Next-Generation 15.5-kV Manual Vista® UDS.

S&C is pleased to present a new generation of 15-kV Vista Underground Distribution Switchgear (UDS). This latest innovation in the Vista design offers the same benefits of the original design, and then some.

The new design of Manual Vista UDS is available for 15-kV models rated 12.5-kA short circuit, in pad-mounted, vault-mounted, and UnderCover™ styles. The new gear features a tank that is only 24 inches tall — a full 9 inches shorter than existing Vista UDS. And while the new gear was designed to match the footprint of previous-generation Vista, the tank itself is not quite as deep, providing extra space for cable terminations. With the smaller tank, the enclosure for pad-mounted styles is also reduced, resulting in an even more aesthetically pleasing installation.

The next-generation Vista UDS provides an even more obvious open gap and ground position. Closed, open, and grounded positions are more easily discernable through the standard large viewing windows. Plus, the simplified fault-interrupter design uses a three-position switch with arc-spinning contacts for all interrupting duties, for an extremely straightforward operating sequence.

These new designs are combined with the usual array of unique Vista features such as integrated potential indication and low-voltage phasing features. Virtually all routine operating tasks can be performed without any exposure to medium-voltage cables, and without special cable accessories such as grounding elbows.

An Overview of the Phenomenon Behind the Rotating-Arc-Interruption Technology

The new 15.5-kV Manual Vista UDS offers a number of design advancements, adding to the number of benefits already provided by Vista. One advancement includes the use of a three-position switch with arc-spinning contacts for all interrupting duties, for an extremely straightforward operating sequence. The rotating arc contact design allows for a more compact profile and provides an even more obvious open gap.

Rotating arc interrupters, also known as arc spinners, consist of a moving contact, a stationary contact, and a magnetic coil.

Figure 1 illustrates the interrupting phenomena associated with the S&C rotating arc interrupter during an opening operation (the stationary contacts have been removed for illustration purposes).

The interrupter uses a swinging blade assembly as the moving contacts, which make or break the electrical circuit. When the blade initially separates from the stationary contact during opening, the dielectric properties of the SF6 gas break down and an arc is drawn between the two contacts. As the blade continues to open, the arc is transferred from the stationary contacts to the magnetic coil. The current in the coil creates a toroidal magnetic field (“B field”) which, in turn, forces the arc to accelerate along the rim of the coil. This “spinning” along the rim cools the arc and also allows the SF6 gas to rapidly recover its dielectric properties. To further aid in the dielectric recovery of the SF6 gas, the magnetic field is optimized to be out of phase with the current and keeps the arc moving even as the current approaches zero. The arc will be extinguished at the current zero and will not re-ignite since the dielectric properties of the SF6 gas have recovered sufficiently, and the blade will continue to the fully opened position.