JPH04200241A - Digital relay for protecting harmonic filter equipment - Google Patents

Abstract

PURPOSE:To surely extract fundamental wave components of a current and to prevent secular change and temperature change by selecting certain three sample values, by conducting the extract operation of the fundamental wave components of a current and by operating an apparatus on the basis of the fundamental wave components of the current. CONSTITUTION:Currents flowing through filter circuits 1, 2 are detected by current transformers CTi, CTj and respectively inputted to a digital relay 3. Sample and hold circuits 13a, 14a sample the current values of an arbitrary time, the time after (p) periods from that arbitrary time and the time before (p) periods therefrom. First operation parts 13d, 14d leave fundamental waves included in data as they are, but remove harmonic components. Second operation parts 13e, 14e operate effective values. The current difference of the fundamental waves are computed by a current difference computation circuit 15. A command output circuit 16 gives an operating output to a breaker according to the discrimination results of the difference current computation circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a digital relay provided for protecting harmonic filter equipment.

<Prior Art> In places that generate a large amount of high-frequency current, 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,, 13
) order harmonics are passed through the n-th branch (this branch is equipped with a dedicated filter), and the branch that passes all higher-order harmonics is called the HP branch (this branch is equipped with a dedicated filter). is provided with a dual-purpose filter).

One of the accidents in this harmonic filter equipment is failure of the capacitor element or the accelerator element that constitutes the harmonic filter equipment. The method for detecting these failures is
There are several methods that can be considered, including methods that detect impedance, but a method that focuses on the fundamental wave current constantly flowing in each shunt and detects the same-phase fundamental wave difference current between shunts is a better method. has been done. 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 disadvantage of the impedance method is that it is affected by frequency fluctuations.

Figure 3 shows a circuit diagram of a conventional analog protection relay that detects the same-phase fundamental wave difference current (Nissin Electric Technical Report Vol. 1).
．． 23. No. 2 (1978, 4)). In the figure, a fifth branch 5L and an eleventh branch 11L are high frequency branches.
, the 11th branch 11L, and the HP branch HPL.
A protection relay is shown that monitors the differential current between each shunt. Below, we will explain the protective relay that monitors the differential current between the fifth shunt 5L and the eleventh shunt 11L, and also explain the operation of the protective relay that monitors the differential current between other shunts. Since the operations are similar, the explanation will be omitted.

As shown in FIG. 3, the fifth branch 5L has a capacitor C5.
, a filter circuit consisting of a reactor L5, a resistor R5, etc. is installed, and a filter circuit consisting of a capacitor C1l, a reactor Lll, a resistor R11, etc. is installed in the 11th branch 1LL, and the current i 5 flowing through each shunt 5L, IIL is ．．
i 11 detecting current transformer CTI, CT, 2. CT3
and CT4. CT5. CT6 is installed. Among these, the output terminals of the current transformers CTI and CT5 are connected to the compensation current transformer C
CT1. They are cross-connected to each other through CCT2 and current transformer CTI.

CT5 and compensation current transformer CCT1. A difference current Δl of the current corrected by CCT2 is taken. compensation current transformer CC
Tl and CCT2 are for correcting the difference in fundamental wave rating values between the shunts at the time of initial adjustment. Each harmonic component of this difference current Δi is absorbed by the fifth harmonic pass filter F5 and the eleventh harmonic pass filter Fil, and only the remaining fundamental wave component is introduced into the shunt failure detection relay 5A and LIB.

The shunt failure detection relay 5A has a current of 15 that flows through the fifth shunt.
is a relay that detects an increase in the current flowing through the fifth branch based on an increase in the difference current Δ1 with reference to (ipol),
The shunt failure detection relay LIB is a relay that detects an increase in the current flowing through the eleventh shunt based on a decrease in the differential current Δ1 with reference to the current 111 flowing through the eleventh shunt.

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 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. As the relay 5A operates, the increase in the difference current between the HP and the 5th shunt causes the relay 5B installed between the HP and the 5th shunt to operate, so the trip command is issued by the operation of these relays. can be produced.

