Week 10 - Lecture 46 : Introduction to Systems Approach in PHM

Hi friends. So uh our subject prognostics and health management a systems approach uh and all of you you would have seen that AI and ML uh that is artificial intellig in intelligence machine learning even and deep learning uh have been playing um very vital role uh in prediction actually. So uh it will not be wrong to say that that a IML are the enable uh enabler in uh uh this course or the subject uh that is prognostics and health management. Uh second point is uh we are all talking about systems approach. Um uh in open literature you will find uh uh systems approach or systems PHM and all. But if you see those approaches they are rem remaining limited to I think on a electronic card um or some dedicated system uh but when uh why we are calling system here system means plant. Okay. uh a a complex engineering system uh where uh all mechanical, electrical, electronics uh and thermal hydraulics they play a synerggetic role uh to ensure that the plant's uh performance uh is excellent in terms of uh reliability and uh safety. Of course, safety is an overriding factor. Um so when you use the word safe uh system uh instead of hardware only uh it has got lot of uh uh implication and those implications that we'll be talking about uh which enables PHM to be used uh as part of a complex engineering system uh and and then uh it works both ways uh it improves the system reliability uh and at the same time it improves the safety These two things they otherwise look uh uh opposite uh but or contrary but it is not that uh it is not that because if there are some safety issues the plant loses its availability uh and reliability also um so um in this lecture at least for the purpose of this lecture we'll see that we are meeting both the ends okay of course the path is uh difficult because it requires R&D research and development, data collection and then understanding the degradation which is tough task but once the ball is set in motion uh probably we should be able to solve uh the problems uh when it comes to uh using this approach at the plants level. So when I use plant it means uh uh uh when I use the word system means it means plant here in this lecture. So and the core module that is systems approach. Of course we are not able to talk of um u many dimensions of systems approach but we are uh we are covering the essential features uh which are at the core of systems modeling. So this lecture that is uh first lecture 10 oblique one is an introduction to the uh subject. Okay. So uh when I talk about the u system uh what it means uh there is a input and there is output uh which is enabled by uh synergetic operation of many many components uh you can say almost like 500 to 1,000 type of component and then uh each one if you see their rating their construction feature and all that it might go in lags and this system they have to work in tandem to uh enable delivery. Okay. Uh and then there is a human factor. So that means these system they cannot be considered as linear system uh which is a much more simpler option but they are they they exhibit a nonlinear characteristic uh whether uh whether it is reliability or safety. Um and that is where we talk about the complex engineering system. um uh we have uh I tried to give a sort of a uh feeling uh that you know if here is the energy is produced. These are the symbolic for steam generator. These are inlet outlet from the uh for from from the core uh where and then it is a barrier. This kind of barrier you find only in uh nuclear systems where in case of in case of a very rare accident event probability uh the the hazard should not go out. So they are basically physical barrier physical pive barrier essentially passive barrier so that everything is contained but these these are basically even for the rare pro uh occurrences these kinds of provisions are made and everything is housed in one containment. Okay. And then you have many equipments you required to support the uh operation of the system. Uh there are some cooling towers they are required. Uh and so you can see this this is a uh cooling tower of uh a nuclear power plant. This is the ST uh you know. So these essential features of a uh um system that I have maybe maybe next slide I'll take little more time to explain on this. Um so we will discuss here. Uh first will be the introduction uh for this course. uh that is uh week 10 uh then state-of-the-art and requirement of PHM that we'll discuss at the system level. Okay. Then there is a uh riskbased approach for system modeling. So here you can say essentially uh probabistic risk assessment plays a key role uh for modeling and uh since we are saying that the safety should be overriding factor the orientation of risk comes when we discuss a system. approach and then of course we have to identify and prioritize uh for PHM implementation because uh PHM cannot be uh can cannot be u facilitated on each and every uh SSC or subsystems uh because uh because uh it is a very expensive proposition uh PHM because not only PHM implementation it's a monitoring and then corrective action program that also have to be equally efficient. So, so um we are talking about ident identification and prioritization. Uh so that um I I would explain my point that if I do PHM implementation on very important uh SSC uh that is 20% of uh SSC then it in terms of safety improvement and reliability improvement it gives me 80% benefits. So, so, so that's how it is and for remaining 20% uh we can have our usual routine uh approach uh okay and that's it that is what it works when you when because everything is uh centered around uh having a operation and maintenance management system so so if I can take care of 20% component which were contributing to the 80% risk uh then I have um my job is very Well done actually. Um so because I have a I have a safety significance things that I have covered actually uh PHM performance metrics and standards. Um there are not uh there are supporting standards available like condition based maintenance uh maintenance management standards are