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Measurement & Metrology Current Transformers For Low Voltage Power Grid
General Aperture Series For Either Cables Or Busbars
Low-voltage current transformers mainly refer to transformer products used in industrial AC distribution cabinets below 1000V, low-voltage ring network cabinets, high-density drawer cabinets, or other electrical equipment for strong electrical isolation, measurement, monitoring and sampling of current, power and power quality of corresponding circuits.
Generally, low-voltage transformers are used for primary through-core. For smaller current specifications, the primary is used in a multi-turn through-core manner. For extremely small currents, closed-type, primary terminal input products can be used.
According to the application environment, low-voltage current transformers are divided into three categories: circular window series products suitable for cable distribution, rectangular window series products suitable for copper bus distribution, and combined window series products that take into account both cable distribution and copper bus distribution.
According to the application purpose, there are also current transformer products for measurement, current transformer for protection, and combined current transformer for measurement and protection.
Generally, due to the relatively large primary current of low-voltage transformers, the secondary output is a standard 5A/1A current signal; with the improvement of production technology, there are also products that output smaller mA-level signals. In a complex high-voltage environment, it is not recommended to use a very small current signal output to reduce the error increase caused by the crosstalk of the secondary transmission signal loop.
Since low-voltage current transformers are basically used in three-phase power distribution environments, the marking of the polarity end of the current transformer is very important. Generally, the primary wiring is input at P1 and output at P2, and the secondary wiring is output at S1 and input at S2; the secondary output S1 and the primary input P1 have the same name, and the secondary input S2 and the primary output P2 have the same name.
General low-voltage current transformers are marked with rated loads. The connection from the transformer output to the instrument or equipment input together with the input load inside the equipment, the closer to the rated load, the better the accuracy of the transformer. The total load of the circuit connected to the secondary of the transformer should not exceed the rated load of the transformer, otherwise it will affect the accuracy of the transformer, and the dynamic range of the transformer will also be reduced. When the location of the installation equipment is far from the installation location of the transformer, a current transformer product with a secondary current output of 1A should be selected.
The long-term working current of the transformer shall not exceed 1.1 times the rated value, and it is allowed to be used for a short time at 1.2 times the rated value, and the time shall not exceed 1 hour.
Under the condition that the accuracy requirement is lower than level 0.2, the low-voltage transformer is wound with oriented cold-rolled silicon steel strip, and the secondary winding wire is wound with high-strength electromagnetic enameled wire, which is stable and reliable in operation and has strong environmental applicability; when the accuracy requirement is better than level 0.2, the amorphous and nanocrystalline material core with higher magnetic permeability is used to ensure accuracy while reducing the use cost as much as possible.
The product shell is made of high-strength polycarbonate material or PC/ABS alloy plastic, which has high temperature resistance and good strength. Some products use epoxy resin encapsulation technology, high insulation strength, moisture-proof and waterproof, and can work stably in harsh environments. The output mode can be terminal output, wire direct output, etc. according to the use environment; electromagnetic shielding structure can also be added as needed to improve the product's anti-interference ability.
Since the current of the detected circuit is generally large, when selecting products, reliable low-voltage current transformers that meet national standards must be selected. Otherwise, after installation, the transformer may heat up during operation, which may cause safety accidents and bring great losses.
During the installation of the product, select the appropriate installation method according to the installation environment, and then fix it in a reliable way to avoid the equipment falling off due to loose fixation during transportation. And during the wiring process, it is necessary to ensure reliable connection to prevent the transformer from opening the secondary circuit and causing damage to the equipment.
Generally, low-voltage transformers are used for primary through-core. For smaller current specifications, the primary is used in a multi-turn through-core manner. For extremely small currents, closed-type, primary terminal input products can be used.
According to the application environment, low-voltage current transformers are divided into three categories: circular window series products suitable for cable distribution, rectangular window series products suitable for copper bus distribution, and combined window series products that take into account both cable distribution and copper bus distribution.
