JPH01170318A - Ratio differential relay - Google Patents

Abstract

PURPOSE:To effectively distinguish a detection current due to an internal accident from that due to an external accident by obtaining an operation amount and a suppression amount at the time of nonsaturation in each cycle of a line current, and detecting the amplitude of a differential value due to a phase difference with an accident current. CONSTITUTION:A ratio differential relay is composed of operation amount calculating means, suppression amount calculating means and accident discriminating means. The operation amount calculating means calculates the sum of the momentary values of two line currents, calculates the operation amount of the relay on the basis of the absolute values of the difference of the present value of the sum of the calculated momentary values and a value before a predetermined time, calculates the scalar sum of the momentary values of the two line currents, and calculates the suppression amount of the relay on the basis of the absolute value of the difference of the present value of the calculated scalar sum and a value before a predetermined time. The accident discriminating means calculates the difference value between the operation amount and the suppression amount, and discriminates the content of the accident on the basis of the difference value.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a ratio differential relay for power system protection, and is particularly suitable for preventing malfunctions when a current transformer used in a signal input circuit becomes magnetically saturated. Regarding ratio differential relays.

[Conventional technology]

A ratio differential relay is used to trip a pair of circuit breakers that define an area to be protected in a power system line, thereby protecting the area to be protected from an accident and preventing the impact on other systems. This ratio differential relay calculates the amount of operation from the two line currents flowing into the protection zone, determines the amount of suppression that applies suppression to the amount of operation from compensation for accuracy, and determines the magnitude of the difference value. This determines whether the circuit breaker is operable or not.

An example of a conventional ratio differential relay is “IEEJ Papers, 54.
-819 (March 1978), page 148, Fig. 9 is publicly known. This ratio differential relay converts both the operation amount and the suppression amount into a signal equivalent to the effective value for the fundamental wave based on the integral value over a half cycle or one cycle of the fundamental wave (commercial frequency of the power system), and determines an accident. It is something.

[Problem that the invention seeks to solve]

According to the configuration of the conventional ratio differential relay described above, when the current transformer becomes magnetically saturated during one cycle of the fundamental wave due to the DC component included in the external fault current flowing through the line, a large differential current is generated. There is a risk that malfunction may occur when it should not be operated. That is, the generation of a large operating current is because the current transformers at each terminal of the protection zone are not necessarily saturated in the same way, and there are variations among the current transformers. From this point of view, there are problems in terms of accuracy, sensitivity, and high-speed operation.

Therefore, an object of the present invention is to provide a ratio differential relay that can accurately detect the details of an accident at high speed even if a current transformer transiently experiences magnetic saturation.

[Means for solving problems]

In order to achieve the above object, the present invention focuses on the fact that the magnetic saturation phenomenon of a current transformer does not occur over the entire period of the line current waveform, but that there is always a non-saturation region in each cycle. At the time of non-saturation in each cycle, the operating amount and the suppression amount are determined, and based on the magnitude of the difference value due to the phase difference associated with the fault current, it is clearly determined whether the detected current is due to an internal fault or an external fault. This is designed to prevent malfunctions caused by accidents other than the above.

That is, the present invention provides protection sections (100) of power system lines.
(7) Two line currents (iA # iB) at both ends are detected by current transformers (110°120) installed at both ends, and based on the detected values (i^211a2), the current is generated in the protection zone. In a ratio differential relay that detects a fault that occurs, the sum of the instantaneous values of the two line currents is calculated (In = I
AS+In5) L/, the current value of the calculated instantaneous phase (
The absolute value (Ioz(t), = Based on l Iut (t)l, the operating amount of the ratio differential relay (Ioa(t) ”
operation amount calculation means for calculating Ioz(t)+ID2(t-1)); and a scalar sum of each instantaneous value of the two line currents (IR=lI
^^I+1IBBl) is calculated, and the current value of the calculated scalar sum (KRIR(t)) and the value a predetermined time ago (KRIR
(t-1)) and the difference (KRIRI(t)=KRIR(
t) - KRIR(t-1)) absolute value (KRIR2(t
)=l KRIRt(t) Suppression amount of the ratio differential relay based on l (KRIpa(t)=KuIRz(t)
+KRIRz (t-1)) and a difference value between the operation amount and the suppression amount (Ill (t)=
Ioa (t) - KRIRa (t)) and determine the details of the accident based on the difference value (IRv (t) ≧ P
).

