JP2704089B2 - DC protection relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital operation type DC protection relay used in a DC circuit such as a DC power transmission or a frequency converter.

[0002]

2. Description of the Related Art FIG. 3 shows an example of the configuration of a DC protection relay applied to a frequency converter, and FIG. 3, the DC protection relay 1 introduces secondary currents i _A and i _B of the DCCT 3 provided in each of the A system and the B system of the frequency conversion station 2. The introduced currents i _A and i _B are respectively insulated by the insulation amplifier 4 and
The signal is converted to a level suitable for internal judgment, and the analog filter 5 filters high-frequency components. This current is sampled at a fixed sampling frequency by a sampling and holding circuit 6, sequentially selected by a multiplexer 7, sent to an A / D converter 8, and converted into a digital quantity. The protection operation unit 9 performs a protection operation based on the digital data output from the A / D converter 8 and performs a protection operation such as detection of a fault in the DC circuit and transmission of a protection output.

The operation of the protection operation unit 9 will be described with reference to FIG. The currents i _A and i introduced as shown in FIG.
_B represent the times t ₀ , t ₁ , t at the sampling interval τ, respectively.
Sampled sequentially as ₂ ,. In normal operation state, i
_{Since A (m)} and iB _(m) are equal in size, the left side is "0" in the judgment formula of FIG. Next, if an accident occurs in the system, for example, as a result, the current i _A will increase and i _B will decrease. At Thus the time t ₅ i _{A (m)} and i _{B (m)}
And a difference is made between the two and the operation is performed when the left side of the judgment expression in FIG.

[0004]

The above prior art has the following problems. For example, when the DC system to be protected is charged, the currents i _A and i _B simultaneously flow with the same magnitude, but at this time, due to the difference in the transient response of the analog filter and the like provided inside the DC protection relay. , FIG.
As shown in FIG. 4B, at time t ₃ , a difference occurs between the sampling data of i _{A (m)} and i _{B (m)} depending on the sampling timing. As a result, the left side of the judgment formula of FIG. Therefore, there is a possibility that a malfunction may occur even though no accident has occurred in the system. The present invention has been made to solve the above problems, and has as its object to provide a DC protection relay having high operation reliability.

[0005]

According to the present invention, as shown in FIG. 1, means for obtaining the maximum value of each of the three consecutive sampled data including the latest data of the input electric quantity sampled is provided for each input. It is determined whether or not the difference between the terminal currents corresponding to each terminal current data is equal to or larger than a predetermined value by using the sampling data one sampling before the latest from each terminal data and the maximum value of the three sampling data obtained by the above means. With such a configuration, the operation reliability is improved.

[Operation] Even if the sampling data mismatches transiently at the time of system charging or system disconnection, in order to determine the magnitude of the difference between the terminal currents, the self-end data uses the data one sample before the latest, By using the maximum value of the three consecutive sampled data including the latest data as the other end data, no difference occurs in the calculation result and malfunction can be prevented.

[0006]

An embodiment will be described below with reference to the drawings. FIG.
FIG. 1 is a configuration diagram of an embodiment of a DC protection relay according to the present invention. The DC protection relay of the present invention is also applied as shown in FIG. The protection operation unit of the present invention differs from the protection operation unit 9 shown in the conventional example in the content of the operation processing. The contents of the arithmetic processing will be described with reference to FIGS. Figure 2 _{i A (m), i B} (m) is the same as FIG. 4 (b) and the previously described ,, during system charging, the terminal current i _A, i _B increases identical in size at the same time Shows a case where a difference occurs in sampling data i _{A (m)} and i _{B (m)} at time t ₃ due to a difference in a transient response of an analog filter or the like provided inside the DC protection relay. According to the protection operation processing of the present invention shown in FIG. 1, at time t ₃ , the maximum value of three consecutive samplings including the latest data of each terminal current is

I _{AM (t3)} = i _{A (t3)} , i _{BM (t3)} = i
_{B (t3) = i B (} t2) = i B (t1) , and the difference is whether the calculation result above a predetermined value for each terminal current _{is, Y 1 = i A (t2} ) -i BM (t3) = iA _(t2) -iB _(t2) = 0
, Y ₂ = iB _(t2) −iAM _(t3) = iB _(t2) −iA _(t3) <
0, and none of them is established and no malfunction occurs. or,
At same time _{t 4, i AM (t4)} = i A (t3) = i A (t4), i BM (t4) = i B (t4) , and the difference between the terminal current of whether more than a predetermined value the operation result _{is, Y 1 = i A (t3} ) -i BM (t4) = i A (t3) -i B (t4) = 0
, Y ₂ = iB _(t3) −iAM _(t4) = _{iB (t3)} −iA _(t3) <
Similarly, neither 0 nor 0 is established and no malfunction occurs. According to the present embodiment, even if there is no difference in the input current due to the difference in the transient response of the analog filter or the like, even if a difference occurs in the sampling data, the difference does not exceed the predetermined value in the calculation determination result. Thus, a DC relay having high operation reliability without malfunction can be obtained. In the above embodiment, the case where the present invention is applied to a frequency conversion station has been described.However, the present invention is not limited to this case. For example, even when each terminal current is introduced from both ends of a DC transmission line, an operation protection operation is performed. The same applies.

[0008]

As described above, according to the present invention, the maximum value of three consecutive sampled data including the latest sampled data of each terminal current of the DC circuit is obtained, and the latest value of the opposing terminal current data is obtained. Since it is configured to determine whether or not the difference from the sampling data one sample before is greater than or equal to a predetermined value, the sampling data is not affected by the difference in the transient response of the analog filter or the like, even though the input current is not different. Even if a difference occurs, it is possible to provide a DC relay with high operation reliability without malfunction.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a DC protection relay according to the present invention.

FIG. 2 is an output signal response diagram of the protection operation processing content of the DC protection relay of the present invention.

FIG. 3 is a configuration example diagram of a DC protection relay.

FIG. 4 is a view for explaining a conventional protection operation process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC protection relay 2 Frequency converter 3 DCCT 4 Insulation amplifier 5 Analog filter 6 Sample hold circuit 7 Multiplexer 8 A / D converter 9 Protection operation part

Claims (1)

(57) [Claims] 1. A DC protection relay which inputs an electric quantity from two terminals of a DC circuit and sends out a protection output when a difference between the electric quantities is equal to or more than a predetermined value, wherein the input electric quantity is sampled at a predetermined time interval. A first means for obtaining a maximum value of three consecutive sampled data including the latest data of the sampled data with respect to each input; and a first input among input electric quantities from two terminals. of,
From the sampling data one sampling before the latest,
A second means for subtracting the maximum value of the three sampling data of the second input obtained by the first means and determining whether or not the value is equal to or more than a predetermined value; From the sampling data before sampling, the first
A third means for subtracting the maximum value among the three sampling data of the first input obtained by the means, and judging whether or not the value is equal to or greater than a predetermined value; and any one of the second and third means And a fourth means for sending a protection output when one of the conditions is satisfied.