between the unit and the the computer. So on that way, we will be able to create isolation, and then so that is the basically okay. Well, for this for the safe of the equipment and for the safe of the person. And, so for this one here, the staff carrometer is based on the STM fifteen nineteen fifty nine. So this is the four centimeter. And, with the one point three one point three minute the basically okay. That the depth of the copper is the basically, one point six millimeter thick, and then it's eighteen gram. So then you drill a hole in the middle and you put the thermocouple over there, and the behind of it is, this is the insulator, and, it's a air chamber over there. Okay? So on this way here, that temperature rise, that translate if you if you do it at eighteen gram over there, so if you one degree temperature rise equal to zero point zero point one three five carat. Alright? So that is the basically, it has a direct translation, and then we can measure the temperature rise and then get into the instant energy. So on this way here, you can see here the surface is a flat brac. And during the test, we did some some experiment with a different with the with the silver tone and then try to see, okay, how much difference will be. And, also, since it's difficult to predict, we have well, we can predict somewhat predict the trajectory of the plasma. So but, we try to basically make sure we cover all the range. So every test, we have we put in seven parameter over there, and then with the metrics over there, so we will be able to find because the when you try to do the calculation, you we basically look at the highest temperature rise because the the the damage is not based on the average temperature rise. The damage is based on the the most severe temperature rise part. Then the other one is the sound. Alright? So, yes, if you look at it, okay, that is diff different way the sound that for the for the people, and then that is basically on this way here. In the in our testing, we use the a weighted applied to the instrument major sound level in the effort to account for the relative loudness. And, you know, the the OSHA have a requirement that basically for the hundred forty dB, you need, hearing protection. Alright? And, so the sound measurement that basically we use the microphone, and then that basically use the the all the microphone comply with the n c s one point four, and the whole event is less than two hundred milliseconds. So weighted c peak is recorded, and then so the sound level affected by because the the the when you do the experiment, the sound level is are affected by the size and the shape of the test lab, the magnitude of the short circuit current. So that is basically the correlation between the sound level and the activation is very small because the the the the other bump boom. It's basically at the beginning. So, normally, it's just happened at the beginning. So the actuation, that doesn't doesn't really really change the match. Okay? And, so we basically try to look at it, okay, on the first time waiting or slow time waiting and the impulse time waiting that based on the based on the specification. Then this is the basic this is the microphone over there, and, this is the the sum of the test result. Okay? It's a three meter away, and you can see here all it basically every test is more than hundred forty dB. So on this way here, this is a twenty seven hundred volt. And, since that that basically we don't have enough information, and then we run the test at different lab. So that, basically, the the basic conclusion is a hearing aid should be included as part of the PPE because the you see, it's more it's always more than hundred forty dB. And then the pressure measurement. The pressure measurement? Okay. Well, if you look at the some of the report or the some of the information on the website, and then they will tell you that is the basically, okay. It's a it's twenty one that I'd remember the the number is twenty one hundred psi. It's a pound per square inch. Twenty one hundred pound per square inch. That is a lot. Okay? Because the if you look at your chest area, you have about, okay, well, probably hundred hundred square inch. And then you basically have a one ton of the force applied to well, more than one ton. It's a twenty one hundred. The basically, twenty one hundred psi then times one one hundred square. So it's one almost one hundred top. And then if this is a correct number, then the the worker will be squeezed to death. So this is not the the basic case. Then we try to look at it, how to and, of course, in some case, the worker can knock off the the ladder, and then we try to see, okay. Well, what kinds of what kinds of pressure that really happened during the incident. And, so at the beginning, I thought it was an easy one just to put the pressure sensor over there. So this is the pressure sensor we use, and, it's a piezo piezo electric sensors. And, of course, the a lot of sensor, they use a very it's a diaphragm inside. And, when they use a diaphragm inside, that basically they are heat sensitive. So we don't want the the during the test, the first test, we destroy one sensor. Okay? This this sensor, it's about nine hundred dollars. So we say, okay. Well, then let's put it in in the site. And, put it in the side, and then you measure a negative pressure. Alright? Because the Bernoulli effect, then you have a airflow flow through, and then you basically get the negative measurement. So it doesn't work. Then so I come out the idea and say, okay. Well, let's use a pendulum here. You can see here. I have a pendulum here, and, I know during the arc, it's going to have a lot of smoke, so I tie a knot here. And then this is the metal plate. So when you have a metal plate over there, they push it over, so you can see here. And then you during the arc, then you you see okay. Here, you can see how they move. Okay? So this one that move over, and, so on that way, I