Lower Costs and Customer Focus Regenerates Distribution Automation
By Wayne Beaty, Contributing Editor
Don`t wait–automate. This was the battle cry of a few utilities and vendors for promoting distribution automation (DA) about a decade ago. However, because of costs and lack of appropriate incentives, automating very many of the distribution functions just didn`t happen very fast. A few notable exceptions, however, are providing the impetus for others to take another look at the benefits of DA–especially in this competitive, customer-focused era. In some cases, public service commissions are taking a hard look at outages and linking those to cost of service and penalties for utilities.
Southern California Edison Co. (SCE) has perhaps the largest DA project in the United States. It has started to automate 4,000 existing distribution switches on its system.
The project will include communications and control-end devices across its 50,000 square-mile service territory. SCE presently is using some 20,000 Metricom packet radios and 90 gateways. SCE has taken a novel approach in an effort to make DA affordable. The direct benefits of this make it possible to:
Reduce interruption time for customers,
Restore service to at least half of the customers on any given lockout outage to just a few minutes,
Respond faster to outages and equipment failures, and
Reduce the patrol time for restoration crews.
The traditional methods of utilizing current sensors or fault detectors are not being employed. SCE`s approach to restoring service is to locate the fault by automatically opening all the switches that are fed by the faulted breaker and then reclose the switches one at a time until the breaker is re-tripped. This method locates the fault without utilizing sensors and expensive remote terminal units (RTUs).
A Cleaveland/Price automated distribution motor operator (ADMO) opens the switches using an automatic opening feature. The “auto actuate device” responds to loss of ac voltage coming into the battery charger from the distribution circuit. The device can be inhibited via radio. The motor operator can include an inexpensive industrial RTU, saving another $1,000. The device can be conveniently installed on a pole or in a pad-mounted gear. The package houses the motor, charger, battery, radio, RTU, auto actuate device and a vandal-proof antenna. On every switch SCE automates, it saves about $2,400 for sensors, $3,000 in installation expense and $400 for analog capability on the RTU.
Overhead switch automation will be installed on existing pole-top switches and tilting-insulator overhead midpoint and tie switches. SCE will also install a stored-energy operator (SEO), RTU with Netcomm radio and potential transformer.
Loss of voltage operators (LVA) will be installed on most mid-point switches. Mid-point switches will automatically open on loss of ac from circuit breaker tests (see figure). Remote control options for both opening and closing mid-point and tie switches will be available at switching centers.
SCE will install automated padmount switches in existing padmount locations and on completely underground circuits. They will use the same LVAs as those installed on overhead remotely controlled switches (RCS) as well as the open and close control for mid-point and tie switches from switching centers.
Automatic Recloser Automation
SCE is automating all existing automatic reclosers and will install RTUs with Netcomm radio and interface boards. The remote control functions (both open and close) will be augmented with block and unblock operations of the reclosers. Operations of the automatic reclosers will also include the ground trip function from the switching center.
SCE`s DA project also includes circuit and automatic recloser lockout alarm (CARLA). A Netcomm battery-backed radio will be installed on circuits and downstream of automatic reclosers. The distribution control and monitoring system will include a UNIX computer system on Hewlett-Packard workstations. It will control all RCSs and automatic reclosers, as well as monitor the system and generate alarms when needed. The outage monitoring system will enable system operators at the switching centers to control outages and restoration procedures, allowing quicker analysis and restoration service.
By late 1997, SCE had completed the following remote control switch work:
1,000 overhead switches;
700 mid-point and tie switches;
850 in remote operation;
430 in loss-of-voltage automatic operation;
300 stored-energy operators;
6 automated pad-mounted switches; and
60 Cleaveland/Price switches.
Remote automated recloser (AR) work included:
429 existing ARs automated;
327 with RTUs (102 with status-control radios); and
365 in remote operation.
