Electrical debugging is a key content in the work of power installation engineering projects. In the electrical debugging work, the secondary circuit inspection is also a key adjustment content. It is related to the precise measurement, maintenance, communication and other functions of the power supply system. A prerequisite that cannot be fully utilized. In the secondary circuit, whether the wiring of the transformer is appropriate is also the basis for whether the secondary circuit of the current quantity is appropriate, so the wiring accuracy of the current transformer is very critical.
A current transformer wiring standard
1. Open circuit is not allowed on the secondary side of the transformer. The secondary open circuit is likely to cause serious harm. First, the inductance coil is overheated, and even damages the transformer; second, because the number of turns of the secondary winding coil is too many, it will induce the high voltage of the electromagnetic coil risk, which will seriously endanger personal safety and industry. equipment safety performance.
2. The secondary side of the high-voltage current transformer should be grounded as much as possible. Because the primary side of the transformer is high voltage, when the high voltage passes between the primary and secondary magnet electromagnetic coils due to the destruction of the insulating sleeve, the high voltage will be embedded into the low voltage. If the secondary magnet electromagnetic coil is grounded at one point, the high voltage will be introduced.
It can ensure personal safety and the safety performance of industrial equipment. But it should be noted that the secondary circuit of the current transformer only allows one point to be grounded, and no more grounding is allowed, otherwise it may cause current shunting and damage the application. The secondary magnet solenoids of low voltage current transformers should not be grounded. Because the working voltage of the low-voltage transformer is relatively low, the insulation sleeve between the primary and secondary magnet electromagnetic coils has a large degree of desire, resulting in a small probability of passing through the primary and secondary magnet electromagnetic coils. In addition, the secondary magnet electromagnetic coil is not grounded. It will improve the working skills of the insulating casing of the secondary circuit and the instrument panel, and also reduce the safety accident rate of the instrument panel damaged by lightning. In addition, the differential protection is composed of differential protection relays (such as BCH-2, etc.). The current transformers on both sides of the differential protection are only grounded at one point. Generally, the grounding point is built at the protective screen, and when the differential protection uses a microcomputer When protecting mechanical equipment, the current transformers on both sides should be grounded separately.
3. The precise measurement level and maintenance level of the current transformer cannot be reversely inserted.
Because the thickness and thickness of the design scheme of the winding inductance coil for accurate measurement and maintenance are not the same, if it is reversed, the first is to reduce the accuracy of the precise measurement in normal operation, making the electromagnetic energy measurement and verification inaccurate; the second is to cause short-circuit faults when common problems , Because the design scheme of the winding inductance coil for metrological verification ensures that the inductance coil is saturated when the short-circuit current exceeds a certain rate of the rated voltage, which limits the increase of the secondary current to maintain the instrument panel. The relay protection winding inductance coil is unsaturated fat, and the secondary current is expanded correspondingly with the short-circuit capacity, so as to make the relay protection accurate posture. If it is reversed, the relay protection will be inflexible, and the metering and verification instrument panel may be damaged.
4. Because the secondary winding of the current transformer cannot be opened, the windings that are not needed by the current transformer should be wired as much as possible.
However, there are current transformers with many taps. The unnecessary taps should be empty and cannot be wired. For example, a current transformer has secondary taps 1S1, 1S2, and 1S3. Here, 1S1 and 1S2 are 300/5A, 1S1, 1S3. It is 600/5A. When 300/5A is used as much as possible, it should be connected to 1S1 and 1S2. It should not be connected to 1S1 and 1S3, otherwise it will damage the measurement accuracy of the application tap.
5. When connecting the measurement verification winding of the current transformer and the relay protection winding that involves the orientation, grasp two points to establish the connection.
First, look at the installation position of the current transformer, that is, on which side the L1 of the current transformer is installed; Depending on the function of the winding or the type of relay protection, the above two points can be used to re-establish the wiring of the current transformer.
Two common problems of current transformer application
(1) The polarity connection should be paired. Current transformers are generally marked with decreasing polarity. If the polarity connection is wrong, it will affect the measurement verification, and even when several current transformers are connected in the same route, it will lead to the occurrence of short-circuit fault safety problems.
(2) The secondary circuit should have a defensive grounding point and be connected reliably. In order to prevent the high voltage from entering the low voltage side after passing through the intermediate insulating sleeve of the primary and secondary windings, which will seriously endanger personal safety and the safety performance of the instrument panel, a defensive grounding point should be set on the secondary side of the current transformer, and only one grounding point is allowed. Generally, the terminal of the box close to the current transformer is grounded.
(3) The secondary winding is not allowed to open circuit during operation. Otherwise, the following serious hazards will be caused: the secondary side will cause high voltage, which will seriously endanger personal safety and the safety performance of the instrument panel; cause over-temperature, which is likely to destroy the windings; expand the measurement and verification deviation.
(4) The secondary circuit of the current transformer used for the measurement and verification of electromagnetic energy cannot be connected to the relay protection mechanical equipment and maintenance machinery equipment, etc., to prevent mutual damage.