know how how far the the pendulum move, and then what is the speed, and then we can basically come here and calculate what is the what is the pressure. And on this on this particular case, we have about point six to point eight psi. And, the other one that we have used is to basically use the during the arc flash, I have a high speed video over there. So based on the two consecutive frame, I will be able to look at what is the airflow airflow speed. And then from the airflow speed, I will be able to estimate the pressure. And, but for this one here, because the it it's you need the open open field here so it doesn't obstruct the airflow. And, a fresh test is relatively expensive. So it's basically okay. Normally, you are talking about fifteen hundred to two thousand dollars per test. So we basically say, okay. Well, yes, it works, but, it's not really economic solution. We have a limited budget. So then I come up another one, use the LOVDT, the linear linear voltage differential transducer. So this is the basically based on the transducer, the the movement of the transducer here. They have a two coil, and this is the basically, the move. And then try to look at it. On this way here, we will be able to look at how fast that they move, the speed, and also the distance. So this is the basically, the very simple Hooke's law, and then we can change the the the size of the plate. So on that way, we can basically adjust the sensitivity. And here is the okay. This is a metal one. So here, this is the insulator here. So it will the the they are not going to have any induced current get into the transducer. So for this one here, come up. It's basically okay. You are you are talking about about this point seven one five psi, and then it's about one zero three pounds per square feet. So this is the basic from the from the distance. And, well, unfortunately, we did not we designed the test equipment. However, we did not have enough test results, so I did did not create a model for the pressure. And the the other one is the life intensity measurement. Okay? So, yes, the according to the OSHA, about the forty, the eye injury account for about four point two percent of all airbrush related injury. And then some people experience a temporary brightness due to the sudden bright. Okay. Bright light. And then, also, the high intensity light in the visible infrared and the ultraviolet light can damage the important structure such as the cornea or the retina of the human eyes. So but, on this way here, you can use eye glasses to prop the IR and UV and the the visible light because you rely on the worker rely on the visible light to do the work. So then we try to look at it. Okay. Well, from the visible light point of view, it's about three hundred eighty nanometer to seven hundred and sixty nanometers. And, that that is the human eye. So then you well, also, the human eye to the they, basically, they have a different sensitivity to the different wavelengths. And, also, for this one here, this is the basically, during the the lighted area. So this is your eye sensitivity. This is the the green green one is the the sensitivity of your eye, the typical human eye under the dark dark area, dark environment, and this is the relatively the illuminated environment. And, normally, the workspace, you have certain light level over there, so we are following this curve. And, for this curve, we are we are fortunate to have, to find a an IC, okay, for the integrated circuit that they designed it that you follow the human eye. And, however, this one only can work on up to one hundred thousand luminance. So we have to we have to look at it. Okay. On the one hundred thousand luminance over there, then the airbrush is much higher. So we basically use a neutral density filter, and then I'm using the socket, one one and quarter inch socket as a protection. So on that way and then also have a separate turret. So this is a service mount device, and, that come out a pretty good design. And, basically okay. We also we basically put it into the three three measurement point and, with the three meter, four point five meter, and the six meters. So then you try to aim at the same direct same point over there. So but, well, when you have a three make three you try to use a eye to try to align it. Sometimes you created some misalignment. You can see here the response is a little bit different over there. Alright? This because of the misalignment, because they have a the every chips has a line of sight. So to solve the problem, I basically create a very relatively easy solution, use a laser pointer, and then try to align it. And then this basically okay. It's a one dollar solution. So that basically solved the problem. And, for this one here, this is the basically recorded light. And, on this one here, this is the the blue one is the six meter, and the for the the red one is the four point five meter, and then the green green one is the three meter. So and then with this one here is the basically okay. With the with the different different configuration, different current level. Okay? So for this one here is the ten k ten k a. Okay? And then this is a third twelve cycle and, that, twenty seven hundred volts. Okay. For it's basically four point five inch over there. And, so you can see here that, basically okay. That give you the measurement. And, we have more than fifteen hundred measurement over there. So, yes, there's a paper we have published that that describe how to derive the formula for the light intensity measurement estimation. Alright. And, so on this one here, that I have to basically the basically, the give the credit to the sponsor. We have a platinum sponsor, and, we have a co sponsor, civil sponsor. And, the total budget for this project is about three point seven million dollars cash and in kind. And, so that is the basic. Without their support, that it's impossible to have this project complete. And, if that basically, one