Oil-Immersed Zigzag Grounding/Earthing Transformer for Neutral Grounding-11kV to 35kV

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Key attributes

Brand	ROCKWILL
Series	JDS
Rated voltage	24 kV
Rated neutral current	Up to 3000 A
Rated frequency	50 / 60 Hz

Description

Rockwill three-phase oil-immersed Z-type earthing transformers are designed for medium-voltage power systems requiring a reliable artificial neutral point. Featuring a fully sealed oil-immersed structure with optimized zigzag (ZNyn) winding, these transformers provide stable neutral grounding for ungrounded or low-current grounded systems from 11 kV to 35 kV.

They effectively suppress arc grounding overvoltage, limit ground fault currents, and enhance grid stability. Manufactured in compliance with IEC standards, these units are suitable for distribution networks, industrial facilities, and utility substations.

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Key Features

Medium-Voltage Neutral Grounding ： Provides an artificial neutral point for ungrounded or delta-connected systems from 11 kV to 35 kV, enabling connection of arc suppression coils or neutral grounding resistors.
Optimized Z-Type Winding： Zigzag (ZNyn) winding configuration delivers low zero-sequence impedance, ensuring efficient fault current path and sensitive relay protection.
Oil-Immersed Fully Sealed Construction：Durable sealed tank design with mineral oil insulation ensures long service life, strong overload capacity, and maintenance-free outdoor operation.
Flexible Cooling Options:Available with ONAN or ONAF cooling systems to match application load profiles and ambient conditions.
Customizable Secondary Winding:Optional 0.4 kV auxiliary winding enables dual use as station service transformer, supplying local LV loads.

Technical Parameters

Parameter	Value
Highest voltage for equipment (Um)	12 / 24 / 36 / 40.5 kV
Rated frequency	50 / 60 Hz
Number of phases	Three
Connection group	ZNyn11
Rated neutral current	Up to 3000 A (customizable)
Rated short-time duration	10 s / 30 s / 60 s (customizable)
Zero-sequence impedance (Zo)	Per project specification (tolerance ≤ ±10 %)
Cooling method	ONAN / ONAF
Insulation medium	Mineral oil
Auxiliary winding	Optional 0.4 kV, up to 500 kVA
Ambient temperature	–25 °C to +40 °C
Installation	Indoor or outdoor
Enclosure options	IP-rated cabinet; optional CT, VT, or isolation switch

Insulation Levels by Voltage Class

System Voltage	Um (kV)	PF (kV)	LI (kV)
11 kV	12	28	75
20 kV	24	50	125
22 kV	24	50	125
30 kV	36	70	170
33 kV	36	70	170
35 kV	40.5	95	200

Applications

Medium-voltage distribution network neutral grounding (11 kV – 35 kV)
Wind farm and photovoltaic power station grid connection
Railway traction power supply systems
Industrial and mining enterprise power distribution
Regional substation grounding protection projects
Urban power grid upgrading and renovation

Standards

IEC 60076-6 — Power transformers – Part 6: Reactors (grounding transformer requirements)
IEC 60076-1 — Power transformers (general)
IEC 60071-1 — Insulation coordination
ISO 9001 — Quality management system

Solutions for grounding/earthing transformers

Intelligent Maintenance Services and Sustainable Solutions for Z-Type Grounding Transformers

Intelligent Maintenance Services and Sustainable Solutions for Z-Type Grounding TransformersZ-type grounding transformers are critical for stabilizing ungrounded or delta-connected power systems by providing a low-impedance path for zero-sequence currents during faults. Integrating intelligent maintenance and sustainability practices enhances their reliability while minimizing environmental impact. Below is a structured analysis of advanced solutions:I. Intelligent Maintenance Services Real-Time

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FAQ for grounding/earthing transformers

Q: What are the standards for the "fault withstand time" of earthing/grounding transformers, and how to match them during selection?

Fault withstand time is the maximum duration an earthing transformer can endure fault-current thermal and mechanical stresses under rated short-time capacity, with standard durations of 10s, 30s, 60s, or 1 hour per IEEE 32/IEC 60076‑5. Selection must ensure withstand time ≥ protection clearing time plus redundancy—e.g., a 15‑second relay trip requires a 30‑second withstand rating to prevent damage.

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