We have a GE Frame 3 turbine on our site. When trying to start the emergency pump, a momentary voltage drop is detected in the control panel.
Voltage drop in Mark VIe control panel
- Thread starter sonacontrol
- Start date
What is the control system used for this Unit
Are you tryin to start the ELOP in Manual or Auto from MCC rack or from Control system
Any alarm/trip annunciated during this operation?
Are you tryin to start the ELOP in Manual or Auto from MCC rack or from Control system
Any alarm/trip annunciated during this operation?
Are you sure that there is no DC ground fault ??
We use the GE Speedtronic Mark VIe as our control system. Currently, we're trying to start ELOP from the toolbox following a routine PM, as the machine is undergoing HGPI inspection. Although an imbalance voltage has been detected, it hasn't previously impacted the machine's startup.
Furthermore, we disconnected the power cable and measured the voltage in the control cabinet, finding no drop. Knowing that ELOP, the control cabinet, and emergency lighting share the same voltage source.
Okay thank you for these clarifications
Again any alarm displayed ? during the ELOP operation?
So no DC ground fault can you confirm
Again any alarm displayed ? during the ELOP operation?
So no DC ground fault can you confirm
Any job like retrofit or upgrade of the MCC rack for the ELOP has been done ?
No undervoltage relay & protection installed for this ELOP ?
@sonacontrol,
How old is the machine?
If the Mark* VIe was an upgrade from a prior turbine control system, how long ago was the Mark* VIe installed and what did it replace?
You say: "... Although an imbalance voltage has been detected, it hasn't previously impacted the machine's startup...." So, a ground has been existing for some time (approximately how long?) and it's been ignored. The voltages you listed aren't a serious problem, but it sounds like when the ELOP is started there is some kind of issue that's making the battery voltage even worse. Can you tell us what the voltage just one of the DC inputs legs (positive OR negative) is with respect to earth (ground) when the ELOP is started?
Yes; there are a lot of devices powered directly from the 125 VDC battery--not just the Mark* VIe DC-to-DC power supplies (because the Mark* VIe actually runs on 28 VDC).
WHAT HAS BEEN DONE TO TRY TO RESOLVE THE PROBLEM?
Since this is an HGPI it's most common for some devices to be removed from the machine during the disassembly. Are you CERTAIN the wires of any devices that were removed were properly insulated so they aren't touching ground? The ONLY devices which would affect the 125 VDC battery supply would be switches (temperature switches; pressure switches; level switches; etc.) and solenoids--both of which are directly powered by the 125 VDC battery through the Mark* VIe. Also, if the machine is an older machine (20 or 30 years old) it's highly likely if it still has the original fire detection system the heat detectors are also powered by 125 VDC--and it's likely the detectors in the turbine compartment/area were removed or "moved" to make the HGPI work easier, so those devices can cause problems.
You also mentioned the DC emergency lighting. That is directly powered by the 125 VDC battery, and often the light fixtures are also removed from the areas where work is happening. Just open the DC breaker in the 125 VDC distribution panel that supplies the emergency lighting as it's not (or shouldn't be) necessary for HGPI activities/work.
If the machine is older it's entirely possible that the DC emergency L.O. Pump motor needs to be checked out/refurbished. It has brushes and those can wear out over time. Also, the stationary field(s) of the DC emergency L.O. Pump motor are continually powered when the ELOP motor starter breaker is closed--this is done to keep those fields energized so that when the pump needs to start and run it is ready for immediate operation AND to drive off any moisture in the motor enclosure because those fields will be warm when they are energized. The DC contactors in the ELOP motor starter only apply 125 VDC to the rotor commutator of the DC Emergency L.O. Pump motor when they ELOP is started and needs to run.
Has anyone looked inside the ELOP motor starter to check the devices and terminations inside that enclosure to see if they are all good and none show signs of excessive heating or burning? (CLEAR digital photos can be posted to threads in Control.com.)
GE-design Frame 3 heavy duty gas turbines often drive centrifugal compressors, not just generators. Sometimes some of the devices (switches; solenoids) of the centrifugal compressor are powered by 125 VDC, including emergency seal oil pump motors. They can be the sources of 125 VDC battery grounds, also.