[Effect]

It is already known that the actual operation of the ratio differential relay is performed by comparing the difference value between the operation amount and the suppression amount with a predetermined standard, and using the resulting value. However, the present invention is not intended to simply detect internal accidents, but is characterized in that it is configured to accurately distinguish between internal accidents and external accidents.

That is, in the present invention, the operation amount calculated by the operation amount calculation means is the sum of the instantaneous values of the line current (Io==I
The difference (I
This is a value based on the absolute value of ol(t)=Io(t) In(t-1)). On the other hand, the suppression amount calculated by the suppression amount calculation means is the scalar sum of each instantaneous value of the line current (IR
=lI^^l + l l5al=lI^1+ l I
difference (KRIR(t) = KRIR(t)
-KRIR(t-1)).

Therefore, each operation amount and suppression amount is always determined by comparing with the previous data in terms of time, so the relay will not operate as is using incorrect data, and reliable and accurate operation will be achieved. The amount and amount of inhibition can be calculated. Then, based on such accurate data, it is possible to make an accident determination using the determination means.
Accurate relay operation can be expected.

Further, it is possible to determine whether the accident is an internal accident or an external accident by determining and setting the determination criteria in the determination means in advance to a value associated with the accident mode.

In other words, the phase relationship between the two line currents and the difference in the difference value based on the phase difference clearly appear depending on the mode of the accident. Generally, the phase difference for internal accidents is 90
There is a phase difference of 180 degrees, but in the case of an external fault, the current on one line flows out from the protected section, resulting in a 180 degree phase difference.

Furthermore, since the line current is alternating current, the non-saturation region of the current transformer always exists once in each cycle, so it is sufficient to find this region by sampling.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

An embodiment of the present invention is shown in FIG. 1, and each element will be explained separately below.

In FIG. 1, 100 is an object to be protected, for example, power system equipment such as a power transmission line, a transformer, a bus bar, or a generator. The figure shows a two-terminal configuration, but
It is clear from the following operation description that the present invention is applicable even when more lines are connected. 110 and 120 are current transformers. The current transformers 110 and 120 are insulated converters for inputting the current signals i^ and iB applied to the object to be protected into the ratio differential relay according to the present invention, and their outputs are respectively i^2゜. Indicated by iaz.

130 and 140 are power transmission lines connected to the protected object 100, respectively.

The polarities of the current transformers 110 and 120 are the same phase current i.
^, In the direction in which iB flows into the protected object 100,
Set the output currents i^z and ia2 to be in the same phase.

Next, a case will be described in which the ratio differential relay according to the present invention is implemented using a digital calculation type.

This ratio differential relay can be broadly classified as a movement amount calculation means.

It is composed of a suppression amount calculation means and an accident determination means.

Furthermore, depending on the configuration of the accident determining means, it can be divided into three types: those capable of determining internal accidents, those capable of determining external accidents, and those capable of determining both internal and external accidents.

In FIG. 1, 210 and 220 are A/D converters that convert analog signals into digital signals. A/D
Conversion is to convert the values of multiple input signals at the same time.
For example, by implementing a ratio differential relay using a digital computer, sample values at the same time can be obtained by control signals from the computer (not shown). The output of the A/D converter is
Indicated by IIas. Subscripts A and B are terminal symbols.

230 is an adder. The adder 230 adds sample values IAS and Ins of current signals of all power transmission lines connected to the protected object 100. The output of the adder 23Ω is I
Letting D, I o== I AS+ I as
-(1), and if the protected object 100 is healthy, ideally Io = O, and only when a fault current flows inside, Io will show a value corresponding to the fault current, so-called Corresponds to differential current. This current Io is used as a signal source for the operating amount.

