JPH01286727A - Digital bus protective apparatus - Google Patents

Abstract

PURPOSE:To easily discover an erroneous connection by employing a specific voltage as a reference, and calculating and displaying the phase difference of a current thereto in a digital bus protective apparatus. CONSTITUTION:A current from a power source 1 to a bus 2 to be protected and a current from the bus 2 to a plurality of feeders 3 are obtained by a current transformer 4 and an auxiliary current transformer 5, and input to the sample-holding circuit 9 of a digital bus protective relay 8. The voltage of the bus 2 is obtained by a transformer 15 and an auxiliary transformer 16, and sample-held by a sample-holding circuit 9. The sample-held current, voltage are sequentially multiplexed by a multiplexer 10, A/D-converted by an A/D converter 11, and input to a CPU 12. A differential current calculated by the CPU 12 is displayed on a display 14 with the phase designated by a setter 13 as a reference, and its phase relationship is displayed on a display 17. Thus, erroneous connections of many current transformers can be easily discovered to improve its maintenance and reliability.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a protection relay that protects a power system, and more particularly to a digital bus protection device that protects a bus bar by applying a current differential. .

(Prior art) An example of the configuration of an analog type bus protection relay based on the current differential principle according to the prior art is shown in Fig. 4.The configuration of the power system is as follows.
For convenience of explanation, as an example, there is one IE source line and two load lines.
It was a line. In Fig. 4, f! of the current differential principle! #The line protection relay 1 connects two current transformers 4 provided in each feeder 3.
Next IP! In this case, the system currents from each feeder connected to the protected bus are matched by the auxiliary current transformer 5, and these are differentially connected. Then, the level detection circuit 6 detects the difference current 1d generated in the differential circuit when an internal fault occurs in the bus bar, and sends out a protective output.

Here, the waveform observation terminal 7 provided on the busbar protection relay 1 is used to observe the difference current in the steady state of the system, and to check whether there is any erroneous connection in the circuit that introduces the IIc current from the current transformer.

Figure 5 shows the current waveform of each part of the system in Figure 4 and the waveform of the waveform observation terminal. Figure 5 (a) shows the waveform of each part when there is no connection error when the system is steady, and Figure 5 (b) shows a case where the connection error is in the circuit that obtains the current i3 when the system is steady.

In Fig. 5(a), the current 1 flowing from the power supply to the bus bar
1 and the current i2 flowing out from the bus to supply the load.
．． The vector sum 1d with i3 can be obtained from the following formula.

Id=i1+i2+i3 In this case, the vector sum Id becomes zero according to Kirchhoff's law. In FIG. 5(b), the polarity of i3 is reversed due to incorrect connection, and Id has a magnitude obtained from the following formula.

Id=i1+12-i3=iI orderi2+13-(2i3
)=-2i3 Therefore, in FIG. 5(a), it is observed by the waveform observation terminal that the difference current 1d is zero, and it can be confirmed that there is no erroneous connection. In FIG. 5(b), a difference current 1d is observed even in a steady state, which indicates that there is a misconnection in one of the feeders. In the above explanation, we have described the internal formula table phase C of the three-phase power system, but the same applies to the other two phases.1 and above, we have described analog type bus protection relays, but next we will explain about digital type bus protection relays. state

In general, a digital protection relay samples the amount of electricity in the system, converts it into a digital amount, and performs digital processing using a microcomputer to determine relay operation.

FIG. 6 is a schematic diagram of a digital bus protection relay. In FIG. 6, the same reference numerals as those in FIG. 4 have the same functions and are used for the same purpose, so the explanation thereof will be omitted.

In FIG. 6, the current input of the system is introduced through a current transformer 4 and an auxiliary current transformer 5, and the voltage input is introduced into a digital bus protection relay 8 through a transformer 15 and an auxiliary transformer 16.
The sample hold circuit 9 samples the signal at a constant sampling frequency.

This sampled current data and voltage data are
The signals are sequentially selected by the multi-blephr 10, sent to the A/D converter 11, and converted into digital quantities.

The CPU 12 performs protection calculations based on the digital data of the system current and voltage output from the A/D converter 11, and performs protection operations such as system failure detection and protection output. The step setting unit 13 inputs failure detection sensitivity, operating time setting, etc. to the CPU 12. Here, the difference current 1d display circuit 1
Similarly to the waveform observation terminal of the analog bus protection relay, 4 displays the calculation result of the vector sum of currents.

This allows you to check for incorrect connections as described for analog bus protection relays.

(Problem to be solved by the invention) However, in general, in the case of bus bar protection, multiple power supplies and a large number of load feeders are connected, so even if it is possible to confirm whether there is a connection error, it is possible to confirm that there is a connection error in any feeder. It was difficult to limit the

As the number of feeders connected to the bus increases, the difference current 1d generated due to errors in current transformers, auxiliary current transformers, etc. also increases. As a result, the waveform i! from the waveform observation terminal or the difference current display! However, there was a drawback in that it was difficult to confirm whether there was an incorrect connection.

