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What can Elevators and Escalators tell us about "Variance"

Published in People

For some people, ideas of planning are rather straightforward. They know planning is useful, but when there are too many variables and things are not predictable they do not plan or depend on planning. What really matters to them is whether they can do the right thing when you face the challenge. Period.
To a large extent I do not disagree with them. 
It is not hard to convince people that planning is critical to execution, but what is the use of a plan that most likely is going to fail? A plan is credible only if/when we have a good idea about and control over the activities of a project. Let’s say an activity “B” can only be started after another activity “A” is complete. To plan for activity “B”, we must have a fairly good idea how long “A” will take to finish. If “B” cannot be started because “A” is not finished as planned, a lot of time energy and money could be at stake. In planning language, unpredictability about cost or schedule of an activity is called “variance”. 
So what can be done about variance? The first step in that direction is to understand variance and its nature a little further. To understand variance, we have to find simple real life situations where we use different methods and achieve the same results but with different variances. That brings us to Elevators and Escalators.
Let’s say you want to go from the ground floor of a mall to a third floor restaurant. You can take the escalators or the elevators or even the stairs.  Let’s make a comparison of time it will it take if you take the escalator vs. if you take the elevator. You will see the time taken for getting to the third floor with the escalators will take a fairly consistent time. With the elevator the minimum time it takes may be lower than the escalator but there are so many variables during the use of an elevator during crowded hours that the time taken to reach the third floor may be very significantly every time. Sometimes it can take three or four times more than other times. But an escalator on any day at any time during lean or crowed hours will take a fairly predictable time.
As you can see an escalator always takes in passengers without wait, always moves in the one direction only, works in continuous mode and moves people between two pre designated floors. An elevator on the other hand takes in passengers only when it reaches the floor, moves in both directions, works in batch mode and serves all the floors. That is what makes the escalator-travel time between two floors consistently predictable.
Can we design our work processes and systems such that variance is inherently less (e.g. Like Escalators)?
If we can, then the plans that we draw will be more predictable and the  schedules that we promise will be more achievable.
Have a look at this video and listen to the adventure I had with my friend Praveen - trying to explain what "Variance" really is.
Read more...

My First Boss Mr. Wadia

Published in On the Job

If we look at the DNA of the people from EPC world, we will find there are two types. There are people who love drawings, schedules and networks and there are others who love their hard hats and safety shoes.

tmp601451470855864322

Experience from both the worlds gives a unique 360-degree perspective to imagine the proverbial elephant even when you are looking only at its tail. In either world, what matters most is a “Touch and Feel” of the project. As we learn more and understand more about something we become confident and comfortable about the subject - all because we acquire a touch and feel of the subject. But life is complicated and unpredictable and will always surprise us. That is when we put the sum total of your life long experiences together and take decisions to solve problems. Other people may call it risky but life has put you in that situation and the rest of the world is waiting for your decision. You can take a gamble and win a jackpot or watch the opportunity pass by to repent later. If you take the gamble and win, you learn and if the gamble did not work you learn even more – for the next time. Here is how I learned risk taking from my boss.
For all of us, our first boss is a very important person in our lives.  He comes in to our lives at a very important time and molds our career and to a good extent sets the the perspective to how we approach job everyday for the rest of our working life. Mr. Wadia was my first boss at Tata Power at Trombay, Mumbai. A tall stocky balding Parsi man in his late fifties, Mr.Wadia was THE engineer at Tata Power. He appeared always happy because he never seemed worried. The engineer inside him was always visible even under the most difficult conditions. Everyone loved him for his trademark open door and welcome smile. But what most pleased him was when you say “you did not understand what the problem was”. That is when he will make all the efforts in the world to explain the most difficult engineering concepts in as simple words as possible, bringing out brilliant examples from his experiences. 
At Tata Power, Trombay Unit 4, Boiler Feed Pumps were of Worthington make. These high speed pumps were of 9000 RPM (revolutions per minutes) speed and overhauling of these pumps was great learning experience for any mechanical engineer responsible for maintenance. Early in my career as a fresh mechanical Engineer in Maintenance department, I had the opportunity to work on the overhaul of one of these pumps.
Pump Shaft with impellers
 
This was a shrunk fit pump, meaning the impellers were interference fit on the shaft. When two items are interference fit on to each other, thermal expansion plays the important trick. Under dissembled condition, when the shaft and the impellers are at same room temperature, the shaft diameter is a little larger than the inner diameter of the impeller. If you try to slip the impeller on to the shaft, it will just not work. But at a higher temperature the impeller will expand and its inner diameter will increase. Similarly, at a lower temperature the shaft diameter will decrease. Now the shaft and the impeller will accommodate each other. In other words, they will not interfere with each other. That is why mechanical engineers call this an interference fit. On a design drawing it will look like this.This means, every time this four stage pump was to be dissembled or assembled, its shaft has to be cooled by dry ice and the impellers were heated by gas welding torches to make them free of each other. For assembling, again the impellers are heated to expand to the required size and slipped on to the right position on the shaft. There at those final positions, the impellers will cool down and shrink in diameter and the shaft will warm up and expand its diameter. Thus the impeller and the shaft will remain locked to each other without a lock and key arrangement as is normally required for many shaft mounted high speed rotating elements. This makes the locking arrangement precise and solid - to work reliably work at high speeds like 9000 rpm which is 150 revolutions every second.
Thermal Expansion 1200
Considering the skill required to do the job, there was a selected group of technicians earmarked who were trusted with the task of handling this task. The process involved precise measurement of predefined expansion of impellers and then mounting the hot impeller on the cold shaft, before the impellers cooled down or the shaft gets back to normal room temperature. After mounting each impeller on shaft, run out of the assembled unit was measured. Run out measurement of the impellers on the shaft is a method that ensures that the impeller discs are mounted on a plane perpendicular to the shaft centerline. This process was repeated after installing each impeller. After all the four impellers are mounted with acceptable runout, the assembled rotor with all the impellers mounted is sent for dynamic balancing. After receipt from dynamic balancing these impellers were again dismantled by another cycle of impeller heating and shaft cooling and then the pump is again assembled, this time with its stationary parts mounted in between the impellers. The stationary guides in between impellers are used in multistage pumps for guiding the fluid from a low pressure stage to a higher pressure stage.
 
