UPS power supply testing generally includes steady-state testing and dynamic testing. Steady-state testing measures output voltage, frequency, output voltage waveform, and power under no-load, 50% additional load, and 100% additional load conditions. The primary purpose of UPS testing is to determine whether the UPS's practical technical specifications meet application requirements. To ensure the UPS system meets normal operating requirements, it must be tested before being put into operation in the data center. This will be discussed in detail today.
1. Waveform
Generally, the waveform is observed under no-load and full-load conditions to check for normality. A distortion meter is used to measure the distortion of the output voltage waveform. Under normal operating conditions, with a resistive load connected, the relative content of the total harmonics of the output voltage is measured using a distortion meter. It should meet the requirements of the product specifications and is generally less than 5%.
2. Steady-state test
Steady-state testing refers to testing the equipment when it reaches its "normal system" state, typically measuring waveform, frequency, and voltage. Frequency can generally be observed using an oscilloscope or measured using a power supply disturbance analyzer. Modern UPS uninterruptible power supplies generally meet the required output voltage frequency. However, if the UPS frequency circuitry or its local oscillator is not precise enough, the UPS output voltage frequency may change when the mains frequency is unstable. The accuracy of the UPS output frequency is generally ±0.2% when synchronized with the mains power.
3. Power
The power rating of a UPS can be determined by measuring its output and input power. The UPS power rating is primarily determined by the inverter design. Most UPS systems only have relatively high power output at 50%-100% load; below 50% load, their power drops sharply. The power ratings provided by manufacturers are mostly based on rated DC voltage and rated load conditions. When selecting a UPS, users should ideally choose one with a power-to-output power curve and power output under DC voltage variations of ±15%.
4. Output voltage
The output voltage of a UPS power supply can be tested and determined using the following methods:
A. When the input voltage is 90% of the rated voltage and the output load is 100%, or when the input voltage is 110% of the rated voltage and the output load is 0, the output voltage should be maintained within ±3% of the rated value.
B. When the input voltage is 90% or 110% of the rated voltage, and one phase of the output voltage is unloaded while the other two phases are 100% loaded, the output voltage should be maintained within ±3% of the rated value, and the phase difference should be maintained within 4 degrees.
C. When the input DC voltage of the UPS power inverter changes by ±15% and the output load changes from 0-100%, its output voltage should remain within ±3% of the rated voltage. This objective appears to overlap with the previous objective, but in practice, it is more demanding. This is because when the input signal of the control system changes over a large range, it exhibits significant nonlinear characteristics, requiring higher circuitry to ensure the output voltage does not exceed the permissible range.
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