The present invention has been made in order to solve the above problems, and provides digital bus bar protection that can detect connection errors from current transformers as well as detect which feeder has an incorrect connection. The purpose is to provide equipment.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, a digital bus protection device is provided with a function of calculating a phase difference of a current with respect to a specific voltage as a reference, and also displays this. It was designed to provide means.

(Function) Using the above means, by comparing and confirming the phase relationship of the current to the displayed voltage and the phase relationship of the current to the voltage that should be in steady state, it is possible to simultaneously know whether there is a misconnection and the circuit in which the misconnection is present. be able to.

(Example) Examples will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a digital bus bar protection device according to the present invention. In FIG. 1, the same parts as in FIG. 6 are given the same reference numerals, and their explanation will be omitted.

In FIG. 1, a phase display circuit 17 displays the phase difference between the voltage and current calculated by the CPU 12, and a setting circuit 13 displays data necessary for the calculation of the CPU 12, such as phase designation of a reference voltage. etc. are input. The other configurations are the same as in FIG. 6.

The operation of the digital bus bar protection device having the above configuration will be explained using the flowchart shown in FIG. FIG. 2 shows a case where the phase display flow is selected by the setting section. In FIG. 2, a code indicating the phase of the reference voltage, for example, the R phase, is inputted at the stage S1.

In STEG S2, the code of the feeder to be calculated is input. In step S3, the phase is calculated using a predetermined phase calculation algorithm based on the previous input code, and this is displayed in step S4. Here, since the phase calculation algorithm is well known, its explanation will be omitted.

Step 35. S6 is a step when phase calculation and display of other feeders and other phases are required, and if unnecessary, phase display is ended and the process proceeds to other processing.

Next, the flow shown in Fig. 2 and the voltage of the system shown in Fig. 3,
A display example of the phase display circuit will be explained using a current waveform.

FIG. 3(a) shows the waveforms of various parts when there is no connection error when the system is steady, and FIG. 3(b) shows the case where there is a connection error in the circuit that obtains the current i3 when the system is steady. In FIG. 3, for example, the R-phase voltage v1 of the voltage input is used as a reference, and the R-phase currents N, i2 . Let us display the phase of i3. The waveform of FIG. 3(a) will be explained below. In step S1 of FIG. 2, it is input that the voltage phase used as a reference for phase calculation is the R phase, and in step S2, the phase of the current 11 is calculated, and in order to display this, the current 1
Enter the feeder code of 1. From the above, step S3
Now, calculate the phase difference of 11 with respect to the voltage of the R phase, and set it to 0°.
The degree is obtained and this value is displayed in step S4. This matches the voltage-current phase relationship that should originally exist. Next, in step S5, the phase of the current 12 is also displayed, so the process advances to step S2. Below, as above, the current i2
．． The phase is calculated and displayed for i3. Here, the current i2. For i3, approximately 180° is displayed, confirming that there are no abnormalities. However, in the waveform shown in FIG. 3(b), the current i1. i2. The phase display of i3 is about 0°, 180', and O°, respectively. The phase relationship that should originally exist is based on voltage v1 and current i1. i
Since 2°i3 are respectively 0°, 180°, and 0°, it can be seen that there is an error in the connection of the circuit that introduces the current i3. The above has described the R phase, which is the representative phase of voltage input, but the S phase,
The same can be done for the T phase, which is step 3 in Figure 2.
6,374: You can select it.

According to the above embodiment, the presence or absence of incorrect connection and the incorrect connection circuit are clarified from the phase relationship of the current of each feeder based on the voltage introduced from the transformer, and the digital bus bar has improved maintainability and reliability. Protective equipment can be provided. In addition, in the above embodiment, a case has been described in which the phase relationship of each phase current is sequentially displayed using each of the R phase, S phase, and T phase of the three-phase voltage of the system as a reference, but the present invention is limited to this. It is needless to say that the same effect can be obtained by outputting the phase calculation result to the glintter.

Although the above embodiment has been described as a configuration that displays the phase difference of the current with respect to the voltage, the present invention is not limited to this. It is clear that a similar effect can be obtained with a configuration in which only the results are displayed. Furthermore, a configuration may be adopted in which the C phase display circuit and the Id display circuit are shared and used depending on the input of the setting section.

[Effects of the Invention] As explained above, according to the present invention, since the phase relationship of current to voltage is displayed, it is easy to see whether there is a connection error from the current transformer and the incorrect connection circuit, which improves maintainability and A digital bus protection device with improved reliability can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the digital busbar protection device according to the present invention, Fig. 2 is a flowchart showing the processing contents of Fig. 1, Fig. 3 is a waveform diagram explaining the action, and Fig. 4 is a conventional one. FIG. 5 is a waveform diagram illustrating the action of the conventional technology, and FIG. 6 is a diagram illustrating the digital bus protection device of the prior art. 2... Protected bus 3... Feeder 4... Current transformer 5... Auxiliary current transformer 8... Digital bus protection Relay 9...
...sample hold circuit

Claims (1)

[Claims] A digital bus protection device that protects power system buses using the differential principle, which is equipped with a means to calculate the phase relationship of the currents introduced by multiple transformers using a specific voltage as a reference, and to display the calculation results. A digital busbar protection device characterized by: