Small solutions to big underground distribution problems through 38 kV . . . with tap protection through 900 amps

Vista Underground Distribution Switchgear provides a major advancement in operating simplicity and safety for medium-voltage switchgear.

Conventional elbow-connected switchgear requires that operating personnel move, test, and ground cables during routine operations. Such procedures are awkward and time consuming, and—most importantly—personnel are not fully isolated from medium voltage once a cable is removed from its bushing.

Vista UDS introduces a new level of safety and simplicity by eliminating the need for cable handling during routine operations. It’s all made possible by Vista gear’s numerous innovations, including:

• Simpler, safer, one-person operation. No cable handling or high-voltage exposure during switching, grounding or cable testing. Cuts cost through smaller crews, quicker operation
• Site gear without compromising aesthetics. Pleases customers and saves money through reduced trenching, shorter cable runs
• Up to six switches and single- or three-phase tripping fault interrupters. Saves money by handling more loads per unit
• Superior coordination, flexibility, reliability. Innovative TCCs can be optimized using a PC. No knobs or dials to challenge security
• Exclusive arc-resistant construction meets requirements of IEC Standard 298, Appendix AA
• Contamination- and corrosion-proof. Sealed SF₆ design handles any environment . . . even subsurface
• Consistent operating practices. Same gear for subsurface, vault, and pad-mounted applications. Cuts inventory and operator-training costs
• Easily upgraded to SCADA operation

Operating and Safety Benefits

• Clearly visible open gap and ground positions on all switches and fault interrupters
• Especially large viewing windows for positive confirmation of closed, open, and grounded positions
• Operating controls isolated from medium-voltage cable terminations
• Optional built-in voltage indication on operating side of the gear
• Optional low-voltage phasing feature on operating side of the gear
• Ground positions are rated for a minimum of 3 fault-closing operations at maximum rated short-circuit current.Accidentally grounding a live cable is not a potentially dangerous situation, as it can be when physically handling live cables and elbows.
• Plus, Vista is certified arc resistant per IEC 60298 Annex AA for currents up to 12.5 kA symmetrical for 15 cycles. In the unlikely event that all the above safeguards are bypassed, arc resistance adds another level of safety not found in most other switchgear.

Remote Supervisory

S&C Remote Supervisory Vista Underground Distribution Switchgear provides automated switching and fault protection and — when applied in S&C’s High-Speed Fault-Clearing System — can also perform auto-sectionalizing without tripping the main breaker. It incorporates the same outstanding features as Manual Vista Switchgear and can be specified with a communication and control equipment group, for a completely integrated, self-powered switching and protection package.

Available in ratings through 38 kV, Remote Supervisory Vista Switchgear features carefully integrated components that ensure compatibility — all factory-assembled and checked-out.

• Your choice of remote terminal unit, including S&C’s 6800 Series Automatic Switch Controls. These sophisticated controls support S&C’s self-healing, scalable IntelliTeam® SG Automatic Restoration System — a universal Smart Grid solution offering unmatched interoperability.
• Your choice of communication device, including S&C’s SpeedNet™ Radio.
• Motor operators provide three-second operation of load-interrupter switch ways and three-pole group-operated fault interrupter ways. They’re easily moved between ways . . . no reconfiguration necessary.
• Large viewing windows for load-interrupter switches and fault interrupters. It’s easy to verify open gap and grounded positions.
• Three-phase current sensing and line-to-ground voltage sensing for every motor-operated way.
• Optional potential indication with phasing.
• Exceptionally rugged enclosure construction, with the industry’s finest finish. Provides extraordinary resistance to the elements, keep high-voltage components securely isolated from unauthorized access.

Source-Transfer

S&C Source-Transfer Vista Underground Distribution Switchgear provides fully automatic primary-selective service and fault protection for one, two, or three critical load circuits. This Smart Grid solution incorporates the same outstanding features as Manual Vista Switchgear, plus S&C’s Micro-AT® Source-Transfer Control, motor operators, three-phase voltage sensing on source ways, and voltage transformers for control power. It's available in common-bus and split-bus configurations. Furnished in ratings through 38 kV, Source-Transfer Vista Underground Distribution Switchgear features carefully integrated components that ensure compatibility — all factory-assembled and checked-out.

