26MW TURBINE SHEAR PINS BREAKING ISSUE
- Thread starter bilal.bhatti
- Start date
bilal.bhatti...
Following is what I believe is the Cause of the Problem...
1) Think of a Weight-Lifter trying to throw a heavy weight over a bar 3 meters above his head. He's successful. But then he tries when the bar is 1 cm higher... he fails. The 26-MW machine problem is similar. It reached its limit, years ago!
2) The trend-charts of 2022, show that PF operating value was higher than listed on the generator's nameplate rating. There is a reason for a limit, but too often... unless otherwise agreed between Buyer and Manufacturer, it is overlooked.
3) Further, I believe there was decision to improve Load-Bus voltage by installing a 3rd, but larger Aluminum cable, in parallel with the 2 Copper cables already installed. But because it's Aluminum, it's resistance is 30.5% greater (even allowing for size difference) than Copper. More importantly, there is a Reactive-component, almost equal to the Resistance-component, that was totally ignored!
3) When I initially ran the no-loss situation for the 2-gen situation nothing appeared like the Trend-Charts of 2022. But, when I started to include components like Armature-Resistance and Armature-Reactance which impact Generated-Emf (GEMF) and Terminal-Voltage (VT), and Load-Bus Volage VL, a different situation emerged, especially for a high PF... nearly 1.00 PF appeared. A great stress is placed on the 26-MW machine.
4) The 3-Gen case Trend-Charts of 2023, clearly show that pressure is being placed on the 12-MW and 16-MW machines because both are being operated at 1.00 PF (Probably due to Melting or Smelting Furnaces in the Steel Plant!)
5) 26-MW Machine Torque Statistic:
o Yr 2022, 2-Gen Situation = 29.8x10^6 N.mt !
o Yr 2023, 3-Gen Situation = 23.2x10^6 N.mt !
6) Some advice for future... Consider PF-Correction for machines serving the Steel-Plant... Unless you have an agreement with the
Generator's Manufacture to exceed nameplate PF values!
In closing, its been a pleasure helping you.
Regards, Phil Corso
Following is what I believe is the Cause of the Problem...
1) Think of a Weight-Lifter trying to throw a heavy weight over a bar 3 meters above his head. He's successful. But then he tries when the bar is 1 cm higher... he fails. The 26-MW machine problem is similar. It reached its limit, years ago!
2) The trend-charts of 2022, show that PF operating value was higher than listed on the generator's nameplate rating. There is a reason for a limit, but too often... unless otherwise agreed between Buyer and Manufacturer, it is overlooked.
3) Further, I believe there was decision to improve Load-Bus voltage by installing a 3rd, but larger Aluminum cable, in parallel with the 2 Copper cables already installed. But because it's Aluminum, it's resistance is 30.5% greater (even allowing for size difference) than Copper. More importantly, there is a Reactive-component, almost equal to the Resistance-component, that was totally ignored!
3) When I initially ran the no-loss situation for the 2-gen situation nothing appeared like the Trend-Charts of 2022. But, when I started to include components like Armature-Resistance and Armature-Reactance which impact Generated-Emf (GEMF) and Terminal-Voltage (VT), and Load-Bus Volage VL, a different situation emerged, especially for a high PF... nearly 1.00 PF appeared. A great stress is placed on the 26-MW machine.
4) The 3-Gen case Trend-Charts of 2023, clearly show that pressure is being placed on the 12-MW and 16-MW machines because both are being operated at 1.00 PF (Probably due to Melting or Smelting Furnaces in the Steel Plant!)
5) 26-MW Machine Torque Statistic:
o Yr 2022, 2-Gen Situation = 29.8x10^6 N.mt !
o Yr 2023, 3-Gen Situation = 23.2x10^6 N.mt !
6) Some advice for future... Consider PF-Correction for machines serving the Steel-Plant... Unless you have an agreement with the
Generator's Manufacture to exceed nameplate PF values!
In closing, its been a pleasure helping you.
