JPH01231621A - Protective relay for transformer - Google Patents

Abstract

PURPOSE:To manufacture a highly reliable protective relay with relatively low cost, by locking a ratio differential relay by use of outputs from a circuit for detecting currents in the types of wires in a transformer, a circuit for detecting the scalar sum current and a circuit comprising elements for detecting the variation on a reducing side. CONSTITUTION:Under a condition where load current is flowing, currents I1, I2 and i1, i2 flow in the direction of the arrows, and a ratio differential relay is not actuated. Circuits 8a1, 8a2 detect variations of currents an reducing side while an adder 8b outputs a scalar sum current corresponding to the variations. Since a comparator 8c produces no output for a constant load current, the relay 5 is disabled. When wire breakage occurs on the secondary side of a transformer 4b, the operational status of the relay 5 changes from one that the current i1 flows in the relay 5 and the current i2 flows out from the relay 5 to another that the current i1 flows in the relay 5 only. Since the scalar sum current varies from ¦i1'¦+¦i2'¦ to ¦i1'¦ the element 8 for detecting variation at the reducing side also functions to detect variations on the reducing side.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention provides a transformer protection relay that prevents malfunctions due to faults in the current transformer circuit of a ratio differential relay used to protect a transformer. Regarding electrical equipment.

(Prior Art) A ratio differential protection method is generally used as a method for detecting short circuits and ground faults in transformers.

This method will be explained using figures. Figure 3 shows a ratio differential relay on a single-line diagram, in which power is supplied from a power source 2 to a load 3 via a transformer 1 in a star-to-star connection. An input with several types of taps is input to the ratio differential relay 5 from the current transformer 4a for meters installed on the primary side of the transformer 1 and the current transformer 4b installed on the secondary side of the transformer 1. Current input is provided via transformers 5a□ and 5a2.

The input transformers 5a1 and 5a2 have a ratio of the primary and secondary current L1. of the differential relay 5 to the current passing through the transformer. This is to achieve so-called current transformation ratio matching so that the magnitudes of □ are made equal so that no current flows through the operating coil 5b.

In reality, it is impossible to configure the input transformers 5a1 and 5a2 so that an arbitrary number of turns can be selected so that the transformer capacity, transformer ratio, and current transformer ratio can be perfectly matched. Input current of relay 5 □.

The magnitude of E also causes a slight difference in the passing current.

This current ratio matching error, current transformer error, and relay error act as operating quantities of the ratio differential relay 5, and in order to prevent malfunction due to these quantities, the ratio differential relay 5 has the ratio characteristics shown in Fig. 4. have.

In FIG. 4, the horizontal axis indicates the primary current i input to the ratio differential relay 5, with the direction flowing into the transformer 1 being positive, and the vertical axis indicating the direction flowing out from the transformer 1 being positive. This shows the secondary current j2 input to the ratio differential relay 5.
The dotted line 6 indicating j-1=i2 is the ideal relay input in the event of a transformer external fault or under normal conditions, and is therefore the dead area of the ratio differential relay 5. However, in reality, the above-mentioned current transformation ratio matching error, current transformation ratio error, and relay error exist, so the operating range is narrowed as a characteristic as shown by the solid line 7 in FIG. 4 to prevent malfunction due to these errors.

Conventionally, protection systems for transformer protection devices using ratio differential relays have been represented by block diagrams such as those shown in FIGS. 5 and 6. In Fig. 5, only a ratio differential element 87 leads to a tripping circuit T, and is applied to an electromagnetic type ratio differential relay, which is thought to be less likely to malfunction due to element failure. It is a method. FIG. 6 shows a dual ratio differential element 87, 87A, which is generally applied to a static ratio differential relay.

(Problems to be Solved by the Invention) In the case of FIG. 5, a single defect in the ratio differential relay causes erroneous disconnection, which poses a reliability problem. The system shown in FIG. 6 was devised to compensate for this drawback, but although it is possible to prevent erroneous cut-off in the case of a defective relay, it has the drawback that erroneous cut-off of the current transformer circuit cannot be avoided. In other words, if the secondary side of the current transformer 4b shown in Fig. 3 is disconnected for some reason, the ratio differential relay 5 will be supplied with current only from the current transformer 4a, so it will not operate even with only the normal load current. Put it away. This means that even in the configuration shown in FIG. 6, the circuits are connected to the same current transformer and operate together, resulting in erroneous disconnection.

To prevent this, it is necessary to duplicate the current transformers used in 87 and 87A, which is very expensive and economically disadvantageous.

As mentioned above, there was no way to prevent accidental disconnection due to a single failure in the current transformer circuit or relay.

Therefore, it is an object of the present invention to provide a highly reliable transformer protection relay device that will not be erroneously disconnected due to a single defect in a current transformer circuit or relay.

[Structure of the invention]

(Means for Solving the Problems) The present invention focuses on the scalar sum current of the current transformer secondary currents of each winding of the transformer, and when the current transformer circuit is defective, this scalar sum current decreases, and the transformer Since it increases when an internal failure occurs, when a decreasing change is detected, the output of the ratio differential relay is locked to prevent unnecessary operation.

(Function) In other words, when the current transformer secondary circuit is disconnected, the variable ratio relay and the element that detects the change on the decreasing side (hereinafter referred to as the element that detects the change on the decreasing side) operate together, but the latter Since the output of the former is locked by the output, unnecessary shutoff is prevented.

