First, the design of open-mouth Hall current sensor
1.1 Structural characteristics
The open-mouth Hall current sensor is developed on the basis of the traditional closed-mouth Hall current sensor, with a novel structure and beautiful appearance. The whole is composed of shell, iron core, sampling circuit board and fixed resin, the shell material adopts PC/ABS alloy, which has the characteristics of high temperature resistance, high mechanical strength and environmental protection; the iron core adopts oriented cold-linked silicon steel sheet, which has the characteristics of stable performance, high mechanical strength and extremely high permeability; the circuit board and external wiring adopt green pluggable terminals, and the on-site wiring is convenient and reliable.
1.2 How it works
Hall current sensor is based on the Hall effect, electromagnetic induction principle design of a sensor, according to the principle can be divided into open loop mode (direct discharge) and closed loop mode (magnetic balance type), open-end Hall current sensor is the traditional open-loop (direct discharge) Hall sensor based on the improvement, and the traditional single core, single Hall chip design is different, in order to design as a split structure, the iron core separation symmetrical installation, the hardware using dual Hall chip parallel complementary differential input.
When the primary current IP flows through a long wire, a magnetic field will be generated around the wire, the size of the magnetic field is proportional to the current flowing through the wire, the generated magnetic field is gathered in the magnetic ring, measured by two Hall elements in the magnetic ring air gap, the two Hall element marker surfaces are placed in the same magnetic field oppositely, the output signal has complementary characteristics, the output voltage is differentially amplified output, not only can suppress common-mode interference, but also the influence of temperature drift, the output voltage VS accurately reflects the primary current IP. The typical rated output is DC±5V or DC4-20mA.
1.3 Product Installation
Taking the square hole product as an example, the mounting screw of the open Hall current sensor is opened to remove the lower body of the sensor; the upper body of the open Hall current sensor is loaded into the primary busbar of the power distribution system, the lower body of the sensor is closed, and the mounting screw and gasket of the sensor are passed through the fixed holes of the upper and lower bodies, and the upper and lower bodies of the sensor are fixed together. If the site can be powered off installation, you can open two corresponding threaded holes on the copper plate according to the sensor spacing requirements, and fix the sensor on the busbar threaded hole through the installation fixing hole on the rear side to complete the installation of the sensor; if the field requires continuous power installation, the supporting rubber pad can be embedded in the shell and the copper plate to fix, to ensure that the sensor can work reliably under vibration conditions, and the entire installation process is relatively fast and simple.
1.4 Advantages of open Hall sensors
Compared with traditional DC current metering, which typically uses shunt or transformer measurement methods, open-mouth Hall sensors have the following advantages:
1) The insulation strength of the primary side and the secondary side is high, up to AC12kV isolation;
2) No insertion loss;
3) Good dynamic performance: the response time is less than 20us tracking speed di/dt is higher than 20A/us;
4) There is no need to disassemble the original cable or busbar during installation, especially for the reconstruction and construction of equipment that is not allowed to lose power.
Second, the application of open Hall current sensor
Open-type Hall current sensor is mainly used in the factory transformation of DC distribution system, such as power plant DC power system transformation, substation DC system transformation and transformation, communication room transformation, railway locomotive transformation and other projects, it can convert the original DC current signal of the system into a standard DC±5V or 4-20mA output, played a monitoring and electrical isolation role, can be used with multi-circuit monitoring instruments or other electrical measuring instruments.
2.1 Application examples
From the perspective of transformation cost, such as the use of traditional closed-mouth Hall sensor or shunt scheme, construction, must first disassemble the DC bus copper bar, and then install the sensor, and then reinstall the busbar to restore, and the entire installation process, at least two construction personnel need to cooperate with the construction, while the rectification line must be blackout cooperation; and if the use of open Hall sensor scheme, in the 1.3 installation method installation, only one construction worker, while the construction time is expected to only need 1/20 of the traditional program time, Factory power outage time can also be reduced accordingly, and even in some occasions, the construction and installation of continuous electricity is not available, and the use of this scheme obviously saves time, effort and labor. Compared with the purchase price of the sensor, the open Hall sensor of the same open hole shape is slightly higher than the purchase price of the closed Mouth Hall sensor by about 10%. From the analysis of test performance, as long as the upper and lower body screws of the sensor are tightly fixed when installed, the accuracy and stability of the open sensor and the closed sensor are basically the same.
In summary, whether it is from the superiority of on-site construction or from the comprehensive cost of overall procurement and construction of project transformation, the use of open Hall current sensors is undoubtedly the most cost-effective solution.
Taking the DC distribution cabinet of a well-known domestic enterprise as an example, the multiple DC inputs are summarized into a current output, and each channel has a protective device (circuit breaker, fuse, etc.), anti-reflection diode, etc., and each voltage and current can be monitored, and remote communication can be realized. Eight open-mouth Hall current sensors are used to monitor DC current, which is more convenient than traditional Hall installation and safer and more practical than shunt solutions.
DC distribution system is usually composed of high-frequency switching power supply and battery, which is used to provide reliable DC power supply for control, signal, relay protection and automatic devices, accident lighting, etc. in the DC system, and has high requirements for the reliability, stability and quality of its power supply. Therefore, it is urgent to adapt some DC systems that have been in service for a long time. And the DC system transformation does not stop power, engineering transformation is difficult, and the use of traditional closed-mouth Hall current sensor or shunt can not be solved, so the use of open Hall current sensor to solve the problem of DC current measurement in the transformation project, to ensure that the transformation process without blackout and safe operation.