Conference Papers. Keith Malmedal P.E., P.K. Sen Ph.D /08/$ IEEE. Paper No. 08 C3

Transcription

1 Conference Papers Comparison of Some Randomly Selected Utilities Interconnection Requirements and the Compliance with the IEEE Std Interconnection Guidelines Keith Malmedal P.E., P.K. Sen Ph.D. Paper No. 08 C /08/$ IEEE C3

2 Comparison of Some Randomly Selected Utilities Interconnection Requirements and the Compliance with the IEEE Std Interconnection Guidelines Keith Malmedal P.E. Member, IEEE, P,K. Sen Ph.D. P.E., Senior Member, IEEE Abstract Electric Utilities permitting interconnection of generation (small and/or large) on their power systems have long had standards which any entity wishing to interconnect has to meet. Recently the growing importance of distributed generation (mostly less than 10MVA), especially using renewable sources, has prompted the creation of IEEE Std which sets requirements and guidelines for interconnecting a distributed resource with an electric power system. This paper will examine the requirements of the Std. IEEE 1547 and compare them with the interconnection requirements currently used by a number of randomly selected utilities. Index Terms Distributed Energy Resources, Generators, Interconnection, Renewable Energy. IEEE Std Guideline. An analysis is also added with respect to these data to enhance the understanding and applicability of these requirements. In 1978 the Public Utility Regulatory Policies Act (PURPA) was passed which encouraged the creation of n-utility owned generation and cogeneration. The Energy Policy Act of 2005 modified PURPA and its provisions will further encourage the creation and interconnection of distributed generation on utility facilities. These developments have lead to the creation of IEEE Std and the further creation of utility interconnection standards for power plants and distributed resources which wish to connect with utility facilities. I I. INTRODUCTION EEE Standard titled IEEE Standard for Interconnection Distributed Resources with Electric Power Systems was developed in its own words to provide a uniform standard for interconnection of distributed resources (DR) with electric power systems (EPS). It provides requirements relevant to performance, operation, testing, safety considerations, and maintenance of the interconnection [1]. The standard also states that the requirements contained within it are universally needed for interconnection of DR, including synchrous machines, induction machines, or power inverters/converters and will be sufficient for most installations. Many utilities had developed their own standards some of which have been in use for many years prior to the IEEE Standard Guideline. An examination of a variety of interconnection standards shows that there is a wide variation in the acceptance of the requirements stated in the Std. IEEE This paper will examine, in detail, a number of such randomly selected guidelines and compare them with the Manuscript submitted January 18, 2008 for 2008 IEEE Rural Electric Power Conference, April 28-29, Charleston, SC. This work was partially supported by the NSF IUCRC Power Systems Engineering Research Center ( K. Malmedal is a principal engineer with NEI Electric Power Engineering, Arvada, CO USA. and a doctoral student at Colorado School of Mines, Golden, Colorado 80401, kmalmedal@neiengineering.com P. K. Sen is Professor of Engineering with Colorado School of Mines, Golden Colorado psen@mines.edu II. INTERCONNECTION REQUIRMENTS AND IEEE STD The table shown at the end of this paper in Appendix II is designed to quickly show how a variety of utilities and state requirements for generation interconnection compare with the requirements of IEEE Std Of the standards (available in public domain) examined only two utilities completely the implementation of IEEE Std. 1547, PacifiCorp and the New York State Public Utilities Commission. Several others, such as Otter Tail Power, partially accept the requirements of IEEE Std.1547 while others, independently develop their own requirements. The only meaningful guidelines of IEEE Std which seems to be universally accepted is the provision of requiring a utility to have accessible disconnect switch at the point of common coupling (PCC) with the utility (Fig. 1)[1]. Ather requirement which is well, although t universally, accepted is the requirement that some type of testing (usually field testing) (Appendix 1 Table 4)[1]be done before the distributed energy resource (DER) is released for operation. An area of (wide) common concern is the (voltage) flicker and voltage fluctuations that may be caused by a DR. IEEE Std states a level of acceptable voltage fluctuation which some utilities accept while other simply makes the blanket statement that abrmal voltages will be created by the DR. IEEE Std also states that the DR must be grounded in a way t to produce over voltages without stating how this is to be done. The interconnection standards are generally more specific on grounding and ground fault protection issues, sometimes requiring a transfer trip to the DR to insure over voltages are produced. C3-1

