The most important consideration when buying a diesel generator set (genset) is to seek professional assistance from a genset supplier that will consider the entire electrical infrastructure, including the appropriate recommendation of the genset power rating, and not just the genset in isolation, says motors, controls, electrical products and solutions provider Zest WEG Group.
The company’s rotating machines manager, David Claassen, further points out that, because State-owned power utility Eskom encourages both private and industrial users to reduce their electricity consumption and lessen the strain on the national power grid, various issues related to standby power have arisen for the commercial and residential sectors.
These issues include the need to determine the correct generator size, the requisite power rating and startup capabilities for the various applications.
In light of this, Claassen believes that a key advantage of approaching Zest WEG Group for standby power is the company’s in-house knowledge, experience and applications expertise, in addition to its superior product range.
He adds that customers frequently ask what size diesel generator will be sufficient for residential, commercial and industrial applications. He explains that the choice of size, or power rating (kVA), of a generator takes into consideration several factors, including the absorbed power ¬– which is the power expected to be drawn by the load ¬– the type of load and the duration that this load is required to be powered.
“The first step in sizing a genset is to establish what load needs to be met during a power outage. A qualified team from a genset supplier, such as Zest WEG Group should measure the type of load and the total power drawn before that supplier recommends a particular diesel genset. Following this, accurate load calculations can be provided and a suitable system recommended,” Claassen reiterates.
Another method for determining the power rating of a genset for commercial and industrial applications is to analyse the client’s utility bill, which will usually provide a breakdown of real power (kW) and reactive power (kVAR) consumed. From these values, it is possible to calculate the apparent power (kVA) consumed.
“Electric motors are used in almost all commercial and industrial facilities and analysing the starting methods of these motors is critical when determining the power rating of the genset,” says Claassen.
Motors that are started with direct online (DOL) starters typically require a startup current of six to eight times the rated current of the motor. This implies that the genset needs to be capable of producing enough power to cater for this.
“However, it is not optimal to design the genset for these conditions, as the client will end up with a unit capable of supplying a substantially bigger load than required under running conditions, which has a negative impact on cost and technical implications for the engine, too,” cautions Claassen.
Nevertheless, this challenge can be countered with a step-load configuration, which means that one would start loads sequentially, instead of all at once. Another option is to consider changing the starting method of the motors from DOL to variable speed drive, which limits the start-up current less than 150%.
“Several factors and solutions are available and an innovative approach to each installation is necessary to optimise the capital cost and running expense of the installation,” says Claassen.
He therefore emphasises Zest WEG Group’s reliable standby power options, which are guaranteed to ensure uptime of any operation, from mining and construction to general industry operations. “We can supply standard off-the-shelf gensets, in addition to custom-built, application-specific units,” says Claassen.
Zest WEG Group’s genset capacities range from 15 kVA to 2 500 kVA and can be increased upwards with multiple synchronised gensets. Options include both stationary and portable configurations, all manufactured according to stringent quality standards.
