Several Common Current Detection Methods, The Use OF Current Detectors

Electromagnetic Current Transformer

Electromagnetic current transformer is the most used measuring equipment in power system, with mature technology, low cost and very high precision. It is the most used measuring equipment at present. However, electromagnetic current transformers have many limitations:

1, insulation is difficult, especially above 500kV, due to insulation and make the transformer volume, quality, price are increased;

2, when the dynamic range is small and the current is large, CT will appear saturation phenomenon, saturation will make the secondary protection can not correctly identify the fault phenomenon;

3, the transformer output signal needs to lay the cable to the secondary equipment, but also twice converted into digital;

4, CT open circuit will produce high pressure, endangering personal and equipment safety;

5, easy to produce ferromagnetic resonance;

6, the current transformer in the specified operating frequency has a high accuracy, but it can adapt to the frequency range is very narrow, especially can not transmit DC 2 In addition, the current transformer when there is an exciting current, so it is an inductive component, there are the same shortcomings as the shunt.

Hall Current Sensor

Hall current sensor, DC and AC current can be measured, common current transformer can only measure AC current, common current transformer, when used, the secondary side cannot be open, Hall current sensor can be open. The output voltage of Hall current sensor is proportional to the size of the current flowing through the primary side, and the output polarity of the primary side current changes, so it can measure alternating current and direct current, and there is no special requirement for the waveform. The applicable frequency range is also wide. Generally used in electronic circuits, such as frequency converters. Ac transformer can only measure AC, and the frequency must be rated frequency, such as 50Hz transformer measurement 60Hz error is relatively large, the output signal can not be directly into the electronic detection circuit. Other advantages of Hall sensor are: 

1, good linearity: better than 0.1%; 

2, good dynamic performance: response time is less than 1μs tracking speed di/dt is higher than 50A/μs, Hall sensor module this excellent dynamic can improve the performance of modern control system provides a key basis. Compared with the common transformer response time of 10-12ms, it can not meet the needs of the development of work control system; 

3, the working frequency band is wide: the accuracy is 1% in the frequency range of 0-100kHz. The accuracy is 0.5% in the frequency range 0-5kHz. 

4, the measurement range is large: Hall sensor module is a system product, current measurement up to 50KA, voltage measurement up to 6400V. 

5, overload capacity: when the original current overload, the module reaches saturation, can be automatically protected, even if the overload current is 20 times the rated value, the module will not be damaged; 

6, wide measurement range: it can measure any waveform of current and voltage, such as DC, AC, pulse, triangular waveform, etc., and even the transient peak current and voltage signals can be faithfully reflected; 

7, fast response speed: the fastest response time is only 1us; 

8, good dynamic performance: fast response time, can be less than 1us; The response time of common transformer is 10~20ms;

Shunt

A shunt is a resistor that is connected in parallel with the current circuit of a measuring instrument to extend its measuring range. The shunt is based on the principle of voltage generated at both ends of the resistor when the direct current flows through the resistor, and the shunt is actually a small resistance. The measurement is simple, and the DC measurement accuracy can reach a relatively high degree. The biggest problem with the shunt is that there is no electrical isolation between the input and output. In addition, when the shunt is used to detect high frequency or high current, it is inevitably inductive, so the access of the shunt can not only affect the measured current waveform, but also cannot transmit the non-sinusoidal waveform.

Rothschild Coil

A Rothschild coil is a hollow toroidal coil that can be placed directly over the conductor being measured. The alternating current flowing through a conductor creates an alternating magnetic field around the conductor, which induces an alternating voltage signal in the coil that is proportional to the current ratio. 

The output voltage of the coil can be expressed by the formula Vout=Mdi/dt. Where M is the mutual inductance of the coil, and di/dt is the ratio of the current. Another AC voltage signal can be obtained by integrating the voltage signal from the coil with a special integrator. 

This voltage signal can accurately reproduce the waveform of the measured current signal, but the Roche coil cannot measure the DC component.

Compared with traditional current measuring devices, Roche coils have the following outstanding advantages:

1, no saturation;

2, good linearity, easy calibration;

3, the transient response ability is outstanding, can be used for high pressure protection;

4, the frequency range of the current to be measured is wide, from 0.1Hz to 1MHz, which can be used to measure harmonics;

5, the current range to be measured is large, from 1mA to 1MA;

6, the phase difference is less than 0.1 degrees at the intermediate frequency;

7, coil insulation voltage 10kV;

8, the use of safe, no secondary open danger, no overload danger;

9, small size, simple and convenient installation, open coil, easy access, no need to destroy the conductor, simple and convenient maintenance.

TMR Current Sensor

TMR sensor is a new type of magnetoresistance effect sensor that has been applied in industry in recent years, which uses the tunnel magnetoresistance effect of magnetic multilayer material to sense the magnetic field, and is widely used in modern industrial and electronic products to measure the current, position, direction and other physical parameters by sensing the magnetic field strength.

1, lower power consumption, large resistivity, small working current, low working current;

2, high accuracy, high sensitivity, good signal-to-noise ratio, high resolution, good linearity, wide linear range;

3, small size, good process, magnetic coupling, non-contact, anti-interference ability, good stability, can work in oil, dust, rain and other harsh environment;

4, good temperature stability, wide operating temperature range, up to 200 degrees Celsius.