On the other hand, the sum of absolute values (scalar sum) of passing currents of all power transmission lines applied to the object to be protected is used as a signal source for the amount of suppression of the ratio differential relay.

240 and 250 are absolute value detectors, and IAA=l IAS for the input signal ^s and Ias, respectively.
l - (2) IBB: l
This gives I as I - (3).

260 is an adder, and its output IR is IR=I^^+
IBB = l IAS l + l Ias l
-(4).

265 is a multiplier for adjusting the amount of suppression. The input of the multiplier and the IR output are set as KRIR.

The operating amount signal source Io and the suppression amount signal source KRIR are both signals obtained from sample values of the AC signal, and as they are, internal faults cannot be continuously detected even if ratio differential calculation is performed.

Therefore, in the present invention, the differential filters 270, 300,
Absolute value detector 280, 310° addition filter 290, 3
20.

Letting the signal source of the operation amount at time t be Io(t), the calculation output In5(t) of the differential filter 270 is 1o1(t
)=Io(t) −In(t−1) (5).

However, t-1 indicates a value one sample earlier than time t. For example, assuming that sampling is performed at 600 Hz with a fundamental wave of 50 Hz, the difference between t and t-1 is approximately 1,666 m s.

It is equal to the difference between signals with a time difference corresponding to 30 degrees in electrical angle of the fundamental wave.

The absolute value detector 280 obtains the absolute value of the input signal Iol(t), and if its output is In2(t), then Ioz(t) = l Iot(t) I
”・(6).

The addition filter 290 receives Ioa for the input signal D2.
(t) = Ioz(t) + In2(t −1)”
- As shown in (7), input signals with time differences are added.

In equation (7), Ioa(t) is the addition filter 290
(1) and (t-1) indicate the same sampling time relationship as explained in equation (5), where Ioa(t) is the amount of operation.

On the other hand, the amount of suppression is determined by the differential filter 300 using the input signal KRIR as KRI*t
(t)=KRIu(t) -KRIR(t-1)...
(8) is obtained, and by the absolute value detector 310, KRIRz(t) = l KRIttz(t) l
...(9) is obtained.

Next, the addition filter 320 calculates KRIRa(t):KRIttz(t)+KRIRz(
t-1)...(10) is obtained.

330 is a difference detector, and if its output is IRv(t), then Itn(t)=Ins(t)−KRI*a(t)・
...(11) Obtains the value.

340 is a level determiner, which generates an operation output, for example, a high-level output RYo(t)=1 when the input signal Inv(t) is higher than a predetermined level KP, and outputs a low-level output without operating when the input signal Inv(t) is lower than Kp. The output RYo(t) remains at O.

A counter 350 is used to check the number of times the input signal Ryo(t) is at a high level. ), and counts the number of high-level times over a predetermined period of time (for example, 11 seconds or more or the number of samplings), and when RYo(t) occurs a predetermined number of times or more, Only RY (t) generates an operational output. This is to prevent the ratio action relay from operating unnecessarily and leads to improved reliability.

Here, details of the ratio differential determination method by the level determiner 340 will be explained separately for three aspects: internal accident, external accident, and both internal and external determination.

First, FIG. 2 shows the configuration for internal accident determination.

Using 3 from the operation amount and the suppression amount KRI R3, Ioa-
Basically, it is determined that it is an internal accident when KRIR3≧P holds.
In order to ensure operation reliability, a counter 350 is used to
Detecting that the operating condition is established for a predetermined sample.

In FIG. 2, 330 is a ratio differential calculation unit, and 34
0 is a level determination section, and 350 is a counter. The counter 350 is incremented at every sampling time when the output of the level determination section 340 becomes YES, and is cleared when the output of the level determination section 340 is NO. The timer T is used for the clearing route to extend the operation duration of the relay, and if necessary, the timer T
The clearing of 50 is delayed by timer T.

