Non-residential Electrical Systems

With the Highest Conductivity of the Commercial Metals, Copper plays a Key Role in Electrical and Electronic Development

Copper has the highest conductivity of the commercial metals and it has played a fundamental role in enabling the development of electrical and electronic applications.

In addition to its excellent conductivity, copper has ideal mechanical properties at low, ambient and elevated temperatures, is easily fabricated or cast to shape and can be readily machined. It has excellent strength and is resistant to oxidation and corrosion.

From high voltage transmission to microcircuits, and from gigawatt generators to computers, in every aspect of electricity generation, transmission and use, copper is the vital, energy efficient metal. In addition, there is a wide variety of less-common high conductivity copper alloys with properties tailored for various applications, such as electrical contacts, slip rings, catenaries for railways and tramways, and more.

Distributed Generation and Renewables

Distributed generation (DG) and renewable energy sources (RES) are attracting special attention. Both are seen as important in achieving two key goals: increasing the security of energy supplies by reducing the dependency on imported fossil fuels such as oil, natural gas and coal and reducing the emission of greenhouse gases, specifically carbon dioxide, from the burning of fossil fuels.

The term ‘renewable energy sources’ refers to natural resources such as sunlight, wind and others that are naturally replenished. Renewable energy systems convert these natural energy sources into useful energy. ‘Distributed generation’ refers to the decentralised generation of electricity, which can in some cases include renewable energy systems. DG units are generally connected to the distribution level and have capacities ranging from a few kW to several tens of MW.

Earthing

Earthing systems are vital to the safety, security and functionality of electrical installations. They provide a safe path for fault current so that over-current protection systems can function, provide a safe path for lightning strikes while containing the voltage rise to a safe value and provide an equipotential surface on which electronic equipment can function without interference.

Energy Efficiency

Energy efficiency is becoming extremely important as energy resources become increasingly scarce, difficult to exploit and expensive. Building generators fuelled by renewable resources will help, but decreasing consumption is an easier and more sensible approach.

Energy efficiency improvements are usually technically simple, relatively low cost and quick and easy to implement. Often, it is simply a matter of sensible purchasing decisions, buying the unit with the lowest lifetime cost rather than the one with the lowest purchase price.

Power Quality

Power quality problems lead to unplanned downtime, wasted resources and higher energy costs, yet they can be easily detected in advance by measurement and monitoring, and cured by the application of the most appropriate mitigation techniques. Best of all, the effects can be avoided altogether by good design practices and by choosing the right equipment. See Power Quality and Utilisation Guide.

For more on these and other issues surrounding copper’s deployment in electrical applications, visit Leonardo ENERGY: a global community for sustainable energy professionals.

FAQs

High conductivity is needed in electrical equipment running at high temperatures. What grade of copper should be used?

At room temperature, Cu-ETP should be used. However, it begins to soften at 150oC, so at higher temperatures the following may be used with only a slight loss of conductivity:

  • CuAg0.10 up to 250 – 300oC
  • CuZr, CuCr1zr, CuNi2Si  to 350 – 400oC
I am making an item which will form part of a compressed air system on a train. The drawing calls for copper tube in grade CW004A (C101). My stockist has offered CW024A (C106). Is this suitable?

Yes. CW004A is an electrical grade of copper and in this application electrical conductivity is not an issue. CW024A is the usual grade for engineering applications and is widely used to carry water, gas and air. The mechanical properties of the two grades are the same.

My process control system is not reliable and I suspect a voltage dip problem. Where do I start?

The steps in identifying the problem are

Monitor at the supply to one or more of the affected devices. One problem is that the monitor threshold settings need to be set carefully so that all interesting events are captured, but the smaller, uninteresting events are not. This can take some trial and error to get right, but it improves the quality of data that you collect and is worthwhile. Alternatively, choose a tool that applies the thresholds retrospectively – these capture all the data, but let you choose what you view. Often, the simple transient capture functions found on hand-held power analysers are useful in the early stages – they are simple to use, the results are easy to interpret and they are easily moved around the installation.

Assuming that the first stage identifies that you do indeed have a voltage dip problem, you now have to find the source.

Move the analyser back to the origin of the supply, i.e. the point of common coupling (PCC) and monitor there. Monitor the current in each phase as well to check for increased current correlating to voltage dips (although it may be difficult to identify them at this measurement position). If the voltage dips are less frequent and have a higher retained voltage, and if there are identifiable correlated current increases, then the dips are caused by equipment in your own installation. Move forward, monitoring the voltage dips at each distribution point together with the current on each sub-circuit, and the source of the problem should be revealed. You can also take a more pragmatic approach and test circuits feeding heavy or cyclic loads first – suspect photocopiers and laser printers, lifts and hoists, heating and ventilating equipment, presses, arc furnaces…

Once you have found the problem, the solution is simple. The disturbing load must be wired directly to the PCC – lowest impedance point in the system – so that it has the least effect on voltage.

