Select Committee on Trade and Industry Written Evidence


APPENDIX 60

Supplementary memorandum by the Energy Networks Association

CLUSTERING OF MICRO-GENERATION

  The current volume of microgeneration connected to distribution networks is very small. Consequently, the impact of microgeneration on networks has not been a significant issue to date. There have been no clustering problems in existing networks as a result of customers choosing to install microgenerators either as a new device or as a replacement, for example, of a previous heating system. In the future, however, local authorities may require developers to install smaller generators on new buildings as a requirement of obtaining planning consent. Where there are new housing developments that contain microgeneration, the network will specifically be designed to cater for the technical issues, but a scenario that could create a challenge is where there is a high penetration of, for example, domestic CHP on existing networks causing reverse power flows during periods of low demand and high generation (eg mornings).

  The existing low voltage (LV) distribution networks have been designed to cater for a unidirectional energy flow from the distribution substation to customer installations. The connection of multiple microgeneration units can have an adverse effect on network operation. The main issues that need to be considered include:[12]

    1.  Impact on voltage levels, both over and under-voltage.

    2.  Short circuit levels.

    3.  System loading.

    4.  Voltage unbalance.

1.   Impact on Voltage levels

Overvoltage

  Export from a microgeneration unit will tend to increase the voltage profile on the LV networks. Under low load conditions, where voltages are at the upper end of the statutory voltage range the voltage level within the installation could increase above statutory limits and this could lead to nuisance tripping of the microgeneration unit.

Undervoltage

  There is a risk that transient disturbances on the HV system could lead to voltage dips on the LV system which in turn could result in widespread tripping of microgeneration units by operation of the undervoltage element within the interface protection. The original disturbance will then be compounded by the sudden increase in demand as the system supports the load that was previously supplied from the microgeneration units.

2.   Short circuit levels

  The connection of a microgeneration unit or units to the LV networks could result in the prospective short circuit current, from the source and the microgenerator, exceeding the short circuit rating of equipment connected to the network. The short circuit contribution from a microgenerator must be considered to ensure that the single and three phase fault duty imposed on Distribution Network Operator (DNO) and customer's equipment does not exceed the equipment rating. The contribution to short circuit currents will depend upon the microgeneration technology.

3.   System loading

  Low voltage distribution networks have been designed with the assumption that power flows from the substation out to the customers. With the wider introduction of microgeneration units, the direction of power flows may reverse. The DNO may need top make an assessment of the magnitude and direction of power flow to ensure equipment thermal ratings are not exceeded.

4.   Voltage unbalance

  For multiple installations of single-phase microgeneration units (eg housing estates), balancing the unit generation evenly against the load on the phases will need to be considered.

  The connection of significant quantities of microgeneration units in the LV networks could also have an adverse impact on the 11kV and higher voltage networks. The issues are similar to those for the low voltage network. In particular, the impact of voltage changes and effect on the primary voltage control needs to be carefully considered.

  It is worth pointing out however that the microgeneration penetration level at which any of the issues mentioned above appears will depend upon the generator and network characteristics.[13] Across the UK there is a range of distribution network designs and operating practices and thus the impact will vary accordingly. Mitigation could take the form of more sophisticated control systems, plant and switchgear upgrade but network augmentation will often be required. Realising the full potential of lower voltage networks in particular will require further clarification of the requirements under ESQCR that would potentially permit a wider (LV) voltage operating range within specified parameters and hence permit a wider penetration of microgeneration into LV networks. Additional governmental support for a few mixed microgeneration based installations could also be helpful here to provide much needed learning experiences for all stakeholders. The network operators in particular would benefit from practical real tests of appropriate scale where the effects of microgeneration technologies can be properly planned for, assessed and tested.

CONNECTION OF SMALL-SCALE EMBEDDED GENERATORS (UP TO 16A PER PHASE) AND SAFETY ISSUES

  The procedures for connection of microgeneration installations delivering electricity have been described in the Engineering Recommendation G83/1—Recommendations for the connection of small-scale embedded generators (up to 16A per phase) in parallel with public low-voltage distribution networks (2003).[14] The procedures are designed to facilitate the connection of microgeneration units whilst maintaining the integrity of the public low-voltage distribution network, both in terms of safety and supply quality.

