| Brand | ROCKWILL |
| Model NO. | 34.5kV 35KV 88kV 110kV Three Phase Zig-Zag Type Oil-Immersed Earthing Transformer source manufacturer |
| Rated voltage | 35kV |
| Rated frequency | 50/60Hz |
| Series | JDS |
Product Overview
As the first specialized manufacturer and source factory of grounding transformers in China, we have dedicated decades to technological breakthroughs and scaled production, establishing a fully integrated industrial chain encompassing R&D design, precision manufacturing, and testing certification. Leveraging decades of technical accumulation and products of consistently reliable, superior quality, we continue to lead the industry’s development direction, becoming a trusted technical benchmark in the field of power grid construction.
Rockwill 34.5kV 35KV 88kV 110kV Three Phase Zig-Zag Type Oil-Immersed Earthing Transformer is specially engineered to provide a reliable neutral grounding point in medium-voltage networks where direct grounding is not available. Designed with a zig-zag winding configuration, this 3-phase transformer ensures optimal zero-sequence impedance, effectively limiting ground fault currents and stabilizing transient overvoltages.
Its robust oil-immersed construction guarantees long-term insulation reliability and thermal performance in outdoor environments.
Key Features
Zig-Zag Winding: Enables controlled neutral grounding and effective zero-sequence current flow for protective device coordination.
High Insulation Performance: Complies with 35kV-class insulation levels and withstand voltage standards.
Efficient Core Design: Made of cold-rolled grain-oriented silicon steel to reduce core losses and no-load current.
Copper Windings: Oxygen-free copper ensures reduced winding losses and superior short-circuit resistance.
Fully Sealed Tank: Maintenance-free with anti-corrosion surface and integrated oil conservator (if required).
Standardized Manufacturing: Built in accordance with IEC 60076, IEEE, and customer-specific utility codes.
Technical Highlights
Some of these earthing transformers cover voltage levels including：3.3kV / 6kV / 11kV / 15kV / 20kV / 22kV / 30kV / 33kV / 34.5kV / 36kV / 44kV / 66kV / 88kV / 110kV / 132kV / 145kV / 150kV / 220kV / 275kV / 330kV / 400kV, etc. The current withstand time ranges from 1s, 2s, 3s, 5s, 6s, 8s, 9s, 10s, 30s, 60s, 1hour to 2hours, and customization is available.
Rated Voltage |
34.5kV 35KV 88kV 110kV |
Rated Capacity |
1MVA / 2MVA / 3MVA / 5MVA (available) |
Winding Connection |
Zig-Zag (Zn) |
Frequency |
50Hz / 60Hz |
Cooling Type |
ONAN (Oil Natural Air Natural) |
Short-Time Neutral Current |
400A–1000A (10 seconds typical) |
Impedance Voltage |
6–8% (customizable) |
Insulation Level |
170/75kV BIL |
Ambient Temperature Range |
-40°C to +40°C |
Installation |
Outdoor, pad or pole mounted |
Typical Applications
Medium-voltage distribution systems
Renewable energy substations (solar, wind)
Isolated generator grounding systems
Utility and industrial MV feeders requiring neutral grounding
Protection system grounding via NGR (Neutral Grounding Resistor)
The core demand of high-resistance grounding systems (such as power plants and chemical parks) is to limit fault current and reduce arc hazards. Therefore, the selection of earthing/grounding transformers must meet three special requirements: ① The fault withstand time should preferably be 60 seconds or 1 hour grade, because the system needs to maintain the fault state for monitoring and positioning to avoid premature disconnection of the grounding circuit; ② The zero-sequence impedance must be accurately matched with the grounding resistance, usually 30-50 ohms per phase, to ensure that the fault current is controlled within the safe range of 5-10A; ③ Models with auxiliary windings are preferred to provide stable low-voltage power for grounding resistance monitoring and system measurement and control (such as 400V auxiliary windings); ④ The insulation grade needs to be upgraded by one level, because the voltage rise of non-fault phases is greater during system faults, requiring enhanced insulation withstand capacity.
They can be used together (common in low-voltage and medium-voltage distribution networks). The core is to realize fault current suppression and rapid positioning through the combination of "earthing/grounding transformer constructing neutral point + arc suppression coil compensating fault current". Three points should be noted when used in conjunction: ① Impedance matching: The zero-sequence impedance of the earthing/grounding transformer must be coordinated with the reactance value of the arc suppression coil to avoid series resonance; ② Capacity coordination: The short-time capacity of the earthing/grounding transformer must cover the working current of the arc suppression coil to ensure the safe operation of both during faults; ③ Protection coordination: The compensation action of the arc suppression coil must precede the overcurrent protection of the earthing/grounding transformer to avoid protection misoperation cutting off the grounding circuit; ④ Integrated design products (earthing transformer-arc suppression coil combination devices) are preferred to reduce on-site wiring errors and improve operation reliability.
