PUBLIC SERVICE OF NEW HAMPSHIRE. Technical Requirements for Non Utility Generation Interconnecting to the PSNH Distribution System

Transcription

1 PUBLIC SERVICE OF NEW HAMPSHIRE Technical Requirements for Non Utility Generation Interconnecting to the PSNH Distribution System September 2013

2 1.0 Purpose of this document Public Service of New Hampshire s (PSNH) Supplemental Energy Sources Department (SESD) has established an administrative process for dealing with all types and sizes of Non Utility Generation (NUG) installations. As the level of Developer interest advances beyond the initial enquiry phase, a formal review process takes place in which the potential impact of a given site on the PSNH electrical grid is reviewed. Except for certain inverter-interfaced Net Metered installations (see section 5.B. of this document), this review includes the execution of a formal Interconnection Study (the Study ) and the production of a formal Interconnection Report (the Report ) in which general and specific requirements for certain design aspects of the facility will be defined. These requirements typically include electrical protection and control design and configuration, interface transformer configuration, required upgrades to local PSNH facilities, metering and supervisory control and data acquisition (SCADA) requirements, and in some cases operating constraints for the proposed generation. Depending on the level of general NUG activity at the time, the process can be time consuming as all proposed installations are placed in a queue and are addressed on a first-come, firstserved basis. In an effort to provide potential NUG Developers with an understanding of typical PSNH interface design requirements, this document (the Guidelines ) was developed and is supplied to all potential NUG Developers at the time of initial contact. The information contained within the Guidelines is intended to help those who are attempting to define conceptual designs to better understand the general nature and extent of typical PSNH requirements for installations of various types and electrical size. Such an understanding will generally allow more accurate estimates for the cost and scope of such designs to be produced. Where the Developer has design flexibility, such advance information may also allow choices to be made which will minimize the duration of the PSNH review and approval path, as well as to limit the overall cost of the installation. It should be understood that no attempt has been made to identify all potential PSNH requirements for each and every possible type of NUG source, technology, size and/or configuration. It should also be noted that generic PSNH metering and SCADA requirements are not included in the Guidelines, other than by reference (see section 4.B.2). All such detail will be defined in the Interconnection Report produced for the site. 2.0 Disclaimer It is very important to understand that the Guidelines are in no way a substitute for the formal Interconnection Report which may be required for a given site. SESD will be able to advise the Developer at the time of initial contact as to whether or not such a report will be required. Where such a report is required, materials purchased and engineering performed to address PSNH requirements must be based on the details contained within the Report. Any commitments which are made by a Developer on the basis of the content of the Guidelines are made entirely at the Developer s risk. 2

3 3.0 Why are NUG Interconnection Studies required by PSNH? The PSNH grid is designed to transmit electrical energy from generating sources to end users in a safe, reliable, efficient manner. As such, provisions must be made to ensure that electrical problems of any type (e.g. overloads, short circuits, high voltage, low voltage, etc) are quickly detected and reliably isolated while leaving the healthy portions of the system intact and maintaining the safety of other PSNH customers and PSNH employees. Additionally, the system must be designed in such a way that normal maintenance may be safely performed while maintaining the integrity and reliability of the balance of the interconnected network. In order to simultaneously meet all of these concerns, the impact of any proposed new source of generation must be carefully evaluated and the electrical configuration of such sources properly structured. While proposed sites of large installed capacity tend to have a greater impact than the smaller sites, even the smaller sites can have a profound impact on system performance and operating safety when not properly configured. It is the goal of the interconnection study/interconnection report process to ensure that all interface issues are properly identified and addressed such that the proper system performance is maintained. 4.0 Technical Requirements The following requirements are generally applicable to all NUGs except for those with inverter interfaces. The inverters approved for installation at "Net Metered" sites (see Section 5.B. of this document) either inherently meet the intent of these requirements or the nature of such systems makes these requirements inapplicable. At this time, the general requirements for other inverterbased NUG interfaces are handled on an individual basis. A. Safety Considerations 1. The connection of the facility to the PSNH system must not compromise the safety of PSNH s customers, personnel, or the owner s personnel. 2. The generating facility must not have the capability of energizing a de-energized PSNH circuit. To this end, the electrically controlled primary element(s) configured to enforce this requirement must have all mechanical close features removed and prominently placarded against reinstallation per PSNH. 3. Emergency shutdown and isolation provisions. a. Unless waived by PSNH, an emergency shutdown switch with facility status indicator lights must be made available for unrestricted use by PSNH personnel. 3

