The High-Reliability Solution for Critical Power Users: As Good As It Gets?

A few weeks ago, S&C featured news about Power Systems Services’ involvement in planning a High-Reliability Distribution System (HRDS) for a new convention center. If you missed it, you can find the article here.

S&C was charged with proposing the most comprehensive High-Reliability Distribution System to date. Not only does the system have to be reliable, versatile, and upgradeable, it also has to be cost-efficient. S&C proposed a number of project approaches with increasing levels of system reliability. Feasibility studies, load flow calculations, and short-circuit studies were conducted to provide detailed analyses of each approach — thus providing a quantitative measurement of system reliability and, in turn, the associated monetary value of each approach. After numerous discussions and permutations, the chosen approach utilizes S&C Vista® Underground Distribution System fault-clearing switchgear in a closed-loop system with SEL-351 directional overcurrent protection relays. To meet the customer’s design criteria, the following schemes will be implemented:

A Permissive Over-reaching Transfer Trip scheme (POTT) will be used to protect the underground feeder cables. Using this scheme with the S&C Vista UDS and SEL-351 relays results in clearing of primary faults in less than 6 cycles. In addition, a Directional Comparison Blocking (DCB) scheme is used as a back-up to the POTT scheme.
Branch line faults will be cleared by the integral Vista Overcurrent Control, which can operate the fault interrupter to clear the fault in as little as 3 cycles.
The system will use two substations in two closed-loop configurations to support load requirements as well as load equalization if a fault occurs on a feeder.
To support new load growth in the area, additional Vista units can be added anywhere along the loop system . . . and will adhere to the system design without any changes in relay settings. Additional switchgear will become part of the POTT scheme.
The proposed design can support an additional source for future load expansion.
The loop configuration can be reconfigured so that two or three loops can be added and still support the existing design requirements.

Two preliminary designs were submitted: one for the interim phase to provide support for existing loads, and one for the final build-out to support the projected load growth. The local utility desires the interim 1 loop system to be completed and operational by 2002 and the final build-out by 2006. Since the 2006 build-out plan was certain, S&C’s interim design utilizes a ‘vision for the future’ concept by using the initial construction phase to lay the cables and foundations for the build-out phase. Thus, the build-out phase will require only equipment installation — saving on total construction costs and overall project time.

View one-line diagram for INTERIM phase (PDF, 196 KB).

View one-line diagram for BUILD-OUT phase (PDF, 279 KB).

The preliminary HRDS design was accepted by the customer and PSS is presented with the opportunity to refine the scheme and implement the latest HRDS solution.

S&C’s HRDS solution offers reliability, versatility, and affordability to those requiring a higher level of power reliability. Contact S&C’s Power Systems Services to see how we can help you attain your goals for your electric power system.