With the rapid development of optical fiber sensing technology and optical fiber communication technology, the application of photoelectric technology in power system is more and more extensive. Electronic transformer is one of them. Electronic transformer has small volume, light weight, wide frequency response, no saturation phenomenon, the electromagnetic interference resistance is good, no oil, insulation and reliable structure, easy to digital, development of computerization, and many other advantages, will be widely used in digital substation. Aluminum plate spot welding machine.
The birth of electronic transformer is the inevitable result of the accuracy of sensor, the transmission of light and the digital development trend. Electronic transformer is one of the key equipments in digital substation. The sensing method has great influence on the structure system of electronic transformer. The optical principle of electronic mutual inductor is simple, it is a passive electronic transformer. The electronic transformer is an active electronic transformer.
Advantages of electronic transformer.
1.1 high and low pressure complete isolation, high safety, excellent insulation performance, no iron core, eliminate magnetic saturation and ferromagnetic resonance.
The test signal of electromagnetic type transformer is coupled with the secondary coil through the iron core, and the insulation structure is complex, and the cost of the electromagnetic transformer increases exponentially with the voltage level. The non-conventional transformer transfers the high voltage side signal to the secondary equipment through the optical fiber with good insulation performance, which makes the insulation structure greatly simplified, and the higher the voltage level is, the more obvious the cost performance advantage is. Unconventional transformer instead of fiber optic cable cable as a signal transfer tool, realized the high and low voltage complete isolation, there is no voltage transformer secondary circuit short circuit or current transformer secondary circuit open the damage to the equipment and the personal, safety and reliability is greatly increased.
Because of the use of the iron core, magnetic saturation and ferromagnetic resonance are inevitable. Unconventional transformers on the principle and the traditional transformer is the distinction that having essence, generally don't have to do core magnetic coupling, thus to eliminate the phenomenon of magnetic saturation and ferromagnetic resonance, so that the transformer running good transient response, good stability, ensure the high reliability of the system operation.
1.2 the anti-electromagnetic interference performance is good, and the low-voltage side has no open high pressure danger.
The secondary circuit of electromagnetic current transformer cannot open the road, the low pressure side exists open road danger. Unconventional high side and low voltage side of transformer only exist between optical fiber connection, signal through the optical fiber transmission, high voltage circuit and the secondary loop in complete isolation in the electrical, transformer has a better ability to resist electromagnetic interference, low voltage side without open circuit caused by the high voltage danger.
1.3 the dynamic range is large, the measurement accuracy is high, and the frequency response range is wide.
The current transformer is not much current when the power grid is running normally, but the short circuit current is generally large, and with the increase of the power grid capacity, the short circuit current becomes larger and larger. Electromagnetic current transformer is difficult to realize large scale measurement because of the magnetic saturation problem. It is difficult for the same transformer to meet the needs of measurement and relay protection. The non-conventional transformer has a wide dynamic range, which can meet the needs of measurement and relay protection.
The frequency range of the non-conventional transformer mainly depends on the relevant electronic circuit part, and the frequency response range is wider. Unconventional transformer high-voltage power lines can be detected on the harmonic, power grid transient current, high frequency and large current and dc measurements, and electromagnetic transformer is difficult to carry on the work.
1.4 strong anti-interference ability of data transmission.
Electromagnetic transducers transmit analog signals, and the measurement, control and relay protection in power stations are traditionally transmitted by coaxial cables to the control room by electrical signals measured by electrical sensors. Complex secondary wiring is required when multiple devices need the same transformer signal, and this traditional structure is inevitably disturbed by electromagnetic fields. And photoelectric transformer output digital signal data communication can be easily, can be and need to use transformer signal of photoelectric transformer device constitute a fieldbus network. Realize data sharing and save a lot of secondary cables; Optical fiber sensor and optical fiber communication network at the same time the inherent electromagnetic interference resistance, in a terrible power station environment shows the incomparable superiority, optical fiber system to replace the traditional electrical system is the inevitable trend of the future power plant construction and retrofit
1.5 there is no potential for oil filled letter of inflammable, explosive and other dangerous abnormal transformer insulation structure is relatively simple, generally do not use oil as dielectric, won't cause fire and explosion danger.
1.6 small and light weight.
The non-conventional transformer has no iron core and its weight is much smaller than that of the electromagnetic type transformer with the same voltage grade.
Above all, unconventional transformer with its superior performance, to adapt to the power system digital, intelligent and networked development needs, and has obvious economic benefits and social benefits, to ensure that the increasingly large and complex power system safe and reliable operation and improve the degree of automation has far-reaching significance.
Classification of electronic transformer.
2.1 active electronic transformer.
The active electronic transformer USES the principle of electromagnetic induction to detect the signals. For the current transformer, it adopts the ROGOWSKI coil, and the voltage transformer USES the resistance, the capacitor or the inductance. Active electronic current transformer platform for the high pressure sensing head part is subject to power electronic circuits, on a platform to complete analog numerical sample (i.e., the remote module), using the optical fiber transmission of digital signal transmission to the secondary protection, control and measurement system.
