Manuel Bolotinha
Introduction to Emergency Generator Set
Hospitals, airports, shopping malls and office buildings, just to mention some examples, are very sensitive, in what concerns safety of people and goods, to power outages caused by faults in medium (MV) and low voltage (LV) distribution networks and even in high voltage (HV) transmission networks.
When a power outage occurs is necessary that communication systems, emergency lighting, smoke exhaust fans, fire fighting water pumping stations, security, lighting in buildings and other critical electrical systems and equipments, designated as essential loads (or critical), continue running.
To solve such problems common solution is the installation of LV diesel emergency generator sets, whose applications, characteristics and installation procedures must be in accordance with IEC Standard 60034.
Rated Power and Neutral Grounding of Emergency Generator
Rated power of LV diesel emergency generator sets depends on the operation regime: standby, prime and continuous, as defined in ISO Standard 8528.
In standby regime the available power supplied by the generator set varies with the value of the load during the lack of normal power supply and average power output is 70% of emergency standby power rating. Typical operation of this regime is 200 hours per year with a maximum of 500 hours per year.
In prime regime the available power supplied by the generator set varies with the value of the load for an unlimited period of time and average power output is 70% of prime power rating. Typical peak demand of 100% of prime-rated ekW with 10% of overload capability for emergency use for a maximum of 1 hour each 12 hours; overload functioning may not exceed 25 hours per year.
In continuous regime output is available without varying load for an unlimited time. Average power output is 70 – 100% of the continuous power rating. Typical peak demand is 100% of continuous rated ekW for 100% of operating hours.
According to the definitions stated above is easy to understand that the same generator set has different rated powers for each operation regime. Rated power in standby regime is higher than rated power in prime regime, which is higher than rated power in continuous regime.
Rated power of generator sets main be defined in kVA or kW for a cos Φ (Power Factor) = 0.8. It is also necessary to define the network frequency (50 Hz or 60 Hz).
In Table 1, as an example, are shown the values of rated power (kVA) of some generator sets of the same manufacturer and the same manufacturing series, according to the operation regime (f = 50 Hz).
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