available but targeted prognostics and health management standard there are few and I have got one uh probably I can say here even I was involved in this standard development it was it e standard so I can talk about it and systems approach and overview it's just concluding so five lectures and the these are the five titles okay uh so let Let's try to see uh how we see a uh first we'll we'll see what is system. We know in thermal uh thermodynamics we studied system is having a interconnecting part and surrounded by a boundary and there is a input and there is output. But now this was something 30 years or maybe before that this definition was but now we have a complex engineering system. So we need to redefine uh the system and they have to be in different category. So that we'll try uh here and then I've been talking about I think you would have seen some slide uh slides on complex system in uh an engineering plant when I say system word here because you know a plant is made up of many sub systems and subsystems and then components like that. So uh so safety system process system then then that safety system will have many subset system. So when we say sift system here it might mean the system itself or it might mean an uh engineering plant complex engineering plant. Okay. And uh complex engineering plant we know that uh number of components are u uh used uh you know and the they have to work uh reliably reliably to ensure the output and safely also. So and then the human factor is one of the important uh thing in the uh complex engineering system. uh and then you have a software, you have a hardware and uh you have many many new components into the systems uh which are like you know first of kind and all that. So that that that makes the situation u complex and sometimes challenging also. the major categories and requirement that we will see what are the different uh major category of systems uh and then uh what what are the integration requirement there and of course business case and major metrics you know uh that we'll be discussing again the same photograph I have given you know um because I was talking about a complex system uh probably you can understand that you know uh the basic objective of this system is that u even whatever Whatever is the rare possibility for an for an accident the public should not get affected. You know this is the bottom line. So that means risk level should be very high. And u uh here we are taking a case of uh nuclear systems. Nuclear systems why we have taken this case I'll be explaining but basically because the nuclear industry has maintained uh high standard of safety. Okay. um 430 plus plants are operating world over and what we talked about probabistic risk assessment has been done for all the 430 plants and many other uh complex systems uh to ensure that the traditional method is either complemented or supported in a manner that the net benefit is on ensuring higher level of uh safety. So uh uh I showed you outside view of the plant. A simple uh uh reactor core is there and this is a fuel which produces heat and uh then uh how it uh it happens that it is heat is being removed and it is being put into the system. Okay. And there is a coolant uh the heat exchanger which is getting cooled and it is uh removing the heat. So coolant in coolant out over here. And then we have a turbine which is located outside the reactor building. Uh and uh where the steam goes and uh then we turbine rotates produces power and there is a condenser and again it will join back the the closed loop actually and this is just a symbolic thing actually. So it is something like I was trying to explain what is engineering uh energy system uh they operates. Uh okay. So if I take a clue from here um what definition I'll give for a system um because it has got input it has got output uh sometimes it is passive sometime it is very active so let us try to define uh a system is a group of interacting or interrelated elements there are component which are related and they are there to do certain jobs uh to set a rule to form a unified hole. What is the system? So it will deliver a flow then it will go back and all. So this you can say talk in terms of a rule that it will take a suction it will provide a ditcher and to heat exchanger and heat exchanger will cool it. So like we talk in production rules uh anticedent and consequences. Okay consequences here you can take it as an output. A system surrounded and influenced by its environment. Yes, we talked about uh that you know the system operation will be smooth if the environment is good. Let's say um my plant is operating if the uh if the temperature in the plant increases my electronics the first one if a coolant uh received if a if a oil uh lubrication oil uh is received and if the quality is not proper then also so it it defines about a complete ecosystem or environment where uh even it includes procurement and uh this thing and then what we say is the the physical Physical system has a boundary. Physical system has a boundary. I mean making a boundary or imagining a boundary is uh up to us. Suppose if I am analyzing a pump then I can create a boundary around the pump by dotted line and I'll say I'll be doing analysis of this. So in that boundary one is inlet line one is another is outlet line. There could be power supply also that will create a boundary. So similarly for a plant also there is a boundary that means it is it is u it is generating energy extracting energy that the steam produced is being translated it into electrical production and then finally electricity is output and then finally it joins back and it operates in. So what is our system you know so system has a boundary that point we should not uh okay and it is surrounded by some external element but we are focusing on the system alone in that sense systems are the subject of study of system theory and other system yes we are studying those systems only uh and we are seeing what is the input probably next slide will explain it in better way so it can have a input and output but that should be indicated in and out of a