Gas turbine control system MK-VIe input power supply redundant


Thread Starter

Vimal Gupta

We have gas turbine with mark-vie control system.

Presently 125VDC input power is given to control system through single feeder 32A. It is connected to JPDC card JD1 connector through CPF filter and LPFI card. We have 125VDC extra feeder 32A and want to provide redundant power supply to control system to avoid turbine trip in case of one power failure. We checked at JPDC card and found it have two 125VDC input provision which is JD1 AND JD2.

At JD1 already connected and now want to connect at JD2 redundant power source though extra CPF but problem is for LFPI card supply redundant. Mind you, We can not connect DACA because we have UPS floating voltage and DACA needs 110VAC.

Kindly suggest
How will provide dual power source LPFI.

2. Any circuit diagram suggest for dual power for control system through extra feeder.

3. If we do not connect dual power to LFPI card then what will happen in case of existing power failure of LFPI card; running GT will trip or not.

4. What is role of LFPI card in turbine.

5. If we make one bus bar for both feeder with positive and negative wire looping and connect to LPFI card, is it possible.
vimal gupta,

It seems more appropriate to answer question 4 first and then refer you back to your drawings--and to the very fine Mark VIe System Guide, GEH-6721, Voll II, Power Distribution section.

LFPI stands for 'Legacy Fire Protection Interface' which is typically only used in retrofit (upgrade) applications. It is intended to provide interface functionality for older Speedtronic turbine control systems which used Speedtronic components as part of the fire detection and fire extinguishing agent discharge systems.

Typically, the LFPI is (or should be) wired in parallel to the Mark VIe 125 VDC power supply, not in series with the 125 VDC power supply. So, if you were to connect a 125 VDC source to JD2 it sounds like <b>from the information provided</b> that it (the LFPI) is connected in parallel, and downstream of the incoming 125 VDC power supply inputs--which is how it should be connected.

Since the LFPI is integral to the fire protection system, it is very important to the turbine protection scheme. If the Mark VIe was an upgrade from a previous control system the Wiring Documentation drawing should show the components that are connected to the LFPI, and how the LFPI is connected to the Mark VIe.

Now, to the subject of connecting a "second" 125 VDC source to the JPDC. Refer to the Power Distribution' section of Vol. II of GEH-6721, the Mark VIe System Guide for details of the JPDC 125 VDC input. I don't have access to the document at this writing, but the JPDC needs to have a "high-select" diode to use the higher of the two inputs--and I don't recall if it does or not.

Next, when two 125 VDC sources are connected to the JPDC then any grounds on either source will "appear" on both sources. And, both sources MUST be free of any ground reference circuits/components. So, if you have an independent 125 VDC source that powers other systems and devices, any ground on that system wil be detected by the Mark VIe. Making troubleshooting grounds that much more difficult.

So the second 125 VDC source MUST NOT have its own ground reference/detection circuit, <b>and</b> if it powers other systems and/or devices a ground on either 125 VDC will be detected by the Mark VIe.

A LOT of people (mistakenly) believe a Speedtronic control system will ONLY detect grounds on devices connected to the Speedtronic--and that's not true. It detects grounds on any circuit or device powered by the 125 VDC source(s). And so if a second source is used and that source powers other system and/or devices the Speedtronic will detect grounds on any system or device powered by <b>BOTH</b> sources.

Many people want to use a separate breaker from the same battery as a second source, and while that protects against a single breaker failure it doesn't protect against a loss of the battery. Which is really pretty unlikely anyway--if proper battery maintenance is routinely performed and any grounds are quickly resolved.

So, have a review of your Mark VIe Wiring Documentation drawing for more details about the interconnection of the LFPI to the Mark VIe and the fire protection system, and have a read of the schematics of the JPDC in the Mark VIe System Guide. Also, consider where the second 125 VDC source is to be provided from, and how that my affect the ground detection systems of both sources as well as the ground trulblesbooting of two systems connected together at the JPDC.

Also consider how often your site has experienced a loss of 125 VDC to the Speedtronic in the past--and also consider the circumstance(s) of the failure(s), and if the failure(s) could have been prevented by better maintenance practices and/or foresight.

To answer the next question, No. To the best of my knowledge it's NOT possible to isolate two separate 125 VDC systems and still parallel them at the JPDC. I'm sure it might be possible, but the cost of components and engineering would likely be prohibitive.

I think that covers the basic questions, and the future question.