Different Types of Fit 1200
 

After completion of all the tasks involved in the overhaul, the pump cartridge was finally assembled and inserted in its barrel casing, centered and aligned. The design of this pump was so precise that the acceptable interference, clearance, centering and alignment tolerances were in the range of one thousandth of an inch. The width of human hair falls in this range.
I have some interesting observations during many project experience. One of these is that important mile stone activates at project sites eventually spill over to late evenings when the energy levels are at the lowest. On one such late evening, before coupling this pump, the lube oil system was started and was kept running for some time to see everything was fine. One of our technicians was instructed to start manual rotation of the pump. The pump rotor was freely rotating without much of problem. But the fitment of the rotor must have made the manual hand rotation of the pump rotor a little hard for the technician who became tired and requested another technician to take over the task. During the transition, the rotor must have briefly come to a standstill before the next technician took over. Panic took over the entire group when the second technician could not restart the rotation. I had a shock of my life, when he said, “Sir - ye pump nahi ghoom raha hai” (“Sir - this pump wont rotate”). We tried for some time with all our energy, but did not apply more force trying to rotate the pump. We thought we might damage something in the pump if we do that.

We all sat down trying to think – what next? But we could not imagine anything new. We were physically tired but mentally getting prepared to restart working to dismantle the pump again. However, wisdom prevailed on us, and we called up our Maintenance Head Mr. P.R.Wadia and told him about the status of the pump and how it got jammed during manual operation. I looked at my watch before we called his number. It was 11.30 PM. Mr.Wadia promptly took the call and said very coolly, “Couple the pump and give it a kick start”. We all looked at each other. In any case the pump has to be dismantled if there was any fitment or other problems. So why not give it a kick and see if it frees up? We did not do any risk benefit analysis at that point of time. We were just waiting to follow instruction only - like a bunch of robots. So, we coupled the pump to the motor and then took name of God and gave a start command to the motor. Without any observable problems, the pump started and was operating smoothly. Relived and relaxed, we went home and had a peaceful night of sleep. This was 1998.

Fast forward 17 years to 2015. In my assignment as Project Head of Jhabua Power Ltd., one of my engineers working in Boiler called me up one evening. He said, they were supposed to take trial run of ID Fan. Since, this trial run was being conducted after a long gap several months after erection of fan, it was agreed with EPC contractor to manually rotate the fan to see if the fan is free and then start it. Even after lot of effort the fan did not move manually. I knew it was my turn to return the favor and learning. I told him to go ahead and give it a kick start. Although I was confident that there was no problem with the fan, I was eagerly waiting for a return call from Bhupinder. And then Bhupinder called me back and told me that the fan was operating smoothly.
I looked up to the sky and thanked Mr. Wadia.

That is where he lives now.

What a “first boss” he was.

Read more...

No place for another relay

Published in On the Job

Here are four relays and an ice cube.

Different Relays and Ice CubeThe four relays shown above are called ice cube relays because they look like ice cubes. But what does a relay actually “relay” and why is it so called?

Read more...
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On the Job

On the Job

These are narration of actual on the job experiences. Someday, someone, at some project, did something that was memorable to you. That someone could be you or your friend or your boss or your supervisor or any one on the job at the site or office. Was it a call beyond the duty that was taken? Passion, dedication, pride to do something better are the central theme.

My First Boss Mr. Wadia

Published in On the Job

If we look at the DNA of the people from EPC world, we will find there are two types. There are people who love drawings, schedules and networks and there are others who love their hard hats and safety shoes.

tmp601451470855864322

Experience from both the worlds gives a unique 360-degree perspective to imagine the proverbial elephant even when you are looking only at its tail. In either world, what matters most is a “Touch and Feel” of the project. As we learn more and understand more about something we become confident and comfortable about the subject - all because we acquire a touch and feel of the subject. But life is complicated and unpredictable and will always surprise us. That is when we put the sum total of your life long experiences together and take decisions to solve problems. Other people may call it risky but life has put you in that situation and the rest of the world is waiting for your decision. You can take a gamble and win a jackpot or watch the opportunity pass by to repent later. If you take the gamble and win, you learn and if the gamble did not work you learn even more – for the next time. Here is how I learned risk taking from my boss.
For all of us, our first boss is a very important person in our lives.  He comes in to our lives at a very important time and molds our career and to a good extent sets the the perspective to how we approach job everyday for the rest of our working life. Mr. Wadia was my first boss at Tata Power at Trombay, Mumbai. A tall stocky balding Parsi man in his late fifties, Mr.Wadia was THE engineer at Tata Power. He appeared always happy because he never seemed worried. The engineer inside him was always visible even under the most difficult conditions. Everyone loved him for his trademark open door and welcome smile. But what most pleased him was when you say “you did not understand what the problem was”. That is when he will make all the efforts in the world to explain the most difficult engineering concepts in as simple words as possible, bringing out brilliant examples from his experiences. 
At Tata Power, Trombay Unit 4, Boiler Feed Pumps were of Worthington make. These high speed pumps were of 9000 RPM (revolutions per minutes) speed and overhauling of these pumps was great learning experience for any mechanical engineer responsible for maintenance. Early in my career as a fresh mechanical Engineer in Maintenance department, I had the opportunity to work on the overhaul of one of these pumps.
Pump Shaft with impellers
 
