Hey Folks,

Just wondering if anyone has any info on nexus meters as they relate to generator control.

We recently upgraded our frame 7AE to include a nexus meter during a recent outage. Since, we've seen the machine drop load unexpectedly and even run itself offline. The short term fix has been to force DWATT 1 to read -5MW which I understand removes the nexus meter from the loop and leaves us running on the old transducer signal only, DWATT 2.

Has anyone had a similar experience or have you been required to troubleshoot a nexus meter in the past?

Thanks

 

We would need a drawing to assist.

Does the NEXUS provide PT/CT signal to your exciter?

Forcing dwatt should produce other alarms as well. dwatt 1 and 2 not agreeing should also cause alarms.

More info = better feedback.

 

Jeff, as curious one has stated, more info helps us provide better answers, and ask less/better questions.
Was this a controls upgrade?
If so, what was the old system, and what is the new?
Was there previously only 1 dwatt transducer and now there are 2?
Nexus meters were typically included with GE units starting in the 90's I think? In my experience they have been fairly reliable. Typical GE logic has both MW transducers coming into a hi select block, so it seems strange if this is a GE machine/GE Controls that the Nexus is driving the unit offline, unless it is somehow reading a higher value than actual. More info/details would be appreciated. I do not have any special troubleshooting skills for the Nexus meters, in my experience they typically work, until they die. At which time most people have never backed up the configuration file, and don't have a spare. Please write back.

 

Jeff, as curious one has stated, more info helps us provide better answers, and ask less/better questions.
Was this a controls upgrade?
If so, what was the old system, and what is the new?
Was there previously only 1 dwatt transducer and now there are 2?
Nexus meters were typically included with GE units starting in the 90's I think? In my experience they have been fairly reliable. Typical GE logic has both MW transducers coming into a hi select block, so it seems strange if this is a GE machine/GE Controls that the Nexus is driving the unit offline, unless it is somehow reading a higher value than actual. More info/details would be appreciated. I do not have any special troubleshooting skills for the Nexus meters, in my experience they typically work, until they die. At which time most people have never backed up the configuration file, and don't have a spare. Please write back.

Thank you MIKEVI,

Although I have used the software provided by the vendor to configure both the Shark and the Nexus, I have never backed up the configurations on several of my 7EA.

Looks like I have some work to do.

 

Curious_One, you are definately welcome. Don't want to get too far off from the OP, but I have found as with other products getting talking to the device is half the battle sometimes. The older Nexus being serial only, getting a backup of the configuration guarantees the unit will last forever, and takes only a few minutes. Take care.

 

Hi guys,
Thanks for the reply. The nexus meter is connected to the generator PT and CT- which is why I've been told we cannot replace it while the unit is running.

We do have an alarm in G1.LDWATT_ALM "megawatt transducer signal trouble" and an alarm for "signal forcing enabled" which I assume are both related to having forced the output of DWATT 1 to -5MW.

The installation was supposed to be an upgrade- not sure exactly why a nexus meter is better or worse than the redundant transducers that we had initially. (if you have any thoughts I'd be interested to hear them)

As for the signal, I assume it must feed in to the FSR or megawatt controller since it was able to run the machine off although I'm not sure if it is involved with excitation.

Unfortunately I do not have a diagram or any vendor specific info on this piece. I'm honestly not even sure what a 'nexus meter' is

Thanks for any info you can share.

Cheers

 

https://www.electroind.com/products/nexus-1252-energy-and-power-quality-meter/

 

Can you provide any more detail on how the signal from the nexus meter relates to the control of the unit? Is it just generator load control or is it part of the excitation loop as well? Also, is this something that would vary between sites or is it generally the same between units?

 

Without generator protection drawings and control system information, EVERYTHING I share is just a guess.

My best GUESS is that the NEXUS is connected to your generator PT and CT and is producing an 4-20 ma output(MW) that is connected to your turbine generator control system.

Since your post refers to dwatt1, I am guessing that the NEXUS output is DWATT1. By forcing dwatt1 you are basically removing it from the compare loop with dwatt2. If dwatt2 fails, the unit will not be able to produce MW.

As far as the exciter, I have no idea what model/type of exciter you have. I have encountered EX2000 exciters that receive signals from the NEXUS rather than being connected directly to PT/CT.

 

Thanks for the reply- you're right about the forcing removing DWATT 1 from the loop, as MIKEVI mentioned above there is a high select block in there that chooses which transducer controls the machine.

I'm still trying to wrap my head around why a malfunction with the nexus meter ran the machine off- unless it holds last value or something when it loses indication and the control system was trying to lower generation at that time? In your experience, how does the nexus meter react when it loses indication or cycles power? Does it drop out or does it fail high/low? I suppose if it failed high it would explain how we ran off as well.

 

Thanks for the reply- you're right about the forcing removing DWATT 1 from the loop, as MIKEVI mentioned above there is a high select block in there that chooses which transducer controls the machine.

I'm still trying to wrap my head around why a malfunction with the nexus meter ran the machine off- unless it holds last value or something when it loses indication and the control system was trying to lower generation at that time? In your experience, how does the nexus meter react when it loses indication or cycles power? Does it drop out or does it fail high/low? I suppose if it failed high it would explain how we ran off as well.

The answers you seek are in the NEXUS configuration file.