JPH04347919A - Digital relay for protection of harmonic filter equipment - Google Patents

Abstract

PURPOSE:To surely extract a fundamental wave component and to cut a DC component to make the secular change and the temperature change difficult to occur by detecting the fundamental component of a high frequency branch of a high frequency filter equipment. CONSTITUTION:A sample value im which is sampled by sampling and holding circuits 13a and 14a at intervals of a certain time t and is digitally converted by A/D conversion circuits 13b and 14b is momentarily stored in RAMs 13c and 14c. First operation parts 13d and 14d read out a value im sampled at an arbitrary Lime t=tm, a value im+p sampled p periods after the time tm, and a value im-p sampled p periods before the time tm from RAMs 13c and 14c to calculate iotam based on a formula iotam=(im-p)+2im+im+p. Consequently, the high frequency component included in calculated data iotam is cut but a fundamental wave remains as it is.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital relay provided for protecting harmonic filter equipment.

0002

2. Description of the Related Art In places where a large amount of high frequency current is generated, such as a frequency conversion station, harmonic filter equipment is installed in parallel with the ground in order to absorb harmonic current. Harmonic filter equipment is a combination of a dedicated filter for removing a single frequency and a dual-purpose filter that simultaneously removes multiple harmonics. For example, for the fundamental wave, the 5th, 11th, The 13th harmonic is removed by a dedicated filter, and the higher harmonics are removed by a dual purpose filter. Note that the nth (n=5, 11, 1
3) The shunt through which harmonics of higher order are passed is called the n-th shunt (this shunt is equipped with a dedicated filter), and the shunt through which harmonics of higher orders are passed together is called the HP shunt (this shunt is is equipped with a dual-purpose filter).

[0003] Accident 1 in this harmonic filter equipment
One of these is the failure of capacitor elements and reactor elements that make up the harmonic filter equipment. There are several ways to detect these faults, including a method to detect impedance. The detection method has been adopted as an excellent method. The reason why we are looking at the same phase here is that if it is the same phase, it will not be affected by unbalanced phase voltages. Another reason is that the impedance method has the disadvantage of being affected by frequency fluctuations.

FIG. 3 shows a circuit diagram of a conventional analog protection relay for detecting the same-phase fundamental wave difference current (see Nissin Electric Technical Report Vol. 23. No. 2 (1978, 4)). In the figure, a fifth branch 5L as a high frequency branch,
11th branch 11L, 13th branch 13L, HP branch HPL
There are four of them, and a protection relay is shown that monitors the differential current between each shunt. The protection relay that monitors the differential current between the 5th shunt 5L and the 11th shunt 11L will be described below, but the operation of the protective relay that monitors the differential current between other shunts also applies to this protective relay. Since the operations are similar, the explanation will be omitted.

As shown in FIG. 3, a filter circuit consisting of a capacitor C5, a reactor L5, a resistor R5, etc. is installed in the fifth branch 5L, and a filter circuit consisting of a capacitor C11, a reactor L11, and a resistor R11 is installed in the eleventh branch 11L. A filter circuit consisting of 5L and 11L is installed in each branch.
Current transformers CT1, C detecting currents i5, i11 flowing through
T2, CT3, CT4, CT5, and CT6 are installed. Output terminals of current transformers CT1 and CT5 are cross-connected to each other through compensating current transformers CCT1 and CCT2.
A difference current Δi between the currents detected at and corrected by the compensation current transformers CCT1 and CCT2 is taken. Compensating current transformer CCT1
, CCT2 are for correcting the difference in fundamental wave rating values between the shunts at the time of initial adjustment. This difference current Δi is
Each harmonic component is absorbed by the fifth harmonic pass filter F5 and the eleventh harmonic pass filter F11, and only the remaining fundamental wave component is introduced into the shunt failure detection relays 5A and 11B.

The shunt failure detection relay 5A is a relay that detects an increase in the current flowing through the fifth shunt based on an increase in the differential current Δi, with the current i5 flowing through the fifth shunt as a reference (ipol), The shunt failure detection relay 11B is the first
This relay detects an increase in the current flowing through the 11th branch based on the current i11 flowing through the 1st branch based on a decrease in the differential current Δi.

