The LCT Harmonic Limits project will undertake desktop research and investigate how many Electric Vehicles (EVs) and Heat Pumps (HPs) can be connected to an LV network prior to harmonic violations being exceeded. This project will model both urban and rural networks, consider the background emissions that are already in existence and also consider varying diversities of LCTs in terms of percentage of EV against HP and also the distribution of LCTs along a given feeder.
The outcome of the project will aim to enhance our current design processes and standard techniques that focus on the minimum and maximum source impedance requirements before intervention is needed. Updating these standards will give greater confidence in our network and also result in quicker connections to customers.
Benefits
It is common knowledge that we foresee a significant increase in LCT connections surrounding EVs, HPs and BESS within this time period and in doing so, due to the harmonic output that they provide, they may require some form of harmonic assessment from NGED prior to the network being confident the connecting asset will not cause non-conforming issues.
Carrying out these assessments can be a time consuming process, and having a process that allows these assessments to be reduced will inevitably increase staff cost savings. The following page highlights the high level assumptions and information used to inform the potential financial benefits LCT harmonic Limits will bring.
These assumptions are:
- The number of NGED Pole Mounted Transformers (PMT) is 58,000
- The number of NGED Ground Mounted Transformers (GMT) is 127,000
- Harmonic assessment is needed for at least 50% of these sites
- Time take for harmonic assessment is between ½ day to 1 day
- Day rate for assessment is network service day rate of £445
- Assume inflation rate for assessment of 2.5%
- LCT Harmonic Limits process allows 35% reduction of assessments
Spreading out the total number of sites (185,000) over a 16 year period (2024-2040, End of ED4) results in a total number of 11,562 assessments needed to be carried out per year out to the end of RIIO-ED4 (not including additional PMT and GMT that will exist in that time period). As stated in the assumptions, a conservative minimum 50% of sites will need some form of harmonic assessment with the taken for between ½ day and 1 day. The bullet points below outlines the labour cost to carry out assessment based on number of sites and duration it takes.
- 50% of sites, ½ day assessment (£1.29m / year)
- 80% of sites, ½ day assessment (£2.06 / year)
- 100% of sites, ½ day assessment (£2.57m / year
- 50% of sites, 1 day assessment (£2.57m / year)
- 80% of sites, 1 day assessment (£4.12m / year)
- 100% of sites, 1 day assessment (£5.15m / year)
Based of the above calculations, the below table highlights the baseline costs assessments have to NGED out to the end of the ED4 price control period (2040).
- 50% of sites, ½ day assessment yielding a summated cost of £26.8m out until 2040
- 80% of sites, ½ day assessment yielding a summated cost of £42.9m out until 2040
- 50% of sites, 1 day assessment yielding a summated cost of £53.7m out until 2040
Having established the baseline figures, it is worthwhile understanding the proposed counterfactual in order to understand the underlying benefits the LCT Harmonic limits project brings. The assumption is that with the LCT Harmonics process in place, the reduction of assessments carried out will be 35% less than the base case. Applying this information to the calculations above, it yields updating costings that will be spent by NGED on carrying out harmonic assessments.
- 50% of sites, ½ day assessment yielding a summated cost of £17.4m out until 2040
- 80% of sites, ½ day assessment yielding a summated cost of £27.9m out until 2040
- 50% of sites, 1 day assessment yielding a summated cost of £34.9m out until 2040
Annually, the benefits are estimated to be between £390k-£790k, over the ED2 period between £1.56m-£3.15m and out to 2040, between £6.30m-£12.6m.
Learnings
Outcomes
Project deliverables, analysis and closedown reports can be viewed on the project page:
National Grid - LCT Harmonic Limits
Or on the ENA Smarter Networks Portal:
LCT Harmonic Limits | ENA Innovation Portal
Deliverables include details and approach around the network model structure used for analysis and the summer and winter studies that include numerous DFES projections and the harmonic effect up to the 50th order.
Lessons Learnt
The studies show that the most likely issue as the penetration of Low Carbon Technologies increases within the LV network is the thermal capacity of the network. The harmonic emissions of high-capacity loads such as EV chargers and heat pumps appear to be being controlled in line with the emission limits of IEC 61000-3-12 such that they are not subject to conditional connection. This is resulting in little additional distortion being seen as penetrations increase.