This was a shrunk fit pump, meaning the impellers were interference fit on the shaft. When two items are interference fit on to each other, thermal expansion plays the important trick. Under dissembled condition, when the shaft and the impellers are at same room temperature, the shaft diameter is a little larger than the inner diameter of the impeller. If you try to slip the impeller on to the shaft, it will just not work. But at a higher temperature the impeller will expand and its inner diameter will increase. Similarly, at a lower temperature the shaft diameter will decrease. Now the shaft and the impeller will accommodate each other. In other words, they will not interfere with each other. That is why mechanical engineers call this an interference fit. On a design drawing it will look like this.This means, every time this four stage pump was to be dissembled or assembled, its shaft has to be cooled by dry ice and the impellers were heated by gas welding torches to make them free of each other. For assembling, again the impellers are heated to expand to the required size and slipped on to the right position on the shaft. There at those final positions, the impellers will cool down and shrink in diameter and the shaft will warm up and expand its diameter. Thus the impeller and the shaft will remain locked to each other without a lock and key arrangement as is normally required for many shaft mounted high speed rotating elements. This makes the locking arrangement precise and solid - to work reliably work at high speeds like 9000 rpm which is 150 revolutions every second.
Thermal Expansion 1200
Considering the skill required to do the job, there was a selected group of technicians earmarked who were trusted with the task of handling this task. The process involved precise measurement of predefined expansion of impellers and then mounting the hot impeller on the cold shaft, before the impellers cooled down or the shaft gets back to normal room temperature. After mounting each impeller on shaft, run out of the assembled unit was measured. Run out measurement of the impellers on the shaft is a method that ensures that the impeller discs are mounted on a plane perpendicular to the shaft centerline. This process was repeated after installing each impeller. After all the four impellers are mounted with acceptable runout, the assembled rotor with all the impellers mounted is sent for dynamic balancing. After receipt from dynamic balancing these impellers were again dismantled by another cycle of impeller heating and shaft cooling and then the pump is again assembled, this time with its stationary parts mounted in between the impellers. The stationary guides in between impellers are used in multistage pumps for guiding the fluid from a low pressure stage to a higher pressure stage.
 
Different Types of Fit 1200
 

After completion of all the tasks involved in the overhaul, the pump cartridge was finally assembled and inserted in its barrel casing, centered and aligned. The design of this pump was so precise that the acceptable interference, clearance, centering and alignment tolerances were in the range of one thousandth of an inch. The width of human hair falls in this range.
I have some interesting observations during many project experience. One of these is that important mile stone activates at project sites eventually spill over to late evenings when the energy levels are at the lowest. On one such late evening, before coupling this pump, the lube oil system was started and was kept running for some time to see everything was fine. One of our technicians was instructed to start manual rotation of the pump. The pump rotor was freely rotating without much of problem. But the fitment of the rotor must have made the manual hand rotation of the pump rotor a little hard for the technician who became tired and requested another technician to take over the task. During the transition, the rotor must have briefly come to a standstill before the next technician took over. Panic took over the entire group when the second technician could not restart the rotation. I had a shock of my life, when he said, “Sir - ye pump nahi ghoom raha hai” (“Sir - this pump wont rotate”). We tried for some time with all our energy, but did not apply more force trying to rotate the pump. We thought we might damage something in the pump if we do that.

We all sat down trying to think – what next? But we could not imagine anything new. We were physically tired but mentally getting prepared to restart working to dismantle the pump again. However, wisdom prevailed on us, and we called up our Maintenance Head Mr. P.R.Wadia and told him about the status of the pump and how it got jammed during manual operation. I looked at my watch before we called his number. It was 11.30 PM. Mr.Wadia promptly took the call and said very coolly, “Couple the pump and give it a kick start”. We all looked at each other. In any case the pump has to be dismantled if there was any fitment or other problems. So why not give it a kick and see if it frees up? We did not do any risk benefit analysis at that point of time. We were just waiting to follow instruction only - like a bunch of robots. So, we coupled the pump to the motor and then took name of God and gave a start command to the motor. Without any observable problems, the pump started and was operating smoothly. Relived and relaxed, we went home and had a peaceful night of sleep. This was 1998.

Fast forward 17 years to 2015. In my assignment as Project Head of Jhabua Power Ltd., one of my engineers working in Boiler called me up one evening. He said, they were supposed to take trial run of ID Fan. Since, this trial run was being conducted after a long gap several months after erection of fan, it was agreed with EPC contractor to manually rotate the fan to see if the fan is free and then start it. Even after lot of effort the fan did not move manually. I knew it was my turn to return the favor and learning. I told him to go ahead and give it a kick start. Although I was confident that there was no problem with the fan, I was eagerly waiting for a return call from Bhupinder. And then Bhupinder called me back and told me that the fan was operating smoothly.
I looked up to the sky and thanked Mr. Wadia.

