JP3064503U - AC current sensor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To eliminate a measurement error caused by temperature rise, resistance temperature coefficient and resistance load effect, to measure a current very accurately, and unnecessary power loss at the time of current measurement. To provide an alternating current sensor capable of reducing power consumption. The AC current sensor according to the present invention includes an iron core, a current input coil, a current output coil having high stability and a low temperature coefficient, and a leading coil, and combines a current input coil and a measurement standby current circuit. The secondary side sensitive current of the iron core flows almost completely through the current output coil, and finally the detector measures the sensitive voltage above the leading coil.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to an alternating current sensor, and more particularly to an alternating current sensor that utilizes a transformer structure having two sets of secondary coils and achieves the purpose of measuring an alternating current with high accuracy.

[0002]

[Prior art]

 With the ever-evolving science and technology, almost all equipment cannot operate independently without electricity. In terms of the power system, it should be convenient to monitor the current condition of the power system at any time to ensure the normal operation of each power system, and to monitor the operation of the system. Appropriate measures can be taken even if there is a mistake in operation. In the area of precision electronics such as integrated circuits, the number of control signals and data signals transmitted between electronic devices is enormous, and if the detection of any one current signal fails, the entire system will operate incorrectly. There is a possibility. Therefore, how to accurately measure current is a very important issue at present. Commonly used current sensors are divided into resistance detection and current transducer detection. In the resistance reconnaissance method, as shown in the circuit diagram of FIG. 1, the sense resistor is combined with the circuit of the measurement standby current, and after reading the voltage value above the resistor, the resistance of the resistor is determined based on the ohmic constant (Ohm raw). It can be converted to the measurement standby current flowing above (Iin = Vout / R), and the structure is simple, but the heat effect (P = Iin2R) generated after the current flows through the resistor raises the temperature of the resistor, and the resistance value becomes higher. The measured current value has a very large error and causes a considerable loss of power. The current converter reconnaissance method uses a current converter (a kind of instrument transformer) as shown in the circuit diagram in Fig. 2, and combines the measurement standby circuit and the primary coil (current input coil) of the current converter. Then, the secondary coil (current output coil) flows a relatively small current Iout proportional to the measurement standby current I (ie, Iin), the proportion of which is inversely proportional to the run ratio of the coil, which is then detected by the detector. The current Iout is measured. After measuring I out, the measurement standby current Iin can be estimated by the formula Iin = Iout × (M / V). However, in general, processing for current is more difficult than processing for voltage. Therefore, a sense resistor is usually connected to a secondary coil, and the voltage value Vout above the sense resistor is measured. At this time, the magnitude of the measurement standby current Iin can be calculated by the formula Iin = (Vout / R) × (M / V), as shown in the circuit diagram of FIG.

[0003]

[Problems to be solved by the invention]

 In the current conversion method described above, the measurement standby current is converted to a relatively small current by the current converter, and the current flowing through the sense resistor is relatively small, so that the power loss is smaller than the resistance method described above and the resistance value is temperature. Although the rate of change with effect is relatively small, errors can be reduced, but there are still some severe drawbacks: Resistance is still the main load, power loss leads to temperature rise and changes in resistance, which is very disadvantageous for accurate measurements and of relatively good quality (ie relatively low temperature coefficient). A (small) resistor should be used to remedy this drawback. 2. The current converter itself also has impedance (wandering resistance, magnetic core equivalent resistance, coil reactance and flux reactance generated by coil flux and coil magnetic reactance), and the voltage drops after the current flows. Therefore, an error occurs in the current value estimated based on the output voltage Vout. 3. As shown in the equivalent circuit diagram of FIG. 4, even if a resistor of excellent quality is selected to form a sense resistor R, the copper wire used by the secondary coil M itself is a resistor R2 having a large temperature coefficient. If it is very sensitive to temperature and is connected to the sense resistor R, its accuracy is greatly reduced under the condition that two conductors having different temperature coefficients are connected. 4. The point where the coil copper wire and the sense resistor R contact each other is a contact of a dissimilar metal, and the resulting work function interferes with the measurement and, at the same time, produces a contact resistance Rc at the contact, which is also one of the temperature coefficients. Element. 5. If the measurement standby current is very large, the required current converter coil current ratio will be very large, that is, its run ratio will be very large, making it very difficult to manufacture, and in this case, usually many As shown in the circuit diagram of FIG. 5, the voltage value Vout of the secondary coil of the last one current comparator is taken out by the resistor R as shown in the circuit diagram of FIG. However, under the situation where the current converters are combined in this way, the inner impedance after the current converters are connected cannot be overlooked, and the precision is greatly reduced.

