JPH0542213B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transformer protection differential relay device for protecting a transformer that is capable of tap switching during load.

[Conventional technology]

Figure 6 is a connection diagram showing a conventional transformer protection differential relay device. In the figure, PS is the power supply of the power system, MTR is the protected transformer, TC is the on-load tap changer, and R ₁ , R ₂ ,... _R10 ,C, _L1 , _L2 ,...
L ₁₀ is the tap position, for example, the maximum tap R ₁₀ is +
15%, minimum tap L ₁₀ is -15%, 1 tap 1.5%
It is a step. CT _H is the transformer high voltage side current transformer,
CT _L is the low voltage side current transformer, N _H is the current transformation ratio of the high voltage side current transformer CT _H , N _L is the AC ratio of the low voltage side current transformer CT _L , 10
is a differential relay (hereinafter simply referred to as differential relay),
RC _H is a high voltage side suppression circuit, RC _L is a low voltage side suppression circuit,
DF is the differential circuit, 1 is the ratio differential element, V _H is the high voltage side voltage, V _L is the low voltage side voltage, I _1H is the high voltage side primary current,
I _1L is the primary current on the low voltage side, I _2H is the secondary current on the high voltage side, I _RH
is the high voltage side relay input current, I _RL is the low voltage side relay input current, I _DT is the tap fluctuation differential current, IDF is the internal fault current, ACT is the compensation current change with the number of turns n ₁ on the primary side and n ₂ on the secondary side When the on-load tap changer TC is at the center position C, the high voltage side 2 is set so that the high voltage side relay input current I _RH and the low voltage side relay input current I _RL are equal.
Convert the next current I _2H to I _RH . F _O is the external failure point, F _I
is the internal failure point. Moreover, FIG. 7 is a ratio differential characteristic diagram of the conventional differential relay device 10.

Next, the operation will be explained.

(b) On-load tap changer (hereinafter simply referred to as tap changer) When TC is at center position C and in good condition or due to external failure
F _O time.

The current transformation ratio of the compensation current transformer ACT is set to n ₁ /n ₂ = V _H・N _H /V _L・N _L so that the high voltage side relay input current I _RH and the low voltage side relay input current I _RL are equal. Therefore, the differential current of the differential circuit DF is
Ignoring the slight error of the current transformer, even when the load current (low-voltage side relay input current I _RL ) is 100%, the external fault current (low-voltage side relay input current I RL )
Even when I _RL ) is 1000%, each is zero.

(b) When the tap changer TC is at the maximum tap R ₁₀ position (+15%) and it is healthy or there is an external failure F _O.

The high voltage side relay input current I _RH is 15% smaller than the low voltage side relay input current I _RL , and the differential circuit DF
A -15% tap fluctuation differential current I _DT flows due to the fluctuation of the tap changer TC, but the ratio characteristic of the ratio differential element 1 is such that the maximum tap fluctuation differential current I _DT reaches 15% as shown in Figure 7. , 20% with a margin of 5% (considering current transformer error and differential relay error),
In other words, load current (low voltage side relay input current I _RL )
20% for 100% and 1000% for external fault current (low voltage side relay input current I _RL )
Since it has a characteristic that it operates when each differential current I _D of 200% flows, the ratio differential element 1 does not output.

(c) The tap changer TC is at the minimum tap L ₁₀ position (-
15%) when in good condition or when an external _failure occurs.

The high voltage side relay input current I _RH is 15% larger than the low voltage side relay input current I _RL , and the differential circuit DF
A +15% tap-fluctuation differential current _IDT is flowing through, but since the ratio characteristic of the ratio differential element 1 is 20%, the ratio differential element 1 does not output as in (b) above.

(d) When the tap changer TC is in the center position C and there is an internal failure.

As shown in Figure 8A, the tap fluctuation differential current
I _DT is zero, and the internal fault current I _DF flowing from the power supply PS to the fault point _FI is 20% or more compared to 100% of the load current, and the ratio differential element 1 outputs.

(E) Internal failure occurs when the tap changer TC is at the maximum tap R ₁₀ position (+15%).

As shown in Figure 8B, at 100% load current,
Since a tap fluctuation differential current I _DT -15% is generated due to the tap changer TC position, if the power factor angle of the load current and internal fault current I _DF are equal, then
The ratio differential element 1 outputs when the internal fault current I _DF from the power supply PS is equal to or greater than 20% + 15% = 35% after subtracting the above differential current -15%.