By configuring the protection relay as described above, it is possible to carry out a protective operation against typical accidents such as element failure in a single branch or element failure in two branches of the same phase. For example, if the impedance decreases due to an element failure of the capacitor in the 5th shunt, the fundamental wave current passing through the 5th shunt will increase, and the 5th shunt side difference current between the 5th and 11th shunts will increase. When relay 5A operates, relay 5B installed between HP and fifth shunt operates due to the increase in the difference current between HP and fifth shunt, so the trip command is issued by the operation of these relays. I can put it out.

[0008] Furthermore, when element failure occurs in capacitors in the same phase of the two shunts, for example, in the same phase of the 5th shunt and HP shunt, the currents in the 5th shunt and HP shunt In order to increase the current, the relay 5A operates due to an increase in the fifth branch side difference current between the fifth and eleventh branches, and
Since the relay HPB operates due to an increase in the HP shunt side difference current between the 13th-HP shunt, a trip command can be issued under this condition.

[0009]

However, in the differential current relay for protecting harmonic filter equipment, the compensation current transformer C
Requires incidental equipment such as CT1, CCT2, filters F5, F11, etc., and mostly uses analog elements such as relays 5A, 11B, filters F5, F11, etc., so characteristics are likely to change due to aging or temperature changes. , Therefore, there was a risk that the detection accuracy would deteriorate. Therefore, the characteristics of the differential current relay, including the auxiliary equipment, must be periodically inspected at short intervals, and elements must be adjusted or replaced as necessary, resulting in a time-consuming maintenance process.

[0010] Furthermore, it has been difficult to completely remove high frequency components close to the fundamental wave, such as the fifth harmonic, using an analog filter. For this reason, active filters with sharp cutoff characteristics using operational amplifiers have been used, but the circuits become complicated and capacitors and
There still remained the problem that the characteristics of the resistor changed over time and due to temperature changes.

[0011]Furthermore, if a DC component remains, the sensitivity of the relay to the DC component is high, causing the relay to malfunction. The present invention has been made in view of the above problems, and provides a digital relay for protecting harmonic filter equipment that reliably extracts the fundamental wave component, cuts the DC component, and is resistant to aging and temperature changes. The purpose is to

0012

[Means for Solving the Problems] To achieve the above object, the harmonic filter equipment protection digital relay of the present invention includes a current detection means for detecting a current flowing into a shunt of the harmonic filter equipment, and a basic a sampling means for sampling the output wave of the current detection means at each point in time when time corresponding to one period of the wave is equally divided at predetermined intervals; and a sample value im (
m is an integer indicating a sampling point), a predetermined number p
Using, three equally spaced sample values im-p,i
Select m, im+p, ιm=im-p +2im +im+p
...(1) Using the first calculation means that calculates the value ιm and the value ιm calculated by the first calculation means, the difference ιm −ιm−k between ιm and the value ιm−k separated by half a period.
...a second calculation means for calculating (2);
and third calculation means for extracting and calculating the fundamental wave component of the current using the value obtained by the calculation means, and operates based on the fundamental wave component of the current extracted by the third calculation means. .

[0013]

[Operation] The instantaneous value i(t) of the current is changed to the fundamental wave component In(
n=1) and harmonic component In(n=2,3,...), i(t) = ΣIn sin(nωt+θn)
...(3). n is the order, ω is the frequency of the fundamental wave, θ
n is the phase of the n-th wave, and the sum Σ is taken for n (
Hereinafter, unless otherwise specified, the sum Σ is taken for n.)

Here, if i(t) is sampled at each point in time when one period 2π/ω is divided into 2k equal parts, im
=i (2mπ/2k ω) =ΣIn sin(nmπ/k+θn)
...(4).

[0015] Also, im+p is: im+p =ΣIn sin{n(m+p)π/k+θ
n}...(5) im-p is, im-p =ΣIn sin{n(m-p)π/k+θ
n}...(6).

