JPS6089761A - Wide band current transofrmer measuring current of power transmission line - Google Patents

Abstract

PURPOSE:To improve a frequency characteristic by connecting resistances dispersedly to the secondary winding of a window type current transformer, and also protect a light emitting diode for transmisson by connecting a saturable reactor to the secondary winding in parallel. CONSTITUTION:The secondary winding 1b of the window type current transformer body 1 using a ferrite troidal core 1a is provided with taps at intervals of a constant number of turns. Resistances 2 provided with taps at intervals of constant resistance are connected to the respective taps of the winding 1b correspondingly. The saturable reactor 3 for overcurrent protectionis connected across the winding 1b. Light emitting diodes 4 and 5 are connected to the winding 1b of the current transofmer body 1 and a positive and a negative half-wave component are converted into light signals, which are sent to a receiver 9 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a broadband current transformer for measuring current in a power transmission line.

Conventional current transformers that measure the current flowing in power systems use a silicon steel plate as a core and are constructed with multiple windings depending on the transformation ratio, so they inherently have a narrow frequency response range. Although commercial frequency current can be measured, it has been difficult to measure surge current waveforms when an accident occurs in a power transmission line system.

Therefore, an object of the present invention is to provide a broadband current transformer for measuring current in a power transmission line that can faithfully measure high frequency currents such as surge currents.

The broadband current transformer for measuring the current of a power transmission line according to the present invention has two
A through-type current transformer main body having a tap at every fixed number of turns in the secondary winding, and a tap at every fixed resistance value, which is connected in parallel to the secondary winding of the through-hole current transformer main body, and each tap is connected to the secondary winding of the through-hole current transformer main body. 2
A resistor connected to each tap of the next winding in a corresponding manner, a saturable reactor connected in parallel to this resistor, a light emitting element connected between both ends of this saturable reactor, and an optical signal output from this light emitting element. It is characterized by having a configuration that includes an optical fiber for transmission and a receiver for receiving the optical signal transmitted by the optical fiber.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a block diagram of a broadband current transformer for measuring four currents in a power transmission line according to an embodiment of the present invention. In Fig. 1, 1 is the main body of a through-type current transformer using a ferrite toroidal core, and the secondary winding lb has a number of turns depending on the current transformation ratio.
This secondary winding lb is provided with taps at regular intervals. 2 is a resistor made of nichrome wire, which has a total resistance value of R, and is connected in parallel to the secondary winding lb of the main body 1 of the through-hole type current transformer with taps provided at each constant resistance value (low value). , and each tap is sequentially connected to each tap of the secondary winding lb so as to provide a distributed load to the secondary winding lb. 3 is a saturable reactor y for overcurrent protection connected in parallel to the secondary winding lb of the feedthrough current transformer main body 1. 4 and 5 are light emitting diodes with the same characteristics, which are connected in antiparallel and connected between both ends of the secondary winding lb of the feedthrough current transformer body 1 via a current limiting resistor 6 (resistance value R2); The positive and negative half-wave components of the input current are each converted into optical signals. The current limiting resistor 6 also incorporates a negative characteristic thermistor for temperature compensation of the light emitting diode 4.5.

7 and 8 are optical fibers that transmit the optical signal output from the light emitting diode 4.5, and 9 is a receiver that receives the optical signal transmitted through the optical fiber 7.8.

If the primary current of the feedthrough current transformer main body 10 is IP and the current transformation ratio is 1, the secondary current I8 of the feedthrough current transformer main body 1 is 1-''LS, ......(11). Therefore, if the forward resistance of the light emitting diode 4.5 is ignored, the terminal voltage V of the resistor 2 is expressed by the following equation.

Further, the drive current i flowing through the light emitting diode 4.5 is expressed by the following equation.

2-input current of feedthrough current transformer body work in non-saturation region■8
Since the current increases in proportion to one input current Ip, the current flows up to about 400 times the rated value in the event of a power transmission line fault.

Therefore, the terminal voltage V of the resistor 2 also rises, but this value is an important issue related to the destruction of the light emitting diode 4.5. Therefore, the best operating voltage at the rated time is selected in consideration of linearity, and the surge Although the voltage is allowed to be about 400 times the rated voltage, it is necessary to suppress the commercial frequency voltage to about 4 times.