On MOST GE-design heavy duty gas turbines there is a TEST button on the door of the ELOP motor starter enclosure that can be used to start and run the ELOP. The button has to be manually pushed in to start and held in to run the ELOP and when released the ELOP will stop. If the ELOP is only being used to provide lubrication to bearings while the machine shaft is being rotated using that button is very common during the maintenance outages. Yes; the starters make noise when the ELOP is starting--but that's NORMAL and to be expected. It isn't, or shouldn't be, necessary to force logic to run the ELOP from the Mark* VIe, but that's also possible. PRECISELY WHAT LOGIC SIGNAL IS BEING FORCED TO START AND RUN THE ELOP?
Anyway, if the ground worsens when the ELOP is started and run and at other times the ground is not very serious (as indicated by the two voltages you provided that is not what's referred to as a "hard" or serious ground) then it's likely the problem is somewhere in the circuits connected to the ELOP motor starter, or the DC Emergency L.O. Pump motor itself. This is again presuming appropriate precautions were taken as devices were removed during disassembly at the beginning of the maintenance outage.
To reiterate: 125 VDC BATTERY GROUNDS ARE NOT ALWAYS AND ONLY CAUSED BY DEVICES CONNECTED TO THE MARK* VIe TURBINE CONTROL SYSTEM. ANY device or circuit that is powered by the 125 VDC battery can cause a 125 VDC battery ground--so have a long hard look at all devices and circuits powered by 125 VDC power, NOT JUST DEVICES CONNECTED TO THE MARK* VIe TURBINE CONTROL PANEL. Yes; a LOT of devices powered by 125 VDC ARE connected to the Mark* VIe, but there are also devices NOT connected to the Mark* VIe that are powered by the 125 VDC battery and since there aren't usually a lot of them they can be easy to eliminate as the cause of the ground.
Finally, this should be a lesson that when the 125 VDC battery supply differentials start to drift from a typical +65 VDC and -65 VDC split that some action should be taken to start investigating the cause of the problem. Left alone for long periods of time these can become serious problems--and there can even be more than one ground on one leg of the battery and when that happens finding them all can be difficult and time-consuming. The concept of having an ungrounded battery on a GE-design heavy duty gas turbine is, yes, to permit operation with one or more grounds on one leg of the battery--but it's also to make conscious operators and technicians to the fact that a ground--or grounds--exist and should be investigated and resolved. Before they become a serious problem. Because even with just one "hard" ground on, say, the negative leg of the DC battery when a ground develops on the positive leg of the battery that's just like taking a thick cable and connecting the positive and negative terminals of the battery to each other--LOTS of arcing and sparking will occur. LOTS of fuses can open ("blow"). LOTS of wires and printed circuit cards can be damaged. AND, in the worst case, serious damage to the machine can happen if the ELOP doesn't start and run when it needs to!!! Grounds should not be ignored; the DC supply voltages should be monitored and any significant change (such as the voltages above) should be investigated and resolved as soon as possible. Because left alone they can and do get worse and more difficult to find. Also, when noted early sometimes a possible cause (abnormally high compartment temperature, for example, causing wire insulation to be melted/damaged) can be noted as a possible cause and investigated and resolved. Left uninvestigated for weeks or months the potential cause can be forgotten (after the compartment ventilation problem was resolved) and be very difficult to find.
You want help? We need more information.
How old is the machine?
If the Mark* VIe was an upgrade from a prior turbine control system, how long ago was the Mark* VIe installed and what did it replace?
You say: "... Although an imbalance voltage has been detected, it hasn't previously impacted the machine's startup...." So, a ground has been existing for some time (approximately how long?) and it's been ignored. The voltages you listed aren't a serious problem, but it sounds like when the ELOP is started there is some kind of issue that's making the battery voltage even worse. Can you tell us what the voltage just one of the DC inputs legs (positive OR negative) is with respect to earth (ground) when the ELOP is started?
Yes; there are a lot of devices powered directly from the 125 VDC battery--not just the Mark* VIe DC-to-DC power supplies (because the Mark* VIe actually runs on 28 VDC).
WHAT HAS BEEN DONE TO TRY TO RESOLVE THE PROBLEM?