3 IEEE Std contains a number of requirements to limit harmonics created by the DR. Those interconnection standards addressing harmonics commonly include compliance with IEEE Std. 519 rather than referring to IEEE Std (Appendix I Table 3)[1]. There appears to be two areas of considerable disagreement between the IEEE Std and many utility interconnection standards. The first is in the area of frequency protection. IEEE Std has requirements for tripping the DR at certain abrmal frequencies within certain times (Appendix I Table 2) [1]. These requirements disagree with several of the interconnection standards. In some cases, the interconnection standards do t permit tripping in part of the frequency range which IEEE Std requires tripping. In general, where IEEE Std appears to be more concerned with removing the DR from the system during an abrmal frequency event, the utility interconnection standards seem more concerned with keeping generation on to try to prevent an abrmal frequency event from becoming worse due to the removal of generation. The second area of disagreement is the protection that must exist at the point of common coupling (PCC). Fig. 1[1] shows how the DR and EPS may be interconnected and illustrates where the PCC may occur. This is an area t well addressed in the IEEE Std which states: the requirements shall be met at the point of common coupling (PCC), although the devices used to meet these requirements can be located elsewhere. [1] Most utilities, however, require protective devices to be located at the point of common coupling. Fig. 2 shows a typical distribution system including the locations where DER may be connected. This point is commonly protected with fuses only. However, many interconnection requirements call for increased protection at the PCC. This is done to prevent disturbances caused by the DR from affecting the utility, and is often also to insure that there is protective relaying which backs up the relaying which may exist at the DR. Among the protection often by the utility at the PCC are over and under voltage protection, frequency protection, ground fault protection, and occasionally some type of backup system protection such as a 51V relay. Utility interconnection standards often also require additional relaying for the generator which is t by the IEEE Std [2]. Some utility interconnection standards require utility grade relays a certain generation size, and provisions for periodic relay testing by the utility. The periodic re-testing of interconnection equipment is also a requirement often seen as important by utilities, but t well addressed in the IEEE Std. 1547[2]. III. CONCLUSION The table in the Appendix II shows some of the more important requirements of the IEEE Std and compares them with selected utility interconnection standards. It can be seen that there is considerable variation between the standards and the various utilities examined. Although some utilities do accept all of IEEE Std. 1547, most of those also have other standards which must be met. It also appears that from the standpoint of many utilities allowing generation interconnection the provisions of IEEE Std are t, as stated in the standard universally needed and sufficient for most installations [1] and many utilities have other stringent requirements than those stated in IEEE Std Fig. 1 Relationship of Interconnection Terms. 30/40/50 MVA T1 115KV KV 7%Z G 51G 79 C S ST 115KV 50 50G 51 51G 51 51N 50G 51G 79 T3 750KVA 3Ø 12.47KV-480V INDUSTRIAL LOAD 40E WITH DER 87T Voltage Regulator G 51G SECTIONALIZER T2 30KVA 1Ø 7.2KV-120/240V 5E D1 LATERAL RES. LOADS WITH DER Fig. 2 Typical Power Distribution System with Protection Shown. The Energy Policy Act of 2005 (EPACT) specifically states that interconnection services be based upon the IEEE Standard It also states that agreements and procedures shall be established whereby the services offered shall promote current best practices of interconnection for distributed generation, including but t limited to practices stipulated in model codes C3-2