Regards, Phil Corso
| Hello Good Day Thanks for the expert observations. Below pl. find my comments against your observations. Ans-1) Agreed and Noted your observation. Ans-2) Normally PF value on generators name plates listed as 0.8. An improved PF within the capability curve of the generator set reduced the consumption of KVA, this relief the system. The utilities companies in Pakistan i.e., WAPDA imposes penalties to the consumer's falling their PF below 0.9. On the other hand never the utility Companies advise to contact the generator manufacturers to improve the PF above listed name plate. Ans-3) The decision of 3rd aluminum cable was to meet the load requirements with the addition of 2nd furnace. All these cables are in room temperature, not exceeding 26C, these cables are running under load and cool. Ans3.1) Yes, it’s your observation and noted pl. Ans.4) Yes, depending on load. Ans-5) yes, this is torque observation. Ans-6) Thank you for your help. Keeping in view the whole discussion we understood that fluctuations in PF may cause such failures. Secondly no separate machine fixed for the operation of steel plant. Now we have informed to the steel plant authorities to maintain PF 0.94 to 0.98. Because generator manufacturer provides the protection. As soon as PF will exceed 1.0 the generator will trip. What do you think about it? My Dear, we will appreciate if you please advise some solid steps, by adopting those we may get rid of this problem. Thank you once again. Regards Best Regards |
Isn't the generator nameplate power factor value the power factor the generator can be operated at and produce the KVA (watts; kVA; MVA) at without causing damage to the generator components--specifically overheating for lagging power factors and end-turn heating for leading power factors? Isn't this reflected in the Reactive Capability Curve for the generator (sometimes calld the D-curve)?
So, in this case the generator nameplate power factor seems to be 0.8 (lagging, I presume) which is pretty typical of many 3-phase synchronous generators. That would mean that any power factor between 0.8 (lagging) and 1.0 (unity) is acceptable. (What is a power factor above 1.0???) And isn't the condition of the power factor (lagging or leading) just as important as the magnitude?
And, if the coupling bolts are properly rated for unity power factor (plus a safety margin, I would think) then why are the coupling bolts breaking--repeatedly?
So, in this case the generator nameplate power factor seems to be 0.8 (lagging, I presume) which is pretty typical of many 3-phase synchronous generators. That would mean that any power factor between 0.8 (lagging) and 1.0 (unity) is acceptable. (What is a power factor above 1.0???) And isn't the condition of the power factor (lagging or leading) just as important as the magnitude?
And, if the coupling bolts are properly rated for unity power factor (plus a safety margin, I would think) then why are the coupling bolts breaking--repeatedly?
bilal.bhatti
My last word (On Ash-Wednesday) on the subject:
The problem of Generator Coupling destruction is related to:
a) A very high Turbine-Input torque, attested to by the Power Plant Manager! And,
b) My calculation revealing the Generator's over-excited, and operating as if connected to an Infinite-Bus
Both are easily verifiable!
Phil Corso ([email protected])
My last word (On Ash-Wednesday) on the subject:
The problem of Generator Coupling destruction is related to:
a) A very high Turbine-Input torque, attested to by the Power Plant Manager! And,
b) My calculation revealing the Generator's over-excited, and operating as if connected to an Infinite-Bus
Both are easily verifiable!
Phil Corso ([email protected])
MANY times the original poster has an agenda that they are desperately trying to have verified/justified and so they have it in their mind(s) that the problem is [this or that] and nothing is going to change their minds. They will only provide information that suits their agenda/purpose and kind contributors here spend a great deal of time trying to persuade them to open their focus and be open to other possibilities. PhilCorso has put a great deal of effort into this thread and he's done all he can do. The machine is not being operated properly or within the bounds of the equipment as supplied. But, that doesn't seem to agree with the agenda/purpose of the original poster.
What more can a fella do, eh?
Bravo Zulu, Phil.
What more can a fella do, eh?
Bravo Zulu, Phil.
Hello,
Thanks for the detailed response.
Would like to comment as follows.