system okay Then engineering systems are of two major types. Active and passive side like and then it has got their own definition. It is not a very universal definition of passive and active system. But luckily uh we have our own uh translation of active and passive system for the purpose of our PHM and then international level also uh this definition have been clarified keeping in view the system requirement. So let us have that approach what we require and how to how we have to define. So uh it can be a closed loop, open or isolated. I'll show you in the next slide. Um this thing I have uh taken from this source I have adopted I would say I changed little bit here but essentially the things remain um by and large same actually. So broad category of engineering systems are like like you know we have a two matter and energy how they are transitioning from the system or not matter transitioning from the system or not or it is remaining isolated that enables us to define the closed system open system and isolated system. First let us see the closed system. Closed system receives material matter. Okay. And then it exchanges energy to and fro. Some energy uh it will give out and uh and it will give in also some energy. So energy is exchanged that is from inside to outside and from outside to inside. So this these are called closed systems. Okay. Open systems are what? where the matter and energy both are exchanged okay from the surrounding okay and then there are isolated system where energy and matter both goes in um we have some vacuum chamber where we are performing some experiment we create a vacuum and then we supply uh energy and the matter and the experime experiments are performed uh in isolated way Okay. So they have different examples uh you know like now this definition is very fundamental to understand what are the two uh or three categories of the system that we have. This is one way of looking at it. But basically the subject we are dealing in it requires us to understand the active and passive system. Okay. So the concept of active and passive system uh passive system concept it was there even 50 years ago. Uh for simple example you have a plant and it is producing energy and if any disturbance come the plant will shut down but the still the cooling is required. So it will provide by uh by elevated tank uh which is kept at higher height uh so that water will flow one uh check wall which is again called as a passive system it will cool it will open up due to pressure difference. Okay. It will open up and it will cool the system. Okay. So even those kind of systems are called passive cooling system because only one check wall was there. So it is not purely passive but it is a intermediate stage because in check walls uh there is one motion that is opening and closing other than that and it doesn't require any energy. It is the pressure difference that operates. So essentially it can be put in the category of passive system. For the purpose of this lecture, we will have uh we will define the active and passive system. Uh you know and uh and in fact there are uh there are domains where the classification further defines rating like passive 1, pive 2, pive 3 or active 1, active 2, active 3. for our lecture also in terms of in the context of nuclear systems we'll deal with those things because the these are the things which are uh which are relevant for our study uh because uh active and passive is one thing but in between our phm comes you know active systems are not preferred like say pump I want to avoid a pump into the uh system because if it if it fails uh then it it will pro it will uh uh it will be a disturbance in the plant in terms of safety in terms of availability also but PHM comes in between uh and the question is whether PHM can detect the uh degradation a priority so the question of uh question of the pump failure doesn't arise and then management action can be initiated so uh that is why we are discussing the active and passive systems um whether online monitoring or analysis or intelligent algorithm whether it can help. Of course in complex engineering system accepting new uh they are the very conservative in nature. So unless until they see that there is no flip side of any new system even it could be a IML um they are not used. So it has to be subjected to regulatory it's a different domain altogether you know. So active systems are component that actively engage in processing managing and if I have pump it has to start then only process will start and then only uh management action will start whether what should be the uh mode of plant operation and all that you know they require power. Of course pump require a power and are dynamic in nature. fluid is recirculated. The pump is uh the uh the uh the system itself is having relative motion. So they are active components you know. So so this is one hint at what is active system. A specific attribute of active system is to have a relative motion. Pump has a relative motion. The impeller has a relative motion compared to the casing. uh and uh bearings are also rotating but there is bearing may inner race uh doesn't have uh any relative motion with the uh shaft it is moving with the shaft okay and in in principle that we are talking about okay so um but then actually they are active system because there are relative motions occurring uh in in the uh in the system itself okay uh pump impeller example of course uh we have a shaft bearing and All that a reciprocating piston moves to and fro and uh that is why it is called an active systems you know but the same the active systems are not like because there is some phenomena of uh erosion uh you know uh or friction which is happening. So it it's uh it uh plays out in terms of the life of the component of in between failure also due to maybe lubrication issues or now there are having a non-lubricating materials. Uh so they bring in the new component of the issue. So but then there is a active uh active systems are there even if you talk about electronics there is a breaker electric breaker which uh which moves for closing and