(f) The tap changer TC is at the minimum tap L ₁₀ position (-
15%) at the time of internal failure.

As shown in Figure 8 (c), a tap fluctuation differential current I _DT +15% occurs due to the tap changer TC position when the load current is 100%, so the power factor of the load current and internal fault current I _DF occurs. If the angles are equal, the internal fault current I _DF from the power supply PS is 20% - 15% = 5
% or more, the ratio differential element 1 outputs.

[Problem that the invention seeks to solve]

Since the conventional transformer protection differential relay device is configured as described above, if the tap fluctuation operating current at the position of the tap changer TC is ±15%, the ratio characteristic of the ratio differential element 1 is It must be set to 20% or more, taking into account the margin, and therefore, the sensitivity to internal failure is 5%, 20%, and 35% as in (d), (e), and (f) above. There were problems such as fluctuations depending on the position of the sensor, low sensitivity, and insufficient detection of minor failures.

This invention was made to solve the above-mentioned problems, and provides highly sensitive transformer protection that has constant sensitivity regardless of the position of the tap changer TC and allows detection of minor faults. The purpose is to obtain a differential relay device.

[Means for solving problems]

The transformer protection differential relay device according to the present invention includes:
A suppression circuit and a differential circuit are provided in the current transformer circuit installed at each terminal of the protected transformer, and a change differential circuit for deriving the change in differential current is connected to these. The output of the dynamic circuit and the output of the above-mentioned suppression circuit are introduced into a ratio differential element, so that a highly sensitive ratio characteristic is obtained regardless of the range of variation in tap switching.

[Effect]

The change differential detection circuit in this invention derives the change in differential current according to the switching of the taps,
Based on this, the ratio actuation elements of differential relays are
It functions to input a true internal fault differential current from which the differential current caused by tap switching has been removed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 2 denotes a differential differential circuit that derives a differential current, and as shown in FIG.
Subtraction circuit 2 that subtracts the output of 1 and the above differential current.
It is composed of 2. Note that the memory circuit 21
The follow-up time constant may be arbitrary as long as it is shorter than the moving speed of one tap of the tap changer TC and longer than the operating speed of the ratio differential element 1. For example, if the moving speed of one tap is 1 second, the tracking time constant of the ratio differential element 1 operating speed is 50ms
If so, set it to about 0.1 seconds. Further, the primary side of the protected transformer is defined as a high voltage side, and the secondary side is defined as a high voltage side.

The ratio differential element 1 determines the operating sensitivity by introducing the outputs of the high-voltage side suppression circuit _RCH and the low-voltage side suppression circuit _RCL , and responds within the output time of the differential differential circuit 2.

FIG. 2 is a diagram showing the ratio differential characteristics of the differential relay 10 of the present invention. 6.5% including differential relay error)
In other words, for 100% of the load current (low voltage side current I _RL )
6.5%, also external fault current (low voltage side current I _RL )
The characteristic is that it operates when a differential current I _D of 65% compared to 1000% flows.

Next, the operation of the transformer protection differential relay device according to the present invention will be explained.

(a) When the on-load tap changer TC is at center position C and is healthy or when an external failure _occurs .

In this case, the high voltage side relay current I _RH and the low voltage side relay current I _RL are equal, and the differential circuit current is zero.

(b) When the tap changer TC moves from tap R ₉ +13.5% to tap R ₁₀ +15% when it is healthy or when there is _an external failure.

In the stationary state at tap R ₉ position, the high voltage side relay input current I _RH is the low voltage side relay input current I _RL
It is 13.5% smaller than , and the tap fluctuation differential current _IDT flows by -13.5% in the direction of _-IDT in Figure 1.
In the variation differential circuit 2 of FIG. 3, the output of the memory circuit 21 and the non-memory differential current are equal in magnitude, and the output of the variation differential circuit 2 is zero.

Next, at the moment when the tap moves from the position of tap R ₉ to the position of tap R ₁₀ , the output of the memory circuit 21 remains at -13.5% for the time constant time, that is, 0.1 seconds.
On the other hand, the non-memory differential current instantaneously changes from -13.5% to -15%, and therefore a 1.5% differential current is generated as the output of the differential circuit 2 for 0.1 seconds.

