JPH04322121A - Transformer protective relay - Google Patents

Abstract

PURPOSE:To enhance protection reliability by eliminating time lag when a fault is removed and to prevent unnecessary function due to exciting surge current in a transformer protective relay wherein a circuit breaker is tripped through a ratio differential relay element which functions based on the ratio between the difference of currents flowing into/out from an objective transformer and a suppression current. CONSTITUTION:Overcurrent relay elements 11, 12, 13 provided with second higher harmonic suppressing function and having operating time characteristics reversely proportional to the difference between the basic wave component and second higher harmonic component in a differential current are provided for respective phases. AND circuits 14, 15, 16 produce logical products of the operational outputs from the elements 11, 12, 13 and the operational outputs from ratio differential relay elements 1, 2, 3 for corresponding phases and an OR circuit 17 determines logical sum of the logical products thus tripping a circuit breaker.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer protection relay device for protecting a transformer using a ratio differential relay or the like.

0002

[Prior Art] A conventional transformer protective relay device is shown in Fig. 4, for example.
It was structured as follows. In Figure 4, 1, 2, 3 are 3
This is a ratio differential relay element provided for each phase, and operates based on the ratio between the differential current Id and the suppression current Ir. The output signals of these ratio differential relay elements 1, 2, and 3 are supplied through an OR circuit 4 to a non-inverting input terminal of an AND circuit 5 with an inverting input terminal. Second harmonic locking elements 6, 7, and 8 are provided for each of the three phases, and operate based on the ratio of the fundamental wave component current and the second harmonic component current included in the difference current Id. The output signals of these second harmonic locking elements 6, 7, 8 are outputted by an OR circuit 9.
The signal is supplied to the inverting input terminal of the AND circuit 5 through the input terminal. The output of the AND circuit 5 serves as a trip signal for a breaker (not shown) inserted in an electric line connecting the transformer and the power system. Note that the characters in parentheses in the figure indicate the three phases.

In the device configured as shown in FIG. 4, the differential current Id is the difference between the current flowing into the transformer and the current flowing out of the transformer, and is normally approximately zero. Further, as the suppression current Ir, a scalar sum of each terminal of the transformer is generally used. The ratio differential relay elements 1, 2, and 3 operate when Id/Ir exceeds a predetermined value, as shown in the operating characteristics shown in FIG. 5(a). The second harmonic locking elements 6, 7, and 8 have operating characteristics as shown in FIG.
It operates when becomes 0.15 or more. Note that If1 is set to a predetermined value I0 in order to be inactive in a region where the differential current Id is small.
It is designed not to operate when f is below.

[0004] When an internal fault occurs in the transformer, the differential current Id increases, the ratio differential relay element of the corresponding phase operates, and the non-inverting input terminal of the AND circuit 5 becomes high level. On the other hand, at this time, since If2/If1 of all phases does not exceed 0.15, the second harmonic locking elements 6, 7, and 8 become inoperable for all three phases, and the inverting input terminal of the AND circuit 5 becomes low. level. Therefore, the AND condition of the AND circuit 5 is satisfied, and the breaker is tripped without being trip-locked.

Furthermore, when the transformer is turned on, a magnetizing inrush current flows as a difference current Id, but since this inrush current contains a large amount of second harmonic component current If2, I
The condition f2/If1>0.15 is satisfied. Therefore, one of the second harmonic locking elements 6, 7, and 8 operates, and a high level signal is output from the OR circuit 9, thereby locking the trip output of the AND circuit 5. Note that before this trip lock is applied, any ratio differential relay element 1, 2,
3 outputs a mistrip signal, so by delaying the operation time of the ratio differential relay elements 1, 2, and 3, time-limited coordination is implemented to prevent the mistrip signal from being output.

[0006]

[Problem to be Solved by the Invention] Since the If2 component included in the excitation inrush current changes depending on various factors such as residual magnetism, closing phase, and iron core structure, in all cases, the second harmonic locking element ( 6, 7, 8) operating conditions (I
f2/If1>0.15). Particularly recently, the content of the second harmonic component current If2 has become smaller. However, as shown in FIG. 4, a method is generally adopted in which the trip is locked when If2/If1<0.15 for all three phases at the same time. However, the locking method using the three-phase OR of second harmonic locking elements as shown in FIG. 4 has the following problems.