When the output KK of the counter 350 is equal to or higher than a predetermined level N0, the relay is activated; otherwise, the relay is deactivated.

In this case, the limit of the operating range of the relay is the line shown at 502 in FIG.

Next, FIG. 3 shows the configuration for external accident determination.

FIG. 3 shows, contrary to FIG. 2, the operation amount Ioa and the suppression amount KR.
Using I R8, detect whether it is an external accident or not,
When an external accident is detected, the relay is rendered inactive to prevent malfunction.

In the ratio differential calculation section 330 Find I Rv = KRI Rs - I ns By the level determination section 340 IRY>P When this happens, it is determined that an external accident has occurred, and the counter 350 is incremented.

360 is a level determination section, and the output K of the counter 350
When K is greater than a predetermined value N1, the relay is deactivated.

In order to detect an external fault before the current transformer reaches saturation in the event of an external fault, set the relay to a non-operating state, and maintain this state even when the current transformer is saturated, the contents of the counter are set by a timer T. It is possible to postpone clearing and prevent malfunctions when the current transformer is saturated.

Next, FIG. 4 shows an example of a configuration in which both internal and external accidents can be clearly determined.

In other words, when it is determined that it is not an external accident,
When the level determination unit 360 determines NO, there is an internal accident or a healthy state in which the passing current is smaller than the level determination value P. Therefore, it is inconvenient to simply put the relay in the operating state. The relay can be activated on the condition that Figure 4 is an example.

FIG. 4 shows that by combining the detection methods shown in FIGS. 2 and 3, internal accidents and external accidents can be detected using the ratio characteristics shown in FIG. Can be implemented.

In Figure 4, the confirmation on the relay operation side is I os-K
Counter K K indicates how many consecutive samples RI R3≧P continues.
＞N.

The operating conditions are confirmed, and it is determined by the counter K K > N l that there is no external accident and that KRI R3-I oa> P holds true.

In this case, it is better to determine the external accident as early as possible, so N1 may be 1.

Furthermore, once it is determined that an external accident has occurred, the reliability of the relay determination can be improved by delaying the clearing of the counter 351 using the timer Tx in addition to preventing malfunction due to saturation of the current transformer.

Based on the outputs of the level determining units 360 and 361, the relay is activated based on the matching condition where it is determined that the former is not an internal accident and the latter is not an external accident.

In addition, all other relays are rendered inactive.

FIGS. 5(a) and 5(b) show an example of the operation at the time of an internal accident according to the present invention. Symbols in this figure that are the same as those in FIG. 1 have the same meaning. In FIG. 5, the positions where the input signal current i Any i ax was sampled are indicated by marks on the waveform.

Below, the calculation results of each part shown in FIG. 1 are shown at each point in time when the input signal signal S and IBS are taken in as samples. FIG. 5 shows the waveforms (calculation results) of the main parts in FIG. 1. As the internal fault current in Fig. 5,
An example is shown in which i^ and 18 are equal and a phase difference of 60 degrees occurs.

There is no saturation in the current transformer, and the output current of the current transformer is 1Aztiax.
are similar to i^ and ia, respectively.

Input signal i A! , i at each sample value I
In corresponds to the added value obtained by ^2°18B, that is, the differential current. Since this current Io is an alternating current signal, it passes through the zero point once every half cycle.

However, the differential current Io is passed through a differential filter 270° and an absolute value detector 280. By passing it through the addition filter 290, it becomes a pulsating flow as shown at ID8 in FIG. Ins is the amount of operation.

On the other hand, the waveform for deriving the suppression amount is shown below. KRIR (however, an example of KR=0.5 is shown in FIG. 5) is a waveform corresponding to the scalar sum current of the currents passing through each line. This KRIR is a scalar sum of AC waveforms, and the inflow current iA
Since there is a phase difference between z and iax, the flow becomes a pulsating flow that does not touch the zero point.

