how much electricity does a high-voltage transformer use

A high-voltage transformer's electricity consumption depends on its **efficiency** and **load**, primarily determined by

 **iron losses** (core losses) and **copper losses** (winding losses). Here's a breakdown:

**1. Iron Losses (Fixed Losses)**

- **Causes**: Eddy currents and hysteresis in the铁芯.  

- **Characteristics**:  

  - Occur **even when no load is connected** (e.g., a transformer "idling" on the grid).  

  - Dependent on **voltage level** and design (e.g., high-quality silicon steel reduces losses).  

- **Typical Values**:  

  - For large power transformers (100+ MVA):  

    **0.05%–0.2% of rated power** at rated voltage.  

    - Example: A **100 MVA** transformer might have **50–200 kW** of iron loss.

 **2. Copper Losses (Variable Losses)**

- **Causes**: Resistance in the primary and secondary windings.  

- **Characteristics**:  

  - Increase with the **square of the load current** (e.g., higher at full load).  

  - Zero when unloaded.  

- **Typical Values**:  

  - For large power transformers:  

    **0.5%–1% of rated power** at full load.  

    - Example: A **100 MVA** transformer might have **500–1000 kW** of copper loss at full load.

**3. Efficiency Formula**

- **Typical Efficiency**:  

  - High-voltage power transformers: **98%–99.5%** (e.g., 99% efficiency means 1% total losses).  

  - Smaller transformers (e.g., distribution transformers): Slightly lower (95%–98%).

 **4. Example Calculation**

For a **100 MVA**, 99% efficient transformer at **full load**:  

- **Output Power** = 100,000 kW  

- **Total Losses** = 1% of 100,000 kW = **1000 kW**  

  - Iron Losses = 100 kW (fixed, even at 0% load)  

  - Copper Losses = 900 kW (only at 100% load)  

- **Annual Electricity Consumption** (assuming 8,760 hours/year):  

**5. Key Takeaways**

- **No-load Consumption**: Transformers always consume power (iron losses) when energized, even if unused.  

- **Load Impact**: Copper losses dominate at high loads (e.g., 100% load), while iron losses are constant.  

- **Design Matters**: High-voltage transformers are optimized for minimal losses (e.g., using low-loss cores 

and thick windings).

 **Real-World Context**

- A utility-scale **500 kV transformer** (1000 MVA) might have **~1 MW iron loss** and **~5 MW copper loss**

 at full load.  

- In power grids, transformer losses account for **1%–3% of total electricity transmitted**, making efficiency 

critical for reducing waste.