JPS63265519A - Ratio differential relay - Google Patents

Abstract

PURPOSE:To equalize each current value input to a relay body and reduce an error and to improve the accuracy of detection by correcting the secondary currents of a current transformer by using a matching coefficient computed from the primary-side tap voltage and secondary rated voltage of a transformer and the ratio of current transformation of a current transformer and correcting the secondary currents of the current transformer. CONSTITUTION:The secondary rated voltage V2 of a transformer LRT, each ratio of current transformation ct1, ct2 of current transformers CT1, CT2 and the values of a plurality of primary side tap voltage V'1 are input previously from a setting panel 5, and stored beforehand in a memory, etc., in a device. A microcomputer selects the value of tap voltage V'1 of interest in response to a tap positional signal S1 successively input during the operation of the transformer LRT, and computes a matching coefficient KC1 in succession from the value of the tap voltage and voltage V2 and the ratios of current transformation ct1, ct2 and sets it to a multiplier 2 while setting a matching coefficient KC2 (=1) to a multiplier 3. Accordingly, currents I''1 passing through the multiplier 2 are equalized to currents I''2 passing through the multiplier 3 at all times regardless of the position of a tap for the transformer LRT, thus reducing the error of a current value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention aims to prevent accidents that occur inside a transformer with on-load tap changer from occurring in current transformers connected to the primary and secondary sides of the transformer. The present invention relates to a ratio differential relay that detects a difference in secondary current.

(Prior art) Conventionally, in this type of ratio differential relay, the relay is connected to the relay via the main transformer connected to the primary and secondary sides of the transformer with on-load tap changer, which is the object of protection. The magnitudes of the primary and secondary currents input to the transformer are not equal even if no internal fault has occurred in the transformer.In other words, ideally, the magnitude of the transformer's transformer ratio and the main current transformer are not equal. If there is an inverse proportional relationship with the current transformation ratio, the magnitude of each current input to the relay will be equal, and the differential current will not become zero and the relay will not operate.

However, in reality, the transformation ratio and primary of the transformer.

Since the selection of the current transformation ratio of the secondary main current transformer does not necessarily correspond to each other, the transformation ratio and current transformation ratio are not inversely proportional, causing a difference in each current value input to the relay, which is the operating value of the relay. This will result in an error.

For this reason, conventionally, in order to match the current transformation ratio and reduce the above-mentioned error, a compensation current transformer, which is a type of autotransformer with many taps, is connected to the secondary side of the main current transformer. , the selection of the taps equalizes each current value flowing into the relay, thereby reducing the error.

(Problems to be Solved by the Invention) However, even when this compensation current transformer is used, it is difficult to reduce the above-mentioned current value error to 10% or less of the rated current.

In addition, a transformer with an on-load tap changer usually has a tap on its primary side, and this tap position changes at any time during operation of the transformer, so the primary side voltage of the transformer is actually Not equal to the rated primary voltage v1, generally ■1±10
The tap voltage v1 is within the range of %.

Since the primary current of the transformer changes with this change in tap voltage v4'', the current input to the relay via the main current transformer on the primary side of the transformer also changes within a range of ±10%, The difference between this current and the current from the main current transformer provided on the secondary side of the transformer causes an operating value error.

Therefore, the operating setting value of a ratio differential relay needs to be approximately 30% of the rated current so that it will not malfunction even if there is an error of 30% including the above-mentioned error and other errors. There is a problem in that it is not possible to detect internal faults in transformers that generate the following differential currents, and fault detection accuracy is poor.

The present invention was proposed to solve the above problems, and its purpose is to provide a matching coefficient calculated from the primary side tap voltage of the transformer, the secondary rated voltage, and the current transformation ratio of the current transformer. To provide a ratio differential relay that can reduce errors by equalizing each current value input to the relay body by correcting the secondary current of a current transformer using be.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for increasing the tap voltage on one winding side (for example, the primary side) of a transformer with an on-load tap changer to be protected. Find a matching coefficient based on the rated voltage of the line side (for example, secondary side) and each current transformation ratio of the first and second current transformers connected to the primary side and secondary side of the transformer,
It is characterized in that the secondary current of the first or second current transformer is multiplied by this matching coefficient and input to the relay body.

(Function) In the present invention, a plurality of primary side tap voltage values are provided depending on the tap position of a transformer with an on-load tap changer.

Store the secondary rated voltage and the current transformation ratios of the current transformers connected to the primary and secondary sides of the transformer in advance in a memory, etc.
A predetermined tap voltage value is selected in accordance with the tap position signal that changes sequentially during operation of the transformer, and this value and the above two
The primary and secondary sides of the transformer are determined using the following rated voltage and each current transformation ratio.
Calculate the matching coefficient on the next side.

At this time, set the matching coefficient of either the primary or secondary side to 1 so that the secondary current of one current transformer is input directly to the relay body, and set only the matching coefficient of the other side to 1. Find this, multiply it by the secondary current of the other current transformer, and then input it to the relay body.

(Example) An embodiment of the present invention will be described below with reference to FIG.

The figure schematically shows the configuration of the main parts of the present invention.