Therefore, in the differential ratio between the differential current Io and the scalar sum current KRIR, the amount of suppression exceeds the amount of operation at the point where the differential current Io becomes zero once every half cycle, so it becomes inoperable and the simple It can be seen that it is inconvenient to detect an internal fault by focusing on a single sample value for high-speed judgment due to the phase difference of the input current.

However, in the present invention, the operation amount ID3 is a pulsating flow without a zero point, and the suppression amount KRI R& is also set so that the scalar sum current KmIu is passed through the differential filter 300. Absolute value detector 31
0. It is made into a pulsating flow by passing through the addition filter 320,
As a result, the input signal I for final level determination
Since RY never crosses the zero point, reliable continuous operation is possible even with an internal fault current having a one phase difference. In FIG. 5, the final output RY becomes the operating condition after time Tl from the determination output RYo.

The time T1 is measured by a counter 350. This time Tz is selected based on a value that will not cause a malfunction due to saturation of the current transformer in the event of an external fault.

FIGS. 6(a) and 6(b) are explanatory diagrams of the response of the ratio differential relay according to the present invention when the current transformer generates magnetic saturation due to the passage of a transient DC component during an external fault. Each symbol indicates the same content as the symbol in FIG.

FIG. 6 shows an example in which only the current transformer 120 generates magnetic saturation and the input current signal ia2 causes waveform distortion. As a result, In corresponding to the differential current is Only one current is zero, and the other values are equivalent to the excitation current of the current transformer 120.

IDI is the output of the difference filter of the signal IQ, and FIG. 6 shows an example in which differences are taken at 30° intervals. The differential filter can remove the DC component and at the same time emphasize the output of the exchange meeting. ID2 is the absolute value of the input signal Iot, Ioa
is the summation filter output of the input signal Ioz.

Ins is the output that is the operating amount, but as shown in Figure 6, for the differential current when the current transformer is saturated, there are many zero levels (for example, several points even when sampling at 30 @ lJl intervals). It is a characteristic.

On the other hand, the amount of suppression is derived based on the scalar sum value IR of each current, and the scalar sum current IR is as shown in FIG.
IIKRIR, which has a waveform different from the scalar sum of the fundamental waves due to the magnetic saturation of 0, represents the value obtained by multiplying the input signal IH by the coefficient KR. KRI R1 is the output waveform of the difference filter 300 of the input signal KRIR, and the difference is set at 30'' intervals.

KRIR2 is the absolute value of input signal KRIR1.

KRI R3 is the output of the input signal KRIuz17) addition filter 32°, and in this example, addition is performed at 30” intervals. KRIRa is the suppression amount. IRY is the operation amount I
It shows the value obtained by subtracting the suppression amount KRIRI from D3.

During an external accident, the characteristic is that there is a time period in which the signal IRY takes a negative value, and the output RYo of the level judgment result is 1.
With discontinuities of action and inaction during the cycle.

Therefore, when checking the timer 350, I? JffT1 to 1
By taking more than one cycle, the final judgment output RY will not indicate the operation in the event of an external fault, and even if an error current occurs due to magnetic saturation of the current transformer, the ratio differential relay according to the present invention will not malfunction. do not have.

FIGS. 7(a) and 7(b) show the calculation flow when the ratio differential relay shown in FIG. 1 is performed by a digital computer. Symbols in FIG. 7 are the same as those described in the explanation of FIG. 1, and equivalents are indicated by the same symbols, and their explanation will be omitted.

In the above explanation, the sampling period is treated as a 30'' interval of the fundamental wave, and the values of the input signals to be operated on for the difference filter 270 and the 300° addition filters 290 and 320 are treated as time t and time t1 that is one sample older than that. However, the sampling period may be other than that, and the interval between times t and tl is not necessarily limited to one sample interval.

