JPS60162414A - Transformer protective relay - 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 [Field of Application of the Invention] The present invention relates to a current differential type transformer protection relay, and more particularly to a fault detection type protection relay that is capable of highly sensitive determination even in the case of distorted waves of fault current.

[Background of the invention]

Conventional transformer protection relays detect internal faults when the difference in equivalent current passing through the transformer, that is, the current differential output signal, is greater than a predetermined value and the content of the second harmonic component is less than a predetermined value. A method is used to determine this.

However, in the conventional method, if the fault current contains harmonics, especially low-order harmonics close to the second harmonic, it is mistakenly recognized as an excitation inrush current, and the desired protection performance cannot be obtained.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art,
The purpose is to detect internal faults in transformers with high sensitivity.

[Summary of the invention]

In order to achieve the above object, the present invention uses a conventional excitation inrush current detection method using second harmonic suppression and a time width in which the instantaneous value of the current differential output signal reaches a predetermined level within a fixed interval. It is determined whether or not the excitation inrush current causes a break using the energization angle detection element that detects the energization angle.

[Embodiments of the invention]

FIG. 1 is an overall configuration diagram for explaining the present invention in detail. The contents of the operation shown in the figure will be explained.

Symbols 1p and Is in the same figure are the windings of transformer 1 to be protected.
Let p k be the primary side, and 18 be the secondary side. Hereinafter, the numerical subscript P indicates the primary side of the transformer, and S indicates the secondary side of the transformer. For convenience of explanation, the winding ratio of IP and 18 is assumed to be 1:1.

2p and 2tr are current transformers υ, and the protection relay BY of the present invention
This is for converting the signal appropriately and inputting it. 2P
Let the output signal of 2s be Ip, and the output signal of 2s be k I s.

Ip is the input current of the primary side IP of the transformer, I+i is the input current of the transformer 2
3p which is a signal proportional to the input current of the next side 18
, 3m is a circuit breaker, which is used to disconnect the transformer 1 from the system when a shutdown command output is given from the protection relay BY due to internal fault determination. Next, protect relays R, Y
I will explain the contents.

4 is an adder for adding input signals Ip and Is, and its output corresponds to a so-called current differential output.

Let the output of adder 4 be kID. Reference numeral 5 denotes an overcurrent relay, which generates an operational output when ID is equal to or greater than a predetermined value. However, since the overcurrent relay 5 may provide an operational output when a magnetizing inrush current flows through the transformer winding IP or 1s, a separate measure to prevent malfunction due to the magnetizing inrush current is required. In addition, the current input Ip is also affected by the ratio error of the current transformers 2p and 2s.

The difference current Iv occurs when the power supply 8 becomes a large current such as during an external accident.
may enter the operating range of the overcurrent relay 5, and the current Ip
, Is, etc. may be used as a countermeasure by using a ratio differential relay in which the detection sensitivity can be completely varied depending on the absolute value of , Is, etc. However, in any case, the relay 5 may malfunction due to the excitation inrush current. 6 and 7 are relay elements for preventing 5 from malfunctioning due to excitation inrush current.

6 is the ratio of the second harmonic included in the ID below a predetermined value,
It is a so-called harmonic ratio detection element that generates an operational output only when the level of the difference current In is above a certain level. Reference numeral 7 denotes an energization angle detecting element of the present invention that determines the level of the absolute value of Iv and generates an operational output when a level higher than a predetermined value exists for a certain period of time. 8
is an OR gate which generates an operating output when at least one of relay elements 6 and 7 operates. Therefore, since relay elements 6 and 7 must not operate in response to the excitation inrush current, it is necessary to have a device that can reliably detect the excitation inrush current. 9 is an AND gate, which connects the output of overcurrent relay 5 and OR gate 8.
The operational output is only when the operational output signals of the outputs of the ip.

18 accident judgment output money is given, and a cutoff command is given to 3p and 3g.

Here, the operating method of the relay elements 6 and 7 will be explained in more detail.

The operation formula of 6 is 1IoI KRrl KL≧0 ・・・・・・
...It is expressed as (1).

However, KE: harmonic suppression coefficient KL: judgment level IDIII): harmonic component included in ID,
For example, a signal centered on the second harmonic.

It is.

However, the waveform of the excitation inrush current varies depending on the magnetization characteristics of the transformer, the turning-on phase angle of the applied voltage, etc., and there are differences as shown in FIGS. 2(a) and 2(b), for example.

Fi(a) is a case in which the magnetic saturation is in a small range, the excitation inrush current is applied for a short time, and the second harmonic content is relatively large. In such a case, relay element 6
Detection by Kzk is also not so large and is possible under low sensitivity conditions. However, in the case shown in Figure (b), which shows the excitation inrush current waveform when magnetic saturation is significant, the fundamental wave component occupies a large proportion, and the transient DC component is superimposed on the fundamental wave that occurs during an internal fault. This is an example in which it is difficult to distinguish this from the 7'C case. For this reason, it is necessary to determine whether to increase π in equation (1) (strengthening the harmonic suppression power). Even if the magnetizing inrush current shown in FIG. 2(b) can be determined by increasing Kg, the reverse effect is that the harmonic superimposed current at the time of an internal fault tends to cause the device to become inoperable. As a means to solve all of these problems, the following 7
The energization angle detection element is used.

Note that the embodiment of the relay element 6 is already known, and a detailed description of its circuit will be omitted.

An example of the operation of the energization angle detection element 7 will be described below.

