Big Fault at Power Transformer 550Mva

Switch it off, before all those MVArs become MWs and kill someone.

Look, your schematic shows exactly what the problem has to be. Do you see it now that I'm pointing at? Why can't you guys read and understand your own documentation?

get a network analyzer and lets look at the vectors

I bet it's running rather hot right now!

Odds ar you have a partial short circuit in one or more of the phases and it will need to be taken out of service and sent to whom ever built it in order to have it repaired.

More information is required.

1. "...leakage current at power transformer 280 ampere at 220kv side...", Please define leakage current

2. "...the transformer mvar loss equal 95mvar...", MVARs are never "lost", what direction are they moving, from hi to low or low to hi, similar for MWs

3. "...3 singel phase auto transformet...", Are they identical, same manufacturer, same impedance, how are they connected, what is the vector group, and most importantly, are they all set to the same tap?

4. Is this a new problem or has it always been this way?

5. What has changed about the network/grid that this is installed in?

Without seeing a SLD (Single Line Diagram) showing the loadflow analysis it is tough to know exactly what is going on, but a couple of things come to mind:

1. All three transformers must have the same tap setting,

2. Are you sure the vector groups are all the same,

3. Use an infrared camera to check all the connections, there may be a loose one that is radically changing the impedance of the group.

4. Get a PQA (Power Quality Analyzer) and check the harmonic content on both sides, high THD (Total Harmonic Distortion), especially third harmonics, may cause core saturation resulting in excessive currents and overheating.

5. What kind of heavy loads are nearby (electrically)? Things like faulty rectifiers on smelting operations can cause massive harmonics.

6. Of course you're sure that your instrumentation/metering CTs and PTs are correctly wired.

That's for starters, once you report back with the answers we may be able to get more specific. No response = no further assistance.

At any voltage I would never call 280 amperes a "leakage" current. An unexpected added or unbalancing load, maybe.

If this unexpected path is a purely resistive load (most are) then the 60 megawatts should be drying this out or making it glow pretty darn fast.

Someone needs to do a real load flow analysis of your system, and determine what is going on in the 500kV and 220kV systems. The problem is probably NOT in your transformer. The MVAR you see in the transformer's metering is probably what is actually there, due to conditions at the generating plant you mentioned (they are likely "exporting" VARs), the lengths and configurations of the transmission lines, other infeeds, and system loads. You cannot look at the transformer in isolation from the rest of the system.

You mention what the MVAR load of the transformer is, but you did not tell us what the actual MVA load is. 50C winding temp and 40C oil temp may be normal for the units if they are fairly heavily loaded and the ambient conditions are hot. Those temps shouldn't be a problem for the transformer to handle.

Since they are single-phase autotransformers, they are pretty much constrained to be connected in a wye configuration, and if you were measuring "leakage" (= neutral??) current, that would suggest that your phase angles are not neatly 120º apart and you probably don't have equal loading on all 3 phases. So as I said, get someone qualified to do a system analysis.

This is a plausible scenario. Leakage current is actually neutral current. If the added neutral current is because the reactive loading of each phase is different then strategic application of capacitors might help but if the neutral current is due to non-linear loads causing harmonics then live with it.

You have a very plausible guess about the actual system conditions. Unfortunately it is only one of many possible actual scenarios. I'm tired of playing twenty questions with an OP that does not understand the vernacular.

One more thing, you haven't specified how (or if) the network and these transformers are grounded.

It says how it is grounded right on the paperwork.

Power Plant Consultancy - Business Directory - IndiaMART

Please point a Webcam at it, and publish a YouTube when something happens.

Can you help? I have this strange humming glow in our main power substation and everything is too hot to get close to now.

Any ideas? Here is video and BTW I am senior electrical engineer for our power distribution network.

Substation noise and heat issue.

Don't worry, the problem will quickly resolve itself.

<BOOM>

_{Jack - Assuming this is actually a homework and not a serious question}

Then why has nobody turned this OFF yet. A fault of more than 10% of a massive transformer will usually quickly reveal itself with a bang.

