Principle and Application of Photoelectric Current Transformer
Photoelectric current transformerHigh voltage current transformer is a device that the power system transforms and transmits the high-voltage signal in the power grid into low-voltage small current signal, so as to provide unified and standardized current signal (analog quantity in the tradition and digital quantity in the modern times) for the measurement, monitoring, relay protection and automatic device of the system; At the same time, it is an important equipment to meet electrical isolation and ensure personal and electrical safety.According to the principle, high voltage current transformer can be divided into electromagnetic current transformer and electronic current transformer. According to the working mode of primary sensor, electronic current transformer can be divided into active type and passive magneto-optical glass type.
1 electromagnetic current transformerElectromagnetic current transformer is a transformer that realizes current conversion through the principle of electromagnetic induction.Because it has been widely used in power system. Now only the main saturation problems are analyzed.
There are two kinds of common current transformer saturation: steady-state saturation and transient saturation. The steady-state saturation is mainly because the primary current value is too large and enters the saturation area of the current transformer, resulting in the secondary current can not correctly transfer the primary current. Transient saturation is due to the existence of a large number of aperiodic components into the saturation region of current transformer.1.1 steady state simulation analysis of current transformerCurrent transformer model built in ATP
For excitation curves of nonlinear components, please visit: transmission and distribution equipment network for more information1.2 transient simulation analysis of current transformerTransient saturation waveform with secondary load as resistance (r = 5)
Transient saturation waveform with inductive secondary loadFrom the system simulation software ATP, different excitation elements are used to simulate the steady-state and transient waveforms of current transformer. It is known that before the core is unsaturated, the primary current and secondary current are completely in positive proportion. When it reaches saturation, the excitation will not increase, and after saturation, electromotive force will not be generated.2 electronic current transformer
2.1 active electronic current transformerThe active electronic current transformer is characterized in that the primary sensor is a hollow coil, and the electronic devices on the high voltage side can work only when powered by the power supply | voltage regulator | voltage regulator. Its principle is shown in the figure below:2.2 passive magneto optic glass type electronic current transformer
Passive magneto-optical glass type electronic current transformer is characterized in that the primary sensor is magneto-optical glass and does not need power supply.3 working principle3.1 Faraday magneto optic effect
Faraday magneto-optical effect: if the current passing through the primary wire is I and the magnetic field intensity generated around the wire is h, when a beam of linear polarized light passes through the magnetic field, the polarization angle of the linear polarized light will be polarized, and its polarization angle The calculation formula is:Where: V is the Verdet constant of magneto-optical glass, and l is the light path length of light in magneto-optical glass.3.2 application of Faraday magneto optic effect in products
L is designed as a loop in the electronic current transformer. According to the principle of Faraday magneto-optical effect, then:According to Ampere's loop law, in the loopAvailable:
According to Marius' law, in this product:4 secondary control system and interface connection form4.1 secondary treatment system
4.2 interface connection form4.2.1 connection form of analog interface4.2.2 connection form of digital interface
5 features(1) no oil or gas filling, safe and maintenance free. the sensor is free of ferromagnetic materials, hysteresis, remanence and magnetic saturation.
the primary and secondary sensing signals are connected by optical cables, with excellent insulation performance and strong anti electromagnetic interference ability.(4) small volume, light weight, easy installation and use.(5) there is no danger of introducing high voltage due to open circuit at low voltage side.
(6) it has optical and electrical digital interface function to facilitate the upgrading of secondary part and the construction of digital substation.
