Oil-Immersed Power Transformer for Regional Transmission-138kV

Attributes Description Documentation Resource Library

Key attributes

Brand	ROCKWILL
Model NO.	Oil-Immersed Power Transformer for Regional Transmission-138kV
Rated frequency	50/60Hz
Series	S (F)

Description

33MVA three-phase oil-immersed power transformer is designed for 138kV class regional transmission networks, stepping down high voltage to medium-voltage levels (11–35kV) for substations, industrial parks, and urban distribution systems.

Featuring low-loss silicon steel cores and optimized copper windings, it delivers stable power flow over medium distances while minimizing transmission losses. Equipped with on-load or off-circuit tap changers, overcurrent relays, and temperature sensors, it ensures reliable and fault-safe operation. The robust sealed-tank design withstands harsh environmental conditions, and each unit undergoes full type and routine tests to guarantee long-term operational safety.

Product Advantages

Regional transmission optimized — 33MVA rating matched to 138kV class substations for medium-distance power delivery (50–100km)
High efficiency & low loss — Low-loss silicon steel cores and copper windings minimize no-load and load losses
Flexible tap changer options — On-load (OLTC) or off-circuit (NLTC) tap changers for voltage regulation under varying loads
Robust sealed-tank construction — Withstands temperature extremes, humidity, and pollution with corrosion-resistant coating
Proven safety devices — Overcurrent/overvoltage relays, temperature sensors, and pressure relief valves for fault protection
Compact footprint — Space-efficient design for urban substations and confined installation sites
Smart grid ready — IoT-compatible monitoring for real-time oil quality, winding temperature, and partial discharge tracking

Parameters

Model	Rated Power (MVA)	HV (kV)	LV (kV)	Freq (Hz)	Connection	Winding	Cooling	Impedance (%)	Regulation
S-33000/138	33	138	11–35	50/60	YNd11	Double	ONAN/ONAF	8–10	OLTC/NLTC ±5%

Three-Phase 160 MVA 138 kV Power Transformer

33MVA138kV transformer for electrical transmission

Environmental Conditions

Ambient temperature: −25 °C to +40 °C (24h average ≤ +35 °C)
Altitude: ≤ 1000 m
Relative humidity: ≤ 90% (at +25 °C)
Solar radiation: ≤ 1000 W/m²
Pollution level: Light to heavy

FAQ for transformer

Q: What are the main classification dimensions of power transformers in international and domestic standards, and what are the specific types?

Power transformers are classified by insulation and cooling method, voltage function, and core structure. By insulation and cooling, they fall into liquid-insulated (oil-immersed) and dry-type — oil-immersed transformers dominate transmission applications up to 345 kV and above with standardized cooling like ONAN, ONAF and OFAF, while dry-type transformers are primarily used indoors at lower voltages up to 35 kV.

By voltage function, they are divided into step-up transformers (used in power plants to raise generator voltage to transmission levels), step-down transformers (used in substations to reduce transmission voltage for sub-transmission or distribution), and autotransformers (employed for fixed-ratio system interconnections, offering high efficiency in transmission grids). By core structure, they include core-type transformers (with windings surrounding core limbs, common in EHV applications) and shell-type transformers (with core surrounding the windings).

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Model

S (F)-160MVA138kV

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