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WENFEI ELECTRICAL
WENFEI ELECTRICAL
OIL-IMMERSED TECHNOLOGY

Oil-immersed Induction Voltage Regulators

High-capacity automatic voltage regulation with superior heat dissipation and overload capability for heavy-duty applications.

Utilizing transformer oil as cooling medium and insulation system, these regulators deliver exceptional thermal performance and sustained overload capacity. Engineered for outdoor substations, industrial facilities, and power distribution networks requiring robust, long-term voltage stabilization under extreme load conditions.

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10-110kV
Voltage Range
50-10000kVA
Capacity
150%
Overload Capacity
Oil-Immersed Induction Voltage Regulator
Series -- OIVR-2500/35

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Application
Sectors

Oil-immersed induction voltage regulators excel in high-capacity outdoor installations requiring sustained overload capability

Power Grids

Grid voltage regulation

Heavy Industry

Steel & aluminum plants

Mining

Excavation equipment

Rail Transit

Traction substations

Solar Farms

Grid interconnection

Wind Energy

Turbine voltage control

Chemical

Process equipment

Defense

Critical infrastructure

Product
Series

Comprehensive range of oil-immersed induction voltage regulators engineered for diverse power requirements

Servo Motor Voltage Regulator
HIGH PRECISION

Servo Motor Type

Servo-controlled automatic voltage regulation, ultra-fast response, ideal for precision equipment and fluctuating loads

Capacity 0.5-3000 kVA
Input Range ±20% ~ ±30%
Accuracy ±1%
Response Time < 0.02s
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Contactless Voltage Regulator
BEST SELLER

Contactless Type

No mechanical wear, maintenance-free operation, microprocessor-controlled for long-term reliability

Capacity 5-1000 kVA
Input Range ±15% ~ ±25%
Accuracy ±2%
Efficiency > 98%
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Three-Phase Voltage Regulator
INDUSTRIAL GRADE

Three-Phase Type

Independent phase regulation, balanced output, engineered for heavy industrial loads and asymmetric conditions

Capacity 10-3000 kVA
Input Range ±20% ~ ±30%
Accuracy ±1.5%
Phase Balance < 3%
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Client
Testimonials

Real-world performance in critical applications

"We've installed 12 SCB13 transformers across our manufacturing facilities in Vietnam. Zero failures in 3 years of operation. The low-loss design has reduced our energy costs by 18%. Wenfei's technical support during installation was exceptional."
MN
Michael Nguyen
Facilities Manager, TechParts Vietnam
"Our data center required precise voltage regulation for sensitive server equipment. Wenfei's SCB10 series delivered exactly what we needed. The compact design saved valuable floor space, and the ultra-low noise level was crucial for our operations."
SA
Sarah Al-Mansoori
Infrastructure Director, CloudHub UAE
"Working in remote mining locations across Africa, reliability is everything. Wenfei transformers have operated flawlessly in harsh desert conditions for over 4 years. The moisture-proof design and robust construction are unmatched. Highly recommended."
JM
James Mwangi
Operations Manager, AfriMine Resources
"For our hospital expansion, we needed transformers that could handle critical life-support systems without any risk of failure. Wenfei's medical-grade transformers exceeded all expectations. The installation team was professional and thorough."
RC
Dr. Rosa Cardoso
Chief Engineer, Hospital São Paulo
10-110kV
Voltage Classes
50-10000kVA
Capacity Range
ISO 9001
Quality Certified
CE/IEC
Standards Compliant