In addition, the coefficient KR multiplied by the amount of suppression is shown as 0.5 in the example, but as a ratio differential relay, it can be varied depending on the magnitude of the source signal scalar sum current IR of the amount of suppression so that variable ratio characteristics can be obtained. Alternatively, a plurality of ratio differential relays shown in FIG. 1 may be provided, and their coefficients KR, level judgment values Kp,
The confirmation time TI may be set as a set value that is appropriately varied, and may be used as a match condition or an OR condition for the determined operational output.

In addition to the positions of the multipliers shown in FIG. 1, the positions of the differential filters 300. It may be attached after the absolute value detector 310, addition filter 320, etc., or may be distributed. Furthermore, the signal of δ is 1/K from the operation amount.
It may also be R.

Further, the addition filters 290 and 320 may be collectively provided in one stage after the difference detector 330.

Furthermore, similar results can be obtained even if the positions of adder 260 and differential filter 300 are switched.

Fig. 8 shows an example in which a plurality of ratio differential relay determining sections (three in Fig. 8) according to the present invention are provided.

Reference numerals 501, 502, and 503 in FIG.
This shows the range after obtaining ns, and the same calculation as the content of the calculation flow in FIG. 7 is performed.

211 and 221 are data buses, respectively, and the input signals iAx and Iax are digitally converted signals IAS.
, Ias as ratio differential relay determination unit 501, 502゜5
For transmission to 03 respectively.

510 is a coincidence gate, and ratio differential relay determination unit 50
1, 502, and 503 generate an operational output only when all of them generate an operational output.

In the ratio differential relay determination units 501, 502, 503, the fourth
By adjusting the coefficients KR, Kp + Tt, etc. shown in the figure, various ratio characteristics can be obtained.

FIG. 9 shows the ratio differential relay determination unit 501 shown in FIG.
Examples of operating limit lines 502 and 503 are shown.
An example is shown in which the hatched area is the operating range. Due to the above,
Depending on the degree of magnetic saturation of current transformers 110, 120, variable ratio characteristics are obtained.

In addition, in FIG. 8, the ratio differential relay determination section, 501.5
02 and 503 are shown with the same configuration, but each can be calculated in common, for example, the calculation of differential current In 230. Difference filter 270, absolute value detection 280. The addition filter 290° timer 350 and the like may be used as pre-processing or post-processing calculations for the ratio differential relay determination units 501, 502, and 503, respectively.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a ratio differential relay that is not affected by the magnetic saturation of a current transformer and does not malfunction. It is possible to reduce the

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a flowchart showing an example of the configuration of a level determiner for internal accident determination, and FIG. 3 is an example of the configuration of a level determiner for external accident determination. FIG. 4 is a flowchart showing an example of the configuration of a level determiner capable of determining both internal and external conditions. FIG. 5 is a waveform diagram of each part in the case of internal accident detection, and FIG. 6 is a flowchart of each part in the case of external accident detection. FIG. 7 is a calculation flowchart showing another embodiment of the present invention, FIG. 8 is a block diagram showing an application example of the present invention, and FIG. 9 is a characteristic diagram showing the operating range of the ratio action relay. . 100...Object to be protected, 110...Current transformer, 240
... Absolute value detector, 270 ... Difference filter, 29
0... Addition filter, 330... Difference detector, 340
...Level judge, 350...Timer.

Claims (1)

[Claims] 1. Two line currents at both ends of a protection section of a power system line are detected by current transformers provided at both ends, and an accident occurring in the protection section is detected based on the detected values. In the ratio differential relay to be detected, the sum of each instantaneous value of the two line currents is calculated, and the ratio difference is determined based on the absolute value of the difference between the current value of the calculated instantaneous value sum and the value a predetermined time ago. operation amount calculating means for calculating the operation amount of the dynamic relay; and calculating the scalar sum of each instantaneous value of the two line currents, and calculating the absolute value of the difference between the current value of the calculated scalar sum and the value a predetermined time ago. a suppression amount calculation means for calculating a suppression amount of the ratio differential relay based on the ratio differential relay; an accident determination means for calculating a difference value between the operation amount and the suppression amount and determining the content of the accident based on the difference value; A ratio differential relay characterized by comprising: