JPS64895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transformer protection relay, and more particularly to a transformer protection relay such as a current comparison or current differential relay that includes a load regulation transformer as a protection target.

In conventional transformer protection relays, the main transformer combined with a load voltage regulation transformer (hereinafter referred to as LVR) is protected, and current differential relays,
Or when using a current comparison relay,
Since the transformation ratio changes depending on the LVR operating tap value,
In order to obtain ideal protection characteristics, it is necessary to change the transformation ratio or current comparison judgment value during differential calculation of the relay as the LVR operation tap value changes.

However, conventional measures have been taken by generally keeping the operation determination level constant and reducing the sensitivity of the relay, which has resulted in the problem of reduced protection performance.

This will be explained below with reference to the drawings. FIG. 1 is a block diagram showing an example of a conventional transformer protection relay.

N ₁ , N ₂ , and N ₃ are windings of the main transformer 1, and are assumed to be a single-phase autotransformer with a tertiary winding added. N ₁ is series winding, N ₂ is shunt winding,
_N3 is the tertiary winding.

N _T and N _E assume a single-phase winding of LVR2, where N _T is a tap winding and N _E is an excitation winding.
In reality, it is necessary to consider triangular connections between N _E and N ₃ and other phases, but here they will be explained as single-phase independent circuits (star connections).

CT _P , CT _S , CT _K , CT _T , and C _E are each current transformers, and are used to convert the current value of each line to a level that can be easily handled as an input signal for a protection relay.

87T is a current differential relay for collectively protecting the main transformer 1 and LVR 2. Also, 61
LR is a current comparison relay that protects LVR2.

B _P , B _S and B _K are each circuit breakers;
Controlled by trip mechanism TR. The OR is
Current differential relay 87T and current comparison relay 61
It is an OR circuit with two inputs, the output of LR, and the output energizes the trip mechanism TR, which activates the circuit breaker.
Open B _P , B _S , and B _K .

In the following explanation, the input signal and output signal of each CT are shown as the same signal. That is, for example, the primary current and secondary output current of CT _P are both
Let's call it _IP . In addition, as shown in Figure 1, the currents I _S , I _K , I _T , and I _E of each line have their respective subscripts CT,
They are shown in correspondence with the subscripts of PT.

As is well known, the operating formula of the current differential relay 87T is as shown in equation (1) as an equivalent differential for current I _P , assuming a differential relay that determines the level of a simple differential output. It can be expressed as

｜I _P +N ₂ +N _T /N ₁ +N ₂ +N _T I _S +N ₃ /N ₁ +N ₂ +N _T I _{K |} ＞ _I be. In equation (1), the absolute value of N _T changes depending on the position of the tap on LVR2, and its sign (polarity) also changes.
It becomes the same polarity as N ₁ and N ₂ or becomes the opposite polarity.

However, since the conventional transformer protection relay cannot accurately detect the value of N _T during use, it has not been possible to correctly calculate the above equation (1) in accordance with the actual situation of use. For this purpose, the value of N _T is fixed, and the judgment level is set so that the failure detection sensitivity is low.
I had set _IX to a large value.

Further, as shown in FIG. 1, a 61LR current comparison relay is often used to protect the LVR 2, and equation (2) is known as an example of this operating equation.

｜I _E ／I _T ｜＞K _X ...(2) However, in equation (2), K _X is the judgment level, I _E
is the current flowing through the excitation winding N _E , I _T is the tap winding N _T
is the current flowing through.

Judgment using equation (2) above is made by finding the turns ratio between N T and N _E as shown in equation (3): |I _E /I _T |= | _{N T} /N _E |> _K , it is similar to detecting the abnormality based on this.

However, as described above, the polarity and absolute value of the number of tap turns N _T changes depending on the operating tap value of the LVR2. Therefore, in the conventional protection system, as in the case of 87T, measures against malfunctions, etc. are taken by setting a judgment level _KX that is larger than the variable range when it is healthy, and by making the sensitivity low. For this reason, failure detection sensitivity is reduced.

