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An initial analysis on the reactive power capacitor compensation modes for the power distribution system

An initial analysis on the reactive power capacitor compensation modes for the power distribution system

  • Categories:Industry News
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  • Time of issue:2021-05-20
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(Summary description)The reactive power capacitor compensation cabinet, which is abbreviated as the compensation cabinet, plays an important role in improving the power factor of the power grid in the electronic power sup

An initial analysis on the reactive power capacitor compensation modes for the power distribution system

(Summary description)The reactive power capacitor compensation cabinet, which is abbreviated as the compensation cabinet, plays an important role in improving the power factor of the power grid in the electronic power sup

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2021-05-20 14:31
  • Views:
Information
The reactive power capacitor compensation cabinet, which is abbreviated as the compensation cabinet, plays an important role in improving the power factor of the power grid in the electronic power supply system, reducing the loss of in the power supply transformer and the transmission lines, improving the power supply efficiency and improving the conditions for power supply. Therefore, the reactive power capacitor compensation cabinet is an indispensable part of and in a very important position in the power supply system. In case that a reactive power capacitor compensation cabinet has been selected in a reasonable way, the loss of the network can be minimized and the quality of the power grid can be improved. In this paper, the principle and mode of the reactive power capacitor compensation cabinet in the power supply and distribution network are discussed, an analysis and discussions are made combining the cases.  
The principle of the reactive power capacitor compensation cabinet: The device with the capacitive power load and the device with the inductive power load are connected to the same circuit in parallel. When the capacitive load releases the energy, the inductive load will absorb the energy; while the inductive load is absorbing the energy, the energy is being exchanged between these two kinds of loads. In this way, the reactive power absorbed by the inductive load can be compensated by the reactive power outputted by the capacitive load. This is the principle of the reactive power capacitor compensation cabinet. Both the SVC and SVG are the reactive power compensation devices, in which the device with the capacitive power load and the device with the inductive power load are connected to the same circuit in parallel. When the capacitive load in the power supply and distribution system releases the energy, the inductive load of the reactive power compensation device is started to absorb the energy in the system, and when the inductive load releases the energy, the capacitive load of the reactive power compensation device is activated to absorb the energy, thus ensuring that the capacitive and inductive components in the power supply and distribution system are always balanced so as to improve the power supply quality level in the power supply and distribution system.
I. The principle and modes of the reactive power compensation cabinet in the power supply and distribution network
1. The principles of the reactive power capacitor compensation cabinet
In The technical principles of the configuration of the reactive power capacitor compensation cabinet used in the power system of State Power Grid Company, it is clearly stipulated that the capacity of the reactive power capacitor compensation cabinet in the power distribution transformer in the power supply and distribution system should be determined taking into consideration that the maximum load rate of the power distribution transformer is 75%, the natural power factor of load is above 0.85 and, in addition, the power factor on the high voltage side should not be less than 0.95 after the reactive power capacitor compensation cabinet begins to work till the maximum load condition of distribution transformer is reached; or the capacity configuration of the reactive power capacitor compensation cabinet according to 20% ≤ 40% of distribution transformer capacity.
2. The operation mods of the reactive power capacitor compensation cabinet in he power supply and distribution system
(1) The centralized operation mode of reactive power capacitor compensation cabinet  in the substation. The reactive power capacitor compensation cabinet performs the operation in a centralized way in the power transformer distribution station. This is implemented mainly through the proper operation of the reactive power capacitor compensation cabinet to improve the power factor of the transmission and distribution line. The reactive power capacitor compensation cabinet is usually set on the 10kV bus bar of the transformer distribution station, and the on-load voltage regulating connector is used to properly adjust the voltage of the power supply and distribution system in order to achieve the purpose of energy saving and consumption reduction.
(2) The centralized operation mode in which the reactive power capacitor compensation cabinet perform the operation on the low voltage side of the distribution transformer. This centralized operation mode of the reactive power capacitor compensation cabinet is adopted on the low voltage 380V side of the distribution transformer. The reactive power capacitor compensation cabinet can perform the operation in the range of tens to hundreds of Kvar by combining the microcomputer control and other technologies. This kind of compensation method used by the reactive power capacitor compensation cabinet is more suitable for used as the rreactive power capacitor compensation cabinet for the special transformers such as those in the factories and enterprises. For the common transformers, which have many kinds of load and complicated types, if the reactive power capacitor compensation cabinet is installed on the low voltage side of each transformer, the comprehensive investment on the equipment is too large, and the economic benefit performance of the reactive power capacitor compensation cabinet is not ideal.
(3) The local distributed operation mode of the reactive power capacitor compensation cabinet at the user terminal of the power supply. The reactive power low voltage capacitor compensation cabinet is adopted at the user terminal of the power supply so that the reactive power low voltage capacitor compensation cabinet can perform operation in a distributed local way, which can reduce the losses in the transmission line and maintain the stability of the power supply voltage in the power supply and distribution system to the greatest extent. In GB50052-2009 Code for design of power supply system, it is clearly pointed out that for electricity consuming equipment with a large capacity and a stable load and intended for frequent uses, the decentralized local reactive power capacitor compensation cabinet should be adopted, so that the effect of energy saving and consumption reduction is good.
II. An analysis of the necessity of the reactive power capacitor compensation cabinet  in the power supply and distribution system