That is where he lives now.

What a “first boss” he was.

Read more...

No place for another relay

Published in On the Job

Here are four relays and an ice cube.

Different Relays and Ice CubeThe four relays shown above are called ice cube relays because they look like ice cubes. But what does a relay actually “relay” and why is it so called?

Read more...

All Well that Ends Well

Published in On the Job

Engineering Design usually has a very definitive approach and one has to work through a given input conditions for an intended output utilising calculated/predicted performance/behaviour of individual equipment and systems. But commissioning is always a challenging and thrilling task as we try to match the behaviour of actual equipment and systems at the site with predicted design values under different environmental conditions as well as uncertainties in the process of equipment manufacture.

Read more...
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People

People

This is purely about people; about everyday heroes. This could be technical and at the same time human. Description of Managing a difficult situation or feeling that is common under stressful situations at project sites. Wisdom from Technicians, mechanics, electricians, welders can make excellent narratives. Funny misunderstandings, cultural musings with foreigners, languages differences, etc.

What can Elevators and Escalators tell us about "Variance"

Published in People

For some people, ideas of planning are rather straightforward. They know planning is useful, but when there are too many variables and things are not predictable they do not plan or depend on planning. What really matters to them is whether they can do the right thing when you face the challenge. Period.
To a large extent I do not disagree with them. 
It is not hard to convince people that planning is critical to execution, but what is the use of a plan that most likely is going to fail? A plan is credible only if/when we have a good idea about and control over the activities of a project. Let’s say an activity “B” can only be started after another activity “A” is complete. To plan for activity “B”, we must have a fairly good idea how long “A” will take to finish. If “B” cannot be started because “A” is not finished as planned, a lot of time energy and money could be at stake. In planning language, unpredictability about cost or schedule of an activity is called “variance”. 
So what can be done about variance? The first step in that direction is to understand variance and its nature a little further. To understand variance, we have to find simple real life situations where we use different methods and achieve the same results but with different variances. That brings us to Elevators and Escalators.
Let’s say you want to go from the ground floor of a mall to a third floor restaurant. You can take the escalators or the elevators or even the stairs.  Let’s make a comparison of time it will it take if you take the escalator vs. if you take the elevator. You will see the time taken for getting to the third floor with the escalators will take a fairly consistent time. With the elevator the minimum time it takes may be lower than the escalator but there are so many variables during the use of an elevator during crowded hours that the time taken to reach the third floor may be very significantly every time. Sometimes it can take three or four times more than other times. But an escalator on any day at any time during lean or crowed hours will take a fairly predictable time.
As you can see an escalator always takes in passengers without wait, always moves in the one direction only, works in continuous mode and moves people between two pre designated floors. An elevator on the other hand takes in passengers only when it reaches the floor, moves in both directions, works in batch mode and serves all the floors. That is what makes the escalator-travel time between two floors consistently predictable.
Can we design our work processes and systems such that variance is inherently less (e.g. Like Escalators)?
If we can, then the plans that we draw will be more predictable and the  schedules that we promise will be more achievable.
Have a look at this video and listen to the adventure I had with my friend Praveen - trying to explain what "Variance" really is.
Read more...

Calculated Risk

Published in People

IRMore often we hear engineering and construction feats that technical staff at project sites achieve under extreme and challenging conditions. Acquiring land required for the project, and managing the expectations and aspirations of local people and land oustees is a challenge that is faced by and left to HR department (erstwhile P&A dept. of the hey days). Heroic stories of personal risk-taking beyond the call of duty from the early phases of project life are neither popular nor shared widely. Here is a story that I was involved first hand as a young executive in NTPC, which left a lasting impression on me.

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Walk the Talk

Published in People

When we have hands on real life experience about how certain things work, we can go to great lengths to demonstrate what we know so that others can learn and take correct decisions. But it needs fearless fortitude to uphold what you believe in - when it means putting your career and sometimes your own life at risk.

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Pearls of Wisdom

Pearls of Wisdom

These are your one liners, that life has given you. You remember them because someone explained you something complex or even simple very well and them summed up it for you so well that it is still there in your memory. If related to technology it will be wonderful. But that is not necessary. The background and the situation are the key ingredients. Simple situations seen from a different angle by wise people.

Who is the Boss here ?

Published in Pearls of Wisdom

Today is Teachers day. Here are some memories of a great teacher.
Some of the most wonderful gifts that God sends our way are the people we come across in our working career. And if such a person happened to be your boss, the experience is memorable and life changing. When I met him, it was as if I stumbled upon the best teacher life could offer after twenty-one years of working life. 

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The Magic of Simple Ideas

Published in Pearls of Wisdom

The human mind, it is said is a bundle of ideas. Everyday ideas, big and small come and hit us. We put them through different filters. What we do with them decides what we become in life.

We consider some as too big for us.
We consider some as too small us.
Some we think are not workable.
Some we do not attempt because others have failed at them.
We think some will only work for us if ......
We think some will not work for us because ........ So on and so fourth.
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Unleashing People Power

Published in Pearls of Wisdom

In NTPC, a large number of measures were introduced right from the inception to ensure the welfare and growth of not only employees but also their family members. Such efforts included energizing Ladies Welfare Organizations, sports competitions for children of employees, coaching facilities for competitive exams for children besides making available good educational facilities at projects. We innovated substantially, with involvement of employees, their families and the HR executives in the field and based on the feedback and appraisals took a lot of initiatives to update the services that were being provided.

