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THREE PHASE DISTRIBUTION POWER TRANSFORMERS
TECHNICAL SPECIFICATION
A technical specification for a three-phase distribution transformer details the electrical, mechanical, and thermal parameters required to ensure the unit can safely and efficiently step down medium-voltage electricity (e.g., 11kV or 33kV) to consumer-level voltage (e.g., 400V/230V).
General Ratings & Electrical Parameters
These are the “nameplate” basics that define the capacity and voltage limits of the unit.
| Parameter | Typical Specification |
| Rated Power (kVA/MVA) | 16, 25, 63, 100, 250, 500, up to 2500 kVA |
| Input Voltage (HV) | 11kV, 22kV, or 33kV |
| Output Voltage (LV) | 415V, 433V, or 480V (Line-to-Line) |
| Number of Phases | 3 Phase |
| Frequency | 50 Hz or 60 Hz |
| Vector Group | Dyn11 (Delta Primary, Star Secondary with Neutral) |
| Cooling Type | ONAN (Oil Natural Air Natural) |
| Insulation Class | Class A (for oil-immersed) |
Technical Performance Requirements
- Efficiency & Losses: Modern units must meet specific “Star Ratings” or DOE efficiency levels.
- No-load loss: Power lost in the core (iron losses); typically minimized using CRGO (Cold Rolled Grain Oriented) steel or Amorphous metal.
- Load loss: Power lost in the windings (copper losses) at $75^\circ\text{C}$.
Temperature Rise:
- Top Oil: $\leq 35^\circ\text{C}$ to $40^\circ\text{C}$ above ambient.
- Winding: $\leq 40^\circ\text{C}$ to $45^\circ\text{C}$ above ambient.
- Impedance: Typically 4% to 5% for distribution units. This helps limit short-circuit currents.
- Flux Density: Usually limited to 1.6 to 1.9 Tesla to prevent core saturation during over-voltage.
Standard Accessories & Fittings
A standard technical bid usually requires the following to be included:
- Conservator Tank: (For ratings >50kVA) to allow for oil expansion.
- Silica Gel Breather: To remove moisture from the air entering the tank.
- Buchholz Relay: For internal fault detection (standard on larger units, typically >500kVA).
- Tap Changer: Usually an “Off-Circuit” Tap Changer with a range of $\pm 5\%$ in steps of $2.5\%$.
- Oil Level Indicator and Thermometer (Oriti/Wti).
- Pressure Relief Device (PRD): To prevent tank rupture during internal arcs.
Contact Detail
- St.No. 21/2", Industrial Oswal Complex, G.T. Road Daba Road, Ludhiana - 141 001.(Punjab India).
- gurmitpassi.154@gmail.com
- info@jyotitransformers.com
- gurmitpassi6@gmail.com