However, since the sensitivity of the ratio differential element 1 is 6.5% as described above, no output is produced. After 0.1 seconds have passed after the movement, the differential current returns to zero again.

(c) When the tap changer TC moves from tap L ₉ -13.5% to tap L ₁₀ -15% and is in good condition or when there is an external failure F _O.

Similarly to (b) above, in the stationary state at the tap L ₉ position, the tap fluctuation differential current I _DT flows by +13.5% in the direction of +I _DT in Figure 1. The output of 2 is zero.

Next, for 0.1 seconds from the moment of moving from tap L ₉ to tap L ₁₀ , the change is 1.5% from differential circuit 2.
A differential current of 1 is output, but the ratio differential element 1 does not output any output, and this differential current also returns to zero after 0.1 seconds have elapsed.

(d) Tap changer TC is at center position C and internal failure occurs.
F _I time.

As shown in Figure 4A, the tap fluctuation differential current I _DT caused by the tap changer TC is zero, and the internal fault current I _DF flowing from the power supply PS to the fault point _FI is 6.5% compared to 100% of the load current. With the above, the ratio differential element 1 outputs.

In this case, at the moment when an internal failure occurs, the differential differential current is output from the differential differential circuit 2 for only 0.1 seconds, which is the follow-up time constant of the memory circuit 21. The ratio differential element 1 reliably responds and outputs within this output time.

(E) When the tap changer TC is in a position other than center position C and there is an internal failure F _I.

As shown in Figure 4 B and C, for example, when the tap changer TC is in the tap R ₁₀ position (+15%),
As shown in Figure 4B, a -15% tap fluctuation differential current _IDT is generated, and the tap changer TC
When L is at the ₁₀ position (-15%), a +15% tap fluctuation differential current _IDT is generated as shown in Figure 4C, but the variation differential circuit 2 Since only the differential current IDT is derived and applied to the ratio differential element 1, the internal fault current detection sensitivity is 6.5% regardless of the magnitude and direction of the tap fluctuation differential current _IDT .

In addition, in the above embodiment, the protected transformer MTR is 2.
Although we have explained the case of a wire-wound transformer, it can also be applied to the case of a three-winding transformer.According to this, the current transformer C _M is installed at the medium voltage winding terminal of the transformer as shown in Figure 5. , medium voltage side suppression circuit on current transformer CT _M
RCM is connected and the same effect as above is achieved. Note that the medium voltage winding terminal is provided in the secondary winding newly provided in the protected transformer MTR.

〔Effect of the invention〕

As described above, according to the present invention, a differential differential circuit for deriving a differential differential current is provided in the differential circuit, and the output of this differential circuit and the output of the two suppression circuits RCH _{and RCL} are connected to a ratio differential circuit. Since the element 1 is configured to respond, the sensitivity is not affected by positional fluctuations of the tap changer TC, and there is an effect that a small fault in the transformer can be detected with high sensitivity with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of a transformer protection differential relay device according to an embodiment of the present invention, FIG. 2 is a ratio differential characteristic diagram according to the present invention, and FIG. 3 is a block connection diagram of a differential differential circuit. FIG. 4 is a diagram explaining the detection sensitivity of the differential relay device of the present invention, FIG. 5 is a connection diagram showing another embodiment, FIG. 6 is a connection diagram of a conventional transformer protection relay device, and FIG. FIG. 7 is a conventional ratio differential characteristic diagram, and FIG. 8 is a diagram explaining the detection sensitivity of the conventional differential relay device. MTR is the protected transformer, CT _H , CT _M , CT _L are current transformers, R _H , RC _M , R C _L are suppression circuits, DF is a differential circuit, 1 is a ratio differential element, 2 is a change difference dynamic circuit,
10 is a differential relay. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A suppression circuit connected to each of the primary and secondary sides of the protected transformer via a current transformer, and each relay on the primary and secondary sides inputted via each of the current transformers. Introducing a differential circuit that calculates a differential current based on the input current, a variation differential circuit that derives only the differential current change in response to tap switching of the protected transformer, and the output of each of the suppression circuits. and a ratio differential element that determines the operating sensitivity and responds within the output time of the differential differential circuit.