ISO 8528 (BS7698) part 6 is the standard for test methods of engine-driven generating sets. It sets out general test requirements and defines a functional test and an acceptance test. Functional tests must always be done and usually occur at the manufacturer's factory. Acceptance tests are optional, may be done on site and are often witnessed by the customer or a representative.
In all cases tests must be done with reference to the agreed specification of the generating set. Prior to operational tests, environmental data must be recorded and a preliminary inspection is specified. This includes safety checks, earth connections and guarding, insulation tests, fluid levels checks etc. On initial start-up emergency stop system must first be checked, followed by frequency, voltage and phase rotation checks, and an inspection for leaks and vibration.
Only after these preliminary checks are load tests started. These include load duration tests or a 'heat run', with recording of steady-state voltage and frequency followed by load acceptance tests, when transient responses to load changes are recorded.
The standard defines three performance classes - G1, G2 and G3. A further class, G4, is reserved for performance criteria which are agreed between the supplier and the buyer.
Each performance class has different criteria for a range of characteristics of the generating set. G1 is the least stringent and generally applies to small, simple generating sets intended to supply unsophisticated loads. G2 is broadly equivalent to commercially available power, while G3 is intended for sets which are powering strategically critical loads, or those which particularly require a stable and accurate power supply such as hospitals and data centres.
Engine governing is measured by testing frequency, and alternator voltage regulation is measured directly. Specified characteristics relating to frequency include steady-state variation, dip when maximum power increase is applied, rise when 100 % power is removed and the time before the frequency returns within limits in both cases. Voltage characteristics again include the permissible dip when maximum power increase is applied, the rise when 100 % load is removed and the recovery time.
Some of these criteria are as follows:
|Steady-State Frequency Band||2.5 %||1.5 %||0.5 %|
|Maximum Frequency Dip||-15 %||-10 %||-7 %|
|Maximum Frequency Rise||+18 %||+12 %||+10 %|
|Frequency Recovery Time||10 Sec||5 Sec||3 Sec|
|Steady-State Voltage Deviation||5 %||2.5 %||1 %|
|Maximum Voltage Dip||-25 %||-20%||-15 %|
|Maximum Voltage Rise||+35 %||+25 %||+20%|
|Voltage Recovery Time||10 Sec||6 Sec||4 Sec|