What is the difference between zero sequence current transformer and current transformer
Zero sequence current transformer
The zero sequence current transformer is a line fault current monitor. Generally, there is only one iron core and secondary winding. When in use, pass the primary three-core cable through the iron core window of the transformer and pass it twice.
The lead wire is connected to a dedicated relay, and then the output terminal of the relay is connected to a signal device or alarm system. Under normal circumstances, the three-phase current in the primary circuit is basically balanced, and the resulting synthetic magnetic flux
It is also close to zero. No current is induced in the secondary winding of the transformer. When a single-phase grounding fault occurs in the primary circuit, an unbalanced current (meaning mold current) will be generated in the primary circuit.
A tiny current is induced in the winding to cause the relay to act and generate a signal. The current that makes the relay operate is very small (mA level), which is called the sensitivity of the secondary current or zero sequence current transformer (also available
-The sub-small operating current is expressed), which is the main operating index.
The current transformer located inside the switch in the 10kV feeder switch cabinet is generally divided into two-phase or three-phase depending on the wiring mode. The current transformer consists of a primary winding (1, L2) and a secondary winding,
The iron core is cast with silicone rubber.
The current transformer converts the large current of the primary equipment into the small current used by the secondary equipment. Its working principle is equivalent to a transformer with a small impedance. Its primary winding and primary circuit
In series, the secondary winding is connected to the load. The transformation ratio of the current transformer is generally X/5A or X/1A (X is not less than the possible long-term load current of the device), so that the secondary current transformer can be guaranteed
The side current is not more than 5A or 1A.
In power plants and substations, if the high-voltage power distribution device is far away from the control room, in order to increase the secondary allowable load of the current transformer, reduce the wire interface of the connecting cable and improve the accuracy level,
Use a current transformer with a secondary rated current of 1A. Correspondingly, the microcomputer protection device should also select products with an AC current input of 1A.
In substations, current transformers are used in three types of circuits: microcomputer protection, measurement and metering, and these three types of circuits have different requirements for the accuracy of current transformers. According to the accuracy level
The winding of the current transformer can be divided into 10P10 (protection), 0.5 (measurement) and 0.2S (measurement). The windings used for measurement and measurement focus on accuracy, and the windings used for protection focus on capacity to avoid iron core saturation from affecting the actual transformation ratio.
There are three commonly used connections for the secondary windings of current transformers, complete star connection, incomplete star connection and delta connection.