Grounding in high-voltage electrical systems plays a decisive role in safeguarding the integrity, stability, and safety of power grid operations. Among the most widely used grounding schemes are four primary types: direct neutral grounding, grounding through arc-suppression coils, resistance grounding, and ungrounded systems. Each method has its unique technical profile and is suitable for different scenarios based on the system voltage level, fault current magnitude during single-phase ground faults, overvoltage susceptibility, and protection scheme configuration. Selecting an appropriate grounding method is not merely a technical formality—it fundamentally influences insulation design, power supply continuity, and overall operational security. Below is an in-depth exploration of each grounding method and its application domain.

01 Classification of Grounding Methods in High-Voltage Distribution Systems

(1) Grounding Schemes in Power Distribution Networks

The choice of grounding for a power system's neutral point is intricately linked to the voltage grade, anticipated single-phase fault current, permissible overvoltage thresholds, and the sophistication of the relay protection layout. This choice impacts not only the insulation coordination and safety margins but also affects radio frequency interference and cross-talk in communication systems adjacent to the grid.

(2) Categories of Grounding Techniques

In China, grounding systems are commonly categorized into effectively grounded and non-effectively grounded systems. The main techniques include:

• Direct Neutral Grounding

• Neutral Grounded via Arc Suppression Coil (Petersen Coil)

• Neutral Grounded via Resistor

• High Resistance Grounding

• Low Resistance Grounding

• Ungrounded Neutral System

Each configuration responds differently to insulation failure, fault clearance, and operational reliability under stress conditions.

02 Characteristics of Each Grounding Method in Power Systems

(1) Direct Neutral Grounding

This method connects the system’s neutral point directly to earth, or through a low-resistance path, constituting an effectively grounded system, also referred to as a high-current grounding system.

Advantages:

• Keeps the system overvoltage level low.

• Reduces insulation requirements for equipment and transmission lines.

• Economical in terms of both equipment and infrastructure cost.

Disadvantages:

• During a single-phase ground fault, high fault currents arise.

• Automatically triggers circuit breakers, interrupting the power supply.

• Reduces supply continuity and degrades system reliability.

(2) Ungrounded Neutral System

The neutral point is left floating—not connected to ground.

Advantages:

• During a single-phase fault, no complete circuit forms.

• Only capacitive leakage current flows through the fault point.

• The system can often self-heal, and the fault arc may extinguish naturally.

• This configuration ensures high reliability and uninterrupted power supply.

Disadvantages:

• Faults may generate transient overvoltages due to arc reignition.

• Insulation breakdown, flashover of bushings, or cable failure is more likely.

• Requires higher insulation levels and thus leads to increased capital expenditure.

(3) Grounding via Arc Suppression Coil

Also known as reactive grounding, this method uses a coil (Petersen coil) to compensate for the system's capacitive fault current during a single-phase ground fault.

Key Features:

• The coil tunes the system to near-resonance, neutralizing ground fault current.

• Enables extinction of fault arcs almost instantaneously, minimizing damage.

• If the transformer lacks a neutral point, a grounding transformer must be installed with capacity matching the arc-suppression coil.

Application:
Ideal for distribution systems where capacitive ground currents are significant but must be controlled without allowing high fault current magnitudes.

(4) Resistance Grounding

The system neutral is connected to ground through a resistor, which controls the ground fault current to manageable levels.

1) High Resistance Grounding

The resistor's impedance is high, typically in the hundreds to thousands of ohms.

Advantages:

• Limits fault current to below 10A.

• Prevents transient overvoltages and reduces the likelihood of insulation breakdown.

• Allows the system to continue running under fault conditions without immediate shutdown.

Disadvantages:

• Requires high-grade insulation across the system.

• Equipment cost is relatively high due to the stringent design requirements.

2) Low Resistance Grounding

Used in 6–35kV cable-dominant distribution networks, where ground fault capacitive currents are substantial.

Characteristics:

• Resistors typically range between 10–20Ω.

• Fault currents lie in the range of 100A to 1000A.

Advantages:

• Enables rapid isolation of the faulted circuit.

• Keeps overvoltage levels minimal during fault clearance.

• Suited for urban distribution grids, industrial power networks, and power plant auxiliary systems where faults must be cleared swiftly and safely.

Conclusion

Grounding methods in high-voltage power systems are more than technical constructs—they are the architectural pillars supporting grid resilience. Whether prioritizing reliability, insulation economy, or fault clearance speed, each grounding technique serves a specific niche. As power systems evolve with increasing complexity and urban density, judicious selection and precise application of grounding methods remain essential to achieving a robust, safe, and sustainable electrical infrastructure.