POWER GENERATION
advantages that they bring. This is often the case when we look at the healthcare environment.
Governing Standards / Performance Class ISO 8528-1: 2018 – 8 The standard lays out four performance classes: G1-G4, with G4 being the most onerous. In simple terms the performance classes set out the maximum voltage and frequency deviations permitted on the application of a first set load, and the time over which the generating set needs to return to a steady state condition and other operational considerations. It is in this area where it is the author’s view that the standard, while seeking to provide an all-embracing minimum standard, is failing to keep up with product development. With the harmonisation of standards
across Europe, and to a lesser extent globally, the performance of electrical equipment generally has improved, particularly in relation to the efficient use of energy, and reduction of reinjected waveform distorting harmonics prevalent in non-linear devices. These older devices, such as UPS and inverter / soft start drives serving larger mechanical plant, can be the primary loads of any hospital. Class G2:2
This applies to generating
set applications where the voltage characteristics are very similar to those for the commercial public utility electrical power system with which it operates. When load changes occur, there can be temporary but acceptable deviations of voltage and frequency.3 Class G3 speaks more about the
‘connected equipment making more severe demands on the stability and level of the frequency, voltage, and waveform characteristics’,3
and then cites examples
such as telecommunications and thyristor- controlled loads. Both rectifier and thyristor-controlled loads can need special consideration with respect to their effect on generator-voltage waveform.3 Class G4 similarly refers to ‘Data-
processing equipment or computer systems’ as its examples.
Three categories By inference, the standards suggest that a hospital operates equipment falling into all three categories: for example, performance classes G3 or G4 as it uses ‘telecoms and data processing equipment or computer systems’. While those statements are in essence true, in a vast majority of cases, the type of products referred to, i.e. thyristor-controlled loads, are a thing of the past. If they aren’t, they must now meet all of the current harmonic reinjection requirements of a modern world. In many, if not all cases, a modern well- designed generating set equipped with the appropriate method of excitation can deal with the harmonic impacts of a given load. It should also be noted that all the
Figure 3: Illustration of PRP / Prime Rating.
critical equipment is fed via and protected from mains variation by a UPS package – the same UPS package available in the commercial market, and widely used in much less critical applications. The same is also true for the cooling plant – equipment widely used across many different applications exposed to the same mains or generator supplies. As we highlighted above, HTM 06 section 9.74 directly relates to BS ISO 3046 (Engine only). BS EN 8528 G2 performance is aligned with HTM 06-01 for Category-3 / 60% load acceptance at the PRP rating, but frequency recovery will be within 5 seconds (as per G2 ISO 8528). Section 16.8 indicates that the generator terminal voltage on starting should not overshoot the nominal terminal voltage by more than 15%, and return to within 3% of the rated voltage within 0.15 s. The generator terminal voltage should not vary by more than 15% following a step load increase from 0% load to 60% load, and then return to within 3% of the rated voltage within 0.5 s. Only a grossly oversized machine will be able to meet this requirement. It is key during the design phase that
an assessment be made of the actual site-specific first step load acceptance requirements. The loadings of various categories of risk areas, and any BMS or EMS load management capabilities that might be available etc, need to be considered. These matters should
fall within the realms of the project specification, and not be reliant on a ‘general standard specification’.
Understanding Generator Power Rating Categories – BS ISO 8528 – 1; 2018 Section 14.3 For commercial reasons, generating set manufacturers use the same engine (with model variations) across a range of power nodes. In addition, a single model of generating set can carry a number of different capacity ratings, i.e. 1000 kVA ESP, 1000 kVA PRP, and 700 kVA COP; the set rating is dependent on the operational duty / types of loading applied to the generating set, rather than the maximum engine capacity.
Section 14.3 of the ISO standard
covers the five different ways in which a generating set can be ‘rated’. These are COP, PRP, ESP, LTP, and DCP. Some of these ratings, for example PRP (Prime) rated sets, have their power ratings set against their ability to deliver into a varying load.
Section 9.73 of HTM-061 states that
‘Engines should be specified prime-rated. They should be capable of operating at the rated load for a period of 12 consecutive hours inclusive of an overload of 10% for a period not exceeding 1 hour, the prescribed maintenance having been carried out. This is known as a Class A rating.’ In the case of a Prime rated set the maximum permitted output of the set
August 2024 Health Estate Journal 43 t time
P power a Prime power (100%)
b Permissible average power during a 24h period (Ppp)
P a P 3 P 4
b c
P 1 P 2 P 6
c Actual average power over a 24h period (Ppa)
d Stop NOTE: t1 + t2 + t3 + … … … tn = 24h
30% P 5
t1
t2
t3 t4 d
t5 t6
t
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