Voltage shut-down, output

Answer Any component can be shorted or opened by the safety agency during their testing. Even the possibility of a solder connection coming undone anywhere, or a bad via between layers of a PCB would be taken into account. Any such single-point failure is expected to usually cause the power supply to simply shut down gracefully, or even fail catastrophically. That is fine, but in the process, no hazardous voltage is permitted to appear on the outputs, even for a moment. 

The type of load-transfer switch used in the UPS system is another critical design parameter. The continuity of AC power service to the load is determined by the type of switching circuit used. An electromechanical transfer switch, shown in Fig. 10.137, is limited to switch times of 20 to 50 ms. This time delay can cause sensitive load equipment to malfunction, and perhaps shut down. A control circuit actuates the relay when the sensed output voltage falls below a preset value, such as 94% of nominal. A static transfer switch, shown in Fig. 10.138, can sense a failure and switch the load in about 4 ms. Most... 

Protection Over current, over voltage, short circuit, over temperature, and under voltage. No damage caused by output short circuit. The inverter must shut down if the input voltage dips below the minimum input of 42 V. Inverter should not self-reset after a load-side fault. IEEE Standard 929 is a useful reference. 

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