(1) When a transformer that has already had a fault is turned on, the fundamental wave current If1 of the phase with the fault increases, so If2/If1 of that phase decreases rapidly, and the second harmonic of that phase increases. The wave lock element is restored. However, in the phase with no fault, the second harmonic locking element continues to operate until the fundamental wave current If1 becomes less than I0f in Fig. 5(b), so as a result, the breaker trip output continues to be locked, and as a result, the breaker trip output continues to be locked. When the fundamental wave current If1 becomes smaller than I0f, a breaker trip output is generated, which lengthens the fault removal time. Particularly in the case of large transformers, the decay time of the magnetizing inrush current is long, so the delay in the fault clearing time becomes a serious problem.

(2) In the system shown in FIG. 4, it is necessary to achieve time coordination in which the ratio differential relay element operates more slowly than the second harmonic locking element in all cases of excitation inrush. Therefore, even in a region where the fault current is large, the operation time of the ratio differential relay element becomes slow, and the fault removal time is delayed.

(3) When configuring a transformer protection relay for each phase type due to mounting space, the conditions for the second harmonic locking element should be exposed outside the case in order to take the three-phase OR of the second harmonic locking element. It is necessary to exchange signals with each other. This complicates the external circuitry and the internal sequences of each phase unit, increasing costs and reducing reliability. Furthermore, since the conditions of other phases also affect the test, it becomes complicated and problems with test equipment arise.

(4) If the second harmonic locking element of any phase fails on the active side, the operation of the ratio differential relay elements of all phases is locked, reducing the reliability of protection.

The present invention has been made in view of the above-mentioned points, and an object thereof is to provide a transformer protection relay device that does not cause a delay in fault removal time and provides highly reliable protection.

0012

[Means for Solving the Problems] The present invention has a ratio differential relay element that operates when the ratio between the difference current flowing into and out of the transformer to be protected and the suppression current is equal to or higher than a predetermined value. In a transformer protection relay device that protects the transformer by tripping a circuit breaker connected to the transformer using the operating output of a ratio differential relay element, each of the three phases to which the transformer to be protected is connected is provided. a ratio differential relay element that operates when the ratio of the difference current and the suppression current is equal to or higher than a predetermined value; an overpass with a second harmonic suppression function, which has an operation time characteristic inversely proportional to the difference, and operates when the fundamental wave component is above a predetermined value and the content rate of the second harmonic component is below a predetermined value; AND for calculating the logical product of the operating output of the current relay element, the overcurrent relay element with a second harmonic suppression function, and the operating output of the ratio differential relay element of the phase corresponding to the element. circuit, and the circuit breaker is tripped when an AND condition of at least one of the AND circuits is satisfied.

[0013]

[Operation] Normally, the difference in current flowing into and out of the transformer to be protected is approximately zero, so the ratio differential relay element does not operate. When a fault occurs, the ratio of the differential current to the suppression current exceeds a predetermined value, and the ratio differential relay element provided in the fault phase operates. At this time, the ratio of the second harmonic component included in the difference current is less than a predetermined value, and the fundamental wave component is quite large, so the overcurrent relay element with a second harmonic suppression function operates at high speed. Therefore, the AND condition of the AND circuit of the fault phase is immediately satisfied, the circuit breaker is tripped, and the fault section is immediately disconnected.

[0014] Since an AND circuit is provided for each phase in this way, even if the AND condition of the AND circuit on the other healthy phase side does not hold, for example when a transformer with an internal fault is turned on, the The breaker can be reliably tripped without being affected.

The operating time of the entire device is determined by the operating time characteristics of the overcurrent relay element with second harmonic suppression function (which is inversely proportional to the difference between the fundamental wave component and the second harmonic component). component is large and the second harmonic component is small), the protection operation is performed at high speed.

When the transformer is turned on, an excitation inrush current flows as a differential current, but if the second harmonic component content in this excitation inrush current is greater than a predetermined value, an overcurrent relay element with a second harmonic suppression function is activated. doesn't work.

