What Is High Resistance Grounding in Medium Voltage Systems?

A high-resistance grounding in a medium-voltage system is the method in which the neutral point of a transformer or generator (e.g., 6-35kV) is connected to the ground by a high resistance of several hundred to several several thousand ohms. Its core principles, technical features and advantages are as follows:
I. Core Principle
Fault Current Limitation: High resistance limits single-phase grounding fault current to less than 10A (usually 5 than 510A), preventing equipment damage or fire risks caused by excessive arc current.
Residual Charge Discharge: after the fault arc is extinguished, the residual charge discharge in the ground capacitance of the system is reduced by neutralizing neutralizingpoint resistance, and intermittent arc-fault overvoltages is suppressed.
Resonance Damping: A high resistance parallel to a resonant circuit that acts as a damper, interferes with resonant conditions, and eliminates resonant overvoltages generated by capacitive current and inductive current. Technical features
Resistor Value Range: Usually in hundreds to thousands of ohms, specific values must ensure that the system's equivalent zero-sequence resistance (Rn) is not greater than one third of the distributed capacitive reactance (Xc0) per phase to limit transient overvoltages.
Fault Current Control: by adjusting the resistance value, ground fault current is strictly controlled to less than 10A, ensuring that the system can be electrified for 2 hours in the event of a fault, improving power supply reliability.
Reduced Insulation Requirements: Due to low fault current, the system insulation level can be designed according to phase voltage, reducing equipment costs.
III. Key Advantages
Improved Power Supply Continuity: Allows the system to operate briefly in case of a single-phase grounding fault, avoiding immediate tripping. Suitable for high reliability of power supply reliability (e.g. offshore oil platforms, hospital, data centers, etc.).
Overvoltage Suppression: effectively limit arc-flash grounding overvoltage and resonant overvoltage, reduce the risk of equipment insulation damage.
Fault Location is convenient: zerosequence current or negative sequence current can be used as the basis for fault diagnosis, and it is convenient to locate fault quickly. Improve safety: reduce damage of arc to human body and reduce the shock risk caused by stray ground fault currents.
IV. INTRODUCTION INTRODUCTION Typical Application Scenarios
Medium voltage distribution network: such as 6-35kV urban power grids, high resistance grounding, etc., can limit fault current and minimize the power outages range.
Power plant auxiliary system: protection generator neutralization point, to prevent arc ground faults caused equipment damage.
Offshore oil platforms: In enclosed space, high resistance grounding avoids potential danger of overarc current while maintaining power supply continuity.
V. Limitations and solutions
Resistive Load Issues: The fault currents in the resistor generates heat and requires a heat dissipation solutions (such as high-power resistors or forced air cooling).
Fault Current Limitation: When ground fault current exceeds 10A, high resistance grounding is no longer applicable, but low resistance grounding or arc suppression coil grounding required.
Sensitivity of protective device: highresistance grounding fault information is weak, which may lead to miscalculation or failure of protective device. This requires optimization protection algorithms or the use of specialized ground fault line selection devices.