ISO 8528: the Generator Set Standard Explained
ISO 8528 explained: the 13 parts of the generator set standard, power ratings in Part 1 and the G1–G4 performance classes with ISO 8528-5 limit values.
Contents
When a tender asks for a generator “according to ISO 8528”, it refers to a series of thirteen standards that together describe how a diesel generating set is rated, built, controlled and tested. Knowing which part says what makes it easier to write a specification and to compare offers on the same basis.
The parts of ISO 8528
The table below lists the parts and their scope. Parts 1 and 5 are the ones most often quoted in specifications: Part 1 defines the power ratings and the performance classes, Part 5 gives the limit values for each class.
Power ratings (Part 1)
ISO 8528-1 defines how the power of a set is declared. Emergency standby power (ESP) is for variable load during mains failures, up to 200 hours per year. Prime rated power (PRP) is for variable load with unlimited hours. Limited-time running power (LTP) is for constant load up to 500 hours per year, and continuous operating power (COP) is for constant load with unlimited hours. The 2018 edition added data centre power (DCP) for data centres with a reliable utility supply. Details and typical uses are in our article on standby, prime and continuous power.
Performance classes G1–G4
The performance class describes how well the set holds voltage and frequency, in steady state and when load is suddenly applied or removed:
- G1: loads that only need basic voltage and frequency, such as general lighting and simple electrical loads.
- G2: loads comparable to those on the public grid, where short deviations are acceptable: lighting, pumps, fans, hoists.
- G3: loads with stringent requirements on frequency, voltage and waveform, such as telecommunications and thyristor-controlled loads.
- G4: exceptionally stringent requirements, for example data processing equipment; the values are agreed between manufacturer and customer.
The second table shows the main ISO 8528-5 limit values for G1, G2 and G3. A class always refers to a stated load step: a set that meets G3 when accepting 50% of its rating in one step may not meet it at 100%. A good specification therefore states the class and the load steps.
What ISO 8528 does not decide
The standard does not set the noise limit at your site, the fuel autonomy or the transfer time of the ATS. Those are project requirements and belong in the specification. Noise is measured to ISO 8528-10 or ISO 3744/3746, but the permitted value comes from local rules or the client. Ambient temperature and altitude change the available power; see derating for temperature and altitude.
How we use it
Our data sheets give power ratings on the ISO 8528-1 basis at 25 °C, sea level and power factor 0.8, and every set is load-tested at our factory in Tuzla, Istanbul before shipment. If your tender names a performance class and load steps, send it to us and we will confirm the model against those values: contact us.
Parts of the ISO 8528 series
| Part | Scope (title of the standard) |
|---|---|
| ISO 8528-1 | Application, ratings and performance |
| ISO 8528-2 | Engines |
| ISO 8528-3 | Alternating current generators for generating sets |
| ISO 8528-4 | Control gear and switchgear |
| ISO 8528-5 | Generating sets |
| ISO 8528-6 | Test methods |
| ISO 8528-7 | Technical declarations for specification and design |
| ISO 8528-8 | Requirements and tests for low-power generating sets |
| ISO 8528-9 | Measurement and evaluation of mechanical vibrations |
| ISO 8528-10 | Measurement of airborne noise by the enveloping surface method |
| ISO 8528-11 | Rotary uninterruptible power systems — Performance requirements and test methods |
| ISO 8528-12 | Emergency power supply to safety services |
| ISO 8528-13 | Safety |
Performance classes G1–G3: ISO 8528-5 limit values
| Parameter | G1 | G2 | G3 |
|---|---|---|---|
| Frequency droop | ≤ 8 % | ≤ 5 % | ≤ 3 % |
| Steady-state frequency band | ≤ 2.5 % | ≤ 1.5 % | ≤ 0.5 % |
| Transient frequency deviation (100 % load rejection) | ≤ +18 % | ≤ +12 % | ≤ +10 % |
| Frequency recovery time | ≤ 10 s | ≤ 5 s | ≤ 3 s |
| Steady-state voltage deviation | ≤ ±5 % | ≤ ±2.5 % | ≤ ±1 % |
| Transient voltage dip (load application) | ≤ −25 % | ≤ −20 % | ≤ −15 % |
| Transient voltage rise (100 % load rejection) | ≤ +35 % | ≤ +25 % | ≤ +20 % |
| Voltage recovery time | ≤ 10 s | ≤ 6 s | ≤ 4 s |
G4: values are agreed between manufacturer and customer. Transient values apply to the stated load step; the load step must be specified separately.
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Frequently asked questions
What is ISO 8528?
ISO 8528 is the international standard series for alternating current generating sets driven by reciprocating internal combustion engines. Its parts cover ratings and performance, the engine, the alternator, controlgear and switchgear, test methods, vibration, noise measurement and safety.
What do G1, G2, G3 and G4 mean?
They are performance classes defined in ISO 8528-1. G1 is for simple loads, G2 for loads comparable to the public grid, G3 for loads with stringent frequency, voltage and waveform requirements, and G4 for exceptionally stringent requirements agreed between manufacturer and customer. The limit values for G1–G3 are given in ISO 8528-5.
Which performance class should a hospital or data centre specify?
Critical sites usually specify G3, together with the load steps the set must accept and the required recovery times. G4 is used only when the values are agreed case by case. A school or office building with ordinary loads is usually specified as G2.
Is ISO 8528 the same as ISO 3046?
No. ISO 3046 covers reciprocating engines themselves, including their power declaration and reference conditions. ISO 8528 covers the complete generating set; Part 2 refers to ISO 3046 for the engine.
Featured models
Technical data of models in frequently requested power ratings:
- 38 kVATRX QZ TA 0038Quartz Q490ZD
- 58 kVATRX QZ TA 0058Quartz Q4105D
- 77 kVATRX QZ TA 0077Quartz Q4105ZD
- 105 kVATRX QZ TA 0105Quartz Q4105AZLD
- 155 kVATRX QZ TA 0155Quartz Q6105AZLD
- 260 kVATRX SD TA 0260SDEC SC9D310D2
- 300 kVATRX SD TA 0300SDEC SC9D340D2
- 400 kVATRX SD TA 0400SDEC SC15G500D2
- 520 kVATRX SD TA 0520SDEC SC25G610D2
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