By Tom Thompsen and Jim Goodfellow
In an era of utility deregulation, ours is anything but a business-as-usual industry. The competitive pressures that arise from deregulation, combined with governmental siting constraints and citizens' environmental concerns are taxing our ability to design and construct new distribution substations in a cost-effective manner. At Southern California Edison (SCE) we found a way to not only reduce our total owning costs over the conventional way of doing business, but to also increase reliability and operational performance; to minimize the impact on the environment, while at the same time simplifying project design and management. Our solution: A pad-mounted substation.
Background
During SCE's normal planning process, it was determined that another 33/12 kV substation was needed in the Arrowhead Operating District. The Arrowhead District is located at 6200 feet above sea level in the San Bernadino mountains, a beautiful and pristine winter and summer resort area about 70 miles east of downtown Los Angeles. There are many vacation homes in the area and because of this, environmental siting got a high priority in our decision making process.
A 33 kV voltage system is used as the source to four other 33/12 kV substations in the area. All of these stations are operated and maintained by SCE's Substation Group. These stations are of a conventional design: open steel rack with exposed bushings on equipment. We initially approached this project doing what comes naturally - we opted to build a station similar to all the rest and to have it operated and maintained by Edison's substation personnel.
The total project cost estimate for our conventional station came in at $2.8 million. Engineering approvals were obtained, and we were well on our way to having another standard Edison distribution substation, when local District management voiced concern over the cost. "Could we do it for less? Could Arrowhead District personnel construct, operate, and maintain a pad-mounted substation?"
Dave Anderson, the distribution engineer assigned to the area at the time, and Jim Goodfellow, Cooper Power Systems Sales Engineer, shed some new light on the subject. Dave developed a design that equated electrically to that achieved with our standard conventional design. Jim pitched in with cost estimates and application suggestions.
"The key to the success of this project was Edison's field engineering open-mindedness and willingness to evaluate new products that, while different, would improve both construction and operating efficiency," notes Jim Goodfellow.
The Cooper equipment allowed for easy integration of distribution automation that, given the remoteness of the site during the winter months, allowed us to include remote monitoring and automation features in the new substation design. The new estimated total project cost came in at $0.8 million, a project cost savings of $2.0 million. Needless to say, District management was very pleased with the projected cost savings and approval was given to proceed.
Implementing the Project
Edison area engineering, construction, and operating personnel formed an integrated project team from concept to completion. Meetings were held to ensure that there were no adverse operating restrictions and to explore "What if" service scenarios. Since area personnel were to manage the project form start to finish, it was important to ensure that our construction crews were fully in the informational loop. This was particularly true since the project introduced equipment which was new to the Edison system. Among these were:
Because the equipment proposed by Cooper was distribution class switchgear, we found it practical and cost-effective to use our local distribution crews instead of out-of-the-area substation personnel. This contributed significantly to crew pride of ownership while at the same time boosting morale which greatly enhanced productivity. During the construction period, the distribution crew became intimately familiar with both the equipment and its operation. The equipment familiarization and training time normally required during project commissioning were greatly reduced because of this.
Benefits
During the project evaluation and planning process we tried to anticipate potential problems along with expected benefits. Project management presented the greatest unanticipated problems: timing of project material deliveries to correspond with the construction schedule needed better tracking. In addition, material ordered for the project wasn't segregated, with the invariable result that some of it found its way out of the yard to be used on other projects.
Many of the benefits that we anticipated grew in stature as we progressed with the project. Crew familiarization with the equipment, coupled with deadfront construction (cable elbows installed directly on apparatus equipment bushings) proved that we had developed a truly dependable 33 kV distribution substation.
Other benefits anticipated, but not fully appreciated until construction was complete, were the environmental and aesthetic benefits realized. The low profile distribution class equipment enclosures, neatly snuggled off a remote radial road in a mountain ravine essentially eliminated the substation from public view. Even those who wander off onto this lonesome path pay little attention to the small group of green boxes sitting near the road as they drive by. What a breath of fresh air from the originally planned open rack substation design. Deadfront construction brings another benefit: it is free from interruptions so common to conventional substation, i.e., forest creatures, rodents, birds, snakes, etc.
To complement these features we installed satellite monitoring and remote control of switches and reclosers to ensure an absolute minimum of outage and downtime for those served from this mountain resort substation. Parallel transformers and feeder reclosers are easily sectionalized with a remotely operated motorized switch. This assures continuity of service during equipment maintenance and service restoration in the unlikely event of equipment failure.
Other Challenges
It was possible to use conventional equipment available from Edison stores for station lighting and power. To accommodate standard available equipment we needed to develop solutions for several other installation requirements:
Operating Experience
After three and one half years of successful operating experience, which is a good foundation for evaluating our decisions, we are completely satisfied with the pad-mounted substation design. We continue to remotely monitor voltage, load currents, and switch positions via satellite communication. Except for periodic maintenance inspections, we have not yet needed to remotely isolate any individual gear with our by-pass switching arrangements. To sum it up, it has been a successful project from inception to satisfactory operation.
"The fun part of this project was watching the enthusiasm grow; first by the engineers in the design phase and then by the local distribution crews during installation. The care of workmanship they exercised in installation reflected both professional and personal pride. Each person associated with the project was both proud of his participation and extremely pleased with the outcome," observes Jim.
A neighbouring utility, Bear Valley Electric service Company, was so impressed with what they saw at SCE's substation while still under construction, that they too shifted substation design criteria in the planning stages.
They elected to build a 33/2.4 kV 10 MVA regulated pad-mounted substation with dual transformers and four feeders. The Bar Valley Village substation includes R-VAC pad-mounted regulator by-pass switches with key interlocks, a unique feature.
Bear Valley Electric's substation, a totally 100 per cent Cooper pad-mounted installation, has also operated flawlessly from initial commissioning to present, according to Bear Valley Electric personnel.
Tom Thompsen is a Distribution Field Engineer with Southern California Edison Company and Jim Goodfellow is a Senior Sales Engineer with Cooper Power Systems. ET