The main object of the present invention is to divide the secondary coil into two sets, thereby eliminating the errors in the current measurement that could be effected by the temperature increase, the resistance temperature coefficient and the resistance load effect, and very accurate measurement can be performed. An AC current sensor is provided. Another object of the present invention is to provide an alternating current sensor that can reduce unnecessary power loss when measuring current.

[0005]

[Means for Solving the Problems]

 The AC current sensor of the present invention has an iron core structure similar to a transformer, and the primary coil and the measurement standby AC current path are connected to each other in the same manner as the conventional current converter connection method. There are two sets of secondary coils. The first set of coils is wrapped around a resistance wire (for example, manganese copper wire) with high stability and low temperature coefficient, and both ends are short-circuited by welding. The coil is open and serves as a detector to measure the leading coil of voltage. The AC current sensor of the present invention has the following advantages over the conventional AC current sensor: Since the second set of secondary coils (ie, the leading coil) in the present invention is in the open state, the secondary current almost completely flows through the first set of secondary coils (ie, the current output coil), ie, the second set of secondary coils. The heat dissipation situation is good because the whole set of secondary coils themselves is the current load resistance on the secondary side; and it uses a low temperature coefficient resistive material and the temperature coefficient is the same everywhere, so the resistance value is low. Hardly any; it is a conductor of the first metal and does not come into contact with other dissimilar metals, so that it does not cause interference and contact resistance of the contact work function. 2. The voltage sensed on the second set of secondary coils and the voltage of the first set of secondary coils is proportional (this proportion is the run ratio of the first set of coils and the second set of coils); The sensing voltage is measured by connecting the reader to the second set of coils, but the impedance of the reader is so high that the current through the reading coil is very small (can be considered as open). Therefore, the voltage drop of the electric shock and the voltage drop of the resistance caused by the iron core and the coil are so small that they can be overlooked and not included in the calculation, and there is no load effect of the conventional current converter. 3. Since almost all of the current flows through the first set of secondary coils (current output coils), the loss power in the present invention is almost entirely in the first set of secondary coils, and the resistance value of the coil is a general resistance. Since it is much larger than the value, its loss power is smaller than the power consumed by the resistance method and the current comparison method. 4. When the standby current for measurement is very large, the current flowing through the secondary coil will be very large unless the run ratio of the primary coil and secondary coil is increased. If the method of class connection is not adopted, the measurement standby current will not be able to withstand large heat generation power and will be destroyed. Even if the resistance can withstand such high power, the voltage will be extremely high on the resistance. Large, difficult to measure and prone to danger. However, according to the present invention, since the resistance of the second set of secondary coils is very small, the heat generation power is very small, the voltage is relatively small, and even if the measurement standby current is very small. Even if the voltage of the first set of secondary coils is too high because the voltage is large, the voltage is read from the second set of coils, so the run ratio of the second set of coils to the first set of coils is changed. In addition to being able to lower the sensitive voltage value on the second set of coils, the resistance value of the first set of secondary coils is reduced directly (if a coarser resistance wire is used), As a result, the sensitive voltage of the second set coil can be reduced, so that it can be easily measured. Therefore, when measuring a large current with the AC current sensor of the present invention, it is not necessary to use a multi-stage shunting method. You only need to change the value, it is very convenient to operate, saves volume and cost, and can increase the economic advantage. 5. Since a general current transformer avoids opening on the secondary coil side, a short-circuit tangent should usually be added at the secondary coil when not yet measured, but this short-circuit tangent is always too large in current. Burn down. Since the first set of secondary coils in the present invention has a short-circuit coil structure, more secure measurement can be provided, and the present invention is well known when measuring a large current. Can be shown to be superior to

[0006]

【Example】

 Hereinafter, the features and effects of the present invention will be described in detail with reference to the accompanying drawings by way of specific embodiments. FIG. 1 is an electric circuit diagram when the current is measured by the resistance method. As shown in the figure, after reading the voltage value Vout on the sense resistor R, the measurement standby current value Iin can be converted at a constant ohm rate.

FIG. 2 is an electric circuit diagram when the current is measured by the current converter. After measuring the current value Iout of the secondary coil as shown in the figure, the standby measurement current value Iin is measured by the run ratio of the coil. Can be converted.

FIG. 3 is an electric circuit diagram in a case where a voltage is measured by connecting a sense resistor with a current converter. Inside the dotted line is a current sensor, which measures the voltage value Vout of the sense resistor R on the secondary coil and then converts the measurement standby current value Iin by the formula Iin = (Vout / R) × (M / V). it can.

