Electricity and Control April 2024

ENERGY MANAGEMENT + THE INDUSTRIAL ENVIRONMENT

Standby, prime or continuous – choose the right genset Load shedding in South Africa has cast a whole new light – so to speak – on the selection of generator sets, making the concept of a ‘standby’ generator less applicable than has historically been the case. As a leading local manufacturer of gensets,WEG Africa explains the importance of understanding a unit’s duty – the purpose it is to serve – before deciding on a power rating.

S outh African businesses have come to rely increas ingly on generator sets to keep the wheels of indus try turning, but there is still much confusion about selecting the right genset for the specific duty it is to serve. “Customers tend to make the mistake of choosing gensets based purely on the nameplate rating,” says Craig Bouwer, Senior Manager Gensets at WEG Africa. “The most important aspect of the selection is the application of the genset, which needs to be clearly understood before choosing the genset with the correct rating to serve that application.” Distinguishing the applications Genset applications can be generally categorised as standby, prime or continuous. Part of the confusion in the market is that the frequency of load shedding means few gensets in the country today are used as ‘standby’ units. A standby application is one in which the genset is seldom used. It may even be that a standby unit runs more during its regular maintenance and testing than it runs operationally. A standby unit is in place to take over the power supply in an emergency situation. “When a genset is specified for standby purposes, there is a limit to the number of hours it can be run each year,” says Bouwer. “The load factor also needs to be taken into consideration.” More common in the current South African context are prime and continuous applications. A prime application is one in which the genset can run for an unlimited number of hours each year. Importantly, the load that is applied to the genset is variable, but it has to run at an average load factor, which is specified by the relevant original equipment manufacturer (OEM) of the engine. A continuous application is also unlimited in terms of the hours the genset can run, but the load is constant and pre determined. “Many people get confused between a prime rating and a continuous rating, because they focus only on the runtime factor when thinking about ratings,” Bouwer says. “With both prime and continuous ratings having unlimited running time, the difference is the load factor. In a prime application the load is variable, whereas in a continuous application it is fixed. The load factor is therefore critical in choosing a genset for the respective application – whether that is a prime or continuous application.” “These definitions are key to ensuring that gensets

3 000 kVA 400 V primary equipment before being installed in its enclosure. perform as required,” notes Damian Schutte, Engineering Manager at WEG Africa. Both the customer and the OEM need to be clear about the conditions under which the genset will operate prior to selecting a suitable system. “Consider the analogy of a vehicle on cruise control,” says Schutte. “A continuous application for a genset is like a car travelling a long distance at a steady and reasonable speed, rpm and load – all well within the engine’s output capacity. A prime application, in contrast, can be compared to a vehicle needing to perform at higher speed and power output at variable intervals and for variable periods of time.” He explains that each category of application will place different demands on the genset, and this will affect the choice of rating and the expected lifespan. Just as a car will usually experience less wear and tear from being driven at a suitable and constant speed, so a genset’s life cycle can be extended – and total cost of ownership reduced – by operating it similarly. As an example of continuous power, a mine may need additional power when its grid power is partially limited during load shedding. The genset solution is designed to bridge the gap between normal supply and reduced supply, and the units will run during these times to cater for a more-or-less fixed load. For an industrial application like a workshop, the load is likely to be much more variable – with machines being turned on and off depending on the time of day and the

APRIL 2024 Electricity + Control

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