JPS63148815A - Sampling apparatus of digital relay - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention samples alternating currents such as voltages and currents in power systems such as power transmission lines and layout ams at frequencies that are integral multiples of the alternating currents, and digitally converts the sampled values. This invention relates to a sampling device in a digital relay that calculates a value using a microcomputer in accordance with desired relay characteristics and outputs the calculation result.

[Conventional technology]

For example, as a relay for detecting failures in power systems, characteristics such as the amount of change in voltage, current, etc. before and after the failure, specifically, the amount of change in values of voltage, current, etc., or the amount of vector change including phase, etc. are widely considered. Detection of such a change amount is difficult to realize using an analog method due to its configuration and operation. On the other hand, the digital system has excellent memory and calculation capabilities, and therefore relays having the above-mentioned characteristics can be easily realized and are currently widely used.

Incidentally, in digital relays, it is necessary to sample alternating current amounts such as voltage and current in order to detect the amount of change before and after a failure. For this reason, in the past, the amount of alternating current was sampled using a sampling signal whose sampling period was synchronized with the voltage of the power system and whose frequency was an integral multiple of the voltage.

FIG. 4 shows a block diagram of a conventional digital relay configured as described above. In FIG. 4, 1 is a power system, 2 is a current transformer, and 3 is a transformer, by which the current and voltage of the power system are detected.

Current transformer 2. The current and voltage obtained by transformer 3 are transferred to auxiliary current transformer 4. Each output of the voltage from the voltage divider circuit 6 is guided to the auxiliary transformer 5, isolated there, and converted to an appropriate level by the voltage divider circuit 6. Each output is comprised of a low-pass filter for eliminating aliasing errors. The signal is applied to a sample and hold circuit 9.10 via an analog filter 7.8. A sampling signal from a sampling signal generation circuit 11 is applied to each sample-and-hold circuit 9, 10 at a predetermined period (this will be described later), whereby the voltage and IT current are sampled and held.

The sampled values by the sample and hold circuits 9 and 10 are applied to an A/D converter 13 via a multiplexer 12, where they are converted into digital quantities. This digital quantity is stored in memory circuit 14. And the central processing unit 1
5 reads necessary data from the memory circuit 14, executes a predetermined relay operation, and outputs the result to the output circuit 16. The content of calculations by the central processing unit 15 differs depending on the operating characteristics of the relay, and is determined as appropriate depending on the characteristics of the relay to be obtained.

The sampling signal from the sampling signal generation circuit 11 has a sampling frequency fs (Hz) of 1/N.
It will be emitted at intervals of fs (seconds). N is a positive integer, and for example, in the case of 30-degree sampling, which is generally performed, N=12 is selected. This sampling frequency is synchronized with the voltage frequency of the power system 1. For this purpose, a part of the voltage output from the voltage dividing circuit 6 is given to the sampling signal generating circuit 11. The fundamental frequency component of the power system 1 may be extracted from this voltage output, and then a frequency output synchronized with this may be generated. A PLL circuit is suitable as a configuration for this purpose.

[Problem that the invention seeks to solve]

In the conventional digital relay sampling device as described above, in order to perform sampling using a sampling signal synchronized with the frequency of the voltage of the power system 1, the system voltage, for example, the line voltage Vl between the A phase and the B phase, is input to the power system 1. Let us consider the case where this signal is used as a signal for fundamental frequency extraction. When this signal is input to the PLL circuit, a sampling signal is output from the PLL circuit. It goes without saying that this sampling signal must be normally output even when the power system 1 is out of order.

Now, let's consider resistance-grounded or ungrounded power system construction.

Phase voltage VA of A phase, B phase, and C phase when power system 1 is healthy
, 9m, VC and each line voltage VAII"C' le+
'';'The CAs are out of phase by 120 degrees from each other as shown in the vector diagram of FIG. 5(A).

In the event of a power system lO1 line ground fault, the voltage between each line of A, B, and C phases <I A11I simply by changing the neutral point potential.
Q @c+ f CA does not change at all. However, for example, in the case of a 2M short-circuit failure in phases B and C, the voltage of each phase is VA.

