Chapter 10
Related standards and specifications
Abstract
Related standards and specifications present standards and specifications relating to the microgrid in and outside China.
Keywords
standards and specifications
microgrid standard system
grid-connected operation standards
islanded operation standards
The rapid development of the microgrid technology and various distributed resources (DRs), such as wind, photovoltaics (PV), and biomass, is changing the traditional radial pattern of power systems, and poses challenges to the security and stability of the grid. Unified standards and specifications for power quality, active/reactive power control, security, protection, and communication of DRs must be available to ensure orderly development of DRs and security and reliability of the power system.
10.1. Related international standards and specifications
The microgrid is an emerging type of power network. Up to now, there has been no unified, systematic standard or specification officially issued in China for the microgrid, but some international standards have incorporated related specifications.
Currently, the IEEE 1547 IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, IEC TS 62257 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification, and DG interconnection and power quality standards in some countries form the framework of international standards on distributed generation. Among them, the IEEE 1547 is the most widely accepted standard. The provisions pertaining to the microgrid in these standards provide reference for the preparation of microgrid-specific standards in the future. However, only IEEE 1547.4 has incorporated such provisions, which are just a draft version and have not been officially issued.
10.1.1. Related IEEE standards
An early international standard on DRs is IEEE 446-1995 Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications, which states how emergency and standby power sources are installed and applied, and that users can power loads with DRs, and such generators are mainly for reliable power supply in an emergency and not interconnected to the grid.
The IEEE 1547 was officially published by the IEEE in 2003, and established as a national standard of the United States. It lays down the basic requirements for all aspects on interconnection of DRs with an aggregate capacity of 10 MVA or less, including power quality, system reliability, system protection, communication, security criteria, and metering.
The IEEE 1547 standard is not inclusive of interconnection of all DRs; it has some limitations. Specifically, it is applicable only to inverter-based DRs with an aggregate capacity of 10 MVA or less, and installed on a 60 Hz primary or secondary distribution system; it does not deal with DR self-protection and power system planning and design. As such, the IEEE 1547 has been gradually expanded to a series (as listed next), in order to standardize the interconnection of DRs, and reduce the costs for construction and operation of infrastructure related to renewable energy:
1. IEEE 1547.1 Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems. This standard, released in 2005, specifies the design, production, commissioning, and periodic connection test of DRs to determine whether DRs are suitable for interconnection.
2. IEEE 1547.2 Application Guide for IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems. This standard provides technical background and application details to support understanding of IEEE 1547.
3. IEEE 1547.3 IEEE Guide for Monitoring, Information Exchange, and Control of Distributed Resources Interconnected with Electric Power Systems. This standard permits intentional islanding of a part of the distribution network to improve power reliability.
4. IEEE 1547.4 Draft Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems. This guide provides alternative approaches and good practices for design, operation, and integration of DR island systems, including the ability to separate from and reconnect to the grid.
5. IEEE 1547.5 Draft Technical Guidelines for Interconnection of Electric Power Sources Greater than 10 MVA to the Power Transmission Grid. This standard provides requirements for the design, construction, commissioning, acceptance, test, maintenance, and performance of DRs greater than 10 MVA interconnected to the transmission network.
6. IEEE 1547.6 Draft Recommended Practice for Interconnecting Distributed Resources with Electric Power Systems Distribution Secondary Networks. This standard provides guidance for interconnecting DRs with electric power systems distribution secondary networks. It was sponsored by the IEEE Standards Coordinating Committee 21 on Fuel Cells, Photovoltaics, Dispersed Generation, and Energy Storage.
7. IEEE 1547.7 Draft Guide to Conducting Distribution Impact Studies for Distributed Resource Interconnection. This guide gives an engineering study method for analyzing the potential impacts of DR interconnection on regional distribution systems.
8. IEEE 1547.8 Draft Recommended Practice for Establishing Methods and Procedures that Provide Supplemental Support for Implementation Strategies for Expanded Use of IEEE 1547. This standard, providing more flexible design methods and procedures, expands the use of IEEE 1547.
Among them, the IEEE 1547.4 details the design and operation of the microgrid in grid-connected mode and islanded mode, the main considerations in planning and operating the microgrid, and discusses the strategies for grid-connected and islanded operation, thus providing reference for the preparation of microgrid-specific standards in the future.
