by Fred Urban, Orlando Utilities Commission
Under more pressure than ever, electric utilities must answer consumers’ demands for more affordable, reliable electricity. To accommodate this new demand, power utilities are reconsidering outdated technologies. After 50 years without a technology evolution, electric utilities will undergo a considerable transformation in the years ahead.
Upgrading low-functioning components in remote terminal units (RTUs) used for supervisory control and data acquisition (SCADA) systems with modern versions or adding new features or capabilities can enhance reliability. This can add years or even decades to the lives of larger, more expensive equipment. These enhancements also improve safety-reducing required maintenance for a piece of equipment or control cabinet minimizes staff exposure to potential hazards.
|The original punch down standard 66 blocks were open, and wires could work themselves loose, putting personnel at risk.|
Higher Demand Calls for Stronger Building Blocks
Although 30- or 40-year-old terminal blocks might be structurally sound, they fall short of the capacity and capabilities that newer versions offer. Replacing older terminal blocks with newer versions can improve current-carrying capability and interrupting duty.
More modular products have fewer parts to maintain and are easier to replace, making them more reliable.
Modular substation power plants can reduce production and commissioning costs by upgrading to new technologies. These increasingly common systems call for on-site pluggable wiring solutions to connect prefabricated sections of a power plant with its substations. Prefabricated cable systems can be plugged into each unit to connect modular units. Important to substation operators, energy-measuring devices are basic elements that can be preinstalled individually to meet the demands of specific applications. These devices aid in measuring and controlling critical circuits in equipment cabinets.
|The new modular terminal blocks were not touch-safe, but the push-in connection technology reduced installation time significantly.|
Secure and Ready for the Future
As the second-largest municipal utility in Florida, the Orlando Utilities Commission (OUC) provides electric and water services to some 231,000 customers in Orlando, St. Cloud and parts of unincorporated Orange and Osceola counties. In addition, the company maintains more than 2,300 miles of electric lines and 1,700 miles of water lines.
OUC electric substations contain RTUs used for SCADA communication systems. They employ a cable interface that allows technicians to isolate and test cables between the field equipment and the RTU. OUC had been using telephone system “punch-down” 66 terminal strips with metal bridging clips. The 25-pair standard split 66 block contains 50 rows; each row has four columns of clips that are electrically bonded. For years, they have served as a telecom standard for termination of voice cabling and supported 22 through 26 AWG solid copper wires.
OUC engineers and technicians, however, often prefer working with stranded wire. In time, these wires could work themselves loose in the 66 block or break at the v connector. Substation personnel frequently applied 120 V AC or 130 V DC power to these blocks, raising a safety issue, as the open connector could be exposed to metal and wire contacts.
|A side-by-side comparison of the new wiring compared with the legacy blocks.|
During a substation retrofit, OUC switched from standard 66 terminal strips to a raised rail assembly with modular PT 2.5 Quattro-MT terminal blocks from Phoenix Contact. Each PT 2.5-Quattro-MT terminal block includes a knife disconnect lever integrated in its housing and supports four connections in a compact 5.2-millimeter-wide design. With UL current ratings of 300 V and 20 A, this PT block supports 12 through 26 AWG copper conductors. Although these new terminal blocks cost more than standard 66 blocks, they have reduced long-term costs significantly because of their faster installation and reduced maintenance. Push-in connection terminal blocks are characterized by an innovative system of accessories (plug-in jumpers, test plugs and adapters, and partition plates) and by easy and tool-free wiring with ferrules or solid conductors. The compact design and front connection entry enable wiring in a confined space.
As a result of the RTU retrofit, OUC saved some eight man-hours in wiring time with modular PT terminal blocks over a 66 block. To change out wiring, man-hour savings would be close to 80 hours. The new product solution saved additional time because OUC did not have to change legacy stranded wire to solid.
Other advantages accompanied the new solution. Namely, open connector exposure to metal was eliminated, increasing operator safety. The new solution also offered built-in disconnect functionality for testing and measurement.
To date, PT 2.5 Quattro-MT terminal blocks have been installed at three substations. OUC plans to retrofit all existing substations as time and funding permit with PT terminal blocks.
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