Vm, Vc and each line voltage <lAl1+ Veer
The VCA will look like the vector diagram in Figure 5 (B),
A phase change occurs in the line voltage 9□, which serves as a reference for synchronization of the sampling signal. The PLL circuit is influenced by the transient phenomenon at this time, and its output, that is, the sampling signal transiently deviates from the normal cycle. In other words, the sampling frequency changes transiently. As a result, relay calculations may be performed using incorrect sampling values, and the digital relay may malfunction.

The purpose of the present invention is to provide a digital relay that can sample alternating current amounts such as voltage and current at accurate intervals without changing the sampling timing even in the event of a power system failure, and that can prevent digital relays from malfunctioning. An object of the present invention is to provide a sampling device.

[Means for solving problems]

The digital relay sampling device of the present invention includes a positive-sequence voltage calculation circuit that calculates a positive-sequence voltage from three-phase pressure or line voltage of an electric power system, and a positive-sequence voltage calculation circuit that calculates a positive-sequence voltage from the three-phase pressure or line voltage. a sampling signal generation circuit that synchronizes and generates a sampling signal with a frequency that is an integral multiple of the sampling signal;
a sample-and-hold circuit that samples and holds an alternating current amount such as voltage of the power system in response to a sampling signal output from the sampling signal generation circuit; and A/D conversion of the output of this sample-and-hold circuit. and an A/D converter for supplying the data to the relay arithmetic unit.

[Effect]

According to the configuration of the present invention, a positive-sequence voltage calculation circuit is provided, and the positive-sequence voltage is calculated from the phase voltage or line voltage of three phases of the power system, and a sampling signal synchronized with this positive-sequence voltage is sent to the sampling signal generation circuit. Since the positive-sequence voltage causes almost no phase change even in the event of a power system failure, alternating current voltages, currents, etc. quantity can be sampled and can prevent digital relay malfunction.

〔Example〕

Embodiments of the present invention will be described based on FIGS. 1 to 3. This digital relay sampling device, as shown in FIG.
A, <Is, Vc as auxiliary transformer 26°27.28
Therefore, the line voltage < IA, ? ,,, <1. ^, and introduce these into the positive-sequence voltage calculation circuit 22 to obtain the positive-sequence voltage V
Calculate + and get this positive sequence voltage! , is added to the sampling signal generation circuit 23, and the sampling signal generation circuit 23 generates a positive sequence voltage! , and generates a sampling signal SP having a frequency that is an integral multiple of , and this sampling signal S
In response to P, the sample and hold circuits 42 to 49 sample and hold the voltage and current of the power system 21, and the A/D converter 51 converts the voltage and current into A/D to perform a relay operation using a microcomputer or the like. A device (not shown) is supplied thereto.

The digital relay sampling device will be described in detail below. This digital relay sampling device
As shown in the figure, from the bus 21a of the power system 21 to the three-phase transformer 24, the phase voltage of each phase <IA, Vi, 'J
c and zero-sequence voltage! . The three-phase current transformer 25 detects the phase current ia of each phase from the power transmission line 21b of the power system 21.
, im, ic and zero-sequence current 10 are detected.

Phase voltage obtained by three-phase transformer 24 and three-phase current transformer 25? A, Vm, Vc + zero-sequence voltage! . , phase current i^, is
, lc+ zero-sequence current 10 is guided to auxiliary transformers 26 to 29 and auxiliary current transformers 30 to 33, where it is insulated and then sampled and held through analog filters 34 to 41, which are low-pass filters for eliminating folding errors. Circuit 42~
49 is given.

