Part 2 – Sizing Generator

When is a generator required?

If electrical equipment has to be supplied with power beyond the run time of the UPS, a generator will be required.

Synchronisation

When a generator starts up it needs time to synchronise with the UPS electrical current. If the generator is working close to full capacity, there is a chance that the generator will drop the load. To stop this from happening, a larger generator is the cure.

Quick Checklist

•Verify the effect on your company should certain electrical equipment fail

•Identify levels of power protection required for different pieces of electrical equipment

•Identify generator power loading

•Increase size to cater for surge current, UPS power efficiency, harmonics and synchronisation. operating temperature and future electrical loads

•A rule of thumb is that the generator size should exceed the UPS power rating by a factor of between 1.25 to 3.00, or more

Lets Get To It!

Surge current

Once all electrical equipment has been identified, careful consideration should be given to electrical inrush or surge current. This is a phenomenon experienced when electrical devices start up and where the initial start-up power consumption greatly exceeds the normal working load.

The generator needs to support both the UPS power rating and an additional 20%-30% to cover the ‘power conditioning’ process.

If you're unsure about what you need or would like further explanation, please contact us and we are happy to help

Harmonics

Harmonics are a distortion of the smooth waveform of the AC electrical supply. They can be explained by looking at the waveform of the basic or first harmonic, which cycles at 50Hz. You will have noticed on many European electrical appliances, 220V 50Hz. The 50Hz refers to the first harmonic, and these appliances are designed to work at this frequency.

Temperature

Temperature also plays a significant role. With the generator running, a rise of 10°C is usual within the plant or engine room. If the ambient temperature is already 20°C the resultant 30°C temperature will be detrimental to the generator.

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