The effect of these high-capacity long duration loads being encouraged to use electricity at particular times of day by the offering of advantageous tariff prices can be expected to lead to a loss of diversity between these loads which will adversely affect the network assets.
The following shows some learning from key areas of the analysis undertaken:
Loading effects
The typical LV domestic network is designed using a value of demand for each connected customer known as the After Diversity Maximum Demand (ADMD) with total demand expected usually calculated as nA +P where n is the number of connected customers, A is the ADMD value and P an addition to allow for loss of diversity when n is low. Typical values for A and P are 2.5kW and 8kW respectively. The new LCT loads will in normal operation exhibit some natural diversity of their own. However, these additional loads still represent a significant increase in electrical demand compared to the previous value used to initially design the networks and to consider any additions/changes made since their initial installation. The nature of these loads is such that they tend to be at their peak demand for longer periods when compared to other high load devices in the domestic setting such as electric showers and cooking appliances.
The studies have shown that the increase in harmonic distortion arising from the increased penetration of the LCTs does not appear to be the limiting factor for the capacity of the network to absorb this additional load. Rather the thermal capacity of the network is reached before the individual and aggregate levels of harmonic voltage distortion will typically be exceeded. In many ways this is a reflection on the success of the electromagnetic compatibility standards in controlling the emissions of harmonic generating equipment. The market acceptance of these LCTs is, in part, affected by the ease of connection. Were the emissions to be of such a level that the LCT would fall into the conditional connection category the additional work required to assess each new connection would be a considerable burden on the network operators and result in longer times to get connected.
The rate of penetration and the number of customers connected to a circuit will affect the time at which reinforcement or other mitigation may be required and additional monitoring applied to each LV circuit may need to be considered to identify when the thermal capacity of the individual networks is being compromised.
Uncontrolled usage
In a completely uncontrolled scenario, the charging patterns for EVs might be expected to be similar in that customers will most likely connect their car to the charger when they return home at the end of the day. However charging would not necessarily take place every day as typical usage patterns would take several days before the battery was close to fully discharged. In this way some natural diversity is achieved between individual users and a diverse value can be used to assess the likely demand placed on the network.
However, even allowing for diversity it must be expected that network demand will significantly increase, average miles per year of 10,000 and around 3.5 mile per kWh would suggest that for a single EV a household demand would increase by around 2800 kWh almost doubling, similarly heat pump demand with a coefficient of performance of 4 would add another 2500kWh for the typical property.
Effect of Tariffs
A number of suppliers are offering tariffs which incentivise use at particular times of the day when demand might otherwise be expected to be lower than the available supply. The effects of these tariffs must inevitably reduce the level of diversity that would otherwise be expected across the customers. Tariffs which encourage the use of load types which typically have a higher magnitude and a longer expected duration than other types of loads in the domestic environment will reduce the level of diversity that can be applied to them during such periods and would be expected to lead to higher levels of maximum demand. This needs further investigation to ensure our modelling of future loads is reaslistic. This may require the introduction of different diversity factors at different times of day.
Existing Policy
Based on the outcomes of previous projects NGED have already put in place a design policy for all new domestic networks that the customers supply loop impedance will not exceed 0.144Ω for entirely underground circuits and 0.245Ω for circuit including overhead conductors. These values which are lower than the typical maximum previously assumed across the industry will ameliorate the feeder voltage rise conditions anticipated when PV output is at its highest with little local load to utilise the exported energy as well as reducing the voltage drop effects under maximum load conditions which may be expected when the penetration of EV charging, and Heat Pumps increases. Having a limit on the impedance for the customer connection will also necessarily further limit the impact of harmonics on the network as it must result in either a reduction in circuit length and therefore the number of customers that can be served along the route or an increase in the size of the of the main circuit conductors.
Given the potential advantages offered and the expectation that thermal capacity will likely be the limiting factor in the future with increased deployment of LCTs the continued use of this policy appears to be reasonable.
