Smart grid standards

Several standardization efforts for smart grids in US and Europe are currently in progress, because standardization is seen as a key issue for a proper technical interoperability. Roadmaps about standardization of smart grids have been listed by Uslar et al. (2010).

For example in US available DER and smart grid related IEEE standards include IEEE 1547 series of interconnection standards and IEEE P2030 series of smart grid interoperability standards. IEEE Standard 1547 defines mainly the electrical issues related to the interconnection of DER units while IEEE P2030 concentrates on the communication and control issues. In the following communication related smart grid standardization is briefly viewed in Section 2.5.1 and DER interconnection related in Section 2.5.2. Power quality standards are discussed later in Section 5.1.1.

2.5.1 Communication

The most important aspect is that a totally new kind of ICT infrastructure is required for smart grids (Uslar et al. 2010). For example over 100 IEC Standards have been identified as relevant to the smart grids. Below is a list of the core IEC standards for smart grids defined by IEC (2011):

– IEC 62357: Service Oriented Architecture (SAO)

– IEC 61970: Common Information Model (CIM) / Energy Management – IEC 61850: Substation Automation

– IEC 61968: Common Information Model (CIM) / Distribution Management – IEC 62351: Security

– IEC 62056: Data exchange for meter reading, tariff and load control

– IEC 61508: Functional safety of electrical/electronic/programmable electronic safety-related systems

Standard IEEE P2030 – Draft Guide for Smart Grid Interoperability of Energy Technology and Information Technology Operation with the Electric Power System (EPS), and End-Use Applications and Loads consists from the following parts (IEEE SCC21 2011a):

– IEEE P2030.1: Draft Guide for Electric-Sourced Transportation Infrastructure

– IEEE P2030.2: Draft Guide for Energy Storage Systems Interoperability with Electric Power Infrastructure

– IEEE P2030.3: Draft Standard for Tests Procedures for Electric Energy Storage Equipment and Systems for Electric Power Systems Applications The most promising standard for DER, microgrid and smart grid communications is IEC 61850. IEC 61850 is a part of the IEC Technical Committee 57 (TC57) reference architecture for electric power systems and originally a standard for the design of electrical substation automation (IEC 61850 standard 2003). The abstract data models defined in IEC 61850 can be mapped to a number of different protocols. Current protocol mappings in the IEC 61850 are for example for manufacturing message specification and Generic Object Oriented Substation Event (GOOSE). These protocols can run over TCP/IP (Transmission Control Protocol / Internet Protocol) -networks and/or substation local area networks using high-speed switched Ethernet to obtain the necessary response times of < 3 ms for protective relaying. (Strauss 2009)

Oyarzabal et al. (2009) have stated that communication architectures in future microgrids and smart grids should take advantage of all technologies available, like radio, Ethernet, power line carrier and services like GSM, GPRS or ISDN.

This means that it will be necessary to develop new mappings of IEC 61850 to be able to make use of existing infrastructure other than Ethernet. (Oyarzabal et al.

2009)

IEC 61850 specifies for example: i) data models for DER devices and substations, ii) services for accessing the functions provided by the devices and iii) specific low level communications mapping (Oyarzabal et al. 2009). The range of devices which can be controlled includes gas turbines, diesel generators, converters, meters, load banks, switches, batteries etc. (Oyarzabal et al. 2009). More exactly IEC 61850-7-420 is the part of IEC 61850 which covers communications with DG units and also microgrids to some extent (Ringelstein & Nestle 2009).

However, from the perspective of microgrids some technologies are still missing in IEC 61850-7-420 (Oyarzabal et al. 2009). Wind power has a separate standard named IEC 61400-25. Utilization of IEC 61850 based communication has also

been suggested to Loss-of-Mains (LoM) protection of DG units by Rintamäki &

Kauhaniemi (2009).

