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Analyzes and evaluations of example power quality recording performed with SONEL PQM series analyzers
FAILING LOW-POWER SINGLE-PHASE LOAD
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It would seem that low-power devices have little impact on the quality of the power supply. Indeed, appearing singly, this is true. However, in large office buildings a natural multiplication phenomenon occurs, which, with synchronous energy consumption at the same moments of the voltage sine wave, is not without consequences. If there is an element of unreliable design solutions related to the minimum price criterion, then trouble is guaranteed.
Description of the identified problem The continuously operating induction motor of the circulation pump in the chilled water circuits of the air conditioning is a suboptimal solution, but it does not introduce any disturbances to the network. The use of an inverter gives many more possibilities. During operation, there were failures of the pump electronics, requiring the device to be replaced several times. Is it possible that the pump electronics is damaged due to incorrect power installation? Is there any other explanation?
Measuring equipment used PQM-703 Power Quality Analyzer Set of C-6 current clamps 2x10A AC Sonel Analysis software
Fig. 1. MIN / MAX image of voltages and currents during operation and during power interruption
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Fig. 2. Picture of voltages and currents during start-up
Initial conclusions 1. Occurring inrush currents to switch on the voltage do not indicate the possibility of damaging the device. 2. During normal operation, for unknown reasons, the device increased the instantaneous current above 37 A, saturating the C-6 clamps. 3. This behavior was not due to a change in operating conditions or voltage disturbances and could have been caused by a design flaw in the inverter. 4. In the steady state, the nature of the current indicates the absence of low-pass filters, which results in high current rise rates and a short flow time, generating a high level of harmonics.
FAILING LOW-POWER SINGLE-PHASE LOAD
During the continuous operation of the device (Fig. 1.), there were unplanned power interruption. A detailed analysis of the voltage recovery waveform is presented below (Fig. 2.) The inrush current after voltage recovery did not exceed an amplitude of 3 A (See 1.), and in steady-state operation, the phase current did not exceed the value of 0.5 A RMS (See 2.). The RMS current values of the device do not indicate any deviations that could explain the incomprehensible failures.
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FAILING LOW-POWER SINGLE-PHASE LOAD
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Fig. 3. Oscillographic picture of unusual behavior
Fig. 4. Oscillographic image of steady operation
Conclusions: 1. The device unjustifiably generates short-term short-circuit states (Fig. 3) that may indicate a design fault, because the damaged equipment was replaced with an identical one. 2. Very unfavorable properties of the device (Fig. 4.) due to current harmonics.
Recommendations: 1. Consider changing the hardware manufacturer due to: • occurring instantaneous short-circuit conditions, • no filters reducing the levels of currents harmonics from the mains. 2. Consider changing the lowest price criterion to more expensive but with advanced technologies for reducing disruptions, which will eliminate the costs of downtime, repair and losses caused by inferior power quality during operation.