In addition, if a capacitor element failure occurs in the same phase of two shunts, for example, if a capacitor element failure occurs in the same phase of the 5th shunt or HP shunt, the current in the 5th shunt and HP shunt will increase. , the relay 5A operates due to an increase in the difference current between the 5th and 11th branches on the 5th branch side, and the 13th HP
Since the relay HPB operates due to an increase in the HP shunt side difference current between the shunts, a trip command can be issued under this condition.

<Problem to be solved by the invention> However, in the above-mentioned differential current relay for protecting harmonic filter equipment, the compensation current transformer CCT1. CCT2, filter F5
．． Requires incidental equipment such as Fi1, mostly relays 5
A, IIB, filter F5. Since analog elements such as F11 are used, characteristics are likely to change due to aging or temperature changes, which may lead to deterioration in detection accuracy. In the past, the characteristics of differential current relays, including auxiliary equipment, had to be inspected at short intervals, and elements had to be adjusted or replaced as necessary, making maintenance and management time-consuming.

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
As circuits became more complex, there remained the problem that the characteristics of capacitors and resistors changed over time and due to temperature changes.

The present invention has been made in view of the above problems, and aims to provide a digital relay for protecting harmonic filter equipment that reliably extracts the fundamental wave component and is resistant to aging and temperature changes. .

<Means for Solving the Problems> The digital relay for harmonic filter equipment protection of the present invention, which achieves the above object, 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 the time corresponding to one period of the wave is equally divided at predetermined intervals; and a sample value i m (+n indicates a sampling point) sampled by the sampling means. Using a predetermined number p from among (integers), calculate three equally spaced sample values i m-p, i m, i m, im+p
Select ' t mpromp-p +2
in+im+p-(1)
and a second calculation means that performs an extraction calculation of the fundamental wave component of the current using the tffl obtained by the first calculation means, and the second calculation means extracts the fundamental wave component of the current. It operates based on the fundamental wave component of the current.

Effect> The instantaneous value of the current 1(t) is converted into the fundamental wave component I n(n-1)
and harmonic components I n (yr2, 3...), i (t) −Σ I n sin [n
ω t+θ b] ...(2).

n is the order, ω is the frequency of the fundamental wave, and θn is the phase of the n-th wave.

Here, at each point in time when −period 2π/ω is divided into two
(t), im-i(2mπ/
ω to 2) 1Σ I n sin [nll1π/to 10n]
−(3).

Moreover, i map is i map−Σ I n sin [n(g++p) y
r /+θn ] −(+4i m−p is expressed as i m−p−Σ I n sin [n(m−p) π+θn ] . . . −(5).

Now, consider only the 8th wave (S is a natural number). Rewriting equation (1) above, ιm −im−p +2 ia+ +im+p−21m
+ I s sin [s (map) π / + θ S co + I s sin [s (m-p)
π/to + θ S co-2i m + 2 I
s sin [(sn+π/k)+θ S coX
cos(spπ/k) = 2 i m + 2 i m cos(s
pπ/k)−2i ffl [1+cos(spπ
/k) ko...(6).

Hereinafter, 2 [1+ cos(spπc) in equation (6) will be expressed as G (s).

G (S) = 2 [1+ cos(spπ/k
)ko = (7)G (s) corresponds to the gain of the filter.

From the above equation (7), G (s) has a maximum value of 4 in direct current (s=0), and for a given S, cos(spπc)−
By selecting p that satisfies -1, the value 0 is taken. Therefore, it can be used as a kind of digital filter for passing the fundamental wave and removing specific harmonics.

Figure 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
yr /60) is a graph showing the calculation result of
The vertical axis represents gain G(s), and the horizontal axis represents 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.

Therefore, by performing calculations using this first calculation means and determining the fundamental wave component based on the output signal, a digital relay that can pass the fundamental wave and exclude harmonics of a desired order can be realized. I can do it.

<Example> Embodiments will be described in detail below with reference to the accompanying drawings showing examples.

Figure 1 shows the first branch iL and the J branch jL (i, j=5
゜11.13. ) iP) filter circuit l connected between
, 2 and each filter circuit 1.2.

The filter circuit l includes a capacitor Ci and a reactor Li.
The filter circuit 2 is also a series circuit with the capacitor C.
This is a series circuit of reactor Lj and reactor Lj.