4 adopted by associations of state regulatory agencies. All such agreements and procedures shall be just and reasonable, and t unduly discriminatory or preferential. So EPACT recognizes both IEEE Std and utilities interconnection practices and standards. It can be seen that in some cases the a utility s interconnection standards are the same as the requirements of IEEE Std. 1547, however, in most cases there is considerable variability between what the utility requires and what is suggested in IEEE Std Some states are proposing to use IEEE Std as the basic standard to determine if a new DR can automatically be connected to a system without further review or if further study of the system is by the utility before the DR can be allowed to connect (which will be paid for by the customer). The procedure might require a new DR customer to fill out a form which would include a number of questions about the new DR. If the answers provided proved that the provisions of IEEE Std were satisfied, the interconnection of the new DR could proceed without further study. The basic IEEE Std is t sufficient to determine if a certain type of interconnection is safe for the rest of the system. IEEE Std mainly addresses the generator and PCC itself, while t concerning itself with other parts of the system or system operation. For example, the requirement that the DR t cause over voltages may be met at the point of common coupling (PCC), but may t be met in other parts of the distribution system. The customer filling out the forms may have way of kwing that this is true and examination of the system with DR by a distribution engineer might be needed to determine that this problem even existed. This problem may become more prounced when the DR is connected at the residential level and every effort is made by simplifying the procedure. Ather area of concern is reclosing and the effect DR may have on the existing utility reclosing scheme. Nearly every distribution system in the U.S. incorporates multiple-shot reclosing. However, how this scheme may be impacted by the addition of DR is certainly t clear to the customer who is designing only the equipment in the new power plant at the PCC. IEEE Std doesn t address the impacts of DR on reclosing and line sectionalizing schemes. As long as the penetration level of DR is small (say less than 5% of the feeder capacity) the addition of an additional unit, especially small inverter based DR, may cause minimum impact to the system and can be connected without further review by the utility s engineers. However, when DR penetration level on a distribution system becomes sufficiently high (presently estimated at 20% or higher) this may cause problems with the system [3]. Will the latest DR to connect be to pay for all the system upgrades to make it possible to safely connect this generator? Or will all the DR s on the system, old and new, be to contribute to this cost? This question has to be addressed. As DR penetration levels become high the impacts become more widespread and the IEEE Std concentrates on impacts at the PCC and does t address what may become widespread future effects on both distribution and transmission systems and their operation. These are valid questions currently imposed and must be addressed in the future revision of the Standard. Utilities need to be more careful in allowing interconnections base only on the IEEE Std It is evident that utilities have seen the necessity of providing their own standards, which may or may t include provisions of IEEE Std in the foreseeable future, to insure their systems can continue to operate safely and reliably as DER becomes a more important part of the generation mix. The attempt to make a more general Standard by the IEEE was good, but future revisions must address a number of additional issues. Additional Std. of the 1547 series may also include some of the questions raised by this paper. REFERENCES [1] IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, IEEE Standard , IEEE Piscataway, NJ. [2] K. Malmedal, P.K. Sen, and J. P. Nelson, Application of Out-of-Step Relaying for Small Generators in Distributed Generation, IEEE Transactions on Industry Applications, Vol. 41, No. 6, Nov./ Dec. 2005, pp [3] K. Malmedal, B. Kroposki, and P.K. Sen, Distributed Energy Resources and Renewable Energy in Distribution Systems: Protection Considerations and Penetration Levels, (In Review), 2008 IEEE Industry Applications Society 43 rd Annual Meeting, Edmonton, Alberta, October 5-9, [4] IEEE Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems, IEEE , IEEE, Piscataway, NJ. [5] XCEL Energy Interconnection Guidelines for Transmission Interconnected Producer-Owned Generation 20MW and less. Version 1, Xcel Energy, June 15, [6] PacifiCorp Cogeneration and Parallel Generation Interconnection Guide, ificorp/pplengin.pdf [7] AESO Generation and Load Interconnection Standard, [8] Otter Tail Power Company, Guidelines for Generation, Tie-Line, and Substation Interconnection, [9] Rules for Interconnecting Distributed Generation Systems, Wisconsin Public Service Commission PSC 119, [10] Distributed Generation Interconnection Manual, Public Utility Commission of Texas May 1, [11] Guidelines for Interconnection of Customer Generators, City of Anaheim Public Utilities Department, Electrical Engineering, s2-1.pdf, December [12] New York State Standardized Interconnection Requirements and Application Process for New Distributed Generators 2 MW or Less Connected in Parallel with Utility Distribution Systems, New York State, Public Service Commission, September [13] SRP Interconnection Guidelines for Distributed Generators, December [14] Application Guide for Distributed Generation Interconnection: 2006 Update, The NRECA Guide to IEEE 1547, Resource Dynamics Corporation, Final.pdf, March [15] K. Malmedal, B. Kroposki, and P. K. Sen, The Energy Policy Act of 2005 and its Impact on Distributed Generation, IEEE IAS Magazine, January 2007, pp [16] K. Malmedal, B. Kroposki, and P.K. Sen, The Energy Policy Act of 2005 and it s Impact on Renewable Energy Applications in the USA, 2007 IEEE Power Engineering Society General Meeting Conference Record, Annual Summer Meeting, Tampa Bay, Florida, June [17] Energy Policy Act of 2005, Washington, DC, C3-3