The IEEE 519-1992 regulates that the installation of DG shall in no case cause voltage flicker beyond the limit, and defines the voltage flicker limit curve. The IEEE P1547 and IEEE 929-2000 are completely compatible in establishing standards for harmonics. The total harmonic distortion (THD) shall not exceed 5% of the rating at a voltage frequency of 60 Hz, or for any DG, the THD at the PCC shall not exceed 3% of the rating.
DGs are mostly connected to distribution systems at a low- or medium-voltage level. Currently, no country has specified the maximum voltage that DGs can connect to, and different standards give different voltage limits.
Most standards require that the voltage fluctuation at the PCC caused by installation of DG shall not be more than ±5% of the rated voltage. Almost no standard permits voltage control by DGs.
10.1.2. Related IEC standards
The main IEC standard relevant to the microgrid is IEC TS 62257 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification, which gives instructions on siting, equipment sizing, system design, and management of rural electrification projects. It applies to renewable energy and hybrid systems with AC voltage below 500 V and DC voltage below 50 V. It consists of the following nine sub-standards:
1. IEC TS 62257-1-2003 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 1: General Introduction to Rural Electrification
2. IEC TS 62257-2-2004 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 2: From Requirements to a Range of Electrification Systems
3. IEC TS 62257-3-2004 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 3: Project Development and Management
4. IEC TS 62257-4-2005 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 4: System Selection and Design
5. IEC TS 62257-5-2005 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 5: Protection Against Electrical Hazards
6. IEC TS 62257-6-2005 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 6: Acceptance, Operation, Maintenance and Replacement
7. IEC TS 62257-7-2008 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 7: Generators
8. IEC TS 62257-8-1-2007 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 8-1: Selection of Batteries and Battery Management Systems for Stand-alone Electrification Systems-Specific Case of Automotive Flooded Lead-acid Batteries Available in Developing Countries
9. IEC TS 62257-9-1-2008 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 9-1: Micropower Systems; IEC TS 62257-9-2-2008 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 9-2: Microgrids
Among these standards, IEC TS 62257-9-2 Recommendations for Small Renewable Energy and Hybrid Systems for Rural Electrification-Part 9-2: Microgrids provides special requirements for the design and implementation of dispersed rural microgrids and procedures to ensure personal and property safety, and detailed instructions and technical requirements on the limits, composition, voltage drops, protection against electric shocks, protection against overcurrents, selection and erection of equipment, and verification and acceptance of microgrids. It applies to low-voltage (LV) AC microgrids, three-phase or single-phase, with a capacity of 100 kVA or less.
10.1.3. Other related standards
Almost all countries in Europe have established their own requirements on the interconnection of DRs. The United Kingdom, France, Germany, and Belgium have developed standards, but they do not cover all DG technologies. The standards of the United Kingdom and Canada mainly focus on the requirements and specifications for connection of DGs, response of DGs to abnormality of distribution networks, and protection configurations, including islanding protection, power quality, and operation, security and tests of DGs.
Through discussions, the European Committee for Electrotechnical Standardization, CENELEC, issued Requirements for the Connection of Micro-generators in Parallel with Public Low-voltage Distribution Networks (draft). The United Kingdom’s standard ER G75/1 Recommendations for the Connection of Embedded Generating Plant to Public Distribution Systems above 20 kV or with Outputs over 5 MW specifies the respective responsibilities of utilities and power producers, defines the basic operating parameters, including voltage, frequency, grid structure, short-circuit current, and relay protection, analyzes the security, reliability, and stability of the electric power system, and considers islanded operation, making it a comprehensive standard on the grid-connection of a microgrid.
Canada established its interim codes on the development of a microgrid in July 2003, which focus on inverter-based microsources rated below 600 V, and include two interconnection standards, C22.2 No. 257 Standard for Interconnection of Inverter-based Microsources with the Distribution Network and C22.3 No. 9 Standard for Interconnection between Distributed Electric Power Systems. The former sets forth requirements for secure interconnection of inverter-based DRs with distribution networks below 0.6 kV, and the latter applies to DRs interconnected to a distribution network below 50 kV and with an aggregate capacity up to 10 MW and provides requirements and criteria for the performance, operation, test, and security of the DRs.
The Business Council of Australia formulated a renewable energy development guide titled Guide to Connection of Microsources to the National Electric Power Market in September 2003. This guide, in light of the Electricity Industry Act, provides guidance for application of microsources and briefly describes the process of and requirements for connecting microsources to the grid. It is applicable to microsources with a capacity up to 100 kW.
