Mark-Vie JPDF card used for 125VDC supply. In JPDF card, two 125VDC input supply provision is available.

1. Battery supply
2. Direct supply

We are connecting our 125VDC supply at battery supply. Direct supply is vacant. We want to use this vacant direct supply source. Kindly tell me for may i connect 125VDVC supply on direct supply source terminals.

What will be implications?

Kindly guide us.

 

VKGUPTA,

Without understanding where the "new", direct 125 VDC source comes from that you want to supply, it's not possible to say what the implications would be.

It's also not clear why it is felt it is necessary to supplement (back up) the 125 VDC battery supply. Is there some history of loss of the 125 VDC battery supply to the control system?

Many sites with Speedtronic turbine control systems have opted for some kind of AC-to-DC converter as a "back-up" source to the control system. This provides a false sense of security in that site personnel believe they can continue to run the turbine in the event of a loss of the 125 VDC battery--which is extremely dangerous, since the 125 VDC battery usually provides the power for the Emerg. L.O. Pump in the event of a turbine trip and loss of station AC. Yeah, sure, the control system won't trip the turbine if the 125 VDC battery is lost, but if the condition isn't resolved quickly and the unit is running and there's no 125 VDC battery to power the Emerg. L.O. Pump--then we're talking about possibly wiping the bearings and damaging the shaft bearing journals on a turbine trip. (This HAS happened--and the site<b>S</b> (plural) HAVE insisted that the turbine should not have tripped, or should not have been shut down, because the control system didn't trip when the 125 VDC battery was lost. Their [erroneous] contention was that they believed that because the control system didn't trip when the 125 VDC battery was lost they believed the "back-up" 125 VDC source was capable of powering the Emerg. L.O. Pump in the event of the loss of the 125 VDC battery.)

About the only thing a back-up 125 VDC source for the turbine control system should be expected to supply is to power the control system during a station loss of AC event and turbine trip so that conditions (bearing metal temperatures in particular) can be monitored during the loss of AC, and that when the station AC gets restored the unit can be quickly put on cooldown ("turning gear"; ratchet; etc.). If the 125 VDC battery is lost even if there is a back-up 125 VDC source operations should shut the turbine down (if it's running) if the 125 VDC can't be quickly restored.

Again, you haven't provided all of the details of the 125 VDC source, nor why it is felt this is a prudent modification. And, unless the back-up 125 VDC source for the control system can also power the Emerg. L.O. Pump in the event of loss of station AC during a turbine trip then this is just a false sense of security.

If there is a history of problems with the 125 VDC supply <i><b>to the Mark VIe</i></b> then the prudent course of action would be to resolve this issue.

Finally, if you decide to implement this modification, you need to be aware that the 125 VDC source you will be connecting to the JPDF must be floating--that is, ungrounded, <b>and without any ground detection circuitry of its own.</b> If the source has it's own ground detection circuitry it will interact with the ground detection circuitry of the JPDF/Mark VIe and cause nuisance and erroneous ground alarms. The 125 VDC source should be clean and free of excessive ripple (a 125 VDC batter charger output without a 125 VDC battery has a LOT of ripple; the battery acts to smooth out some of the ripple from the charger). There have been problems with "direct" 125 VDC sources with dirty outputs and excessive ripple causing problems with Speedtronic power supplies and cards (and network switches and I/O Packs in the case of the Mark VIe).

And, proper education of operations (operators AND their supervisors) is also required so that appropriate action can be taken in the event of loss of the 125 VDC battery supply.

Hope this helps!

 

Our frame 9E units are the opposite. We connect to the the direct input and the battery input is left vacant. No idea why, probably just from a different GE factory. Consistently inconsistent.

 

P.S. (Post Script),

I believe GEH-6721, the Mark VIe System Guide, has lots of information on the various power distribution cards and requirements. It's probably best described in the "Installation" section what the basic power requirements for the system are (in terms of voltage range and cleanliness (ripple)), but the card descriptions (usually in Vol. II) should also have some similar information.

Lastly, I neglected to add that there is probably diode selection of the two 125 VDC inputs to provide some isolation of the two as well as to choose one or the other for the power supply to the Mark VIe and it's components and functions (one of which is NOT powering the Emerg. L.O. pump motor). This should be available on the schematic descriptions of the cards--including the JPDF.

 

Thanks for response.

