Short Answer:

Grounding systems in substations are used to protect people, equipment, and the electrical system from faults, surges, and lightning. There are different types of grounding systems based on how the current is directed safely into the earth. The main types include solid grounding, resistance grounding, reactance grounding, resonant grounding, and isolated grounding.

Each grounding system has a specific use depending on the substation voltage level, fault control needs, and safety requirements. Choosing the right type helps ensure proper fault current flow, system stability, and personal safety during normal and abnormal conditions.

Detailed Explanation:

Types of Grounding Systems Used in Substations

Grounding (or earthing) in substations refers to the connection of parts of the electrical system to the earth to provide a common reference point and a path for fault current. It is a very important safety feature in any substation, as it protects both equipment and human life from high voltages during faults or lightning strikes.

The type of grounding system used depends on the voltage level, system design, location, and load requirements. Proper grounding ensures that any leakage current, fault current, or lightning surge is safely carried to the ground without causing harm or interruption.

1. Solid Grounding

• In solid grounding, the system (usually the neutral point of a transformer or generator) is directly connected to the ground with no resistance or reactance in between.
• It allows a large fault current to flow quickly, which ensures that protective devices like circuit breakers operate immediately.

Usage:

• Common in low voltage and medium voltage systems.
• Ensures fast fault clearance.

Advantages:

• Simple and low-cost.
• Immediate detection and clearing of faults.

Disadvantages:

• High fault current can damage equipment if not quickly cleared.

2. Resistance Grounding

• In this system, a resistor is placed between the system neutral and the ground.
• It limits the fault current to a safe level, reducing stress on equipment and improving safety.

Types:

• Low-resistance grounding (allows moderate current).
• High-resistance grounding (limits current to a very low value).

Usage:

• Used in industrial substations where control over fault current is required.

Advantages:

• Reduces equipment damage.
• Controls overvoltage during ground faults.

Disadvantages:

• Requires extra components and maintenance.

3. Reactance Grounding

• A reactor (inductor) is used instead of a resistor between the neutral and ground.
• It limits the fault current but allows it to flow long enough to activate protective relays.

Usage:

• Sometimes used in medium voltage systems.

Advantages:

• Controlled fault current.
• Better coordination with protection systems.

Disadvantages:

• Not effective in limiting voltage rise during transient conditions.

4. Resonant Grounding (Peterson Coil Grounding)

• A Peterson coil (tuned reactor) is connected between the neutral and ground to cancel out capacitive fault current.
• Commonly used in systems with frequent single-line-to-ground faults, especially in rural or forested areas.

Usage:

• In high-voltage and distribution networks, especially where continuity of service is important.

Advantages:

• Reduces arc damage during faults.
• Allows the system to continue operation after single-line faults.

Disadvantages:

• More complex and expensive.
• Requires tuning and skilled maintenance.

5. Isolated or Ungrounded System

• In this system, the neutral is not connected to the ground at all.
• No fault current flows for the first ground fault; instead, voltage imbalance is detected.

Usage:

• Used in control systems and special industrial systems where uninterrupted operation is critical.

Advantages:

• System can continue operation during a single fault.
• Less wear on equipment.

Disadvantages:

• Ground faults are hard to detect.
• Risky if a second fault occurs before the first is fixed.

Conclusion

Substations use different types of grounding systems depending on the voltage level, protection needs, and operational priorities. Solid grounding provides fast fault clearing, resistance and reactance grounding limit fault current, resonant grounding handles transient conditions, and isolated grounding is useful in special cases. Each system has its own advantages and disadvantages, but all serve the key purpose of ensuring safety, protection, and stability in the power system. Selecting the right grounding method is essential for efficient and secure substation operation.