[0016] Now, only the s-th wave (s is a natural number) will be considered. Rewriting equation (1) above, ιm =im-p +2im +im+p=2im +
Is sin {s(m+p)π/k+θs}+Is s
in {s(m-p)π/k+θs}=2im +2Is
sin {(sm π/k)+θs}×cos(spπ
/k) =2im +2im cos(spπ/k)=2im{
1+cos(spπ/k)} (7).

Hereinafter, 2{1+cos(sp
π/k)} is expressed as G(s). G(s) =2{1+cos(spπ/k)}
...(8) G(s) corresponds to the gain of the filter. From the above equation (7), G(s) is DC (s=0)
takes the maximum value 4, and for a given s cos(spπ/
k) Takes the value 0 by selecting p that satisfies =-1. Therefore, it can be used as a kind of digital filter for passing the fundamental wave and removing specific harmonics.

FIG. 2 shows that when one cycle of the target wave is divided into 120 equal parts and the target wave is sampled at each time point, and the predetermined number p is 12, G(s) = 2 {1 + cos (12s π/60)}, where the vertical axis is the gain G(s)
, the horizontal axis represents the harmonic order s.

From the figure, it can be seen that the filter is designed to pass the fundamental wave and cut off the vicinity of the fifth harmonic. Next, when the second calculation means calculates the difference between ιm and the value ιm-k separated by half a cycle, ιm -ιm-k = 2(im - im-k ) {1+cos(spπ/k
)}=2Is{sin(smπ/k+θs)−sin(
s(m-k)π/k+θs)}{1+cos(spπ/
k)}=4Is sin (sπ/2) cos(sm
π/k+θs +sπ/2) {1+cos(spπ/
k)}
…
(9) Looking at this formula, when the wave order s is an even number,
The gain of ιm −ιm−k is zero.

[0020] Therefore, if the fundamental wave component is determined by the third calculation means based on the output signal of the second calculation means, it is possible to cut the direct current, pass the fundamental wave, and exclude harmonics of a desired order. It is possible to realize a digital relay that can perform

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples will be explained in detail below with reference to the accompanying drawings showing examples. Figure 1 shows the i-th branch iL and the j-th branch jL (i, j
=5, 11, 13, HP) It is a circuit diagram of filter circuits 1 and 2 connected between them and a digital relay 3 that protects each filter circuit 1 and 2.

The filter circuit 1 is a series circuit of a capacitor Ci and a reactor Li, and the filter circuit 2 is also a series circuit of a capacitor Cj and a reactor Lj. The current flowing through filter circuit 1 is detected by current transformer CTi, and the current flowing through filter circuit 2 is detected by current transformer C
Tj is detected and input to the digital relay 3, respectively.

The digital relay 3 includes harmonic attenuation circuits 11 and 12 that attenuate harmonic components of current, and cuts DC components from outputs i(t) of the harmonic attenuation circuits 11 and 12 to extract fundamental wave components. fundamental wave extraction circuits 13 and 14, a difference current calculation circuit 15 that calculates the difference current between the fundamental wave components extracted by the fundamental wave extraction circuits 13 and 14, and a threshold for the difference current detected by the difference current calculation circuit 15. It has a command output circuit 16 and a time limit circuit 17 that output a command signal when a gap of a certain value or more occurs and this state continues for a certain time or more counted by a time limit circuit 17.

The fundamental wave extraction circuits 13 and 14 control the output voltages of the harmonic attenuation circuits 11 and 12 for a certain period of time Δt (Δt is set to, for example, 0.000139 seconds. The frequency is 60 Hz.
In the case of , it corresponds to a phase angle of 3°, and the number of samplings is 2k =
It becomes 120. ), A/D conversion circuits 13b and 14b that digitally convert the sampled and held values, RAMs 13c and 14c that store the digitally converted sample values (referred to as im), and settings. The predetermined number p(
In this example, p = 2, 5, 12) is used to calculate three equally spaced sample values im-p, im, im+p.
Select ιm=im-p +2im +im+p
...(10) The first calculation units 13d and 14d calculate the values ιm and ιm calculated by the first calculation units 13d and 14d, and the value ιm− which is half a cycle away.
Difference of 60 Ιm = ιm −ιm − 60
A second calculation unit 13f that calculates (11),
14f, the value Ιm calculated by the second calculation units 13f, 14f
Using the following formula, {(1/120)ΣIm 2} 1
/2... It has third calculation units 13e and 14e that calculate the effective value according to (12) (the sum Σ in the above equation (12) is taken from m=0 to 119).