Furthermore, even if the second harmonic component content in the excitation inrush current is below a predetermined value, the overcurrent relay element with a second harmonic suppression function does not operate immediately due to its operating time characteristics. . During the delay time of the overcurrent relay element with second harmonic suppression function, the second harmonic component content in the excitation inrush current increases with time, and the second harmonic component content becomes equal to or higher than a predetermined value. . As a result, when the excitation inrush current flows, the AND condition of the AND circuit will not be satisfied, and the breaker will not trip erroneously.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the explanation thereof will be omitted. The difference between FIG. 1 and FIG. 4 is that overcurrent relay elements 11, 12, and 13 with a second harmonic suppression function are provided for each of the three phases, and a time limit portion 51t is provided for each of the three phases.
AND circuits 14, 15,
16, the outputs of the AND circuits 14, 15, and 16 are input to the OR circuit 17, and the output of the OR circuit 17 is used as a breaker trip output. Ratio differential relay elements 1, 2,
The operating characteristics of No. 3 are the same as those shown in FIG. 5(a).

In the device configured as described above, the characteristics of the overcurrent relay elements 11, 12, and 13 with second harmonic suppression function are shown in FIG. 2(a). In this example, If
It operates when 1/If2>0.15 and If1>If0 are established at the same time. Note that this value of 0.15 can be changed depending on the conditions of the magnetizing inrush current.

Overcurrent relay element 11 with second harmonic suppression function
, 12, 13 are shown in FIG. 2(b). That is, when If2>0.15If1, the overcurrent relay element (51) with a second harmonic suppression function does not operate, so the time limit section (51t) also becomes inoperative. If2<0.
When 15If1, I=[(0.15If1)2-(If
2) It operates in inverse proportion to 2].

When a fault occurs, the ratio between the differential current Id and the suppression current Ir becomes equal to or higher than a predetermined value, and the ratio differential relay elements (1, 2, 3) provided in the fault phase operate. At this time, the fundamental wave current If1 in the difference current Id becomes large, but the second harmonic current If2 becomes a considerably small value, so the above-mentioned I becomes large and the overcurrent relay element with second harmonic suppression function (11
, 12, 13) operate rapidly. Therefore, the AND condition of the AND circuit (14, 15, 16) of the fault phase is immediately established, a breaker trip signal is output from the OR circuit 17, and the fault section is immediately disconnected. In this case, since the operation of the ratio differential relay element is instantaneous, the operation time of the entire relay device is determined by the time of the time limit part (51t) of the overcurrent relay element with second harmonic suppression function.

[0022] In this way, for each phase, the logical product of the operating outputs of the ratio differential relay element and the overcurrent relay element with a second harmonic suppression function is determined, and the logical sum thereof is determined. Therefore, even if the AND condition of the AND circuit on the other healthy phase side does not hold, such as when a transformer with an internal fault is turned on, the breaker can be reliably tripped without being affected by it. .

When the transformer is turned on, the excitation inrush current is the difference current Id
However, this difference current Id contains many second harmonic components, and when If2>0.15If1 holds, the overcurrent relay element with second harmonic suppression function does not operate. Further, the content of the second harmonic component is small and If2>0.
If 15If1 does not hold, the overcurrent relay element with the second harmonic suppression function operates, but it takes time for the time limit section 51t to output its operating output. Here, the second harmonic current If2 content in the excitation inrush current after the transformer is turned on increases as shown in FIG. Especially when the If2 content in the first wave is small, the rate of increase in the If2 content is large (
This is clear from measured data and simulations). Therefore, even if the If2 content is smaller than 15% in the first wave, If2 content is smaller than 15% during the integration time of the timer 51t.
Since 2/If1 becomes larger than 0.15 (the constant Kt is set in this way), the time limit portion 51t of the overcurrent relay element with the second harmonic suppression function does not operate. This prevents the AND conditions of the AND circuits 14, 15, and 16 from being satisfied, and prevents the breaker from accidentally tripping when the transformer is turned on.

