We normally use autotransformers for 230 kV / 69 kV and 400 kV / 135 kV transformers as well. While the advantage is less significant than in 400 kV / 230 kV units, we still find it beneficial.
I agree, there is no difference between Dyn1 and Dyn11. On the other hand, it seems like a strange setup to me. Why not use 400/230 kV and 230kV/66kV autotransformers instead? It would reduce costs and losses, and provide solid neutral grounding for the 66 kV network — which, in turn, would...
We’ve been using autotransformers insulated with natural ester (from various suppliers) since 2016, with tens of units currently in operation, and we haven’t encountered any major issues. These are typically 400 kV, 250 MVA units.
It’s important to note that these transformers were specifically...
Hello 082399,
if I remember correctly, IEEE standard 980 recommends that the oil pit extends at least 1,500 mm beyond any part of the equipment filled with oil.
IEC 61936-1 reccomends instead that the length and width of the oil pit be at least equal to the length and width of the oil-filled...
Hello,
In GIS installations, currents of similar order of magnitude as those in the phase conductors are induced in the enclosures. These induced currents become larger as the enclosure thickness increases; consequently, they tend to be higher in EHV switchgear. When multiple grounding points of...
Yes, SPAR is Single Phase Auto Reclosing, here is widely adopted on 400 kV and 230 kV lines; it's instead much less common on 150 and 132 kV lines.
Our network code prescribes the following:
"Automatic Rapid Reclosing (RRA) and Automatic Slow Reclosing (RLA) of transmission lines
Automatic...
Each CVT includes an Electromagnetic Unit (EMU) whose primary winding is connected to the capacitive divider and has an output voltage of a few kV. If a CVT is energized from the low-voltage side (i.e., from the secondary winding of the EMU), the CVT will behave as a voltage source with a no...
Hi, bacon4life, I expect the carbon fiber core (ACCC) solution to be significantly more expensive than ACSS but also somewhat lighter. In principle, I would not rule out other solutions using high-temperature aluminum alloys (ZTACIR or KTACIR) either. These latter options have far fewer...
Interesting question: given the prices I observe in my geographical area, if the required conductor has a relatively small diameter, for a 66 kV line, it might be cost-effective to use lattice or tubular steel supports (with steel crossarms and glass insulators or, alternatively, insulating...
Hi cyriousn,
when specifying such a large transformer with the objective of limiting the short-circuit current to a reasonable value for CBs, a three-winding transformer is undoubtedly the best solution. We are currently manufacturing several dozen transformers for renewable energy collection...
The surge arrester connected between the neutral and ground is used to ensure that, in the event the ground disconnect switch is open, no overvoltages exceeding the design specifications appear on the transformer's star point. This is typically employed when dealing with transformers with...
Submarine ac cables have been installed for voltages up to 500 kV.
A 400 kV double circuit submarine cables link, 42 km long, 2 x 1000 MW, has been in service between Sicily and Italy for about 10 years. A total of 1032 Mvar of shunt reactors are installed for reactive power compensation.
A...
I would have also said that it was the fault of loose metal components/accessories on the tank, as suggested by prc; otherwise, the only thing that comes to mind is the presence of a very strong 5th harmonic in the load current.
Hi kartracer087,
I fully agree: split bus operation seems to me the most efficient solution. In the absence of other information, connecting 3 x 50 MVA transformers to the same 11 kV busbars, IMHO, is not a good solution. Even if it is possible to design 50 MVA 11 kV transformers with...
Hi cyriousn, we adopt a very similar solution for our "standard" renewable energy collection substations:
we use three-windings transformers, rated at 150 kV / 36 kV / 36 kV, YNdd, with a power rating of 250/125/125 MVA, with the two MV winding connected each one to a distinct 36 kV busbar.
As...
Yes cranky108, regarding clutches I was only referring to gas or steam turbines. Here in my area, for example, there are several gas turbines equipped with clutches for synchronous compensator operation. In the latter case, the inertia constant decreases dramatically to about H=1.7 s.
As far as...
Yes YKC,
to evaluate system inertia at a given time, you should only consider the generator connected to the grid (i.e. operating synchronously in parallel with the grid) at that time.
Note that some generators could, in principle, operate at zero active power as synchronous condensers. This is...
Hi YKC,
Regarding Q1, although both the inertia constant and the installed capacity remain the same, different generators could be in service at different times, according to the system load and renewable generation share.
Regarding Q3, your inertia constant has to be large enough to avoid...
Hi Balaji,
to my knowledge, the only requirements regarding clearances are reported in the European Standard EN 50341-1.
In principle, the armonized standard requires basic clearances and reports the attendant formulae.
A "basic" height of 5 m is assumed for objects beneath OHLs in "normal"...