Figure 2 shows the protection current comparison relay 6 of LVR2.
The operating range of equation (3) using the conventional 1LR method is shown below.

That is, in Fig. 2, the current I _T in the tap winding N _T
With reference to (0°), the ratio of the excitation winding N _E to the current I _E
It represents I _E / I _T , and - on the 0°-180° axis.
The range a to a is the range of the current ratio or turns ratio that changes by changing the tap when the LVR 2 is in operation.

Therefore, in order to prevent the relay from operating when the ratio is between -a and a, the determination level _KX must be set higher than that. That is, in FIG. 2, the current comparison relay 61LR is set not to operate within the circle indicated by _KX .

For this reason, the conventional method has been unable to avoid the drawback that the sensitivity of failure detection is reduced.

In order to improve the above-mentioned drawbacks, it has been proposed to switch the setting value and operating value of the protective relay in conjunction with the operation of the tap change switch to compensate and prevent the sensitivity of failure detection from decreasing. There is (Jitsukai 56-
141529, Utility Model Application Publication No. 53-127144, etc.).

However, in these proposals, it is inevitable that some time difference will occur between the switching time of the tap change switch and the time required for actual winding switching connection, and that the tap change switch Due to faults, incorrect wiring, or local short circuits in the windings, the tap information used for compensation may differ from the actual number of turns and polarity of the tap windings. The disadvantage is that the operating values may be incorrectly compensated.

The purpose of the present invention is to eliminate the aforementioned drawbacks and to
By automatically correcting the relay setting value according to the actual operating tap value, that is, the actual number of turns of the tap winding used and its polarity, a smaller judgment level than before can be set and high sensitivity is achieved. Our goal is to provide transformer protection relays that can be used.

In order to achieve the above-mentioned object, in the present invention, the actual operating tap value of the LVR - that is, the ratio of the number of tap windings actually used to the number of excitation windings, is determined by The voltage ratio is calculated, and the setting value of the transformer protection relay is corrected based on the calculation.

Next, the present invention will be explained in detail with reference to the drawings. FIG. 3 is a block diagram of one embodiment of the present invention. In the figure, the same reference numerals as in FIG. 1 represent the same or equivalent parts.

PT _T and P _E are voltage transformers, and are used to measure the terminal voltage of the LVR. Also, 61V
is a voltage comparator and is used to measure the transformation ratio of the LVR.

In the present invention, the value of N _T under the usage conditions is measured by comparing the output voltages of P _T and P _E with a voltage comparator of 61 V, and N _T in equation (1) is adjusted correctly to the usage conditions. Do it like this.

In other words, when measuring the tap winding voltage V _T and the excitation winding voltage V _E of LVR2, since the number of excitation windings N _E is fixed, N _T in the operating state is expressed by equation (4) N _T = N It can be determined by _E V _T /V _E ...(4).

However, in equation (4), since V _T and V _E are vector quantities, N _T is also a vector quantity. (4)
By substituting N _T into equation (1), the equivalent difference current can be calculated correctly.

Although equation (1) uses a simple differential relay, it is easy for those skilled in the art to use a ratio differential relay in which a suppressing force is added by a scalar sum of passing currents.

In this way, even if a ratio differential characteristic is provided, the basic idea of the present invention can be applied as is, since the basis of the operating force is nothing other than equation (1).

In addition, calculation of N _T using equation (4) is performed when the transformer is healthy, and when a failure occurs, the calculation of N
If we calculate equation (1) using N _T data, we get
It is possible to shorten the calculation time of the operating force.

The tap switching time can be considered to be sufficiently long compared to the operating time of the protection relay, which is approximately 1 to 3 cycles, so for practical purposes, N _T should be calculated in a healthy state.
No particular problem will occur even if this is used in the calculation of equation (1).

