How to test current transformer
What items are included when you test a current transformer?
1. CT Test
2. CT Loop Resistance & Single Earth Point
3. CT Secondary Injection Test
4. CT Primary Injection Test
First of all, let's discuss about current transformer tests and later we will discuss the secondary and primary injections. The current transformer is one of the most important measuring & protection devices in modern Substations. Correct selection & performance of CT is mandatory for the correct operation & function of the substation. If CT specification or functioning is not match it can affect the overall protection system, Revenue meter & energy meter performance & lace of decision-making to take specific action in case of active & reactive power management systems.
Therefore, before energization, the following electrical test needs to be conducted so that the overall health, performance & accuracy of CT should be perfect.
a. Insulation resistance test
b. Winding Resistance Test
c. Polarity Test
d. Knee Point Test
e. Current Ratio Test
Before performing the electrical test Visual Inspection & Mechanical check is also need to be done.
Inspect for physical damage
Verify connection as per approved drawing
Check the tightness of all connections
Check nameplate details
Check all grounding is ok & secured
Now, let's talk about electrical tests. In modern substations, only one kit is used to perform all the tests. We have to connect the primary & secondary connection from the kit like CT analyzer with the easily accessible terminal to the CT but we have to make sure that the direction of the injected current should be from P1-P2, fill out the informative form & run the test & it will give the report for all the above- mentioned test except IR test. We have to make sure that the CT is used for metering or Protection while filling to form & the expected result should be in accordance with the FAT report.
Due to character limitations, I added complete text in photo format which is available in the attachment.