  The purpose of this Engineering Recommendation is to simplify and standardise the technical requirements for connection of small scale embedded generators (SSEGs) by addressing all technical aspects of the connection process from standards of functionality to site commissioning. The ER G83/1 was drawn up by an all stakeholder group (including DNOs, Generators and taking input from DTI and Ofgem) and drafted and approved in accordance with the Ofgem agreed rules on the governance of standards.

  The Engineering Recommendation provides sufficient information to allow:

    —  SSEG Manufacturers to design and market a product that is suitable for connection to the public low voltage distribution network.

    —  Users, manufacturers and installers of SSEG units to be aware of the requirements that will be made by the local distribution network operator before the SSEG installation will be accepted for connection to the DNO's network.

    —  DNOs to confirm that the SSEG installation is compliant with the relevant international, national and industry standards.

  The Engineering Recommendation outlines generic requirements related to the connection, installation and network design requirements for all types of SSEG unit. The specific requirements for each different type of technology of SSEG (eg domestic CHP, photovoltaic, fuel cells, microhydro) are defined in the annexes. The annexes also describe a methodology for testing the particular types of SSEG in order to demonstrate compliance with generic requirements of this Engineering Recommendation. By satisfying the test conditions in the relevant annex the SSEG can be considered as "Approved" SSEG for connection.

  In accordance with the Electricity Safety, Quality and Continuity Regulations (ESQCR) 2002, Regulation 22(2)(c) the Installer is to ensure that the DNO is made aware of the SSEG installation at or before the time of commissioning. The DNO may not refuse to accept the connection providing the installation complies with the requirements of ESQCR Regulation 22. However under the terms of ESQCR Regulation 26 the DNO may require a SSEG unit to be disconnected if it a source of danger or interferes with the quality of supply to other consumers.

  In the case of a single microgeneration installation, in addition to the notification required under ESQCR the Installer shall provide the DNO with the commissioning form (which provides a template for all the technical details required by the DNO) within 30 days of the SSEG unit being commissioned.

  In the case of a planned installation project where the proposal is to install multiple SSEG units in a close geographic region (eg part of a new housing development, housing refurbishment programme in the same street etc) it is strongly recommended that the Installer discusses the installation project with the local DNO at the earliest opportunity. The Engineering Recommendation provides a template for initial application. The DNO will need to assess the impact that these connections may have on the network and specify conditions for connection. The confirmation of commissioning will need to be made within 30 days of commissioning (ie as in the case of single installation).

  Each micro-generator installation must also comply with BS 7671 (IEE Wiring Regulations). All wiring between the supply terminals and the SSEG shall be protected by a suitably rated protective device; and shall be of suitable size and type for the rating of the SSEG. The SSEG shall be connected directly to an isolation switch where for single-phase machines the phase and neutral are isolated and for multi-phase machines all phases and neutral are isolated. In each instance the manual isolation shall be capable of being secured in the "off" (isolated) position; this switch is to be located in an accessible position within the Customer's installations.

  The interface protection is also required so as to ensure that the connection of a SSEG unit will not impair the integrity or degrade the safety of the distribution network. The protection function can either be incorporated within the SSEG or afforded by separate devices. In either case the interface protection shall meet the requirements of IEC 60255-5, or equivalent standard and comply with all other relevant standards as described in the annex for specific technologies.

  The Installer shall provide labelling at the Supply terminals (Fused Cut-Out), meter position, consumer unit and at all points of isolation within the customer's premises to indicate the presence of a SSEG. In addition to the safety labelling, the Engineering Recommendation requires the following information to be displayed at the point of interconnection with the DNO network:

    —  A circuit diagram showing the circuit wiring, including all protective devices, between the SSEG and the DNOs fused cut-out. This diagram should also show by whom all apparatus is owned and maintained.

    —  A summary of the protection settings incorporated within the equipment.

  It is worth mentioning that the ER G83/1 has received international acclaim for its innovative approach to facilitating the connection of micro-generation.







12   "ENA Engineering Recommendation G83/1-Recommendation for the connection of small-scale embedded generators (up to 16A per phase) in parallel with public low-voltage distribution networks", September 2003. Back

13   "The Impact of SSEG on the Operating Parameters of Distribution Networks", K/EL/00303/04/01, URN 03/1051. Back

14   According to the ESQCR, any unit above 16A per phase requires permission to connect from DNO. The network operator would carry out a proper assessment of each connection application before granting a permission. The Engineering Recommendation G59/1 covers the connection requirements for generation up to 5MW by specifying the generic requirements for the connection of generation to public distribution networks. Back


 
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