Frequently Asked
Questions

Technical answers about oil-immersed induction voltage regulators

What is the induction principle and how does it enable stepless regulation?
Induction voltage regulators use a rotating magnetic field to continuously vary output voltage without mechanical contacts or tap changers. The primary winding creates a rotating field that induces voltage in the secondary winding. By mechanically adjusting the angular position between primary and secondary (typically via motor-driven rotor), output voltage changes smoothly from 0% to 100% of rated value. No arcing, no contact wear, no switching transients. Regulation speed typically 1-2% per second, ideal for dynamic loads requiring gradual voltage adjustment.
Why do oil-immersed regulators have superior overload capacity?
Transformer oil has 3-4× the thermal capacity of air, absorbing and dissipating heat more efficiently. Large oil volume (typically 15-20% of unit weight) acts as thermal buffer, delaying temperature rise during overload. Natural oil circulation transfers heat from hot windings to tank walls and radiators. Typical overload ratings: 125% continuous, 150% for 2 hours, 200% for 30 minutes. Compare to dry-type at 120% continuous, 130% for 1 hour. Critical for welding equipment, motor starting, and cyclical industrial loads where peak demand exceeds average by 50-100%.
What maintenance do oil-immersed regulators require?
Annual oil testing (dielectric strength, moisture content, acidity) ensures insulation integrity. Dissolved gas analysis (DGA) every 2-3 years detects incipient faults (arcing, overheating, partial discharge). Quarterly inspection of oil level, gaskets, and bushing seals. Oil filtration/replacement every 10-15 years depending on load and environment. Bushing cleaning in polluted areas. Motor-driven rotor requires lubrication per manufacturer schedule. Total annual maintenance cost typically 1-2% of purchase price. Properly maintained units achieve 30-40 year service life with mid-life refurbishment.
How do oil-immersed regulators compare to tap-changing transformers?
Induction regulators provide stepless adjustment (infinite resolution) vs. discrete steps (typically 17-33 positions) in tap-changers. No arcing or contact wear extends maintenance intervals 3-5×. Regulation speed faster (1-2%/sec vs. 5-10 sec per step). Better for dynamic loads requiring frequent adjustment. However, induction regulators have higher no-load losses (2-3% vs. < 1% for tap-changers) and cost 20-30% more for equivalent capacity. Optimal applications: arc furnaces, welding, motor test stands, voltage-sensitive manufacturing processes.
What are the environmental and fire safety considerations?
Modern mineral oil is biodegradable (> 90% in 28 days per OECD 301B) with low toxicity. Sealed tank construction prevents spills under normal operation. Secondary containment (bunds) required for outdoor installations per environmental regulations. Fire risk managed through: (1) oil flash point > 140°C, (2) pressure relief devices prevent tank rupture, (3) Buchholz relay detects internal faults before combustion, (4) automatic fire suppression systems in high-risk areas. Alternative: silicone or ester fluids (higher fire point, biodegradable) for environmentally sensitive locations, at 2-3× oil cost.
Can oil-immersed regulators operate in extreme climates?
Yes, with appropriate oil selection. Standard mineral oil: -40°C to +50°C ambient. Arctic climates: use low-pour-point oil (< -60°C) or silicone fluid. Desert installations: oversized radiators or forced-oil cooling maintain temperature rise within limits. High altitude (> 1000m): derate 0.5% per 100m for cooling, 1.2% per 100m for insulation. Sealed tank with nitrogen blanket prevents moisture ingress in humid tropical environments. Oil viscosity changes minimally across temperature range, maintaining cooling efficiency. Field-proven in Siberian gas fields (-50°C), Saharan solar farms (+55°C), and Himalayan hydropower (4000m altitude).
How is dissolved gas analysis (DGA) used for predictive maintenance?
DGA detects incipient faults by analyzing gases dissolved in oil: hydrogen (H₂) indicates partial discharge, methane (CH₄) and ethane (C₂H₆) from overheating, acetylene (C₂H₂) from arcing, carbon monoxide (CO) from cellulose degradation. Key ratios (Rogers, Duval, IEC) diagnose fault type and severity. Online DGA monitors continuously transmit data to SCADA for real-time condition assessment. Trending analysis predicts remaining life and optimal maintenance timing. Typical intervention thresholds: H₂ > 100ppm, C₂H₂ > 5ppm, total combustible gas > 1000ppm. DGA prevents catastrophic failures by enabling planned outages before fault progression.
What are the seismic design considerations for oil-immersed regulators?
Seismic-rated regulators withstand horizontal acceleration up to 0.5g (zone 4) per IEEE 693. Tank structure reinforced with internal bracing and external stiffeners. Core and coil clamping prevents displacement during vibration. Flexible bushing connections accommodate differential movement. Anchoring system transfers seismic loads to foundation without overstressing tank. Oil conservator design prevents sloshing-induced pressure surges. Finite element analysis validates structural integrity under combined static and dynamic loads. Field testing includes shake table verification to simulated earthquake profiles. Critical for substations in California, Japan, Chile, Turkey, and other high-seismicity regions.

