Generator Sizing For Compatibility With Uninterrupted Power Supplies

Most critical power protection solutions, goldshell Miners incorporating uninterrupted power supplies (UPS), today are interfaced with an alternative source of back-up power, which could be a fuel cell or flywheel but more usually it is a diesel generator. Generator sizing and UPS compatibility are fundamental to power continuity and must be taken into account at the outset of any power protection plan.

Power Rating For Standby Power Solutions A generator must be sized correctly so that when it’s required to do so it will be able to power the UPS (taking into account any allowance for harmonics that the UPS’s rectifier will generate) and the load/s that the UPS is supplying. Generators are typically rated in two ways:

Prime Power Rating (PPR) – whereby the generator supplies power as an alternative to the mains power supply, but on an unlimited basis.

Standby Power Rating (SPR) – whereby the generator supplies power as an alternative to the mains power supply but for a short duration, typically one hour out of every twelve. A generator rated under SPR can be as much as 10 percent larger than one sized using PPR. This provides an overload capability for a short duration, perhaps to meet sudden load demand changes, for example.

For an uninterrupted power supply installation, PPR is the more suitable method of rating. It is extremely important, for achieving greater resilience (fault tolerance), that a generator and its UPS are suitably matched. Not only must a generator be able to accept the load of the uninterrupted power supply but the UPS rectifier and static bypass supplies must be able to operate with, and synchronise to, the output of the generator.

Generator set manufacturers have four recognised categories of load acceptance: one = 100%, two = 80%, three = 60% and four = 24%. Categories two, three and four are used in practice for PPR-rated generators. Load acceptance is closely related to the turbo charging system and the Break Mean Effective Pressure (BMEP) of the engine. This is a function of engine speed, number of cylinders and the swept volume of each cylinder.

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