400 MVA Transformer

The 400 MVA transformer is a three-phase, oil-immersed autotransformer with forced air and oil circulation cooling. It is a double-winding unit with a rated capacity of 400,000 kVA and voltage classes of 330 kV (HV) and 165 kV (LV). Designed for temperate climates and suitable for outdoor installation, it operates efficiently at altitudes of up to 1,000 meters and in ambient temperatures ranging from -40°C to +45°C.

Key Specifications

• Rated Capacity: 400,000 kVA
• High Voltage (HV): 330 kV
• Medium Voltage (MV): 165 kV
• Winding Connection: Yna
• Longest Permissible Current: 979 A
• Cooling System: Three-stage ONAN/ONAF/OFAF
• Transformer Efficiency (PEI): 99.797%

Insulation and Voltage Ratings

• Full Wave Lightning Impulse (LI):
  • HV Winding: 950 kV
  • MV Winding: 550 kV
• Chopped Wave Lightning Impulse (LIC):
  • HV Winding: 1050 kV
  • MV Winding: 600 kV
• AC Withstand Voltage (LTAC):
  • HV Winding: 395 kV (ph-ground), 525 kV (ph-ph)
  • MV Winding: 230 kV (ph-ground), 275 kV (ph-ph)
• Neutral Insulation Class: 35 kV
• AC Neutral Input Test Voltage: 85 kV

Cooling and Maintenance

• Oil Preservation System: Elastic membranes air-bag type
• Tank Design: Bell type with lower connector and additional oil sump
• Cooler Group: Shut-off valves with visual indicators and easy maintenance access

Safety and Monitoring

• Gas Relay: Two-float design with separate ‘alarm’ and ‘trip’ settings
• Oil and Winding Temperature Indicators: Equipped with contacts for monitoring
• Pressure Relief Valve: Includes actuation signalling contacts
• Control Cables: Routed in stainless steel sleeves for protection against mechanical damage and sunlight

Additional Features

• Control Cabinet: IP55 protection, automatic temperature maintenance, dual power sources, and LED lighting
• Voltage Control Device: Vacuum diverter switch of OLTC with a 1250 A rated current
• Tap Changer Range: ±8.4% to +7.2% with 8 steps

Reliability and Longevity

• Mean-Time-Between-Failures (MTBF): Minimum 25,000 hours
• Operational Service Life: Minimum 30 years

This 400 MVA autotransformer combines advanced technology with rigorous standards to ensure exceptional reliability and efficiency for high-demand power applications.