Presently 125VDC input supply is connected on battery point. We are facing of 125VDC voltage drop in Mark-Vie up to +40VDC on positive LEG P125vdc in stead of +65VDC during EOP stopped. Voltage dropped for miliseconds, after normalised +65VDC. But at same time battery charger supply remains same +65VDC at Mark-Vie battery input terminals (at MCB input).

So also have DACA provision in our system 230VAC-115VDC. Checked same test on DACA by isolating the power supply, no voltage dropped observed.

So we are questioning on JPDF battery point circuit diagram. So we want to connect this battery input supply to direct supply point.

Our 125VDC supply is floating supply. Kindly guide us, can we connect on direct supply for test purpose & what will be implications.

Regards,
Vimal Gupta

 

Hi..

In your system JPDF card is installed or any other card installed.
In your system DACA AC-DC convertor unit is installed or only 125VDC single supply is installed at direct terminals.

Kindly confirm.

>Our frame 9E units are the opposite. We connect to the the
>direct input and the battery input is left vacant. No idea
>why, probably just from a different GE factory. Consistently
>inconsistent.

 

I thought this was familiar, and on researching the control.com archives I can see this has been discussed previously. Is the application code in the Mark VIe "exercising" the Emer. L.O. Pump on every START? And is the Mark VIe experiencing problems when there is a momentary (200-400 milliseconds) dip in the positive DC supply? What is the issue, specifically?

Why hasn't BGGTS (BHEL-GE Gas Turbine Services) resolved this problem? What has been their response?

I reiterate that when a DC contactor (such as is used in an Emer. L.O. Pump starter) opens there is an inductive kick. And, in the typical GE-design Emer. L.O. Pump starter, the negative leg of the 125 VDC supply is directly connected to the motor (not through a contactor), and the positive leg of the DC supply is switched through a DC contactor. Some DC contactors have suppression on the poles; some don't. What's so different about this installation/application that is causing these problems?

GE-manufactured DACAs are legendary for causing more problems than they solve. They DO NOT filter spikes and dips on the AC supply, and in fact, can amplify their effect on the DC output. They are really very crude AC-DC converters--again, with NO filtering. So, if the AC supply to the DACA isn't clean then the DC output of the DACA will not be clean, and can cause even more problems.

It's now clearer what you're trying to "resolve" but it's not at all clear what problem is being caused by the momentary drop in positive supply voltage. It's also not clear if this is a control system retrofit (a Mark VIe replacing an older control system) or a new unit installation (a new turbine-generator supplied with a Mark VIe). And, why is this a problem at your site--because I've not run across this complaint from any other site with Mark VIe. There's something about the installation--as you have previously noted there was sparks and arcs during the original commissioning--which is causing weakening failure of the I/O packs and printed circuit cards.

Perhaps it's the spike you're attributing to the opening of the Emer. L.O. Pump contactor. Has anyone looked at the DC contactor poles/construction as the potential source of the problem? Has anyone tried replacing the DC contactor? Has the wiring been meggared between the started and the motor? Have the brushes/brush rigging/field coils been analyzed (visually and electrically) to be sure there is no problem with the DC motor components?

I said it in previous responses to your previous posts--there's something amiss with the installation of the Mark VIe at your site. Not being there, it's not possible to say precisely what it is--but there's definitely something not right. I have seen this with Mark IVs, Mark Vs, and Mark IVs--when they are not properly installed and commissioned--which includes a review of the wiring drawings and wiring practices used during installation and commissioning--then these kinds of "intermittent" and nuisance problems occur, and they can be quite maddening.

It's usually a grounding/earthing issue, and if the Mark VIe is an upgrade/retrofit of an older control system on an existing unit then it's very likely that there is only one earthing pit (ground system) in use at the plant and that means the instrument earth and the functional earth must be jumpered together to the single earthing system. If the plant is new and was built with two earthing pits/grounding systems, the Mark VIe earth bars must be separated and independently connected to the appropriate earthing pit.

The problem with the latter (newer systems) is that many construction electricians and their supervisors don't understand the two earthing systems--and inadvertently connect motor earths to the instrument earth, and connect instrument earths (transmitters, usually) to the functional earth system. I've measured the voltage between the two earth systems on some sites and found as much as 25-40 VDC and as much as 10-30 VAC between them. And there should be NO potential difference. This causes lots of problems--not only for the Mark VIe, but also for other control systems and devices in the plant.

