KR20200071471A - Apparatus for protecting OLTC of main transformer - Google Patents

Abstract

The present invention discloses an OLTC protection device of a main transformer, in which an On Load Tap Changer OLTC (On Load Tap Changer) block can be executed even in an event of a temporary failure of a secondary distribution line of the main transformer of a distribution substation, and the PT failure of a directional relay on the distribution line can be monitored. The disclosed device includes: a PT failure determination unit that outputs an alarm signal by determining whether the voltage transformation measurement equipment (PT) has failed based on three signals of a current measuring device of the distribution line and three phase voltages of the secondary side of the main transformer; and an OLTC block signal generator that generates an OLTC block signal based on an alarm signal from the PT failure determination unit and the state of three phase voltages on the secondary side of the main transformer.

Description

Apparatus for protecting OLTC of main transformer

The present invention relates to an OLTC protection device for a main transformer, and more particularly, to an OLTC protection device for a main transformer capable of controlling a malfunction of an on load tap changer (OLTC) of a main transformer of a 154kV substation.

In the current domestic substation, as shown in FIG. 1, a main transformer 10 that transforms a primary side voltage of about 154 kV to a secondary side voltage of approximately 23 kV is installed. Circuit breakers 16 are installed on the primary and secondary sides of the main transformer 10, respectively. A current meter 12 and a distribution line (DL) are connected to the secondary side of the main transformer 10.

The current meter 12 is installed between the main transformer 10 and the distribution line, measures the current on the secondary side of the main transformer 10 and sends it to the protection panel 14.

The protection panel 14 includes an OLTC block circuit portion 14a. Typically, the OLTC block circuit unit 14a determines whether the input current is 150% or more of the rated current and sends an OLTC block signal to the main transformer 10 if it is 150% or more of the rated current. Then, OLTC (On Load Tap Changer) (not shown) in the main transformer 10 cannot be operated. OLTC is a device that changes the voltage on the secondary side by changing the tap on the primary side of the transformer during transformer operation.

Here, the OLTC block circuit portion 14a is the OR gate 18 and the OR gate 18 connected to the input terminal of the three-phase current I _a , I _b , I _c on the secondary side of the main transformer 10 as shown in FIG. 2. ) Includes a timer 20 connected to the output terminal. Therefore, if any one of the three-phase currents I _a , I _b , and I _c applied from the secondary side of the main transformer 10 is maintained, the OLTC block circuit 14a maintains 150% or more of the rated current for a certain period of time. The OLTC block signal can be sent to the main transformer 10.

However, in FIG. 1, if a temporary failure occurs in the distribution line located on the secondary side of the main transformer 10, the OLTC block circuit unit 14a does not generate the OLTC block signal even though it must be generated.

In other words, the OLTC block circuit unit 14a generates an OLTC block signal when the input current is 150% or more of the rated current (for example, 2240A or more). However, when a failure of approximately 1140A occurs in the distribution line, the current flows to the secondary side of the main transformer 10. Therefore, the OLTC block circuit portion 14a cannot function properly at a current of about 1140A, so that an OLTC block signal cannot be generated despite a failure in the distribution line.

As a result, the OLTC of the main transformer 10 results in driving at a low fault current (approximately 1140A), which may be a failure factor for the OLTC of the main transformer 10 continuously. That is, since the OLTC of the main transformer 10 operates at a low fault current (approximately 1140A), there is a high probability that the transition resistance inside the diverter of the main transformer 10 may be lost due to continuous failure. Here, the diverter reduces transmission shock by simultaneously touching two taps when moving between transformer taps.

Of the total failures of the main transformer from 2010 to the present, the OLTC failure rate is approximately 10.4%.

Meanwhile, in recent years, small-scale power generation facilities using renewable energy resources such as solar power, wind power, and ESS (Energy Storage System) have been widely distributed to 23kV distribution lines. As the distributed power sources (solar power, wind power, ESS, etc.) continue to increase, the total fault capacity increases, but the fault current supplied from the transformer primary side decreases. In addition, it is difficult to lower the correction criteria (150% of the rated current) for the OLTC block operation due to the overload operation of the transformer.

Due to the continuous increase of distributed power sources in the 23 kV distribution line, the use of the directional relay 22 on the distribution line side is increasing as shown in FIG. 1. At this time, a current meter (CT) is installed on each distribution line. The directional relay 22 of each distribution line uses the value of PT (Potential Transformer) installed on the busbar of the distribution line when determining direction.