5 Keith Malmedal (Member, IEEE) received his BSEET degree from Metropolitan State College of Denver in 1995, a MSEE degree (Power) and a MSCE degree (Structures) from the University of Colorado at Denver in 1998 and 2002, respectively. Keith is presently a PhD candidate at Colorado School of Mines in Engineering Systems (Electrical Specialty). He has over sixteen years combined experience in electrical power system analyses and system study, teaching and research and is presently the President and a senior project manager at NEI Electric Power Engineering, Arvada, Colorado, specializing in all aspects of power system design. Keith has published over a dozen technical papers in archival journals and conference proceedings and taught (and co-taught) regular university courses, short courses on a variety of subjects related to the interrelated areas of power systems, machines, protections, renewable energy applications, and energy policy issues to hundreds of practicing professionals. Mr. Malmedal is a member of the American Society of Civil Engineers and a registered professional engineer in 14 states. TABLE 1 Interconnection System Response to Abrmal Voltages. TABLE 2 Interconnection System Response to Abrmal Frequencies. Pankaj K. (PK) Sen (Sr. Member, IEEE) received his BSEE degree (with hors) (1966) from Jadavpur University, India, and the M.Eng. (1971) and Ph.D. (1974) degrees in electrical engineering from the Technical University of Nova Scotia (Dalhousie University), Halifax, NS, Canada. He is currently a Professor of Engineering and Site Director of the Power Systems Engineering Research Center ( at Colorado School of Mines in Golden, Colorado. His research interests include application problems in electric machines, power systems, protection, renewable energy and distributed generation and power engineering education. He has published more than 130 articles in various archival journals and conference proceedings and has supervised over 120 students with MS and PhD degrees. Dr. Sen taught a number of regular advanced level graduate and many undergraduate university courses, and conducted workshops and taught short courses on machines, power systems, transmission and distribution, renewable energy, energy policy and energy ecomics to literally thousands of practicing engineers and is a registered professional engineer in the State of Colorado. TABLE 3 Maximum Harmonic Current Distortion in Percent of Current. TABLE 4 Sequence for Conducting Design Test. APPENDIX I Selected Sketches from the IEEE Std. 1547[1] Fig. 3 Schematic of Interconnection. TABLE 5 Synchronization Parameter Limits for Synchrous Interconnection to an EPS or an Energized Local EPS to an Energized Area EPS. TABLE 6 Maximum Harmonic Distortion in Percent of Rated Voltage for Synchrous Machines. C3-4

6 APPENDIX II TABLE 7 Comparison of Utility Requirements with IEEE Std. No Requirement IEEE 1547 XCEL Interconnection Standard for <20MW PacifiCorp Alberta Electric Must Comply with IEEE 1547 (DR) shall t regulate voltage at (PCC) (4.1.1) Voltage Regulation may be allowed Otter Tail Power Flicker requirements only Generation must control line-ground voltage if islanded Wisconsin PUC For paralleling equipment only Texas PUC City of Anaheim New York State PUC Salt River Project Grounding scheme shall t cause over voltages or disrupt ground fault protection. DR shall parallel with EPS without causing voltage fluctuation greater than 5%. Network protectors shall t be used to isolate a network to which DR is connected unless protectors are tested and rated for the purpose. DR shall t prevent the reclosing of any network protectors and shall t require changes in protector clearing times. (4.1.2) (4.1.3) ( ) ( ) Must be effectively grounded Must be effectively grounded Generation must control line-ground voltage if islanded and several schemes may be used to prevent over voltages Isolation Trans. may be DR shall t cause cycling of network protectors. ( ) Network loading and fault interrupting capacity shall t be exceeded with the addition of DR. DR shall t energize the EPS when the EPS is de-energized. DR <250kVA at the PCC shall monitor real and reactive power, and voltage at its PCC ( ) (4.1.5) (4.1.6). C3-5