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Lessons for Life

Lessons for Life

Many times lessons learnt from small things and simple events are profound and  act as a beacon for the rest of our life. Many times it may be about how something must not be done as against smartness of ready wit that can make the most drama in life. You learnt the trick for many years and one day a small incidence turned your opinion upside down. Why? That will make a wonderful narrative. Such stories are contagious. Readers will be compelled and encouraged to respond, comment and may even write.

Measuring up to a recruitment drive

Published in Lessons for Life

This story is from my experience while I was working at the Auriya Gas Power Project (AuGPP) of NTPC. I remember this story vividly; like it happened yesterday.

When this incident took place I was posted in the HR (erstwhile known as P&A) department and was looking after Administration. During those early formative years, the project was my learning ground. Being at the initial stage i.e construction, the project was a hub of activities. I was simultaneously involved in many complex and hectic activities, dealing with administration, security related issues, liaising with State Government Authorities and interaction with local people, etc.

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The Case of 2 IT Pros

Published in Lessons for Life

The weekend drew near. 6 pm to be precise, on a fine Friday evening, with a light gentle rain splattering on my window at the AT&T Office in Tech Mahindra. Possibly about 20 degrees centigrade if I guessed right. Perfectly fine , I thought to myself . “Ideal weather to stop work “, my inner voice told me. “Absolutely” ! , I told my inner voice, heartily agreeing to these brilliant suggestions.

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Technology

Technology

For experts, this one is going to be the most difficult. Because in the long years that we become experts, we almost forgot the perspective of simplicity. We forgot the questions that were in our mind when you were young, novice, like a newbie. Somewhere, someone, something, cleared those dreadful questions that normal people don't ask experts. If you remember those questions and who, how, what, when, which book, which movie helped in making you an expert, write about it here. Be very worry some of the language because the terms that you use may not mean anything to domain outsiders.

Now What?

Published in Technology

There are times when life puts a wall in front of us, when no medicines work, when all available tools are of no use, when all that we know is irrelevant, when none of our experience comes in handy. At moments like these, all that goes on in our mind translates in to one simple question - Now what? This simple but profound question stirs our emotions, baffles our intelligence, makes us helpless, forces us to reboot and relearn and leaves us with memories for a life time. Times when we came to face this question are the turning points in our lives. They shape our lives, build our characters and make us who we are.

But those are also the moments when innovation triggers in some corner of the human brain. New concepts, new instruments, and new methods evolve. The initial spark of imagination in the mind of one passionate and fearless individual appears absurd at first but slowly gets refined and gains acceptance. Over the years it spreads to impact everything - companies, industries, communities, societies and even countries. Thus the old appears irrelevant and often incorrect and gives way to new.

The life cycle of large infrastructure projects is no different. They also go through this inevitable process of evolution. When major components of large projects cannot be interfaced correctly to work properly because wrong components have been delivered at project site, this question comes back to hunt everyone - Now what?

Whenever items delivered to a project are incompatible, site Field and Commissioning engineers take on the challenge. If possible and acceptable, they try to modify the interface in such way that the item can be used without extensive rework and modification to avoid costly reorder. But once in a while the sheer physical size of a component is so large that it is just not possible to carry out any physical modification whatsoever in any manner because suitable interface changes are just not possible. This is exactly what happened at one NTPC power station, where during the commissioning of the generator transformer it was found out that the generator bus ducts were of wrong design. This story describes what the impacts were and what was done at site to resolve the problem to go ahead with the project.

Large utility generators like those of 500 MW capacity, have three bus ducts, one for each phase that connect the generator to the generator transformer. These are aluminum tubes of about a meter and half in diameter, more than a few centimeters thick with an aluminum conductor centrally supported by insulators. These tubes come in pre-fabricated transportable spools and are welded together at site. When the spools are welded together as designed, the bus duct takes the shape it is intended to and connects the generator, generator transformer and the unit auxiliary transformers in a pre designed manner.

Assembly Of Bus Duct 1200

The main GT at the project comprised of three single-phase transformer units (connected externally through the generator bus duct) to act as a three phase transformer. On the generator side, the low voltage windings of the three single-phase units are connected as a "delta". For forming a delta on the LV winding, each bus duct coming out of the generator is split into two smaller ducts. R&Y go to the first transformer, Y&B go to the second and B&R to the third transformer. On the grid side, the high voltage windings of the three single-phase units connect as "star". This particular connection creates a phase angle difference of 30 degrees between the HV and LV of the GT. Keeping this phase shift in view, the unit auxiliary transformers are so designed that this phase shift is compensated.

 

Main Bus Duct Graphics 1200

 

Why Generator transformer, unit auxiliary transformer and the startup or station transformer must be so chosen that the two voltage sources are in-phase? This is necessary to ensure that uninterrupted auxiliary power can be available to the power station through a station transformer when the generator transformer trips.
Read on for some more explanation.
 
To generate electricity in a power plant, a number of equipment have to run and all of them consume electricity. Typically, 5 to 10 percent of power generated by a power plant gets consumed in the very process of generating that power. This power is called - auxiliary power. Even when a power plant is under shut down (not running), it consumes some auxiliary power for equipment safety and maintenance.
 
