Voltage management at source

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The average supply voltage in the UK is 242V. Because of that electricity supplied to many sites across the UK is higher than necessary and responsible for energy losses in voltage dependant equipment. Electrical Review spoke to Wilson Power Solutions.

Voltage management is an energy saving technique addressing this issue by modifying supply voltage to a site in order to reduce losses in voltage dependent equipment. There are a number of dedicated voltage management solution providers in the UK. But it’s an increasingly well know “secret” that for sites with MV supply, a simple, straight forward and cost effective solution exists that doesn’t require any dedicated voltage management equipment: Managing site supply voltage at source via MV/LV supply transformer(s).

Tap down your existing transformer - The basic option

Most distribution transformers have off-circuit selectors installed to allow for manual ratio adjustment to LV side voltage. These ‘tap changers’ typically offer a range of ±5% either in one per cent or 2.5% steps. Tapping down an existing transformer where site supply voltage is higher than required is a low cost option which can lead to a quick, if limited, reduction in energy use. Despite the comparatively moderate savings it is always worthwhile to ensure that transformers are running on the best possible tap setting for a site’s requirements and can be a temporary measure where installation of new equipment is not an option.

Replace existing MV/LV transformer(s) with modern super low loss amorphous transformers

Many sites with MV supply are currently operating a supply transformer that is designed to provide a nominal phase voltage of 240V. Where sites can benefit from reducing supply voltage, replacing existing transformer(s) with modern units (such as a super low loss amorphous transformer) that offer a nominal voltage of 230V alongside an extended tapping range which would operate satisfactorily down to 207V can be an extremely cost effective solution. That is because replacing the supply transformer does not require any additional equipment to be installed. This avoids additional system losses, minimises the total plant footprint and is virtually maintenance free. In addition site owners benefit from guaranteed energy efficiency savings through reduced transformer losses and improved site resilience.

Independently verified in hundreds of applications

Numerous case studies by independent power quality experts such as IPMC have shown that optimising site voltage through supply transformers can achieve the same (if not better) levels of savings as comparable, fixed ratio voltage management units – at no extra costs. What’s more, in addition to savings made through voltage management site owners benefit from often significant energy savings through reduced transformer losses. A recent case study at a large hospital in Tayside showed for example that combined savings from voltage management and reduced transformer losses will deliver cost savings of over £7,300 pa.

Addressing 'dirty' supply from the grid - Distribution transformers with on load tap changers

Most sites in the UK experience some level of network supply fluctuations. These are typically cyclic with voltage levels rising during the night as a result of overall drop in demand and are usually moderate. There are however instances where supply to site fluctuates significantly. This can be due to temporary industrial loads (for example an in-store bakery in a large supermarket) that are causing network voltage drops for periods of time. In addition the integration of intermittent generation from renewable sources and increasing loads from electric vehicle chargers for example is causing further strain. 

To mitigate the risk of supply voltage fluctuations and increase site resilience as well as maximise the savings that can be obtained from optimising site voltage, more and more customers are choosing a new generation of super low loss distribution transformers. These units operate on load tap changers (OLTC’s) that maintain the required LV side voltage within a desired bandwidth. Investing in a distribution transformer with OLTC’s will help secure safe and resilient operation of sites under increasing pressure from ever increasing challenging supply scenarios.

Modern supply transformers are a cost effective, simple and easily replicable energy efficiency measure 'beyond the low hanging fruit'. 

Transformers are ubiquitous infrastructure components across many public and industrial estates in the UK. With an ageing transformer population across many sites, transformer replacement projects can deliver substantial benefits on comparatively modest investments (time and capital).

Early indications show that the replacement project at a large hospital in Tayside will deliver energy savings of 60,862kWh per annum for a single 1967 transformer replacement. Payback on the complete project (including installation costs) will be achieved in less than 5 years. The typical life expectancy of the replacement transformer is 30 years and will therefore provide 25 years of savings that can be invested in other projects.

This demonstrates how energy and carbon savings can be realised at the same time as meeting infrastructure life-cycle replacement and upgrade needs, thus resulting in major financial, environmental and site resilience benefits for decades to come.

* Ageing electrical supply infrastructure common issue for estates across the UK

* Old supply transformers waste significant amounts of electricity through losses (would not commute to work in a car from 1967!) 

* Transformer technology has improved significantly – super low loss transformers already exceed strict new Eco Design losses requirements for transformers due to come into force in 2021 – even when compared to modern standard units super low loss transformers offer significant opex benefits 

* Modern supply transformers have a lower nominal voltage (11kV/415V) and are typically supplied with an additional tap setting (+7.5%). Because of that they can serve as cost efficient voltage management devices that regulate site supply voltage at source offering substantial additional savings (older transformers are rated 11kV/433V and only have limited tap changer positions)

* Comprehensive power quality studies are recommended prior to any large scale replacement project in particular to assess presence of harmonics that can require de-rating of transformers (where appropriate filters have not been installed or are faulty), amount of voltage dependent loads, voltage drop across the site and requirement for existing power factor correction equipment.