POWER GENERATION
Geoff Halliday Figure 4: Generator and LV distribution.
should not exceed an average load of 70%1 of the Prime Rating over a 24-hour period (Load Factor). Within that 24-hour period the generating set is able to deliver a 10% overload for one hour in 12. They deliver an average load level over a 24-hour period while still being able to provide a 10% overload, for one hour in 12. Section 14.3.3 of the standard describes Prime Power rating as2
‘…being the
maximum power which a generating set is capable of delivering continuously while supplying a variable electrical load when operated for an unlimited number of hours per year under the agreed operating conditions with the maintenance intervals and procedures being carried out as prescribed by the manufacturer’. It is important to note that the way in which these ratings are allocated will vary from manufacturer to manufacturer, based on engine performance, connected rating of alternator performance, and maximum operating ambient temperature.
A daunting task With this extensive range of generating set capacities and rating options, it can be daunting for the design team to fix the direction of this aspect of the design. For most European markets, the grid is a very stable source of power, and it is very unlikely that power will be off for more than a few hours per year (testing included in this number). This is why a PRP rated set should be an acceptable option. When designing a generating set package for any application, it is important to consider the likely maximum operating ambient temperatures required, as this does play a big part in how the generating sets are designed, and rating capacity determined. In a hospital / healthcare setting, the generating set solution must always be rated to supply the peak site load, on the
44 Health Estate Journal August 2024
hottest day of the year, unless there is clear alternative direction. As we identified in an earlier section, the electrical load of a hospital is very diverse in nature, being dependant on many factors. Some of the critical areas often have an additional layer of protection such as EPS, UPS, or power via a battery- backed system of varying duration, all aimed at providing an uninterrupted supply to the critical area served. An EPS, UPS, or DC system only looks
for stability of input supply, be it mains or generating set. When returning from battery to either mains or generator, the UPS’s input power requirements slowly ramp up over a period of 5-10 seconds, not in one single ‘lump’ of load. This is an important factor when assessing first step load requirements, as none of these load types would be part of the first step load. Central cooling systems have a UPS
equivalent – a buffer or reservoir vessel of cooling water which can maintain water temperatures within range for around 30 seconds. This buffer vessel is there to provide time for the generators to start and pick up the cooling / mechanical loads essential for operation of a hospital. Some of the compressors and pumps within this system can be significant in size, and can present some quite large load steps to the system. Bringing these back online can be delayed and staggered; this should be catered for in the design process.
Sophisticated BEMS equipment Most, if not all, modern hospitals have sophisticated building and energy management systems (BMS /EMS). The key points here are that these loads: n Can and will be managed on by the BMS/EMS in a controlled way.
n When these loads are applied the generating set will already be ‘under
Geoff Halliday, Business consultant at WB Power Services, started his career as an apprentice working for Square D (later part of Schneider), before moving into the critical power sector, where he has now worked for over 40 years, splitting that time equally between both the UPS and standby diesel generation sectors. During this period Geoff has held several roles – including Customer Service engineer, Project manager, Technical director, Sales director, and managing director. The Critical Power market exposes the individual to a wide and diverse range of market sectors – including Healthcare, Life Science, Water Treatment, Banking and Finance, Military, Manufacturing, Process Control, and Data Centres of all sizes. Drawing on his management skills, product knowledge, and vast application experience amassed throughout his career, Geoff now enjoys sharing his knowledge with others.
load’, meaning that the application of the cooling load ‘isn’t a first step load’.
This means that the generator(s) never get close to seeing anything approaching a 60% load step, negating the need for this measure and the associated G3 or G4 requirements that accompany them. Regular and thorough maintenance of all plant is key to a reliable M&E infrastructure. In the case of a generating set(s), this should include all control functions and testing the engine at load. See the WB white paper, Greening Standby Power Generation.
Acknowledgements, clarification, references, and bibliography 1 Thanks to the writers of HTM 06 for all direct quotes and references.
2 Information directly from BE EN ISO 8528. 3 Some Kohler generating sets offer 75% load factor.
4 Figure 4 – Information provided by KUP, a Kohler Power Systems Company.
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