When a power plant generates power, it takes its auxiliary power requirement from its own generation through unit auxiliary transformers. When it stops or is not running it takes this auxiliary power requirement from a station transformer that is always connected to the grid. This switching over of power from one source to the other is called "change-over". Change-over of auxiliary power to plant has to happen without interruption, otherwise, all the plant equipment will trip during the interruption. This means, there is a small time interval during which both the unit auxiliary transformer and the station transformer have to remain connected together to the auxiliary loads, after which the source not required can be switched off.
 
For two power sources to be connected together, their voltages have to be in same phase angle. For this to happen, the phase shift due to the GT must be compensated by the unit aux. transformer. This requires that the vector group of the GT and the unit aux. transformers must complement each other in such a way that the unit transformers should bring back the phase angle of the voltage by the same angle that is shifted by the GT.
 
When the bus duct was and assembled at site, we observed that Y phase of generator was going to the R phase of the transformer and R phase of the generator was going to the Y phase of the transformer. Similarly, B&Y (in place of Y&B) and R&B (in place of B&R) was going in to the second and third transformer. This was applying a voltage with 180-degree phase shift to each transformer. This meant the phase angle between the high voltage and low voltage of the transformer would now be (180+30) or 210 degrees in stead of 30 degrees as designed. The phase shift a transformer introduces is conventionally represented on a clock face - e.g 30 degrees represents 1 O clock, 150 representing 5 O clock etc. By that convention, the GT was connected as a YdN7 and not as YdN1 as intended.
 
 
Phase Angle 1200
 
 
 
The massiveness of the mistake was such that virtually nothing was possible to rectify the problem. As far as the GT and the bus duct were concerned, there was no possibility of any modification at site. Period.
 
But so what if the phase angle is 210 degrees instead of 30 degrees? 
Will there be any problem in synchronization to the grid? The answer is - No. The generator is a free running source and once synchronized, will keep generating happily without any problem. But after synchronization, the output voltage of the unit auxiliary transformers will be out of phase with the station auxiliary bus voltage coming from the station transformer. Because of this, the two sources cannot be connected in parallel and switching from one source to the other source will not be possible without interruption of power to the plant. This will pose serious problems in reliable and safe operation of the plant. There was nothing that could be done with bus duct. There was nothing that could be done with the generator transformer. Therefore, on everybody's face there was that question we began with - Now What?
 
 
 
Vector Group Matching1 1200
 
 
 
The only way to match these two voltages was by changing the vector group of the unit auxiliary transformers in such way that the new connection will shift the voltage by another 150 degrees so that the total shift becomes 360 degrees which is equivalent to 0 degrees. 150 degree phase shift is possible with a DyN5 connection. Thus the only option was to reconnect the unit auxiliary transformers as DyN5 from their existing configuration of DyN11. This could be only possible by changing the connections of the winding inside the transformers.
 
We did not know if this was possible and practical. We contacted transformer manufacturer and discussed the problem. The designers of the manufacturer agreed to carry out connection changes inside the transformer at the site to change the vector group from Dyn11 to Dyn5.
 
The design practice for generator transformers of this service are generally of YdN1 type. However, with the wrongly manufactured bus duct, this was not possible and the change described above was the only solution possible. Nevertheless, using GT of YdN7 vector group has not resulted in any problems that can be attributed to this rather unconventional choice of the vector group. 
 
The generating unit and the transformer are running satisfactorily since over 25 years.
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THE STORY OF PUMPS - 3

Published in Technology

In our first story, we have seen the evolution of pumps. In the second, we have learnt how centrifugal pump infuses energy into the fluid through the impeller. Besides, there are positive displacement pumps, which also impart energy into the fluid through physical movement of the liquid mass. So how do we decide which type of pump is best suited for a hydraulic system design? Let’s take a glimpse at the classification of pumps and understand the basic working philosophy of each type.

Broad classification of pumps based on working principle can be seen in Figure 1 below –

TSOP 3 F 1
Figure 1 - Broad Classification of Pumps

A.    Rotodynamic
Leading by the term, rotodynamic pumps work on the philosophy of continuously adding kinetic energy to the working fluid through a rotating device i.e., the impeller. The category has been further divided into three (3) sub-categories based on impeller construction vis-à-vis the direction of fluid flow exiting the impeller. Figure 2 below provides typical sectional view and characteristics of these categories of impellers.

TSOP 3 F 2Figure 2 – Typical impeller construction & characteristics in Rotodynamic Pumps

•    The Radial Vane or Centrifugal type
Impellers under this category will force the fluid to exit the impeller in the radial direction by the influence of centrifugal force while the fluid enters the impeller eye in the axial direction. The discharge fluid gets collected at the pump volute casing and guided to the discharge. Please refer to Figure 3a. Technically, this type of pumps has low Specific Speed and is useful for developing high discharge head and can handle the relatively lower quantity of fluid. Impellers can be open / semi-open or shrouded type depending on the process fluid characteristics. Refer to typical sectional details of the pumps in Figure 3b, 3c & 3d below for clarity.

TSOP 3 F 3a1  TSOP 3 F 3a2 

Fig 3a – Working Principle of a centrifugal pump

 TSOP 3 F 3b1  TSOP 3 F 3b2

Fig 3b – Cut away view of a centrifugal pump

 TSOP 3 F 3c

TSOP 3 F 3d

Fig 3c - Sectional view of a double suction pump
Fig 3d - Typical view of multistage centrifugal pump

•    Mixed Flow type
Impellers under this category and Francis type force the fluid to exit the impeller in an angular direction as can be seen in Figure 4a. Pumps with mixed flow type impellers have medium Specific Speed as can be seen in Figure 2 and is useful for developing medium discharge head. It can handle comparatively higher flow than a centrifugal unit. Typical view of open and closed type mixed flow impellers and sectional view of single stage mixed flow pumps are shown in Figures 4b & 4c below.

