JPH0641347U - AC filter equipment digital relay for protection - Google Patents

Abstract

(57) [Summary] [Purpose] The current flowing through the AC filter equipment contains a component other than the frequency shunted by the AC filter equipment, for example, a DC offset component. It is desirable to remove this DC offset component as much as possible in order to eliminate the error factor of the digital relay operation. [Structure] A sample value im of current (m = 0,1,2, ...) is summed over a certain period and divided by the number of data to obtain a DC offset value, which is subtracted from the sample value im, and the subtracted data A digital relay 1 which operates in response to the above is constructed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a digital relay for protecting an AC filter equipment, and more specifically, it responds to an effective value of a high frequency component flowing in an AC filter equipment provided to remove a high frequency component superimposed on a current flowing in a power system. Improvement of digital relay for protection of AC filter equipment.

[0002]

[Prior art]

 The AC filter equipment installed at the period converter is composed of a coil, a reactor and a resistor connected in series.It has low impedance for specific high frequency components and low impedance for other high frequency components. It has high impedance. Therefore, the AC filter equipment is installed in parallel with the power system and has the function of allowing only specific high-frequency components contained in the current flowing in the power system to flow to the ground.

By the way, an excessive current may flow from the power system to the AC filter equipment. If this condition is left unchecked, the AC filter equipment will be overloaded, so it is necessary to detect the overcurrent by the relay and install a circuit breaker to interrupt the inflow of current.

[0004]

[Problems to be solved by the device]

 The current signal input to the relay contains a component other than the frequency shunted by the AC filter equipment, for example, a DC offset component. Furthermore, the relay includes an analog signal processing circuit such as an analog high-pass filter, a sample hold circuit, an A / D converter, etc., but since the gain of this processing circuit is large, the DC offset component is amplified.

Therefore, even when the input current is 0, the measured display value of the panel is not 0 (it may reach 4% at maximum), or the zero-phase current display value is not 0. Display the value (up to 8% may be reached). Therefore, in the analog signal processing circuit, it is desirable that the DC offset component is not generated as much as possible in order to eliminate the error factor. However, if the DC gain of the analog high-pass filter is sufficiently reduced, the filter characteristics (27th to Since the 37th harmonic characteristic is sacrificed to some extent, there is a limit to the improvement of the analog signal processing circuit.

The present invention has been made to remedy the above-mentioned drawbacks, and an object of the present invention is to provide a digital relay for AC filter equipment protection capable of reliably blocking a DC offset component.

[0007]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the digital relay for protecting the AC filter equipment of the present invention sets a constant frequency ω corresponding to the frequency of the fundamental wave included in the target wave, and makes one cycle of the target wave 2π / ω. Sampling means for sampling the target wave at each time point equally divided by 2k, and sample values im (m = 0,1,2, ...) sampled by the sampling means are summed over a certain period and divided by the number of data. It is a digital relay which has a calculating means for obtaining a DC offset value by means of and subtracts it from the sample value im, and which responds to an effective value obtained based on the subtracted data.

[0008]

[Action]

The instantaneous value i (t) of the target wave is generally calculated using the DC component I ₀ , the fundamental wave component In (n = 1), and the harmonic component In (n = 2,3, ...). It can be expressed as follows: i (t) = I ₀ + ΣIn sin (nωt + θn) (1) Σ (sum) is taken for n. n is the order, ω is the frequency of the fundamental wave of i (t), and θn is the phase of the n-th wave.

Here, if i (t) is sampled at each time point where one cycle 2π / ω is equally divided into 2k, then im = i (2mπ / 2kω) = I ₀ + ΣIn sin (nmπ / k + θn) (2 ).

When the sampled values are summed from m = 0 to 2k−1, A = 2kI ₀ + ΣΣIn sin (nmπ / k + θn) (3) Σ is taken for n and m. If the sum of m is taken, the right side of the equation (3) will be all 0, so the sum A will be A = 2 kI ₀ . Therefore, if this A is divided by the number of samples 2k, the DC component I ₀ contained in the target wave can be obtained. Therefore, by subtracting I ₀ from the sample value im, it is possible to obtain data that does not include the offset component.