4 The shutdown switch shall be installed in a PSNH padlock-lockable enclosure at a location acceptable to PSNH operating personnel. The operation of the switch shall cause all of the facility s generation to be disconnected from the PSNH system, and shall block all manual and automatic reconnection of generation to the PSNH system until the switch is reset. The status lights, mounted with the shutdown switch, shall be located outdoors at a position acceptable to PSNH Operating Division personnel. Red and green lights are to be visible from the road. A red light shall indicate that the facility has generation connected to the PSNH system. A green light shall indicate that all generation is disconnected from the PSNH system. The red and green lights shall be driven by interrupting device auxiliary switches. b. Unless waived by PSNH, a PSNH padlock-lockable load break device with visible contacts must be made available for unrestricted use by PSNH personnel. The device shall be installed at a location acceptable to PSNH operating personnel. The device must be electrically located to interrupt all facility generation output and must be rated by the manufacturer to do so. 4. Protection systems included to address PSNH requirements must utilize utility grade components as approved by PSNH. This requirement includes protective relays as well as auxiliary tripping relays. 5. All PSNH-required voltage relaying applied to three-phase energy sources must be applied on a three-phase basis. 6. All devices utilized to supply PSNH-required protective functions must be equipped with provisions to aid in the post-mortem analysis of their operation. In the case of singlefunction protective elements, these provisions will include properly configured targets. In the case of multifunction numerical devices, these provisions will include properly configured event recording facilities as well as targets. 7. Dedicated relays must be reserved for PSNH required functions. These relays will provide no functions except for PSNH required functions. PSNH will determine, at the Developer s expense, the generic set points for the PSNH-required protective functions. In the case of numerical relays, depending on PSNH s familiarity with the relays being utilized, the Developer may be responsible for developing the balance of the settings (logic, etc.) in these relays, along with the actual electronic settings files themselves. 8. Any relay failure contacts on PSNH-required protective devices shall be wired to (1) trip the site generation and (2) initiate an alarm when the contacts indicate relay malfunction. 9. Under frequency protection on NUGs 1 MW and greater will be set with due regard for the NPCC under frequency load shedding program. NPCC Document Directory # 12 sets forth the requirements for automatic under frequency load shedding and automatic under frequency load shedding associated with generator under frequency tripping. NPCC Document B-07 presents relay application and testing requirements necessary to 4