1. What I understand from whole the discussions that everyone is assuming the coupling pins break during synchronization. This never happened. Pins broken after 20 days operation at 15-17 MW load and leading a bit high vibration at that moment. It is observed through DCS vibration trends of the machine. On the other hand, both the alignments (axial and radial) are within the permissible limits as per the Trevieni catalogue. Alignment readings can be provided.
Further we have no National Grid synchronization (we are not IPP).
Regards
Hello,
Below Pl. Find the response of your queries.
- The 26MW-Gen'r: PDF of its nameplate; and is its exciter brushless or slip-ring!
2) The 16MW-Gen'r: ditto! slip ring
3) The 12MW-Gen'r: ditto!
4: The Trevini Gearbox: HP or Torque, and Input/Output RPM Ratio
Gear Box
Make :TEIL-Mysore
Type: DOUBLE Helical
Model: N3119C
Speed/input/output: RPM: 6141/1500. Ratio 1: 4.094
And My last word on the subject:
The problem of Generator Coupling destruction is related to:
- A very high Turbine-Input torque, attested to by the Power Plant Manager!
b) My calculation revealing the Generator's over-excited, and operating as if connected to an Infinite-Bus
Both are easily verifiable!
we have already declared that no infinite bus (wapda) at almoiz and over excitation limiter OEL in AVR to prevent the generator from over excitation (safety available and tested.
Regards
bilal.bhatti,
We understand English is not your first language. Metal shear pins (coupling bolts we are presuming) break because of mechanical forces. Full stop. Period. Mechanical forces in an AC (Alternating Current) synchronous, three-phase generator can be the result (combination) of many different sources and stimuli, but they are mechanical. No one (including myself) has asked if all the shear pins are found broken at the same time or if only one or two (of HOW MANY???) are found to be broken? How many shear pins are there in total on this coupling?
It's been said MANY times before on Control.com: Graphs and charts from DCS-based data archival systems are generally not very useful for high-speed event troubleshooting. The rate at which data is gathered and stored is usually rather slow and only useful for long-term trending, though for SOME situations the rate may be sufficient. In this case, you say vibration increases around the time of the shear pin failures--could that be because only or two of the shear pins have separated (broken; failed) and is causing the increase in vibrations?
This is pretty disheartening for me--not being able to communicate and get meaningful answers and responses. PhilCorso has done a LOT of work to try to explain how electrical phenomenon can cause very high mechanical forces which can certainly cause shear pins (coupling bolts) to fail. AND, as has been said in this thread--if there are problems during the act of synchronization (paralleling one turbine-generator with one or more other turbine-generators) then the cumulative effects of multiple synchronizations over time can weaken the shear pins (coupling bolts) and eventually cause issues. VERY great, momentary mechanical forces can be generated when the generator breaker is closed during the act of synchronization if the voltage and frequency are not within certain limits.
It's pretty certain you have photographs of the failed shear pins (coupling bolts), from before they are removed from their locations and when they are laying out on the floor or a table for visual review, and of the coupling or whatever houses these shear pins. POST THESE PHOTOS to this thread for all to see and examine.
You haven't told us what the supplier of the Trevini turbine-generator says about the problem--or what the shear pin (coupling bolt) supplier says about the problem. To quote a former colleague: "This ain't rocket science." Mechanical forces break shear pins (coupling bolts). Full stop. Period. Maybe the alignment specifications aren't correct for the your site--the turbine-generator supports; the steam piping; the condenser supports. Steam turbine supports and alignment are very critical. Perhaps you need to temporarily set up some laser equipment to monitor movement, and perhaps install some temporary vibration monitoring equipment to capture high-speed vibration data (instead of relying on the DCS graphs).
Either the shear pins (coupling bolts) aren't correct for the application (maybe the coupling itself isn't correct for the application.?.?.?), or there is something about the turbine-generator installation/supports that needs to be understood and communicated to the turbine-generator supplier/manufacturer, or the synchronization scheme (including the generator closing time) needs to be investigated, or some kind of temporary "strain gauge" measuring/monitoring scheme needs to be used to capture high-speed data, or some laser equipment needs to be set up to monitor turbine-generator or support movements, or some kind of three-phase electrical monitoring equipment needs to be hooked up to capture high-speed data (phase waveforms; voltage- and current sinewave data; real- and reactive currents; etc.). But, it's for pretty damn sure: Those shear pins are breaking--time and time and time again--because of as-yet unknown mechanical forces. Full stop. Period. End of discussion.
