DTE Energy is committed to distributed generation (DG) in a big way. In fact, support for DG comes from the top of the corporation. Consider this statement provided by DTE Energy Chairman and CEO Anthony F. Earley Jr.:
“In the electric industry, the day of large central station power plants has already given way to modular, combined cycle gas powered plants. We envision a day when the next step, distributed generation, will play a major role. DTE Energy intends to lead that transformation. DTE Energy believes that today's existing electric and gas system will be around for a long time. But we will also see a vibrant market for personalized power that uses distributed generation technology. In fact, utilities will be among the first real-world, large-scale users of distributed generation. Distributed generation will increasingly become a cost-effective alternative to the expansion and reinforcement of T&D infrastructure.”
DTE Energy believes that moving the generation of energy as close to the point of consumption as technology will allow is the way of the future. DG is the best way for DTE Energy to leverage its existing infrastructure, manage its short duration peaks, improve customer reliability and continue its environmental stewardship. DTE Energy feels this so strongly that it has created a non-regulated business, DTE Energy Technologies, to bring distributed generation to market under the energy|now™ brand.
Many good ideas fail because of the lack of application engineering necessary to pave the way for end-use integration. DTE Energy and Detroit Edison, the electric-utility company within DTE Energy (Detroit, Michigan, U.S.), are developing the application engineering associated with DG.
Detroit Edison is integrating DG into its distribution planning and operating process as an alternative to traditional means (construction of new lines and substations) of satisfying distribution needs.
Analysis and Integration
Detroit Edison has been implementing and personalizing EPRI's Distribution Engineering Work Station (DEW) as its power flow and short-circuit modeling tool. The DEW system can model inverter and synchronous DG power flow, as well as multiple-source fault analysis.
Quantifying the impact of DG on the electric utility's existing circuit-protection system is one of DG's biggest technical integration hurdles. Detroit Edison is developing an algorithm to quantify and simplify that analysis. These programs are steady-state evaluation tools, but they need modifications to perform time-varying analysis.
Another part of the DG integration is the customer interface. Detroit Edison is testing a Customer Premium Power Program on targeted overloaded circuits to determine if customers are willing to share the cost of installing DG at their facility, while allowing the utility to operate the units remotely to meet electrical system needs.
The actual DG installation is a crucial part of the integration process. As part of Detroit Edison's DG integration strategy, it installed various types of distributed resources as demonstrations and test installations of the new technologies.
A 200-kW/400-kWh zinc-bromine flow inverter/battery for peak shaving at an overloaded pole-mounted substation.
Two grid-connected solar installations for renewable energy for sale as green power.
Two Plug Power fuel cell installations to augment the control battery charging system at a black-start peaker site.
In 2002, Detroit Edison installed four DG projects operating in parallel on its distribution system:
A 150-kW energy|now natural gas internal combustion (ENI 150) engine-driven generator (ENI 150) installed in a non-sell back mode to offset a building load.
Three ENI 150s (450 kW) in a sell back mode on an overloaded circuit.
An ENR 2000, a 2-MW diesel generator installed on the tag end of an overloaded circuit to solve low-voltage problems.
An ENI 1000, a 1-MW natural gas internal combustion generator connected to a distribution circuit to relieve an overloaded substation transformer.
The ENI 150 installations are part of the Premium Power Program Detroit Edison is testing in 2002. All generators are monitored and controlled using a Web-based energy|now System Operations Center™ developed by DTE Energy Technologies.
Now to focus on Detroit Edison's first endeavors at integrating DG into the distribution system.
DG Installed — Collins Site
The area just south of Interstate 94 near Ann Arbor, Michigan, currently at the tag end of three separate substations, is a 13.2-kV, multi-ground Y radial system. The area has experienced rapid load growth in the past few years. Detroit Edison recognized this and began a project to build a substation named Collins to serve the area. After finding a suitable parcel of land for Collins, Detroit Edison had difficulty obtaining community approval to build. This delay, coupled with larger-than-expected load growth and an abnormal number of hot days, resulted in cable overloading at the substations. Several load transfers and a portable substation resolved most of the overloads, but the new substation area was still experiencing low voltage.
Detroit Edison decided to install a new 2-MW diesel generator on the new substation site. The utility notified the community of its intention and began installing a ground mat and portable fence to house the generator. A cable pole was installed and underground cable was run to a primary switching cabinet, then to a 13.2-kV to 480-V 1500-kVA live-front transformer. From the transformer to the generation output, covered wire was simply laid on the ground. The switching cabinet also housed monitoring and control circuits. Relay protection consisted of under/over voltage and under/over frequency to protect the system from the generator. The generator also has its own protection. The generator operating strategy is to run whenever the ambient temperature is over 80°F (27°C).
The entire construction took five days to complete. After seeing the utility's commitment to serve the area, the community recognized the need for Collins and accelerated the approval process granting Detroit Edison permission to build the new substation. Construction began this fall with completion by summer 2003.
DG Installed — Adair Substation
Adair is a 41.57- to 4.8-kV ungrounded delta substation serving an area about 50 miles (80 km) northeast of Detroit. This rural area, in the thumb of Michigan, has low load growth but is fed by a single 2.5-MVA transformer with not much capacity margin for new growth and extra demand associated with above normal temperatures.
