Generating sets: prime or standby decides the rating, and most enquiries leave it out
The same load needs a different set depending on how many hours a year it runs. Here is why that matters to the price.
Most of the industrial sites our machinery goes into do not have a reliable mains supply, so generation is quoted alongside the plant more often than it is quoted alone. One question decides the specification and it is the one most often missing from an enquiry: is the set prime power or standby?
Prime and standby are not the same machine
A standby set runs when the mains fails - a limited number of hours a year, at a rating it can hold for that duration. A prime set is the site's normal supply and runs continuously. The same electrical load requires a larger set in prime service than in standby, because the rating is defined against the duty, not just the kilowatts. Buy a standby-rated set and run it as prime and you have bought a short service life at a good price.
Tell us which it is, and the load in kW rather than in kVA where you can - the power factor matters and assuming one is how a set ends up marginal.
The other figures
- Starting load. Motors draw several times their running current at start. On a site with large motors this, not the running load, sizes the set.
- Fuel. Availability and quality at the site, which in some markets is a more serious constraint than price.
- Supply voltage and frequency. 230 V or 240 V at 50 Hz across most of the African markets we supply; parts of South America and the Caribbean run 60 Hz, and that is an alternator difference.
- Ambient and altitude. Both derate a set. At altitude the derating is substantial and it is a specification question, not a margin.
Conformity: generators are often in scope where machinery is not
This is worth knowing before you order. Several destination conformity schemes list generating sets, motors and transformers specifically, even where general industrial machinery is outside the scheme. Ethiopia's programme, for example, works from a closed list of products that includes generators and transformers. Zimbabwe schedules by tariff heading and the electrical chapter is substantially inside it. So for this division the first question on an enquiry is the HS code and the destination, because it decides whether a certificate is needed at all.
Substations and distribution
Where the project is distribution rather than generation, our outdoor substations up to 400 kV range covers the equipment, and those are quoted against a single-line diagram rather than a load figure. Send the diagram.
Supplier questions
- What rating standard is the quoted output against, and is it prime or standby?
- Which engine and which alternator, by name?
- What derating applies at the site ambient and altitude?
- What is included - canopy, tank, controller, cabling - and what is not?
Send the load in kW, prime or standby, the fuel and the site. Request a quotation, or see the power generation range.