their property, most people don’t think about the implications for grid connection until late in the planning process. Increasingly, network operators are severely restricting the level of generation that they will permit and this needs to be considered in planning a micro-generation system from the start. This presentation will summarise the issues with connecting micro-generation to a property, the process to obtain the correct consents and some indications of future developments in the low voltage network and how these affect micro-generation.
a highly regulated activity and generators need to ensure that they operate safely and without disrupting the grid • Micro-generation or “Embedded Generators” is governed by the local DNO • Under the Distribution Code administered by the ENA, the DNO operates a 2 tier process: – Connect and inform – G83/2 – Consent and Connect – G59/2 • This presentation outlines the factors driving the DNO’s decision on connections and the process of obtaining consent 4
electricity to UK homes is a multi-stage process from the Power Stations, Wind Farms and other sources that provide electricity to the end user. • Large generators will feed direct to the HV network under a power purchase agreement • We will be looking only at LV connections where the primary purpose is on-site use 5
mounted (note 2 insulators): 3 Phase pole mounted (note 3 insulators): Ground mounted Single or 3 Phase: Capacity Plate Typical Site – 25kVA transformer 500m from meter and shared with 3 properties
defined by the maximum export current of the generator: – <16A per phase (about 3.7kW) is a G83/2 connection – >16A per phase but less than 17.5kW is a G59/2 connection • G83/2 process requires the customer to advise the DNO that the equipment has been connected along with evidence that it has been type tested to the G83/2 standard • G59/2 process requires the customer to seek prior permission to connect along with evidence that it has been type tested to the G59/2 standard 8
to allow connection of any generator the equipment must comply with the appropriate standards (G83/2 or G59/2) which in practice are now aligned and cover: – Control of harmonics to primary 50Hz – Voltage Fluctuation and Flicker – DC injection – Power Factor – Safety Protection for loss of mains, frequency and voltage – Fault level contribution 9
been revised recently in order to take account of recent issues with brown-outs • Embedded generation needs to disconnect if the supply moves outside normal operation parameters as this usually indicates a supply fault • However in some circumstances – eg a brown out – if all the embedded generation disconnects it exacerbates the issue • 2-stage settings have therefore been introduced 10
have all the correct type approval data and the system is below 16A per phase, you can connect and inform • If you are above 16A you need to ask permission and this may not be granted • There are two main considerations taken by the DNO in permitting connection: – Will the export current exceed the capacity of the supply? – Will the export current create a voltage rise at the meter that would take it outside the grid permitted voltage? • In assessing these two parameters, the DNO must consider not only your property but also any other properties on the same LV supply 13
– A typical LV “wet string” supply may have an impedance of around 0.002 Ohm/m so with 400m between site and inverter the voltage drop under load will be 0.8V/amp. If we want to transmit 20A the voltage at the meter will be 16V above the Transformer output. – If the transformer is at a nominal 240V this will take the site connection voltage to 256V and above the D-code standard – ie a “fault” – Note that at the inverter output the protection settings can allow up to 263V so you also only have 8V to allow for voltage drop between the inverter and the meter before the inverter will trip – If the supply were at the “standard” voltage of 230V there would not be a problem but if the transformer was tapped down, under load you could only take 26A (about 5.5kW) before your supply was below the lower limit 14
• If there is insufficient supply capacity for your scheme there is no obligation on the DNO to do anything about it • Most DNOs will give you an estimate of the cost of an upgrade • This is likely to be anything from £6,000 for a minor change up to £20-30,000 or more for running a complete new supply to the 11kV system • If you are planning a 200kW PV array this is probably worthwhile and you then start a lengthy process of obtaining connection offer and paying for the upgrade • This process can be very slow! 15
All of this leads to the important conclusion that if your generation scheme is over 16A per phase, before you spend money on anything else – apply for permission to connect • The application is not complicated and your system installer can do this for you • At the moment this service is free • There is a comprehensive guide issued by the ENA at http://www.energynetworks.org/modx/assets/files/electricity/engineering/distribute d%20generation/Jan%202013/DGCG%20G59%20Jan2013.pdf 16
major issue that the rural energy network has no capacity for significant changes in patterns of use or generation • For this reason a plan is under development for major investment into the network to enable both changes in consumption eg for moves to heat pumps or electric vehicles and generation • In the meantime the customer must pay if an upgrade is needed • There is also debate about re-introducing charges to give permission 17
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