Salt River Project Power (SRP) had a mystery in its transmission network – some disturbances were unexplained. By installing a COSI-CT and my newly-developed VT, and a GE-Reason recorder at the Perkins Substation, GE would get some valuable operational data from a local substation, and SRP would find out the cause of the problem.
It would be great to have ongoing telemetry from our equipment in the substation, but of course SRP cannot allow another company like GE to have access to its computer network. I was asked to find a wireless way to communicate with the system.
I asked if SRP would allow us to put up an extra antenna – they were already installing a GPS antenna for us – and they agreed. So I undertook to do a quick survey of potential means of communications, and ended up with a cellular phone router – one of the Multi-Tech MTR-H5 family devices.
I was going to get a SIM through GE Corporate, but the required effort & justification was huge. My manager needed this done quickly. So, I went down to my local T-Mobile store and got a “data & SMS only” SIM (intended for tablets etc.). It was only US$10 a month – which, because I was travelling so much, just put on my expense account thereafter.
Then I tried to contact the router – but couldn’t. Apparently incoming connections to T-Mobile’s wireless devices isn’t generally allowed. This is probably a good thing!
We were also installing a GE DAPserver, which would serve as a data concentrator. I dug around a bit and got root access to the DAPserver (no, it wasn’t easy because we were GE – they don’t give that information out!). I then created a Digital Ocean droplet and coded a continuous SSH connection from the DAPserver to the droplet. There were actually two connections – one by IP address, and one by dynamic DNS hostname – just in case one failed. Each one had reverse traffic tunnels brought up, that would link to the various local devices, like each COSI-CT and the recorder.
Well, it turned out that the COSI-CT only provides a serial interface to its administration functions. The process data comes out on an Ethernet link (generally fibre, but could be twisted pair), but the Management Processor interface is RS-232, ugh. So, I had to buy a Lantronix Xpress-DR+ 2-port serial-to-Ethernet gateway… which was fine.
In any case, it all worked well, in the end. I was actually able to log into the recorder and display phasors – although the link was relatively slow, and performance was poor. For text-based communications, like talking to the COSI-CT, it mostly worked fine. The COSI-CT Control Panel didn’t like the link, because turn-around latency was too slow. Well, Control Panel wasn’t designed for Ethernet either, but Scott Picker added this feature for me, but there was some complication in the negotiation of the link (possibly the original serial auto-line-rate detection) that caused it to drop every time. No matter, my little LINUX Test Tool worked just fine, and enabled me to read and write configuration values as needed.
Although it was clunky and slow, it did work – so I considered it a success!