AND, it's time to stop speculating. Troubleshooting is OFTEN a process of elimination. Make a list of all the possible causes of mechanical forces which can act on the shear pins (coupling bolts) and then start investigating them beginning with the most likely culprit, but work through them until you ultimately find the root cause. You've been given some good information in this thread; don't discount any of them until you have proven beyond a reasonable doubt they are not the culprit for the high mechanical forces which are causing the shear pins (coupling bolts) to break.
We would like--very much--to hear what is ultimately found to be the cause. We have invested a good deal of time and effort in trying to understand the problem based on the information provided and in providing possible causes and even resultant forces. Please write back to let us know what you find. Best of luck!
We understand English is not your first language. Metal shear pins (coupling bolts we are presuming) break because of mechanical forces. Full stop. Period. Mechanical forces in an AC (Alternating Current) synchronous, three-phase generator can be the result (combination) of many different sources and stimuli, but they are mechanical. No one (including myself) has asked if all the shear pins are found broken at the same time or if only one or two (of HOW MANY???) are found to be broken? How many shear pins are there in total on this coupling?
It's been said MANY times before on Control.com: Graphs and charts from DCS-based data archival systems are generally not very useful for high-speed event troubleshooting. The rate at which data is gathered and stored is usually rather slow and only useful for long-term trending, though for SOME situations the rate may be sufficient. In this case, you say vibration increases around the time of the shear pin failures--could that be because only or two of the shear pins have separated (broken; failed) and is causing the increase in vibrations?
This is pretty disheartening for me--not being able to communicate and get meaningful answers and responses. PhilCorso has done a LOT of work to try to explain how electrical phenomenon can cause very high mechanical forces which can certainly cause shear pins (coupling bolts) to fail. AND, as has been said in this thread--if there are problems during the act of synchronization (paralleling one turbine-generator with one or more other turbine-generators) then the cumulative effects of multiple synchronizations over time can weaken the shear pins (coupling bolts) and eventually cause issues. VERY great, momentary mechanical forces can be generated when the generator breaker is closed during the act of synchronization if the voltage and frequency are not within certain limits.
It's pretty certain you have photographs of the failed shear pins (coupling bolts), from before they are removed from their locations and when they are laying out on the floor or a table for visual review, and of the coupling or whatever houses these shear pins. POST THESE PHOTOS to this thread for all to see and examine.
You haven't told us what the supplier of the Trevini turbine-generator says about the problem--or what the shear pin (coupling bolt) supplier says about the problem. To quote a former colleague: "This ain't rocket science." Mechanical forces break shear pins (coupling bolts). Full stop. Period. Maybe the alignment specifications aren't correct for the your site--the turbine-generator supports; the steam piping; the condenser supports. Steam turbine supports and alignment are very critical. Perhaps you need to temporarily set up some laser equipment to monitor movement, and perhaps install some temporary vibration monitoring equipment to capture high-speed vibration data (instead of relying on the DCS graphs).
Either the shear pins (coupling bolts) aren't correct for the application (maybe the coupling itself isn't correct for the application.?.?.?), or there is something about the turbine-generator installation/supports that needs to be understood and communicated to the turbine-generator supplier/manufacturer, or the synchronization scheme (including the generator closing time) needs to be investigated, or some kind of temporary "strain gauge" measuring/monitoring scheme needs to be used to capture high-speed data, or some laser equipment needs to be set up to monitor turbine-generator or support movements, or some kind of three-phase electrical monitoring equipment needs to be hooked up to capture high-speed data (phase waveforms; voltage- and current sinewave data; real- and reactive currents; etc.). But, it's for pretty damn sure: Those shear pins are breaking--time and time and time again--because of as-yet unknown mechanical forces. Full stop. Period. End of discussion.