And, rectifying this issue is virtually impossible after the plant has been commissioned. The only thing that can be done for the Mark VIe is to disconnect one earth bar from the earthing pit and jumper the two earth bars together to the other earthing pit. Most I&C people will SCREAM when this is recommended or attempted, but when it's done, the intermittent problems go away--magically. When the two earths have no potential difference, the system(s) work much better. Of course, if the plant is prone to lightning strikes, this doesn't work very well during/after a lightning strike--but then it works just fine all other times. But, correcting all the improper construction wiring practices is difficult if not impossible on a running plant.

To sum up, if you want to connect a DACA to the "direct" input, there probably won't be any issue with that. But, if the AC power supply to the DACA isn't clean, then expect there to potentially (likely) be other problems. (I've seen very poor inverter outputs which had lots of ripple and spikes used to supply DACAs problems on the DC output--bad problems in Speedtronic control panels.)

I think you're trying to mask one problem and possibly creating other problems in the process. There's something amiss with the Mark VIe installation/application, and this isn't likely to resolve the underlying, root issue(s).

I wish I could be of more help, but it's not possible not being able to see and analyze the installation/application. In general, the Mark VIe is pretty robust and reliable--as long as proper installation and commissioning practices are followed, and good on-going maintenance practices are also followed. There have been cases over the years of extremely poor construction practices and bad commissioning practices causing intermittent, long-term operating problems--but that's not really a Mark VIe problem. If it's not installed or commissioned or maintained properly, it's not going to be very reliable in the long run.

I sense--and empathize with--your frustrations. But, trying to provide help for a case like this over a World Wide Web forum is virtually impossible. We just don't have--and can't get--enough information to be of much help. With all of the issues you've raised over the last couple of years it's clear: a knowledgeable person needs to go to site during a maintenance outage and be afforded the time to analyze the installation and make recommendations. I don't see any way we can address these issues on an issue-by-issue basis given the multiple failures and problems you are reporting in multiple control.com threads. It's pretty clear--there is some common issue or issues that are contributing to the multitude of problems, but without being able to be on site to help with inspecting and analyzing them it's virtually impossible (no pun intended) to help via this electronic medium.

 

Emergency stop contact inverted action is happening on low voltage dip in Mark-Vie during this momentary time limit (Physical emergency push button contact is ok).

And subsequently GT trip command actuates on emergency stop contact actuation. Our Mark-Vie system & gas turbine Frame-V is totally new installation by BHEL in last year. Two separate earth pit was made & connected separate bus bar for functional as well as panel earth. Kindly tell me again how i will check earth pit connection wiring is ok or not. Electrical team has checked DC contactor & their observation is DC contactor is ok.

I have one doubt; let i assume problem in DC contactor, why voltage is not getting down at the terminal of mark-vie input supply positive leg with respect to ground? Even we have checked with CRO & set resolution time is 20ms. It is coming +68VDC voltage. If problem in DC contactor, it should be get down.

One more observation is: DACA output is 115VDC and battery charger output is 125VDC. When voltage is getting down through battery charger, DACA system is not take over. What is role of DACA system, when it will come into picture? Only when 125VDC battery charger supply totally cut off then DACA will comes into picture.

 

VKGUPTA,

>Emergency stop contact inverted action is happening on low
>voltage dip in Mark-Vie during this momentary time limit
>(Physical emergency push button contact is ok).

I don't have a copy of GEH-6721 to refer to at this writing, but you would do well to look at the circuit schematic for the E-Stop inputs to the TREG (if I recall correctly) and where the voltage for that circuit is derived. Also, as has been documented in other related threads on control.com, if the wiring for the E-stop P/B circuit is NOT twisted, shielded pair wiring with the shield drain wire(s) properly grounded along the length of the circuit then DC voltage spikes on nearby wiring will cause problems with this circuit. Of course, the push-button contact isn't changing state--but something is causing the voltage in the circuit to change and the circuitry on the input card to interpret that change as an open circuit, resulting in a trip of the ETR relays. I've seen unshielded, twisted pair wires used for this circuit cause problems, and when untwisted wires are used for this circuit and they are run in wire channels/troughs with high-voltage wiring they usually almost always result in issues with this circuit.

Unfortunately, GE Salem doesn't get enough proper data and feedback about this condition and therefore doesn't acknowledge any problems with the circuitry.

But, by routing the circuit wiring such that it doesn't run in close proximity to high voltage wiring (125 VDC) and using properly grounded twisted, shielded pair wiring the issues can be worked around. So, this is again, likely an application issue--the packager of the Mark VIe is not using proper wiring practices for this particular circuit.