opening uh the contacts uh circuit breakers. So they are example of active system. Now let us see what is passive system. So just uh high higher level characteristic and we defi define the passive systems are those system where there is no mechanical relative motion between two mating parts. Further they do not require energy input or power for their function. I want a flow. Okay. So pressure difference can be created and it can have the flow. I I I have a device which ruptures on its own. So there is no relative motion. So uh though rupture itself is a high energy phenomena but then we are not seeing any mechanical moment. In principle we have decided when the pressure goes up it ruptures. Simple. Okay. For example, a piping system delivers the flow without any relative mechanical motion about of course flow flow is uh you know symptomized as a uh as a motion but the piping doing its uh its function providing a barrier uh to contain the pressure fluid and that is doing its job. It is facilitating flow. So but there is no movement like pump there's no movement the in the piping sections a civil foundation support the structure it is a excellent example of a it is doing its job but without any movement for greater part the electronic board uh is a passive system because there are no relative motion except when we have a uh relay uh or you know few devices which have some like uh relay or switches which have some motion so it is a paceive system and when you analyze a PC system to a great uh extent our problem is solved. Why? Because now you have to look into the component uh its operational characteristic and we can deise a PHM relatively easily. It's not even that also requires us to go into the physical properties how the component degrades which are the environmental stresses they play over the uh degation. uh so like that you know um in reliability for the purpose of reliability and risk engineering it is accepted that passive systems SS are more reliable and compared to the activism this is in principle true but designing a passive system which is meeting its intended function that is removing let's say if I talk about the uh if I talk about the complex system it is removing the heat and for different conditions and still maintaining the margin. Uh that requires a complete understanding of thermal hydraulics. Okay. What are the what are the losses that are taking place across the system and what is the that critical energy input that is required to keep the flow in the loop so that the heat is removed on perpetual basis like nuclear reactor. There is a decay heat removed. The decay heat keeps producing even if it is 5% 1%. But that should be removed and it is very essential. So my pive system should be working in that fashion. Then only it will call yes it is a P system and it is reliable also. It is addressing all the situation including common cause failures. If there is some outside uh flooding, fire or you know any other phenomena which might disturb uh the my loop cooling loop it becomes a problem actually. So it has to be tested and validated from from different angles. Uh of course elevation provides a very big advantage for keeping it uh keeping the function going. Even some electromagnetic phenomena we have to take care of it and all that. then mechanical relative motion uh uh power supply requirement and uncertainty should be evaluated uh to ensure the uh reliability of pive system. So like I was giving this example there is a reactor there is a fuel hot water goes in it is a py system you you don't have any active component here but then this loop design is a master art actually because it has to satisfy all the um all the scenarios known scenarios or anticipated scenarios under which it is going to operate. Let's say simple example if this loop is located at some in in a uh to uh place where the temperature goes to minus30. So that means in that condition also it should work if the temperature goes to plus 30 if there is a seismic uh issue. So uh so in different condition it should work that the the heat is continuously being removed and it is cooled and then of course I have made a distinct boundary. It is a continuous one and there is a fuzzy boundary in between you know like gradual gradation and then only cold water. Cold water means it is not exactly cold water compared to the hot water it is get temperature is down and it is entering here again heat decay heat is even if the it is shown decay heat is produced. In fact the the plants are being built even with the full power operation also the passive mode heat it is removed and that is the how gravity works uh principle is utilized how ensure that it is safe. So IA to a great extent they have provided uh some definition of uh passive systems you know and this IA tech I have given the reference over here. Um category A passive system what they call this category is characterized by the following. No signal input. There is no signal input here. No external power source. There is no power source available here. No moving mechanical part. And no moving working fluid. So we are not betting this last matrix. Okay. So no moving but here there is a working fluid which is going going on here. So then this is not a a category system. It will fall into the uh B. This category is characterized by no signal input, no external power, no force, no uh mechanical parts but moving working fluid. So only working fluid is moving. So this is a category B uh passive systems. So uh then category C system. Category system is this category is characterized by no signal input, no external power nor force but moving mechanical moving mechanical parts whether or not moving work flu working fluids are this thing. So like if I install a U non-return check wall in a cooling circuit the wall open opens because of when the plant was operating uh there was a pressure wall was kept open and the moment pressure got uh reduced because of plant shutdown the the the decay heat removal fluid uh water enters and a non-written wall opens it okay again when you start the plant the uh the fluid can flow in one