5 accomplish the objectives of Directory # 12. Note that where a NUG is unable to accommodate the NPCC program settings due to turbine or other issues, additional compensating under frequency protection will be required to account for the lost generation. Any costs associated with obtaining the compensating load shedding will be the responsibility of the NUG. 10. A PSNH approved testing company will be required to verify the proper functioning of those protective systems required by PSNH. This work will be performed at the Developer s expense. 11. The generating facility has full responsibility for ensuring that the protective system and the associated devices are maintained in reliable operating condition. PSNH reserves the right to inspect and test all protective equipment at the generator site whenever it is considered necessary. This inspection may include tripping of the breakers. 12. The short circuit interrupting device(s) must have sufficient interrupting capacity for all faults that might exist. The PSNH system impedance at the facility will be supplied on request. 13. All protection systems utilized for synchronous generator protection must utilize a battery power source. AC-powered inverters are not an acceptable DC supply. The battery must be equipped with appropriate charging and monitoring facilities. The monitoring facilities must annunciate battery high voltage, battery low voltage, and battery grounds. Interrupting devices associated with PSNH-required protection and supplied power from the DC battery must be equipped with facilities configured to trip the associated generator interrupting device with an alternate supply immediately on loss of DC system trip capability. Direct AC trip and capacitor trip devices are acceptable for this backup function 14. Any protection scheme utilizing AC control power must be designed in a fail-safe mode. That is, all protective components must utilize contacts which are closed during normal operating conditions, but which open during abnormal conditions or when control power is lost to de-energize the generator contactor coil. These schemes may be utilized only with non-latching contactors and may not be used with synchronous generators. 15. A protection one line diagram and a complete set of AC and DC schematic (a.k.a. elementary) diagrams showing the implementation of all systems required by PSNH must be supplied for PSNH review. These drawings should be supplied as soon as possible so that any non-conforming items may be corrected by the Developer without impacting the scheduled completion date of the facility. 16. All voltage transformers driving PSNH-required protection systems must be formally rated by the manufacturer as to accuracy class, and must be capable of driving their connected burdens with an error not exceeding 1.2 percent. The NUG is responsible for supplying PSNH with VT manufacturer s documentation supporting VT performance and any 5

6 additional information (e.g. relay manufacturer s data) required by PSNH to verify scheme adequacy. 17. All current transformers driving PSNH-required protection systems must be rated by the manufacturer as to accuracy class and must be capable of driving their connected burdens with an error not exceeding 10 percent under worst-case fault conditions. The NUG is responsible for supplying PSNH with CT manufacturer s documentation supporting CT performance and any additional information (e.g. relay manufacturer s data, cable lengths, etc.) required by PSNH to verify scheme adequacy. 18. The secondary windings of instrument transformers feeding PSNH-required protection equipment will be grounded at one point, and one point only. 19. All PSNH-required protective relays and auxiliary tripping relays must be equipped with test facilities which allow secondary quantity injection and input contact and output contact isolation while the protective relays remain in their cases 20. All PSNH-required tripping and associated logic must be hard wired from protective relays to the interrupting device(s). Tripping and or/logic derived from programmable logic controllers (PLCs), computers, or other similar devices is not acceptable for PSNHrequired protection. 21. It is not the policy of PSNH to maintain a stock of protective relays for resale to facility Developers. Since many protective devices have delivery times of several months, Developers are strongly advised to order them as soon as possible after PSNH typeapproval is received. 22. Protection of the generating facility equipment for problems and/or disturbances which might occur internal or external to the facility is the responsibility of the Developer. Any fault located within the NUG should be detected and interrupted by NUG equipment at the NUG facility. The settings for such equipment whose failure to perform properly during such a fault could result in loss of service to PSNH customers will typically be developed by the NUG and reviewed by PSNH. PSNH s involvement with such equipment is limited to ensuring that coordination exists with upstream PSNH devices, and that the critical interrupting device is capable of interrupting the PSNH fault duty which exists at the point of application. 23. No operation of the facility s generation is allowed until all PSNH requirements have been met, all related systems, are in place, calibrated, and proven functional, and the Developer has received formal signoff from SESD. This requirement may be waived by PSNH for a given system if generation is required to demonstrate the proper functioning of that system. 6

7 B. Service Quality Considerations 1. The connection of the facility to the PSNH system must not reduce the quality of service currently existing on the PSNH system. Voltage fluctuations, flicker, and excessive voltage and current harmonic content are among the service quality considerations. Harmonic limitations should conform to the latest IEEE guidelines and/or ANSI standards. 2. In general, induction generators must be accelerated to synchronous speed prior to connection to the PSNH system to reduce the magnitude and duration of accelerating current and resulting voltage drop to PSNH customers to acceptable levels. 3. In general, synchronous generators may not use the pull-in method of synchronizing due to excessive voltage drops to PSNH customers. 4. Power factor correction capacitors may be required for some facilities either at the time of initial installation, or, at some later date. The installation will normally be done by the Developer at his expense. 5. Automatic reclosing of the PSNH circuit after a tripping operation may occur after an appropriate time delay. If additional voltage blocking of automatic reclosing is required, it will be added at the Developer s expense. C. Metering Considerations 1. Except for protection/control and metering voltage sensing and generator and/or capacitor contactor supply voltage, no unmetered station service AC shall be taken from the station service transformers. D. SCADA and Other Considerations 1. The Electric System Control Center (ESCC) requires the logging of all generator trips caused by relay action, as well as the time and the associated relay targets, for system operation analysis. 2. All NUGs must comply with the requirements of OP-0045 NH-LCC Minimum Interconnection Requirements of Merchant Generators. OP-0045 outlines the minimum metering, telemetering and voice communications requirements. 5.0 Special Considerations 7

