JPS58179122A - Transformer protecting relay unit - 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 The present invention relates to a transformer protective relay device, and more particularly to a transformer protective relay device that prevents malfunctions caused by excitation inrush current of a transformer.

Conventionally, transformer protection in the event of an abnormality such as a winding failure in a transformer is achieved by using a current differential signal taken out by a current transformer as an equivalent current signal corresponding to the total transformation ratio of the current passing through each terminal of the protected transformer. Alternatively, a current ratio differential method is often used. In current differential or current ratio differential systems, differential current is generated when there is an internal fault in the transformer, but due to the so-called excitation inrush current that occurs when the transformer is energized with no load or when the voltage rotates when removing an external fault, etc. A differential current also occurs.

Conventionally, magnetizing inrush current and internal fault current are distinguished from the uniqueness of the magnetizing inrush current waveform to prevent malfunctions caused by magnetizing inrush current. One method is to fully utilize the fact that the proportion of the second harmonic component in the magnetizing inrush current is higher than that in the fault current, and when the proportion of the second harmonic component in the differential current is above a certain value, A method is used in which the current is determined to be an excitation inrush current and a breaker tripping command is not output.

However, with this method, it takes at least one cycle to detect the characteristic of the excitation inrush current that has a high proportion of second harmonic components, and even in the event of an internal failure, the breaker trip command is output for at least this time. There is a problem in that the process must be delayed, which hinders high-speed operation. Furthermore, recently, cable systems have been widely used, and it has been pointed out that due to an increase in ground capacitance, the fault current in the event of an internal fault in a transformer includes many harmonic components. Depending on the ground capacitance, reactance, and transformer impedance of the system, the fault current may contain low-order harmonics near the second harmonic, and in this case, the conventional method described above may delay the operation of the transformer protection relay device. There is a risk that the transformer tank may be destroyed due to malfunction or malfunction, resulting in a serious disaster.

Another conventional method for preventing malfunction of the transformer protective relay device due to transformer excitation inrush current is to prevent the output of the breaker trip command for a certain period of time at the beginning of no-load excitation of the transformer. There is.

In the case of this method, the protective operation against an internal failure at the time of no-load excitation of the transformer is delayed, and there is a drawback that malfunctions due to inrush current when removing an external failure, inrush current when turning on a parallel transformer, etc. cannot be prevented.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to detect the transformer's magnetizing inrush current at high speed, and to completely block the breaker tripping command, thereby preventing malfunctions caused by the magnetizing inrush current. The present invention provides a transformer protection relay device that can operate at high speed in the event of an internal failure.

The present invention is a means for detecting the magnetizing inrush current of a transformer at high speed, by focusing on the fact that when the magnetizing inrush current is flowing, the transformer core is magnetically saturated and a large amount of magnetic flux leaks out of the core. When the amount of leakage magnetic flux or the change in the amount of leakage magnetic flux exceeds a certain value, it is determined that there is an excitation inrush current, and a breaker trip command in the current differential or current ratio differential method is blocked.

In order to clarify the features of the present invention, first, the relationship between the magnetizing inrush current phenomenon of the transformer and the leakage flux from the iron core, and the leakage flux detection means will be explained. Figure 1 shows the excitation current of the transformer.
The relationship between B and magnetic flux density B in the iron core is shown. As is well known, when the magnetic flux density B exceeds the saturation magnetic flux density of 8 R of the transformer core material, the exciting current 0 increases rapidly. When the transformer is operated normally, the magnetic flux density B is the saturation magnetic flux density B-
The magnetic flux generated by the exciting current generator 0 circulates in a closed magnetic path within the iron core, and hardly leaks out of the iron core.

