Uninterruptible Power Supplies   Diesel Generator FAQs -----------------------------------------------------------------------------------------------------------------------------------------     500va to 10kVA Comms rack and tower UPS models for small sized applications >   What type of generator? - Gas or Diesel Powered? It should be considered that gas sets are not ideal for standby applications as their cold start capabilities are usually quite poor, typically 40-50% - they are often better as base load or prime sets running most of the time - this is why they have a permanent gas supply as this eliminates the need to 'top up' diesel constantly. Gas generators are basically petrol engines converted to run on gas, they still use a butterfly valve for speed control and as such they run on a lean mixture giving low torque and poor speed regulation What output is required? – Calculating the size of the set It needs to be established if the whole building is to be supported, in which case electricity bills can provide historical information useful in obtaining peak load levels or monitoring of the load to check demands. Future expansion of building facilities or additional equipment must also be taken into account when sizing the generator. If loads can be sequentially started, this helps to reduce the ‘cold start’ demand on the set and could allow a smaller set to be used thereby reducing capital costs. If only supporting part of the building load, usually referred to as essential, it is necessary to determine which loads are most important, these are typically emergency lighting, UPS, essential air-conditioning, building lifts and a limited amount of small power. It must also be considered that many loads of this type have high start up currents or impose non-linear demands on the generator, so care must be taken when calculating the size of set needed. What type of generator duty cycle? – How often is the set required to operate? Base load or Continuously rated – usually required where there is no power supply authority to provide commercial or industrial power to your facility, in this instance the generator may be required to operate continuously for 24 hours a day, 7 days a week – however, it must be considered that rotating machinery needs to be serviced every two weeks when operating this type of duty cycle – so another generator may be needed during these service periods. Short-term overloads of up to 10% for one hour are usually permissible Prime rated – similar to the above application but usually in an area where the mains power is more reliable, in this case the set is expected to carry 75-80% load for several hours but not necessarily continuously. Standby rated – usually installed in an area where the mains is generally healthy but the user cannot tolerate any power loss to certain areas of their business, typically for process control, computer or communications related industries. These sets are rarely used for full building support and usually back up essential loads. A time restriction of a few hundred hours per year is typical and no overload capacity is available. Where do you intend to position the set? – Inside or outside? Inside the building – there is often an ideal basement or ground floor room to locate an open generator, this does not interfere with the fabric of listed buildings, but is more complex in terms of cooling air inlet and discharge, engine exhaust and silencers, acoustic noise limitations, fuel deliveries, vibration and access. All these issues often make open set installations more expensive and require a great deal of planning for the site services. -------------------------------------------   10 to 80kVA Single and three phase UPS models for medium sized applications > -------------------------------------------   100 to 800kVA Large UPS models to cater for whole floors or entire buildings >   Service Agreements Spares, callout preventative maintenance & 'CPSWatch' >     Rental Agreements ------------------------------------------- Installation, Removal, Disposal ------------------------------------------- Low Voltage Switchgear  ------------------------------------------- Site Surveys and Pre Sales ------------------------------------------- Diesel Generator Sets ------------------------------------------- UPS Network Monitoring   External to the building – this is usually the most straightforward installation and totally enclosed weatherproof housings can be both cost effective and environmentally friendly. Local authorities often need to be consulted to check acoustic noise restrictions in the area, in particular residential locations need to be carefully considered. Exhaust emissions are also critical near buildings and may need special treatment. If considering a roof top installation, weight and vibration also need to be carefully checked by specialists. Self-contained sets have the added benefit of being easily moved to new locations if necessary. How do you want the set to work? – Local manual, remote or automatic Manual start – a simple electric pushbutton or keyswitch is often used for short term hire sets or for installations where the site is permanently manned and the load can suffer a break in supply. Remote start – the set can be started by a remote signal from a manual changeover device. Automatically – usually referred to as AMF, auto start upon mains failure, the set receives a signal from a remote sensing device or phase failure relay usually located in an automatic changeover panel that switches from mains to generator either by interlocked Contactors, Moulded case circuit breakers or Air circuit breakers depending upon the rating of the set. The return to mains can be automatic or manual depending upon the site requirements. With automatic starting there is always a brief delay of several seconds whilst the engine gets up to speed and ready to accept the load. (If this is unacceptable for certain types of load it is necessary to install a UPS to ‘bridge this gap’ and ensure a seamless transition of power) How do you cool the generator? Fan cooled radiators are the most common form of engine cooling; the fans are either engine driven or electrically powered. Flexible couplings usually provide the link to either a sound attenuated louvre or ductwork that ensures that hot air is correctly discharged from the enclosure or plantroom. Occasionally remote mounted radiators are employed in difficult plantroom installations where ductwork is not a suitable option. How do you get rid of exhaust gases? For plantroom installations, it is normal to simply discharge the exhaust to atmosphere alongside the hot air discharge louver, however, this is not always acceptable due to site limitations or local legislation and it is often necessary to route the discharge gases through a flue pipe either fixed to an external building wall or through an internal riser. Both options need careful planning to keep back pressure to a minimum, typically by reducing the number of bends and increasing the pipe diameter. External pipework can be installed using in stainless steel for a more durable finish although painted mild steel is often acceptable in view of the cost differential. Enclosed sets generally employ an internal silencer system consisting of primary and secondary mufflers with the gases routed out through the canopy via a weatherproof discharge point often known as a bird’s beak. Catalytic converters are becoming more common in an effort to reduce harmful emissions. How to store fuel and re-fill the Generator Most simple enclosed sets incorporate a double skinned or bunded base tank, built into the main base frame or skids of the set, these can usually provide adequate running time for standby applications, typically 8-20 hours. Longer run times or permanently running sets generally use a separate double skinned bulk fuel tank, with a fuel transfer system consisting of one or two pumps and a fuel fill point incorporating overfill alarm, high and low level detection and various other options such as leak detection, pipework insulation etc What about the noise of the generator? Engines will always create high levels of noise and the process of reducing this noise is achieved by using a combination of attenuators, silencers and acoustic enclosures. Audible noise levels are measured in decibels over a given distance; site conditions and local legislation usually dictates the level that can be tolerated. Enclosed sets are typically 75-80dBA at one metre, higher levels of attenuation can achieve 65dBA or even less, but the cost and physical size often becomes prohibitive. © copyright cps ltd | terms & conditions | site by boxred.co.uk downloads | contact | recruitment