As the UPS power supply is widely used in all walks of life, certain loads installed by users (such as HP minicomputers, IBM servers, etc.) will have higher requirements for the UPS power supply to output zero ground voltage, and generally require <1V.
However, during actual engineering installation and commissioning, it was found that measuring the output zero ground voltage when the UPS power supply is not turned on still meets the requirements. After the power is turned on, measuring the output zero ground voltage of the UPS power supply will rise. Scope. The reason why the device cannot work normally or even damage the device is mainly due to the following two reasons:
1) The user's own power distribution system does not meet the requirements. When the capacity of the zero line is too small, the current on the zero line will cause a certain voltage difference between the zero line and the ground. In this way, at the input of the UPS, the zero ground voltage Will increase and fail to meet the equipment requirements;
2) The UPS power supply is a switching power supply, and the input and output terminals are equipped with EMI suppression circuits. Due to the presence of inductance and capacitance, there will be a voltage difference between the output zero line and the input zero line, thus causing the output zero line The voltage difference between the ground and the ground.
In order to effectively reduce the zero-ground voltage of the output and ensure that the load can be powered on normally, the usual method is to install an isolation transformer to isolate the electrical connection between the input and output, and short-circuit the zero ground on the secondary side of the transformer. So as to reduce the ground voltage. For small and medium-power UPS, it is generally used to install an output isolation transformer at its output end; for high-power UPS with three inputs and three outputs, it is generally used to install a bypass isolation transformer at its bypass input.
The UPS power supply system formed by this connection method will not cause any negative impact on the power grid and load. However, care should be taken not to connect the load neutral line to the grid neutral line. At the same time, it must ensure that the grounding of the grounding bar meets the grounding specifications of the equipment room and guarantees reliability. Unreliable grounding bar may cause equipment damage or even personal injury.
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