7 Requirement Interconnection system shall withstand EMI and EMI shall t cause misoperation. Interconnection system shall withstand voltage and current surges per IEEE C or C Paralleling device shall withstand 220% of interconnected system rated voltage. DR shall t energize faults on the EPS circuit to which it is connected. DR shall de-energize the EPS prior to any reclosure on the EPS. DR protection system shall detect voltages at terminals if DR<30kW, interconnection equipment is certified to pass a nislanding test, or DR is less than 50% of local EPS minimum demand and export of power is t permitted. Shall trip in 0.16 sec if V<50%, Shall trip in 2.00 sec if 50%<V<88%, Shall trip in 1 sec if 110%<V<120%, Shall trip in 0.16 sec if V>120% Freq trip settings shall be adjustable for over 30kW Shall trip in 0.16 sec if F>60.5Hz Shall trip in 0.16 sec if F<59.3 Hz IEEE 1547 ( ) ( ) ( ) (4.2.1) (4.2.2) (4.2.4) (4.2.4) (4.2.4) XCEL Interconnection Standard for <20MW PacifiCorp Alberta Electric Otter Tail Power Wisconsin PUC Texas PUC City of Anaheim New York State PUC Salt River Project 1-5 sec Yes 1-5 sec Yes 1-5 sec ; 30 cy at 105% Yes Yes Tripping t permitted below 60.5 Hz Tripping t permitted 10 cycles 61 Hz 6 cycles below 59 Hz Tripping t permitted below 60.6Hz. 3 min. 60.6Hz, 30 secs Hz 3 minutes; 30 secs. below 58.4Hz; 7.5 secs. below 57.8Hz; 45 cycles below 57.3 Hz Tripping t permitted below 60.5 Hz Tripping t permitted 59.5 Hz 0.25 sec Yes 0.25 sec Yes C3-6

8 Requirement If DR>30kW shall have adjustable trip set point for F<59.8 to 57 Hz and adjust between 0.16 and 300 sec No DR reconnection shall occur if voltage and frequency are out of range. DR shall have adjustable time delay or a delay of 5 minutes before reconnection. DR shall t inject more DC current than 0.5% of its rated output. DR shall t produce objectionable flicker Shall t produce more than 4% harmonic below the 11th. Shall t produce more than 2% harmonics between 11th and 17th. Shall t produce more than 1.5% harmonics between 17th and 23rd. Shall t produce more than 0.6% harmonics between 23rd and 35th. Shall t produce more than 0.3% harmonics greater than the 35th. Total harmonic distortion shall t exceed 5% DR shall detect and de-enrgize an island. DR shall undergo testing at factory or in field. IEEE 1547 (4.2.4) XCEL Interconnection Standard for <20MW Tripping permitted below 58.5 Hz. PacifiCorp Alberta Electric Tripping t permitted 59.4 Hz Otter Tail Power Wisconsin PUC Texas PUC City of Anaheim New York State PUC Salt River Project Yes (4.2.6) (4.2.6) (4.3.1) (4.3.2) <1% below the 7th IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 IEEE 519 (4.4.1.) If islanding is possible SCADA is (5.1) C3-7

9 Requirement Goverr must operate between 59.5 and 60.5 HZ and be adjustable 0-10% droop. IEEE 1547 XCEL Interconnection Standard for <20MW PacifiCorp Alberta Electric Otter Tail Power Wisconsin PUC Texas PUC City of Anaheim New York State PUC Must have Circuit breaker at PCC For synch. mach. 25 relay Salt River Project 59 relay 27 relay 1MW 50kW Yes 81 relay 51N relay 51V or 21 relay 32 relay may be may be 1MW 1MW 50kW May be 47 relay 15 relay for induction machines System Study Required Must t increase voltage unbalance by more than 1% Information must be available for units 5MW may be Utility grade relays 100kW System must be UL listed Must provide test switches for protection testing interrupting device UL kW Disconnect Switch and interrupting devices C3-8