The current flowing through the filter circuit 1 is detected by a current transformer CTj, and the current flowing through the filter circuit 2 is detected by a current transformer CTj, and each of them is input to a digital relay 3.

The digital relay 3 includes a harmonic attenuation circuit 11.12 that attenuates harmonic components of current, and a harmonic attenuation circuit 11.1.
Fundamental wave extraction 8 to extract the fundamental wave component from 2-8 force 1(t)
circuit 13.14, a difference current calculation circuit 15 that calculates the difference current between the fundamental wave components extracted by the fundamental wave extraction circuit 13.14, and a threshold value and a constant value for the difference current detected by the difference current calculation circuit 15. A command output circuit 16 that outputs a command signal when the above gap occurs and this state continues for a certain period of time counted by a time limit circuit 17, and a time limit circuit 1.
7.

The fundamental wave extraction circuit 8 circuits 13 and 14 are the harmonic attenuation circuits 11.
12 a force voltage for a certain period of time Δt (Δt is, for example, 0.0
It is set to 00139 seconds. In the case of a frequency of 60 Hz, this corresponds to a phase angle of 3°, which is k-60. ) In particular, sample and hold circuits 13a and 14a for sampling, and A/D conversion circuits 13b and 14b for digitally converting the sampled and held values.

The RAMs 13c and 14c store the digitally converted sample value (referred to as im), and the predetermined number p(
In this example, p-2, 5, 12) are used to obtain B sample values i m-p at equal intervals.

i llN, i I"l) and ιm-im-
The first calculation units 13d, 14d and the first calculation unit 1 calculate the value p +2 im +im+p − (8)
Using the value ιm calculated by 3d and 14cl, the following formula, m/120) Σ zm2 ko 1/2
...(9) to calculate the effective value
It has calculation units 13e and 14e.

The operation of the digital relay 3 will be explained below.

The samples are sampled by the sample and hold circuits 13a and 14a at the above-mentioned fixed time intervals Δt, and the A/D conversion circuit 13b
, 14b are stored in the RAMs 13c and 14c every moment. The first calculation units 13d and 14d calculate a value 1■ sampled at an arbitrary time t=tH, a value iHip sampled p cycles later, and a value iB−p sampled p cycles earlier. is read out from the RAMs 13c and 14c, and ιm is calculated based on the above equation (8). Above (8)
The harmonic components included in the data ιm calculated by the formula are cut, and the fundamental wave remains as it is, which is already the second
This is as explained using the diagram.

The results of calculating the gain G (s) in each case of p-2, 5, and 12 are shown in the table below.

First, in the case of p-12, G (s) = 2 [1+ cos(12s
yr/80), and the values of G(s) near the fundamental wave s-1 and the fifth harmonic s-5 are as shown in Table 1. Here, ΔS is the frequency deviation (%) from s-1 and 5, respectively, and the value of G (s) is set to 100 with respect to s-1, and the relative value from this is shown.

From the table above in Table 1, 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, since the fifth harmonic can be removed, it can be seen that it is appropriate to use it for the fifth branch.

Next, in the case of p-5, G (s> -2, [1+ cos(5sπ/130)
], and the values of G (s) near the fundamental wave s=1, the 11th harmonic 5-11, and the 13th harmonic 5-13 are as shown in Table 2.

From the table above in Table 2, it can be seen that the filter gain is almost constant and maximum near the fundamental wave, and the filter gain becomes almost O near the 11th and 13th harmonics (the filter gain becomes completely 0). (This is true for the 12th harmonic). Since the 11th harmonic and the 13th harmonic can be removed, it can be seen that they can be used for the 11th and 13th shunts.

Then, for p-5, G (s) = 2 [1+cos(2sr /60)
], and the values of G (s) near the fundamental wave and the 23.25th and 35.37th harmonics are as follows. (Left space below) From the table above in Table 3, the filter gain is almost constant and maximum near the fundamental wave. Although the filter gain cannot be said to be 0 near the 23rd, 25th, 35° and 37th harmonics, 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 as a HP shunt.