Technical
Reference

Comprehensive guide to oil-immersed induction voltage regulator technology

What Are Oil-Immersed Induction Voltage Regulators?

Oil-immersed induction voltage regulators are automatic voltage stabilization devices that use the electromagnetic induction principle to provide continuous, stepless voltage adjustment. Unlike tap-changing transformers with discrete voltage steps, induction regulators employ a rotating magnetic field to smoothly vary output voltage from 0% to 100% of rated value. Windings and core are immersed in transformer oil, which serves dual functions: electrical insulation and heat dissipation. This combination enables high overload capacity, extended service life, and reliable operation in harsh outdoor environments.

Operating Principle

Induction Mechanism

The regulator consists of two main components: a stationary primary winding (stator) and a rotatable secondary winding (rotor). Input voltage applied to the primary creates a rotating magnetic field. This field induces voltage in the secondary winding, with magnitude proportional to the cosine of the angular displacement between primary and secondary axes. By rotating the secondary winding (typically via servo motor), output voltage varies continuously without switching or contact-making.

Mathematical relationship: V_out = V_in × cos(θ), where θ is rotor position (0° to 180°). At θ = 0°, output voltage equals input (unity). At θ = 90°, output is zero. Intermediate positions provide proportional regulation. Series connection with input voltage yields additive or subtractive regulation, typically ±10% to ±20% of nominal voltage. Parallel operation of multiple units enables higher current capacity while maintaining voltage regulation range.

Construction Details

Core and Windings

High-grade grain-oriented silicon steel laminations (0.27mm or 0.23mm) minimize core losses. Stator windings are concentric copper or aluminum coils with Class A insulation (105°C) or Class F (155°C). Rotor windings mounted on precision bearings enable smooth rotation with minimal friction. Inter-turn and layer insulation uses oil-impregnated paper or Nomex for high dielectric strength. Winding design optimized for low impedance and high short-circuit withstand capability.

Tank and Cooling

Welded steel tank with internal oil volume 15-20% of total weight. Corrugated walls or detachable radiators increase heat dissipation surface area. Natural oil circulation (ONAN) for units up to 2500kVA; forced oil/forced air (OFAF) for larger capacities. Oil conservator with silica gel breather maintains positive pressure and prevents moisture ingress. Buchholz relay detects gas accumulation from internal faults. Pressure relief device prevents tank rupture during catastrophic events.

Control System

Servo motor or stepper motor rotates secondary winding in response to voltage error signal. Microprocessor-based controller compares output voltage to setpoint, generating correction signal. PID algorithm ensures stable regulation without hunting. Typical response time: 1-2 seconds for 10% voltage step. Manual/automatic mode selection, local/remote control capability. Digital display shows output voltage, load current, rotor position. RS-485 or Modbus interface for SCADA integration.

Protection Devices

Winding temperature monitoring via PT100 RTDs with alarm/trip setpoints. Oil temperature gauge with over-temperature protection. Buchholz relay for gas detection (alarm on slow accumulation, trip on rapid gas generation). Pressure relief valve prevents tank over-pressure. Differential protection relay detects internal faults. Overcurrent and short-circuit protection via circuit breakers or fuses. Lightning arresters on high-voltage bushings protect against transient overvoltages.