FIG. 4 is an equivalent electric circuit diagram of FIG. The dotted line is the equivalent current path of the actual current exchanger, the bold line is the ideal transformer, the current exchanger is a type of transformer, and the transformer itself has impedance (winding resistance, magnetic core equivalent resistance). Because the leakage reactance of the coil and the magnetic reactance of the coil exist, and the winding resistance in them has a decisive effect, the equivalent current path of the actual current converter is ideal.・ Includes resistance R1 and R2 of transformer and coil on both sides. Besides this, there is an interference work function f and a contact resistance RC, since the current transducer is combined with the measurement standby resistance.

FIG. 5 is an electric circuit diagram in the case where several current converters are connected to each other to measure a large current. As shown in the figure, after combining multiple current converters and reducing the current one by one, the voltage value of the secondary coil of the last current converter is taken out with a resistor, and the formula Iin = (Vout / R ) × (M ₁ / N ₁ ) × (M ₂ / N ₂ ) ×... (Mn / Nn) can convert the measurement standby current value.

FIG. 6 is an electric circuit diagram of the AC current sensor of the present invention. As shown in the figure, it has a core structure similar to that of a transformer, and has a primary coil (current input coil, which is looped N times over the iron core) in the same manner as a conventional current converter. The measurement standby AC current paths are connected to each other (if the hollow iron core structure is used, the measurement standby current path may be passed through this core). There are two sets of secondary coils. The first set of coils (current output coils) has a high stability, low temperature and low coefficient of resistance wire (for example, manganese copper wire) wrapped around the M core, and both ends. With a welded short circuit; the second set of coils (which may be regular copper wire) is wrapped around the P core, both ends of the coil are open, and the sensing voltage is measured as a detector. It is a leading coil for Since the inner resistance of the detector is high impedance and the current above the leading coil is very small, after connecting the detector the coil can still be considered as open and therefore the secondary side The current flows almost entirely through the first set of primary coils (current output coils), i.e. the current above this coil completely cancels out the magnetic motive hose that the primary coil made on the iron core, And the first set of coils (leading coil) is used to read the sensitive voltage, and the current over it is very small. By connecting such a structure, the effect borne by the secondary coil of the conventional current converter (to offset the magnetic motive hose made by the primary coil by flowing the current and to read the voltage) Effect), and complete each with two coils. Thus, completely conventional current exchangers can completely eliminate the measurement errors caused by temperature rise, temperature coefficient of resistance and resistive load effects, and reduce the power loss worn in the current sensor, And the purpose of measuring very accurately can be achieved. In order to explain the principle of the present invention in more detail and to derive the results after actually applying the present invention, it is necessary to perform analysis on the actual equivalent effective circuit in the present invention, and the analysis is as follows. It is like.

FIG. 7 is an equivalent electric circuit diagram of the AC current sensor according to the present invention. The sensor according to the present invention includes an ideal transformer (a thick line indicates an ideal transformer, and an ideal transformer formula can be used). The effect can be equivalent to the coil resistances r ₁ , r ₂ , r ₃ on both sides, and r ₄ is the inner resistance of the detector. The current value Iout = Iin × (N / M) above the current load coil in the present invention can be obtained from the run ratio, the coil resistance of the current output coil is r ₂ , and both ends are short-circuited. since it has, and the voltage V1 = Iout × r ₂ forms a current and a positive proportional measurement standby. This voltage cannot be measured by an external detector, but its value can be measured by a second set of secondary coils (leading coils). According to the ideal trans theory, the sensitive voltage of each coil above the iron core is directly proportional to the rate of change of the magnetic flux over the entire core, and hence the voltage above the leading coil V ₂ = V ₁ × (P / M) = Iin × (N / M) × r ₂ × (P / M) In the inner-resistance r ₄ is high impedance of the detector (millions ohms or higher), a leading coil can be regarded as the opening of the state, there is almost no current flowing thereon, and coil resistance are few ohms Since there is almost no voltage drop, ie, no load resistance effect of the conventional current converter, the voltage value Vout measured on the detector is equal to V2, which is directly proportional to the measured standby current Iin. Thus, the value of the measurement standby current can be converted, and the conversion formula is I in = V ₂ × M ² / N / P / r ₂ . The sample has already been provided to the Republic of China Standard Laboratory for this invention, and the results of the experiment have proved to be exactly the same as the theoretical analysis. The above specific examples serve to explain the purpose, features and effects of the present invention in detail, and do not limit the patent scope of the present invention, but become familiar with this kind of art. If a person does not depart from the spirit of the art of the present invention by a local change or modification based on the specific embodiment, the invention belongs to the claims of the present invention.

[0013]

[Effects of the Invention] As described above, the present invention has a clever structure design, improves the drawback that the conventional current sensor cannot measure the current very accurately, and reduces the actual necessity (range of the measurement standby current). Can be used to adjust the run ratio, and can be applied to any equipment to obtain very accurate survey results.

