The requirement to increase the penetration of Low-Carbon Technologies (LCTs) on the electricity distribution network has led to concerns for the capacity available to cope with additional demand.
Applicable LCTs of interest include heat pumps, renewable generation, energy storage, electric vehicle chargers, LED street lighting etc. More recent advancements in power electronic devices has resulted in commercially viable Voltage-Source Converters (VSC) for a range of Direct Current (DC) applications. The use of Low Voltage Direct Current (LVDC) networks to improve the power transfer capability of feeders and the improvement in overall efficiency of the system (many loads are essentially DC). However, many practical aspects need to be considered when converting existing Low Voltage Alternating Current (LVAC) networks to DC. This includes the impact on network components especially cables, as the original design intention was for AC operation.
Project objective
This was a follow on Network Innovation Allowance (NIA) project to LVDC phase 1 which formed the literature review and drafting test specifications. The project considers the potential challenges of switching aged low voltage AC network apparatus to DC energisation. In order to achieve this, a test programme considered the behaviour of the assets in a range of DC test scenarios.
This is an emerging area of interest and there are no established test houses for LVDC testing (well established at HVDC). Bespoke test rigs were developed to deliver the challenging test specification on service aged LVAC cables under LVDC conditions.
Delivery
DC load cycles, a DC accelerated aging regime and DC faults were applied to the apparatus.
All network apparatus for test was carefully selected by the team at SP Energy Networks to allow the test programme to assess the impact of DC voltages on the most relevant cables, joints and linkboxes.
Accelerated aging was performed on all of the samples, one group of samples experienced 40 years of accelerated aging and the remaining groups experienced 10 years of accelerated aging. Extrapolations of the sample health are made for the samples which experienced 10 years of aging. The remaining useful life of the conventional network apparatus, failure modes and the effect of failure were considered.
PNDC assets that were used included DC power supplies, thermal aging rig, DC fault thrower, insulation resistance test set, LCR meter, and bespoke measurement system (applied voltage, surface temperatures, ambient temperature and humidity) with cloud integration.
Impact
Based on the overall performance of the network assets in this study, the recommendation is to continue further investigations on potential LVDC applications. All samples completed the test programme and performed well given the current condition, sample age and historical loading.
PNDC project lead: Eddie Corr .
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