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Why CT SECONDARY NEVER KEPT OPEN CIRCUITED
Why CT secondary not kept open circuited
CT (Current Transformer) secondary is not kept open circuited because doing so could be dangerous and can lead to damage or malfunction of the transformer.
When the secondary winding of a CT is open-circuited, it means there is no load connected to it. This causes the secondary current to drop significantly or even become zero. Without a load, the CT could saturate, causing a very high voltage to appear across the secondary terminals, potentially damaging the insulation and other connected equipment.
Additionally, CTs are designed to work under specific load conditions, and open-circuiting the secondary can result in inaccurate measurements of the primary current, defeating the purpose of using a CT for current measurement or protection.
In normal operation, the secondary winding of a CT should always be connected to a burden resistor or a measuring device to ensure the transformer operates within its intended parameters and provides accurate current measurements.
Why CT secondary kept short when no primary current flowing
Keeping the CT (Current Transformer) secondary short-circuited when there is no primary current flowing is a standard practice to ensure the safety and proper functioning of the CT. This is done to prevent high voltages from building up across the secondary winding when there is no current on the primary side.
When the primary current is zero or negligible, the CT could still have residual magnetic flux present due to remanence or external electromagnetic interference. If the secondary winding is left open-circuited, the voltage induced by this magnetic flux can cause a dangerous high voltage across the secondary terminals, which can lead to insulation breakdown or other hazards.
By short-circuiting the secondary winding, any induced voltage is dissipated across the short-circuit path, preventing hazardous voltage levels and ensuring the CT remains safe. This practice is essential to protect the equipment connected to the CT and to maintain the transformer's accuracy and reliability during periods of no primary current flow.
What is the function of Choke coil
The choke coil in metering current transformers (CTs) serves to limit the inrush current during the CT's energization. It helps to protect the CT and connected devices from excessive current surges that can occur when the CT is first energized. This ensures the proper operation and accuracy of the CT during its normal functioning.
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