JPH10144541A - Burden device for instrument transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small, light, and stable device for an instrument transformer capable of easily and externally setting a rated second current, burden capacity, burden power factors, and so on, during error measurement of the instrument transformer. SOLUTION: An impedance component setting device 5, a burden current detector CT0 , and a power amplifier 15 are connected to a burden circuit A, and an impedance is variably set by the setting data D1 and D2 of CPU calculated from a set condition, and a reference voltage vector es is generated by making reference to an indicated data of CPU based on a phase conversion voltage of the current detector CT0 , and the difference voltage eg between the reference voltage vector es and the proportional voltage ex , 1/K of a burden voltage, is entered the power amplifier 15 which automatically compensates the difference of the set impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burden device used for measuring an error of an instrument transformer.

[0002]

2. Description of the Related Art It is specified that an error measurement of a current transformer or the like is performed by setting predetermined specified conditions for a device to be measured.
For example, in the case of a current transformer, it is necessary to set the rated secondary current, load capacity, load power factor, and the like to specified values.
It is practically difficult to construct this condition setting only by a combination of passive elements, and it is conceivable that a large number of passive elements prepared in advance in order to obtain this combination by an external operation are switched and connected by a relay or the like. However, the accuracy is lowered due to the influence of the contact resistance of the contact and the like, so that it is not practical. An apparatus as shown in FIG. 6 in which this setting is performed electronically by external control has been proposed and commercialized by the present applicant company. This device will be described in terms of a current transformer device. The transformer RT of the power amplifier 15 for providing the load current I ₂ detector CT ₀ and the necessary impedance to the load circuit (secondary circuit) A of the current transformer CT to be measured. Are connected in series, and a circuit 10 for converting the detected current of CT ₀ into a voltage and a phase is used as a voltage vector e, je (or -je) as a load power factor (cos θ) setting unit 11 and sin θ.
Since the setting unit 12 (√ (1-cos ² θ), sin θ
Is automatically set) to the operational amplifier 13. Since the operational amplifier is set to the load capacity (VA) specified by the variable resistor 14, a voltage vector e _s having a predetermined magnitude and phase angle is obtained at the amplifier output. PT ₀ is a voltage detection transformer for obtaining a voltage e _x to the load voltage e ₂ and ₁ × n ₂ / n. The difference voltage e _g a e _s and e _x as an input of the power transistor amplifier PA of the power amplifier 15. Based and specified volume with the phase angle if the amplification degree of an infinite e _s is the winding terminals of the output transformer from equal to e _x burden voltage e ₂ based on the specified power factor than load current I ₂ of the PA The specified condition is maintained by generating a voltage drop e ₀ such that the voltage value becomes equal to the voltage value. As a practical example, the rated secondary current is 5A,
When the load capacity is set to 50 VA and the load power factor is set to 0.5, 0.5 is set to the power factor setting unit 11 and the operational amplifier dial 1 is set.
When the scale of 4 is set to 50 and the secondary current I _{2 of} CT is adjusted to 5 A, the power amplifier 15 sets the burden voltage e ₂ to a voltage (10 V) delayed by 60 ° from the current I ₂ by 60 °.
The output circuit operates such that a voltage drop e ₀ is generated at the output terminal, thereby creating an apparent impedance component in the burden circuit A. However the apparatus described above, responsible for total impedance the power amplifier PA requires, to e _s = e _x will be impossible to obtain accurate unless intended is very large amplification of the PA. However, since this device is a two-terminal device in which the input terminal and the output terminal are connected, if the amplification is increased, oscillation is likely to occur and the device is likely to be unstable, and the power amplifier 15 needs to have a large power capacity. There are problems such as an increase in size.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to improve the above-mentioned problems, and it is possible to simplify the adjustment of impedance to be inserted into a burden circuit by setting each designated condition in a computer (CPU) and to reduce the power capacity of a power amplifier. Is to provide a burden device that can be significantly reduced in comparison with the capacity of the conventional device. In addition, the number of passive elements and the number of switching contacts constituting the impedance are reduced, and this switching connection is reduced by C.
An object of the present invention is to provide a device which can be easily operated by an output from a PU.

