Application Engineering

Please read the Warranty Statement carefully before proceeding with any design or ordering materials or labor.

These documents are in PDF format. To view them, you will need Adobe Reader® software.

Understanding the load characteristic is a vital factor in generator sizing. An accurate load schedule should be assembled early in the design phase of power generation projects.

Various load types, such as motors, uninterruptible power supplies, variable frequency drives, medical diagnostic imaging equipment and fire pumps all have significant and different effects on the generator set.

Generator sets are a more finite source of power when compared to the public utility supply. Application of loads can have a far greater impact on the quality of output obtained from the generator than for a utility supply.

This chapter explains the effects of various loads and the influence these have on the choice of generator.

Requirements and Recommendations:

• Whenever loads are connected to or disconnected from a generator voltage and frequency disturbances should be expected. The magnitude of the disturbance will be in proportion to the magnitude of the change of load relative to the generator size.
• The power required to start a motor will generally be considerably greater than the full load steady-state power requirement of the motor.
• Variable frequency drives and UPS systems generally have least arduous starting conditions, but may cause high levels of waveform (harmonic) distortion, which may be worst at partial loads or during starting.
• Transient disturbances of frequency and voltage can affect other loads connected to the generator set. Sizing must take into account the requirements of all system loads that may be connected.
• Load sequencing may assist in reducing the size of the generator. Ensure that the sequence chosen is valid for all load conditions and that loads that become disconnected can be restarted with other loads still connected.
• High inertia motor loads take more engine power to accelerate; however the instantaneous voltage dip at the instant of starting is not dependent upon the inertia of the load.
• Generator load acceptance can be assisted by the ‘Under-frequency Roll-Off’ effect of the automatic voltage regulator. This ‘softens’ the generator voltage recovery characteristic and relieves the load on the generator engine.
• Input filters may be used to limit harmonic distortion. Any capacitive elements in the filter must not result in the generator experiencing a leading power factor at any stage in loading or unloading.
• Power factor correction should be applied to the equipment causing the poor power factor (unit power factor correction). If bulk power factor correction is applied, this must not result in the generator experiencing a leading power factor at any time, even when load is shed.
• Applications that result in re-generative power need special consideration. Generators should not be expected to absorb more than 10% of their rated continuous power otherwise overspeeding may result. Distribute single-phase loads as evenly as possible to reduce possibility of poor voltage control or generator overheating.

For information regarding your application contact your nearest distributor.

To comment on any of this documentation please use our feedback form.