Earthing method classification

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1. Purpose of grounding

There are several reasons for grounding electrical installations:

- Prevents accidents caused by electric shock by ensuring that exposed metal structures maintain equipotential.

- By forming a low-impedance current path between the system conductor and the ground, the fault current due to ground fault is reliably detected and the protective device is activated.

- Prevents voltage from rising between phase and ground or phase and neutral during normal operation.

- Limits the voltage rise between phase and ground in abnormal conditions, preventing the voltage from exceeding the operating conditions or insulation class of the equipment.

 

2. Relationship between grounding and surge

- Surge currents of several thousand amps can induce high voltages in the ground wire. A 10kA current flowing through a 0.1Ω ground impedance induces 1,000V across the cable.

- Even if there seems to be no ground resistance at all, thousands of volts can be induced between the two ends of the ground due to surge current. This is because surge current has a very high frequency, so inductance has a greater effect than ground wire resistance.

3. Comparison of grounded and ungrounded systems

Grounding system

- In a grounded Y system, power can be supplied to three-phase power loads and single-phase lighting loads without installing additional transformers.

- In case of an accident between the upper and lower parts, a lot of current flows, so the accident can be easily detected.

- During an accident, the voltage does not exceed the line-to-ground voltage.

 

Ungrounded system

- Even if an accident occurs between the phase and ground during equipment operation, the three-phase power load can continue to operate.

- It cannot be completely ungrounded, and sometimes the system is unstable.

- Even if there is no conductor to ground the secondary winding of the power transformer, capacitive coupling exists between the conductors of the system and the ground.

 

 

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