A portable transformer oil cooler was previously installed to maintain low oil temperatures for loading above two times nameplate. A 1-MW natural gas fired reciprocating engine was installed to avoid continued operation at this excessive loading level. The oil cooler afforded Detroit Edison the time necessary to install the unit.
Relay protection was the same as at the Collins site with some additional required interconnection protection as shown in the photo above. This includes blocking automatic reclosing of the 4.8-kV distribution circuit's recloser when the generator is running; tripping of the generator if the generator output exceeds the circuit load; and tripping/lockout of the generator when the circuit recloser opens, before automatic reclosing is permitted. The utility operates this generator when the transformer is over its day-to-day rating.
The ENI 1000 is compatible with Detroit Edison's protective tagging (red tagging) specifications. Visible open breaks are available on all power and control circuits, and knife switches are available as a tagging point to protect from backfeed.
Detroit Edison contacted the community, which, in turn, granted the utility permission to proceed. The community allowed the installation in part because the generation was for their use only and not for resale as in a merchant plant. As a side note, the community was very receptive to the utility's substation expansion plans and wanted assurance that the substation expansion would be completed in the next couple of years. The entire construction took 12 days to complete after the community granted approval.
Integrate into the Planning Cycle
Detroit Edison plans to continue to address DG initiatives. The thrust of its efforts in 2003 will require integrating DG into the planning cycle, improving its DEW modeling and analysis system, and implementing DG into the Customer Premium Power Program.
To integrate its DG strategy matrix into its 2003 planning cycle, Detroit Edison will first identify the planning criteria shortfall in kilowatts, estimate the duration and calculate the cost to resolve. It is also examining other elements, such as new land needed and specific customer load additions. Detroit Edison will implement DG solutions when it is economically viable. This requires distribution engineers to review past summer peak loads and project the uses of DG to meet next summer's peak. This requires the utility to preplan (both emergency and temporary needs), document installations and perform continual design improvements. To better control time and cost factors, Detroit Edison is standardizing the installations.
To speed the process of leveraging DG to support the distribution system's 2003 peak, Detroit Edison needs lease agreements to access emergency generators. To speed installation of packaged DG solutions, fabricated trailers will house equipment, including the DG switching cabinets, pad-mount 480/4800 or 480/13,200 V step-up transformers and masts (similar to portable substations) for overhead or underground connection.
DEW Modeling and Analysis
Detroit Edison will continue to work to develop a speedy and accurate analysis tool to determine the impact of DG on the electrical system, whether for Detroit Edison or others who may want to connect DG to the Detroit Edison system. This requires updating the DEW equipment database for all of DTE Technologies' commercially available generation as well as other generator companies.
In this way, Detroit Edison can equip its planning, operations and relay engineers with the ability to drag and drop various types and sizes of DG for power flow and system protection studies. The utility also will integrate time-varying analysis into DEW to aid in the evaluation of DG's impacts on selectivity and nuisance fuse blowing.
Note: The fault current a synchronous generator provides decreases considerably in a matter of seconds. Detroit Edison has defined an algorithm and methodology for determining the effect of the sub-transient, transient and either saturated or synchronous reactance impacts of DG on a distribution circuit's protective devices. Software based on this algorithm will help determine the effect of time-varying current on typical protective devices.
Customer Premium Power Program
Detroit Edison will evaluate the impact of its Customer Premium Power Program on targeted overloaded circuits. While there are many objectives of the program, the main objective of the customer-sited generators is to test customer acceptance and willingness to pay for on-site generation as an alternate high-quality power source.
This project will allow DTE Energy to evaluate and monitor the use of these specific DG units to validate the distribution and customer benefits. The utility plans to install several kilowatt-hour sizes of DG, partnered with distribution customers (non-sell back), as a peak shaving and customer-retention strategy.
The utility will ask the customer to sign up for a three-year program, pay a monthly service charge per kilowatt installed and agree to retain Detroit Edison as their energy provider. In this way, the company is offering customers both higher-quality power and improved reliability, allowing Detroit Edison to remotely operate the units from a systems need.
DG is not the Problem
With these DG installations, DTE Energy is demonstrating its belief that DG can support the distribution grid at the engineering and customer levels. Distribution engineers have choices when addressing distribution problems, whether upgrading lines, adding capacitors, installing distribution automation or a myriad of other solutions. DTE Energy doesn't see DG as a threat, but as another choice available to resolve utility and customer needs.
Haukur (Hawk) Asgeirsson is the supervising engineer of Distributed Resource Planning at Detroit Edison, responsible for integrating distributed resources into the T&D planning and operating process. He is involved in a collaborative effort with Sandia National Laboratory to test a transportable advanced 200-kW/400-kWh zinc-bromine flow battery to be used as a distributed resource on the distribution system. He is a member of IEEE and a registered professional engineer in the Michigan. Asgeirsson received the BSEE and MSEE degrees from the University of Michigan.
Richard Seguin is a principal engineer distributed resources with System Planning and Engineering at Detroit Edison. Seguin has championed several engineering applications of new technologies for the electrical system planning and operations areas with a focus on customer power-quality and capital utilization. Currently, Seguin is the project manager responsible for implementation of EPRI's DEW at Detroit Edison. He received a BSEE degree in power system and control from Clarkson University.