The Ministry of Economy, Trade, and Industry of Japan issued the Guide to Interconnection of Distributed Resources in May 1986, legalizing the interconnection of DRs to the grid. Later, the Ministry issued EAG 970-1993 Technical Recommendations for Connection of Distributed Generation to the Grid in 1994, amended the Electric Power Law in December 1995, and further revised the Guide to Interconnection of Distributed Resources, permitting the DR operators to sell the surplus energy to utilities and requiring the utilities to provide reserve for DR operators.
Most international interconnection standards and requirements can be classified into general requirements and specifications, security and protection requirements, and power quality requirements. Most interconnection standards are based on some common principles, including that the installation of DRs should not put other customers, the public or operators in danger, or affect the coordination of mechanical and electrical protections, reduce the reliability or limit the capacity of the electric power system; DRs should be equipped with protection devices and manual disconnection devices; only when the phase sequence, magnitude, phase, and frequency of the voltage of DRs are within the normal range can the DRs be connected with the electric power system and produce limited power.
10.2. Related standards and specifications in China
China’s studies on DRs and the microgrid are still at an infant stage, and no uniform and systematic standards or specifications on the microgrid are available. At present, China’s standards relevant to the microgrid mainly include power quality standards, interconnection standards for PV and wind power systems, and related distribution network standards.
China’s power quality standards, mainly including the following, may be directly referenced or modified based on the specific conditions of the microgrid for interconnection of the microgrid to a utility grid:
1. GB/T 12325-2008 Power Quality – Deviation of Supply Voltage
2. GB/T 12326-2008 Power Quality – Voltage Fluctuation and Flicker
3. GB/T 14549-2003 Quality of Electric Energy Supply – Harmonics in Public Supply Network
4. GB/T 15543-2008 Power Quality – Three-Phase Voltage Unbalance
5. GB/T 15945-2008 Power Quality – Frequency Deviation for Power System
China has also formulated or amended standards on interconnection of wind and PV power systems, including GB/Z 19963-2005 Technical Rule for Connecting Wind Farm to Power System, Q/GDW 392-2009 Technical Rule for Connecting Wind Farm into Power Grid, GB/T 19939-2005 Technical Requirements for Grid Connection of PV System, GB/Z 19964-2005 Technical Rule for Connecting PV Power Station to Electric Power System, and Q/GDW 147-2010 Technical Rule for Connecting PV Power Station to Power Grid (Interim). But for grid connection of other types of DRs, including biomass (agricultural biomass, forest biomass, methane, and waste), natural gas, coalbed methane, waste gas, industrial heat recovery, industrial excess pressure, geothermal energy, and ocean energy, as well as batteries and fuel cells, no uniform standards are available, thus making it difficult to determine the technical indices for interconnection of such DRs.
In November 25, 2011, as required in the Notice of the Plan on Preparation and Revision of Energy Sector Standards (second batch) in 2011 (GNKJ (2011) No. 252) issued by the National Energy Administration of China, the China Electric Power Research Institute organized parties of interest to draft industry standards including Test Technical Specifications for Equipment Connecting Distributed Resources with Power Grid, Specifications for Connecting Distributed Resources with Power Grid, Technical Specifications for Connecting Energy Storage System to Power Grid, and Operation and Control Specification for Electric Energy Storage System Interconnecting with Power Grid.
With a view to providing guidance for the planning, design, and operation of various DRs for interconnection, and mitigating their impacts on the power system and ensuring the power quality, security, and reliability of the LV power system, the SGCC, taking into account the characteristics of various DRs, structure of grid at 35 kV or below, and requirements of grid operation on power sources, formulated the standard Q/GDW 480-2010 Technical Rule for Distributed Resources Connected to Power Grid, which provides specific technical requirements for grid connection of DRs, power quality, power control and voltage regulation, voltage, current and frequency response, security, relay protection and security automatic equipment, communication and information, energy metering, and grid connection tests.
10.3. Development trend of microgrid standards
Up to now, there has been no official standard on the microgrid in China and around the world. Most microgrids are connected to a medium-voltage or LV distribution network, and thus mainly affect the planning and operation of the distribution network. Existing standards relevant to the microgrid mainly specify the planning, operation reliability and power quality of the distribution network, technical requirements and planning and design requirements for microgrid equipment, and requirements of microgrid operation for power quality and reliability. The establishment of microgrid standards should not only ensure security of people and systems, and meet various national rules and regulations, but also allow for noninterference operations; specifically, the integration of DRs should not change the current system and its characteristics, the impacts on the system due to undesired operations should be minimized, including not introducing harmonics, not causing loss of synchronization or scintillation, and not resulting in unintentional islanding. Besides, interconnection rules and standards should apply to all types of DGs and stakeholders.