Furthermore, in the present invention, as described above, the usage state of N _T - that is, the operation tap value of LVR2 is changed to V _T
Detected by and V _E. Then, using the turns ratio of N _T and N _E immediately before the failure of the LVR 2, the following equation (5) is used to compensate equation (2), which is the basic equation for calculating the operating force of the relay 61LR. With this, the judgment level
K _X can be made smaller than _before .

｜I _E ／I _{T −NT} ／N _E ｜＞ _K
It becomes possible to always set the range of ~a to 0.
That is, since the determination level K _X ' can be made smaller than in the conventional case, a highly sensitive current comparison relay 61LR can be realized.

FIG. 4 shows an example of a calculation flowchart when the present invention is implemented using a digital computer. In this figure, the same parts as in FIGS. 1 and 2 represent equivalents.

The contents of the calculations shown in the figure will be explained.

F1 is the data input that is the basis for calculating the setting value, and N ₁ , which is determined by the transformer to be protected.
Set N ₂ , N ₃ , N _E , K _X ′ and I _X .

At F2, the instantaneous values of the input signals I _P , I _S , I _K , I _E , I _T , V _E , and V _T are input at scheduled time intervals by predetermined sampling.

F3 is a determination step for detecting the presence or absence of a system failure, and as a determination element, for example, sudden change in voltage V _E or overcurrent detection such as undervoltage detection I _P or _IS can be used.

When a system failure is detected at F3, it goes to F6 and connects the transformer protection relay 87 as described later.
Perform calculations equivalent to T, 61LR, and conversely, when the system is healthy, proceed to the F4 side and calculate the number of tap windings N _T
Perform calculations to find.

In F4, the same calculation as in equation (4), N _T =N _E V _T /V _E , is performed, and in F5, N _T is rewritten with new data.

In the case of a system failure, at F6, calculate the differential current I as in equation (1) above using the latest number of tap windings N _T stored at F5, and by the judgment at F7. , When I > I _X , it is determined that there is an internal failure. Then, proceeding to F9, the trip mechanism TR is energized and a trip command is generated in order to disconnect the transformer from the system.

_{In addition} , if _{1 > I} ＞K _X ′ is calculated. When the above formula is established and it is determined that there is an internal failure, the process proceeds to F9. This energizes the trip mechanism TR and gives a trip command to each circuit breaker B _P , B _S , B _K .

As is clear from the above description, according to the present invention, the time difference between the switching time of the tap change switch and the time required for actual winding switching connection, and the failure or error of the tap change switch can be avoided. Even if there is a local short circuit in the wiring or winding, the actual number of turns used in the tap winding and its polarity can be detected and calculated without error, and the setting value can be adjusted according to the actual turns ratio of the LVR. Since the adjustment is accurate and automatic, it is possible to detect failures with high sensitivity and has the effect of reducing economic burden.

Although the present invention has been described as an embodiment using a digital calculation method, analog calculation can also be implemented without any problem.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional transformer protection relay, Fig. 2 is an explanatory diagram of the operating range of a current comparison relay, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a calculation diagram of the present invention. It is a flowchart showing an example of the method. 1...Main transformer, 2...LVR, N ₁ ...Series winding, N ₂
...Shunt winding, N ₃ ...Tertiary winding, N _E ...Excitation winding, N _T
...Tap winding, 87T...Current differential relay, 61
LR...Current comparison relay, 61V...Voltage comparator.

Claims (1)

[Scope of Claims] 1. In a transformer protection relay that protects a transformer having a winding with a tap for adjusting voltage on load, the voltage at each terminal of the excitation winding and the tap winding of the voltage adjusting transformer on load is detected. means for calculating the number of turns used in the tap winding and its polarity based on the detected terminal voltage; and means for calculating the number of turns used in the tap winding and its polarity based on the detected terminal voltage; A transformer protection relay comprising: means for compensating the operating force calculation of the transformer protection relay.