JPS62207118A - Protective device for current limiting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] A. Industrial application field The present invention relates to a protection device for a current limiting element.

B. Summary of the Invention The present invention provides a method for suppressing overcurrent by being installed in a power system.
Detects liquefaction and vaporization from changes in resistance of the current-limiting element,
The breaker connected in series with the current limiting element is tripped and controlled by liquefaction detection and vaporization detection, the number of times of vaporization is determined by vaporization detection, and the breaker is tripped when the continuous allowable current flows through the current limiting element for a predetermined period or more. With this structure, the life of the current limiting element can be extended and it can be managed reliably while obtaining sufficient current limiting action.

BACKGROUND OF THE INVENTION In recent years, as power systems have expanded in scale and strengthened their wide-area connections, overcurrents during short circuits and ground faults have increasingly increased. As a result, system equipment such as circuit breakers and new line switches, as well as busbars, have become larger to withstand higher currents, increasing power equipment costs. Furthermore, an increase in electromagnetic induction interference,
Many problems have arisen, including increased damage at the failure point.

One method for suppressing this overcurrent is to install a current limiting element in series in the power system, which suppresses the current by increasing its resistance value due to Joule heat when a large current flows.

D8 Problems to be Solved by the Invention The current limiting water element described above suppresses overcurrent by rapidly increasing the resistance value by liquefying and even vaporizing the solid resistance due to the Joule heat generated when current flows. In such a current limiting element, if the temperature reaches a temperature that exceeds the limit of the element, the life of the element will be extremely shortened. For example, if the current continues to flow until it reaches a vaporized state, the life of the element will be reduced to a fraction of what it is. There was a problem. When this element reaches the end of its lifespan, it will no longer be able to perform its current limiting function, causing failures such as inability to shut off the circuit breaker in the power system, so protection and reliable management of the current limiting element is required.

Means and Function for Solving Problem E5 The present invention provides a resistance value detection means for detecting a change in the resistance value of a current limiting element, and a detection signal from the resistance value detection means that determines the resistance value at which the current limiting cord liquefies. a liquefaction detection means that detects that the current limiter has reached a value and controls the tripping of a breaker connected in series with the current limiter, and a detection signal from the resistance value detection means that detects that the current limiter has reached a resistance value that causes vaporization. vaporization detection means for tripping the breaker at high speed and determining the number of times the current limiting element is vaporized; The device is equipped with a time-limited overcurrent detection means for controlling the current-limiting element, and detects the current-limiting element in a liquefied state in which the current-limiting element can obtain its sufficient life, and trips the breaker, thereby extending the life of the current-limiting element in a relatively small overcurrent region. It reduces the number of times of vaporization, which has a large effect on The current is cut off by overcurrent detection to minimize deterioration and to prevent the structure heating limit from being exceeded due to a long-term continuation of a small overcurrent condition that slightly exceeds the continuous allowable current value.

F. Example FIG. 1 is a circuit diagram showing one embodiment of the present invention.

A breaker 2 is provided in series with the current limiting element 1 .

This breaker 2 is prepared for protecting the current limiting element 1 itself, and may be one that utilizes an existing breaker in the power system. The primary side of a voltage transformer 3 is connected in parallel to the current limiting element 1, and a voltage signal proportional to the voltage of the current limiting element 1 is taken out to its secondary side. The resistance value detection circuit 4 is configured to obtain the resistance value of the current limiting element l as a voltage signal from the detected voltage signal of the transformer 3 and the current detection signal from the current transformer 5 connected in series with the current limiting element 1. .

The liquefaction detection circuit 6 detects that the current-limiting element 1 has entered the liquefaction state by comparing the resistance value detection signal from the resistance value detection circuit 4 with a comparison standard. Similarly, the vaporization detection circuit 7 detects the vaporization state of the current limiting element l from the resistance value detection signal.

The overcurrent detection circuit 8 detects that the current flowing through the current limiting element l from the current detected by the current transformer 5 exceeds its continuous energization tolerance, and the timer 9 receives this detection signal as input. Detects that the process has continued beyond the set time limit.

The OR gate 10 obtains the trip output of the breaker 2 when at least one of the timer 9, the liquefaction detection circuit 6, and the vaporization detection circuit 7 has a detection output.

