The type current transformer

By Application
According to different purposes, the current transformer can be broadly divided into two categories:
Measuring Current Transformer (or current transformer measuring winding): In the normal operating current range, the measuring, metering and other devices to provide current information to the grid.
Protective current transformer (or current transformer winding protection): the grid fault condition, and other devices to provide power protection fault current information.
Measuring current transformer
Current transformer
In the measurement of large currents alternating current, in order to facilitate the secondary instrument measurements need to be converted to more uniform current (Chinese specified current transformer secondary is rated for 5A or 1A), another relatively high voltage on the line, such as direct measurement is very dangerous. Current transformer

Is to play the role of the current transformer and electrical isolation. It is the power system measurement instrumentation, electrical protection and other secondary devices to obtain information on a loop current sensors, current power transformers to convert high current proportionally low current, the current transformer primary side connected to a

Systems, measuring instruments connected to the secondary side, protection and so on.
Normal working hours transformer secondary side is similar to short-circuit condition, the output voltage is very low. In the operation of the secondary winding open or abnormal current flows through the primary winding (thundering current, over-current resonant capacitor charging current, the inductor current starts, etc.), will be in the secondary

Generate thousands of volts or even thousands of volts over voltage. This is not only harmful to the secondary system insulation, but also the radical and burning electric transformer , and even endanger the lives and safety of operating personnel.
Current transformer
1 side only one to a few turns, wire cross-sectional area, the string into the circuit under test. Number of turns on the secondary side, fine wire, and the smaller the impedance meter (meter / power meter current coil) constitute a closed circuit.
Equivalent to the operation of the current transformer secondary side of the transformer short circuit, ignoring the excitation current, ampere turns equal I1N1 = I2N2
Current transformer primary winding and the secondary winding current I1 I2 current ratio, called the actual current ratio I1/I2 = N2/N1 = k.
Magnetizing current is the main source of error.
Measuring current transformer accuracy class 0.2/0.5/1/3, 1 ratio error is less than ± 1%, in addition to 0.2S and 0.5S level.
Protective current transformer accuracy class 5P/10P, 10P labeled composite error does not exceed 10%.
Protective current transformer
Protective current transformer with primary and relay device, a short circuit in the line overload fault, the relay device provides a signal to cut off the fault current
Protective current transformer
Road to protect the security of the power supply system. Protective current transformer working conditions and measuring current transformer is completely different, protective current transformer is several times larger than the normal current of a few times when beginning work effectively. Main transformer protection requirements

: 1. Reliable insulation, 2. Sufficiently large accuracy limit factor, 3. Sufficient thermal stability and dynamic stability.
Protection of transformers at rated load level to meet the exact requirements of the maximum rated accuracy limit primary current is called primary current. Accuracy limit factor is rated accuracy limit primary current and the rated primary current ratio. When a current is large enough, since the core will saturate

Not reflect the role of the primary current, accuracy limit factor is expressed this feature. Precise level of protection transformer 5P, 10P, that a current at the rated accuracy limit the allowable current error of 1%, 3% of the composite error of 5%, 10%
Line failure inrush current to generate heat and electromagnetic force, protective current transformers must withstand. Secondary winding short-circuit conditions, the current transformer within one second can withstand without damage a current rms, nominal rated short-time thermal current. Secondary windings shorted

Case, a current transformer can withstand without damage a current peak, called the rated dynamic current.
Protective current transformer is divided into: 1. Overload protection current transformer, 2. Differential protection current transformer, 3 ground protection current transformer (zero sequence current transformer)