Grounding Transformer: Essential Equipment for Power System Safety and Stability

In modern power systems, reliability is a fundamental requirement. However, many industrial networks—particularly those with delta-connected windings or no native neutral point—face the engineering challenge of how to safely ground the system, limit fault current, and protect equipment and personnel. The solution lies in a specialized yet often under-recognized device: the grounding transformer.

As a professional manufacturer specializing in transformer exports, we recognize that selecting the correct grounding scheme is critical to long-term system performance. This article provides a technical overview of grounding transformers, covering working principles, application scenarios, selection criteria, and future development trends.

1. Principle and Working Mechanism

The grounding transformer does not perform conventional power transmission functions. Its purpose is to construct a neutral point in ungrounded or delta-connected systems to achieve neutral grounding.

1.1 Basic Principle

The grounding transformer connects the system neutral point to earth via a low-impedance path. It typically employs a zigzag (Z) winding or star-connected winding, which presents high impedance to positive- and negative-sequence currents but low impedance to zero-sequence currents. This characteristic enables fault current to flow to earth during single-phase-to-ground faults.

1.2 Core Functions

Neutral Point Construction: Provides an accessible neutral point for systems that originally lack one (e.g., delta-connected networks).

Fault Current Diversion: Conducts ground fault current away from equipment, limiting damage and enabling selective protection tripping.

Zero-Sequence Current Elimination: Reduces system instability by eliminating zero-sequence components.

Overvoltage Suppression: Prevents transient overvoltages during intermittent arcing ground faults.

System Stability Enhancement: Reduces neutral point potential drift and voltage imbalance.

2. Functions of Grounding Transformers in Modern Power Systems

For system operators and plant engineers, the grounding transformer is a necessary piece of equipment.

Personnel and Equipment Safety: Limits touch voltage and step voltage during faults.

Asset Protection: Prevents insulation stress caused by resonant overvoltages.

Regulatory Compliance: Meets requirements of IEC 60076, IEEE C57.32, and local grid codes.

Power Quality: Reduces harmonic distortion and neutral voltage displacement.

Fault Localization: Enables zero-sequence protection schemes to isolate faulty feeders.

3. Grounding Transformer Selection Methodology

Selection of a grounding transformer is based on overall system parameters. Key parameters are as follows:

Prerequisite for Selection: System capacitive current to earth and target fault current limit should be calculated before determining impedance and resistance values.

4. Common Types of Grounding Transformers

Depending on system configuration and installation environment, grounding transformers include the following types:

Zigzag (Z) Grounding Transformer: Widely used, low impedance, compact structure.

Star-Delta Grounding Transformer: Selected when a secondary auxiliary winding is required.

Single-Phase Grounding Transformer: Suitable for small-scale systems or specific phase-to-ground scenarios.

Three-Phase Grounding Transformer: Standard configuration for industrial and utility substations.

Fixed Installation Type: Permanent substation installation.

Mobile/Skid-Mounted Type: Used for temporary grounding, mine relocation, or emergency backup.

5. Typical Application Scenarios

Grounding transformers are applied across various industries and environments:

Mines and Offshore Platforms
In ungrounded systems (IT systems), grounding transformers with high-resistance grounding limit fault current to below 10A.

Urban Distribution Networks
In 10–35kV resonant grounded systems, grounding transformers provide a neutral point for arc suppression coils, enabling automatic compensation of single-phase-to-ground faults.

Data Centers and Hospitals
When constructing a TN-S grounding system from a delta distribution side, a 0.4kV grounding transformer is used to ensure grounding impedance ≤4Ω.

Renewable Energy Generation
Large-scale photovoltaic and wind farms adopt low-resistance grounding on the 35kV collector side. Grounding transformers, in coordination with zero-sequence protection, achieve fault clearance (≤0.5s) and comply with islanding detection and grid code requirements.

6. Technology Development Trends in Grounding Transformers

Grounding transformer technology continues to evolve. Major development directions include:

6.1 Smart Monitoring Integration

Modern products integrate IoT sensors to monitor neutral current, winding temperature, and partial discharge in real time. Combined with predictive maintenance algorithms, this reduces unplanned outage risk.

6.2 Eco-Friendly Insulation Materials

Transition from traditional epoxy resin to biodegradable, halogen-free insulation systems reduces life-cycle carbon emissions.

6.3 Compact Modular Design

Adoption of amorphous alloy and other high-permeability, low-loss materials reduces core volume, enabling miniaturization and low noise.

6.4 Coordination with Power Electronic Devices

In microgrids, grounding transformers can operate in coordination with power electronic-based neutral forming devices to achieve dynamic adjustment of grounding impedance.

7. Technical Support Capabilities of Professional Manufacturers

Grounding transformers are critical equipment. In practice, procurement may involve parameter mismatches or project delays.

As an export-experienced professional manufacturer, we provide:

Customized Engineering Solutions: Each unit is designed according to system parameters.

Full Project Cycle Testing: Includes short-circuit withstand, temperature rise, lightning impulse, partial discharge, and other type tests.

End-to-End Technical Support: From technical specification review to on-site commissioning guidance.

Conclusion

Grounding transformers play an important role in power system safety and reliability. In new substation construction, industrial distribution system upgrades, or renewable energy grid connection projects, correctly selected grounding transformers constitute a equipment selection link that ensures continuous operation.

If you are in the equipment selection phase for a project or require review and optimization of an existing grounding scheme, please contact our technical engineering team.

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