In our utility, we do functional flow tests on the transformer deluge while the transformer is energized regularly. These are tailrace deck mounted generator step up transformers 13.8kv (in enclosed iso-phase bus through the wall) to 138 or 230kV depending on the plant, exposed aluminum bus...
Sure. We have protection schemes that will trip off the GSU that don't have anything to do with electrical quantities on the bus. So more often than not, we will have transformer trips that have nothing to do with electrical faults whatsoever.
Oil samples are standard for us, but electrical testing is only done if the transformer has been subjected to a through-fault, or if recordings from the TFR lead us to believe testing is warranted. Following a through-fault, we do ratio, winding resistance and capacitance bridge.
Edit: Saying...
I will also add that I likely wouldn't recommend an attempted re-sync to the grid following a protection trip like this.
Excessive VARs out (over-excitation condition) had a basic worst case scenario of overheating and insulation breakdown over time, possibly volts/hertz damage.
Excessive...
Faulty PT signals incorrectly indicating a higher-than-actual bus voltage, faulty AVR retarding the firing pulse too much or external system conditions. Narrow it down to inputs, outputs, or control/feedback issue. Our generators regularly take in VARs as part of system operating conditions...
We use the Anton Parr and the Alber analyzer. We have a visual inspection weekly as part of our weekly plant checks, voltage checks monthly, integrity inspections (essentially a more thorough visual) every 3 months. Full maintenance (SG, analyze) annually. We do equalize on demand (only if...
Palletjack, yes, oil level in conservator tank low, main tank still full (above bushing turrets and gas relay piping). In our case, these are generator step up transformers for ~100MW units on a tailrace deck in Northern Manitoba. Significant heat cycling when online/offline. This has always...
Strange, it's our standard operating procedure to top up transformers while on line. Open the vent cap and throttle the flow into the conservator tank, ensuring pressure isn't being built up. The only time we ever had an issue was when a crew didn't open the proper vent and caused the unit to...
In our 12 100MW unit plant, four units have been rewound since 2009. The first one was the result of a core clamping finger breaking off and riding around the air gap, destroying everything. Three more units, built with the same materials and methods, have been rewound from 2014 until 2017...
We've done it before in exceptional circumstances, and the results were satisfactory. 100MW-rated hydro unit supplying a megawatt or so of loading between our hydro plant and the associated HVDC converter station. This was a 1 time event to perform tie-ins of a new HVDC bipole. I had my...
We use FRC/ARC flash rated clothing as per assessment, hard had, face shield, hearing protection, steel toe boots and rubber gloves. Procedurally, we are taught to identify escape routes in the event something goes wrong.
Thank you, waross.
A couple of points of clarification: This is a generator step up transformer. Primary side would technically be the low voltage winding, which is 13.8 kV. The secondary side would be the high side, 230 kV. Winding resistance measurements were being performed on the high...
So last night, I was speaking with Technician 2 again regarding this incident. He informed me that he was now questioning the integrity of the ground connection on the low side winding. X1,2,3 were positively bonded, but the connection to "ground" was simply a copper braid wrapped around a...
Thanks for the input so far.
A couple of points: I can understand a high voltage charge testing insulation with a high voltage megger. I've felt what a stator meggered at 5kV can feel like if you don't properly discharge it. The working voltage of the multiamp transformer ohmmeter is 30Vdc I...