On the other hand, each line voltage<IAI+vlc+QcA obtained from the analog filters 34 to 36 is input to the positive-sequence voltage calculation circuit 22, and the positive-sequence voltage calculation circuit 22
, the positive sequence voltage t1 is calculated from the line voltage □r VIC+vcA and output. The sampling signal generation circuit 23 receives the above-mentioned positive-sequence voltage t1, and receives the positive-sequence voltage 9. A sampling signal SP is generated in synchronization with the frequency and has a frequency that is an integral multiple of that frequency, for example, 12 times, and this sampling signal SP is used to control the sample and hold circuits 42 to 49.
is the line voltage VAII <IIC+ 9CA+zero-sequence voltage<
1. , phase currents ja, is, ic, and zero-sequence current i, respectively, are sampled and held and input to the multiplexer 50. The multiplexer 50 sequentially switches the outputs of the plurality of sample and hold circuits 42 to 49 to the A/D converter 5.
1, and the A/D converter 51 converts the sampled values into digital values as they are sequentially input from the sample/hold circuits 42 to 49 and sends them to the microcomputer that constitutes the relay calculation device. It turns out.

Note that 52 to 55 are resistors.

In this embodiment, a positive-sequence voltage calculation circuit 22 is provided to convert the phase voltages Va, Qm, and Qc of the power system 21 into a positive-sequence voltage 9I, and a sampling signal S synchronized with this positive-sequence voltage V+.
P is generated by the sampling signal generation circuit 23, and the positive-sequence voltage 91 hardly changes the phase even when the power system 21 fails, so the sampling timing does not change and is accurate even when the power system 21 fails. line voltage<1□,9. ,,v. 4. Zero-sequence voltage! . ,
Phase currents IA, l+++ Ic, and zero-sequence current i can be sampled, and malfunctions of digital relays can be prevented.

Here, it will be explained in detail that the phase of the positive-sequence voltage t of the power system 21 hardly changes when the power system 21 fails.

FIG. 2 is a model of a resistance-grounded power system 21, and in the case of a directly grounded system, it can be assumed that the neutral point resistance Rn is zero.

In FIG. 2, a, , a, , e. is the power supply voltage of each phase, White l = α1 White ^ ・・・・・・ (1) Warehouse.

-α white, ...... (2),
However, .

17 is the neutral point current; 2. is the impedance behind the bus bar, 2
E is the line impedance up to the failure point, VA, Vm,
Vc is the phase voltage, Ia, L,! c is the phase current.

Now, from Figure 2, 9A=QA Rnj, 2s L --+419
m=es Rnl-2s fs --(5)Qc"
Qc Rni, 2s lc --(611^
+11+1c=iA (7) From equations (4) to (6), positive sequence voltage 9. When calculating, 3V+=Va +αt, +α”Vc = 3kura, -2s (IA +αli+(r”lc)
(8) In addition, the positive sequence voltage calculation circuit 22 calculates the line voltage t□r.
The positive sequence voltage 9. is determined by VICI'';/cA, but this case will be discussed later.

Here, a case will be considered in which a one-wire ground fault occurs, for example, a ground fault occurs in the B phase. From Figure 2, i3=□ Rn+2= +21 α8kura Rn+2= +2j! i＾ -ic ”O... α・This number (9)
By substituting the relationship in Equation 01 into Equation (8), it becomes.

If the power system 21 is directly grounded (Rn-0), 3V+
-(3k,) white, ...... (2). However, the impedance behind the busbar, which is 2°, is 28. Most of the line impedance 2β beam actance up to the failure point is
k can be considered as a real number of 0≦, ≦1...α.

In addition, if the power system 21 is a resistance grounding system or a non-grounding system, Rn>)2.・・・・・・ 0Rn force 21 ・・・・・・
Since it is αυ, it becomes 39, Σ3 white, ...... αη.

Therefore, in case of lvA ground fault, the direct earthing system,
In both resistance-grounded and non-grounded systems, the positive sequence voltage <
/1 is in phase with the power supply voltage white. The same applies to ground faults in other phases.

Next, consider the case of a failure in two or more wires.

Since the positive sequence current 11 is i^+αi3+α”Ic”3L...α碍, the formula (8) is 3Q+-3kura A 32sl+...O
It becomes l.