Furthermore, in the event of an internal failure in the transformer, the change detection element on the decreasing side does not operate, so tripping of the ratio differential relay becomes effective.

(Example) Figure 1↓2 shows an example of the configuration of the present invention. 3 in Figure 1
The same reference numerals as those in the figure indicate the same devices and elements, 8 is a change detection element on the decreasing side that detects disconnection of the current transformer according to the present invention, and 8a1 and 8a2 are the elements on the secondary side of each current transformer. A connected circuit for detecting the magnitude of current, 8b is 8a1, 8a,
An adder circuit that forms the scalar sum of outputs; 8c is a comparison circuit that compares the current output of the adder circuit with the output from a certain period of time ago; and outputs an output when the scalar sum current changes in the decreasing direction; 8d is its output; It is. Fig. 2 is a configuration diagram of a trip circuit of a transformer protective relay device, where 50 is the output of the ratio differential relay, 8d is the output of the change detection element 8 on the decreasing side, and 9 is an AND circuit with 8d as the inhibit input. , T is the trip output.

In Figure 1, when the load current is flowing, I,
, I, and jul, 112, and the ratio differential relay 5 is inoperative. On the other hand, the change detection elements 8a1 and 8a2 on the decreasing side detect the respective currents, and the adder circuit 8b also outputs a corresponding scalar sum current.If the load current is constant, there is no output from the comparator circuit 8C. It is inactive. At the moment when the load current increases, the output of 8b changes and a change occurs in 8C, but this is a change on the increasing side, and since the output of 8C cannot be obtained, it is still inoperable. If the load current further decreases, the scalar sum current 1 i1'
Since l+l-2'1 decreases, a decreasing change occurs in the comparator circuit 8C, and the trip circuit is locked by the output 8d, but this is not a transformer failure, so there is no actual damage.

The response of the transformer when an external failure occurs and when the fault is cleared is the same as the increase or decrease of the load current, but since it is a response to an external failure, there is no problem with the protection function.

For example, if the secondary side of the current transformer 4b is disconnected while the load current is flowing, the ratio differential relay 5 changes from the state where 11 is an inflow and 12 is an outflow to only the inflow of J is activated. On the other hand, the change detection element 8 on the decreasing side also has a scalar sum current l z1'
Since l + l t2' l becomes 1λ1'1, the operation is performed by detecting the change on the decreasing side. Therefore, in FIG. 2, since the output 8d locks the trip caused by the output 5c, the trip command T is not generated, and unnecessary shutoff can be prevented.

On the other hand, in the case of an internal failure, the current increases by the amount of the failure current, so the failure current flowing through 8a□ and 8a2 is reduced to LfxrLl□
Then, the scalar sum current is 110'1+1λ2'1 to l J-x'+ Lt1'l +lY2' +b f
z'l, the change is on the increasing side, and the output of 8d is not generated. Therefore, in Fig. 2, the output 5c of the ratio differential relay is
is operating, and the decreasing side change detection element 8d is not operating, so AN
Output T of D circuit 9 is generated and tripping becomes possible.

For this reason, it is possible to perform a normal response to internal and external failures, and to prevent unnecessary interruptions even if a malfunction such as disconnection of the current transformer circuit occurs.

Although the above explanation has been made using a two-winding transformer as an example, the present invention is not limited to this, and can also be applied to a multi-winding transformer with three or more windings. This is obvious if we take this as an example.

〔Effect of the invention〕

As mentioned above, it consists of a circuit that detects the current for each line of the transformer, a circuit that detects the scalar sum current, and an element that detects the change on the decreasing side of the output. Relatively inexpensive and reliable transformer protection that locks the relay, allowing normal operation due to an internal failure of the transformer, and non-operation due to external failure, changes in load current, disconnection of the current transformer circuit, etc. A relay device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram of the trip command of the present invention, Fig. 3 is a block diagram of a conventional transformer protective relay device, and Fig. 4 is a ratio difference diagram. Characteristic diagram of dynamic relay,
FIGS. 5 and 6 are configuration diagrams of trip commands. 1...Transformer 2.Power source 3...Load 4a, 4b...Current transformer 5
... Ratio differential relay 5a115a2 ... Input transformer 5b ... Operating coil 5c ... Ratio differential relay output 6 ... External failure locus 7 ... Ratio characteristic 8 ... Change on the decreasing side Detection element 8a118a2...Detection circuit 8b...Addition circuit 8c...Comparison circuit 8d...Output 9 of change detection element on the decreasing side...AND circuit with one side as inhibit input Patent attorney rules near
Yudo Ken Daishimaru Ken Figure 2 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] The transformer is connected to each of the primary and secondary windings of the transformer that transforms the AC voltage, and is connected to the secondary winding of the current transformer that measures the AC current flowing in the transformer circuit. In a transformer protection relay device including a ratio differential relay for detecting internal failure, a detection circuit for detecting current values on the primary side and secondary side of the transformer is connected to the secondary winding of each current transformer. an adder circuit that forms a scalar sum of the outputs of this detection circuit; and a comparator circuit that compares the current output of this adder circuit with the output before a certain period of time and detects a change in the output of the adder circuit on the decreasing side. and a lock circuit that locks unnecessary operation output of the ratio differential relay other than an internal failure of the transformer using the output of the comparison circuit.