8 The following sections describe several interface issues of significance arising from the technical characteristics of certain types and/or electrical sizes of NUG installations. Where the Developer has a choice of configurations, interface technologies, and/or sources, he/she may wish to choose a design approach which offers the least complexity, associated costs, and potential study delay. A. Closed-transition automatic transfer schemes Closed-transition automatic transfer schemes, sometimes referred to as no-break transfer schemes, are typically designed to automatically transfer a load between the PSNH grid and another source, usually a generator, without any interruption of power to the load. As a consequence, there will be a period of time where the two sources are connected together. The duration of time that the sources are tied together during the transfer has a major impact on PSNH requirements for the schemes. 1. Transfer schemes involving PSNH grid-generator paralleling times of 0.5 seconds or less usually require relatively modest supplementary circuitry to that supplied by the manufacturer of such equipment. Such an approach minimizes the associated additional costs, complexity, and PSNH engineering review efforts. 2. Transfer schemes involving PSNH grid-generator paralleling times of greater than 0.5 seconds will require full NUG interface protection. Such an approach will typically result in significant additional cost as well as substantial PSNH engineering review effort. B. NUG Sites Configured for Net Metering The State of New Hampshire has adopted Administrative Rule Puc 900 NET METERING FOR CUSTOMER-OWNED RENEWABLE ENERGY GENERATION RESOURCES. The rule defines the administrative process as well as the minimum technical requirements for the interface of NUGs utilizing renewable resources (wind, water, solar, etc.) having an installed capacity of 100 kilowatts or less. Such installations do not sell their output to the host utility, but are allowed to reduce their energy use with their generation. If they generate more energy than they use, the excess generation delivered to the host utility will be metered and can be used to offset their future energy use. The full text of this rule is available on-line at the State of New Hampshire Public Utilities Commission website ( and anyone contemplating the installation of such facilities should review the document in its entirety. While all details of the Rule will not be repeated here, it is particularly important to note that there are two primary interface types commonly utilized for such facilities, and the chosen method will have a major impact on the complexity of the interface, the extent of PSNH technical requirements, and the amount of time the entire application/approval process will typically take. 1. Net Metering inverter interfaces An inverter is a device which converts direct current (DC) energy into alternating current (AC) energy. Such devices are normally utilized where the NUG energy source consists of solar panels, certain wind mills, or any other DC source. Modern inverters are static 8