Can be divided into the enclosed gas insulated active electronic current transformer (GIS) and independent type, combination of GIS for current, voltage commonly combined type electronic transformer, its acquisition module is installed on the GIS grounding shell, because of the insulation is solved by GIS, remote acquisition module on the ground potential, can be directly use substation 220 v / 110 v dc power supply. Independent acquisition unit installed in the electronic instrument transformer insulation porcelain column, due to the insulation requirements, acquisition unit's power supply with laser, small current transformer, voltage divider, photovoltaic cells, such as a variety of ways, the actual engineering application generally adopt laser power supply, or laser works in harmony with the small current transformer of power supply, namely line flow by small current transformer of power supply, when no flow by the laser power supply. For independent type electronic transformer, in order to reduce cost, reduce area, generally using combined, the current transformer, voltage transformer installation on the same composite insulator, remote module, collection of current and voltage signal can share power supply circuit
2.2 passive electronic transformer.
Passive electronic transformer is also known as optical transformer. The passive electronic current transformer USES FARADAY's magneto-optic effect to detect signals, and the sensor head is divided into block glass and whole fiber. The passive electronic voltage transformer USES the POCKELS electro-optic effect or is based on the inverse piezoelectric effect or the electroinduced secondary contraction effect. The optical voltage transformer is mainly based on the POCKELS effect. The sensor head of passive electronic transformer does not need complicated power supply device, and the whole system is better linearity. Passive electronic instrument transformer using a current, voltage sensing optical fiber transmission signal, to master control room or to protect small room for modulation and demodulation, digital signal output to MU, for the use of protection, measurement and control, and measurement. The sensor head of passive electronic transformer is a complex optical system, which can be affected by many environmental factors, such as temperature and vibration, and influence its practical process.
3. Comparison between active mutual inductor and passive transformer.
The key technology of active electronic transformer is power supply technology, reliability of remote electronic module and maintainability of acquisition unit. Based on the operation experience of traditional transformer, the maintenance of the fault of ROGOWSKI coil and voltage divider (resistor, capacitor or inductor) is not considered. The GIS type electronic transformer is directly connected to the dc power supply of the transformer substation. No additional power is required. The collection unit is installed on the earth's crust which is closely connected with the earth. This method has strong anti-interference ability, easy to replace and maintain, and the abnormal processing of collection unit does not require a system power failure. For the independent type of electronic transformers, on the high platform of power supply and the remote module long-term work in the environment of high and low temperature alternating frequently, its service life is much less than the installation in the master control room or to protect the protection of the small chamber measurement device, also need to accumulate practical experience; In addition, when the power or remote module is abnormal and needs to be maintained or replaced, a system outage is required.
The key technology of passive type electronic current transformer is the stability of the optical sensor and sensing head assembly technique, weak signal demodulation, temperature influence of the impact on the accuracy, vibration, long running stability. However, because the electronic circuit of passive electronic transformer is installed in the main control room or the protection chamber, the operating conditions are superior and the maintenance is convenient. The application of active or passive electronic transformer has greatly reduced the floor area and reduced the secondary cable connection of the traditional transformer, which is the development direction of the transformer. The reliable and convenient maintenance of passive electronic transformer is the ideal solution for the independently installed transformer.
The main problems existing in electronic transformer.
Exists in the engineering application of electronic transformer is the main problem is: because of the need to power sensors, high-power laser power for a long time can affect the service life of the optical devices, roche coil has a strong correlation between output signal and its structure, temperature change will lead to structural changes, affect the electronic circuit measurement accuracy.
Photoelectric current transformer is the main problems existing in the engineering application, the change in temperature can cause the change of optical path system cause the crystal except with electro-optical effect of elastic-optic effect and thermal effect of light interference effect, results in a weakened the working stability of optical voltage sensor in the insulator. Measurement error and the effect of temperature on the photoelectric transformer has always been a focus of people, in practice, the temperature change of the influence of measurement error, should improve the optical path system, such as photoelectric diode anti-interference ability. Such as using the temperature stability is good, and the wavelength drift small glowing light, pure, and after many mentions the electro-optic crystal, etc., to raise the temperature stability study, concerned by scholars at home and abroad in recent years has a temperature control method, the temperature of double light path compensation method, double crystal temperature compensation, such as hardware circuit and software compensation method. And the birefringence effect of magneto-optic material impact on optoelectronic current transformer accuracy due to the birefringence effect of magneto optical materials, magnetic linear polarized light medium shot people become elliptically polarized light, the result is: from aspects of partial output current to be measured are not in proportion with light intensity changes, the sensitivity of photoelectric current transformer is not stable, which reduces the measurement accuracy of photoelectric current transformer.
Common problems of these two types of transformers:
(1) the conventional current transformer of the interface compatibility, its output interface is no uniform standard, product standard has not been standardized, frequency response, dynamic range and signal-to-noise ratio, waveform distortion and stability of the test requires special specification;
(2) the field calibration problem of the non-conventional transformer, the output is the weak current signal and including the digital quantity, the new calibration method must be explored;
(3) reliability problems of equipment, including electromagnetic compatibility, system thermal stability and reliability of electronic components, need to be further tested in engineering applications.

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