In the figure, LRT is a transformer with an on-load tap changer to be protected, and this transformer is connected, for example, to an adult, and a tap changer is provided on its primary side.

First and second current transformers CT and CT2 are connected to the primary and secondary sides of this transformer LRT, respectively.
These secondary sides are connected to a ratio differential relay 1 according to the invention.

In the ratio differential relay 1, 2.3 are current transformers C, respectively.
A matching coefficient KG, which is a multiplier connected to the secondary side of T,,CT, and is calculated by a microcomputer (not shown) in the ratio differential relay @1.

KC, is set as a multiplier. Note that one multiplier 2 receives a tap position signal St indicating the tap position from the primary side of the transformer LRT. A relay main body 4 having a differential coil, a suppression coil, etc. is connected to the output sides of these multipliers 2 and 3, and a setting panel 5 is connected to the relay main body 4.

Next, this operation will be explained. First, the primary and secondary currents of transformer LRT 1. , I, as is well known, is the primary side tap voltage V□′ of the transformer LRT, and the secondary rated voltage v2
Because it is inversely proportional to the size of

E□／I z =V z / V t'...
・・・・・・・・・・・・・・・・・・■ holds true,
Also, the current It flowing to the secondary side of the current transformers CT, , CT
's I, ° is the primary of transformer LRT.

The secondary currents I, , I, are converted to current transformation ratios Ct1 . Because it is the value divided by at.

11'=I, /c tL ・・・・・・・・・・・・・
・・・・・・・・・・・・■I,'=1. /at, ・
・・・・・・・・・・・・・・・・・・・・・■ holds true.

Therefore, the current 18' (=1.
'XKC,) and I,''(=I,' X K C,
) are equal, if we set KC,=1.

I,'XKC,=I,' ・・・・・・・・・・・・
・・・・・・・・・■That is.

KC□=I! '/Eng% ・・・・・・・・・・・・
・・・・・・・・・・・・■ Must be 0~
If we consider equation 0.

KCL=CQ tt/c tl)X(V,'/V,)・
...−...■.

Here, v, t Q jay Q tz is the transformer LRT
and current transformer CT1. It is a known value determined by the rating of CT, and a plurality of values for vl are predetermined for each tap position of the transformer @LRT. Therefore.

The values of V,, c t, , c t, and a plurality of v1' are inputted in advance from the setting panel 5 and stored in the internal memory of the device, and the microcomputer inputs the values of the transformer LRT.
The corresponding value of vl is selected according to the tap position signal St inputted sequentially during operation of V2. at□, ct
, and by the above equation 0 and set it in the multiplier 2, and set KC, (=1) in the multiplier 3.

As a result, the current 11'' that has passed through the multiplier 2 is always I,''=KC,XI□'=KC,XI,':I,'' regardless of the tap position of the transformer LRT, and is input to the relay body 4. Therefore, the error in the current value becomes only a calculation rounding error and is reduced to, for example, 1% or less.As a result, conventional ratio differential relays can be Whereas we could only detect an internal fault in the transformer LRT that generated a differential current of 30% or more of the rated current due to current value errors due to tap position fluctuations of the transformer LRT and other errors, we detected a differential current of approximately lθ%. Internal accidents can now also be detected.

In this embodiment, the matching coefficient KC2 of the multiplier 3 on the side of the current transformer CT is set to 1, but the multiplier 2 on the side of the current transformer CT
KC with matching coefficient KC1 set to 1.

In either case, it is possible to omit one of the multipliers and contribute to shortening the calculation time associated with multiplication. Also, V,, Vz, c t,, c t.

The value of KC varies depending on the ratings of the transformer LRT and current transformers CT, CT, but for example, the matching coefficient KC
Since the calculation formula for □ is always the above-mentioned formula 0, the present invention can be applied by a single device to protective relay devices for a wide variety of transformers with on-load tap changers and current transformers. .

Further, from the setting panel 5, a plurality of tap voltages V 1
Instead of ', the primary rated voltage v1 of the transformer LRT may be input, and v□' may be calculated each time using this vi and the tap position signals inputted sequentially, and used for the calculation of equation 0.

(Effects of the Invention) As described in detail above, according to the present invention, the input current to the relay body can be matched regardless of the tap position of the transformer, and the differential current in normal conditions can be made zero.

``This has the effect of significantly improving the detection accuracy and significantly improving the protection performance of transformers with on-load tap changers. Further, since the configuration of the device requires only the addition of a tap position signal generation means and a simple multiplication means, it has the advantage that it can be realized at low cost.

[Brief explanation of drawings]

The figure is a configuration diagram of main parts showing an embodiment of the present invention. 1... Ratio differential relay 2.3... Multiplier 4... Relay body 5... Setting panel LRT... Transformer CT with on-load tap changer, C
T,...Current transformer

Claims (1)

[Claims] The tap voltage on one winding side and the rated voltage on the other winding side of the transformer with an on-load tap changer to be protected, and the first and second windings connected to the primary and secondary sides of the transformer. A matching coefficient is determined based on each current transformation ratio of the current transformer, and the secondary current of the first or second current transformer is multiplied by this matching coefficient and input to the relay main body. Differential relay.