If the voltage dip performance at the PCC is similar to that at the load, then it is more likely that the source of the dips is outside your installation. Now you have the evidence to talk to your Distribution Network Operator.

My system suffers from voltage dips that appear to originate outside my installation. What can be done to resolve the issue?

The correct way to proceed is via the Distribution Network Operator (DNO). It is the responsibility of the DNO to ensure that no consumer causes interference to another. Of course – every consumer affects and is affected by all other local consumers to some extent, so whether the interference is excessive or not is a matter of judgement.

In the real world, problems such as this can only be solved by co-operation starting from an assessment of the real nature of the problem.

This type of problem is common where several small factory units are fed from a single transformer. Consumers are simply ‘tapped off’ a single feeder cable, so that a problem load, especially if it is located at or near the remote end, will affect other users.

One obvious solution is to up-size the feeder cable and/or transformer to reduce the system impedance (= increase the fault level) or to run a dedicated cable from the transformer (or an additional transformer) to the problem facility. Both these solutions are expensive and, of course, someone has to pay.

If the supply is adequate for normal running, but suffers problems when starting large equipment – like a sheet metal guillotine, for example, where a flywheel has to accelerated up to speed, or when particular equipment is in use, such as a spot welder, other solutions may be more acceptable.

Starting currents are large but last for only a few seconds or tens of seconds. ‘Soft starters’ are available that reduce the acceleration rate so that the starting current is reduced in magnitude but increased in duration. This has an impact on the duty cycle of the driven equipment that may or may not be acceptable.

The impact of cyclic loads, such as spot welders, can be mitigated by the use of a static VAR compensator that corrects power factor ‘on the fly’ and reduce the impact on the system.

What effect does heavy cold working have on the electrical conductivity of copper?

It reduces by about 3%.

What is TN-C-S?

TN–C-S is the most common type of earthing employed in the UK. The name, defined in French in European standards, indicates that the earth (Terre) and Neutral are connected together by the supplier, that the earth and neutral are Combined on one conductor in the supply system and that they are Separated at the consumer’s point of common coupling. This separation of earth and neutral is maintained throughout the installation. In other words, the neutral is treated in the same way as the phase – insulated and isolated from earth throughout.

This is important because keeping the neutral and earth separate within the building reduces stray currents in the earthing system, and improves electromagnetic compatibility.

Other types of earthing system are described in section 3.2 Earthing on LV Systems and Within Premises in Pub 119 Earthing Practice.

What steps should I take to deal with earth leakage currents?

Earth leakage currents arise mainly from the EMC filters built into electronic equipment with switched mode power supplies. Standards limit the leakage current from non-fixed equipment (i.e. equipment that plugs into a standard socket outlet) to less than 3.5 mA. When a lot of electronic equipment is in use, the total leakage current in the protective conductor can become significant. If there is a break in the CPC the earthed conductive parts of all equipment connected to the isolated section will rise to about half the supply voltage. To reduce this risk, special rules apply when the leakage current in a CPC is likely to exceed 10 mA. In the current edition of BS7671, these regulations are contained in clause 534.7, replacing section 607 of previous editions.

What values of electrical conductivity can be obtained in high purity copper castings? Are they comparable to the values available for wrought alloys?

Generally the values of International Annealed Copper Standard for conductivity (IACS) values are lower than those of the wrought alloys due to the presence of a small % of gas porosity and a small % of impurities such as iron. A value of 93% IACS is guaranteed but with a very low porosity % and very pure copper, values up to 102% IACS may be obtained. Reputable foundries carry out careful conductivity checks on the copper raw material used for casting, such as offcuts of busbars or cathode copper, to ensure that as high a conductivity as possible is obtained.

Which copper alloy has a good electrical conductivity and retains strength up to 400°C?

Copper-chromium CW105C (CC101) – conductivity is 80% IACS – strength good up to 400°C.

Why are installations earthed?

In general an earthing system needs to satisfy three demands

  • It must conduct lightning and short-circuit currents without introducing intolerable step and touch-voltages
  • It must protect the occupants, equipment and fabric of the building against damage due to short-circuit currents and lightning strikes
  • It must provide a suitable environment for electronic equipment by providing a low impedance path to interconnect equipment.

Although requirements for these three aspects are very different and are often specified separately, the implementation of them requires an integrated systems approach.

Section covering coppers and copper alloys for conductivity applications and providing details of properties and uses.

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