Since this is an HGPI it's most common for some devices to be removed from the machine during the disassembly. Are you CERTAIN the wires of any devices that were removed were properly insulated so they aren't touching ground? The ONLY devices which would affect the 125 VDC battery supply would be switches (temperature switches; pressure switches; level switches; etc.) and solenoids--both of which are directly powered by the 125 VDC battery through the Mark* VIe. Also, if the machine is an older machine (20 or 30 years old) it's highly likely if it still has the original fire detection system the heat detectors are also powered by 125 VDC--and it's likely the detectors in the turbine compartment/area were removed or "moved" to make the HGPI work easier, so those devices can cause problems.
You also mentioned the DC emergency lighting. That is directly powered by the 125 VDC battery, and often the light fixtures are also removed from the areas where work is happening. Just open the DC breaker in the 125 VDC distribution panel that supplies the emergency lighting as it's not (or shouldn't be) necessary for HGPI activities/work.
If the machine is older it's entirely possible that the DC emergency L.O. Pump motor needs to be checked out/refurbished. It has brushes and those can wear out over time. Also, the stationary field(s) of the DC emergency L.O. Pump motor are continually powered when the ELOP motor starter breaker is closed--this is done to keep those fields energized so that when the pump needs to start and run it is ready for immediate operation AND to drive off any moisture in the motor enclosure because those fields will be warm when they are energized. The DC contactors in the ELOP motor starter only apply 125 VDC to the rotor commutator of the DC Emergency L.O. Pump motor when they ELOP is started and needs to run.
Has anyone looked inside the ELOP motor starter to check the devices and terminations inside that enclosure to see if they are all good and none show signs of excessive heating or burning? (CLEAR digital photos can be posted to threads in Control.com.)
GE-design Frame 3 heavy duty gas turbines often drive centrifugal compressors, not just generators. Sometimes some of the devices (switches; solenoids) of the centrifugal compressor are powered by 125 VDC, including emergency seal oil pump motors. They can be the sources of 125 VDC battery grounds, also.
On MOST GE-design heavy duty gas turbines there is a TEST button on the door of the ELOP motor starter enclosure that can be used to start and run the ELOP. The button has to be manually pushed in to start and held in to run the ELOP and when released the ELOP will stop. If the ELOP is only being used to provide lubrication to bearings while the machine shaft is being rotated using that button is very common during the maintenance outages. Yes; the starters make noise when the ELOP is starting--but that's NORMAL and to be expected. It isn't, or shouldn't be, necessary to force logic to run the ELOP from the Mark* VIe, but that's also possible. PRECISELY WHAT LOGIC SIGNAL IS BEING FORCED TO START AND RUN THE ELOP?
Anyway, if the ground worsens when the ELOP is started and run and at other times the ground is not very serious (as indicated by the two voltages you provided that is not what's referred to as a "hard" or serious ground) then it's likely the problem is somewhere in the circuits connected to the ELOP motor starter, or the DC Emergency L.O. Pump motor itself. This is again presuming appropriate precautions were taken as devices were removed during disassembly at the beginning of the maintenance outage.
To reiterate: 125 VDC BATTERY GROUNDS ARE NOT ALWAYS AND ONLY CAUSED BY DEVICES CONNECTED TO THE MARK* VIe TURBINE CONTROL SYSTEM. ANY device or circuit that is powered by the 125 VDC battery can cause a 125 VDC battery ground--so have a long hard look at all devices and circuits powered by 125 VDC power, NOT JUST DEVICES CONNECTED TO THE MARK* VIe TURBINE CONTROL PANEL. Yes; a LOT of devices powered by 125 VDC ARE connected to the Mark* VIe, but there are also devices NOT connected to the Mark* VIe that are powered by the 125 VDC battery and since there aren't usually a lot of them they can be easy to eliminate as the cause of the ground.