thing that, we have to I'm sorry. That's it. I have it. I have to close the door. Yeah. One thing that I always try to emphasize is okay. So this is the carabiner, and, that this is the this is the measurement point. Down the side is the insulator. So you can see a lot of copper deposit on the insulator side. And, this is the this part, it's basically you're going to see a hot spot over there, and it's difficult to do the measurement. The other one is okay. This is the lens. You see on on my the light measurement. Okay. I'm using a neutral density filter, and this is ten feet away. So the nobody want a cover cover droplet on their their eye. So the eye protection is very important. So this is I always tell people, you only have one pair, no spare. So that eye protection is very important. So with that, I would basically stop it here, and then I'll ready for your question. That was fascinating. So the first question has come in, doctor Li, is from Okay. Andrea. Mhmm. The question is, can you comment on when the single phase arc flash standard may be published? Well, it's a it's ongoing process, and then we we are basically okay. Well, right now, I don't I we don't have a timeline, but, because the well, that is for this three phase, it takes a long time. So try to get a single phase, try to regroup, then the basically, that the the there's a there's a lot of discussion. Okay? Are we going to go through go through the single phase or going to the DC? And, so this is the basically, again, that it's it it I'm we have the experience that but, it's basically the time and the and the resource to do the work. Because the during, actually, during the three phase test, in one lab, during the test, they are inside the lab, the the wall shift. So because the because of the pressure. So if the some lab refused to run the test. Don't blame them. Yeah. Because the when you look at the circuit breaker test, you have a two two level. Is that right? You have a current and a voltage. It's a separate source. But for the arc brush, it's a high power. It basically combine the voltage and current that another force. So just on on average, the the intensity of the copper melted copper spray, is there some cutoff point when the lower energy, it's not that prevalent? Well, that, basically okay. Well, the the copper by itself, you are going to see it's a function of activation. And, of course, it's it's also a function of the acting current. So it's a combined. And, yep, because the in the if you put it in line, then erode the copper will increase the gap, and eventually, arc is going to it it's it's it's extinguish. Correct. But the the configuration we use in the Afrash test is the parallel configuration, so the gap doesn't change. If you let it go, it will continue. Understand. Here's a question from Habib. He's saying, do we have DC arc flash standards now? Currently, now I think he's too much battery management systems. He's he's having issues with battery. This is, yeah, this is the important one. And, I think that, basically okay. Well, when we try to look at it here, it's it's it's an interesting one because the we we like actually, I personally really like to have a DC model. But, again, it's basically, we try to look at the resource. And, currently, we have basic, NFPA seventy has two model. They all one model. It's basically tandem model, the maximum power. And, a lot of people think this is, more it's too conservative. And then Everman and the PKSN also put out the model. Okay? And for that one, it's basically they they derive it from the base the a lot of reference. And then the third model, actually, we we also publish a third model. It's basically use use a ANSYS. Okay? It's a thermodynamic flow and then try to do the it's a again, it's a theoretical one. Okay? So, yeah, that requires some validation process. Alright. Here's the I think that, I think the one of your competitor tried to implement our model into their their software. Mhmm. But, again, this is the basic okay. Well, I I want I want the the gentleman. I say, okay. Well, this is the more like a theoretical one. And, it's bit but, it's it's not validated yet. And I would like to validate the result so I can basically feel comfortable say, okay. Well, this is the this is the basically a reasonable one. Right. So the the next question is, about the two second rule. Mhmm. How can you just explain the resolution and sustainability of ARCS versus the two second rule? Okay. The two second rule is basically it's a human response. Okay? And, if you are in the open area, if you are in the confined area, then two second rule doesn't apply. If you are in open area, normally, you will be able to the breakaway from the arc in two second. Okay? And, I we always think where the two second rule came from. And, I did some study. It was published actually, it is, from the DOT, Department of Transportation. And, they tried to design the traffic light. So according to their study, human response, it's about two second. So I suspect even there's no direct evidence, I suspect that two second rule we use is came from there. It's the traffic light traffic light response and all the basically, when they designed it, okay. Well, what is the response time of the human? And, that two second rule. I remember when I did the the traffic light design. The first car is the three point eight second, and then it continue dropping the the basically, okay, the the one in the queue eventually go down to about two point two second. So that I suspect that that the two second rule come from there. And can you comment on whether or not the advice ability of applying the two second rule at at other than low voltage? Well, that that basically okay. The two second rule, it's it's act the base activation, you should look at the the equipment operation, okay, your fuse. If your fuse is higher than two second to to blow the fuse, then you apply the two second rule. If the fuse you blow the