Some 1,428 circuit and automatic recloser lockout alarms have been installed with 1,100 of them on circuits and 328 on automatic reclosers. Training has been provided for all switching centers. So far, DA system results include a reduction of 1.5 million customer-minute interruptions per month saving an estimated $225,000 per month.
SCE has planned more work in 1998 that includes more remotely controlled switches, automatic reclosers, capacitor controls and moving the distribution control and monitoring system (DCMS) to an IBM redundant (failover) computer system. Plans also include interfacing the DCMS to the outage monitoring system with new graphic software.
In 1994, Commonwealth Edison Co. initiated a sectionalizing project using distributed intelligence to improve the performance of the 34 kV system. The goal was to reduce both outage frequency and duration while holding the budget levels to those historically used for 34 kV rehabilitation. ComEd had no distribution SCADA at the start of the project, so it used automatic sectionalizing devices to accomplish the improvements.
ComEd`s typical 34 kV lines utilize distance relays which provide good protection of long lines during emergency switching, but limit coordination with fuses and reclosers. The typical line has reclosing and trips three times before locking out.
The 34 kV system consists of 268 lines with an overall length of about 3,200 miles. Interrupting devices are typically located only at the substation in the form of the line circuit breaker and in the form of fuses at transformers. There are a few intermediate sectionalizing fuses, recloser or automatic sectionalizers on the lines.
Distributed intelligence allowed ComEd to provide sectionalizing before the source circuit breakers locked out. It was necessary to find equipment that would operate correctly on the 34 kV system, while providing the flexibility of adding SCADA capability in the future. Reclosers were ruled out because of the difficulty in coordinating them with the distance relays and the fact that 200 kV BIL (basic insulation level) reclosers were not readily available. ComEd had experience in a 34 kV DA pilot project and was able to use this knowledge in designing a system using two types of gang-operated sectionalizers, one using vacuum and the other using SF6 gas as the interrupters. ComEd worked with S&C Electric to develop two automatic sectionalizing algorithms for their switch control. One was an automatic line sectionalizing algorithm, where after seeing an over current followed by a three-phase loss of voltage, the switch would open after a specified time delay provided voltage wasn`t restored.
The other was an automatic network line sectionalizing algorithm for closed loop applications, in which the switch would open after seeing a loss of three-phase voltage followed by a specified time delay. Energyline helped ComEd develop an IntelliTEAM system that featured local communications between switches, allowing ComEd to provide more complex sectionalizing schemes than would have been possible with a standard sectionalizer.
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Remotely controlled switches (left) help SCE lower costs and improve service to its customers. Compact automated distribution motor operators provide remote control equipment that mounts easily on a pole to provide an inexpensive alternative to RTUs.
Pad-mounted switches can also be easily automated with the package that incorporates several “smart” electronic circuit features for improving service reliability.
PennWell Publishing Research
PennWell Publishing Co.`s Distribution Automation Market Data Report projects 195 DA projects through 1999 with a total value of $83 million plus another $28 million for RTU Add-On Projects. Some $6 million will be spent on consulting and communications projects.
Experience has shown that project delays will occur and that 58 percent of the projects will actually be awarded in a 12-month time frame with the remainder delayed. Therefore, about 86 DA projects will be awarded through June 1998 with a value of $46 million and the remaining 62 projects will be delayed. About 60 percent of planned projects will have some form of SCADA control. Only 14 percent will have independent control.
The PennWell research report points out that the Personal Computer (PC) platform is favored by 39 percent of the utilities planning new or upgraded distribution systems. Workstations (UNIX-based) run a close second with 35 percent. About 21 percent plan on a microcomputer and the remaining 5 percent will use a mainframe platform.
Currently, some 40 percent of installed systems are running on a PC operating platform and 36 percent are workstation-based. The communications methods vary widely. Frequently, a combination of two or more communications methods is used in DA systems. Radio, by itself or in combinations with other methods, is the most widely used and planned form of communications. Cellular telephone is emerging as a new communications method in DA systems.