6kV 6.3kV 6.6kV 10kV 10.5kV 11kV Neutral Grounding/earthing Transformer Dry Type Power Transformer direct supply

The focus of operation and maintenance varies due to differences in insulation cooling methods: ① For oil-immersed type, it is necessary to focus on monitoring oil quality (moisture, dielectric loss), oil level, and the operation status of the cooling system (such as ONAF fan start and stop), conduct regular oil chromatographic analysis, and investigate internal discharge hazards; ② For dry-type, it is necessary to focus on checking the insulation appearance of windings (whether there is cracking or fouling), environmental humidity (to avoid condensation), and temperature rise, conduct regular insulation resistance tests, and increase the cleaning frequency especially in humid or dusty environments. Both need to regularly verify the zero-sequence impedance value to ensure matching with the protection setting value.

Special protection devices need to be configured, because their faults may lead to the failure of the system grounding circuit, causing equipment damage or expanding the power outage range. Common protection types include: ① Overcurrent protection: targeting short-time overcurrent during faults, the action time limit matches the fault withstand time (for example, 30-second withstand level is suitable for 0-20 second action time limit); ② Zero-sequence current protection: monitoring abnormal zero-sequence current and distinguishing between normal unbalanced current and ground fault current; ③ Temperature protection: monitoring oil temperature for oil-immersed type and winding temperature for dry-type to prevent overheating damage; ④ Gas protection (only for oil-immersed type): detecting the gas content in oil to warn of internal discharge or overheating faults; ⑤ Overvoltage protection: preventing insulation breakdown caused by operating overvoltage or lightning overvoltage through parallel arresters. These protections need to cooperate with the system relay protection and meet the action logic requirements of the IEEE 32 standard.

The core basis for capacity selection is the system single-phase earth capacitive current. The rated capacity of earthing transformer is defined for short-time fault duty. You need to calculate the total system capacitive earth current first, then match required zero-sequence impedance, short-time fault current and fault duration. Rated system voltage, altitude and ambient temperature shall also be considered.
Please advise whether you need to pair with arc suppression coil or neutral earthing resistor cabinet, and we will help verify the complete neutral earthing system.

Yes. Standard models cover normal capacitive current scenarios. For urban networks with high cable ratio and large capacitive current, custom ZN earthing transformers with low zero-sequence impedance are available to guarantee stable neutral displacement under single-phase earth fault and meet fault current conduction requirements for resistive earthing systems.

Yes. Rockwill earthing transformers are available in both oil-immersed and cast-resin dry-type versions. Oil-immersed units suit outdoor high-capacity applications. Dry cast resin models are preferred for indoor sites with strict fire safety requirements (substations, data centers). Auxiliary secondary winding, PT/CT monitoring assemblies can be equipped for both types.