However, when the magnetic flux density B exceeds the saturation magnetic flux density B@, such as when the transformer is excited with no load, the magnetic permeability of the transformer core becomes almost equal to the permeability of air or transformer oil, so the exciting current I
Of the magnetic flux produced by o, the portion exceeding the saturation magnetic flux density Bl has the same distribution as in the case without the iron core, and leakage magnetic flux φL is generated in the space outside the iron core. Therefore, it is clear that the relationship between the leakage magnetic flux φL from the iron core and the magnetic flux density B in the iron core, as shown in FIG. 2, is almost the same as the relationship between B and Io shown in FIG. 1.

FIG. 3 shows an example of the distribution of leakage magnetic flux φL due to excitation current 0 when the transformer core is saturated. For the sake of simplicity, FIG. 3 schematically shows the case of a center core type single-phase transformer, where 1 indicates the transformer core and 2 indicates the winding.

The means for detecting the leakage magnetic flux φL may be installed anywhere within the transformer tank, but it is necessary to prevent it from being affected by the magnetic flux due to the load current and internal fault current when it is healthy. For this purpose, it is preferable to install it close to the core at a portion of the core yoke portion on the opposite side facing the windings, as shown by, for example, a-b and C in FIG. Since the iron core is not magnetically saturated when it is healthy or when there is an internal failure, the magnetic flux due to the load current and internal fault current passes through the iron core as shown in the leakage magnetic flux φL in Figure 3 and reaches the positions indicated by a, b, (). There is almost no influence that occurs at the position indicated by t be c when it is inserted from the outside.Therefore, among the magnetic flux generated outside the transformer core, the leakage magnetic flux φL due to the exciting current wire 0
It is extremely easy to select and detect only those. In addition, in addition to the following positions shown in Figure 3 as an example, selecting a position where the magnetic flux in the iron core easily leaks to the outside, such as near the joint of the iron core, is important for the high sensitivity of detecting leakage magnetic flux φL. The direction of the leakage magnetic flux φL is 'l b as shown in Figure 3.
, C, etc., the direction of the leakage magnetic flux φL to be detected may be appropriately determined depending on the location where the magnetic flux detection means is installed so as to achieve high sensitivity.

Conventional magnetic flux detection means for detecting the leakage magnetic flux φL from the iron core due to the excitation current Io include elements that utilize the Hall effect of semiconductors, methods that utilize the optical Faraday effect, and so-called search coils that utilize the magnetic induction effect of coils. Various technologies have been developed since then. Although each principle is different, it is possible to obtain an output corresponding to φL. Figure 4 shows the time differential waveforms of the excitation inrush current Io, leakage magnetic flux φL from the iron core, and φL. For example, in the case of an element using the Hall effect, the voltage output is almost proportional to the magnetic flux φL, but, To fully integrate this, it is proportional to φL'
Wa: Pressure is obtained. In addition, the method using the optical Faraday effect has the characteristic that information of the magnetic flux φ can be extracted from the optical fiber, which is an electrical insulator, to the outside of the transformer tank.

When the value exceeds the initial value as described above, it is possible to detect that the transformer core is magnetically saturated and determine that an excitation inrush current is flowing.

Next, the present invention will be explained in detail with reference to FIG. FIG. 5 is a schematic diagram showing an embodiment of the present invention, in which 1 is the core of the transformer to be protected, 2 and 3 are the primary and secondary windings wound around the core 1, respectively, 4 is the core and The transformer tank that stores the windings, 5.6 are the primary and secondary circuit breakers, 7 and 8 are the primary and secondary current transformers, respectively, 9 is the ratio differential joint element, and 1o is the above element. 11 is a magnetic flux detection relay element, 12 is a timer for extending the output of the magnetic flux detection relay element, and 13 is an inhibit circuit.