Technical Specifications

Parameter Standard Range Heavy-Duty
Voltage Class 10kV, 20kV, 35kV Up to 110kV
Capacity Range 50-5000 kVA Up to 10000 kVA
Regulation Range ±10% to ±20% ±30% (wide range)
Output Accuracy ±1.5% ±1% (precision)
Efficiency 96-97% > 98%
Overload Capacity 125% continuous 150% for 2 hours
Response Time 1-2 seconds < 1 second (fast)
Ambient Temperature -25°C to +40°C -40°C to +50°C
Altitude Rating ≤ 1000m ≤ 3000m (derated)
Protection Class IP23 (outdoor) IP54 (harsh environment)

Application Selection Guide

1. Load Analysis

Calculate total connected load, diversity factor (typically 0.6-0.8), and future expansion (20-30% margin). For cyclic loads (arc furnaces, welding), determine peak demand and duration. Motor starting currents: assume 6-8× rated current for 5-10 seconds. Harmonic loads (VFDs, rectifiers): measure THD and apply K-factor derating if > 5%. Unbalanced loads: verify neutral current capacity and phase voltage regulation under asymmetric conditions. Document load profile (hourly, daily, seasonal) to optimize regulator sizing and cooling design.

2. Environmental Assessment

Ambient temperature range determines cooling system design and oil selection. Humidity and pollution levels affect bushing creepage distance and external insulation. Altitude > 1000m requires derating (0.5% per 100m for cooling, 1.2% per 100m for insulation). Seismic zone classification dictates structural reinforcement and anchoring requirements. Coastal installations: specify marine-grade bushings and corrosion-resistant coatings. Extreme cold (< -25°C): use low-pour-point oil or silicone fluid. Flood-prone areas: elevate installation or specify submersible construction.

3. Performance Requirements

Output voltage accuracy: ±1% for precision equipment (laboratories, medical), ±2% for general industrial. Regulation speed: fast response (< 1 sec) for arc furnaces and welding, standard (1-2 sec) for most applications. Overload capability: 150% for motor starting, 125% continuous for heavy-duty cycling. Efficiency: prioritize high efficiency (> 98%) for continuous operation to reduce energy costs. Noise level: specify low-noise construction (< 55dB) for installations near residential areas or noise-sensitive facilities.

4. Integration and Control

SCADA integration: specify Modbus RTU/TCP, DNP3, or IEC 61850 protocol. Remote monitoring requirements: voltage, current, power, temperature, oil level, DGA status. Automatic/manual control modes with seamless transition. Parallel operation capability for redundancy or capacity expansion. Synchronization with other regulators or grid voltage. Alarm and trip functions: over-temperature, over-current, Buchholz gas, oil level, control failure. Data logging for performance analysis and predictive maintenance.

Maintenance Schedule

Quarterly
  • • Visual inspection (leaks, damage)
  • • Oil level verification
  • • Silica gel breather condition
  • • Cooling system operation
  • • Control system functionality
  • • Protection relay testing
Annually
  • • Oil dielectric strength test
  • • Moisture content analysis
  • • Acidity (neutralization) test
  • • Winding resistance measurement
  • • Insulation resistance (megger)
  • • Thermal imaging scan
  • • Bushing cleaning (if polluted)
Biennial/Triennial
  • • Dissolved gas analysis (DGA)
  • • Turns ratio test
  • • Impedance measurement
  • • Partial discharge test
  • • Rotor bearing lubrication
  • • Gasket and seal inspection
  • • Comprehensive performance test

Wenfei Oil-Immersed Advantage

Wenfei Electrical's oil-immersed induction voltage regulators leverage 100+ years of transformer technology evolution combined with modern control systems and materials. Our engineering team, trained by ABB and Siemens experts, applies finite element analysis (FEA) to optimize electromagnetic design and thermal performance. Advanced manufacturing includes automated coil winding with precision layer insulation, vacuum oil impregnation to eliminate voids, and hermetically sealed tank construction preventing moisture ingress.

Every regulator undergoes comprehensive factory testing: no-load loss, load loss, impedance, temperature rise (8-hour rated load), dielectric withstand (induced and applied voltage), impulse voltage, partial discharge, and acoustic noise measurement. We offer customization for extreme applications: Arctic-grade oil for -50°C operation, seismic-rated construction to IEEE 693 Zone 4, marine-grade bushings for offshore platforms, and DGA online monitoring for predictive maintenance. With 5,000+ oil-immersed regulators deployed in power grids, heavy industry, and renewable energy projects across 40 countries, Wenfei delivers proven reliability for mission-critical voltage stabilization.

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Quote

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Direct Line
+86 577 6277 6688
Global Headquarters

Liushi Town, Wenzhou, Zhejiang, China