Finally, this should be a lesson that when the 125 VDC battery supply differentials start to drift from a typical +65 VDC and -65 VDC split that some action should be taken to start investigating the cause of the problem. Left alone for long periods of time these can become serious problems--and there can even be more than one ground on one leg of the battery and when that happens finding them all can be difficult and time-consuming. The concept of having an ungrounded battery on a GE-design heavy duty gas turbine is, yes, to permit operation with one or more grounds on one leg of the battery--but it's also to make conscious operators and technicians to the fact that a ground--or grounds--exist and should be investigated and resolved. Before they become a serious problem. Because even with just one "hard" ground on, say, the negative leg of the DC battery when a ground develops on the positive leg of the battery that's just like taking a thick cable and connecting the positive and negative terminals of the battery to each other--LOTS of arcing and sparking will occur. LOTS of fuses can open ("blow"). LOTS of wires and printed circuit cards can be damaged. AND, in the worst case, serious damage to the machine can happen if the ELOP doesn't start and run when it needs to!!! Grounds should not be ignored; the DC supply voltages should be monitored and any significant change (such as the voltages above) should be investigated and resolved as soon as possible. Because left alone they can and do get worse and more difficult to find. Also, when noted early sometimes a possible cause (abnormally high compartment temperature, for example, causing wire insulation to be melted/damaged) can be noted as a possible cause and investigated and resolved. Left uninvestigated for weeks or months the potential cause can be forgotten (after the compartment ventilation problem was resolved) and be very difficult to find.
You want help? We need more information.
How quickly is the DC motor getting to rated speed? The DCLO pump motors I'm familiar with have resistor circuits and time delay relays to limit the inrush current so that the motor reaches rated speed over ~3-4 seconds.
I've seen situations where issues with the starting circuit and the large inrush caused a unit to trip due to the large drop in the 125dc voltage.
I've seen situations where issues with the starting circuit and the large inrush caused a unit to trip due to the large drop in the 125dc voltage.
I experienced same problem in our machine 9e GT , we found the issue because of only One charger in service and the other one was under maintenance, at the same time we found Electrical department guys removed the batteries for maintenance. That’s way if only one charger working without batteries , 125 VDC goes very low
@OMAR01,
If the power supply to the battery chargers failed/was lost the batteries are sized to provide the power needed by the ELOP.
If the battery (actually a series string of batteries) is incapable of supplying the power required by the ELOP then if one or both battery chargers has a proper mains supply they will attempt to make up for the inability of the battery to power the ELOP. The battery chargers are not intended to supply current to the ELOP--only to the battery. Yes, if the battery charger(s) mains supply was available and the machine needed to ELOP and it was started then the battery charger(s) would kick in to help the battery--but that's NOT their intended purpose. It's only to charge the batteries.
There are two (2) battery chargers for redundancy--in case one fails the second will supply current to the battery. That's all.
Proper battery maintenance checks the specific gravity of the cells and trends those numbers to help identify cells that have begun to feel the effects of sulfation. Equalize charges can help, as can maintaining water and adding acid if necessary.
In a series string of batteries if one (or more) of the cells fails (the bottoms of the plates in the cells are shorted together with the detritus of repeated charging and discharging without proper maintenance) the cell (or cells) will actually reverse polarity and when a high current flows through the batteries it will drag down the voltage of the entire battery as the current is being drawn from the battery. Such a cell can be found with a multimeter measuring the voltages of each cell individually, and on seriously failing cells the voltage polarity will be opposite of what it should be.
But, the battery chargers ARE NOT intended to power the ELOP motor. They are intended to maintain the voltage/charge of the cells of the battery as a whole. Improper maintenance (you said, "... the Electrical department guys removed the batteries for maintenance...."--but you DIDN'T say if the batteries were returned or new ones replaced the batteries...!) will cause this kind of behavior. I have been to sites where the batteries were covered in dust and green crud on almost every single battery terminal, and individual cells were found to have reversed polarity.
Maintenance includes housekeeping as well as specific gravity checks, water level maintenance, equalize charging and regular battery capacity testing. (The test is often referred to as "battery run-down test.") And THAT is done with the charger(s) disconnected. The usual test involves running the ELOP motor and monitoring battery terminal voltage as well as ELOP motor speed and ELOP discharge pressure (while the Aux. L.O. Pump Motor is NOT running).
Finally, lead-acid batteries do fail over time--but that time can be 20 years or more, with proper maintenance. But, they do fail--and the actual failure can be determined by proper battery testing.
And proper testing and timely battery replacement can save a machine when it needs the ELOP.
Thank you very much, @OMAR01, for reminding me of this possibility. But, it's not a problem with the battery chargers. It's a battery problem.
If the power supply to the battery chargers failed/was lost the batteries are sized to provide the power needed by the ELOP.