However, if the fuse of the 23kV PT (Potential Transformer) used as a polarity element in the direction determination is disconnected by opening/closing surge or disturbance, the protection panel 14 is used for the blown fuse of the PT (Voltage Deformation Measurement Equipment). Since there is no alarm function, the probability that the directional relay 22 is wrong is high. Therefore, it is necessary to determine whether the PT (voltage-density measurement equipment) has failed.

Prior art 1: Republic of Korea Registered Patent No. 10-0445225 (Tab-converter blocking system of a peripheral transformer in a distribution substation) Prior art 2: Korean Patent No. 10-0944537 (Transformer OLT control system) Prior art 3: Republic of Korea registered utility model No. 20-0345460 (transformer tap change control device)

The present invention has been proposed to solve the above-described conventional problems, and it is possible to perform an OLTC (On Load Tap Changer) block even in the event of a temporary failure of the secondary side distribution line of the main transformer of the distribution substation and the directional relay on the side of the distribution line The purpose is to provide an OLTC protection device for the main transformer that can monitor the PT failure of the system.

In order to achieve the above object, the OLTC protection device of the main transformer according to a preferred embodiment of the present invention is a voltage transformer measurement equipment based on three signals of the current meter of the distribution line and three phase voltages of the secondary side of the main transformer. (PT) PT failure determination unit to determine whether the failure or not and output an alarm signal; And an OLTC block signal generator for generating an OLTC block signal based on the alarm signal from the PT fault determination unit and the state of three phase voltages on the secondary side of the main transformer.

The PT fault determination unit, if any one of the three phase voltages on the secondary side of the main transformer falls below a certain voltage and any one of the three signals of the current meter of the distribution line is above a certain current, the voltage change measurement equipment fails. It is determined that this has occurred and an alarm signal can be output.

The PT fault determination unit includes: a first current determination unit to determine whether the first signal of the current meter of the distribution line is equal to or greater than a constant current; A second current determining unit determining whether the second signal of the current meter of the distribution line is equal to or greater than a constant current; A third current determination unit to determine whether the third signal of the current meter of the distribution line is equal to or greater than a constant current; A first signal processing element for receiving and processing the result of determining the state of the first phase voltage of the transformer secondary side from the result value of the first current determination unit and the OLTC block signal generation unit; A second signal processing element for receiving and processing the result of determining the state of the second phase voltage on the secondary side of the main transformer from the OLTC block signal generator; A third signal processing element for receiving and processing the result of determining the state of the third phase voltage on the secondary side of the main transformer from the OLTC block signal generation unit and the result value of the third current determination unit; And an alarm signal output element outputting an alarm signal based on outputs from the first signal processing element, the second signal processing element, and the third signal processing element.

The first current determining unit may output a high level signal when the first signal of the current meter of the distribution line is greater than or equal to a constant current.

The second current determining unit may output a high level signal when the second signal of the current meter of the distribution line is equal to or greater than a constant current.

The third current determining unit may output a high level signal when the third signal of the current meter of the distribution line is equal to or greater than a constant current.

The first signal processing element may be configured as an AND gate, the second signal processing element may be configured as an AND gate, and the third signal processing element may be configured as an AND gate.

The alarm signal output element may be configured as an or gate.

The OLTC block signal generation unit may include: a first voltage determination unit to determine whether the first phase voltage of the secondary side of the main transformer has dropped below a predetermined voltage; A second voltage determining unit determining whether the second phase voltage of the secondary side of the main transformer has dropped below a predetermined voltage; A third voltage determining unit determining whether the third phase voltage of the secondary side of the main transformer has dropped below a predetermined voltage; A signal processing element receiving and processing signals from the first voltage determining unit, the second voltage determining unit, and the third voltage determining unit; And an OLTC block signal generation element that generates an OLTC block signal based on the output of the signal processing element and the output of the PT failure determination unit.

The first voltage determining unit may output a high level signal when the first phase voltage on the secondary side of the main transformer falls below a certain voltage.

The second voltage determining unit may output a high level signal when the second phase voltage on the secondary side of the main transformer falls below a certain voltage.

The third voltage determining unit may output a high level signal when the third phase voltage on the secondary side of the main transformer falls below a certain voltage.

The signal processing element may be configured as an or gate.

The OLTC block signal generating element is composed of an AND gate, wherein the first input terminal of the OLTC block signal generating element is a non-inverting terminal connected to the output terminal of the signal processing element, and the second input terminal of the OLTC block signal generating element is the It may be an inverting terminal connected to the output terminal of the PT fault determination unit.

