Voltage Transformer (PT / VT)
A voltage transformer (VT), also known as a potential transformer (PT), is used to step down high voltage to a lower, safe level for measurement and protection systems.
What Is a Voltage Transformer?
A voltage transformer reduces high voltage to a proportional lower voltage that can be safely measured.
- Primary connected to high voltage line
- Secondary provides reduced voltage
- Maintains accurate ratio
Working Principle
Voltage transformers operate on electromagnetic induction:
- High voltage applied to primary winding
- Magnetic field is created in the core
- Voltage induced in secondary winding
- Output voltage is scaled down
Voltage Relationship
The transformer follows the turns ratio:
This means the secondary voltage is proportional to the number of turns.
Important Characteristics
- High accuracy for measurement
- Designed for stable voltage ratio
- Secondary usually low voltage (e.g., 110V)
Types of Voltage Transformers
| Type | Description |
|---|---|
| Electromagnetic VT | Traditional transformer type |
| Capacitive VT (CVT) | Used for very high voltages |
Applications
| Application | Purpose |
|---|---|
| Energy Metering | Measure high voltage safely |
| Protection Systems | Voltage monitoring and relays |
| Power Systems | Control and instrumentation |
| Substations | Voltage scaling for equipment |
Advantages
- Safe voltage measurement
- Provides isolation
- Accurate and reliable
- Protects instruments
Limitations
- Accuracy affected by load
- Limited frequency operation
- Requires proper insulation
Real-Life Example
In a substation:
- Line voltage: 11kV
- VT output: 110V
- Meter safely measures 110V instead of 11kV
Key Points
- Steps down high voltage for measurement.
- Maintains accurate voltage ratio.
- Provides electrical isolation.
- Used in power systems and substations.
- Works on electromagnetic induction.