JPS6325487B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a DC current transformer, for example,
This invention relates to the improvement of a DC current transformer suitable for measuring large currents used in DC power transmission.

[Conventional technology]

As for DC current transformers, in addition to Utility Model Application Publication No. 141322/1963, there is also a book called ``Introduction to Magnetic Amplifiers'' (co-authored by Eijiro Miyazawa and Takeshi Anayama, published by Denki Shoin), the fifth edition of which was published on April 20, 1962. Chapter 2, page 12 discloses the basic form of a magnetic amplifier. A DC current transformer shown in FIG. 1 in which a rectifier circuit is connected to this basic type is known.

In FIG. 1, a DC current transformer 100 is excited by a single-phase AC power source 200 to measure DC current. The DC current transformer 100 has two reactors that have primary windings 1 and 2 that pass through two iron cores 5 and 6, and secondary windings 3 and 4 that are wound around the iron cores 5 and 6. are connected in series, and a single-phase AC power supply 200, a full-wave rectifier 7, and a load resistor 8 are connected in the secondary circuit.
It consists of connecting. Such a DC current transformer 100 has a measured current flowing through the primary winding ± _c
With respect to the input magnetomotive force ±F _c , the output current i _L has a relationship as shown in Fig. 2 when viewed as an average value.

That is, as stated in Chapter 4, page 5 of the above-mentioned document, when the current to be measured is less than the scheduled value, the output current is accurately proportional to the current to be measured, but if the current to be measured exceeds the scheduled value. The saturation period expands so as to narrow the current transformer operating period for each half cycle, resulting in nonlinear characteristics. Furthermore, as the current to be measured increases, the output current finally saturates.

In order to accurately measure direct current, it is desirable to use the proportional region shown in Figure 2, and the design is such that the central magnetomotive force ±F _c1 of this proportional region can be obtained at the center value of the planned current to be measured. This is desirable.
Therefore, the output power i _L of the current transformer 100 obtained from the planned center value of the current to be measured is i _L1 .

[Problem that the invention seeks to solve]

However, the current transformer 100 designed in this way
If an excessive current I _c that gives a magnetomotive force of ±F _c2 flows into the magnet, the output current i _L will be several times as large as i _L2 .

In such a DC current transformer 100, if an excessively large current to be measured flows through the primary winding, the output current _iL will also become excessive, causing problems such as overheating of the secondary winding or, in the worst case, burning out. It was hot.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC current transformer that can solve the above-mentioned problems in the prior art and can prevent the secondary winding from overheating, burning out, etc. even when the current to be measured becomes excessive. be.

[Means for solving problems]

A feature of the present invention is that the AC power source for the DC current transformer is provided with an AC power source having current-voltage characteristics such that the voltage suddenly drops when the current exceeds a predetermined value.

[Effect]

With this configuration, when the current to be measured exceeds the scheduled value, the current transformer operating period in each cycle is narrowed due to the drop in the AC power supply voltage, the saturation period is expanded, and the average output current is suddenly reduced. Decrease.

Although Figures 4 and 4 of the above-mentioned document express an increase in the measured (control) current, this effect shows that even if the measured current is held constant and the AC power supply voltage is decreased, the relative It is clear from the magnitude relationship that a similar phenomenon occurs and the increase in output current is suppressed.

〔Example〕

The present invention will be explained below with reference to the drawings.

FIG. 3 shows a single-phase AC power source of a DC current transformer 100 similar to that shown in FIG.
A single-phase AC power supply 201 having current-voltage characteristics is used. Now, as shown in FIG. 4, when the characteristics of the output current I and output voltage V of the single-phase AC power supply 201 reach a certain scheduled current _I0 , the output voltage V suddenly decreases. shall be taken as a thing.
Single-phase AC power supply 20 with such current-voltage characteristics
1 is used as the power source of the DC current transformer 100, the input-output average value characteristic as a current transformer is as shown in FIG. Now, when the measured current I _c of the primary winding increases and the input magnetomotive force F _c increases, the output current i _L of the current transformer increases in proportion to it, and when the input magnetomotive force further increases, the output The current i _L also increases. However, since the voltage of the single-phase AC power supply 201 that supplies the output current i _L suddenly drops when the current exceeds the scheduled current I ₀ , the output current i _L cannot increase above I ₀ . That is, a and b in FIG. 6 show the AC power supply 201 when a normal magnitude of current to be measured is flowing.
output voltage es, secondary winding current ia and load resistance 8
This is the output current i _L waveform. The figure shows how the iron core 5 of the upper saturable reactor is set and reset (the voltage/time product is the same). The period from time t ₁ to _{t 2} is a current transformer operation (non-saturation) period, and the other periods are saturated periods (current transformer operation period of the lower saturable reactor).

In c and d of the same figure, the current to be measured I _c exceeds a predetermined value, and the output voltage es of the AC power supply 201 is thereby reduced. During the period t ₂ - _{t 3} , the amount (voltage-time product) set on the hysteresis characteristic curve of the iron core 5 of the upper saturable reactor is small, and therefore, during the short period t ₃ - t ₄ The iron core 5 becomes saturated. Therefore, the current transformer operating period is shortened from _t2 to _t4 , and even if the peak value of the output current _iL becomes high, the width becomes narrower, and the average output current tends toward saturation and does not increase.

In the end, as shown in Figure 5, the DC transformation is precisely proportional to the current to be measured I _c in the desired region, and the output current i _L does not increase for the current to be measured that exceeds the planned value. The characteristics of the instrument can be obtained.

