The IEC 60076 standard defines loss limits and efficiency requirements for both dry-type and oil-immersed transformers, although the specific loss values vary based on the transformer's power rating, voltage level, cooling type, and intended application. Below is an overview of typical loss classifications and standards for dry-type and oil-immersed transformers as per IEC 60076.
1. Oil-Immersed Transformers
Oil-immersed transformers use mineral oil or alternative insulating liquids for cooling and insulation. They are widely used in power systems for their higher efficiency and larger capacity compared to dry-type transformers.
Typical Loss Standards for Oil-Immersed Transformers
Loss values are generally specified by the transformer manufacturer in compliance with IEC 60076-1 and IEC 60076-8. Loss limits depend on:
Power Rating: Expressed in kVA or MVA.
Voltage Class: Typically categorized by high-voltage and low-voltage windings.
Cooling Type: ONAN (Oil Natural Air Natural), ONAF (Oil Natural Air Forced), etc.
Loss Components:
No-Load Losses:
Occur due to magnetization of the core.
Typical range: 0.2% to 0.3% of rated power.
Load Losses:
Include winding resistance (I²R losses) and stray losses.
Typical range: 0.5% to 1.5% of rated power.
Total Losses:
Sum of no-load and load losses.
Example: For a 1 MVA oil-immersed transformer:
No-load losses: ~1.0 kW
Load losses: ~7.0 kW
Total losses: ~8.0 kW
Efficiency Levels:
Modern oil-immersed transformers are designed to meet stringent energy efficiency standards, such as Tier 1 or Tier 2 efficiency classes in IEC.
2. Dry-Type Transformers
Dry-type transformers use air or other gases (e.g., SF6 in specific designs) for insulation and cooling. They are commonly used in environments where fire safety and environmental concerns are critical, such as indoors or in high-risk areas.
Typical Loss Standards for Dry-Type Transformers
Loss limits are specified for different insulation classes and cooling methods:
Power Rating: Similar to oil-immersed, expressed in kVA or MVA.
Cooling Type: AN (Air Natural), AF (Air Forced).
Loss Components:
No-Load Losses:
Tend to be slightly higher than oil-immersed transformers due to higher core losses.
Typical range: 0.3% to 0.5% of rated power.
Load Losses:
Slightly higher than oil-immersed transformers due to reduced cooling efficiency.
Typical range: 1% to 2% of rated power.
Total Losses:
Example: For a 1 MVA dry-type transformer:
No-load losses: ~1.5 kW
Load losses: ~8.0 kW
Total losses: ~9.5 kW
Efficiency Levels:
Efficiency is generally lower than oil-immersed transformers. Dry-type transformers are often designed to meet Class A or Class B energy performance levels as per IEC.
IEC Loss Classifications
IEC has introduced standard loss categories (e.g., A, B, C, D) for transformers:
A: Lowest losses, highest efficiency (most energy-efficient designs).
D: Higher losses, used for cost-effective designs in non-critical applications.
Loss values for oil-immersed and dry-type transformers in each class vary based on:
Power rating (e.g., 100 kVA, 500 kVA, 1 MVA, etc.).
Voltage level (e.g., 11 kV, 33 kV).
Comparison of Losses:
| Transformer Type | No-Load Losses (% of Rated Power) | Load Losses (% of Rated Power) |
|---|---|---|
| Oil-Immersed (ONAN) | 0.2–0.3% | 0.5–1.5% |
| Dry-Type (AN) | 0.3–0.5% | 1.0–2.0% |
Standards and References
IEC 60076-1: General requirements for transformer losses.
IEC 60076-8: Guidelines for determining losses and efficiency.
IEC 60076-11: Specifies requirements for dry-type transformers.
IEC 60076-7: Covers load capability and thermal performance.
