Earthing Fault Simulator (IEEE 80)

Industrial-grade Substation Grounding analyzer. Uses Schwarz's Equations for accurate Grid + Rod resistance modeling. Calculates Decrement Factor ($D_f$) for asymmetrical faults and verifies Step/Touch Potentials against IEEE 80-2013 safety limits based on body weight (50/70kg).

1. Soil & Grid Geometry
2. Fault & System Data

The Invisible Mountain: Mastering Earthing Safety

Chapters

1. The Invisible Mountain (GPR)

When a massive fault current ($I_G$) flows into the earth, it doesn't just disappear. The earth has resistance ($R_g$). According to Ohm's Law ($V = I \times R$), pushing thousands of amps into the ground creates a massive pressure spike called the Ground Potential Rise (GPR).

Imagine your substation is sitting on top of an "electrical volcano." At the moment of a fault, the soil directly under the station might jump to 5,000V or 10,000V relative to the "remote earth" (zero volts) a mile away. This voltage decays as you move away, creating a cone-shaped "voltage funnel."

The danger isn't being at 10,000V (birds sit on power lines safely); the danger is bridging a voltage difference.

2. The Physiology of Shock

Why do we calculate limits? The human heart is controlled by tiny electrical impulses. An external current of just 50mA-100mA (0.1 Amps) is enough to disrupt this rhythm, causing Ventricular Fibrillation—a fatal flutter of the heart muscles.

IEEE 80 defines the "safe" energy limit based on body weight. A 70kg person can withstand more energy than a 50kg person. The formula $I_B = k / \sqrt{t_s}$ tells us that the faster the fault clears ($t_s$), the higher the current we can briefly survive.

3. The Crushed Rock Shield

Have you noticed that all substations are covered in crushed rock (gravel)? It’s not for aesthetics. It is a critical safety layer.

Wet soil is a good conductor ($\approx 100 \Omega \cdot m$). Wet gravel is a poor conductor ($\approx 3000 \Omega \cdot m$). By standing on this high-resistance layer, you add a massive "resistor" in series with your body. This limits the current that can flow up through your feet during a fault, significantly increasing your safety margin.

4. The "Electrical High Jump" (Step Voltage)

Step Voltage assumes you are walking across the substation during a fault. Because the GPR decays with distance (the slope of the volcano), the ground potential at your left foot is different from the potential at your right foot (1 meter apart).

This difference drives current up one leg and down the other. While painful, it is generally less dangerous than Touch Voltage because the current path (leg-to-leg) bypasses the heart. It’s like doing the splits on a voltage gradient.

5. The "Deadly Handshake" (Touch Voltage)

This is the killer. Imagine you are standing on the earth (potential = $V_{soil}$) and you touch a metallic fence or equipment frame bonded to the grid (potential = GPR).

You are now the bridge between the full GPR and the local soil potential. Current flows through your hand, straight through your chest (heart), and out your feet. This is why Touch Voltage limits are much stricter than Step Voltage limits.

6. Lightning vs. Faults (Frequency Matters)

Standard faults happen at 50/60Hz. The grid acts like a resistor. However, lightning is a high-frequency impulse (equivalent to 100kHz+).

At these speeds, the inductance ($L$) of the copper conductors becomes dominant ($X_L = 2\pi f L$). A grounding grid that looks like $0.5\Omega$ to a 50Hz fault might look like $50\Omega$ to a lightning strike. The "effective" grid shrinks because the impulse can't travel to the far ends of the mesh before the event is over. This simulator calculates that impedance rise ($Z$).