If you want to further reduce the filter gain at harmonics, connect the first calculation units in series that have the filter characteristics for each of the above p-2, 5, and 12 cases, and then reconnect the first calculation units in series. It may be used as one calculation 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 in the case of ΔS-0. (Margin below) Table 4 The second calculation units 13e and 14e are the first calculation units 13d and 14.
The fundamental wave component is extracted by calculating the effective value based on the above equation (9) using the value ttb calculated in step d.

Then, the difference current of the fundamental wave obtained in this way is calculated by the difference current calculation circuit 15. More specifically, the difference current calculation circuit 15 calculates the initial ratio of the rated value of the fundamental wave current included in the current flowing through the shunt IL and the rated value of the fundamental wave current included in the current flowing through the shunt jL as rO.
1. If the effective value of the shunt iL obtained by the fundamental wave extraction circuit 13 is i, and the effective value of the shunt jL obtained by the fundamental wave extraction circuit 14 is Ij, then the presence of a difference current is detected using the discriminant formula % formula % It is something to do. Above IL
n is the fundamental wave current rating value of the shunt iL, and p is the detection sensitivity.

When the command output circuit 16 learns that the command output circuit 16 has been present for more than a certain period of time counted by the time limit circuit 17 as a result of the determination by the difference current calculation circuit 15, the command output circuit 16 activates a circuit breaker (Fig. (not shown) outputs the operation output. Thereby, the current flowing through the harmonic filter circuits 1 and 2 can be interrupted. 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 (8), harmonic components of the desired order are removed, only data containing the fundamental wave component is extracted, the difference current is determined based on this, and the relay is operated. Therefore, it is possible to suitably configure a protection relay for filter equipment that shunts high frequency waves.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, there were eight differential current detection relays, but the present invention is not limited to this, and may be one that detects a single current. In addition, it is also possible that an effective value calculation circuit was used to extract the fundamental wave component of the current using the value ιm obtained by the first calculation means, or that the fundamental wave component was obtained by performing Fourier integration instead of taking the effective value. You may decide to extract the components.

Further, in the above embodiment, the sampling interval Δt is a time corresponding to a phase angle of 3'', but it is not limited to this. Generally, the smaller the sampling angle, the higher the harmonics can be handled. (sampling theorem),
As the amount of data increases and the sampling angle increases, either the amount of data becomes smaller or the number of harmonics that can be processed decreases.

Various design changes can be made without changing the gist of the invention.

<Effects of the Invention> As described above, according to the digital relay for harmonic filter equipment protection of the present invention, three equally spaced sample values i H-p, i m i
Select s, im+p, t tp-i gap
By calculating the value + 2 i tb + i al-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. Therefore, by configuring a digital relay by setting p according to the order of harmonics that shunt the harmonic filter equipment, the harmonic filter equipment can be suitably protected.

[Brief explanation of the drawing]

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 the digital filter according to the present invention, and Fig. 3 is a diagram of a conventional analog harmonic filter equipment protection relay. FIG. 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, 14
b...A/D conversion circuit, 13c, 14c...RAM
. 13d, 14d...first calculation section, 13e, 14e...second calculation section, 15...difference current ratio circuit, 16...command output circuit,
CTi, CTj...Current transformer patent applicant Representative of Nissin Electric Co., Ltd. Patent attorney Hirokatsu Kamei (and 2 others)

Claims (1)

[Claims] 1. A relay that protects harmonic filter equipment by detecting the fundamental wave component of a high frequency shunt of the harmonic filter equipment, which protects the harmonic filter equipment by detecting the fundamental wave component of the high frequency shunt of the harmonic filter equipment, Current detecting means for detecting; sampling means for sampling the output wave of the current detecting means at each point in time when the time equivalent to one cycle 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 the sampling point),
By setting a predetermined number p, three equally spaced sample values i
Select m-p, im, im+p, ιm=im-p+2
It has a first calculation means for calculating the value im+im+p, and a second calculation means for extracting the fundamental wave component of the current using ιm obtained by the first calculation means, and the fundamental wave component extracted by the second calculation means is A digital relay for protecting harmonic filter equipment that operates based on the fundamental wave component of current.