The OLTC block signal generating element, if any one of the three phase voltages on the secondary side of the main transformer temporarily falls below a certain voltage, and receives an alarm signal from the PT fault determination unit, the OLTC of the main transformer operates An OLTC block signal that is not to be generated can be generated and output.

According to the present invention having such a configuration, it is possible to prevent the OLTC failure by quickly performing the OLTC block function with a low voltage method.

By adding VTF (Voltage Transformer Fail) function to one protection panel, it is possible to monitor the voltage on the distribution line side of each feeder, and the cost reduction effect is higher than the acceptance of the VTF function for each distribution line.

23kV PT Fail monitoring function is provided to promptly respond to failures.

The degradation of the overcurrent operation sensitivity due to the continuous reduction of the fault current of the main transformer due to the increase of the distributed power supply can be eliminated.

1 is a schematic diagram for explaining an OLTC failure of a conventional main transformer.
FIG. 2 is an internal circuit diagram of the OLTC block circuit shown in FIG. 1.
3 is an internal configuration diagram of an OLTC protection device of a main transformer according to an embodiment of the present invention.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the overall understanding in describing the present invention, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted.

3 is an internal configuration diagram of an OLTC protection device of a main transformer according to an embodiment of the present invention.

It is understood that the OLTC protection device of the main transformer according to the embodiment of the present invention is installed on the protection panel in place of the circuit shown in FIG. 2.

The OLTC protection device of the main transformer according to the embodiment of the present invention includes a PT fault determination unit 60 and an OLTC block signal generation unit 70.

The PT fault determination unit 60 receives three signals (I _a , I _b , I _c ) of the current meter (CT) of the distribution line and three phase voltages (V _an , V _bn , V _cn ) of the secondary side of the transformer. On the basis of this, it is determined whether a PT (voltage deflection measurement equipment) has failed (for example, a blown fuse) and outputs an alarm signal (ie, PT_Fail_Alarm).

For example, the PT fault determination unit 60 is less than about 85% of a predetermined reference value (rated voltage of 23kV) of any of the three phase voltages (V _an , V _bn , V _cn ) on the secondary side of the transformer If it falls and any one of the three signals (I _a , I _b , I _c ) of the current meter (CT) of the distribution line is approximately 5% or more compared to the reference value, the PT (voltage deflection measurement equipment) fails (e.g., blown fuse) It is determined that this has occurred and outputs an alarm signal (ie, PT_Fail_Alarm). Here, the alarm signal will be sent to an appropriate place so that the administrator can confirm.

That is, the PT failure determination unit 60 determines that a failure (eg, a fuse blown) has occurred in the PT (voltage denaturation measurement equipment) when the current flows but the voltage falls below a certain level and outputs an alarm signal (ie, PT_Fail_Alarm). Just understand.

To this end, the PT fault determination unit 60 is a current determination unit 36 for determining whether the signal I _a of the current measuring device CT of the distribution line is approximately 5% or more of the rated current reference value, the current in the distribution line The current determining unit 38 determines whether the signal I _b of the measuring instrument CT is approximately 5% or more of the rated current reference value, and the signal I _c of the current measuring instrument CT of the distribution line is set to the rated current reference value. Compared with the current determination unit 40, the current determination unit 36 and the OLTC block signal generation unit 70, the secondary voltage of the transformer secondary side (V _an ) to determine the state The results of the first signal processing element 42, the current determination unit 38, which receives and processes the result value, and the state of the phase voltage V _{bn on the} secondary side of the transformer from the OLTC block signal generation unit 70 The second signal processing element 44 that receives the determined result value and performs signal processing, and the result value of the current determination unit 40 and the state of the phase voltage V _{cn on the} secondary side of the transformer from the OLTC block signal generation unit 70 Based on the outputs from the third signal processing element 46, the first signal processing element 42, the second signal processing element 44, and the third signal processing element 46 for receiving and processing the result of the determination. And an alarm signal output element 48 that outputs a low alarm signal (ie, PT_Fail_Alarm).

The current determining unit 36 outputs a high level signal (eg, “1”) when the signal I _a of the current measuring device CT of the distribution line is approximately 5% or more of the rated current reference value. The current determination unit 36 may be the first current determination unit described in the claims of the present invention, and the signal I _a of the current meter CT of the distribution line may be the first signal described in the claims of the present invention Can be.

The current determining unit 38 outputs a high level signal (eg, “1”) when the signal I _b of the current measuring device CT of the distribution line is approximately 5% or more of the rated current reference value. The current determination unit 38 may be the second current determination unit described in the claims of the present invention, and the signal I _b of the current meter CT of the distribution line may be the second signal described in the claims of the present invention. Can be.