The very few questions that you have tried to answer from us clearly shows that you do not know enough about power distribution to help yourself or us. This forum cannot provide an undergraduate education in a few hours. We cannot trust the information you've given us is accurate. The only information you give us is poorly spelled and improperly punctuated. It looks like you are not taking this situation seriously, why should we take it seriously.

From my perspective I see only three explanations that agree with the flimsy information provided:

1. Your instrumentation is failing in some fashion. The scenario your instrumentation is providing is not what is actually happening.
2. You misunderstand what the instrumentation is telling you. The scenario you portray to us is not the scenario that is actually happening.
3. This is a scholastic question. You are not doing well in your studies and cannot even explain the question well.

If Siemens has been called in to solve this problem, let them do their job. They are a highly qualified manufacturer and engineering firm. They know power distribution problems.

tcmtech said: "Odds ar you have a partial short circuit in one or more of the phases and it will need to be taken out of service and sent to whom ever built it in order to have it repaired."

Agreed.

RAMconsult: I'll bet OP answers none of your questions. We are beating a dead horse here.

Lets see: 280A * 220 kv = 61.6 MVA "leakage current" enough to power a small city. For comparison, our local power plant here is 25 MVA.

So, has it been turned off yet?

Check your lightning arrestors and surge protection.

More than likely one or more are breaking down or have faulted.

I'm not sure why everyone is berating Haysam, he has a real problem the details of which are buried in some of his posts that have been OT'd. We still don't know what made him aware of the problem (overheating, inconsistent meter readings, etc.), but he did have the foresight to measure the neutral current at the source, and 280 amps is not trivial.

The reading alone only tells us that something is way out of balance in his system, but it doesn't tell us what. It could be strictly harmonic current because of the load, it could be a poorly made up connection, it could be largely capacitive or inductive current (again due to the nature of the load), it could be poor system-wide grounding practice, or something as simple as some designer putting all the resistance heaters and lighting on one phase, or an internally faulted machine, etc. But one thing is certain, without more detail no one here will be able to do more than guess what it is.

Haysam, if you want help, provide answers. The same questions I asked you earlier are the same ones I would have expected you to answer before I got on a plane to solve the problem in person. Ultimately you are going to have to provide them to the person you hire to help you out of your situation, and the answers may help you until then.

I don't know about the others but I'll tell you why I am berating him. The only people who should work and troubleshoot massive power distribution devices are trained professionals. Trained professionals that get stumped with a problem should turn to a trusted colleague and not an anonymous forum to help them.

You are absolutely correct that 280 amperes is not trivial. Neither is a quarter to a half a million volts a trivial concern. It is only a plausible guess that implies that the 280 amperes of current is on the neutral. We do not know if this neutral current comes from one transformer to another, from the combined three transformers out to the load, or if it is from the three transformers to earth.

The magnitude of power present in these transformers requires somebody that can analyze the data, system and provide concise explanations on the configurations. Maybe Haysam can clearly communicate these conditions in another language, he hasn't in English. From the English he's provided he should not be inside any power distribution switchyard or control room.

Red, I certainly agree that there is nothing trivial about what is going on there, and I share your concern for his safety, you'll notice that I asked him to do things that do not put him near the transformer. On the other hand he has access to an area that only authorized (not to be confused with well trained) personnel should be in so we have to assume some management types know (or think they know) what he is doing.

Unlike another poster who climbs poles with a clamp on ammeter in hand and reads the neutral current, I think Haysam finds himself with a problem that he has never faced before, but at least he recognizes it as a problem requiring a solution. Again, as my last post noted, he really needs local onsite expertise to help him out. His lack of responsiveness hopefully indicates he has found that person, and maybe he'll let us know what the problem was.

I agree with your assessment but with English not being his native tongue I'm very uncertain of the communication between him and us. As such, our best intentions can just as easily lead him astray as solve this mystery.

Again, has it been turned off yet?