The generation game

1 What output do you require from your generating set?

If you do not know you will need to refer to historical electricity consumption details and peak load demand levels or conduct load monitoring of your supply to determine your required load.

You may have a schedule of loads – if so you will need to know the sequence in which the loads are likely to be applied on the generating set, and in certain circumstances the starting and running current of the loads or maximum re-charge demand.

2 What rating do you require?

Base load/continuous rated

If there is no REC supply available and your generating set is to be the only possible source of power, then you need to consider the duty required. For this kind of application where the generating set is expected to operate 24 hours a day, seven days a week you will usually require a base-load or continuous rated generating set. This type of rating is generally offered with a short term overload capability of 10% for one hour in 12 hours’ operation.

Prime rated

This rating applies to the supply of electrical power when the REC supply is not available (mains failure), and in an area where the REC supply can generally be considered reliable. It is assumed that the load required from the generating set will be variable with an average factor of 70-80% often applied by the supplier. This rating carries no restrictions and is offered with a short-term overload capability of 10% for one hour in 12 hours operation.

Maximum standby rated

This rating applies to the ISO fuel stop output of the engine and again relates to the supply of electrical power when the REC supply is not available (mains failure), and in an area where the REC supply can generally be considered reliable. This rating carries a time restriction imposed by the supplier often between 300-500 hours operation per annum. No short-term overload capability is available with this rating.

3 Where do you intend to

locate your generating set?

Internally

If located internally, you will need to consider the space required for the installation of your generating set together with any noise level restraints.

Where will you source your cooling and combustion air from and where will you discharge your cooling air to? Do you have external walls through which inlet and discharge louvres can be installed? In the absence of external walls you may need to consider ducting of air to/from the plantroom. This is common with basement installations or plant rooms with limited space or only one external wall.

Externally

External generating sets are generally installed within a weatherproof housing often provided with sound reducing properties. Depending on the rating of the generating set required and any noise level restraints imposed, you may consider close fitting, walk-around and containerised solutions.

Acoustic housings can be provided in differing formats depending on space and noise restrictions. These include conventional end in/out attenuation, as well as roof and side mounting of air inlet and or outlet attenuation as required to suit the application and space available.

4 Generating set cooling

Generally generating sets are provided with local engine driven or electrically driven radiators, which provide the necessary cooling of the generating set. These are usually flexibly coupled to sound attenuation or ductwork then a weather louvre to ensure hot air is correctly dissipated from the plantroom, enclosure or container as required and prevents recirculation of the cooling air.

For plantroom installations when it is not possible to incorporate ductwork or attenuation you may need to consider the use of a remote radiator, and depending on its location the incorporation of local heat exchangers for your engine.

5 Discharge of exhaust gases

If permissible, the norm is to discharge your exhaust gases locally external to the plantroom and adjacent to the discharge weather louvre. If not permitted to discharge locally, you will need to consider extending the exhaust flue system to an acceptable location. This will either need to be externally up the wall of the building or internally within a riser. Consideration will be required with regard to the back pressure imposed on the engine and the route of the flue required, this will enable the diameter of the flue to be determined.

The external finish to the flue will also need to be considered. In certain circumstances polished stainless steel will be required, in others brushed stainless may be preferred as well as mild steel painted pipework. Surface temperature may be of concern depending on the flue’s location in relation to other services, and/or the accessibility of the flue to employees or the public.

6 Emissions

Reduction of exhaust gas emissions is becoming more of a consideration. Many applications require a catalytic converter to be provided as standard, whilst others may feel it not so critical. This is generally detailed within the client’s performance requirements.

Typically, the catalytic converters provided are of the two-stage type, designed to reduce CO emissions by 60% and HC emissions by 40%.

7 Fuel system and storage

What is the fuel system storage capacity you require? This will depend on the nature of the business, the reliability of the REC supply, any regulations imposed by the local authorities and DEFRA.

Do you require a local day tank only? Do you require a bulk fuel tank, if so will it be located above ground or below ground? Will the interconnecting pipework be above ground or below? Does it need to be double skinned, insulated, trace heated or provided with some means of leak detection? Will the fuel transfer system required be gravity feed, single pump or twin pumps, etc?

8 Noise level requirements

The noise levels required will determine the construction of the plantroom needed, dimensions of attenuation equipment, exhaust gas silencers and acoustic housing as applicable.

Noise level requirements can also determine the type and quantity of anti-vibration mountings that may be required.

9 What mode of operation?

Key start/manual start

It is necessary to push a button or turn a key-switch on the control module of the generating set before it will start.

Remote start

The generating set will start automatically upon receipt of a start signal from a remote source, usually provided when a manual mains/generator changeover device is used.

Autostart

The generating set will start automatically upon receipt of a start signal from a remote source, usually provided when an automatic mains/generator changeover device is used. The changeover device comprises mechanically and electrically interlocked changeover contactors / mccbs or acbs depending on rating.

Autostart – no break on mains return

The generating set will start automatically upon receipt of a start signal from a remote source, provided when an automatic mains/generator changeover device is used. The changeover device comprises electrically interlocked changeover mccbs or acbs depending on rating. The generating set control system is configured to carry out a controlled parallel operation of both the mains and generator supplies when returning to mains with ramping of load from generator to mains supply before opening the generator changeover device.

10 Telemetry/remote monitoring

Do you have any specific requirements with regard to remote monitoring of generating set availability or status of its protection/alarm devices? This information can be provided in many forms, including VFCs, RS232 or RS485 protocol, Ethernet and others if necessary.