For example, there are three 6kV lines in the primary distribution system in the air compressor station in an enterprise, which are 6kV1# line, 2 # line and emergency inlet line in the air compressor station substation, and all the power supply is from the general voltage reduction transformer of the of oil refining plant. Among them, 1 # line and 2 # line are connected to the bus bar in the 6kVI section and the bus are in the 6kVII section in the  primary system of the air compressor station distribution system through the flame retardant cable, the high voltage 6kV circuit breaker of 1250A is used to protect the incoming line, and the ATS automatic switching device is used to realize the switching on and switching off of 1 # line and 2 # line, which are standbys for each other. The emergency incoming line is connected to the bus bar in the 6kV emergency section of the  primary system in the air compressor station distribution system through the flame retardant cable of 1250A is adopted. The high voltage 6kV circuit breaker is protected by the incoming line and interlocked with the normal incoming line of the emergency section. The bus bar in section I and the bus bar in section II are normally used for the power supply. When the bus bar in section II has failed, it is supplied by the 6kV emergency incoming line to ensure the safety and reliability of the first stage load (the air compressor K-101B/C1500PH/126A, the hot water circulation pump P-101C/D400kW/47.7A and the low voltage emergency transformer). The primary system of the air compressor station distribution system is designed according to the single bus bar segmented connection mode. The bus switch is added in the middle part; on 6kV line coming respectively from the bus bar in section I, the bus bar in section II and the bus bar in the emergency section is used supply power to 1# transformer and 2 # transformer of 6/0.4KV, 1250kVA,Dyn11 as well as the low voltage emergency transform of /0.4kV, 100kVA, Dyn11l. In the primary system of the air compressor station power distribution system, there are the high temperature hot water pump and the hot water circulation pump of 400kW/47.7A and the air compressor of K-101A,1500PH/126A as well as other loads of 6kV, and there are also 0.4kV load such as the air compressor, the pump, the lighting system distribution box and so on. According to the operation statistics, the high voltage power factor of the 6kV high voltage side of the power distribution room is only 0.856 and the low voltage is only 0.856 during the period of the concentrated load consumption. The power factor is only 0.84, and the line loss of the whole power distribution room is quite high. Therefore, in engineering practice, in order to improve the operating environment of the primary system of the air compressor station power distribution system and improve the power factor and reliability of the system as well as to carry out studies in the energy saving and consumption reduction of the primary system of the air compressor station power distribution system, it is of great significance to adopt a suitable scheme for the reactive power capacitor compensation cabinet .
III. The scheme for the reactive power capacitor compensation cabinet used in the power supply and distribution system
1. The scheme for the reactive power capacitor compensation cabinet
In the primary system of the air compressor station power distribution system, the high voltage 6kv is mainly used for the 6kv asynchronous motor load, and the low voltage 0.4kv is also mostly used for the 0.4kv asynchronous motor load and lighting load. according to the principle of the reactive power capacitor compensation cabinet described in Part 1 of this article, the schemes for the local reactive power high voltage capacitor compensation cabinet and the local reactive power low voltage capacitor compensation cabinet are adopted. The bus bar in I section of 6kV and the bus bar in the section II of 6kV are respectively equipped with 300kvar reactive power capacity by the the reactive power capacitor compensation cabinet. As to the low-voltage 0.4kv, the the reactive power low voltage capacitor compensation cabinet with multiple groups of 25kvar capacitors on two sides are used to perform the reactive power compensation operation. The reactive power low voltage capacitor compensation cabinet is controlled by a contactor. The reactive power low voltage capacitor compensation cabinet is equipped with the REGO controller. The switching mode of 1∶2∶2 is adopted. The capacitors adopt the dry capacitors which are connected using the delta connection method. The capacitors are connected in series with the electric reactors and then incorporated into the power grid. The high voltage capacitors adopt the Y connection method, and the power grid is put into operation after the high voltage circuit breaker is closed. In this way, 6kV high voltage and 0.4kV low voltage adopt the local centralized reactive power low voltage capacitor compensation cabinets, which can effectively solve the problems such as the increase in the reactive current and the unsuitability of the cross section of the distribution line.
2. An analysis of the effect of the reactive power capacitor compensation cabinet 
The design and installation of the reactive power capacitor compensation cabinet has been completed according to the described scheme, after the debugging and commissioning of the reactive power capacitor compensation cabinet, the data acquisition is carried out in the high voltage II section. The data show that the voltage distortion rate of the bus bars on the 6kV side and the 0.4kV side of the air compressor station power distribution system has been effectively controlled. After the compensation of the reactive power capacitor compensation cabinet, the total harmonic distortion rates are 0.67% and 0.53%, respectively. The power factor of the high voltage 6kV side is increased from 0.856 to 0.967, and the utilization ratio of the corresponding equipment is increased by 11.48%. At this time, the reactive power low compensation cabinet on the high voltage side produce a reactive power compensation of 300kvar. the selected 300kVar reactive power low voltage capacitor compensation cabinet can meet the actual operation requirements. The dynamic compensation benefit of the selected 0.4kV reactive power compensation cabinet is better than that of the selected 0.4kV reactive power compensation cabinet. The power factor of the low voltage 0.4 kV side is 0.84 before the reactive power capacitor compensation cabinet is equipped. It is 0.94% after the second group of 40KVar is switched on, and the utilization rate of the corresponding equipment is increased by 10.64%. It can be seen that after the technical upgrading of the primary air voltage distribution system with the reactive power capacitor compensation cabinet, the voltage distortion rates of the high voltage side and the low voltage side as well as the line losses have been significantly reduced, the power factor of the system and the power saving rate of the equipment are also greatly improved. The energy saving and economic benefits of the primary system of the air compressor station power distribution system are very good. 

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