LCT Harmonic Limits

Objective(s)

• Comprehensive network studies are carried out that identify the maximum number of LCTs that can be connected to an urban LV network during winter and summer periods.
• Comprehensive network studies are carried out that identify the maximum number of LCTs that can be connected to a rural LV network during winter and summer periods.
• Capture sufficient background harmonic measurements from real life networks
•  Determine the Maximum and Minimum allowable source impedance
• Outputs of deliverables inform and update current NGED design practices and policies.

Problem(s)

With the energy transition to Net Zero being well underway, the move to Low Carbon Technologies (LCTs) for domestic customers is continually on the rise, creating a significant increase in electricity consumption among other potential issues. One of these additional issues is the power quality of the distribution network.

Power quality is the degree to which the voltage, current and frequency of a waveform on the electricity network conform to established standards and specifications. Voltage that is steady and kept within a prescribed range can be classed as good power quality. However, when multiple LCTs, in the form of Electric Vehicles (EVs), Heat Pumps (HPs) and to an extent Battery Energy Storage Systems (BESS) amongst other loads (such as arc furnaces and rectifiers) are connected to the distribution network, the power quality can be disturbed and reduced through the creation and existence of harmonics.

Harmonics are voltage and current sinusoidal waveforms that exist where its frequency are integer values above the fundamental frequency (50Hz). These harmonic frequencies are created due to the aforementioned LCTs being classed as non-linear loads, mainly due to rectifiers and switching from AC to DC within them. The harmonics result in disturbing and modifying the pure 50Hz sinusoid waveform resulting in potential degradation of network assets, mal operation and thermal issues.

Knowing this, DNOs must be aware of the potential effects of connecting too many LCTs on a single feeder. Having said that, a DNO cannot and will not want to be a barrier in the energy transition in blocking the uptake of LCTs.

The LCT Harmonic Limits project proposes to undertake desktop research and investigate specifically how many EVs and HPs can be connected to a network prior to harmonic violations being exceeded. This piece will detail various networks that are present in urban and rural areas of the National Grid geographic, 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.

Method(s) 

The purpose of the LCT Harmonics project will be to refine and further explore this area by calculating the maximum number of electric vehicles and heat pumps that can be connected to the network before harmonic limits are exceeded. This will include both rural and urban models and will contain analysis for various proportions of LCTs and placements along the feeder of the network.

The LCT Harmonic Limits Project will build upon the findings of the Electric Vehicle Emission project, and provide maximum connection information for both EV’s and HP’s combined. Specifically, the maximum number of EV and HP that can be connected on a model-rural and model-urban network will be determined, with the process exploring the sensitivity of the results to:

• Clustering of EV and HP along the feeder. As per the previous study, there will be an investigation into a random distribution and an evenly spread distribution of LCT along the feeder.
• Different proportions of EV and HP within the overall LCT penetration. This will study the effect of differing percentages of EV compared to HP to understand the network impact depending on the weighting of a certain LCT.
•  Background emissions already existing on the network.
• Variation of charging diversity. Economy 7 tariffs were traditionally used in the past for EV charging but current ToU tariffs offer shorter charging windows resulting in more frequent charging per week for a customer.
• The simultaneous harmonic current export from the LCT connected to the feeder based on nominated assumptions about the time of day behaviour of the EV and HP at that particular time of day.
• The effect of local BESS will also be considered.

Measurement Quality Statement 

Measurement quality will form a key part of the analysis. Monitoring devices that will be used are ones that are currently used in standard practice. Multiple devices will be used to validate further and give a greater confidence level. Developed outputs and deliverables will go through multiple rounds of review to ensure the correct process has been followed.

Data Quality Statement 

Data will be captured at through standard LV monitoring during this project. This will be processed and stored using our standard policies and procedures. Data associated with harmonics generated via HPs and EVs will be redacted prior to publishing.

• Scope

  The scope of LCT Harmonic Limits is to understand the maximum number of LCT connections that can be made to an individual rural and urban LV network before harmonic violations are exceeded. Through network modelling and power systems studies, our current policies and procedures relating to the connection of LCTs can be updated, and our insights and assumptions towards the network will be more robust and clear-cut. This will undoubtedly result in faster connections being made associated with LCTs at a domestic scale and create greater security with our network due to improved policies.

  The project will be able to directly create benefits through providing more robust assumptions and procedures and further our understanding of how many LCTs can be connected to a single feeder. In doing so, this will result in less harmonic assessments having to be carried out by network planners creating a labour saving benefit. By not having to carry out harmonic assessments prior to connection, an additional benefit will be that this process will speed up the connection process for a range of LCTs at the domestic scale. This is something quite prudent as the take up of domestic LCTs is only going to increase over the coming price controls.

• Success Criteria

  The Project will be deemed successful if the following outcomes are achieved:

  • Rural and Urban Models designed that are an accurate representation of those seen on NGEDs network.
  • Comprehensive network studies are carried out that identify the maximum number of diversified LCTs that can be connected to an urban LV network during winter and summer periods.
  • Comprehensive network studies are carried out that identify the maximum number of diversified LCTs that can be connected to a rural LV network during winter and summer periods.
  • Maximum and Minimum source impedance identified.
  • Outputs of deliverables inform and update current NGED design practices and policies.
• Potential for New Learning

  The learning generated from undertaking this project will strive towards updating our policies and procedures behind the connection of LCTs at the LV network. Existing policies have been authored on the basis of previous innovation projects and subsequently need to be re worked due to the inclusion of HPs and other LCTs, evolving market conditions such as ToU tariffs which will effect charging assumptions and additional analysis that will give updated insight into the network impact such as spread along the feeder, seasonal conditions and proportion of LCT over another.

  The learning generated will also be able to feed in to other wider standards within the industry that includes other DNOs and ENA.

• Documents and Links

  NIA PEA and Registration Document

• Monthly updates

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