Specifying portable power generators

Mark Taylor, Divisional Manager of Atlas Copco Generators, explains the key issues when specifying portable power generators and looks at the individual requirements for some typical applications.

Customers have always played a key part in the development of Atlas Copco's generator products and the company regularly holds equipment design and review meetings to enable it to produce equipment to meet their requirements.

Considerations of safety, fuel consumption and the environmental impact, in terms of noise and emissions, play a large part in Atlas Copco's design and manufacturing output.

This is particularly relevant for the rental market where these factors can influence the ability to attract customers and, in turn, assist them in securing additional work opportunities.

As a global player, at the forefront of generator technology, Atlas Copco endeavours to provide products that exceed customers' expectations - in terms of providing more power from smaller units, quieter operation and lower exhaust emissions.

But these aspirations are not just customer-led; they are legislative requirements of the market regulations both in the EU and US markets.

** European noise legislation.

With noise pollution recognised as one of the main local environmental problems in Europe, the importance of addressing noise emissions is paramount to the design of outdoor mechanical equipment.

European Union Directives require similar basic laws throughout the Union on protecting workers from the health risks caused by noise.

In the UK, this is covered by the Control of Noise at Work Regulations 2005 which replaced the Noise at Work Regulations 1989 and introduced new requirements for action to be taken by employers.

For example, the Noise Regulations 2005 require employers to take action to protect workers at levels of noise 5 decibels lower than those of 1989.

Regulations now require employers to provide those regularly exposed to 85 decibels or above with hearing protection and an assessment of the risk to workers' health from 80 decibels upwards.

To put that noise level into perspective, 85 decibels is the sound equivalent of a 2- stroke chain saw at a distance of 10m.

However, the trend within the industry is to seek attenuation of noise levels to well below that threshold, down towards 66 dB(A), which is equivalent to normal conversational level.

But it is not only the worksite operatives that need protection from excessive noise.

Sensitive areas in proximity to noise-producing equipment, such as hospitals, schools and residential property need consideration also, especially in the course of night-shift operations.

The answer lies in designing generators with the aim of limiting equipment vibrations, in providing acoustic attenuating enclosures and fitting efficient exhaust silencing systems.

These elements are incorporated as standard within the Atlas Copco portable generator ranges.

*** Emissions standards.

The impact of pollutants on public health as well as the environment has provided an impetus for the government and other organisations to enforce complex legislation and regulations relating to diesel engine emissions for both on-road and non-road equipment.

Continual efforts to curb diesel engine emissions have been taken for the past several years.

However, with the environmental impacts gaining public prominence, stricter and tougher legislation is in place for non-road equipment such as generator sets.

The main challenge for manufacturers of diesel engines and generator sets is thus to reduce the level of harmful substances, while maintaining similar or better performance levels.

EU legislation categorises allowable emissions in non-road diesel engines as Stages I, II, IIIA,IIIB and IV.

Each of these stages specifies a lesser amount of specific pollutants that are allowed on the basis of the number grams per kilowatt-hour of the compounds present in diesel exhaust.

The controls apply to four combustion by-product constituents in diesel exhaust, Nitrogen Oxides (Nox), Hydrocarbons (HC), Carbon Monoxide (CO) and particulate matter - mainly soot particles from unburned carbon.

The emission of these pollutants can be controlled by improvements in combustion efficiency.

In December 2002, the European Parliament adopted Stage II of the Directive 2002/88/ EC, which included portable and rental gas and diesel gensets, but only in the power range of 18 to 560 kW.

This regulation came into effect on 1 January, 2007.

Currently, stationary gensets are exempt from these EU emission regulations.

In contrast, in the United States, stationary diesel engines for generator sets have had to meet Tier 1 emission regulations and, from this year, must comply with Tier 2, 3 or 4 regulations depending on the size.

Stages IIIA and IIIB of the European emission regulations will be fully adopted by 2013.

For non-road 18 to 36 kW and 75 to 560 kW generators, Stage IIIA regulations become effective from 1 January, 2011.

Gensets ranging from 37 to 74 kW must satisfy Stage IIIA regulations from January, 2012.

The effect of these regulations can be seen mostly in the form of NOx and HC reduction, with emissions reducing by over 40 per cent for certain power ranges.

Future stringent controls for Stage IV and beyond will no doubt require aftertreatment systems to reduce pollution constituents, such as selective catalytic reduction and regenerative filters.

*** Health and safety issues.

It is not only noise and pollutants emission that present health hazards, operational safety is a paramount requirement of any generator design.

The provision of four pole main motorised circuit breakers to provide overload and short circuit protection is but one safety measure.

A separated power cubicle opposite the control cubicle is another, as is emergency stop, automatic engine alarms and shut downs operation as standard.

Hazardous spillages also can be prevented with a double skinned, removable fuel tank with leakage sensors, and a spillage-free frame construction that eliminates ground- polluting accidental engine fluids or fuel spills In its latest offering of generators, that now completes a range from 12kVA through to 1250kVA, Atlas Copco incorporates all of these features.

The key driver has been to exceed the limits of current environmental legislation, and to provide reliable equipment that is safe, easy to use and adaptable - units for the many critical power demands of global and national rental companies, construction projects, public utility applications and the events industry.

*** Application examples.

For example, the QAS500 has one of the smallest footprints for a standard built 500kVA generator.

With a length of 4.8m and width of 1.55m, the total mass of the unit is only 5348kg.

One company purchased a number of these units and during the winter installed them on outdoor ice skating rinks, powering the chiller equipment used to produce the ice skating surface.

The recent very cold winter provided a good test for the unit's durability and performance considering that, in some parts of the UK, the temperature dropped to a record-breaking - 17 degrees C.

The QAS500 is designed to operate continuously down to a temperature of -18 degrees C without any modifications and with its very low noise level and operating temperature range these units ran reliably throughout the winter period.

Similarly, generator units built specifically to meet the harsh environment of offshore wind farms have been constructed from stainless steel 316 and supplied together with fire suppression equipment and full remote control and monitoring.

Atlas Copco's latest unit is the QAC1250, the company's first 1MW 50/60 Hz switchable containerised super-silent genset.

One key application for these larger gensets is transformer maintenance on electricity substations.

The units can be simply and safely connected and synchronised to operate on and off the grid to provide a seamless supply of electricity to industry and domestic consumers.

For example, one customer has purchased a fleet of equipment to supply to the principal utility companies throughout the UK.

The generators are to provide emergency supplies and to assist in the planned maintenance of substations throughout the country.

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