• Micro-AT Source-Transfer Control offers self-healing response to distribution system problems. Transfers on loss of source, voltage unbalance, or any source-side open-phase condition. It’s easy to set up . . . all settings are keypad-programmable, calibration is automatic. Optional overcurrent-lockout feature prevents automatic transfer operation that would close a source load-interrupter switch into a fault. Optional communications card lets you rapidly upload event log to your PC, download standard settings
• Motor operators on load-interrupter switch ways provide automatic switching between the sources. Also provide automatic operation of bus-tie switch in split-bus configuration gear
• Three-phase voltage sensing for each source. Three-phase current sensing furnished too when optional overcurrent-lockout feature is specified
• Self-powered by voltage transformers.
• Exceptionally rugged enclosure construction and the industry’s finest finish. Provides extraordinary resistance to the elements, keep high-voltage components securely isolated from unauthorized access.

15.5-kV Loadbreak Switches Rated 40 kA Symmetrical Short Time

S&C Vista Underground Distribution Switchgear models with 15-kV loadbreak switches rated 40 kA symmetrical short time are an ideal fit for sectionalizing underground distribution networks. Switchgear in urban areas is frequently installed subsurface or in street or sidewalk vaults, so a compact size is generally required along with an ability to withstand routine flooding. Available fault-current levels also may be very high and exceed the capabilities of most compact and submersible switchgear. Few switchgear products offer all the capabilities needed to perform reliably under such difficult conditions.

S&C’s Vista Underground Distribution Switchgear offers a superior solution for adding switching points to urban distribution networks. Our 15.5-kV Vista Switchgear models incorporating loadbreak switches with a momentary rating of 40 kA symmetrical provide all the features needed for vault and subsurface switching applications, including a fully submersible design that offers reliable performance even in vaults prone to flooding. Vista Underground Distribution Switchgear is gas-insulated, eliminating the maintenance and safety concerns associated with oil-insulated switchgear. And, unlike lower-rated switchgear, it eliminates the need to incorporate current-limiting devices, which are difficult to coordinate and increase operating complexity.

Pad-Mounted Style

Compact Pad-Mounted Style Vista Switchgear improves aesthetics and reduces real-estate requirements — especially at 34.5 kV, where air-insulated gear is too large to be practical in many applications.

• Compact footprint and low profile — Pad-mounted enclosures feature hinged roofs and removable panels, providing convenient access to both the operating and termination components
• All cable terminations are located on one side of the gear. Minimizes operating clearances, reduces space requirements. A typical 15-kV Vista installation requires just 1/3 the space of conventional pad-mounted gear
• A single Vista unit accommodates up to six load-interrupter switches, fault interrupters, or combination of each. So more loads can be served from a single unit. Eliminates need for redundant switches and extra cabling, trenching, and box pads — and additional operating clearances needed between multiple units
• Operating controls are isolated from the cable compartment. Thanks to Vista’s innovative features, operating personnel are never exposed to medium-voltage during routine operations.
• Certified arc resistant per IEC 60298 Annex AA for fault currents up to 12.5kA symmetrical for 15 cycles . . . adds another level of safety for operating personnel.

UnderCover™ Style

Underground and out of sight — yet easy to operate from ground level — unique submersible UnderCover Style Vista Switchgear is ideal where aesthetics are extremely important, or where space limitations make it difficult to site gear above ground.

• Gear can be installed exactly where it’s needed, reducing the costs associated with trenching and unnecessarily long cable runs
• All operating controls are located on top of the gear, easily accessible from ground level — and isolated from medium-voltage cables
• Integral “closed-open-grounded” positions on every switch and fault interrupter allow easy isolation and grounding of cables with no exposure to medium voltage
• One person, standing above grade, can easily perform all routine operations without handling cables or entering the underground vault
• Eliminates added time and complication of entering a confined space
• Certified arc resistant per IEC 60298 Annex AA for fault currents up to 12.5kA symmetrical for 15 cycles . . . adds another level of safety for operating personnel.

Vault-Mounted Style

Vista Switchgear in the Vault Mounted Style provides a compact switching and protection solution for manholes, electrical rooms, and sidewalk vaults, where space is extremely limited. A single unit accommodates up to six load-interrupter switches, fault interrupters, or combination of each.