In the embodiment of the present invention shown in FIG. 5, the operation time chart when a magnetizing inrush current occurs in the transformer to be protected is shown in FIG. 6.The operation of the embodiment of the invention shown in FIG. Explain. Even in the case of the analog method, the operation of the ratio differential relay element 9 is relatively fast as shown in FIG. As described above, the leakage magnetic flux φL from the iron core has almost the same waveform as the excitation inrush current, that is, the differential current flow. The magnetic flux detection relay element 11 operates based on the output of one or more magnetic flux detection means 1o when it is determined that the leakage magnetic flux φL from the iron core has exceeded a certain value. The timer 12 prolongs the output of the magnetic flux detection network '#1 element 11 by about tl cycles. As described above, no breaker tripping command is issued from the inhibit circuit 13. If the magnetic flux detection relay element 11 is an analog system like the ratio differential relay element 9 and has an appropriate time constant, the timer 12 is not necessarily required. However, in the case of excitation inrush current, it is necessary to configure the magnetic flux detection relay element 11 to operate faster than the ratio differential relay element 9. In order to prevent malfunctions due to differential currents that occur even when the current transformer is in good condition due to current transformation ratio errors, etc., the minimum operating current of the ratio differential relay element 9 is normally set to 10 to 20% or more of the rated current. On the other hand, by selecting the installation location of the magnetic flux detection means 10 as described above, the leakage magnetic flux φL from the core when the transformer core is not magnetically saturated can be made almost zero. The magnetic flux detection relay element 11 can make the ratio differential relay more sensitive than the element 9, and can easily operate quickly. On the other hand, when the circular part fails, the magnetic flux detection relay element 11 does not operate, so a breaker tripping command is output from the inhibit circuit 13 at the same time as the ratio differential relay element 9 operates. In the conventional method, even if the ratio differential relay element operates quickly, it takes more than one cycle to determine the waveform, and the output of the breaker trip command is delayed by this time. High-speed operation is possible.

Another embodiment of the invention is shown in FIG. In FIG. 7, parts that are the same as those in FIG. 5 are given the same reference numerals, and explanations thereof will be omitted. 7th
The difference between the figure and FIG. 5 is that the timer 12t-inhibit circuit is placed at the latter stage. FIG. 8 shows an operation time chart when inrush ta occurs in the transformer to be protected in FIG. 7. If the ratio differential relay element 9 is of a digital type, it can be operated with almost no time delay with respect to the differential current (2), as shown in FIG.

The operation of the magnetic flux detection relay element 11 is the same as that described in FIG. 6, but it operates earlier than the ratio differential relay element 9 and returns later. This is achieved by making the element 11 in the magnetic flux detection joint 1 more sensitive than the element 9 in the differential joint as described above.

Therefore, the inhibit circuit 13 does not operate, and no breaker trip command is output. When an internal failure occurs, the magnetic flux detection relay element 11 does not operate, and the I/HIBIT circuit operates at the same time as the ratio differential relay element 9 operates, and a breaker trip command is output. The one shown can operate at high speed. The timer 12 is used to continuously output a breaker trip command in response to intermittent operation of the ratio differential relay element 9 and the inhibit circuit in the event of an internal failure.

The embodiment of the present invention shown in FIG. 7 has a feature that it can operate at high speed even when the excitation inrush current and internal fault current are superimposed. This will be explained below using the operation time chart of FIG. The differential current circuit in FIG. 9 shows the case where the magnetizing inrush current and the internal fault current that occurs at the same time as the magnetizing inrush current starts to flow are heavy. The difference from FIG. 8 is that the ratio differential relay element 9 responds even to the negative half wave of the differential current, and the I/HIBIT circuit 13 operates. By timer 12]
The output of the enable/hibit circuit 13 is extended, and a breaker tripping command is output. This enables extremely high-speed operation compared to the conventional method in which the magnetizing inrush current is determined based on the second high wave component content rate of the differential current, in which the breaker tripping command is not output until the magnetizing inrush current has attenuated. . When a breaker is turned on and energized without load while an internal fault such as a short circuit in the windings of the transformer remains, or when an internal fault occurs before the transformer core reaches magnetic saturation after the breaker is turned on, etc. Then, before the magnetic flux detection relay element 11 detects the leakage magnetic flux φL, an internal fault current flows and the ratio differential relay element 9 and the I/HIBIT circuit 13 operate, so the breaker tripping command is issued at an even higher speed. It can be output.