The liquefaction indicator 11 outputs the detection signal of the liquefaction detection circuit 6 as an indication of liquefaction of the current limiting element 1 and, if necessary, as a transmission signal to the monitoring room. Similarly, the vaporization indicator 12 displays and outputs the detection signal of the vaporization detection circuit 7.

The vaporization count hand 13 counts the detection signal of the vaporization detection circuit 7 as the number of times to display the number of times the current-limiting element 1 is in the vaporization state, and outputs it as a transmission signal to the monitoring room if necessary.

The protective operation of the current limiting element 1 with such a configuration will be explained in detail below.

First, the characteristics of the current limiting element l will be explained. The Joule heat generated when current flows through the current-limiting element l has a relationship of IR between the current value I and the resistance value R, and when the current value I becomes larger than the continuous current permissible value of the current-limiting element, the current-limiting element When the liquid begins to liquefy, the resistance value R also increases. Therefore, the Joule heat generated by the current limiting element increases exponentially with respect to the current value I. From this relationship between generated Joule heat and electric current,
The time it takes for a current-limiting element to liquefy or even vaporize varies depending on the magnitude of the current flowing through it.

FIG. 2 shows the liquefaction time versus the current of the current-limiting element 1.

Shows vaporization time characteristics. The figure shows the continuous current tolerance of 0.5KA.
(rms), and as shown in liquefaction time characteristic A and vaporization time characteristic B, when the element current is small (
However, if the continuous energization is above the allowable value, the time required for liquefaction and vaporization is extremely long (several hundred seconds to several thousand seconds). On the other hand, for both liquefaction time characteristic A and vaporization time characteristic B, the liquefaction time and vaporization time become exponentially shorter as the element current increases, and as the element current increases, the time difference between liquefaction and vaporization becomes exponentially smaller. .

It is desirable for the current limiting element 1 having such characteristics to extend its life by reducing as much as possible the occurrence of liquefaction due to generated Joule heat and vaporization.

Therefore, in this embodiment, as shown in FIG. 1, a breaker 2 is provided in series with the current limiting element 1, and the liquefaction detection circuit 6 detects the vaporization of the current limiting element 1, that is, the start of liquefaction from the change in resistance value. , This detection signal causes the OR gate IO to trip the circuit breaker 2, thereby preventing the current limiting element l from being vaporized. Here, in order to detect liquefaction from a change in resistance value, the liquefaction time with respect to the element current is determined from the characteristic A in Fig. 2, and compared to the case where the breaker 2 is tripped during this time, the fluctuation of the element current and the characteristics of the current limiting element are determined. It enables reliable liquefaction detection without being affected by changes, and in principle there is no possibility that temporal coordination with vaporization detection will be lost.

In the tripping control of the breaker 2 due to the liquefaction detection described above, there is a certain amount of delay, such as the operating time of the breaker 2, from the time of liquefaction detection until the current is cut off. This lag time is longer than the time from liquefaction to vaporization between characteristics A and B in FIG. 2, and in the large Nm region, the current limiting element is not vaporized. That is,
The current cutoff time due to tripping of the circuit breaker 2 due to liquefaction detection is as shown by the broken line C in Figure 2, and in the high current region where the time from liquefaction to vaporization of the current limiting element is short, the liquefaction time characteristic is If the current limit element 1 deviates from A and the element current exceeds 2.5 KA, the current is cut off after the current limit element 1 is vaporized, and deterioration of the current limit element 1 is unavoidable. Therefore, in this embodiment, the vaporization of the current limiting element l is detected at high speed by the vaporization detection circuit 7, and in addition to being displayed on the display 12, the vaporization count is accumulated and stored in the vaporization counter 13 to manage the element life. Make it sure and easy.

Furthermore, the output of the vaporization detection circuit 7 is also used to trip the circuit breaker 2 through the OR gate 1o, ensuring current cutoff of the current limiting element 1 by double blocking with liquefaction detection, and detecting the vaporization state by high-speed detection of vaporization. To reduce element deterioration by shortening the time as much as possible.

From the above, the liquefaction detection circuit 6 sets its comparison standard small so as to detect the initial stage of the value where the resistance increase of the current limiting element l reaches liquefaction, and the vaporization detection circuit 7 sets the comparison standard to a small value so as to detect the initial stage of the value where the resistance increase of the current limiting element l reaches the point where the resistance increase The standard of comparison is set large enough to detect the late stage of the value leading to vaporization.