AND, it's time to stop speculating. Troubleshooting is OFTEN a process of elimination. Make a list of all the possible causes of mechanical forces which can act on the shear pins (coupling bolts) and then start investigating them beginning with the most likely culprit, but work through them until you ultimately find the root cause. You've been given some good information in this thread; don't discount any of them until you have proven beyond a reasonable doubt they are not the culprit for the high mechanical forces which are causing the shear pins (coupling bolts) to break.
We would like--very much--to hear what is ultimately found to be the cause. We have invested a good deal of time and effort in trying to understand the problem based on the information provided and in providing possible causes and even resultant forces. Please write back to let us know what you find. Best of luck!
bilal.bhatti...
I'm very pleased that you responded to my questions. Before, it was very difficult for me to read the original data:
5) Response #3: Gen'r No. 3 is listed as 12-MW, but photo shows 15-MW?
6) Response #4: I asked for data on the Trevini Speed-Reducing Gearboxes, but, instead it's the Coupling in question?
7) Do you have trending charts of the 16-MW Gen'r?
Regards, and thanks again,
Phil Corso
@WTF... Synchronizing is not an issue!
I'm very pleased that you responded to my questions. Before, it was very difficult for me to read the original data:
5) Response #3: Gen'r No. 3 is listed as 12-MW, but photo shows 15-MW?
6) Response #4: I asked for data on the Trevini Speed-Reducing Gearboxes, but, instead it's the Coupling in question?
7) Do you have trending charts of the 16-MW Gen'r?
Regards, and thanks again,
Phil Corso
@WTF... Synchronizing is not an issue!
bilal.bhatti...
I no longer require answers to earlier questions 5), 6), and 7)!
But, I do need one more piece to solve the puzzle:
In message 1, you said there were 9 coupling failures since commissioning 3 years ago! Please provide the 26-MW and 16-MW motor parameters for the 1st, and 2nd failures.
Regards, Phil Corso
I no longer require answers to earlier questions 5), 6), and 7)!
But, I do need one more piece to solve the puzzle:
In message 1, you said there were 9 coupling failures since commissioning 3 years ago! Please provide the 26-MW and 16-MW motor parameters for the 1st, and 2nd failures.
Regards, Phil Corso
bilal.bhatti...
I won't keep you in suspense. The key to the puzzle is found in message 33, Item 4: The Trevini Gearbox. The Input to Output Speed Ratio (dropping decimals) is 4:1, not 1:4 !
Furthermore, Gearbox Math, involving just 2 gears, 1 input the other output, dictates that Torque-Ratio is the inverse of speed-ratio or 1:4 not 4:1 !
Thus, the Present Coupling is 1/4 the size it should be !
@WTF... You mentioned it, but you were hung up on Synchronization and lost the forest for the trees.
Regards to all contributors to this forum. Have a Good life,
Phil Corso
I won't keep you in suspense. The key to the puzzle is found in message 33, Item 4: The Trevini Gearbox. The Input to Output Speed Ratio (dropping decimals) is 4:1, not 1:4 !
Furthermore, Gearbox Math, involving just 2 gears, 1 input the other output, dictates that Torque-Ratio is the inverse of speed-ratio or 1:4 not 4:1 !
Thus, the Present Coupling is 1/4 the size it should be !
@WTF... You mentioned it, but you were hung up on Synchronization and lost the forest for the trees.
Regards to all contributors to this forum. Have a Good life,
Phil Corso
I had no doubt that you could solve it Phil.
I figured the OP would not provide enough info to solve the equation.
We were "hung up" on the sync etc because the OP insisted that we should look there.
I will never complement your achievements again because you seem to disregard inputs from other as a insult.
You have a Great Day.
Dear PhilCorso,
I am writing to express my sincere apologies for providing you the wrong gear ratio. I understand that such mistakes can cause unnecessary confusion. Actually I collected information from a second source, I realize that I should have double-checked the data to ensure its accuracy.
Thank you for your help. I look forward to continuing work.
Will also share detailed reply in response to message no. 34 soon.
Regards,
M. Bilal Bhatti