If the voltage phase applied to the winding in a healthy part changes due to a short-circuit failure in the transformer winding, or if the voltage becomes higher than when it was healthy, and magnetic saturation occurs in the iron core, the differential current will still change internally. In such a case, the degree of magnetic saturation of the core is lower than when the transformer is excited with no load, and the time for magnetic saturation is one cycle. This is a very short period of time. Therefore, similarly to the above, the ratio differential relay element 9 is operated by the internal fault current during the period when the iron core is not magnetically saturated, and the breaker trip command can be outputted at high speed. If a high voltage is applied to the winding in a healthy part due to an internal failure and the iron core is magnetically saturated on both positive and negative sides, the magnetic flux detection relay element 11 responds only to the magnetic flux in the same direction as the first detected leakage magnetic flux φL. If this is done, the magnetic flux detection element 11 will not operate against the leakage magnetic flux φL due to magnetic saturation in the opposite direction, and the breaker tripping command can be reliably output as in FIG. 9. This is effective in improving the operational reliability and performance of the transformer protection relay device in the event of an internal failure. In addition, when such a configuration is adopted, after the leakage flux detection relay element 11 operates, in order to ensure that the leakage flux detection relay element 11 can operate in response to the next excitation inrush current, an appropriate cycle of approximately one cycle or more is required after the leakage flux detection relay element 11 operates. After the time has elapsed, it is possible to operate with respect to both positive and negative side leakage flux.

In the embodiments of the present invention described above, a current differential system is used as an example of a relay element for detecting an internal failure of a transformer. It is clear that the present invention can also be applied to the current phase comparison method used to protect regulating transformers. In this case, by applying the present invention, even if the relay element that detects the internal fault operates with the excitation inrush current, the breaker tripping command can be reliably blocked, so the internal fault detection sensitivity can be increased. It has the characteristic that it can be done. In addition, in order to improve the reliability of preventing malfunctions of transformer protective relay devices due to excitation inrush current,
For example, the OR judgment output of the conventional output determined to be a magnetizing inrush current based on a differential current waveform and the output of the magnetic flux detection relay element 11 is inputted to the timer 12 in FIG. 5 or the inhibit circuit 13 in FIG. Also good. In short, it should be understood that a structure configured to detect the leakage magnetic flux φLt from the transformer core and prevent the breaker from being issued a tripping command falls within the scope of non-invention.

As detailed above, according to the present invention, the magnetic saturation of the transformer core can be reliably detected with a simple configuration, thereby preventing malfunction of the transformer holding relay device due to excitation inrush current, and preventing the malfunction of the transformer holding relay device due to magnetizing inrush current. This has the effect of reliably outputting the breaker trip command at high speed.

[Brief explanation of the drawing]

1 to 4 are route diagrams for explaining the relationship between the excitation current of the transformer and the leakage magnetic flux from the iron core, FIG. 5 is a route diagram showing one embodiment of the present invention, and FIG. FIG. 7 is a route map showing another embodiment of the present invention, and FIGS. 8 and 9 are time charts for explaining the operation of the embodiment shown in FIG. . 1... Iron core, 2.3... Winding wire, 5.6... Breaker, 1st 22nd 30th

Claims (1)

[Scope of Claims] 1. In a transformer protective relay device that detects an internal failure in a transformer and outputs a breaker trip command, a magnetic flux detection system that detects leakage magnetic flux from the iron core in the transformer. A transformer protection relay device comprising: means for blocking a tripping command for the breaker according to the output of the magnetic flux detecting means. 2. Claim 1, characterized in that the magnetic flux detection means is installed close to the core in a core yoke portion of the protective transformer at a position where the influence of magnetic flux due to load current and internal fault current is small. Transformer protection relay device as described in .