Question

Give the specification of a three-phase transformer as per IS 1180 (Part 1) 1989 (any four).

Answer 1

The IS 1180 (Part 1) 1989 standard specifies various aspects of three-phase transformers. Here are four key specifications outlined in the standard:

1. **Voltage Rating**:
   - The standard specifies the nominal voltage ratings for three-phase transformers. For example, the transformer may be rated for primary voltages of 11 kV, 22 kV, 33 kV, etc., and corresponding secondary voltages such as 415 V or 230 V. The exact ratings depend on the application and design requirements.

2. **Insulation Class**:
   - The insulation class of the transformer is specified to ensure it can withstand the operational stresses. Common insulation classes include Class A (105°C), Class B (130°C), Class F (155°C), and Class H (180°C). The class determines the maximum temperature the insulation can handle without degradation.

3. **Temperature Rise**:
   - The standard defines the permissible temperature rise of the transformer under load conditions. This includes temperature rise limits for windings and the top oil (or cooling medium) to ensure reliable operation and longevity of the transformer. For instance, the temperature rise for windings is typically limited to 55°C or 65°C above ambient temperature, while the top oil temperature rise is usually limited to 35°C or 45°C.

4. **Impedance Voltage**:
   - The impedance voltage of the transformer is specified to determine its short-circuit performance and voltage regulation. This is usually expressed as a percentage of the rated voltage. The impedance voltage affects the voltage drop and short-circuit current levels, and it is critical for ensuring proper protection and stability of the transformer in the power system.

These specifications help ensure that three-phase transformers meet performance, safety, and reliability standards as per the IS 1180 (Part 1) 1989 standard.

Answer 2

The specification of a three-phase transformer as per IS 1180 (Part 1) 1989 includes several key parameters. Here are four important specifications:

1. **Voltage Rating:**
   - The transformer should be rated for a specific primary and secondary voltage. For instance, a common rating might be 11 kV (primary) to 433 V (secondary). The voltage ratings are essential for ensuring that the transformer operates correctly within the electrical system's voltage levels.

2. **Power Rating:**
   - The transformer's power rating is specified in kVA (kilovolt-amperes). This rating indicates the maximum amount of power the transformer can handle without exceeding its design limits. For example, a transformer might have a rating of 500 kVA.

3. **Impedance Voltage:**
   - This parameter, typically expressed as a percentage, represents the voltage drop that occurs across the transformer when it is delivering full-load current. The impedance voltage affects the voltage regulation and short-circuit levels. For example, an impedance voltage might be 5% for a particular transformer.

4. **Cooling Type:**
   - The cooling method used for the transformer is crucial for its operation and longevity. Common cooling types include ONAN (Oil Natural Air Natural), ONAF (Oil Natural Air Forced), or OFAF (Oil Forced Air Forced). The cooling type affects how heat is dissipated from the transformer during operation.

These specifications ensure that the transformer can handle the intended electrical loads and perform reliably within the specified conditions.