The operation of the digital relay 3 will be explained below. The sample value im sampled by the sample hold circuits 13a, 14a at the above-mentioned fixed time intervals Δt and digitally converted by the A/D conversion circuits 13b, 14b is stored moment by moment in the RAMs 13c, 14c. The first calculation units 13d and 14d store a value im sampled at an arbitrary time t=tm, a value im+p sampled p periods later, and a value im-p sampled p periods ago, into the RAM 13c, 14
c, and calculate ιm based on the above equation (10). Data ιm calculated by the above formula (10)
As already explained using FIG. 2, the harmonic components contained in the waveform are cut, and the fundamental wave remains as it is.

The results of calculating the gain G(s) in each case of p=2, 5, and 12 are shown in the table below. First, when p = 12, G(s) = 2 {1 + cos (12s π/60)}, and G(s) near the fundamental wave s = 1 and the fifth harmonic s = 5.
) values are shown in Table 1. Here, Δs is s
is the frequency deviation (%) from = 1 and s = 5, and G(
The value of s) is set to 100 for s=1, and the relative value from this is shown.

[0027]

[Table 1]

From the above table, it can be seen that the filter gain is almost constant and maximum near the fundamental wave, and becomes 0 near the fifth harmonic. Therefore, the fifth
It can be seen that since harmonics can be removed, it can be used for the fifth branch. Next, when p = 5, G(s) = 2 {1 + cos (5sπ/60)}, and the fundamental wave s = 1, the 11th harmonic s = 11, and the 13th harmonic s = 13. The values of G(s) are shown in Table 2.

[0029]

[Table 2]

From the above table, it can be seen that the filter gain is almost constant and maximum near the fundamental wave, and becomes almost 0 near the 11th and 13th harmonics (the filter gain becomes completely 0). (This is true for the 12th harmonic). Therefore, since the 11th harmonic and the 13th harmonic can be removed, it can be seen that it is sufficient to use the 11th and 13th shunts.

Next, when p=5, G(s) = 2 {1+cos(2sπ/60)}, and G near the fundamental wave, 23rd, 25th, 35th, and 37th harmonics
The value of (s) is as follows.

[0032]

[Table 3]

From the above table, the filter gain is almost constant and maximum near the fundamental wave. 23rd, 25th, 35th, 3rd
Although the filter gain cannot be said to be 0 near the seventh harmonic, this does not become a problem because the harmonic components are suppressed in advance by passing through the harmonic attenuation circuits 11 and 12. Therefore, it can be used for HP shunting. In addition, if you want to further reduce the filter gain at harmonics, use the above p = 2,
The first arithmetic units having the filter characteristics in each case of 5 and 12 are connected in series.
It may be used as an arithmetic unit for each branch.

Table 4 lists the filter characteristics of the first arithmetic units connected in series. Note that Table 4 shows relative gains only when Δs=0.

[0035]

[Table 4]

[0036] The second calculation units 13f and 14f perform the above-mentioned (11
) By calculating the difference Im with the value shifted by half a cycle, the DC component can be removed. The third calculation units 13e and 14e use the DC component removed value Im calculated in the second calculation units 13f and 14f to calculate the above ((
12) Extract the fundamental wave component by calculating the effective value based on the equation.

The difference current of the fundamental wave thus obtained is calculated by the difference current calculation circuit 15. To explain in more detail, the difference current calculation circuit 15 calculates the shunt i
The initial ratio of the rated value of the fundamental wave current included in the current flowing through L and the rated value of the fundamental wave current included in the current flowing through shunt jL is ro, and the effective effect of shunt iL obtained by the fundamental wave extraction circuit 13 is When the value is Ii and the effective value of the shunt jL obtained by the fundamental wave extraction circuit 14 is Ij, the discriminant Ii −r
o Ij ≧Ii, n×p/100 to detect the presence of a differential current. The above Ii,n is the fundamental wave current rating value of the shunt iL, and p is the detection sensitivity (%).