direction only so it will it closes back and it seals the system and then again you can operate the plant in a closed loop. Probably one figure would have been sufficient but I think you would have understood the idea over here. Uh category system uh this category addresses the intermediary jon when active and passive where the uh where the execution of safety function is made through passive methods as described in the previous uh categories except that an external signal is required. If I have to open a wallve, I require a signal and then rest will be passive. Okay. So this is called D category system. Okay. And then we know that PC pive system A design principles are generally well studied and design uh designed in accordance with the internationally regarded. So this thing is matured actually. But B and D a lot of work is going on here and then it is a complex task to validate the complete procedure for B and D category of passive system. Um you know so so what what we are saying is uh there are still some challenges when we want to see a practical uh practical passive systems and it has to be proved or validated again in all the condition that it will ensure safety uh first and then reliability of the uh the complex system. Okay. So context of PHM as I had mentioned just now PHM comes between if there is a uh there is a move from active system to passive systems what quotient of uh safety and reliability we can achieve through PHM. Point number one and point number two we successfully successfully go to PHM uh the Pive system and then PHM may not be applicable for the pump or moving components but then again the piping system you need to have health management especially when the plant completes 30 40 years or if there is no correct propagating and all those kind of things. uh that means in the passive part itself some deviation and uh probably PHM will fit very well and that's why it should become part whether active system or passive system it should become part of the because the problem with the pipeline and passive components is they become the life limiting component of the system. Suppose if I have to uh if I have to uh uh change uh some part it could be concrete it could be uh some vessel it could be lining uh normally we keep provision of replacing pel also in once in lifetime but then but then uh that is the last wish if I can ensure through PHM that there is a remaining useful life and I can go for extension of life of the plant from 40 years to 60 years or 60 years to 80 year or 80 year to 100 Who knows we have already gone from 40 years to 60 years and there are applications moving in nuclear from 60 to 80. So so PHM can play a huge role there. Only uh only objective here is that PHM should be PHM again should be reliable. It should not add to the new issues into the system. So aging management and life extension this situation comes that you know there are some parts they replacing that part is uh you know uh it is uh prohibited um so what to do so that means you continue with the aging management that is uh and then health monitoring techniques online and you can go for remaining part of the life so that means PHM will be adding up there actually I'll show you on one slide all these things how it work design stage um why not if I know that this plant plant is going to operate for 100 years why not have a provision right in the beginning itself okay and then common cause failure um common cause failure should be avoided these are related to not only uh environmental temperature humidity ventilation it could be even seismic could be a common cause okay um even low temperature uh which is not considered in the design and operation minus 40 and all it could be a common cause uh high temperature also could be a common cause. So and then micro electronic system uh with redundant trains are the special case for prognostics. So for electronics it is very simple. You have PHM so that safety and reliability is improved and when they become old it is easier to replace the electronic systems. In fact in some plant I I I can tell you uh the electronics and monitoring systems and all they are replaced every 5 years or 10 years because replacing electronics is easier compared to mechanical and structural systems. So here we saw um introduction, definition, background, active passive system probably you would have got at least in terms of complex system you would have understood that you know uh how uh and where PHM fits into it uh uh in the system and the conclusion and remark and reference. Our conclusion is u uh plan different stages which we'll discuss in the next slide we should study and a very sensible use of prognostics and health management technique. uh in fact there could be a debate also whether the PHM monitoring should happen like any other process parameter in three channels or one channel um because we are monitoring threat you know so one channel a latent failure and we will not know okay and some degradation mechanisms are so fast and we have to remember that the rate of uh like fracture if once it becomes critical then we have to have have a very faster system to respond otherwise uh you know so so it requires That's real R&D efforts to have a complete PHM for at system level. At component level you have your task limited. You can apply it. You'll get the advantage also. But for system level the gains are like it can uh it can be somewhere between between active and passive system and it can even support the passive system. So we have passive system in terms of the unanticipated uh conditions and we can have a better system. Yeah, these are some references. Uh uh I have indicated in the slides set for active and passive system. This is number three and there is some closed loop system you know open system here and international atomic energy agency. Actually the good thing is IA provides lot of reference documents where at international level there is a synergy uh it creates and they are used to improve safety and reliability. So both this uh we are talking about I international atomic energy agency document. Thank you.