A Rule of Thumb For Transformers

As fuel costs rise and power outages become more prevalent around the country, the power generation and distribution system in the US has come into sharp focus. So too has the need to conserve energy and the need to invest in energy-efficient products of all types. Of particular interest are products like power transformers that remain energized and consume energy 24 hours a day.

The transformer is a critical component of the energy grid. If even a single unit shuts down for a short period of time, a large number of households and commercial establishments are plunged into darkness resulting in a substantial economic loss.

Unfortunately, a significant amount of equipment in the public utility grid is over 40 years old and needs to be replaced in the near future. According to the Department of Energy (DOE), distribution transformers which are 30 years old or more can waste between 60 and 80 billion kWh annually. A better designed transformer could yield an annual energy savings of up to $1 billion. Thus, maintenance, retrofitting and purchasing of new transformers are fast becoming imperatives.

The Importance of Transformers

The distribution transformer – is the most important single piece of electrical equipment installed in an electrical distribution network. It also has a large impact on a network’s overall cost, efficiency and reliability. Selecting and acquiring energy-efficient distribution transformers which are optimized for –

* A particular distribution network
* The utility’s investment strategy
* The network’s maintenance policies
* Local service and loading conditions

– will provide definite benefits (improved financial and technical performance) for both utilities and their customers.

As climate change looms on the horizon, there is also an increased interest in the protection of the environment from greenhouse gas emissions. The regulatory requirement now is to install high-efficiency distribution transformers that have less energy losses, which eventually results in fewer pollutants being released into the environment.

Transmission Losses

Transformers aren’t perfect devices; they don’t convert 100% of the energy input to usable energy output. The difference between the energy input and that which is available on their output is quantified as energy loss. There are two types of transformer losses: no-load losses and load losses.

* No-load losses

No-load losses are also referred to as core losses. This loss is calculated based on the amount of power required to magnetize the core of the transformer. Since most distribution transformers are energized 24/7, no-load losses are present at all times, whether a load is connected to the transformer or not. When lightly loaded, no-load losses represent the greatest portion of the total losses.

* Load losses

Load losses on the other hand, are those losses incident to carrying a load. These include winding losses, stray losses due to stray flux in the windings and core clamps, and circulating currents in parallel windings. Because load losses are a function of the square of the load current, they increase quickly as the transformer is loaded. Load losses represent the greatest portion of the total losses when a transformer is heavily loaded.

Deciding which Transformer to Purchase

Many electrical distribution utilities claim that they purchase distribution transformers using some type of loss evaluation procedure. However, transformer cost continues to be a major factor in determining which transformer to buy. The components in a transformer, design, construction and installation all affect its cost. For example amorphous metal core transformers have 75% less no-load loss than a silicon steel core transformer but cost 25% more than a silicon steel transformer.

Transformer losses affect the cost of design, construction and installation. The transformer manufacturer typically incorporates the cost of losses in the cost of the transformer in optimizing transformer design.

Most companies buying transformers look at the quotation rather than the total cost of ownership (TCO). The TCO over the life of the transformer tends to be high in less energy-efficient transformers, while the initial cost is higher and the TCO low for energy-efficient transformers.

The payback period for investing in high-efficiency transformers however is relatively short – often less than 2 years. The Internal Rate of Return in energy efficient transformers is consistently above 10% and sometimes as high as 70%.

Making buying decisions for a large power transformer is more complex than simply comparing manufacturer prices. It requires a company to know its requirement and compare not just the cost of transformers but also the TCO over a two- to three-decade period. If this is accurately done, the cost-efficient solution invariably turns out to be the energy-efficient transformer, even though it has a slightly higher initial cost.

When purchasing transformers, there is no question of a ‘short-term’; these infrastructure investments are typically made with 30 to 50 years of service in mind. Energy-efficient transformers are thus definitely the only way ahead, given the strong economic case they make over the long run.

Source by Mike Dickinson

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