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Analysis Of Unstable Causes Of Diesel Generators Running

- Apr 24, 2017 -

In the "mains-generator-UPS" power supply system, because the UPS circuit structure decides its input nonlinearity, the most typical is the traditional dual-transform on-line UPS, since its input-DC converter is a rectifier filter circuit, its input current is current ripple, not only the input power factor is low (~), but also includes a large number of high harmonic currents (30%~40%), while low input power factor and harmonic currents will pass the inductive internal resistance of the generator stator coil, Because the stator coil of the generator set is greater than the short-circuit impedance of the power transformer, the generators are more susceptible to nonlinear loads, i.e., under the same load current waveform distortion (THDI), the voltage waveform distortion (THDU) is greater than the transformer; the harmonic current of UPS increases the loss of generator (hysteresis loss is proportional to the current frequency, the eddy current loss is proportional to the square of the current frequency, and the current skin effect of the conductor), and the output voltage waveform distortion of the generator is significantly increased, which seriously affects the normal work of the generator.
In addition, the step change of load, the capacitive current provided by the filter of the UPS front-end is the main reason that the generator is not working properly.
For example, a computer room configuration of the generator and dual-transformation on-line UPS and systems, measuring the load of the generator with load rate reached 70%, UPS input current waveform distortion%, generator load power factor for tolerance ahead of 3 o'clock, the generator with the load ups will have "bypass power supply phase ultra-limit, system demotion operation, bypass not use" warning information, and the generator power display data change is larger.

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