Common metal support for outdoor CTs and VTs 1

I am working on the project - 44 kV outdoor switchgear where conceptual design provided an installation of three CTs plus three VTs on the same support - steel structure.
CTs will be series connected as usual. My question is how far PTs have to bi installed from the CTs i.e CT-R, CT-Y and CT-B transformer.
Is there any standard rule regulating that case...

 

[dpc]

Well, obviously, you must maintain adequate spacing between the high voltage bushings (live parts), both phase to phase and phase-ground. This should be covered in whatever national code is in effect in the project location. You have to consider how the PTs will be connected - bare jumpers - disconnect switches, fuses, etc and maintain appropriate clearances. There is no problem with mounting both on the same support structure if clearances are maintained.

 

[ivana24]

Good,but how far must be for example VT-R transformer from the same phase CT-R transformer. Drawing what I have as preliminary they are almost touching each other.

 

[rcw retired EE]

"but how far must be for example VT-R transformer from the same phase CT-R transformer?"
If they are the same phase they can touch each other as long as the mounting of one device does not bring grounded components within the other device's phase-ground clearance.

There may be a need to have some separation to allow connecting test leads or ground leads.

 

[Marmite]

I agree with what the others have already said. Other things to consider:- The conductor type and whether it can be bent to accommodate any height differences between the CT and VT connection palms without birdcaging in such a short distance. Is there sufficient space to accommodate compression lugs? Some VT's have a bellows inside which ejects the top connection in the event of a pressure build up inside the VT. This type requires some flexibility in the connection. There would need to be sufficient space to accommodate test leads for primary injection of the CT with the primary connections disconnected.
Have you considered a combined CT/VT unit?

Regards
Marmite

 

[scottf]

How close the VTs and the CTs of the same phase can be depends a bit on the construction of the units.

For our units (Ritz dry-type), the VTs and CTs at 46kV are essentially the same height and have similar voltage grading, thus we advise customers to leave 1-2 inches between units of the same phase.

For other designs that may have significant height differences or differences in construction and voltage grading, more space may be needed. For instance, if you were using oil-filled CTs and VTs, the CTs would typically be head-type (live tank) designs and the VTs would be tank-type (dead-tank) designs. This means that the upper ground plane on the VTs would likely be well at 30-50% of the bushing height of the CT and the lower live part of the CT would be 25% or so down the VT insulator grading. In that case, you would really need to get guidance from the manufacturer.

Marmite...depending on the standard and country, combined units below 115 kV are usually much more expensive that using discrete dry-type units.

 

[Marmite]

Hi Scottf. I don't doubt what you say about pricing of the lower voltage units. You are much better placed to know than I am. Interestingly though, we currently buy 145kV combined CT/VT's cheaper than CT's, which means that overall we are saving $10k (per phase) using a combined unit with the same spec. If you factor in the structure costs as well the saving is even greater.

Regards
Marmite