The current determining unit 40 outputs a high level signal (eg, “1”) when the signal I _c of the current measuring device CT of the distribution line is approximately 5% or more compared to the rated current reference value. The current determination unit 40 may be the third current determination unit described in the claims of the present invention, and the signal I _c of the current meter CT of the distribution line may be the third signal described in the claims of the present invention Can be.

The first signal processing element 42, the second signal processing element 44, and the third signal processing element 46 may be configured as AND gates, respectively, and the alarm signal output element 48 may be configured as an OR gate.

The OLTC block signal generation unit 70 generates an OLTC block signal based on the state of the three phase voltages (V _an , V _bn , V _cn ) on the secondary side of the transformer and the alarm signal from the PT failure determination unit 60. Output.

For example, the OLTC block signal generation unit 70 determines whether the voltage on the secondary side of the transformer (V _an ) has dropped below approximately 85% of a predetermined reference value (for example, a rated voltage of 23 kV). 30), a voltage determining unit 32 for determining whether the phase voltage V _{bn on the} secondary side of the transformer has dropped below approximately 85% of a predetermined reference value (e.g., a rated voltage of 23 kV), the phase voltage on the secondary side of the transformer ( V _cn ) is inputted by the results of the voltage determination unit 34 and the voltage determination units 30, 32, and 34 to determine whether the predetermined reference value (e.g., a rated voltage of 23 kV) has fallen to about 85% or less, and signal processing The signal processing element 50, the timer 52 connected to the output terminal of the signal processing element 50, and the output of the signal processing element 50 passing through the timer 52 and the output of the PT fault determination unit 60 It includes an OLTC block signal generating element 54 for generating an OLTC block signal on the basis of.

The voltage determining unit 30 outputs a high level signal (eg, “1”) when the phase voltage V _an of the secondary side of the transformer falls below approximately 85% of a predetermined reference value. The voltage determining unit 30 may be the first voltage determining unit described in the claims of the present invention, and the phase voltage V _an of the secondary side of the transformer may be the first phase voltage described in the claims of the present invention.

The voltage determining unit 32 outputs a high level signal (eg, “1”) when the phase voltage V _{bn on the} secondary side of the transformer falls below approximately 85% of the predetermined reference value. The voltage determining unit 32 may be the second voltage determining unit described in the claims of the present invention, and the phase voltage V _{bn on the} secondary side of the transformer may be the second phase voltage described in the claims of the present invention.

The voltage determining unit 34 outputs a high level signal (eg, “1”) when the phase voltage V _{cn on the} secondary side of the transformer falls below approximately 85% of the predetermined reference value. The voltage determining unit 34 may be the third voltage determining unit described in the claims of the present invention, and the phase voltage V _{cn on the} secondary side of the transformer may be the third phase voltage described in the claims of the present invention.

The signal processing element 50 is composed of an or gate.

On the other hand, the OLTC block signal generating element 54 is composed of an AND gate. The first input terminal of the OLTC block signal generating element 54 is a non-inverting terminal connected to the output terminal of the signal processing element 50 via a timer 52, and the second input terminal of the OLTC block signal generating element 54 is PT It is an inverting terminal connected to the output terminal of the failure determining unit 60.

That is, the OLTC block signal generating element 54 falls to approximately 85% or less of the temporarily predetermined reference value among any of the three phase voltages (V _an , V _bn , V _cn ) on the secondary side of the transformer, and determines PT failure When an alarm signal (ie, PT_Fail_Alarm) from the unit 60 is applied, an OLTC block signal that prevents the OLTC of the main transformer from operating is generated and output. Here, when an alarm signal (ie, PT_Fail_Alarm) from the PT failure determination unit 60 is applied, it can be said that a high level signal (eg, “1”) is applied.

According to the OLTC protection device of the main transformer according to the embodiment of the present invention as described above, when the existing OLTC block is changed from the 50B (overcurrent) element to the 27B (undervoltage) element, a temporary failure occurs in the secondary side distribution line of the main transformer ( OLTC block can be performed even at low current), and PT fault monitoring of the directional relay on the 23kV distribution line can be performed by adding the VTF function.

As described above, optimal embodiments have been disclosed in the drawings and specifications. Although specific terms have been used herein, they are only used for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the claims or the claims. Therefore, those skilled in the art will appreciate that various modifications and other equivalent embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims.

