CT Ratio Test By Primary Injection/ Phase Angle Error
Sep 03, 2024
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CT ratio test, also known as the current transformer test, is a critical procedure to measure and validate the accuracy of current transformers used in power systems. Current transformers (CTs) are commonly utilized to convert high current levels in a power system to a proportionally lower value suitable for measuring instruments and relays.
The CT ratio defines the relationship between the input current and output current of a transformer and is a crucial parameter to ensure accurate measurements. During the CT ratio test, the transformer's turns ratio is verified, ensuring that the instrument's output current is proportional to the primary current.
• Current ratio test can be done by injecting current in the primary circuit and measuring the current at the secondary by Primary injection test set as per the following schematic diagram
• Check the CT ratio by injecting current as much as near to normal current of the CT primary and measure the corresponding secondary current.
• The test is to be carried out individually for each core and phase.
Use a precision clamp meter and an Ammeter to measure the primary and secondary current respectively.
During the CT ratio test, several factors can affect the accuracy of the measurement results, such as the temperature, the frequency, and the number of turns in the transformer. Therefore, it is crucial to follow the necessary procedures and precautions to obtain accurate and reliable results.
Phase Angle Error
Phase angle can be measured by using CPC100 as shown in the above figure, phase angle is the angle measured between the primary current through CT and the secondary current through the relay
• This test can also be performed by injecting current in the primary of the CT and the angle is measured between the primary and secondary current flowing into the relay.