• Wet-vault-mounted style features a stainless-steel tank and fully submersible wiring, perfect for manholes and other harsh environments
• Dry-vault-mounted style is ideal for electrical rooms and vaults that aren't subject to flooding
• Optional portable motor operator with 50-foot cord and remote control lets you perform switching outside the vault or in an adjacent room
• Operating controls are located away from cables. Personnel are never exposed to medium voltage during routine operations. Cable handling — particularly awkward in vaults — isn't necessary

Wind-Turbine Style

Wind Turbine Style Vista Switchgear is a slim, single-way three-phase version that’s typically applied in wind turbine towers. It can fit through the typical 24-inch wide opening of the turbine door, and provides connection and switching points for the medium-voltage cables from the generator output. It’s generally specified with resettable fault interrupters, but can also accommodate load-interrupter switches.

Since Wind Turbine Style Vista Switchgear is operated from the side, it can be positioned along the inside wall of the tower, providing more space for personnel and equipment.

Manhole Style

Manhole Style Vista Switchgear is a round, single-way, three-phase version that’s typically installed through the manhole access opening of an underground vault. It features either a load-interrupter switch or vacuum fault interrupter, sealed in a rugged, stainless-steel SF6-insulated tank. Cable entrance and exit is via 600-ampere bushings or, optionally, 200-ampere bushing wells.

An optional voltage indicator lifts to expose a large viewing window, allowing a clear view of the switch, open gap, and gas pressure indicator. Manhole Style Vista Switchgear is fully submersible, and can be mounted on the floor, stand, or wall.

“Mobile” Heavy-Duty Style

Developed for the U.S. military, small, lightweight Mobile Heavy-Duty Style Vista Switchgear is specially designed to withstand the rigors of extended air transport at high altitude. Gear stacked two-high (to conserve space aboard an airplane) has passed the MIL Spec E-810 20-hour shaker-table vibration test, verifying that it can withstand 10,000 miles of air travel, and that performance is not affected by the low atmospheric pressure experienced during transport at an altitude of 40,000 feet.

This unique version of Vista gear is suitable for temporary or permanent installations. Comprised of two load-interrupter switch ways and four fault-interrupter ways, it features an enclosure frame and integral skid constructed from heavy-duty I-beams and channels. Eyebolts and alignment pins on the top facilitate lifting and stacking. Turnbuckles, attached to eyebolts on the front and rear sides of the skid, hold the stacked units together during transport. Channels on the bottom allow forklift handling. Reinforced tabs on the skid allow the gear to be dragged along the ground. Plates, attached to the floor of the enclosure, protect the switchgear during transport and storage and can be removed to facilitate cable entry.

Vista Switchgear for Special Applications

Vista Switchgear is suitable for a variety of “special” applications. For example, when an existing conventional metal-enclosed switchgear lineup needed to be expanded to accommodate two additional feeders — but there was only room for one more bay — a new special bay was constructed externally matching the others, containing a unit of Vista gear.

SF6-insulated Vista gear is much smaller than conventional air-insulated metal-enclosed gear. A typical 25-kV conventional metal-enclosed switchgear feeder bay is about 52 inches wide; the two bays required for this application thus would be 104 inches wide. But the three-way Vista UDS unit housed inside the special bay is only 58 inches wide, reducing the space requirement by almost half.

The Vista gear is operated from a control panel that’s completely isolated from medium-voltage components. The position of each fault-interrupter disconnect — open, closed, or grounded — is easily seen through large viewing windows. With the disconnect in full view, operating personnel can verify the open gap and ground cables without having to remove elbows or T-bodies. And by using the optional push-button voltage indicator furnished, they can check voltage without moving cables. A door at the rear of the bay allows access to the elbow connectors.

