If a power transformer has a star-connected primary and a delta-connec...
Power transformer
- A power transformer is a static machine used for transforming power from one circuit to another without changing the frequency.
- A power transformer can increase or decrease the voltage and current, hence can be used as either a step-up or step-down transformer.
Current transformer
- A current transformer is a type of transformer that is mainly designed to reduce the high currents to a lower value for measurement and protection purposes.
- Basically, a current transformer is a voltage step-up and current step-down transformer which means when it reduces the current, it increases the voltage in the same ratio.
- A power transformer and a current transformer are always connected in opposite phase connection.
If a power transformer has a star-connected primary and a delta-connected secondary, the CT connections on its primary and secondary sides should be connected in delta and star respectively.
In order to nullify the phase shift of the Power transformer (PT), The Current transformers (CT) are connected in a reverse configuration.
If a power transformer has a star-connected primary and a delta-connec...
CT Connections in a Power Transformer with Star-Connected Primary and Delta-Connected Secondary
In a power transformer, the primary winding is typically connected in a star (Y) configuration, while the secondary winding is connected in a delta (∆) configuration. The current transformer (CT) connections on the primary and secondary sides of the transformer depend on the winding configurations.
Primary Winding: Star (Y) Connection
- The star-connected primary winding consists of three primary windings, each connected to a phase of the three-phase power system.
- The star point (neutral point) of the primary winding is typically grounded for safety and to provide a reference for zero potential.
- The CT connections on the primary side of the transformer should match the primary winding configuration, which is a star (Y) connection.
- Therefore, the CT connections on the primary side should also be delta (Δ) connected.
Secondary Winding: Delta (Δ) Connection
- The delta-connected secondary winding consists of three secondary windings, which form a closed loop.
- The secondary winding does not have a neutral point since it is not grounded.
- The CT connections on the secondary side of the transformer should match the secondary winding configuration, which is a delta (Δ) connection.
- Therefore, the CT connections on the secondary side should be star (Y) connected.
Explanation of the Correct Answer: Option 'A'
- The correct answer is option 'A', which states that the CT connections on the primary and secondary sides should be delta (Δ) and star (Y) respectively.
- This answer is based on the principle that the CT connections should match the winding configurations of the transformer.
- The primary winding is star (Y) connected, so the CT connections on the primary side should also be delta (Δ) connected.
- The secondary winding is delta (Δ) connected, so the CT connections on the secondary side should be star (Y) connected.
- By following this connection scheme, the CTs accurately measure the primary and secondary currents in the power transformer, providing valuable information for protection, control, and monitoring purposes.
In Summary
- In a power transformer with a star-connected primary and delta-connected secondary winding, the CT connections should be delta (Δ) on the primary side and star (Y) on the secondary side.
- This ensures that the CTs accurately measure the currents flowing through the windings, enabling effective protection and control of the transformer.
- Matching the CT connections with the winding configurations is essential for accurate current measurement and reliable operation of the power transformer.
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