Part 2 – Sizing Generator

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When is a Generator Required?

A generator becomes necessary when the power supply needs to be sustained for a duration longer than the runtime of the UPS.

Synchronisation

When a generator starts, it requires time to synchronise with the electrical current of the UPS. Operating the generator near its maximum capacity poses a risk of load dropping. To mitigate this risk, a larger generator is recommended.

Quick Checklist

To determine when a generator is needed, consider the impact of electrical equipment failure on your business and follow these steps:

• Assess the power protection requirements for different electrical systems.
• Evaluate the power loading of the generator.
• Upgrade the generator size to account for surge current, UPS efficiency, harmonics, synchronisation, operating temperature, and future electrical demands.
• As a general guideline, the generator size should be 1.25 to 3.00 times or more than the UPS power rating.

Surge Current

When identifying all electrical systems, pay attention to electrical inrush or surge current. This occurs when devices start up and their initial power consumption exceeds the normal operating load significantly. The generator should have the capacity to handle the UPS power requirements and an additional 20% to 30% for the power conditioning process.

Harmonics

As the number of electrical devices increases within a building or site, the electrical supply waveform can become distorted and less smooth, generating additional harmonic frequencies. These harmonics can cause issues with sensitive electrical equipment, leading to heating problems and reduced cable capacity. Power conditioning equipment can be utilised to filter out harmonics and enhance the quality of the electrical supply, safeguarding sensitive equipment and improving performance.

Temperature

Temperature is a critical factor to consider. The operation of a generator typically results in a temperature increase of around 10°C within the engine room or plant. If the ambient temperature is already high, such as at 20°C, the resulting 30°C temperature can adversely affect the generator. Monitoring and controlling the temperature are essential to ensure optimal performance and longevity of the generator.

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