What Is The Purpose Of Resistor Grounding?

The main purpose of resistance grounding is to limit ground fault current, suppress overvoltage, and improve the safety and reliability of the system by inserting a resistor between the neutral point and the grounding, while balancing the requirements of equipment protection and power continuity. Here are some details:
1.Limit grounding fault current and protect equipment safety.
Shortcomings of Direct Grounding: If neutral points are grounded directly, single-phase grounding faults (such as single-phase conductor touchdowns) can lead to a sharp increase in short-circuit current, potentially damaging equipment such as transformers, cables and even starting fires.
Resistance grounding's solution: By inserting a resistor (usually from a a a few ohms to several a few several thousand ohms), the fault current is limited to a safe range (e.g. from a a few amperes to a few dozen amperes). For example:
Low-voltage systems (such as 400V): The resistor value can range from several hundred ohms to several thousand ohms, limiting the fault current to a few amperes to prevent equipment damage.
Medium voltage system (e.g. 6-35kV): Resistance is usually several thousand ohms, limiting the fault current to less than 10A to prevent arc overload. Overvoltage suppression, Overvoltage insulation and protection system
Arc-grounding Overvoltage: when the neutral point is ungrounded or grounded through the arc suppression coil, the fault arc is repeatedly extinguished and re-ignited, producing an overvoltage several times the phase voltage and threatening the insulation of the equipment.
Resonant overvoltage: The interaction between the capacitor current and inductive current of the system will induce resonance and further increase the overvoltage amplitude.
Resistor Grounding's Suppressing Effects:
Remaining Charge Discharge: After the fault arc extinguished, the resistor provides a discharge path for the remaining charge in the capacitance of the system, reducing the probability of arc reignition.
Resonance Damping: The resistor acts as a damping element, interferes with the resonance condition, limits the overvoltage amplitude to less than twice the phase voltage, and extends the service life of the device.
3. Improve Power Supply Continuity and Minimizing Power Outages
Limitations of Direct Grounding: In the event of a fault, protective device may immediately jump, causing a widespread power outages.
Advantages of Resistor Grounding:
Short-term license: In the case of a single-phase grounding fault, a medium-voltage system (say, 10kV) can operate for two hours to allow time for repairs. Selective protection: using zero-sequence current or negative sequence current to locate fault point, only disconnect fault lines, to avoid power outages in non-fault areas.
4. Balance equipment protection and system stability requirements
Equipment protection: Resistor grounding limits the fault current to the allowable range of the equipment, preventing insulation breakdown or mechanical damage.
System stability:
Reduce arc hazard: Low fault current reduces arc energy and reduces fire and explosion risk.
Reduced stray current: Restricting ground fault current can reduce corrosion of metal pipes and structural components.
Flexibility to adapt to different application scenarios
Low-voltage systems (such as building distribution systems):
Objective: To prevent electrocution by limiting fault current to a safe level for humans (e.g. less than 30mA).
For example, a residual current device (RCD) is used in household circuits. Its internal resistor works with the tripping mechanism to achieve rapid power outage.
Medium voltage systems (such as industrial power grids):
Purpose: Balancing equipment protection and power continuity in blackout sensitive situationssuch as hospitals and data centers. Case: A chemical plant adopts high resistance grounding, which limits fault current of a 10kV system to 5A and ensures continuous production.
High-voltage systems (such as power plants):
Purpose: Suppressing overvoltage, protecting generator and transformer insulation.
Circumstances: A large generator's neutral point connected to a high resistor (e.g., 1357Ω) through single-phase transformers, limiting fault current to less than 0.5A.
6. Compliance with international standards and safety regulations
Standard Requirements: IEEE, IEC and other standards provide resistance resistance value, temperature resistance and power requirements for resistor grounding.
Temperature Rating: The resistor must be able to withstand the heat generated by fault currents (e.g. 760°C).
Safety certification: Resistors must be certified by the likes of CSA and UL to ensure reliability in extreme working conditions.