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How are current transformers classified? How is it configured? Graphic analysis!
Classification of current transformers (1) According to the installation site, it can be divided into indoor and outdoor. Below 20kV is made indoor type; most of 35kV and above is made outdoor type. Please click here to enter a picture description (2) According to the installation method, it can be divided into through-wall type, support type and built-in type. The through-wall type is installed in the hole of the wall or metal structure, which can save the wall-through bushing; the support type is installed on the plane or pillar; the built-in type is a sleeve sleeved in the tank of a transformer or oil circuit breaker of 35kV and above It is also called casing type. Please click here to enter a picture description (3) According to insulation, it can be divided into dry type, cast type and oil immersed type. The dry type is impregnated with insulating glue, which is suitable for low-voltage indoor current transformers; the cast type uses epoxy resin for insulation, and is mostly used for current transformers of 35kV and below; the oil-immersed type is mostly outdoor. (4) According to the number of turns of the primary winding, it can be divided into single-turn and multi-turn. Please click here to enter a picture description (5) New-type current transformers can be divided into radio electromagnetic wave coupling, capacitive coupling, and photoelectric coupling according to the coupling method of high and low voltage parts. Among them, the performance of photoelectric current transformer is better. The characteristics of the new current transformer are that there is no direct electromagnetic connection between high and low voltage, which greatly simplifies the insulation structure; it does not need to consume a lot of energy during the measurement process; there is no saturation phenomenon, a wide measurement range, fast transient response, and high accuracy; Light weight and low cost. Please click here to enter a picture description Structure of current transformer (1) The single-turn structure has a through type (the primary winding is a single copper tube or copper rod) and a busbar type (the busbar passes through the transformer as the primary winding). (2) Multi-turn type is used for rated current below 400A. Multi-turn connection structure can be divided into coil type, "8" shape and "U" shape. The current transformer with “8” winding structure is only used for 35 ～ 110kV voltage level. 220kV "U" -shaped winding current transformers have been widely used in high-voltage current transformers of 110kV and above. Please click here to enter a picture description In the same circuit, a large number of current transformers are often required. High-voltage current transformers often consist of multiple independent iron cores and secondary windings without magnetic connection and shared primary windings. Device. For current transformers of 110kV and above, the primary winding is often divided into several groups, and the series and parallel of the windings are changed by switching to obtain 2 to 3 mutual inductance ratios. Please click here to enter a picture description Configuration of current transformer The configuration of the transformer in the main wiring is related to the measurement instrument, the selection of the synchronization point, the requirements for protection and automatic devices, and the form of the main wiring. Please click here to enter a picture description (1) In order to meet the needs of measurement and protection devices, current transformers are provided in the circuits of generators, transformers, outlets, bus sections, and bus-connected circuit breakers and bypass circuit breakers. For large ground short-circuit current systems, generally three-phase configuration; for small ground short-circuit current systems, two-phase or three-phase configuration according to specific requirements. (2) For protection current transformers, the unprotected area of the main protection device should be eliminated as far as possible. For example, if there are two sets of current transformers, and when the location allows, they should be located on both sides of the circuit breaker, so that the circuit breaker is in the cross protection range. (3) In order to reduce the damage to the generator caused by internal faults, the current transformer used to automatically adjust the excitation device should be arranged on the outgoing side of the stator windings of the generator. In order to facilitate analysis and discover internal faults before the generator is incorporated into the system, the current transformer used for measurement should be installed on the generator's neutral point side. (2) Model and indication of current transformer Please click here to enter a picture description Note: Meaning of letters in structural form R- sleeve type Z- pillar type Q- coil type F-through type (multiturn) D-through type (single turn) M- busbar type K-Opening and closing type V-Inverted type A-Chain type The meaning of the letter of the insulation medium outside the coil J-Transformer oil is not indicated G-Air (dry type) C-Porcelain (main insulation) Q-Gas Z-Pouring solid K-Insulation shell Outline drawing of LQZ-10 current transformer (Figure 4-17) —Indoor coil epoxy resin cast insulation reinforced current transformer. LQZ-10 is used in 10KV high voltage switchgear. It has two iron cores and two secondary windings, which are 0.5 and 3 grades respectively. 0.5 grade is used for measurement and 3 grade is used for relay protection. Please click here to enter a picture description Outline drawing of LMZJl-0.5 current transformer—Indoor bus bar epoxy resin cast insulation current transformer with increased capacity LMZJl-0.5 is used in low-voltage power distribution panels and other low-voltage circuits. There is no primary winding itself, and the bus bar that passes through its core is its primary winding. Please click here to enter a picture description Current transformer primary symbol Please click here to enter a picture description