Here, since the value of the vaporization detection circuit 7 is higher than the comparison standard of the liquefaction detection circuit 6, it can be designed to be strong against noise etc. even if it has a high-speed detection function, so ultra-high-speed detection is possible. When the device enters a vaporized state, the device current can be cut off as quickly as possible to minimize the effect on the device life.

Next, in an overcurrent region in which the continuous energization tolerance of the current limiting element 1 is slightly exceeded (0.5 in the figure), the liquefaction and vaporization of the element, that is, the increase in element resistance, become extremely slow as described above.

On the other hand, the heat resistance limit of the current limiting element 1 is limited by the allowable energization time due to the heat resistance limit of the structure, as shown by the characteristics in FIG.

The heat resistance limit of this structure is shorter than the liquefaction time and vaporization time in the small current region. Therefore, in this embodiment, the overcurrent detection circuit 8 detects that the current of the current limiting element l exceeds its continuous current permissible value, and when this detection state exceeds the time limit of the timer 9, the breaker 2 is triggered. Remove it to protect the current limiting element l from the structure's heat resistance limit. At this time, the time limit of the timer 9 is set near the time when the structure heat resistance limit time is longer than the liquefaction and vaporization time of the current limiting element 1, and is set to 100 seconds as characteristic E in the second diagram. At this time, when the current limiting element 1 is cut off before it is liquefied, the current limiting element 1 does not perform a sufficient current limiting operation, but the overcurrent value is sufficiently small and the overcurrent is can be cut off.

FIG. 3 shows another embodiment of the invention. The difference from the same figure or FIG. The resistance value detection circuit 4A determines the resistance value from the current detection signal from the current transformer 15.

It is obvious that the same effects as those of the above-mentioned embodiments can be obtained in this embodiment as well, and the explanation thereof will be omitted.

Effects of the G9 Invention As described above, according to the present invention, current is cut off by a series circuit breaker by detecting liquefaction and vaporization from changes in the resistance value of the current limiting element, the number of vaporizations is determined by vaporization detection, and further current limiting is performed. Since the current is cut off so that the overcurrent of the element does not exceed the structure heating limit, the following effects are achieved.

(1) Since the element current is cut off in the liquefied state of the current limiting element, there is no vaporization state that affects the life of the element for small overcurrents.

(2) When a small overcurrent continues, which extremely delays the liquefaction of the current limiting element, the current is cut off by overcurrent detection, which prevents the structure from burning out or breaking down at its heat resistance limit.

(3) Due to large overcurrent, there is a delay in the operation of the circuit breaker, etc. before vaporization. Although it is difficult to cut off tii7tE, the breaking capacity of the breaker can be small due to the overcurrent suppressing effect of the current limiting element, which can minimize the effect on the element life through high-speed cutting due to high-speed detection for vaporization detection.

(4) When vaporization occurs due to a large overcurrent, the element life can be reliably managed from information on the number of vaporizations.

(5) Since liquefaction and vaporization are detected from changes in the resistance value of the current-limiting element, it is possible to reliably detect liquefaction and vaporization and obtain protective action even when there are large fluctuations in overcurrent or changes in the characteristics of the current-limiting element. can.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing liquefaction and vaporization characteristics of a current limiting element, and FIG. 3 is a circuit diagram showing another embodiment of the present invention. l... Current limiting element, 2... Breaker, 4... Resistance value detection circuit, 6... Liquefaction detection circuit, 7... Vaporization detection circuit, 8... Overcurrent detection circuit, 9 ...Timer, 11.
... Liquification indicator, 12... Vaporization indicator, 13... Vaporization count hand, 14... Resistance, 4A... Resistance value detection circuit. - Drum d Yudenkatsu (rms)

Claims (1)

[Claims] In a current-limiting element installed in a power system that suppresses an overcurrent by increasing its resistance value using Joule heat generated during an overcurrent, there is provided a resistance value detection means for detecting a change in resistance value of the current-limiting element, and the resistance value of the current-limiting element. Liquefaction detection means detects from the detection signal of the detection means that the current-limiting element reaches a resistance value at which it liquefies and controls the circuit breaker connected in series with the current-limiting element to trip; vaporization detection means for detecting that the current limiting element has reached a resistance value at which it vaporizes and controlling the tripping of the breaker and determining the number of times the current limiting element vaporizes; 1. A protection device for a current-limiting element, comprising: a time-limited overcurrent detection means for tripping and controlling the breaker when the current flows for a period of time or more.