According to the application purpose, there are also current transformer products for measurement, current transformer for protection, and combined current transformer for measurement and protection.
Generally, due to the relatively large primary current of low-voltage transformers, the secondary output is a standard 5A/1A current signal; with the improvement of production technology, there are also products that output smaller mA-level signals. In a complex high-voltage environment, it is not recommended to use a very small current signal output to reduce the error increase caused by the crosstalk of the secondary transmission signal loop.
Since low-voltage current transformers are basically used in three-phase power distribution environments, the marking of the polarity end of the current transformer is very important. Generally, the primary wiring is input at P1 and output at P2, and the secondary wiring is output at S1 and input at S2; the secondary output S1 and the primary input P1 have the same name, and the secondary input S2 and the primary output P2 have the same name.
General low-voltage current transformers are marked with rated loads. The connection from the transformer output to the instrument or equipment input together with the input load inside the equipment, the closer to the rated load, the better the accuracy of the transformer. The total load of the circuit connected to the secondary of the transformer should not exceed the rated load of the transformer, otherwise it will affect the accuracy of the transformer, and the dynamic range of the transformer will also be reduced. When the location of the installation equipment is far from the installation location of the transformer, a current transformer product with a secondary current output of 1A should be selected.
The long-term working current of the transformer shall not exceed 1.1 times the rated value, and it is allowed to be used for a short time at 1.2 times the rated value, and the time shall not exceed 1 hour.
Under the condition that the accuracy requirement is lower than level 0.2, the low-voltage transformer is wound with oriented cold-rolled silicon steel strip, and the secondary winding wire is wound with high-strength electromagnetic enameled wire, which is stable and reliable in operation and has strong environmental applicability; when the accuracy requirement is better than level 0.2, the amorphous and nanocrystalline material core with higher magnetic permeability is used to ensure accuracy while reducing the use cost as much as possible.
The product shell is made of high-strength polycarbonate material or PC/ABS alloy plastic, which has high temperature resistance and good strength. Some products use epoxy resin encapsulation technology, high insulation strength, moisture-proof and waterproof, and can work stably in harsh environments. The output mode can be terminal output, wire direct output, etc. according to the use environment; electromagnetic shielding structure can also be added as needed to improve the product's anti-interference ability.
Since the current of the detected circuit is generally large, when selecting products, reliable low-voltage current transformers that meet national standards must be selected. Otherwise, after installation, the transformer may heat up during operation, which may cause safety accidents and bring great losses.
During the installation of the product, select the appropriate installation method according to the installation environment, and then fix it in a reliable way to avoid the equipment falling off due to loose fixation during transportation. And during the wiring process, it is necessary to ensure reliable connection to prevent the transformer from opening the secondary circuit and causing damage to the equipment.
This series of products complies with the national standard: GB20840.2-2014.
Basic electrical parameters:
Operating frequency: 50Hz-400Hz
Flame retardant rating: UL94 V-0
Dielectric strength: 2500V/min
Insulation resistance: 1000M Ohms @ 500 Vdc
Impact voltage: 5000V (1.2/50 standard lightning wave)
Operating temperature: -20℃ - +55℃
Storage temperature: -25℃ - +85℃
Naming :
Main structure and composition:
Electrical Schematic:
*The primary current IP flows in from the P1 terminal and out from the P2 terminal; the secondary current flows out from the S1 terminal and in from the S2 terminal.
*Generally, current transformers use the same-name relationship with reduced poles, that is, the secondary output terminal and the primary input terminal are the same-name terminals to indicate the primary and secondary current relationship.
*The secondary side of the current transformer is generally directly connected to the power meter, but due to the large secondary current, the secondary line load RL cannot be ignored.
*IP*N1=IS*N2, generally N1 is 1. When IP is small and IS is 5A, N1 can be 2/3, etc., and the primary multi-turn through-core method is adopted. The transformation ratio needs to be increased accordingly to ensure the rated output is 5A.
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