FIG. 3 is an explanatory diagram of an example of an internal fault current waveform and the response of the energization angle detection element 7. Figure (a) shows an example when only the basic distribution is detected as the ID, and the levels of both positive and negative waves of the ID are detected by the level slicer built in the energization angle detection element 7, and IIDI≧LS ・・・・・・・・・・(2
), the conduction angle is expressed as θH1, and otherwise, it is expressed as θL. Here, for example, in one period T of the fundamental wave, the sum ΣθB of θR and the sum ΣθL of θL are Σθ8−Σθ, ≧θ.・・・・・・・・・(When 3i, 6 is determined to be an internal accident. Figure 2(b) is an example where the fundamental wave and transient DC component are superimposed. It is difficult to distinguish it from the waveform.In relay element 6, this could be countered by strengthening the second harmonic suppression (increasing KIIt), but in relay element 7, it is necessary to increase the level slice sensitivity (lower the slice level). However, there are limits to this in terms of noise resistance, etc. Therefore, this becomes a weak point of the case relay element 7, but since the relay element 6 can cover it, there is no problem with the present relay device as a whole.

FIG. 2C shows an example in which a fundamental wave and relatively low-order harmonics are superimposed. In this case as well, θR9θL occurs intermittently, but operation detection using equation (3) is possible. Although the relay element 6 had a weakness in that it could become inoperable depending on the content of harmonics, this weakness can be covered by the relay element 7. As mentioned above, since relay elements 6 and 7 face each other and cover each other's weak points, the overall characteristics of the transformer protection relay BY are that it can detect harmonic superimposed currents with high sensitivity, and it can also reliably detect magnetizing inrush currents. °There is an effect that can be produced.

A complete embodiment of the relay element 7 is shown in FIG. An explanation of the operation in the figure will be given below. 71 is a level determiner,
When 1Inl exceeds the level Li, a gap mark signal corresponding to θH is output, and when it is below LS, a gap space signal corresponding to θL is output.

72 is a sampling timing generation circuit, and θ3
．． Provides a timing signal for counting the length of θL. 73 is a sampling circuit for θH, and 74 is a θH sampling circuit.
It is a sampling circuit.

Reference numeral 75 denotes an adder, which serves as the output metal of the sampling circuit 73 and takes the output goldfish of the sampling circuit 74, and adds the outputs of both over a predetermined period of time, for example, an interval T corresponding to one cycle of the fundamental wave.

The addition timing and the measurement of the time width T to be added are performed in synchronization with the timing signal of the sampling timing generation circuit 72. Therefore, if the clock of the timing signal has a sufficiently high frequency with respect to the fundamental wave, measurement accuracy can be improved. However, in order to simplify the circuit configuration and save calculation processing time, it is desirable to set the frequency as low as possible. Therefore, the clock is synchronized with an integer multiple of the fundamental wave, and it is possible to perform the process at a frequency 12 times, 24 times, or the like. The output of the adder 75 represents Σθ锳−ΣθL corresponding to the left side of equation (3), and this is judged by the level judger 76 to obtain a judgment result corresponding to equation (3). The output of 76 is the output of FIG.

The embodiment shown in FIG. 4 has a partially digital configuration, but as a modification and application example, the input signal Ip shown in FIG.
, Is'z can be sampled and taken in, and all subsequent operations can be implemented as a digital storage relay. Further, in the present invention, a harmonic ratio detection element is used in FIG. 16, but this is an impedance relay for detecting the excitation inrush current
Alternatively, even if a method is adopted in which the applied voltage of the transformer and the input current waveform are compared with each other, the effect of combining the energization angle detection element of the present invention is great.

In this example, the transformer was explained as having two windings, but
A multi-winding transformer can be similarly implemented as long as current differential signals are used.

Furthermore, the output signal shown in FIG. 1 is configured to be a trip permissible output when an internal failure is detected at 5, a trip prevention output when an excitation inrush current is detected at 6 and 7, and 8 is configured to generate a trip prevention output when an excitation inrush current is detected. The concept and effect of the present invention are the same even if 9 is changed to an inhibit circuit by using an AND gate so that the trip permitting output of 5 can be locked by the trip preventing output of 8.

〔Effect of the invention〕

The effects of the present invention are summarized in FIG. In this figure, the symbol ◯ represents normal operation, the symbol △ represents undefined operation, and the symbol - represents normal non-operation. As shown in the figure, according to the present invention, it is possible to reliably prevent malfunctions caused by the magnetizing inrush current of the transformer, and even when harmonics or DC components are superimposed on the internal fault current, it is highly sensitive and can operate at high speeds. It is possible to judge, and the effect on improving the performance and reliability of transformer protection relays is a dog.

[Brief Description of the Drawings] Fig. 1 is an overall configuration diagram of the device of the present invention, Fig. 2 is an example of the waveform of the excitation inrush current, Fig. 3 is an example of the waveform of the internal fault current and an explanatory diagram of the operation of the device of the present invention, FIG. 4 is a side view of the configuration of the energization angle detection element, and FIG. 5 is a conceptual diagram of the operation of the present invention. RY...Transformer protection relay, 4...Adder, 5...
・Overcurrent relay, 6, 7...Magnetizing inrush current malfunction prevention relay No. 1 No. 3 No. 4 No. 4 57

Claims (1)

[Claims] 1. In a transformer protection relay that detects an internal fault based on a current differential signal of a protected transformer, a first means for detecting an overcurrent of the current differential signal 2. Similarly, a waveform of the signal A second means for detecting distortion and a third means for detecting the magnitude of the energization angle of the signal are provided, and an accident within the protected area is detected by comparing the outputs obtained by each means. A transformer protection relay featuring: 2. In the preceding paragraph, an internal accident is determined based on an OR condition of the trip permissible output obtained by the second means and the third means and a match condition of the trip permissible output obtained by the first means. Transformer protection relay.