The operating time t of the timer 51t is shown in FIG. 2(b).
In this case, we set Kt/(0.15If1)2-If22, but
Not limited to this, t=Kt/(0.15If1-If2)2
Or, t=Kt/(αIf1)2-If22, t=Kt/
(αIf1-If2)2, (Kt and α are design constants)
The same effect can be obtained as well.

[0025]

As described above, according to the present invention, an overcurrent relay element with a second harmonic suppression function provided for each phase detects an accident, including whether or not it is an excitation inrush current. The circuit breaker is tripped by taking the AND with the ratio differential relay element and then taking the OR of these, so the following excellent effects can be obtained.

(1) Even if a transformer with an internal fault is turned on, the AND condition of the fault phase is satisfied and a breaker trip signal can be issued regardless of the operation of other phases, which delays the fault removal time. Never.

(2) Even if a relay failure occurs in any phase, the operation of other relays is not locked, resulting in high protection reliability.

(3) Even when a transformer protection relay is configured for each phase, the internal sequence of each phase relay is not affected in any way, and there is no signal exchange between units, simplifying external wiring and improving reliability. is high and cost is low.

(4) Since evaluation and testing can be performed for each phase, complicated testing is unnecessary and there are no problems with test equipment.

(5) There is no problem in time coordination between the overcurrent relay element with the second harmonic suppression function and the ratio differential relay element, and the fault removal time is longer than that of the overcurrent relay element with the second harmonic suppression function. Determined only by the time limit part. At the time of a transformer fault, the fundamental wave current (for example, 0.15If1) and the second harmonic current (If2
) is large, and since it is squared, high-speed operation can be achieved. Further, since the operating time is inversely proportional to the fundamental wave current If12, the larger the fault current, the more rapidly the operation becomes high speed, which is advantageous in terms of protecting the transformer.

(6) For excitation inrush current, even if the content of the second harmonic component is below a predetermined percentage in the first wave, an overcurrent relay with a second harmonic suppression function is required. There is no unnecessary operation due to the time characteristics of the element (the conventional method shown in Figure 4 is a locking method, so if the second harmonic content of the first wave and second wave is less than a predetermined percentage, the lock is immediately activated. Since this will not work, you will have no choice but to use the 3-phase OR-lock method.)

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 shows the operating characteristics of each element of one embodiment, and FIG.
) is an operation characteristic diagram of the overcurrent relay element with a second harmonic suppression function, and FIG. 2(b) is a time characteristic diagram of the time limit part 51t of the overcurrent relay element with a second harmonic suppression function.

FIG. 3 is a characteristic diagram showing temporal changes in second harmonic content of excitation inrush current.

FIG. 4 is a circuit diagram showing an example of a conventional transformer protection relay device.

5 shows operating characteristics of each element in FIG. 4, FIG. 5(a) is an operating characteristic diagram of a ratio differential relay element, and FIG. 5(b) is an operating characteristic diagram of a second harmonic locking element.

[Explanation of symbols]

1, 2, 3... Ratio differential relay element, 6, 7, 8... Second harmonic locking element, 11, 12, 13... Overcurrent relay element with second harmonic suppression function, 14, 15, 16 ...AND circuit, 1
7... OR circuit, 51t... Time limit section of overcurrent relay element with second harmonic suppression function.

Claims (1)

[Claims] 1. A ratio differential relay element that operates when a ratio between a current difference between currents flowing in and out of a protected transformer and a suppression current is equal to or higher than a predetermined value, and the ratio differential relay element operates. In a transformer protection relay device that protects the transformer by tripping a circuit breaker connected to the transformer according to the output, it is provided for each of the three phases to which the transformer to be protected is connected, and is connected to the difference current and the suppression current. a ratio differential relay element that operates when the ratio of an overcurrent relay element with a second harmonic suppression function, which operates when the fundamental wave component is at least a predetermined value and the content rate of the second harmonic component is at most a predetermined value; an AND circuit for calculating the logical product of the operating output of the overcurrent relay element with second harmonic suppression function and the operating output of the ratio differential relay element of the phase corresponding to the element; A transformer protection relay device characterized in that the breaker is tripped when an AND condition of at least one AND circuit among the circuits is satisfied.