The 230 kV/66 kV ratio is a bit higher than typical for autotransformers. That being said, it seems weird to have the 66 kV system ungrounded.
Many regions are eliminating tertiary windings on 400/230 kV autotransformers.
The GE publication The-whys-of-wyes provides good info on why to choose each configuration.
Your application also matters. Do you have a load, a generation site, or a mix of load and generation? Increased distributed generation is make wye-delta-wye transformers more attractive.
It would be atypical to have ungrounded wye PTs. It is common to have ungrounded PTs in an open delta configuration.
In certain cases grounded wye PTs are used on capacitively (i.e. ungrounded) systems. In this case the PTs must be rated for full LL voltage even though they are connected LL...
My utility specifies an allowable range for each size of transformer size when buying transformers. This allows us to then publish a table of max kAIC for customers to use in their designs. Here is an example:
When designing an installation, it is import for a customer to design for the worst...
No. The typically tests are done on will the transformer filled with oil. Oil is an integral part of the insulation system you are attempting to test.
The one exception I can think of is a sweep frequency analysis (SFRA) test to detect any damage that may have occurred when shipping the...
Substation yard rock has lots of gaps/texture, so it any measurement from the surface of the substation rock would be limited to no better than 0.5 inches. That is find for generals measurement like a 14' truck plus 4' of additional clearance. However, that would be insufficient for...
Prefault current of 17 amps might be a branch/tree sitting on the line for a short duration before the fault evolves to low impedance.
Can you post the waveform recording? When the fault magnitude varies throughout the fault it is unclear to me which instant the relay uses to calculate the...
I have seen shield wires on incoming lines are intentionally isolated from the substation ground grid with a 15 kV class insulator. I too am curious about all your questions.
As I experimented with various configurations, it seemed like X0 and R0 sometimes go in opposite directions for a change in circuit configuration. I don't recall seeing anything change by a factor of 6.5 though.
Perhaps there could be current flows on the distribution circuit cased by the...
I am not sure what you mean by RYB indicator, but please consider what will happen if there is a short circuit between PT and the RYB indicator or fault inside the RYB indicator. I do not recall ever seeing the secondary of a PT directly connected to an instrument with a fuse or breaker as the...
Historically I ignored it based on advice that ground fault relays were typically less accurate than phase relays.
For a recent fault I analyzed, the distance shown by the ground relay element was much shorter than the actual fault location. Once I recalculated the line impedance to include...
There are many ways for utilities to implement power factor penalties. Can you share exactly which utility you receive power from? In my region, small loads like this would not be subject to power factor penalties.
Hopefully the OP can clarify their question.
Casey-Even when I have perfectly balanced loads, I still end up with voltage unbalance at the end of the feeder. I have some balanced circuits where the lack of distribution transposition causes at least a few percent voltage imbalance at the end of...
I had assumed the IEEE standards for arc resistant gear covers the whole package we buy from the switchgear vendor to attach a 115 kV/15 kV transformer to the outgoing 15 kV cables. Even if testing standard doesn't quite cover the cable terminations, I assume a vendor could at least employ...
Safer dissipation of arc products is unrelated to the IP rating. Here are some videos showing normal versus arc resistant design:
Arc flash that blows the door open directly at the operator:
https://videos.eaton.com/detail/video/6256039547001/arc-flash-explosion?autoStart=true&q=arc%20flash%20...
I have see some papers analyzing representative configurations as the basis for localized utility practices. The appropriate amount of surge arrestors is highly dependent upon the frequency of lighting in the area.
Running an EMTP analysis at every pole to determine if it should have an...
I am confused why they have FTB below the power cables and CBS surrounding/above the cables. I haven't ever used CBS, but I thought FTB had better thermal properties.
It is not obvious to me why you need 250 mm of non-native material below the cables. I can see a possible need for a much...
The earthing switch does not clear the fault. It instead turns an arcing fault into a solidly grounded fault, while still relying on the upstream breaker to clear. Before adding a device that intentionally creates a bolted fault, I would want to be sure it provides very clear benefits over an...
