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Implementation of Dg Interconnection System and Monitoring Control
The project is to implement a parallel interconnection between a Power Producer and a Wires Owner. The steps required to implement the interconnection includes the following: 1. Make Application to the Wires Owner for a parallel interconnection 2. Prepare the required Single Line Diagrams, Proposed Design, Type of Generator, Fuel Source, and Type of Service desired. 3. Receive approval of the Wires Owner to proceed with the Interconnection. 4. Finalize the Design, Construction, Testing, Interconnection Agreement, and Operation and Maintenance Agreement between the Power Producer and the Wires Owner. 5. Proceed with the construction of the generator and the interconnection. 6. Inspect the installation periodically during construction. 7. Review Type testing submittals and witness them where necessary. 8. After completion of construction begin Start-up and Design Verification Testing. 9. Energize Generation and Interconnection Facilities 10. Document all functional testing using modern technology such as Numerical Protection Systems as recorders and event loggers before loading and after loading the generator and the interconnection facility. 11. Place in operation and begin maintenance planning for the asset. B. INTERCONNECTION PROTECTION SINGLE LINES To review the required protection for the reliability and performance of the proposed facility, there are four increasingly complex levels to get the job done: • Level 1 - Protection requirements for operating the interconnection system for system disturbances that occur when the two electric power systems are operating in parallel. • Level 2 - Additional protective functions to increase the level of protective elements to enhance the detection of harmful currents while operating in parallel. • Level 3 - Additional protective functions enhance control during normal operation. • Level 4 - Additional control functions. Figure 7 is the single line diagram illustrating the performance capability of the least complex alternative - Level 1. The purpose of the 27/59 and 81U/O functions shown in Figure 7 is to separate the two electric power systems and allow the system with the disturbance to recover to its steady state conditions before restoring the systems to parallel operation. Recording of the system conditions before, during and after the disturbance by the interconnection protection systems available today is a must. The recording of targets, fault current levels, sequence of events, and oscillographic information removes all doubt as to why the tie line tripped. Older technology did not have this capability at a reasonable cost. Figure 8 is the single line diagram for Level 2 and increases the performance capability for protection, however it also adds complexity due to closer interaction between the operating systems. Additions include Over current Protection for system fault conditions and unbalance voltage and current (51C or 51V, 67, 46) and additional voltage protection (59N/G, 27N, and 47). Figure 8: Level 2 (Increased performance capability) The addition of time over current with voltage controller or voltage restrained control allows for more selectivity to differentiate fault current from overload current when system fault current levels and overload levels are close, due to a low system stiffness ratio. The addition of directional over current adds increase selectivity for fault detection of phase faults. The addition of current unbalance (Function 46) will assist in preventing unbalance currents from damaging the interconnection equipment. The addition of the unbalanced voltage (Function 47) will add protection for open or high impedance grounded phases. The addition of the 59N and 27N functions on the high side of a Delta-Wye transformer adds fault detection for phase to ground faults. Figure 9 is the single line diagram for Level 3 and adds additional protection to Level 2 (Protection 32 overpower forward or reverse). Figure 9: Level 3 (additional protection) The addition of an overpower device 32 to the interconnection gives the capability of controlling the import or export of power during normal operation. Figure 8 shows this additional element and directionality is controlled by the polarity of the CT connections. Dual element overpower - forward and reverse allows the Wires Owner to determine if the Power Producer has lost load or lost generation when coupled with a time delay function 62. Figure 10 is the single line diagram for Level 4 and adds control functions to Level 3. (25 w/voltage monitoring) Figure 10: Level 4 (adds control function) When an interconnection is closed, there must be supervision of the closing of the Interconnection/ Generator Breaker. Monitoring of the voltage across the open breaker for the following four conditions will set up the closing logic scheme chosen: a. Live bus - Live line b. Live bus - Dead line c. Dead bus - Live line d. Dead bus - Dead line A 25 sync-check device must only permit the closing of the open breaker when the voltage, frequency and phase angle between the electric systems are within certain differential limits. These limits are Delta V, Delta F and Delta Phase Angle. This function is required any time the interconnection is manually or automatically closed. Otherwise, there are potentially damaging transients to the equipment. DG OPPORTUNITIES TO ENHANCE CUSTOMER SATISFACTION Case #1: Given a local hospital with cogeneration needs for hot water for the hospital laundry. The addition of five 75kW Induction Generators (325kW) is a cost effective use of combined heat and power running in parallel with the hospital's 277/480V electric power system. Figure 11 is a one line diagram of this application. The facility has been in operation since early 1991. The designer used a zig-zag transformer connection to provide a ground source to trip the DG breaker for ground faults on the hospital's electric power system. A possible new application opportunity for this facility is to convert the 500kVA emergency generator to run in parallel with the hospital's electric power system continuously without exporting power to the Wires Owner's electric power system. Case #2: This case is an application whereby existing interconnected electric power systems installed a 24MW diesel power plant. The purpose was for one party to install and operate the 24MW facilities to relieve imported power and energy during peak loads and periods of curtailment within the bulk power systems. Case #3: This case has applied the fuel cell technology to a United States Postal Service facility using five natural gas fueled 200kW phosphoric acid fuel cells. These prepackaged and self-contained fuel cells feed a 480V common bus. The bus is connected to 600V metal-clad circuit breaker switchgear. A site management protection and control system consisting of circuit breakers for the fuel cell side and the grid side, along with a high speed solid state automatic switch between the Post Office 480V switchboard and the grid side circuit breaker. The high speed automatic switch controller provides for detection of grid transients and transfers the fuel cell power plant output from grid parallel mode to grid independent operation. The shift from full plant output to load matching/following is accomplished in one-quarter cycle. The 1MW fuel cell power plant provides electricity and heat to the U.S. Postal facility. Case #4: This application has applied a 6MW diesel power plant at a customer's 35mW Chip Plant manufacturing process in cases of load curtailments. The agreement provides that, upon notification by the Wires Owner, the customer will manually start the three 2MW unit power plant and place the 6MW on line. The process of synchronizing and paralleling with the power grid is fully automated. The objective of paralleling is a seamless transfer to and from the Wires Owner's grid. FUTURE OPPORTUNITIES - DISTRIBUTED GENERATION AGGREGATION Power supply planning is being challenged by continuously growing needs for more capacity in supply, wholesale for retail delivery systems (bulk power supply grid/network) and retail delivery systems (sub transmission and distribution systems). Planners are searching for additional energy sources that can be brought on line quickly and economically to satisfy peaking and mid-range energy demand needs. A key source already exists. Distributed generation units now used for emergency standby or cogeneration purposes already exist. One survey suggests that more than 90,000MW of DG capacity currently exists. Tapping this resource will require some novel approaches to providing system solutions to system opportunities. For instance, suppose a regional wastewater utility has an environmental problem with flaring methane gas to the atmosphere from the digesting process. What if the emergency standby generators could be retrofitted or upgraded with equipment to allow parallel interconnected operation with the Wires Owner system? Technical business practices and regulatory barriers could be overcome with the following Conclusion: Aggregation of these 1 to 10MVA sources could be possible and economical if system solutions were planned, designed, built, tested, and maintained and operated for the life of the asset.
About the Author
Assistant professor in lord venkateswara engineering college.I am doing phd in sathyabama university, Tamil Nadu,India.
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