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The meaning of grounding resistance

time:2020/6/8   source:华天电力  reading:303 time

It is important to provide grounding for electrical installations for the following reasons:


• All components of electrical equipment, like the enclosure of the machine, the enclosure circuit breaker, the oil tank of the transformer must be connected to the ground electrode. This is done to protect various parts of the installation and staff from damage, in case the system insulation fails at any time.


• By connecting these components to grounded electrodes, a continuous low-resistance path can be used to allow leakage current to flow to the ground. This current makes the protection device work, so if a fault occurs, the faulty circuit is isolated.


• The ground electrode ensures that in the event of system overvoltage due to lightning discharge or other system failures, normally dead equipment parts will not reach dangerously high potentials.


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• In a three-phase circuit, the neutral point of the system is grounded to stabilize the potential of the circuit relative to ground.


The ground electrode is only effective when the resistance to ground is low and carries a large current without deterioration.


Because the amount of current that the ground electrode will carry is difficult to measure, the resistance value of the grounding resistance is regarded as a sufficiently reliable indicator of its effectiveness. The resistance of the ground electrode should provide good protection and must be measured.


The main factors that the resistance of any grounding system depends on are:


• The shape and material of the ground electrode of the electrode used.


• The depth of the soil buried in the electrode.


• The soil near the electrode and the resistance.


The specific resistance of soil is not constant, but varies from one type of soil to another. The moisture content in the soil affects the resistivity of its ground electrode is not a fixed factor, but will be affected by seasonal changes. This requires regular testing whether the grounding system is still valid.


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