[0004]

According to the present invention, an impedance element setting device, a current detector, and an output terminal of a power amplifier are connected in series in a burden circuit of a transformer to be measured, and a rating as a measurement condition is provided. CPU with secondary current, load capacity and load power factor set, current / voltage conversion and 90 °
A CPU comprising a phase shift circuit and a reference vector generation circuit;
Outputs impedance element setting data D ₁ , D ₂ calculated from each set value to the impedance element setting device, and supplies vector data D ₃ to the reference vector generation circuit to convert the converted voltage e of the current detector output current to The reference voltage vector e _{s is} obtained from the 90 ° phase shift voltage je (or -je).
Obtained by so as to compensate for the set impedance of the impedance element setting unit by a difference voltage e _g the voltage e _x in proportion to the load voltage and the reference voltage vector e _s is zero in the power amplifier output to generate a is there. In the present invention, since the power amplifier compensates for the excess or deficiency of the impedance of the impedance element setting device specified by the CPU, a small capacity is sufficient. Further, the impedance element setting device in the device of the present invention is characterized in that both ends of each of a plurality of passive elements (R, L, C) in which the value of each passive element is set in a relation of 2 ⁿ / 2 are connected to fixed contacts of a changeover switch. In addition, the movable contact is connected to one end of another passive element and connected in series in multiple stages, and the changeover switch is constituted by a switch register of several bits equal to the number of passive elements. The value or the inductance value can be switched and set. In addition, there is also a device in which the number of windings (voltage) of a primary or secondary winding of a transformer is connected in a similar relational configuration, and a fixed passive element (R, L, C) is connected to the secondary or primary side. Can be used. Furthermore, a certain passive element is connected to the secondary side of Slidac,
The slider may be adjusted by a drive source such as a pulse motor driven by the output of the CPU.
In this case, the output from the CPU need not be a binary signal.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, the same reference numerals are used for the same circuit elements as in FIG. The setting devices 2, 3, and 4 for each designated condition are connected to the CPU 1. Reference numeral 5 denotes an impedance element setting device inserted in the burden circuit, in which a variable resistance circuit 6 and a variable reactance circuit 7 are connected in series, and each circuit is based on a set value by each of the setting devices 2, 3, and 4. The adjustment is set according to the numerical value calculated by the CPU. A reference voltage vector e _s with reference to instruction data D ₃ from the CPU on the basis of the vector generator 8 converts the voltage e and je (or -je), proportional voltage e of this burden voltage e ₂ of 1 / K obtaining a differential voltage e _g by entering the _x to the operational amplifier 9. Power amplifier 15 outputs an output voltage e ₀ as close to zero differential voltage e _g. In order to reduce the power loss of the power amplifier, a transistor complementary circuit can be used instead of the output transformer RT. FIG.
FIG. 5 to FIG. 5 show an impedance element setting device used in the present invention. FIG. 2 shows that four passive elements (R, L or C) Z ₁ , Z ₂ ,. 2R, 4
R, and 2 ⁿ / 2 of the relationship as 8R, the movable contact 23 is connected as shown in FIG respect switching fixed contact points 21 and 22 of the changeover switch 20 connected to both ends of each, each changeover switch C
It is directly driven by a 4-bit signal of the PU, and can be switched in 16 steps from R = 0 to 15R. FIG. 3 shows that a fixed passive element Z (R, L or C) is connected to the secondary side 32 of the transformer 30, and the four windings n ₁ ,... N ₄ of the primary side 31 are connected to 1V, 2V, 4V, respectively. , 8V, and a switch 20 is connected to each winding.
The fixed contacts 21 and 22 and the movable contact 23 are connected to each other and each switch is operated by a CPU signal in the same manner as described above, so that the magnitude and the phase angle of the voltage e ₂ and the current I ₂ of the burden circuit are close to specified values. It can be. FIG. 4 shows a configuration in which a constant impedance Z is connected to the secondary side of a sliderac 34, and the slider 35 is operated by a pulse motor 36 driven by an output pulse from the CPU. FIG. 5 shows an example in which the present invention is applied to a PT burden circuit, in which a secondary winding 42 is divided into four parts with respect to a primary winding 41 of a transformer 40 so as to output voltages of 1 V, 2 V, 4 V, and 8 V, respectively. In addition, by connecting the respective contacts of the switch 20 in the same manner for each winding, the magnitude and the phase angle of the current of the primary winding connected to the burden circuit can be varied. In the above description, the changeover switch is constituted by a 4-bit switch register, but may be replaced by an electromagnetic switch such as a relay.