TSOP 3 F 4a
Figure 4aTypical Mixed Flow Pump working principle

TSOP 3 F 4b1  TSOP 3 F 4b2 

Figure 4b – Typical Mixed Flow Impeller construction

TSOP 3 F 4c1   TSOP 3 F 4c2

Figure 4c – Typical Mixed Flow pump construction

•    Axial Flow type
Impellers under this category are sometimes denoted as turbine type and are designed to push the fluid in the axial direction as can be seen in Figure 5a. Pumps with axial flow type impellers can handle large fluid volume as compared to other two categories and develop low discharge head. The impeller is characterized by the highest band of specific speed as can be seen in Figure 2. Typical impeller construction and sectional view of axial flow pumps are indicated in Figure 5b.

TSOP 3 F 5aFigure 5a – Typical Axial Flow Impeller & pump construction

TSOP 3 F 5b1   TSOP 3 F 5b2 TSOP 3 F 5b3 

Figure 5b – Typical view of Axial Flow Impeller & pump cross-section

Rotodynamic impellers have been further developed through researches by the pioneers in the pump industry to satisfy various process needs, handle dirty water & slurry as well as for pumping fluids other than water. For handling slurry or waste water containing solids, semi-open or open type non-clogging impellers are used. Typical view of these impellers can be seen in Figure 6.

 TSOP 3 F 6 1 TSOP 3 F 6 2  TSOP 3 F 6 3  TSOP 3 F 6 4 

Figure 6 – Typical view of closed, semi-open and open type Impellers

B.    Positive Displacement Type
As the name implies, this category of pumps physically pushes the fluid from suction to discharge. Positive Displacement Pump has an expanding cavity at the suction side and a decreasing cavity on the discharge side. Liquid flows into the pumps due to fall in pressure as the cavity on the suction side expands and the flows out of the discharge as the cavity collapses. Volume flow through the pump is constant in each cycle of operation.
Positive displacement pumps are classified into two main categories based on working principle.
•    Rotary
A rotary pump traps fluid between a rotating element and the closed casing at the suction side and transports the fluid along with the rotary element until it gets discharged at the outlet due to space constraint. It is normally a fixed volume machine and maintains a constant & uniform flow across all discharge pressures. Single or multiple rotor elements can be used in a rotary pump design, as can be seen in the following section. Major distinctive type rotary pump designs are -

  • Gear Pumps
 TSOP 3 F 7 1 TSOP 3 F 7 2 

Figure 7 – Typical working view of Gear Pump and construction

Pumping activity is achieved by teeth of two rotating gears meshing each     other fitted in an enclosed casing. Liquid trapped between the casing and the gear slots at the suction is carried by the teeth and discharges at the pump outlet. The meshing of teeth of two gears at center prohibits liquid backflow from the suction to discharge side. Both the gears are driven by a common driver.

  • Twin Lobe Pumps
    The arrangement is similar to gear pump with the difference that liquid is trapped in the rotating lobes as can be seen in the diagram below. Faces of the lobes continuously touch at the center thereby creating a seal between suction and discharge. Lobes are synchronized and driven through a common drive unit and timing gear.
TSOP 3 F 8 1   TSOP 3 F 8 2 TSOP 3 F 8 3 

Figure 8 – Typical view of Twin Lobe pump & cross-section

  • Vane Pumps
    Vane pump is a single rotor design in which the rotor is placed eccentrically in the pump     housing as shown in Figure 9a so that the rotor keeps a small clearance with the casing on one side. As the rotor rotates, sliding vanes eject out of the rotor due to centrifugal  force and trap the liquid between vane and casing. Trapped liquid rotates with the vane     and gets discharged at the outlet due to a reduction in the trapped volume.
  •  TSOP 3 F 9a1  TSOP 3 F 9a2

Figure 9a – Typical view of sliding vane pump & cross-section

TSOP 3 F 9b1  TSOP 3 F 9b2 

Figure 9b – Typical view of Flexible vane pump

In the case of flexible vane design, vanes collapse to reduce the trapped volume as they     approach closer to casing near discharge point to force the liquid to come out of the pump. Please see Figure 9b.

  • Screw Pumps
    The concept of screw pump was invented by Archimedes around 200 BC, which says that the angular motion of the screw when rotated in a static body (Figure 10a), can lift water from lower to a higher level. The concept is still used in the transportation of granular material. The design has been modified further to have double and triple screw pumps which are extensively used in oil and viscous fluid pumping.

  • Let’s look at the sectional view of a twin screw pump in Figure 10b.  The liquid trapped within screw threads and casing moves along the rotating screws till it reaches at the end. Both the screws are driven by a single prime mover using timing gears.