Usage of IEC 61850 has many advantages (Oudalov et al. 2009):

– Can be applied to every type of electrical installation,

– Guarantees interoperability between devices from different manufacturers, – Standardizes data models and protocol,

– Provides scalability to the microgrids and

– Provides higher performance than other protocols

– GOOSE service of IEC 61850 makes the direct information exchange between intelligent electronic devices (IEDs) possible, accepting any type of data and transmitting the data in less than 3 ms.

One of the main concerns at the time of considering IEC 61850 as a solution may be the cost of switches used for data transfer which were not necessary before.

Switches allow organizing the data traffic within the network, taking into consideration several parameters like the priority of a message, or managing VLANs not to mix different traffics. Switches are necessary, but it is possible to have cheaper architectures by means of the integration of these switches within IEDs. (Oudalov et al. 2009)

Strauss (2009) stated that the combination of IEEE 1547-2003 standard with the IEC 61850-7-420 could be the basis for standardization of the non standardized concepts, such as energy management systems, demand management systems, demand side management, generation control, demand control, ancillary services, interfacing structure for smart and multi-metering, market price signals, multi agent systems, blackstart and voltage control.

In general, IEC 61850 seems to be the most sensible and economical option to meet the communication needs of future microgrids and smart grids. Also for example Ruiz-Alvarez et al. (2010) and Roman-Barri et al. (2010) have chosen to use IEC 61850 in microgrid test bed.

2.5.2 DER interconnection

Many national interconnection guidelines or grid codes for DG units are available today. In Europe CENELEC Standard EN 50438 Requirements for the connection of micro-generators in parallel with public low-voltage distribution networks defines protection principles for micro-generators. EN 50438 defines specific limits for each European country but also some common values are presented.

However, none of the European guidelines take into account microgrid or intentional island operation. (Oudalov et al. 2009)

Standard EN 50438 is meant for production units rated up to 16 A per phase i.e.

up to 11 kVA for three-phase and 3.7 kVA in single phase. CENELEC, through its technical committee TC8X (CLC/TC8X), is also preparing a technical specification called Requirements for the connection of generators above 16A per phase to the low voltage distribution system or to the medium voltage distribution. This standard aims at harmonizing at European level the technical requirements for the connection of distributed energy resource (DER) to the LV and MV networks. DER-Lab which is an EU funded project formed by 11 Laboratories across Europe provides recommendations for CLC/TC8X on how to set harmonized European requirements for the connection of generators to LV and MV distribution system (see Strauss 2009). (Consortium 2009)

US interconnection standard IEEE 1547-2003 IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems includes at the moment the following parts (IEEE SCC21 2011b):

– 1547.1-2005: Application Guide for IEEE Standard 1547, Interconnecting Distributed Resources with Electric Power Systems

– 1547.2-2008: Application Guide for IEEE 1547 Standard for Interconnection of DR with EPS

– 1547.3-2007: Guide For Monitoring, Information Exchange, and Control of Distributed Resources Interconnected With Electric Power Systems

Standard IEEE 1547-2003 sets limitations and regulations for DG, disconnection times, synchronization rules, harmonics, DC injection, grounding and other protection aspects. However, the standard does not take into account intentional island operation. Guide for island operation, i.e. IEEE P1547.4 Draft Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems, is still under development. Also under development is a draft standard IEEE P1547.8 Recommended Practice for Establishing Methods and Procedures that Provide Supplemental Support for Implementation Strategies for Expanded Use of IEEE Standard 1547 which tries to establish a common technical platform to address functionality for the interconnection of distributed resources across the power grid. In USA UL 1741 standard, Inverters, Converters, and Controllers for Use in Independent Power Systems, for DER units etc. has been harmonized with IEEE 1547.

In Section 6.3.1 fault behavior standardization and requirements of converter based DER units in LV microgrids will be discussed in more details after the proposed new LV microgrid protection system has been presented.

3 SIMULATION MODELS FOR LV MICROGRID