JPH06235737A - Digital protective measuring equipment - Google Patents

Abstract

PURPOSE:To embody a downsized multifunctional digital protective measuring equipment being employed in protective measurement of power receiving/ distributing facility in which the influence of a quantization error is eliminated even when the input signal range is wide. CONSTITUTION:An amplifying section 3 comprises a amplifier 31 for one input signal, and a multipole switch 32 connected with the feedback circuit of the amplifier 31 where one arbitrary pole is turned ON and the other pole is turned OFF by a control command fed from an operating section 6. Output voltages 4a, 4b, 4c are converted into digital data at an A/D converting section 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital protection and measurement device used for protection and measurement of power receiving and distribution equipment.

[0002]

2. Description of the Related Art When a main circuit voltage or current is input into a device as an input signal and digital processing is performed to realize multiple functions such as a protection relay function and a measurement function, the range of the current input signal required depends on the function. Different to For short circuit protection, for example, 100% to 200% of the main circuit rating
The input signal range required for each function calculation is about 0%, the rating is 80% to several hundreds% for overload protection, and about 120% or less for the measurement function.

In such a case, for example, if the device is scaled so that the internal data of the device has a full-scale value at the maximum current of the main circuit, a quantization error occurs with a small input signal. For example, when the main circuit current is 10 kA,
If it is scaled to 1000 bits, an error of ± 5% occurs when measuring the main circuit current 100A. If the main circuit current of 1000 A is scaled to 1000 bits, the error at the time of 100 A measurement is reduced to ± 0.5%, but the scale over occurs even when measuring 10 kA. It is impossible to measure. After all, it is desirable that a plurality of scalings be prepared according to the magnitude of the input signal.

FIG. 3 is an example of a device configuration according to the prior art. In FIG. 3, 1 is an input current supplied from an instrument transformer of the main circuit (not shown). Reference numeral 2 is a current-voltage converter that transforms the input current 1 into a voltage signal matched with an electronic circuit. Reference numerals 3a, 3b and 3c are amplification sections having different amplification degrees. 4a, 4b and 4c are amplification sections 3a, 3b and 3c. Is an output voltage, 5 is an A / D converter, and 6 is an arithmetic unit, which is mainly composed of a microcomputer.

FIG. 2 is a desirable input / output characteristic of the amplifying section for preventing a quantization error. The horizontal axis shows the input current and the vertical axis shows the output voltage of the amplifying section. It is shown that the straight line 14a is scaled to be full scale at the input current 1a, and the straight lines 14b and 14c are scaled to be full scale at the input currents 1b and 1c, respectively.

In the amplifiers 3a, 3b and 3c of FIG. 3, the amplification degrees are set so that the respective output voltages 4a, 4b and 4c match the straight lines 14a, 14b and 14c shown in FIG. 2, respectively. The upper limit of the calculation unit 6 is the input current 1a
The output voltage 4a from the amplifier 3a is used when calculating the function of the above, and the upper limit of the output voltage 4b of the amplifier 3b is calculated when calculating the function of the input currents 1b and 1c.
And is programmed to use the output voltage 4c of the amplifier 3c. As a result, each functional operation is executed in the optimal scaling state.

[0007]

Although the influence of the quantization error can be eliminated by performing the calculation with such an apparatus configuration, the number of amplifying sections 3a, 3b, 3c increases, and the apparatus becomes larger. Also, because the amount of data increases,
There is a drawback that a lot of time is spent for data input and the functional calculation is restricted. Therefore, it is an object of the present invention to realize a compact and multifunctional digital protection and measurement device which is not affected by a quantization error even when the input signal range is wide.

[0008]

For one input signal, one amplifier and a feedback circuit of the amplifier are connected,
In addition, the amplifier unit includes a multi-pole switch in which any one pole is turned on and the other pole is turned off by a control command from the arithmetic unit.

[0009]

The operation unit switches the amplification degree of the amplification unit in advance according to the input signal level of the function to be operated and performs the operation after scaling to the optimum value, so that the function having a significantly different input signal range can be realized. The calculation error is not affected by the quantization error.

[0010]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 is an input current and 2 is a current-voltage converter, which are the same as those in the prior art shown in FIG. 3 is an amplifier, 31
Is an amplifier, 32 is a multi-pole switch, 32a, 32b and 32c are contacts of the multi-pole switch 32, 33, 34a, 34
b and 34c are resistors, 4a, 4b and 4c are output voltages from the amplification unit 3, 5 is an A / D conversion unit, 6 is a calculation unit,
7, 7a, 7b and 7c are control data of the multi-pole switch 32 set in the arithmetic unit 6. Reference numerals 71a, 71b and 71c are control signals given from the arithmetic unit 6 to the multi-pole switch 32.

The arithmetic unit 6 decodes the control data 7a of the multi-pole switch 32 and multiplies the control signal 71a before calculating the unillustrated function A in which the upper limit of the input current 1 is the input current 1a shown in FIG. It is given to the pole switch 32. When the control signal 71a is given to the multi-pole switch 32, the contact 32a of the multi-pole switch 32 is turned on, and the contacts 32b, 3
Since 2c is turned off, the amplification degree of the amplification unit 3 is the resistance 3
3. The output voltage 4a is set to a value determined by the contact 32a of the multi-pole switch 32 and the resistor 34a, and the scaled output voltage 4a is output. The input / output characteristic of the output voltage 4a is shown in FIG.
Is indicated by a straight line 14a.

Similarly, the calculation unit 6 has a function B (not shown) in which the upper limit of the input current 1 is the input current 1b shown in FIG.
Is calculated, the control data 7b of the multi-pole switch 32 is calculated.
When the function C (not shown) in which the upper limit of the input current 1 is the input current 1c shown in FIG. 2 is calculated, the control data 7c of the multi-pole switch 32 is decoded and the control signals 71b and 71c are output. To do. The multi-pole switch 32 receives the control signal 71b when it receives the control signal 71b.
When the contact 32b of the multipolar switch 32 receives the control signal 71c, the contact 32c of the multi-pole switch 32 is turned on to output the output voltages 4b and 4c, respectively. Output voltage 4b, 4
The input / output characteristic of c is shown by the straight lines 14b and 14c in FIG.

In this way, the arithmetic unit 6 can input the data with the optimum scaling for each input signal range even when operating a plurality of functions having greatly different input signal ranges, so that the influence of the quantization error is exerted. Never receive.

[0014]

As described above, according to the present invention, it is possible to realize a small-sized, highly accurate, and multifunctional digital protective measuring device without increasing the number of amplifying sections.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a digital protection and measurement device of the present invention.

FIG. 2 is a diagram showing input / output characteristics of an amplifier.

FIG. 3 is a configuration diagram showing a conventional example.

[Explanation of symbols]

1, 1a, 1b, 1c Input current 2 Current-voltage converter 3, 3a, 3b, 3c Amplifying unit 31 Amplifier 32 Multi-pole switch 32a, 32b, 32c Multi-pole switch contact 33, 34a, 34b, 34c Resistor 4a, 4b, 4c, 4H Output voltage from amplification section 5 A / D conversion section 6 Calculation section 7, 7a, 7b, 7c Control data 71a, 71b, 71c of multipole switch Control signal

Claims (1)

[Claims] 1. A digital protection and measurement device that takes in a voltage input of a system as an input signal into a device, performs digital arithmetic processing, and realizes a predetermined function, and one amplifier and one amplifier for each input signal. A multi-pole switch that is connected to the feedback circuit of the amplifier and has one pole turned on and the other pole turned off in response to a control command from the arithmetic unit. A characteristic digital protective measuring device.