[Submission date] July 1, 1999 (1999.7.1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

[Prior art]

 With the ever-evolving science and technology, almost all equipment cannot operate independently without electricity. In terms of the power system, it should be convenient to monitor the current condition of the power system at any time to ensure the normal operation of each power system, and to monitor the operation of the system. Appropriate measures can be taken even if there is a mistake in operation. In the area of precision electronics such as integrated circuits, the number of control signals and data signals transmitted between electronic devices is enormous, and if the detection of any one current signal fails, the entire system will operate incorrectly. There is a possibility. Therefore, how to accurately measure current is a very important issue at present. Commonly used current sensors are divided into resistance detection and current transducer detection. In the resistance reconnaissance method, as shown in the circuit diagram of FIG. 1, the sense resistance is combined with the circuit of the measurement standby current (in this specification, “combined” means connected in series), After reading the voltage value above the resistance, it can be converted to a measurement standby current flowing over the resistor (Iin = Vout / R) by the ohmic constant (Ohm law), and the structure is simple, but the current flows through the resistance The subsequent thermal effect (P = Iin2 R) raises the temperature of the resistor, and the resistance changes due to the heat, so that there is a very large error in the measured current value and not a little. Causes power loss. The current converter reconnaissance method uses a current converter (a kind of instrument transformer) as shown in the circuit diagram in Fig. 2, and combines the measurement standby circuit and the primary coil (current input coil) of the current converter. Then, the secondary coil (current output coil) flows a relatively small current Iout proportional to the measurement standby current I (ie, Iin), the proportion of which is inversely proportional to the run ratio of the coil, which is then detected by the detector. The current Iout is measured. After measuring I out, the measurement standby current Iin can be estimated by the formula Iin = Iout × (M / V). However, in general, the processing for current is more difficult than the processing for voltage. Therefore, usually, a sense resistor is connected to the secondary coil (in this specification, connection means to electrically connect). Measure the voltage value Vout above the resistor. As shown in the circuit diagram of FIG. 3, at this time, the magnitude of the measurement standby current Iin can be calculated by the formula Iin = (Vout / R) × (M / V).

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram when a current is measured by a generally known resistance method.

FIG. 2 is an electric circuit diagram when a current is measured by a generally known current converter.

FIG. 3 is an electric circuit diagram in a case where a generally known current converter is connected to a sense resistor and a voltage is measured.

FIG. 4 is an equivalent electric circuit diagram of FIG. 3;

FIG. 5 is an electric circuit diagram in the case of measuring a large current by connecting several generally known current converters.

FIG. 6 is an electric circuit diagram of the AC current sensor of the present invention.

FIG. 7 is an equivalent electric circuit diagram of the AC current sensor of the present invention.

[Explanation of symbols]

I --- Measurement standby current Iin --- Input current Iout --- Output current R --- Sense resistance R ₁ --- Input current coil resistance R ₂ --- Output current coil resistance R _C --- Contact resistance r ₁ --- Input current coil resistance of the present invention r ₂ ----Output current coil resistance of the present invention r ₃ --- Leading coil resistance of the present invention r ₄ --- Inner resistance of detector Vout --- −Sense voltage N−−Number of turns of input current coil M −−− Number of turns of output current coil P −−− Number of turns of leading coil f −−− Interference work function N ₁ −−− First current converter N ₂ --- The number of turns of the input current coil which connects the second current converter Nn --- The number of turns of the input current coil which connects the n-th current exchanger M _1- --- Connect the first current transducer Number of turns of the output current coil M ₂ --- Number of turns of the output current coil connected to the second current exchanger Mn-Number of turns of the output current coil connected to the n-th current converter

Claims (3)

[Utility model registration claims] An iron core, a current input coil, a current output coil, and a leading coil, wherein the iron core has a loss of an iron core, a loss of magnetic hysteresis, a flux, a magnetic exciting, and a reactance. The current input coil is made of conductive metal, which is made of conductive metal, which is wrapped on the iron core and is connected with the measurement standby circuit; the current output coil is stable Is made of a high-resistance wire with a low temperature coefficient, which is wrapped over an iron core and its both ends are short-circuited by welding; the leading coil is made of a conductive metal, which is wrapped over an iron core and has both ends. Is open and can be connected to the detector to measure the sensitive voltage; with the above structure, the current input coil and measurement standby current circuit can be combined, and the secondary side An AC current sensor characterized in that current is caused to flow through a current output coil and an AC current is measured by measuring a sensitive voltage on a leading coil using a detector. 2. The method according to claim 1, wherein the iron core has a hollow structure, and the measurement standby current circuit does not have to be penetrated through the iron core of the hollow structure and the measurement standby current circuit needs to be separately provided by a current input coil. The alternating current sensor according to claim 1. 3. The current output coil is made of manganese.
The alternating current sensor according to claim 1, wherein the sensor is a copper wire.