CZ306402B6 - Induction type current shunt - Google Patents

Abstract

In the present invention, there is disclosed an induction type current shunt comprising a current transformer (TR) with primary and secondary windings, a current meter (M) and input/output terminals (1, 2), whereby the primary winding input terminal (Z1) of the same sense and the secondary winding output terminal (K2) are connected with the current shunt input current terminal (1), the primary winding output terminal (K1) is connected with input contact of the current meter (M), and the secondary winding input terminal (Z2) of the same sense and output contact of the current meter (M) are connected with the current shunt output current terminal (2).

Description

Induction type current shunt

Field of technology

The invention relates to a current shunt of the induction type for measuring large alternating currents.

Prior art

Currently, resistor-type current shunts are known from resistance values of hundreds of μΩ to about 1 μΩ, which are practically frequency-independent and can measure direct currents, but which have several kilowatts of heat loss when measuring large currents in the order of hundreds to thousands of amperes. , and require intense forced cooling or a large shunt cooling area. However, significant heating of the shunt is in principle undesirable because it changes the resistance value of the shunt and thus impairs the accuracy of the measurement.

An open wire with a small measuring resistor, eg 300 μΩ, is used for measuring large currents, for direct currents, alternating currents, and for direct currents with a superimposed alternating component. However, the inserted measuring resistor heats up significantly and thus leads to power losses, which at a current value of 1000 A and a voltage value of 300 mV reaches 300 W.

In the case of a coil with an iron core, the so-called current transformer, the measured conductor passes through the axis of the core around which the coil is wound. Here, a current is measured which flows through a short-circuited coil generating a magnetic field, which in turn induces a voltage in the secondary winding. However, there is a need to know the gear ratios between the windings. The disadvantage of this solution is that it affects the inductance of the measured conductor and increases it, thus creating problems at high frequencies, as the core acts as a resistor and prevents current flow.

Another solution is a coil without a ferromagnetic core, the so-called Rogowski winding, ie a coil on a glass or plastic ring, which requires an amplifier to be connected in front of the measuring unit, which is a significant disadvantage of this solution.

In exceptional cases, a Hall probe with an amplifier is used, which, however, has a measurement influenced by an interfering ambient magnetic field. Here, too, the disadvantage is the need to use an amplifier.

Thus, a general disadvantage of the prior art is that there is no known method of reducing heat loss in a shunt for measuring large currents without the need for an amplifier, as most current meters require a voltage drop on the shunt of several tenths to hundredths of a volt.

The object of the invention is to construct a current shunt for measuring large alternating currents, the heat losses of which will be at least one to two orders of magnitude lower than the heat losses of the shunt known from the prior art.

The essence of the invention

The above-mentioned drawbacks are largely eliminated by an induction-type current shunt, which comprises a current transformer with primary and secondary windings, a current meter and current shunt input and output terminals, the primary winding input terminal of the same sense and the secondary winding output terminal being are connected to the input current terminal of the current shunt, the output terminal of the primary winding is connected to the input contact of the current meter, and the input terminal of the secondary winding of the same sense and the output contact of the current meter are connected to the output current terminal of the current shunt.

- 1 CZ 306402 B6

Explanation of drawings

The invention will be further illustrated by the figure, where Fig. 1 is a circuit diagram of an induction-type current shunt according to the invention.

Examples of embodiments of the invention

The current shunt according to the invention shown in Fig. 1 is of the induction type and comprises a current transformer TR with primary and secondary windings, a current meter M and input and output terminals 6, 2 of the current shunt. The input terminal Z1 of the primary winding in the same sense and the output terminal K2 of the secondary winding are connected to the input current terminal £ of the current shunt. The output terminal K1 of the primary winding is connected to the input contact of the current meter M. The input terminal Z2 of the secondary winding in the same sense and the output contact of the current meter M are connected to the output current terminal 2 of the current shunt.

The gear ratio p of the current shunt according to the invention is given by the ratio of the number of turns of the primary and secondary windings, see formula (1) where:

Ni is the number of turns of the primary winding,

N ₂ is the number of turns of the secondary winding.

The conversion p is usually chosen as an integer from 9 to 99.

Since the primary and secondary windings are connected in opposite directions and their magnetic fields cancel each other out, the supplied measured current I entering the shunt via the input current terminal £ is divided into a primary measuring current ha 2 into a secondary bypass current I _{2 based on the above ratio.} , see formula (2)

The current meter M is calibrated to the value of the measured current I supplied to the transformer TR and measures the value of the primary measuring current fi, where the formula (3) applies.

I = (p + 1) h (3) where (p + 1) is usually values from 10 to 100.

The advantage of the current shunt according to the invention is the possibility to measure large currents up to frequencies of tens of megahertz using suitable magnetic materials while maintaining zero or slight phase shift to one angular degree between the measured current and the current flowing through the current meter and maintaining high accuracy and linearity of measurement throughout range of measured current. This is particularly advantageous in measurements in the power industry as well as in high-frequency current measurement technology, for example in the technology of radio-frequency transmitters.

The main technical benefit of the invention is that it is a current shunt of the induction type, operating in contrast to the current transformer with zero or very small induction in the magnetic field.

-2GB 306402 B6 core material and with any shape of measured alternating current, and which has at least an order of magnitude to two orders of magnitude less heat loss than a resistor shunt.

The induction-type current shunt according to the invention can be used in the development of electrical circuits in industrial or school laboratories, light and heavy measuring laboratories and test rooms, as an energy meter, or in some specific industrial applications, e.g. as a measuring component of a wireless power supply system for electric vehicles. .

Claims (1)

PATENT CLAIMS Induction type current shunt, characterized in that it comprises a current transformer (TR) with primary and secondary windings, a current meter (M) and current shunt input and output terminals (1,2), the primary winding input terminal (ZI) in the same sense and the output terminal (K2) of the secondary winding is connected to the input current terminal (1) of the current shunt, the output terminal (K1) of the primary winding is connected to the input contact of the current meter (M), and the input terminal (Z2) of the secondary winding of the same sense and the output contact of the current meter (M) is connected to the output current terminal (2) of the current shunt.