Maui Electric Follows HECO Lead on PLC-based Automation
By Steven Shelton, SSR Engineers Inc., and Fred Oshiro, Maui Electric Co. LTD
Maui Electric Co. Ltd. (MECO), a subsidiary of Hawaiian Electric Co. Inc. (HECO), provides electricity and operates the electric system on the Hawaiian island of Lanai. Barely 10 miles across, and about that same distance from neighboring Maui, Lanai has seen its electrical power demand double within the past 10 years. The increase is the result of continuing development of first-class visitor accommodations. These include two luxury hotels, two championship golf courses and two up-scale residential subdivisions–all this on an island once dominated almost exclusively by pineapple plantations.
Faced with such an extraordinary increase in demand, and determined to maintain its high availability of service, MECO recognized the need to add generation and improve the island`s distribution system with additional distribution circuitry and distribution feeder reclosers.
Unlike electric utilities on the mainland, Lanai has no interconnection to an outside power grid. Power on the island is generated with diesel generators at one central location. Power to the entire island is supplied by 12 kV lines emanating from the generating station. To continue to maintain its high reliability of service, MECO also wanted an inexpensive SCADA system to enable power plant operators to better monitor and control the island`s expanding distribution system.
MECO retained SSR Engineers Inc., a Billings, Mont.-based firm providing electrical consulting engineering to the power utility industry, to develop a programmable logic controller (PLC)-based SCADA/automation system. SSR had worked with parent company HECO on a number of other projects, including automation of substations in Honolulu with integrated PLC systems. MECO project engineer Fred Oshiro and operations engineer Kerry Nishida were aware of HECO`s endeavors and realized the advantages of a similar application to meet their requirements. SSR`s directive included design, programming, testing and commissioning of the new system. SSR selected NovaTech LLC, as an integrator to assist on this project.
PLC System Objectives
The Lanai project required electrical design for the installation of a complete PLC-based SCADA and automation system for the island. Three objectives were established in respect to the control and monitoring of the power distribution system. These objectives were to:
provide expanded distribution system operation capability at Lanai`s power generating station by adding SCADA to the reclosers out on the distribution system and on the generating plant distribution feeder breakers;
provide underfrequency loadshedding and restoration on the distribution system; and
provide real-time data to Maui Load Dispatch on the island of Maui for the system operation.
Meeting the Objectives
On the distribution system, remote terminal units (RTUs) were installed on poles next to each of two distribution recloser sites. At each site up to five reclosers were connected to an RTU. The RTU network diagram (Figure 1) shows the major components of each PLC-based RTU.
The SCADA master was installed at the generating station to monitor the two RTU sites and local relays on the distribution feeders. The SCADA master network diagram (Figure 2) shows the major components of the PLC-based master.
The design included installation of a spread spectrum radio system at the master and the two RTU sites, combined with EIA-485 communications to create the SCADA communications network. The SCADA functions available to the generator station operator at the human machine interface terminal are:
recloser control and indications for two recloser sites;
12 kV breaker control and indication at the generator station substation;
feeder measurement parameters (volts, current, watts and vars) for two recloser sites; and
12 kV bus and feeder measurement parameters at the generator station substation.
PowerPlex digital transducers provided by Bitronics Inc., were chosen to also provide the frequency sensing for loadshedding at each RTU installation instead of a separate relay system. The PowerPlex transducer with Modbus Plus high speed and serial output is capable of measuring and communicating data in the 100 msec range–virtually in real time. The PLC programming provided selective recloser tripping for various loadshedding set points. Load restoration is also provided in the PLC program and initiated through the Modbus Plus network.
In addition to requiring the expanded distribution system operation from the local power plant, MECO also required real-time data and control of the remote Lanai island distribution system at their load dispatch center on Maui. The new PLC-based system with Modbus Plus protocol includes a Modicon BM85 bridge mux with NovaTech protocol software which emulates a L&G RTU for communicating with MECO`s existing Maui island SCADA protocol. A telecom link was provided to Maui to allow the MECO SCADA system access. This system allows MECO to monitor and control the remote island distribution system on its SCADA system the same as it does for all electrical facilities on Maui.
SSR`s electrical design included all system physical aspects, the communications network, control schemes, equipment enclosure layouts, wiring drawings and specification of materials. SSR also provided the PLC programming, created the necessary mapping within the BM85 bridge muxes, and programmed the HMI. NovaTech provided the Cooper 2179 Emulator at the RTU as well as the Landis & Gyr 8979 Emulator and Smart Mux at the SCADA Master. NovaTech also provided assembly of the RTUs and master station.
MECO engineers previewed the prototype system at SSR`s office where the opportunity for modifications was available prior to finalizing software programming. SSR also provided on-site commissioning assistance and training to MECO personnel.
The recent advantages in measurement, communication and control techniques created by the new automation system have allowed MECO to maintain its high level of service. They have led to faster restoration, more efficient outage management and improved system reliability.
Flexibility in the operation of the system is another benefit. Operators can remotely operate breakers, as well as control other switching such as breaker and recloser block control and ground trip block control functions.
The utility has a better knowledge of what`s happening on the system with self-diagnostic IEDs and availability of system fault data. Automated features provided by the PLC-based system, such as underfrequency loadshedding and restoration, provide operational flexibility of the distribution system, as well as enhanced reliability and lower installed costs. SCADA control of the distribution system locally from the generation plant, as well as by off-island Maui system load dispatch, provides a realized advantage over the former control of the system. Uninterrupted service to its customers is a priority of every electric utility, and MECO can now face continued commercial and residential development on Lanai with confidence.
Steven Shelton is a senior engineer with SSR Engineers Inc., where he has been employed for over 20 years in the substation and control department. He was project manager for the Maui Electric Lanai SCADA/automation project. He graduated from Montana State University with a bachelor`s of science degree in electrical engineering and is a registered professional engineer in several states including Hawaii.
Fred Oshiro is a staff engineer for Maui Electric Co. LTD where he has been employed for six years in the engineering department. Fred is responsible for distribution planning, project management and technical support for Central, North, East and Upcountry Maui and Lanai. He graduated from the University of Hawaii at Manoa with a bachelor`s of science degree in electrical engineering and is registered professional engineer in Hawaii (Electrical Branch).
View of an RTU installation on the distribution system. The UPS cabinet is located below the RTU, and a distribution recloser is on the adjacent pole.
View of RTU cabinet containing PLC (upper right), Cooper bridge mux (upper left) and Bitronics PowerPlex (back of swing panel). UPS powering RTU is in lower cabinet.