As a result, the input magnetomotive force F _c0 when the output current is I ₀
Even if the above-mentioned excessive input magnetomotive force is applied to the DC current transformer 100, the output current i _L will not increase beyond a certain value, and the excessive current will flow through the DC current transformer secondary winding circuit. It does not flow and can prevent winding overheating and burnout.

The present invention can also be applied to a DC current transformer 101 having a circuit configuration as disclosed in the above-mentioned Japanese Utility Model Application No. 53-141322 as shown in FIG. In FIG. 7, a DC current transformer 101 includes two iron cores 15 and 16.
The primary windings 11 and 12 passing through the cores 15 and 1
Two reactors consisting of secondary windings 13 and 14 wound around diodes 17, 18, 19, 20
It consists of a closed circuit in which a limiting resistor 21 is connected between the cathode of the diode 17 and the anode of the diode 18, and a load resistor 22 is connected between the cathode of the diode 19 and the anode of the diode 20. A single-phase AC power supply 201 having the characteristics of
The diode 20 is connected between the anode of the diode 9 and the cathode of the diode 20. At this time, the DC alternator 10
The input-output characteristics of the DC current transformer 101 having such input-output characteristics are as shown in FIG.
When a single-phase AC power source 201 having current-voltage characteristics as shown in FIG. 4 is used as an AC power source, the input-output characteristics of the current transformer will be as shown in FIG. 9. In other words, the input magnetomotive force F _c due to the current to be measured I _c flowing through the primary winding
When _the output current i _L , which is proportional to Excessive current does not flow through the next winding circuit, and winding overheating, burnout, etc. can be prevented.

FIG. 10 shows a circuit diagram of an embodiment of a single-phase AC power supply having current limit characteristics, and FIG. 11 shows voltage waveform diagrams of various parts for explaining its operation. In Figure 10,
E _s is input AC voltage, Tr1, Tr2 and transformer, SR
is a full-wave rectifier circuit, FL1 is a first filter consisting of an inductance L1 and a capacitor C1,
PWM is a pulse width modulation inverter (DC/AC inverter), GPS is a gate phase shifter, FL2 is a second filter consisting of inductance L2 and capacitors C2 and C3, CT is an AC current transformer, and E ₁ to _{E 4}
indicate the voltage at the indicated position. AC input voltage
E _s is transformed by transformer Tr1, and the full wave rectifier circuit SR
It is full-wave rectified into E ₁ and converted into DC voltage E ₂ by filter FL1. This DC voltage E ₂ is converted into a rectangular wave AC voltage E ₃ by the pulse width modulation inverter PWM, which becomes a sine wave AC voltage by passing through the filter FL 2, and is transferred to the output transformer Tr.
2, it is output as AC voltage _E4 . The current limiter operation is performed as follows. The output voltage _E3 of the pulse width modulation inverter PWM is a rectangular wave voltage with a rest period, as shown in FIG. The peak value when this voltage E ₃ is converted into a sinusoidal AC voltage by the filter FL2 changes depending on the pulse width θ of the rectangular wave voltage E ₃ . Therefore, the output voltage of the pulse width modulation inverter PWM is converted into a sinusoidal AC voltage by the filter FL2, and the AC current of the circuit is detected by the AC current transformer CT, and this current value and the set current value (this set current value is the current (which is the upper limit value),
When the detected current value exceeds the set current value, the gate phase shifter GPS for the pulse width modulation inverter PWM is narrowed down, and the output voltage pulse of the pulse width modulation inverter is adjusted as shown in E ₃ ' in Figure 11. Reduce the width θ'. Since this rectangular wave voltage becomes E ₃ ', the sine wave AC voltage after passing through the filter FL2 decreases, and the output voltage becomes a current limiter mechanism having drooping characteristics at the same time as overcurrent is detected.

〔Effect of the invention〕

According to the present invention, even when an excessively large current to be measured flows through a DC current transformer, overheating and burnout of the secondary winding can be prevented.

[Brief explanation of drawings]

Fig. 1 is a conventional DC current transformer circuit diagram, Fig. 2 is an input-output characteristic diagram of the DC current transformer shown in Fig. 1, and Fig. 3 is a configuration diagram of a DC current transformer according to an embodiment of the present invention. , FIG. 4 is a current-voltage characteristic diagram of an AC power supply used in an embodiment of the present invention, FIG. 5 is an input-output characteristic diagram of a DC current transformer adopting the configuration of the present invention shown in FIG. 3, and FIG. 6 is an explanatory diagram of the operation of the present invention, FIG. 7 is a block diagram of a DC current transformer according to another embodiment of the present invention, and FIG.
Figure 9 is an input-output characteristic diagram of the original DC current transformer shown in Figure 7. Figure 9 is an input-output characteristic diagram when the AC power supply of the present invention is used in the DC current transformer of Figure 7. FIG. 11 is a circuit diagram of an embodiment of an AC power supply suitable for use, and is a voltage signal waveform diagram of each part for explaining its operation. 1, 2, 11, 12...Primary winding, 3, 4, 1
3, 14... Secondary winding, 5, 6, 15, 16...
Saturable core, 8, 22...Load resistance, 100, 1
01...DC current transformer, 200...AC power supply, 20
1...An AC power supply with sudden voltage drop characteristics.

Claims (1)

[Scope of Claims] 1. A pair of saturable reactors having a saturable iron core, a primary winding and a secondary winding through which a current to be measured flows, a load resistor, and a pair of the secondary windings and the load resistor. In a DC current transformer, the AC power source is connected in a circuit through which the pair of saturable reactors alternately have a current transformer operation period and a saturation period in opposite phases to each other. A DC current transformer characterized by being equipped with an AC power source that has current-voltage characteristics that cause the voltage to drop suddenly when the voltage exceeds a certain value.