The safety ground is to connect the outer casing of the high voltage equipment to the ground. One is to prevent the accumulation of electric charge on the casing, causing electrostatic discharge and endangering equipment and personal safety. For example, the grounding of the computer case, the tail of the tanker dragged on the ground, is to release the accumulated electric charge and prevent accidents. Second, when the insulation of the equipment is damaged and the casing is charged, the power supply is protected and the power is cut off to protect the safety of the workers, such as the outer casing of the refrigerator and rice cooker. Third, it can shield the huge electric field of the equipment and protect it, such as the protective rail of the civilian transformer.
When a power electronic device encounters a lightning strike, whether it is a direct lightning strike or an induced lightning strike, if there is no corresponding protection, the power electronic equipment will be greatly damaged or even scrapped. In order to prevent lightning strikes, we generally set lightning rods on the ground (such as the roof and the top of the chimney) to connect with the earth to prevent the safety of equipment and personnel when lightning strikes. Safety grounding and lightning protection grounding are designed to provide safe protection for electronic power equipment or personnel to protect equipment and personnel.
The working ground is a reference potential provided for the normal operation of the circuit. This reference potential is typically set to zero. The reference potential can be set to a certain point, a certain section or a block in the circuit system. When the reference potential is not connected to the ground, it is regarded as a relative zero potential. However, this relative zero potential is unstable, it will change with the change of the external electromagnetic field, and the parameters of the system will change, resulting in unstable operation of the circuit system. When the reference potential is connected to the ground, the reference potential is regarded as the zero potential of the earth, and does not change with the change of the external electromagnetic field. However, unreasonable work grounding will increase circuit interference. For example, interference caused by incorrect grounding points, interference caused by improper connection of the common end of the electronic device. In order to effectively control the circuit to produce various interferences in the work, so that it can comply with the principle of electromagnetic compatibility. When designing the circuit, according to the nature of the circuit, the working ground can be divided into different types, such as DC ground, AC ground, digital ground, analog ground, signal ground, power ground, power ground, and the like. Different groundings should be set separately. Don't mix them together in a circuit. For example, digital ground and analog ground can't share a ground line. Otherwise, the two circuits will generate very powerful interference and make the circuit fall into paralysis!