50/60-Hz ANSI Ratings — IEC Ratings in Parenthesis

kV			Amperes, RMS
System Class	Max	BIL	Main Bus Cont. Current♠	Short-Circuit, Sym.	Fault Interrupter		Load-Interrupter Switch
					Cont. and Load Dropping♠	Ten-Time Duty-Cycle Fault-Interr., Sym.	Cont. and Load Dropping♠	Mom. and One-Second, Sym.
15.5 (12)	15.5 (15.5)	95 (95)	600 (630)	12 500 (12 500)	200 (200)	12 500 (12 500)	600 (630)	12 500 (12 500)
				25 000 (25 000)	600 (630)	25 000 (25 000)	600 (630)	25 000 (25 000)
27 (24)	29 (29)	125 (125)	600 (630)	12 500 (12 500)	200 (200)	12 500 (12 500)	600 (630)	12 500 (12 500)
				25 000 (25 000)	600 (630)	25 000 (25 000)	600 (630)	25 000 (25 000)
38 (36)	38 (38)	150 (150)	600 (630)	12 500 (12 500)	200 (200)	12 500 (12 500)	600 (630)	12 500 (12 500)
				25 000 (25 000)	600 (630)	25 000 (25 000)	600 (630)	25 000 (25 000)

♠ Other ratings are available. Contact your local S&C Sales Office for more information.

 15-kV loadbreak switch models with a momentary rating of 40 kA symmetrical, 0.5 sec., are also available. Refer to Specification Bulletin 681-32 for more details.

Circuit Configurations

Vista Switchgear can be furnished with up to six “ways” per unit, each consisting of a load-interrupter switch, fault interrupter, or bus tap.

Some typical configurations are shown below. The model number indicates the total number of ways, as well as the number of load-interrupter switch and fault-interrupter ways. For example, Model 321 has “3” ways — “2” load-interrupter switch ways and “1” fault-interrupter way, as shown below. Many other configurations are possible.

Manual and Remote Supervisory Models

Source-Transfer Models

Vista Underground Distribution Switchgear furnished with fault-interrupter ways includes a unique microprocessor-based overcurrent control that detects faults and initiates operation of the resettable fault interrupters. Program the control in the shop or in the field using your personal computer via an easily connected USB port. The control offers exceptional flexibility and reliability, and it includes features unavailable in other manufacturers’ devices—or only available at substantial extra cost:

• Five families of curves: Standard “E,” “K,” and “T” speed curves are supported plus special customizable “coordinating-speed” tap and main curves.
• Superior coordination with upstream protective devices and downstream power fuses: Coordinating-speed curves provide optimal coordination on underground distribution systems.
• Custom curve attributes: Coordinating-speed curves can be easily modified to include two separate definite-time delays.
• Separate phase and ground curves are standard: This enables better coordination with source-side breaker trip settings. Negative sequence and sensitive earth fault protection settings are also provided.
• No extra “wake-up” time: If a fault-interrupter way is closed into a fault, the fault interrupter will trip and clear the fault per the selected TCC, with no additional delay.
• Self-powered: Current transformers on fault-interrupter ways provide sensing and power. No batteries or battery maintenance is needed.
• Simple and straightforward programming and access to status information: All programming software is stored in the control. Programming is completed via a browser-based user interface.
• Event log: The log captures information on the last 64 events captured by the control.
• Diagnostic information: Data are available to assess the status of the control.
• Optional external trip provisions for additional functionality: Input from external sources such as transformer sudden-pressure relays can also trip the fault interrupters.

Information Bulletin 680-211 contains curve plots for all Vista Overcurrent Control 2.0 TCCs. It also contains equation parameters for E-speed, T-speed, Tap, Main, IEEE, and IEC curves. Data points for K-speed curves can be found here.

Click here for the original Vista Overcurrent Control TCCs.

The Coordinaide protection and coordination assistant software lets you quickly and easily select the optimal protective device (e.g., fuses, TripSaver® II Cutout-Mounted Reclosers, Vista® Underground Distribution Switchgear, or IntelliRupter® PulseCloser® Fault Interrupters) to:

• Protect transformers against damaging overcurrents and coordinate with primary- and secondary-side protective devices.  See how S&C's novel Transformer Protection Index (TPI) can be used to determine if the primary fuse will protect against certain types of secondary-side faults, including arcing phase-to-ground secondary-side faults.
• Protect capacitor units against case rupture.
• Protect underground cables from insulation damage due to excessive temperatures.
• Protect overhead conductors from damage due to annealing.
• Confirm the proper operation of protective devices against incident-arc energy curves for various Personal Protective Equipment (PPE) levels.
• Selectively coordinate two or more devices in series to minimize service interruptions.
  
  

• S&C Vista Overcurrent Control 2.0 Walkthrough
• Vista Underground Distribution Switchgear Pad-Mounted Installation