[0011]

【Example】

 Embodiments will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an installed state of a digital relay for protecting an AC filter facility. Between the distribution line 21 and the ground, a capacitor C for flowing a specific harmonic, a reactor L, an AC filter equipment 22 having a resistance R and a circuit breaker SW are connected, and the current flowing through the AC filter equipment 22 is It is detected by the galvanometer 23.

The current detected by the galvanometer 23 is input to the digital relay 1 for protecting the AC filter equipment. The digital relay 1 outputs the output voltage i (t) (proportional to the current flowing through the filter equipment 22) of the auxiliary transformer 11, the analog high-pass filter 12, and the analog high-pass filter 12 that steps down the output voltage of the galvanometer 23 for a certain time Δt. (Δt is set to 0.000139 seconds, for example. At a frequency of 60 Hz, it corresponds to a phase angle of 3 °, and k = 60, 120 samplings.) A sample and hold circuit 13 for sampling every sample and analog held and held. The A / D converter 14 for digitally converting the value, the digitally converted sample value (set as im) are stored, and the offset calculation unit 15 for obtaining the offset, the offset component is removed by the offset calculation unit 15. RMS value calculation unit 16 that calculates RMS value based on data, and compares the effective value and the set value The comparison unit 17 has

The operation of the digital relay 1 will be described with reference to the waveform chart of FIG. The horizontal axis of the figure shows the time t, and the vertical axis shows the output voltage i (t) of the analog high-pass filter 12. The sample value im is sampled at the above-mentioned constant time Δt and stored in the memory of the offset calculator 15 every moment. The offset calculator 15 calculates A = Σim based on the sample value im for one cycle, and divides the obtained A by 2k = 120 to obtain the offset component I ₀ Ask for. Then, the offset component I from the sample value im₀Subtract.

As a result, data in which the offset component is cut can be obtained, and the effective value calculator 16 calculates the effective value of the high frequency component based on this data. Then, the comparison unit 17 compares the effective value with the set value, and if the effective value exceeds the set value, outputs the trip output of the circuit breaker SW to ensure the safety of the AC filter equipment 22. As a result, the current flowing through the AC filter equipment 22 can be cut off. In this case, a timed relay may be attached and the operation signal may be output only when the state in which the effective value is the set value or more continues for a certain time.

By performing the offset calculation as described above, only the harmonics that do not include the DC component can be extracted. Therefore, by using the digital relay configured in this way, it is possible to configure a protection relay for filter equipment that can cancel the DC component that causes an error. The present invention is not limited to the above embodiment. For example, in the above embodiment, the offset component is obtained by averaging the sum total of the sample values im for one cycle, but in general, the sum total for a plurality of cycles may be taken. However, although the offset value becomes more accurate as the number of cycles increases, there is a problem that the relay response time is delayed because more data must be stored. Therefore, the number of cycles must be decided in terms of accuracy and relay response time.

[0016]

[Effect of device]

 As described above, according to the present invention, the sampled value im (m = 0,1,2, ...) is summed over a fixed period and divided by the number of data to obtain the DC offset value, and the sample value Since it is subtracted from im and responds based on this subtracted data, it is possible to realize a digital relay for protecting AC filter equipment that responds based on accurate data from which error factors are removed. Therefore, the AC filter equipment can be appropriately protected.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital relay for protecting an AC filter facility.

FIG. 2 is a graph illustrating a sampling method.

[Explanation of symbols]

 1 AC Filter Equipment Protection Digital Relay 12 Analog High Pass Filter 13 Sample and Hold Circuit 14 A / D Converter 15 Offset Calculator 16 Effective Value Calculator

Claims (1)

[Scope of utility model registration request] 1. A digital relay for protecting an AC filter equipment for detecting an overcurrent flowing through the AC filter equipment, wherein a constant frequency ω corresponding to a frequency of a fundamental wave included in the target wave is set to obtain a target wave of the target wave. Sampling means for sampling the target wave at each time point equally dividing one cycle of 2π / ω and sample values im (m = 0,1,2, ...) Sampled by the sampling means are summed over a constant cycle to obtain data. A digital value for protecting an AC filter facility, characterized by having a calculation means for obtaining a DC offset value by dividing by a number and subtracting it from the sample value im, and responding to an effective value obtained based on the subtracted data. relay.