[0006]

According to the present invention, the approximate impedance required is set by the CPU and the impedance element setting device.
Since the power amplifier only works as a variable impedance for fine adjustment, the power amplifier can be small in capacity and can provide a device smaller and lighter than the conventional device. In addition, since the amplification degree of the power amplifier may be small, the circuit operation is stable and troubles such as oscillation are eliminated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a CT burden device of the present invention.

FIG. 2 is a connection diagram of a variable impedance circuit.

FIG. 3 is a connection diagram of another variable impedance circuit.

FIG. 4 is a connection diagram of a continuous variable impedance.

FIG. 5 is a connection diagram of a variable impedance for PT.

FIG. 6 is a circuit configuration diagram of a conventional device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 CPU 2 rated secondary current setting device 3 burden capacity setting device 4 burden power factor setting device 5 impedance element setting device 6 variable resistance circuit 7 variable reactance circuit 8 reference voltage vector generation circuit 9 operational amplifier 10 current / voltage conversion 90 ° shift Phase circuit 15 Power amplifier PT ₀ Burden voltage detection transformer

Claims (5)

[Claims] An impedance element setting device, a current detector, and an output terminal of a power amplifier are connected in series in a load circuit of a transformer to be measured, and a rated secondary current, a load capacity, and a load power factor as measurement conditions. And a current / voltage conversion and 90 ° phase shift circuit and a reference vector generation circuit. The CPU sends impedance element setting data D ₁ and D ₂ calculated from each set value to the impedance element setting device. the generates the reference voltage vector e _s from the reference transformation vector generator to provide vector data D ₃ wherein the current detector output current voltage e and the 90 ° phase voltage je (or -je) outputs reference voltage vector e _s and the by the power amplifier output to zero the difference voltage e _g the voltage e _x in proportion to the load voltage impedance element setting unit setting Lee Instrument transformer burden apparatus being characterized in that so as to compensate for the impedance. 2. An impedance element setting device inserted into a burden circuit, wherein both ends of each of a plurality of passive elements (R, L, C) having a ratio of values of each passive element being 2 ⁿ / 2 are changeover switches. And the movable contact is connected to one end of another passive element and connected in series in multiple stages, and the first fixed contact and the last movable contact of the changeover switch are connected to the burden circuit, 2. The burden device according to claim 1, wherein said changeover switch is constituted by a switch register of several bits equal to the number of said passive elements. 3. An impedance element setting device inserted into a burden circuit, wherein an impedance element of R, L or C is connected to a secondary side of a transformer to form a closed circuit.
A plurality of coils having a coil turn ratio of 2 ⁿ / 2 are provided on the primary side, and both ends of each coil are connected to a fixed contact of a changeover switch, and the movable contact is connected to one end of another coil. The fixed switch at the first stage and the movable contact at the last stage of the changeover switch are connected to the burden circuit, and the changeover switch is constituted by a switch register of several bits equal to the number of the primary side coils. The burden device according to claim 1, comprising: 4. An impedance element setting device inserted into a burden circuit, wherein a passive element of R, L or C is connected to a secondary side of the Slidac, and a slider of the Slidac is output from a CPU. 2. The burden device according to claim 1, wherein the burden device is connected to a pulse motor driven by the impedance element setting data pulse. 5. An impedance required to be inserted into a burden circuit.
The element setting device is a transformer with the primary coil connected to the burden circuit.
The coil turns ratio is 2 on the secondary side of the vessel.ⁿ / 2
Are provided, and both ends of each coil are changeover switches
Is connected to the fixed contact of
Connected to one end of the
Either L or C passive element is the first
Connected to the fixed contact of the stage and the movable contact of the last stage,
The exchange switch has a number of bits equal to the number of secondary coils.
2. The burden device according to claim 1, wherein the burden device is constituted by an switch register.
Place.