TSOP 3 F 10aFigure 10a – Typical Archimedean single screw pump

 TSOP 3 F 10b1 TSOP 3 F 10b2 

Figure 10b – Typical view of Twin Screw Pump & cross-section

  • Progressive Cavity Pumps
    Progress Cavity Pump uses a single screw rotor installed in a flexible casing. As the rotor rotates within the flexible stator, it pushes the trapped liquid in the direction of the screw. These pumps are used for slurry and high viscous fluids transportation. Typical sectional view of a progressive cavity pump is shown in Figure 11.
 TSOP 3 F 11 1 TSOP 3 F 11 2 

Figure 11 – Typical cross-sectional view of a Progressive Cavity Pump

•    Reciprocating
As the name implies, to and fro motion of a moving element is used for pumping the fluid. In a reciprocating pump, the liquid is drawn into the cylinder through the suction valve as the piston or plunger moves away from suction point creating a vacuum in the cylinder. Reaching the other end, piston reverses its motion due to crankshaft arrangement and the trapped liquid is discharged through the outlet valve under positive pressure due to a reduction in trapped volume while the suction valve remains closed. See Figure 12. The discharge from a reciprocating pump is therefore pulsating and the discharge volume is fairly constant for a specific pump size and drive speed irrespective of the discharge pressure. The operation of the pump is also independent of the rotational direction of the drive when compared to a rotary or rotodynamic unit.

TSOP 3 F 12 1  TSOP 3 F 12 2 

Figure 12 – Working Principle of a Reciprocating Piston Type Pump

Reciprocating Type Pumps have been further categorized based on their reciprocating mechanism as can be seen below -

  • Plunger or Piston Type
    Piston or plunger type pumps utilize piston movement as pumping principle, as already explained in Figure 12. Let’s also look at the Figure 13a below. The reciprocating motion of the piston is obtained using a rotating device and cam arrangement. As the piston moves away from piston head, the vacuum created in the cylinder pulls up the ball at inlet check valve and liquid rushes inside. Ball at outlet check valve remains seated preventing backflow from discharge side. With the reversal of piston motion, ball at suction valve goes back to sitting position due to gravity and pressure developed inside the cylinder pushes the liquid through the discharge valve.
 TSOP 3 F 13a1 TSOP 3 F 13a2 

Figure 13a – Working Principle of a Reciprocating Piston Type Pump

 TSOP 3 F 13b1  TSOP 3 F 13b2
Single Acting  Double Acting

Figure 13b – Working Principle of single and double acting Reciprocating Piston Type Pump

The piston or plunger type pumps can be single or double acting type as can be seen in Figure 13b. In a double acting system, two sets of suction and discharge valves are used, one set at each end of the cylinder so that while piston moves from left to right, the left side of the cylinder is in suction mode and right side goes in discharge mode. The situation reverses as the piston moves from right to left.

  • Diaphragm Type
    In a diaphragm pump, movement of a flexible diaphragm using a cam and rotating device creates the changes in the volume of the pumping chamber in a cyclic manner and thereby produce pumping action with the help of suction and discharge valve. See Figure 14a. The capacity of the pumping system is generally low as it is dependent on the size and flexibility of the diaphragm and the rotational speed of the cam. The advantage of this pump is that the wetting of components by the handling fluid is limited to the pumping chamber and the process flow line and therefore useful in handling highly toxic and/or corrosive fluid.
    The design has been further modified to ensure uniform movement of the diaphragm using the plunger and hydraulic mechanism. Reciprocating movement of the plunger by cam arrangement in a confined hydraulic system causes the diaphragm to follow the plunger due to pressure fluctuation in hydraulic fluid and thereby produces pumping action in the process fluid. See Figure 14b.

TSOP 3 F 14aFigure 14a – Working Principle of a Diaphragm Pump

TSOP 3 F 14b1   TSOP 3 F 14b2

Figure 14b – Working of a Diaphragm Pump using hydraulic device

Metering Pumps or the Controlled Volume Pumps are basically a modified version of the diaphragm pump, wherein the stroke or the frequency of the plunger movement is regulated using a stroke control mechanism or a variable frequency drive. Figure 15a below shows how a micrometer adjuster is used to regulate the stroke length of the plunger and thereby discharge volume. Figure 15b shows a cut-away view of the metering pump.

TSOP 3 F 15a
Figure 15a – Working of a Metering Pump using hydraulic

TSOP 3 F 15b
Figure 15b – Cut away view of a Metering Pump

 

I believe it has been an enjoying session for a beginner to understand pump types and their working principle. Further details may be studied in various literature published on the subject.

In our next story, we will talk about performance characteristics of pumps and their behavior in a hydraulic system. Stay Tuned !

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The Story of Pumps - 2

Published in Technology

In our first story, we have already looked at the history of the development of the Pumps and realized that the whole endeavor was to invent a mechanism(s) which can reverse the natural phenomenon of water flow by gravity.

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Nostalgia

Nostalgia

We humans are emotional beings. People, things, places, associations, sometimes leave a lasting impression in our hearts and mind. This section is devoted to those.

When Sholay came back to life

Published in Nostalgia

Sometimes in life, you hear from someone a story from his childhood without him knowing the kind of role you played in the making of the story.

talcher kaniha pts main gateDuring a recent visit to a site, almost 20 years after the glorious project days, while passing around the beautiful fountain in front of the township gate of NTPC's Talcher Kaniha Project in Odisha, the driver of the car narrated his childhood memory of an incident. The incident has become a story of the past. People involved in that fateful incident are now faithful old employees of the company. Although many people might have forgotten the story, there are others like our driver, whose words triggered open a floodgate of vivid memories. We smiled at each other while showing our Identity (ID) cards to the security guards for entry to the township on our way to the Guest House. I closed my eyes and the old incident replayed like a movie in front of me.

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Boss Chronicles

Boss Chronicles

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Gratitude

Gratitude

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In Verses

In Verses

Express yourself in rythmatic verses. Poetry & songs are welcome.