### Direct Loading Test on a Single-Phase Transformer
The direct loading test is a straightforward method used to determine the efficiency and voltage regulation of a single-phase transformer. This method involves applying the rated load directly to the transformer and measuring the necessary parameters.
#### **Circuit Diagram**
Here's a simplified representation of the circuit diagram for a direct loading test on a single-phase transformer:
```
AC Supply
│
│
|◄──────V1─────|
Primary Winding |
(High Voltage) |
| |
| [ ] Ammeter (A1)
| |
| [ ] Wattmeter (W1)
| |
--- [Load] Variable Resistive Load
| | │
| | Transformer
| | Secondary Winding
--- (Low Voltage)
│
[ ] Ammeter (A2)
│
|
|◄──────V2─────|
```
### **Components in the Circuit Diagram:**
1. **AC Supply:** Provides the input voltage to the primary winding of the transformer.
2. **Transformer:** Consists of primary (high voltage) and secondary (low voltage) windings.
3. **Ammeter (A1 and A2):** Used to measure the current in the primary and secondary windings.
4. **Voltmeter (V1 and V2):** Measures the voltage across the primary and secondary windings.
5. **Wattmeter (W1):** Measures the input power to the transformer.
6. **Load (Variable Resistive Load):** The load is applied to the secondary side to draw current.
### **Test Procedure:**
1. **No-Load Test:**
- Initially, the secondary winding is kept open, and the rated voltage is applied to the primary winding.
- Measure the primary voltage (V1), no-load current (I0), and no-load power (W0) using the respective instruments.
2. **Load Test:**
- A variable resistive load is connected across the secondary winding of the transformer.
- Adjust the load so that the transformer operates at its rated current.
- Measure the secondary voltage (V2), secondary current (I2), primary voltage (V1), and power input (W1) under load conditions.
- The load current is varied from no-load to full-load, and the corresponding values of secondary voltage are recorded.
### **Calculating Efficiency:**
The efficiency (\( \eta \)) of the transformer at a given load condition is calculated using the formula:
\[
\eta = \frac{\text{Output Power (P\(_2\))}}{\text{Input Power (P\(_1\))}}
\]
Where:
- **Output Power (P\(_2\))**: \( P_2 = V_2 \times I_2 \times \cos \phi \) (where \( \cos \phi \) is the power factor of the load)
- **Input Power (P\(_1\))**: Directly measured by the wattmeter (W1)
The formula simplifies to:
\[
\eta = \frac{V_2 \times I_2 \times \cos \phi}{W_1}
\]
### **Calculating Voltage Regulation:**
Voltage regulation gives an idea of how much the secondary voltage drops when the load is applied.
\[
\text{Voltage Regulation} (\%) = \frac{V_{\text{no-load}} - V_{\text{full-load}}}{V_{\text{full-load}}} \times 100
\]
Where:
- \( V_{\text{no-load}} \): Secondary voltage when no load is connected (initial V2 value).
- \( V_{\text{full-load}} \): Secondary voltage under full load condition.
### **Conclusion:**
The direct loading test method is practical for small transformers and provides a straightforward way to determine the efficiency and voltage regulation of the transformer under actual operating conditions. This method is less complex but requires that the transformer be loaded to its rated capacity, which can be challenging for larger transformers due to the significant power involved.