Why do 99% of CT scans use depolarization?

As the "eyes" of the power system, the polarity determination of current transformers (CTs) can be regarded as a fundamental skill in the field of electrical engineering. This seemingly simple concept actually hides a mystery - it not only concerns measurement accuracy, but also directly affects the reliability of relay protection devices. Today, let's break it apart and explain it clearly!

1、 Scientific definition of polarity

The requested CT polarity essentially describes the phase relationship of the electromotive force of the primary/secondary winding under the action of alternating magnetic flux. When the iron core is excited by the same magnetic field, if both sides of the coil have high or low potential ends at the same time, these corresponding points are called "same polarity ends". Just like the telepathy of twins, their voltage fluctuations always maintain synchronous rhythm.

2、 Standardized markings P1-P2 and S1-S2

Industry standards have already paved the way for us: the first and last ends of the side are marked as P1 (incoming end) and P2 (outgoing end) respectively; The secondary side corresponds to S1 and S2. The key point is that when a current flows in from P1 and triumphantly exits through P2, the secondary side must be driven out by S1 and eventually merge into S2. This ingenious arrangement ensures that the magnetic flux direction generated by the two windings is completely consistent, forming a textbook level "depolarization" configuration. And reverse operation? That's the easily confused 'polarity'.

3、 Why are 99% of scenes using depolarization?

Don't think this is done casually! When using depolarization design, the magnetic fields of the main and auxiliary windings cancel each other out instead of overlapping, which can effectively suppress the risk of saturation. Imagine two

The stable structure of stock power sumo wrestling competition while maintaining dynamic balance is the cornerstone of the safe operation of the power system. Unless required by special working conditions, the industry

Choose a polarity reduction scheme for all colors.

4、 The three-step verification method ensures that everything is foolproof

1. Check the identification: strictly compare the P1/S1 markings on the nameplate

2. Phase measurement: Use an oscilloscope to capture the phase difference between the waveforms on both sides

3. Logic verification: Observe whether the protection device operates as expected when powered on. Remember that incorrect polarity connections may cause differential protection to malfunction or refuse to operate, with unimaginable consequences!

5、 The fatal cost of polarity error

There was once a real case: a substation had its CT polarity reversed, causing the differential protection of the line to trip due to misoperation when there was a fault outside the area. This accident caused a large area

Power outage, direct economic losses exceeding one million! It can be seen that the small polarity markings affect the safety nerves of the entire power grid.