Many control system packagers are using IEC-rated contactors for motor starters, and while they are perfect for many applications they are not for others. I would still suggest that this is also part of this problem--an application problem: using a marginal piece of equipment for the Emer. L.O. Pump motor starter contactor. Again, the typical wiring for most GE-design heavy duty gas turbine Emer. L.O. Pump motor starters directly connects the negative leg of the 125 VDC supply to the DC motor, and switches the positive leg of the 125 VDC supply using a DC contactor--which should be properly rated for the expected inductive kick which will occur when the contactor is opened. In my experience, some smaller IEC-rated contactors don't have the physical gap (space) and arc-suppression capability for this application. You haven't provided enough information about the contactor used for the application at your site, but it is strongly suggested you work with BGGTS to understand if the contactor used for the application is properly sized/rated for the DC motor provided for the Emer. L.O. Pump.

Again, refer to GEH-6721 for details about the DC supply input circuitry for the two possible DC inputs and I believe you will see that there is diode selection, meaning that the higher of the two supplies will power the Mark VIe and control system. They don't "share" the load, the higher of the two provides the power. Without being able to refer to the schematic drawings.

I believe this problem is related to several application issues: less-than-standard wiring practices; poor wiring signal level separation/routing; poor component selection. It may even be that some of the 125 VDC discrete (contact) input wires are routed with the Emer. L.O. Pump motor power wiring and when current flow through the power wiring is interrupted there is induced voltages in the discrete input wiring causing problems. For years, GE provided documents describing strongly-suggested signal level separation and wiring/routing practices for use in building gas turbine power plants, but that seems to have stopped in recent years. Expected current flows as well as voltage levels all play a large role in determining how wires must be routed between control system and field junction boxes; it's not enough to lump all "high-level" wires into a single conduit or cable.

As for grounding system integrity, that would take a reference book-sized volume to detail. ONLY control system wiring and control system device wiring and grounds should be connected to the instrument earth. ONLY power system component and protective grounds should be connected to the safety earth system. It's quite common for untrained and poorly supervised electricians to just "ground" a device to the closest ground point--regardless of whether or not it is the appropriate ground, especially in the field, where the instrument ground system is not usually routed/available. Usually, the instrument earth ground "pit" is smaller and ground connections are only made available near control rooms. If control system field devices are improperly grounded in the field, then there can be problems with grounding potential differences. Again, reviewing this takes a lot of time and patience and a good understanding of earthing systems.

I'm not saying these are the ONLY causes of the problems you are describing, but I am saying that troubleshooting and resolution of problems is sometimes (many times) a process of elimination. Just looking at a component and saying there's nothing wrong with it is not sufficient in many cases to eliminate that component as a possible cause. And, so, too with the wiring--just looking at the wiring and saying it's new and not damaged is not sufficient to eliminate it as a possible cause of a problem or problems. Most nuisance and intermittent problems such as you are describing can be traced--with diligence and effort--to poor wiring practices, be they in the control system or in the field. Signal level separation is critical to any control system--and, in fact, most Speedtronic turbine control systems are notably more tolerant of poor wiring practices than other manufacturer's control systems (PLCs; DCSs; etc.) just because the designers recognize that poor construction practices can cause problems and so they make an effort to try to counter some of those potential problems.

Using a DACA isn't likely to solve these problems you're describing. Only by diligently working to review wiring practices and component selection can you hope to correct the problems.

Best of luck with your problem resolution. I don't think there's "one" fix which can be applied to the problems you're experiencing based on the information provided in this and other posts.

 

is SIL REVIEW necessary after certain period?

 

Thanks for response.

Presently 125VDC input supply is connected on battery point. We are facing of 125VDC voltage drop in Mark-Vie up to +40VDC on positive LEG P125vdc in stead of +65VDC during EOP stopped. Voltage dropped for miliseconds, after normalised +65VDC. But at same time battery charger supply remains same +65VDC at Mark-Vie battery input terminals (at MCB input).

So also have DACA provision in our system 230VAC-115VDC. Checked same test on DACA by isolating the power supply, no voltage dropped observed.

So we are questioning on JPDF battery point circuit diagram. So we want to connect this battery input supply to direct supply point.

Our 125VDC supply is floating supply. Kindly guide us, can we connect on direct supply for test purpose & what will be implications.

Regards,
Vimal Gupta

Is this issue resolved? If yes what was the learning and how it was resolved?