When the circuit in Figure 2 is transformed into symmetrical coordinates, the zero-phase circuit becomes as shown in Figure 3 (A), the positive phase circuit becomes as shown in Figure 3 (B), and the negative phase circuit becomes as shown in Figure 3 (C). ), and in Figure 3, h, i, j.

k, l, m are failure points, 9° is zero-sequence voltage, 10 is zero-sequence current, 9I is positive-sequence voltage, i is positive-sequence current, ! 8 is a negative sequence voltage, and it is a negative sequence current.

The failure point h in Fig. 3 (A), (B), and (C)
The connection status of ~m changes variously depending on the failure mode.

In the case of a directly grounded system (Rn=O), considering that the impedance behind the bus bar is 2s and the line impedance 21 to the fault point is mostly actance, in the case of any fault, the positive sequence current j+ is , the current lags behind by about 90 degrees. Therefore, the positive phase voltage 91 determined by 3Q + - 3 m - 32 sL ... (to) is almost in phase with the power supply voltage hole.

Next, in the case of resistance grounding systems and non-grounding systems, in the case of a failure that does not involve a ground fault, the zero-sequence circuit is not connected, and the positive sequence current i is 23,2I! The current is constrained by . Therefore, as in the case of a direct grounding system, the positive sequence current 11 is connected to the power supply voltage hole,
The current lags behind by about 90 degrees, and the positive-sequence voltage t1 is almost in phase with the power supply voltage EA.

In addition, in the case of a fault accompanied by a ground fault, a plane fault (three-phase ground fault)
In this case, fault points j and k are connected, and the positive sequence current 11 is white.

Therefore, the positive sequence voltage V+ is the power supply voltage.

It becomes the same phase as . In addition, in unbalanced faults (two-phase ground fault, etc.),
The zero-phase circuit and the negative-phase circuit are connected in parallel, but Rn >> 2 s...
(22) Rn″>) 21 ・= =
Considering (23), the zero-phase circuit can be ignored.

Therefore, the positive sequence current i+ is 2s, 2j! As a result, the positive sequence voltage <II is almost the same as the t source voltage white.

From what has been stated above, the positive sequence voltage V+ is
Before and after the failure in No. 1, the voltage A and white are almost in phase, and it can be said that there is no phase change due to the failure.

Note that in the above, the positive sequence voltage 91 was calculated from the phase voltages Qa, 'Ls, and Vc, but the line voltage<I AhV l
Positive sequence voltage based on e+ <I cA! 1 can also be calculated. In this case, summer□+α9. c+α<J cA = (vA-9m)+α(9m9c)+α” (V
CVA) = (!, +α!, +α1M,) 1α" (Qm +α9.+α" Qc) - (1-α")
l+, and there is no phase variation in the positive-sequence voltage M1 at this time as well.

〔Effect of the invention〕

According to the digital relay sampling device of the present invention, a positive-sequence voltage calculation circuit is provided, the positive-sequence voltage is calculated from the phase voltage or line voltage of three phases of the power system, and a sampling signal synchronized with this positive-sequence voltage is generated. The positive-sequence voltage generated by the sampling signal generation circuit has almost no phase change even in the event of a power system failure, so even in the event of a power system failure, the sampling timing remains accurate and the period is accurate. It is possible to sample alternating current amounts such as voltage and current, and it is possible to prevent digital relays from malfunctioning.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a circuit diagram modeling a three-phase power system, Figure 3 is a circuit diagram obtained by symmetrical coordinate transformation of the circuit in Figure 2, Figure 4 is a block diagram of a conventional digital relay, and Figure 5 is a circuit diagram of a conventional digital relay. It is an explanatory diagram of a defect.

Claims (1)

[Claims] A positive-sequence voltage calculation circuit that calculates the positive-sequence voltage from the three-phase phase voltage or line voltage of the power system, and a sampling signal that is synchronized with the positive-sequence voltage output from this positive-sequence voltage calculation circuit and has a frequency that is an integral multiple of the positive-sequence voltage. a sampling signal generation circuit that samples and holds alternating current amounts such as voltage and current of the power system in response to a sampling signal output from the sampling signal generation circuit; A digital relay sampling device equipped with an A/D converter that A/D converts the output of the circuit and supplies it to the relay calculation device.