If the battery (actually a series string of batteries) is incapable of supplying the power required by the ELOP then if one or both battery chargers has a proper mains supply they will attempt to make up for the inability of the battery to power the ELOP. The battery chargers are not intended to supply current to the ELOP--only to the battery. Yes, if the battery charger(s) mains supply was available and the machine needed to ELOP and it was started then the battery charger(s) would kick in to help the battery--but that's NOT their intended purpose. It's only to charge the batteries.
There are two (2) battery chargers for redundancy--in case one fails the second will supply current to the battery. That's all.
Proper battery maintenance checks the specific gravity of the cells and trends those numbers to help identify cells that have begun to feel the effects of sulfation. Equalize charges can help, as can maintaining water and adding acid if necessary.
In a series string of batteries if one (or more) of the cells fails (the bottoms of the plates in the cells are shorted together with the detritus of repeated charging and discharging without proper maintenance) the cell (or cells) will actually reverse polarity and when a high current flows through the batteries it will drag down the voltage of the entire battery as the current is being drawn from the battery. Such a cell can be found with a multimeter measuring the voltages of each cell individually, and on seriously failing cells the voltage polarity will be opposite of what it should be.
But, the battery chargers ARE NOT intended to power the ELOP motor. They are intended to maintain the voltage/charge of the cells of the battery as a whole. Improper maintenance (you said, "... the Electrical department guys removed the batteries for maintenance...."--but you DIDN'T say if the batteries were returned or new ones replaced the batteries...!) will cause this kind of behavior. I have been to sites where the batteries were covered in dust and green crud on almost every single battery terminal, and individual cells were found to have reversed polarity.
Maintenance includes housekeeping as well as specific gravity checks, water level maintenance, equalize charging and regular battery capacity testing. (The test is often referred to as "battery run-down test.") And THAT is done with the charger(s) disconnected. The usual test involves running the ELOP motor and monitoring battery terminal voltage as well as ELOP motor speed and ELOP discharge pressure (while the Aux. L.O. Pump Motor is NOT running).
Finally, lead-acid batteries do fail over time--but that time can be 20 years or more, with proper maintenance. But, they do fail--and the actual failure can be determined by proper battery testing.
And proper testing and timely battery replacement can save a machine when it needs the ELOP.
Thank you very much, @OMAR01, for reminding me of this possibility. But, it's not a problem with the battery chargers. It's a battery problem.
@sonacontrol...
Measure and record the current-flow at every Control fuse-block! It was something I insisted be done at every Start-Up I was a member of! Another was that the Control-Panel be served by redundant, but separate power sources!
I was called to a plant that said my CMOS-Based Safety System "PRETECT", tripped several times because of power loss. Investigation revealed the the two power source cables were labeled Pnl-xxx, Brkr 3, the other Pnl-xxx, Brk 5.
Regards, Phil Corso (PE, Seems-Never-Retired)
[email protected]
Measure and record the current-flow at every Control fuse-block! It was something I insisted be done at every Start-Up I was a member of! Another was that the Control-Panel be served by redundant, but separate power sources!
I was called to a plant that said my CMOS-Based Safety System "PRETECT", tripped several times because of power loss. Investigation revealed the the two power source cables were labeled Pnl-xxx, Brkr 3, the other Pnl-xxx, Brk 5.
Regards, Phil Corso (PE, Seems-Never-Retired)
[email protected]
@WTF?
Yes actually battery chargers are intended to charge the batteries and in the case of the battery's inability to supply the required voltage at the ELOP starting time, that time one of the charger's should be able to do. But that didn't happen in my case (maybe due to some other problem), I asked the Electrical maintenance guys they actually disconnected the batteries in order to replace it with a new one. also they tried to perform a test( start ELOP manually without batteries and observed that voltage goes down to 70 VDC at ELOP starting time (maybe due to other problem )
Thanks a lot to WTF? for valuable information
Yes actually battery chargers are intended to charge the batteries and in the case of the battery's inability to supply the required voltage at the ELOP starting time, that time one of the charger's should be able to do. But that didn't happen in my case (maybe due to some other problem), I asked the Electrical maintenance guys they actually disconnected the batteries in order to replace it with a new one. also they tried to perform a test( start ELOP manually without batteries and observed that voltage goes down to 70 VDC at ELOP starting time (maybe due to other problem )
Thanks a lot to WTF? for valuable information
@OMAR01,
I respectfully disagree that the battery chargers should be used to power the ELOP--or the Mark* turbine control panel--when the battery is unavailable for any reason.
