DC Reactor
Flat wave reactor refers to an electronic device used in rectified DC circuits. The number of pulses in a rectifier circuit is always limited, and there is always ripple in the output rectified voltage. This kind of ripple is often harmful and needs to be suppressed by a DC reactor. The converter stations for DC transmission are equipped with DC reactors to make the output DC close to the ideal DC. In DC powered thyristor electrical transmission, DC reactors are also indispensable. The DC reactor and DC filter together form the DC harmonic filtering circuit on the DC side of the high-voltage DC converter station. The DC reactor is generally connected in series between the DC output terminal of each pole converter and the DC line, and is one of the important equipment in high-voltage DC converter stations.
The DC reactor and DC filter together form a DC T-shaped harmonic filtering network, reducing AC pulsation components and filtering out some harmonics, reducing interference to communication along the DC line and avoiding unstable regulation caused by harmonics. The flat wave reactor can also prevent the steep wave impact generated by the DC line from entering the valve hall, preventing the converter valve from being damaged by overvoltage.
When certain faults occur in the inverter, it can avoid causing secondary commutation failures. It can reduce the probability of inverter commutation failure caused by AC voltage drop. When the DC line is short circuited, the peak value of the short-circuit current is limited with the coordination of the rectifier side regulation. The larger the inductance value, the better, because the increase in inductance has an impact on the automatic regulation characteristics of the DC transmission system.
In a direct current transmission system, when the direct current is interrupted, high overvoltage will be generated, which is detrimental to insulation and makes control unstable. The DC reactor prevents interruption of DC current by limiting the rate of current change caused by rapid voltage changes, thereby reducing the commutation failure rate of the converter.
Flat wave reactors are used in rectified DC circuits. The number of pulses in a rectifier circuit is always limited, and there is always ripple in the output rectified voltage. This kind of ripple is often harmful and needs to be suppressed by a DC reactor. The converter stations for DC transmission are equipped with DC reactors to make the output DC close to the ideal DC. In DC powered thyristor electrical transmission, DC reactors are also indispensable.
The DC reactor is an important component in rectifier circuits, and its main function in intermediate frequency power supplies is to:
Classified by type:
(1) Oil immersed DC reactor;
(2) Dry type DC reactor.
The structure of oil immersed DC reactor is similar to that of transformer, mainly composed of coil, iron core, oil tank, bushing, cooling system and other components. Oil immersed DC reactors have a non-linear relationship between load current and magnetism due to the presence of an iron core in their structure.
Dry type DC reactors are mainly composed of coils, brackets, insulation pillars, voltage equalization rings, bases, etc. The coil is composed of multiple layers of concentric compressed aluminum wire packages, each layer of which is insulated with epoxy resin and padded with spacers to ensure interlayer insulation and heat dissipation. Each layer of coil is securely fixed with vertical fasteners to ensure that the coil does not deform during vibration. Due to the absence of an iron core in dry-type DC reactors, there is a linear relationship between load current and magnetism.
Advantages of oil immersed DC reactor:
Due to the presence of an iron core, it is relatively easy to increase the inductance of a single oil immersed DC reactor; The oil paper insulation system of the oil immersed DC reactor is very mature and operates reliably; Oil immersed flat wave reactors are installed on the ground, resulting in a low center of gravity and good seismic performance; The oil immersed DC reactor adopts a dry-type bushing to penetrate the valve hall, replacing the horizontal wall bushing and solving the problem of uneven wet flashover of the horizontal wall bushing; The vertical bushing of the oil immersed DC reactor also adopts dry-type bushing, which reduces the probability of pollution flashover.
Disadvantages of oil immersed DC reactor:
The internal insulation is complex. Mainly relying on oil paper insulation, it is easy to catch fire and cause a fire. The noise is quite loud. It is heavy and difficult to transport. The operation and maintenance costs are relatively high.
Advantages of dry-type DC reactor:
Ground insulation is simple. The insulation of dry-type DC reactors is mainly provided by post insulators, which improves the reliability of the main insulation. Oil free, eliminating fire hazards and environmental impacts. The dry-type flat resistance oil-free insulation system has no fire hazard or environmental impact, and there is no need to install protective walls between the valve hall and outdoors. There is no critical mass field strength when the trend flips. High voltage DC flipping requires changing the voltage polarity, which can generate critical field strength in the oil paper composite insulation system due to the capture of charges; But for dry-type DC reactors, changing the voltage polarity only generates stress on the post insulators without the limitation of critical field strength, so the characteristics of the post insulators of dry-type DC reactors are similar to those of other busbar post insulators. The load current is linearly related to the magnetic flux. Due to the absence of an iron core in dry-type DC reactors, there will be no magnetic saturation phenomenon in case of faults, and the same inductance value will be maintained under all circumstances. Transient overvoltage is relatively low. Due to the low capacitance of dry-type DC reactors to ground, the requirements for the impact insulation level of DC reactors are also relatively low. Low audible noise. Lightweight, easy to transport and handle. Low operating and maintenance costs. Dry type DC reactors are basically maintenance free.
Disadvantages of dry-type DC reactor:
The center of gravity is high, but the shock resistance is poor. It occupies a relatively large area. There is no iron core inside, making it difficult to increase the inductance of a single unit and improve overload capacity. It does not come with a through wall sleeve, and a through wall sleeve needs to be installed between it and the converter, which increases the probability of wet and dirty flashing of the through wall sleeve; Sensitive to environmental pollution. It is difficult to detect hotspots and infrared temperature. Due to the installation of a noise cover on the exterior of the dry-type DC reactor, it is difficult and has significant errors in measuring the internal coil heating points.
Product Standard:
GB/T 1094.6-2011 IEC 60076-6：2007
GB/T 1094.1-2011 IEC 60076-1：2011
GB/T 1094.3-2017 IEC 60076-3：2013
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