For this reason, a saturable reactor 3 having excitation characteristics as shown in Fig. 2 is connected in parallel to the resistor 2, and the rise in the commercial frequency component of the terminal voltage V of the resistor 2 is suppressed to about four times the rated value, and the terminal The surge component of the voltage V is designed to increase linearly to about 400 times the rated value. In Figure 2, the vertical axis represents the terminal chamber [EV of the saturable reactor)/L'3, the horizontal axis represents the excitation current I, and the voltage and current at the rated value are f', respectively.
Lvn and In, the 4 times overvoltage is 4vn, the current at that time is 4In, the solid line Yl indicates that the magnetic core begins to saturate at 4I, and the dashed line Y2 indicates that the magnetic core does not saturate. .

The magnetic permeability of the magnetic core is μ, and the air core inductance is . Then, the inductance of saturable react/l/3 is expressed as L2μLo... (4) and changes as a function of μ, and its impedance Z is Z = 2ifL, assuming the AC frequency is fHz.
= 2*fμL□ ”” (5). Therefore, in a high frequency band (surge current), even if the magnetic permeability μ is low, the frequency f is high, so the impedance 2 is sufficiently large. On the other hand, in the commercial frequency band (commercial frequency current), the magnetic permeability μ is high, so even if the frequency f is low, the impedance 2 is sufficiently large. The following relationship is established between the impedance Z, the resistance m2, and the current limiting resistor 6 during normal operation.

R engineering << R2 << Z... (6) When magnetically saturated, the magnetic permeability μ of the magnetic core becomes 1, so in the low frequency commercial frequency band, the impedance 2 is reduced to R engineering and R2. On the other hand, Z <R<< R2・- (71), and when the terminal voltage V of the resistor R2 is suppressed and the primary current of the feedthrough current transformer main body 1 becomes excessive, the light emitting diode 495 is protected. On the other hand, in a high frequency band with a high frequency f, the magnetic permeability μ is low from the beginning, but the frequency f is high, so
The relationship of Equation 61 is maintained, and the terminal voltage V of resistor 2 is not suppressed. Therefore, against surge current, the terminal voltage V of resistor 2 rises to about 400 times the rated value. As a result, the commercial frequency current can be suppressed by about four times, making it possible to measure surge currents during transmission line faults.

The light output of the light emitting diode 4.5 is proportional to the drive current i,
As is clear from equation (3), the drive current i is proportional to the terminal voltage V of the resistor 2, so the light emitting diode 4.5 sends a light output proportional to the terminal voltage V to the optical fiber 7.8. The receiver R installed at the receiving end restores the amplitude modulated optical signal sent out and υ transmitted through the optical fiber 7.8 into an electrical signal, and corrects the threshold distortion of the light emitting diode 4.5 using an appropriate method. It outputs a voltage or current proportional to the primary current IP of the feedthrough current transformer main body 1.

In this way, this embodiment uses a winding l in the feedthrough current transformer main body 102'/ which uses a ferrite core and has good frequency characteristics.
A resistor 2 is connected in parallel to the secondary winding 1b of the through-type current transformer body 1 to further improve the frequency characteristics by distributingly connecting a resistor 2 to the current transformer body 1. The secondary current of the feedthrough current transformer main body 1 is converted into light with good linearity by a light emitting diode 4.5, and the optical fiber 7 is
．． 8 to transmit the measured values, it is possible to faithfully measure the transient current waveform of a power transmission line fault.

As described above, the broadband current transformer for measuring current in a power transmission line according to the present invention has the effect of being able to faithfully measure high frequency currents such as surge currents.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the excitation characteristics of a saturable reactor.

Claims (1)

[Claims] A through-type current transformer main body having a tap for each fixed number of turns in the secondary winding, and a through-type current transformer main body having a tap for each fixed resistance value and connected in parallel to the secondary winding of the above-mentioned through-type current transformer main body, and each tap A resistor connected in a corresponding manner to each tap of the secondary winding, a saturable reactor connected in parallel to the resistor, a light emitting element connected between both ends of the saturable reactor, and light output from the light emitting element. A broadband current transformer for measuring current in a power transmission line, comprising an optical fiber for transmitting a signal and a receiver for receiving the optical signal transmitted by the optical fiber.