I would go so far as to say that it's very likely that in the case of a GE-design Frame 9E heavy duty gas turbine the ELOP motor requires more amperes than a typical GE-supplied battery charger can supply. The largest battery charger I recall was rated at 50A and if I recall correctly an ELOP motor drew something on the order of 60-80A. In fact, it would take some serious re-wiring to "bypass" the battery so that the charger(s) could power the turbine control panel and/or the ELOP motor because the chargers are not supposed to be used in the event the battery is unavailable.
Most redundant battery chargers are fed from two different mains supplies to keep one powered in the event the mains supply to one is lost. And, most power plants with Frame 9E power supplies don't have an emergency diesel generator that can start and load in a matter of seconds to power even one of the battery chargers in the event of loss of AC mains in the plant ("black-out").
As far as the turbine control system is concerned, the battery acts to smooth out the ripple from the typical battery charger to protect the electronics and the power supplies used in the turbine control panel. Connecting the output of a battery charger directly to a Mark* turbine control panel is not advised by the division of GE that makes the Mark*. It may work, but chances are over time the Mark* power supplies will be weakened to the point of failure.
Now, I know that some GE heavy duty gas turbines are now using variable frequency drives to operate the ELOP motor and I've been told that in at least one case the variable frequency drive was connected to the 125 VDC battery as its mains power source. (I've heard that some steam turbines are also using a similar scheme.) Perhaps your machine is one of these machines? We don't know. The presumption is the machine uses a DC ELOP motor.
Anyway, it's not my machine and I hope it's not under warranty by anyone. I wonder what the machine insurance company would say if they knew the DC ELOP was NOT being powered by a (tested and properly maintained) battery.... Especially if the machine was damaged because the ELOP couldn't supply the bearings with lubricating oil when necessary and the insurance company was being asked to pay for repairs. (I'd love to be a fly on the wall of that conference room to hear what was being said and what the outcome of that claim was.)
Just because something is possible does not mean its advisable or even prudent except in extreme emergency when everyone knows all the risks involved.
I respectfully disagree that the battery chargers should be used to power the ELOP--or the Mark* turbine control panel--when the battery is unavailable for any reason.
I would go so far as to say that it's very likely that in the case of a GE-design Frame 9E heavy duty gas turbine the ELOP motor requires more amperes than a typical GE-supplied battery charger can supply. The largest battery charger I recall was rated at 50A and if I recall correctly an ELOP motor drew something on the order of 60-80A. In fact, it would take some serious re-wiring to "bypass" the battery so that the charger(s) could power the turbine control panel and/or the ELOP motor because the chargers are not supposed to be used in the event the battery is unavailable.
Most redundant battery chargers are fed from two different mains supplies to keep one powered in the event the mains supply to one is lost. And, most power plants with Frame 9E power supplies don't have an emergency diesel generator that can start and load in a matter of seconds to power even one of the battery chargers in the event of loss of AC mains in the plant ("black-out").
As far as the turbine control system is concerned, the battery acts to smooth out the ripple from the typical battery charger to protect the electronics and the power supplies used in the turbine control panel. Connecting the output of a battery charger directly to a Mark* turbine control panel is not advised by the division of GE that makes the Mark*. It may work, but chances are over time the Mark* power supplies will be weakened to the point of failure.
Now, I know that some GE heavy duty gas turbines are now using variable frequency drives to operate the ELOP motor and I've been told that in at least one case the variable frequency drive was connected to the 125 VDC battery as its mains power source. (I've heard that some steam turbines are also using a similar scheme.) Perhaps your machine is one of these machines? We don't know. The presumption is the machine uses a DC ELOP motor.
Anyway, it's not my machine and I hope it's not under warranty by anyone. I wonder what the machine insurance company would say if they knew the DC ELOP was NOT being powered by a (tested and properly maintained) battery.... Especially if the machine was damaged because the ELOP couldn't supply the bearings with lubricating oil when necessary and the insurance company was being asked to pay for repairs. (I'd love to be a fly on the wall of that conference room to hear what was being said and what the outcome of that claim was.)
Just because something is possible does not mean its advisable or even prudent except in extreme emergency when everyone knows all the risks involved.
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