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Difference between zero sequence current transform

Time：2017-07-20  Author：  Hit：2309

The zero sequence current transformer
Zero sequence current transformer is a kind of line fault current monitor. Only one core and two windings, when in use, will be the first three core cable through the transformer core fenestrae, two by wire connected to a dedicated relay, and then received by the relay output signal device or alarm system. Under normal conditions, the three-phase current in a primary circuit is basically balanced, and the resulting synthetic flux is near zero. In the two winding transformer in the induced current, when a line single-phase grounding fault, produce unbalanced current in the primary circuit (i.e., zero sequence current) in the two winding induced in small current relay signal. The current of the relay is very small (mA level), which is called the sensitivity of the two current or zero sequence current transformer (which can also be expressed by a minimum action current), which is the main index of action.
In the 10kV feeder switch, the current transformer located on the inside of the switch is generally divided into two phases or three phases. The current transformer is made up of primary winding (L1, L2) and two winding, iron core and silicon rubber.
Current transformer
The current transformer converts a large current of a primary device into a small current used by the two device, which works as a transformer with very small impedance. The primary winding is connected in series with the main circuit, and the two winding is connected with the load. The ratio of the current transformer is generally X/5A or X/1A (X is not less than the maximum long-term load current that may occur), so that the current of the two side of the current transformer is not greater than 5A or 1A.
In the power plant and substation, if the high voltage distribution device away from the control room, two times in order to increase the allowed load current transformer, reducing the connecting cable wire interface and improve the precision level, more than two times the rated current of current transformer 1A. Accordingly, the microcomputer protection device should also choose the product with alternating current input of 1A.
In substation, current transformer is used in three kinds of circuits: microcomputer protection, measurement and measurement. The three circuits have different requirements for the accurate level of current transformer. The winding of the current transformer can be divided into 10P10 (protection), 0.5 (measurement) and 0.2S (measurement) according to the different level of accuracy. The windings used for measurement and measurement focus on accuracy, and the windings used for protection focus on capacity to avoid saturation of the core and affect the actual ratio.
There are three kinds of wiring for the two winding of current transformer, full star connection, incomplete star connection and triangle connection.
Although the neutral point unbalanced current transformer detects the three-phase unbalance of the capacitor bank, the signal passing through the current transformer remains a single-phase current signal, which is not very different from the common current transformer.