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Participant

Join Date: Jan 2016
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Why Use Bently Nevada in Tandem with Mark VI?

03/27/2016 5:29 AM

The gas turbine at my combined cycle power plant uses the Mark VI as its control system. It also uses the Bently Nevada 3500 for vibration monitoring purposes. I have reviewed the Mark VI control logic and it seems just fine on its own i.e. the Mark VI is all the turbine needs for all of its control needs. It also happens to receive direct input from the vibration probes and speed pickups so I don't see why the Bently Nevada is needed at all. I understand that the Bently Nevada 3500 is used for advanced vibration monitoring applications which cannot be realized with Mark VI alone i.e. phase analysis etc. but it also seems to incorporate relay based logic for certain alarms as well.

This is a little confusing for me because on top of it all, we also have ABB DCS tending to the monitoring and control of the turbine. I have yet to review the logic on the DCS but I am sure it is only used for stuff other than the gas turbine i.e. the HRSG, alarms etc.

I guess the Mark VI is the primary controller for the gas turbine. The relay logic implemented on the Bently Nevada is only to provide a bit of redundancy/back-up in case of emergency. Is this a fair assessment?

Thanks.

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#1

Re: Why Use Bently Nevada in Tandem with Mark VI?

03/27/2016 2:43 PM

The Bently Nevada controls may be for other components like pumps and motors as part of the control strategy, it may also present data info at specialized access points....

http://www.ccj-online.com/4q-2014/control-systems-cogen-plant-in-the-oil-patch-gets-a-controls-makeover/

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#2

Re: Why Use Bently Nevada in Tandem with Mark VI?

03/28/2016 1:02 AM

The Bently Nevada is used solely to monitor the vibration on the engine, high vibrations will trip the turbine, the Mark VI system to control the engine and the ABB DCS to control and monitor all the auxiliaries for the HRSG boiler feed pumps, steam valves etc.

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#3

Re: Why Use Bently Nevada in Tandem with Mark VI?

03/28/2016 8:57 AM

Does the Bentley have any S/D controls? Are the output relays shutting anything down directly or do they just tell the Mark VI to shut things down? You seemed to suggest that the Bentley is keyed to the shaft rotation and can see much finer detail than the Mark VI, maybe it is there for just that reason. The next question would be can anyone drag data out of it if you need to. I agree that the DCS is just there to handle the auxiliary stuff; it would be rare for GE to let somebody else control their turbine.

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#4
In reply to #3

Re: Why Use Bently Nevada in Tandem with Mark VI?

03/28/2016 10:00 AM

I am pretty certain, the Bentley Nevada equipment does not have SD capability, however it does transmit vibration readings to the Mark VI system, and that will produce a shut-down in high high limit.

I am just waiting for turbines to all be equipped with the latest active vibration suppression technology in the bearings (mag/other bearings that are actively controlled), and see how that "flies". I heard about this technology being tried a few years back.

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#5
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Re: Why Use Bently Nevada in Tandem with Mark VI?

03/28/2016 11:30 AM

I was at a pump facility recently where they ran a bunch of stuff including bearing temperatures into the Bentley and then ran a signal out of that direct to the Multilin on the switchgear bypassing the PLC and shutting down the pump. It wasn't clear to us why they did that other than to make it difficult for us to troubleshoot what the hell was going on in the unit.

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#6

Re: Why Use Bently Nevada in Tandem with Mark VI?

03/30/2016 10:41 AM

It's called "defense in depth", you can't rely on a single point of measurement to protect your equipment. The Bently Nevada is there to provide an independent, albeit redundant, monitoring point. Since it's a dedicated unit it's also faster and more reliable than the multi-tasking Mark IV, and can provide a calibrating/comparison signal to check the "sanity" of the Mark IV's readings; if they're not reading the same then it's time to find out why.

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