fuse less than two second, then you don't want to apply the two second rule. Because that that is the basically defined the two second rule is defined the arc duration. So if your protective device can cut out the the arc less than two second, then why you why you apply two second rule? Got it. So this question, I'm not sure. He's saying, can you please share the complete reference for DC arc flash models that you're referring to? Yeah. The the seventy e has one. Okay. That's a Dendel model maximum power. Right. It's basically, you look at it, what is the maximum power transfer model? And, this is the voltage drop down to fifty percent. Is that right? So that's that's basically equal impedance. And then the the other one is the Everman model. Okay? So you can I think you can that that paper was published? So you can you can find the from the I triple I x pro. And then for our paper, that also published in the in the I triple I transaction of industry application. And, so it's also that if you can if you are the basic you can download it, and if you are IS member, you can download it free. Got it. The next question says And the old, yeah, the the other one is okay. Some some information that, basically yeah. That that I think that, you will be able to to obtain it over there. If you if you can, just let me know. Do you know are you aware of anyone, doing, testing or modeling above fifteen thousand volts? That was, basically okay. Well, this is a a million dollar question that I know that you a lot of utility, they're trying to actually, during the model debarment, and, April also suggest that we extend the model because the we understand from the from the circuit point of view that, fifteen kV and the thirty five kV, it's basically, has a very relatively similar phenomena. However, at that time, we did not run the test, and, also, the power only specify up to fifteen kV. So we didn't go go for that. And, this is the basically, this is an opportunity for you guys, you know, because the the fifteen eighty four two thousand eighteen was published in two thousand eighteen. So in ten years, we have to revise the, basically, revise the the the standard. Is that right? Otherwise, it would be become act inactive. So, yeah, there are several discussion over there. Are we going to extend it to thirty five kV, or are we going to look for the basically, okay. One thing we we didn't include it is the electrode to the back panel. So which one is more important? And, that that is the that is the the opportunity that we can for the next revision that we think that the higher voltage is more important, then that can be can be, the working group task over there. Good. So here's here's a question. In the HCB testing that you showed, you indicated the breaker had recessed horizontal terminals. And he's saying it's hard to imagine that that would be an actual fault location for an arc. It's basically okay. Well, when you look at it, sometimes the the you have a conductor come out from the come out from the wall. Is that right? Mhmm. So that is the horizontal. And then the other one is sometimes that you you your electrode, you bend it in the basically, in the different way. So it depends on the fault. If you bend it in ninety degree angle, alright, come out with horizontal, bend it with ninety degree downward. If they happen in the downward portion, that is the vertical fault. If you if you the arc happen in the horizontal conductor part, then that will become a horizontal fault. So it really depends on where the arc is initiated. Fair enough. I'm not sure that I understand the question. Does differential bus power protection help in reducing instant energy? Okay. High impede okay. Actually, high impedance grounded does help, okay, in the real life Because the a lot of time, the arc happen in the in the single phase. Right. So then if you have a high impedance grounding system, then we run the test. It's, if you put a oh, I believe we put a one hundred ohms in the twenty two point seven kV system, then it it basically okay. ARC doesn't start. However, if you have a three phase short circuit, then it doesn't matter if you have a sick the high impedance or not. The arc happened. Okay? So, yeah, this is the the argument in the in the two thousand two model. Because in the two thousand two model, the people feel that basically okay. Well, a lot of people prefer the high impedance grounded. And and then they say, okay. Well, in the high impedance grounding, that the arc instant energy is higher if you look at the formula over there. And, so I run the test and look at the look at the the current the current trace. For the solid ground system, you are going to have a because at the beginning, especially the the low voltage. The low voltage, you always start with unbalanced fault. When you have an unbalanced fault, then you're going to have current, return current through the neutral conductor. So in other words, you have less current involved in the arc, then you have less energy released. So your instant energy will be lower, which is correct on their observation in the two thousand two model. However, after one cycle, then it evolved into three phase four, then that it doesn't matter. So that's the reason why in the two thousand eighteen, we we took out that distinct. The basically, okay. Which we didn't try to differentiate is high impedance grounding or a solid grounding because we consider this is a three phase fault. Doctor Li, we appreciate your time. We've kinda reached our limit and very much, value how much wisdom you've shared with us. You're welcome. Hopefully, we'll be able to set you up for a presentation in the near distant future. Okay. Thank you everyone for attending. That that basically yeah. I would I've I'll be more than happy to share with share share share that or discuss with the with all the expert in the field. Alright. Thank you, everyone. Join us in the future to eight. Okay. Thank you. So long.