60: PT failure determination unit
70: OLTC block signal generator

Claims (17)

A PT fault determination unit that outputs an alarm signal by determining whether the voltage variation measurement equipment (PT) has failed based on three signals of the current meter of the distribution line and three phase voltages of the secondary side of the main transformer; And
And an OLTC block signal generator for generating an OLTC block signal based on an alarm signal from the PT fault determination unit and three phase voltage states of the secondary side of the main transformer. . The method according to claim 1,
The PT failure determination unit,
If any one of the three phase voltages on the secondary side of the main transformer falls below a certain voltage and any one of the three signals of the current meter of the distribution line is above a certain current, it is determined that a failure has occurred in the voltage densification measurement equipment and alarms OLTC protection device of the main transformer characterized in that it outputs a signal. The method according to claim 1,
The PT failure determination unit,
A first current determining unit determining whether the first signal of the current measuring device of the distribution line is equal to or greater than a constant current;
A second current determining unit determining whether the second signal of the current measuring device of the distribution line is equal to or greater than a constant current;
A third current determination unit to determine whether the third signal of the current meter of the distribution line is equal to or greater than a constant current;
A first signal processing element for receiving and processing a result of determining the state of the first phase voltage on the secondary side of the main transformer from the result value of the first current determination unit and the OLTC block signal generation unit;
A second signal processing element receiving and processing a result of determining the state of the second phase voltage on the secondary side of the main transformer from the OLTC block signal generation unit and the result value of the second current determination unit;
A third signal processing element receiving and processing a result of determining the state of the third phase voltage on the secondary side of the main transformer from the result of the third current determination unit and the OLTC block signal generation unit; And
And an alarm signal output element outputting an alarm signal based on outputs from the first signal processing element, the second signal processing element, and the third signal processing element. The method according to claim 3,
The first current determining unit outputs a high-level signal if the first signal of the current meter of the distribution line is above a certain current, the OLTC protection device of the main transformer. The method according to claim 3,
The second current determining unit outputs a high level signal when the second signal of the current meter of the distribution line is greater than or equal to a constant current, the OLTC protection device of the main transformer. The method according to claim 3,
The third current determining unit outputs a high level signal when the third signal of the current meter of the distribution line is greater than or equal to a constant current, the OLTC protection device of the main transformer. The method according to claim 3,
The first signal processing element is an OLTC protection device of the main transformer, characterized in that consisting of an AND gate. The method according to claim 3,
The second signal processing element is OLTC protection device of the main transformer, characterized in that consisting of an AND gate. The method according to claim 3,
The third signal processing element is an OLTC protection device of the main transformer, characterized in that consisting of an AND gate. The method according to claim 3,
OLTC protection device of the main transformer, characterized in that the alarm signal output element is composed of an or gate. The method according to claim 1,
The OLTC block signal generation unit,
A first voltage determining unit determining whether the first phase voltage of the secondary side of the main transformer has dropped below a predetermined voltage;
A second voltage determining unit determining whether the second phase voltage of the secondary side of the main transformer has dropped below a predetermined voltage;
A third voltage determining unit determining whether the third phase voltage of the secondary side of the main transformer has dropped below a predetermined voltage;
A signal processing element receiving and processing signals from the first voltage determining unit, the second voltage determining unit, and the third voltage determining unit; And
And an OLTC block signal generating element for generating an OLTC block signal based on the output of the signal processing element and the output of the PT fault determination unit. The method according to claim 11,
The first voltage determining unit outputs a high level signal when the first phase voltage on the secondary side of the main transformer falls below a certain voltage, the OLTC protection device of the main transformer. The method according to claim 11,
The second voltage determining unit outputs a high level signal when the second phase voltage of the secondary side of the main transformer falls below a certain voltage, the OLTC protection device of the main transformer. The method according to claim 11,
The third voltage determining unit outputs a high level signal when the third phase voltage on the secondary side of the main transformer falls below a certain voltage, the OLTC protection device of the main transformer. The method according to claim 11,
The signal processing element is an OLTC protection device of the main transformer, characterized in that consisting of an or gate. The method according to claim 11,
The OLTC block signal generating element is composed of an AND gate,
The first input terminal of the OLTC block signal generating element is a non-inverting terminal connected to the output terminal of the signal processing element, and the second input terminal of the OLTC block signal generating element is an inverting terminal connected to the output terminal of the PT fault determination unit. OLTC protection device for the main transformer. The method according to claim 11,
The OLTC block signal generating element,
When any one of the three phase voltages on the secondary side of the main transformer temporarily falls below a certain voltage and receives an alarm signal from the PT fault determination unit, an OLTC block signal is generated that prevents the OLTC of the main transformer from operating. OLTC protection device of the main transformer, characterized in that the output.

Images