We have Mark VIe control system for Frame-6 Gas Turbine. The Mark-VIe has 125Vdc battery charger supply system along with DACA (DC to AC convertor) as redundant power supply.

During last start-up, while giving Crank + start command to Diesel Engine, a cell of battery bank failed due to heavy starting current of 88DS Motor & subsequently our charger got failed to supply the Mark-VIe. Even though the DACA was available as backup power supply with help of UPS, Mark-VIe panel took the shut down.

Surprisingly, the panel re-booted automatically after 1 hrs by taking power from DACA.

Also, we checked the successful change over from DC 125V to DACA in the past as well as after above incident & It is functioning properly.

Our queries are:
Why DACA did not cater the load in case of 125Vdc battery system failure?

How Panel Re-booted after 1hr of period with the help of DACA?

Your suggestion is most welcome to understand this dilemma

 

I welcome Mark-VIe user to provide the suggestion or answer to the problem.

 

MG,

I have started several times to write a reply, but it was just too long because there is just too much we don't--and can't--know about the configuration of the Mark VIe at your site. We would need to be able to examine electrical schematics and know what power supply cards are used in your panel to understand how this problem might have occurred.

We also don't know if the Mark VIe was provided with the unit when it was new, or if it was installed as an upgrade (retrofit) of an older Speedtronic system.

It has been my unfortunate experience that DACAs have not provided the back-up power that was intended--mostly because of incorrect configuration of the power supply to the DACA. You say it was tested previously, but--was it tested under the conditions you experienced when DC was lost? (And we don't know "how" DC was lost.)

Your post is unclear, because in the summary you say the battery "bank" failed (bank means a group of cells), and in the thread you say a cell of the bank failed. How did the cell fail? Did it cause an open or a short?

I have seen this exact problem of a failed cell causing Speedtronic power supplies to automatically shut off. The cell failed because of sediment in the bottom which shorted the plates together. When a high current is drawn (such as when the diesel starter motor is energized) the cell acted as a voltage "sink" dragging the entire bank voltage down below 90 VDC. Earlier Speedtronic power supplies were mostly designed and built by GE, and had special "crowbar" circuits to automatically shut them off when the DC voltage dropped below approximately 90 VDC or went above approximately 140 VDC.

Did your cell cause the DC battery to "open" and have no output?

Mark VIe panels typically use third-party power supplies (TRACO or Phoenix QUINT) and I don't know if they have similar crowbar circuits. Have you reviewed the information in GEH-6721, Vol. II, the Mark VIe System Guide, in the Power Distribution section to see if there is any useful information there about the power supplies provided in the Mark VIe at your site?

The Mark VIe processor cards are usually powered by 28 VDC from the third-party 28 VDC power supplies. I don't know if they have internal voltage detection that automatically shuts them off in the event of low DC input. If only the processors shut down, then the battery may still have been powering the panel. The drop-out-to-run relays may have all dropped out, causing most of the AC motor-driven pumps and fans to start which may have made it seem like the Mark VIe was "dead" but, in fact, it was not. We just don't have enough information.

Were the IONET switches and IOPACKs powered up when the Mark VIe seemed to be "shut down"? If so, then it's likely only the processors shut down but DC was available in the panel.

While it's correct to say the charger, when operating, supplies the Mark VIe--it does so "through" the battery. The battery acts as a filter, because most chargers have a very "choppy" and electrically "noisy" output which the battery "filters" and cleans up. GE does NOT recommend powering a Speedtronic panel by a battery charger WITHOUT a battery because of the poor DC voltage waveform.

Even if the battery charger output breaker tripped, that usually doesn't open the breaker supplying 125 VDC to the Speedtronic panel. So, was 125 VDC completely lost to the Mark VIe, or did the processors (UCCxs or UCSxs) just lose power?

GE also does NOT recommend putting the battery charger on Equalize when the battery is powering the Mark VIe, because the charger output is at or near 140 VDC and can cause problems for the Mark VIe. So, they recommend powering-down the Mark VIe when equalizing the charge on the battery.

I have seen many times where the UPS (or inverter) is improperly configured and connected to the DACA such that when AC is lost to the UPS the UPS does not switch to its internal battery to produce the AC for the DACA.

Most DACAs are connected to the "main" DC power distribution card by a cable with plug connectors at both ends. The AC that feeds the DACA is connected to terminals on the main power distribution card, and then is routed to the DACA through the plug connector/cable, and back to the main power distribution card through the same cable/plug connector.

When the Mark VIe panel "took the shut down" (which is unclear--do you mean it completely lost all power or just the main processors lost power?) and you say the DACA was available, did you physically measure the DC output from the DACA at the main distribution card terminals? The main DC power distribution card usually includes a diode to perform the selection between the 125 VDC battery and the DACA output, and it's usually possible to measure the DACA output at terminals on the card.

If power was lost to the Mark VIe such that all the drop-out-to-run relays dropped out, that means that a LOT of AC motor-driven pumps and fans all started and ran at the same time. Sometimes, when this happens the Aux. Power Transformer/Supply breaker trips on high inrush, and AC is lost to the turbine auxiliaries as well. Did this happen at your site?

When this kind of event occurs, regardless of whether the AC power gets tripped, people are usually frantically running around trying to, first, determine what the %$#&! just happened, and second, why all the motors started and are running, and if AC is lost, they're looking for torches (flashlights), and third, they're trying to shut off AC motors and/or restore AC. There's usually no one calmly gathering data--like, was there AC power to the DACA, and was there DC power from the DACA.

Did anyone measure the 125 VDC battery input terminals on the main power distribution power card to be sure there was no DC power coming from the battery? Was the 125 VDC breaker supplying the Mark VIe tripped? Or just the charger output breaker?

Someone needs to review the drawings at your site to determine what might have happened and how a similar condition might be prevented in the future. It's not likely that we will be able to do much to help you here on this site since we can't see all of the drawings and understand exactly what happened.

It would be great if you could reply with as much information as you have to the above questions. They are kind of "rambling", but again, there's an awful lot we don't know and was unclear from your post. I have tried to post as much relevant information to try to help with your post-incident analysis, but the most important questions are:

1) Did anyone measure 125 VDC battery input to the main DC power distribution card (JPDx) to verify that DC battery power was, in fact, shut off?

2) Did anyone measure the DACA DC output voltage to be sure it was not (or was) providing DC power to the main power distribution card?

3) Are you sure the ENTIRE Mark VIe panel was without power? Is it possible that the main processors shut down and then after a fashion reset themselves (kind of like a Thermal Overload Relay)? This would be a great question for GE....