As the microgrid is directly connected to the distribution network, current standards concerning the distribution network may need to be revised to adapt to the connection of the microgrid. In grid-connected operation, the microgrid may act as a power source or load; therefore, its impacts on the distribution network should be considered. The earthing mode of the microgrid should be coordinated with that of the distribution network. And as the microgrid communicates with the distribution network, the original communication protocols may be changed appropriately due to the impacts of the microgrid. In addition, the active power and reactive power of the microgrid may be independently controlled, which should be considered in specifying power control of the distribution network. The unidirectional energy metering devices in the distribution network should be replaced by bidirectional ones after connection of the microgrid. The provisions on generator protection in DL 400-1991 Relaying Protection and Security Automatic Equipment are specific to synchronous motors, which need to be expanded in view of the great variety of DRs and that most DRs are interconnected to the power grid via power electronics. The connection of the microgrid changes the original one-source radial power supply pattern into multisource pattern, making the original line protection no longer suitable and necessitating reconfiguration. The original coordination between the protection of the distribution network and the recloser also becomes unsuitable and needs to be reset. The requirements on interconnection of DRs and on planning and design of the power grid interconnected with DRs set forth in the distribution network standards can be referenced in preparing microgrid standards, with the parameters modified according to the specifics of the microgrid. Microgrid standards need to account for more factors than DR standards as the microgrid is a combination of power sources and loads.
10.4. Microgrid standard system
The standards on the interconnection of DGs to the electric power system are not as mature as those on grid connection of large power stations. As such, the lawmakers, academic institutions, utilities, and power producers need to work together to accelerate the development of microgrid standards. Uniform standards are of great importance to the development of DRs. They will facilitate the commercialization of DR technologies, promote transfer of high-quality products and technologies worldwide, and greatly reduce the costs of traditional energy producers and operators.
The advent of the microgrid changes the traditional radial power supply pattern, and poses challenges to the security and stability of the power grid. Hence, it is imperative to establish systematic microgrid standards to guarantee normalized development of the microgrid.
On November 9, 2009, the expert group CEE-SG was set up, consisting of 20 members from 18 organizations including XJ Group Corporation and Xi’an High Voltage Apparatus Research Institute Co., Ltd. It is responsible for drafting framework standards for smart grid equipment (including microgrid), discussing equipment standardization roadmap, and making action plans.
To increase efforts on the study and establishment of a smart grid standard system (including the microgrid standard system), the SGCC set up a special working group consisting of more than 180 members. Besides, one of SGCC’s scientific research programs “Microgrid technology system” also makes studies of the microgrid standard system. After fully considering the basic characteristics of the microgrid, the SGCC proposed a preliminary standard system, comprising equipment specifications, design standards, islanded operation standards, and grid-connected operation standards, as shown in Figure 10.1.
Figure 10.1 Microgrid standard system.
Equipment specifications mainly involve microsources, ESs, inverters, loads (sensitive loads, insensitive loads, and thermal loads), static switches, and protections.
Design standards mainly incorporate provisions on composition, energy management and control of microgrid, types and control modes of microsources, installation position and capacity of ESs, load control, protection configuration, and communication equipment.
Islanded operation standards mainly incorporate provisions on load and generation management, voltage and frequency control, stability, security, protection and control, cold startup, monitoring and communication, power quality, and installation and test.
Grid-connected operation standards, directly determining the impacts of connection of the microgrid on the power grid, mainly consist of general principles, power quality, operation and control, security and protection, communication and information, general technical conditions, energy metering, and system test, as detailed here:
1. General principles: Provide instructions on the composition, capacity, tie-line power exchange, and energy storage configuration of the microgrid.
2. Power quality: Set forth requirements on such indices as harmonics, degree of voltage unbalance, voltage fluctuation and flicker, and injection of direct current.
3. Operation control: Set forth requirements for response speed and power change rate in grid-connected operation and islanded operation modes, and during transfer between the two modes.
4. Security and protection: Give instructions on configuration of interface protection and internal protection of microgrid.
5. General technical conditions: Set forth the technical requirements on electromagnetic compatibility, lightning protection, and grounding.
6. Energy metering: Define configuration and metering rules for energy metering devices.
7. System test: Specify the position, time, and items of the test on grid-connection of microgrid.
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