In a power distribution system where the low-voltage neutral point of the transformer is not grounded, a single-phase earth fault can lead to significant electrical hazards. When such a fault occurs, the ground current flows through the grounding system and spreads into the surrounding earth, creating a potential distribution area centered around the fault location. As a result, different points on the ground surface have varying electrical potentials.
If an electrical device, like a switch or motor, experiences a ground fault and its casing becomes energized, touching it with a hand while standing on the ground can create a potential difference between the hand and the two feet. This potential difference is known as **contact voltage**, and it poses a serious risk of electric shock.
Similarly, if a power line breaks and causes a single-phase ground fault, a person walking near the grounding point may experience a potential difference between their feet. This difference, called **step voltage**, can also be dangerous, especially if the person is in the vicinity of the fault.
The level of contact voltage depends on how close the faulted equipment is to the grounding electrode. The closer the device is to the grounding system, the lower the contact voltage tends to be. Conversely, the farther away the device is, the higher the contact voltage becomes.
Step voltage is similarly influenced by the distance from the grounding point. The closer a person stands to the grounding point, the greater the step voltage they may experience. As they move away, the step voltage decreases. Therefore, it's crucial to maintain a safe distance from fault locations and to use proper protective measures when working in such areas.
Understanding these phenomena helps in designing safer electrical systems and implementing effective grounding strategies to minimize risks to people and equipment.
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