9 devices with few if any moving parts. The fundamental nature of inverters makes it very easy and desirable to integrate control and protection into one box. Further, recent efforts in the industry have resulted in certain design standards which, assuming the inverters conform to those standards, may require nothing in the way of additional interface protection in order to be acceptable in New Hampshire Net Metering installations. As would be expected, the review/approval process for Net Metering NUGs utilizing static inverters which are under 100 kilowatts and are certified to meet the standards as defined in Puc 900 will normally be much shorter than those sites utilizing conventional (non-inverter) interfaces (see next section). PSNH reserves the right to require supplemental protection and control equipment for facilities with inverters rated > 100 kilowatts or at sites utilizing multiple inverters that are each <100 kilowatts. 2. Net Metering conventional (non-inverter) interfaces Conventional generation interfaces are typically applied at those sites utilizing energy production equipment designed to generate 60 hertz alternating current (AC). In conventional interfaces, system protection functions of detection and isolation are separate and distinct from system control functions and must be separately engineered, separately purchased, separately wired, and separately tested. Consequently, non-inverter designs must be extensively reviewed for acceptability by PSNH. As would be expected, the review/approval process for Net Metering NUGs utilizing conventional interfaces will normally be substantially longer that those sites utilizing inverter interfaces. C. NUG sites with conventional (non-inverter) interfaces and installed capacity of less than 1 megawatt 1. Induction generation. a. The following protection functions are always required i. Time overvoltage (59) ii. Time undervoltage (27) iii. Time overfrequency (81O) iv. Time underfrequency (81U) v. Reverse power (32) if generator motoring is not revenue metered by PSNH. b. The following electrical configuration requirements exist for the site. i. The site may not be configured as a source of ground current to the PSNH grid. ii. Generator step-up transformer (GSU) configurations which are prone to ferro-resonance may not be used. 2. Synchronous generation a. The following protection functions are always required 9

10 i. Time overvoltage (59) ii. Time undervoltage (27) iii. Time overfrequency (81O) iv. Time underfrequency (81U) v. Reverse power (32) if generator motoring is not revenue metered by PSNH. vi. Voltage-controlled (not voltage-restrained) time overcurrent (51V) with appropriate phase angle correction to control voltage. vii. Ground overvoltage protection with instantaneous and time elements (59N). The associated voltage transformer primary windings must be rated to withstand phase-to-phase voltage. b. The following electrical configuration requirements exist for the site. i. The site may not be configured as a source of ground current to the PSNH grid. ii. GSU configurations which are prone to ferro-resonance may not be used. D. NUG sites with conventional (non-inverter) interfaces and installed capacity of 1 megawatt or more 1. Synchronous generation and induction generation. a. The following protection functions are always required and are in addition to those defined for sites with installed capacity of less than 1 megawatt. i. Ground time overcurrent (51N). This function will receive operating current from the neutral current transformer of the grounding element described in section 5.D.1.b., below. It will be configured to trip the high voltage side three phase interrupting device described in section 5.D.1.b., below. ii. Long-term system time overvoltage protection (59L). This device requires a very high dropout/pickup ratio and will be configured to trip all site generation. iii. Transfer trip from each remote three phase automatic sectionalizing device will be required if the NUG aggregate capacity (including existing NUGs) is more than 1/3 of the minimum local electric power system (EPS) load. In addition, sites with installed capacity of 5 megawatts or more will require transfer trip from each remote three phase automatic sectionalizing device. The transfer trip equipment shall cause all site generation to be tripped. b. The following electrical configuration requirements exist for the site. i. The site must be configured as a reactance-grounded limited source of ground current to PSNH. This configuration typically requires a neutral grounding reactor in addition to a grounded wye (PSNH side) - delta (NUG side) GSU. The necessary electrical parameters of the neutral grounding reactor will be supplied by PSNH. Depending on several factors, other reactance-grounded 10

11 ii. limited ground source configurations may be acceptable but must be reviewed and approved by PSNH. A three phase fully rated fault interrupting device must be included on the high voltage side of the site between the site and the PSNH grid. 6.0 Protection requirements at locations remote from the NUG. Some NUG installations may require additions and enhancements to the PSNH grid itself due to loading, interrupting duty, protection sensitivity, protection coordination, stability, or other issues. The necessity for any such modifications will be identified in the site Interconnection Report. These enhancements will be the financial responsibility of the NUG Developer and may include but not necessarily be limited to one or more of the following: New substations Line replacements or additions Recloser replacements or additions Circuit breaker replacements or additions Protective relay replacements or additions 7.0 Special Studies Some proposed NUG installations may require additional special studies (e.g. stability) in order to determine their potential impact on the PSNH grid. The need for and the estimated costs of any such studies will be detailed to the Developer along with the estimated cost of the Interconnection Study itself after receipt by SESD of the completed Interconnection Request form. 11