CT Ratio Testing

• Purpose: Verifies the ratio of the primary current to the secondary current in the transformer, ensuring accurate measurement and protection.
• Benefits: A correct CT ratio ensures proper current scaling for metering and protection relays, preventing measurement inaccuracies or system failures due to incorrect scaling. This test helps detect faults such as open or shorted windings or incorrect connections.
• Procedure: Using a precision CT tester, we apply a known current on the primary side of the CT and measure the secondary current. The results are then compared with the transformer’s nominal ratio.

CT Polarity Testing

• Purpose: Checks the polarity of current transformers to ensure the proper flow of current in relation to protection circuits.
• Benefits: Ensures that CTs are connected in the correct direction, preventing issues with differential protection and incorrect operation of protective relays.
• Procedure: The polarity of the CT is tested by applying a known current to the primary side and checking the secondary output using a polarity tester.

CT Excitation Test

• Purpose: Determines the magnetization characteristics of the CT and its ability to operate effectively under different loads.
• Benefits: Identifies potential core saturation or other issues that could lead to inaccurate current measurement or failure under fault conditions.
• Procedure: A test current is applied to the primary side of the CT, and the secondary output is measured to assess the excitation curve and ensure it falls within acceptable limits.

PT Ratio Testing

• Purpose: Verifies the voltage ratio between the primary and secondary windings of the potential transformer.
• Benefits: Ensures that voltage measurements used for metering and protection are accurate, preventing issues such as incorrect voltage readings or malfunctions in voltage-based protection schemes.
• Procedure: A known reference voltage is applied to the primary side of the PT, and the secondary voltage is measured and compared with the expected ratio.

PT Insulation Resistance Testing

• Purpose: Tests the insulation resistance of the potential transformer to ensure the integrity of the insulation system.
• Benefits: Helps detect any potential insulation deterioration or moisture ingress that could lead to short circuits or grounding issues, thus preventing transformer failures.
• Procedure: A high-voltage insulation resistance tester is applied across the PT windings to measure the resistance and ensure it meets industry standards.

Burden Measurement (CT/PT Load Testing)

• Purpose: Measures the burden (resistance) that the CT or PT places on the system, ensuring that the connected load is within specifications.
• Benefits: Ensures the CT/PT operates within its rated burden, preventing inaccuracies or malfunctions that could arise from excessive load, ensuring optimal performance of the measuring system.
• Procedure: Connect a known load to the secondary side of the CT/PT and measure the voltage drop. Compare with the rated burden to confirm system compatibility.

CT/PT Ratio and Polarity Verification for Protection Schemes

• Purpose: Verifies the correct configuration of CTs and PTs in relation to protection relays, ensuring that protection systems function correctly in fault conditions.
• Benefits: This test is vital for ensuring that protection schemes (such as differential protection, overcurrent, and earth fault protection) are triggered correctly during fault events.
• Procedure: Check the CT and PT connections and configurations against system protection schemes, simulating fault conditions and confirming that protection devices activate appropriately.

CT Saturation and Knee Point Voltage Test

• Purpose: Evaluates the saturation level and knee point voltage of the CT to determine the limits of its operating range.
• Benefits: Ensures the CT performs accurately at high fault currents and protects the system from misoperation due to core saturation, which could compromise fault detection.
• Procedure: A test voltage is applied to the CT to determine the saturation point. The knee point voltage is then verified to ensure the CT operates correctly during fault conditions.

Functional Testing of Protection Relays (Using CT/PT Data)

• Purpose: Verifies the performance of protection relays in response to CT and PT input signals.
• Benefits: Ensures that protection relays, such as overcurrent and differential relays, operate as expected in the event of faults, minimizing the risk of equipment damage or system failure.
• Procedure: Simulate fault conditions and check the response of protection relays, ensuring they activate in accordance with the CT and PT measurements.