Three Phase Z-type winding Oil-Immersed Earthing Transformer source manufacturer 10kV-35kV

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Key attributes

Brand	ROCKWILL
Series	JDS
Rated system voltage	10kV-35kV
Connection group	ZNyn11
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 10 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 support a wide range of capacities, cooling configurations, and customization options for distribution and industrial applications.

Key Features

Zigzag (Z-Type) Winding — Low zero-sequence impedance provides an efficient fault-current path for sensitive and reliable relay protection.
Artificial Neutral Point — Creates a stable neutral for delta-connected or ungrounded systems; supports arc suppression coil (Petersen coil) or neutral grounding resistor connection.
System Stability — Suppresses arc grounding overvoltage, balances phase voltages, and prevents ferromagnetic resonance overvoltage.
Wide Coverage — Voltage classes 3.3kV–400kV; capacities 30–10,000kVA; short-time current withstand 1s–2h, all customizable.
Optional Auxiliary Winding (ZNyn11) — Enables dual use as a station service transformer (0.4kV auxiliary supply).

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Technical Parameters

Parameter	Value
Rated system voltage	10 kV / 15 kV / 20 kV / 33 kV / 35 kV
Number of phases	Three
Rated frequency	50 / 60 Hz
Rated capacity range	30 – 10,000 kVA
Connection group	ZNyn11 (zigzag)
Zero-sequence impedance	Low impedance (customizable per project specification)
Cooling method	ONAN / ONAF
Insulation medium	Mineral oil
Short-time current withstand	10 s / 30 s / 60 s (up to 2 h customizable)
Secondary 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, isolation switch

Insulation Levels by Voltage Class

System Voltage	Um (kV)	PF (kV)	LI (kV)
10 kV	12	28	75
15 kV	17.5	38	95
20 kV	24	50	125
33 kV	36	70	170
35 kV	40.5	95	200

Environmental Conditions

Max ambient air temperature	+40°C
Max 24h average ambient air temperature	+35°C
Min ambient air temperature	-25°C
Altitude	≤ 1000 m
Max relative humidity（24h average）	≤ 95%
Max relative humidity（1 month average）	≤ 90%
Max water vapor pressure（24h average）	2.2 kPa
Max water vapor pressure（1 month average）	1.8 kPa
Solar radiation	≤ 1000 W/m²
Pollution level	II

Applications

Medium-voltage distribution network neutral grounding (10 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

Solutions for Earthing Transformer

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 Earthing Transformer

What are the core differences between earthing/grounding transformers and ordinary power transformers?

Earthing transformers are designed to create a neutral point and provide a fault current path, rated for short-time duty and typically featuring Z-type windings, whereas ordinary power transformers are designed for voltage transformation and power transmission, rated for continuous operation and using conventional star or delta windings.

What is an earthing/grounding transformer, and what are its core functions?

An earthing transformer is a special-purpose transformer that artificially creates a neutral point for ungrounded or low-current grounded power systems. Its core functions are to provide a low-impedance path for zero-sequence current to enable rapid fault isolation, and to suppress overvoltage on non-faulted phases, thereby protecting the insulation integrity of the power grid.

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