The command output circuit 16 is a differential current calculation circuit 15.
When it is known that the discrimination result has appeared for a certain period of time counted by the time limit circuit 17,
, 2 from the system, an operating output is provided to a circuit breaker (not shown). As a result, harmonic filter circuits 1 and 2
can interrupt the current flowing to the Note that in this case, the operation signal may be outputted even if a state where the value is equal to or greater than the reference value appears instantaneously without installing a time relay.

As described above, by calculating equation (10), harmonic components of the desired order are removed, only data containing the fundamental wave component is extracted, and by calculating equation (11), DC Since the fundamental wave difference current can be determined based on the fundamental wave difference current and the relay can be operated, it is possible to suitably configure a protective relay for a filter equipment that shunts high frequency waves.

Note that the present invention is not limited to the above embodiments. For example, although the above embodiment is a differential current detection relay, the relay is not limited to this, and may be one that detects a single current. In addition, in the third calculation means, an effective value calculation circuit was used to extract the fundamental wave component of the current, but instead of taking the effective value, for example, the fundamental wave component was extracted by Fourier integration. Good too.

Further, in the above embodiment, the sampling interval Δt is a time corresponding to a phase angle of 3°, but the present invention is not limited to this. In general, the smaller the sampling angle, the more harmonics can be handled (sampling theorem), but the amount of data increases. The order decreases. Various other design changes can be made without changing the gist of the present invention.

[0042]

Effects of the Invention As described above, according to the digital relay for protecting harmonic filter equipment of the present invention, the set number p
Using, three equally spaced sample values im-p,i
Select m, im+p and ιm=im+p +2im
By calculating the value +im-p, it is possible to obtain data ιm that includes the fundamental wave component and does not include the frequency component corresponding to the predetermined number p.

Furthermore, the direct current component can be completely removed by taking the difference between the data ιm and a value that is half a cycle away. Therefore, by configuring a digital relay by setting p according to the order of the harmonics that shunt the harmonic filter equipment, a highly reliable relay can be obtained and the harmonic filter equipment can be suitably protected. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a digital relay for protecting harmonic filter equipment.

FIG. 2 is a graph showing the gain characteristics of a digital filter.

FIG. 3 is a circuit diagram showing a conventional analog harmonic filter equipment protection relay.

[Explanation of symbols]

1, 2 harmonic filter circuit, 3 harmonic filter equipment protection relay, 11, 12
Harmonic attenuation circuit, 13, 14 Fundamental wave extraction circuit, 13a, 14a Sampling circuit, 13b, 14b
A/D conversion circuit, 13c, 14c RAM, 13d, 14d first calculation section, 13e, 14e third calculation section, 13f, 14f second calculation section, 15 difference current calculation circuit, 16 command output circuit, CTi, CTj change sink

Claims (1)

[Claims] Claim 1: A relay that protects harmonic filter equipment by detecting the fundamental wave component of a high frequency shunt of the harmonic filter equipment, wherein the relay detects the current flowing into the shunt of the harmonic filter equipment. a detection means, a sampling means for sampling the output wave of the current detection means at each point in time when the time corresponding to one period of the fundamental wave is equally divided at predetermined intervals, and a sample value im obtained by the sampling means.
(m is an integer indicating a sampling point), set a predetermined number p, and select three equally spaced sample values im-
p, im, im+p and calculates the value ιm=im-p +2im +im+p using the value ιm calculated by the first calculation means, ιm and a value ιm-k separated by half a period. and a third calculation means for extracting the fundamental wave component of the current using the value obtained by the second calculation means, and the third calculation means extracts the fundamental wave component of the current. A digital relay for protecting harmonic filter equipment, which operates based on the fundamental wave component of the extracted current.