KR20240158485A - Fault detection device and method for current transformer using induction current in PO line - Google Patents

Abstract

The present invention provides a current application device and method for detecting an internal fault of a current transformer, which includes a current application device section installed on a P0 line forming a vector sum of U phase, V phase, and W phase on the secondary side of a current transformer between the current transformer and a power meter or a protection relay, and applying a test induction current to the PO line, thereby detecting whether there is an internal fault of the current transformer by the amount of current variation measured in a state where the test induction current is applied to the PO line and a state where the test induction current is not applied.

Description

{Fault detection device and method for current transformer using induction current in PO line}

The present invention relates to a device and method capable of detecting an internal fault of a current transformer more quickly and accurately by measuring a current fluctuation after applying a test induction current to a secondary side PO line of the current transformer, and more specifically, to a device and method capable of detecting an internal fault of a current transformer and a voltage transformer (MOF, Metering Out Fit) by measuring a current fluctuation each in a use state where a test induction current is not applied (injected) to the PO line of the current transformer in a live state and a test state where a test induction current is applied.

The distribution board is equipped with power transformers to stably receive and supply electricity to the load, current transformers or voltage transformers for charging electricity rates, electrical equipment such as instruments and protective relays, and electricity rate metering equipment such as power meters.

Among these devices, current transformers (including voltage transformers) are instruments that measure current, and are generally used in combination with protective relays and/or power meters to protect equipment from fault currents such as overcurrent, or to measure power usage for electricity billing.

In order to provide a stable power supply and calculate correct electricity rates, current transformers must be managed to ensure normal operation at all times. However, if they are used for a long period of time, internal failures such as ground faults may occur due to external stresses such as abnormal voltage and overcurrent that occur during use, which may cause abnormal operation such as metering errors.

When an internal fault occurs in the secondary winding of a current transformer, such as a ground fault, the measurement error of the current transformer increases, although the degree varies, making normal current measurement difficult. Such current transformer failures can cause electrical disasters due to malfunctions in protective equipment caused by abnormal current measurement, and make accurate electricity billing difficult. Internal failures of current transformers generally do not show any unusual signs on the outside, and are easily mistaken for normal operation, making it quite difficult to even determine whether there is a problem.

Therefore, it is necessary to periodically check whether the transformer is operating normally. There are two main methods of inspection. One is in a dead-line state, and the other is in a live-line state.

Testing of current transformers in a diagonal state is a commonly used method, but it has the significant disadvantage of requiring a power outage for a certain period of time while conducting the test, which prevents the user from using electricity.

To solve this problem, there is a method of testing in a live state, which is a method of testing the current transformer using a current error tester that measures the primary and secondary currents.

A prior art is illustrated in Fig. 1, which is disclosed in Patent Publication No. 10-2006-0063829.

The above-mentioned prior art includes a primary detection unit (10) including a hook meter (12) having a hook (15) formed to measure current on the primary high-voltage side, a secondary detection unit (20) including a hook meter (21) having a hook (23) formed to measure current on the secondary low-voltage side, and a main body (30) that receives data measured by the first and second detection units (10, 20) and performs calculation processing such as error to determine whether there is an abnormality in the current transformer.

The live-line test method not only had the problem of causing human casualties when measuring primary current in extra-high voltage (7000 V or higher) or high-voltage lines (600 V or higher), but also required the addition of a special device to the primary current measurement section to prevent this. In addition, there was the problem of incorrectly judging that the current transformer was operating normally even though there was clearly a problem in the transformer when the primary current was low or the load usage fluctuated.

In addition, this conventional transformer inspection method requires considerable specialized equipment, and furthermore, there is a problem in that it is difficult to detect faults and respond to them due to intermittent and temporary testing.

In addition, there was a device that, as a method of testing in a live-line state, installed a burden injection part that injects a test burden that does not exceed the rated burden into the secondary line of the current transformer, and measures the secondary current in the state where the test burden is not injected and in the state where the test burden is injected to determine the failure of the current transformer. This is disclosed in Patent Publication No. 2109414, and the related contents are illustrated in Figure 2.

The method illustrated in Fig. 2, while capable of conducting a test in a live-line state, applies a burden to the secondary side to utilize the variation of the secondary current. Therefore, if the primary current flows low, the secondary current also flows low, and even if a burden is applied, there is a limit to the variation of the secondary current, making it difficult to accurately detect internal faults in the current transformer. In addition, there was also the problem that the burden application device was fixedly installed on the secondary side of the current transformer.

In order to solve the problems of the prior art disclosed in FIGS. 1 and 2, the inventor of this patent application invented Patent No. 2211581.

This is an invention capable of detecting an internal fault in a current transformer regardless of the size of the primary current, without measuring the current for the primary line in a live state, as illustrated in FIG. 3. The invention detects whether an internal fault has occurred in the current transformer by applying an induced current to the secondary line of the current transformer and comparing the size of the secondary current that fluctuates before and after the application.

This was a groundbreaking improvement in the technology for detecting internal faults in current transformers. However, current transformers are three-phase, so it is necessary to measure phases U, V, and W separately to determine whether there is a fault. In addition, even when induced current is applied, the current fluctuation range is relatively small, so the measurement accuracy is somewhat reduced.

(Prior art 001) Patent Publication No. 10-2006-0063829

(Prior art 002) Patent Publication No. 2109414

(Prior art 003) Patent Publication No. 2251581

The present invention is an invention which detects an internal fault of a current transformer regardless of the size of the primary current without measuring the current of a primary line such as an extra-high voltage or high voltage in a live state, and significantly improves the detection speed and accuracy, thereby providing a device and method which can quickly and accurately detect the occurrence of an internal fault of a current transformer by applying an induced current to a P0 line in which the U, V, and W phases of the secondary side of the current transformer are vector-summed and comparing the size of the current that fluctuates before and after the application.

In order to solve the above problem, the present invention provides a current transformer internal fault detection device which is installed on a secondary PO line of a current transformer between a current transformer and a power meter or a protection relay and includes a current application device section for applying a test induction current, and can detect whether there is an internal fault in the current transformer in a live state by the amount of current variation measured in a state where the test induction current is applied and a state where the test induction current is not applied.

The above current transformer internal fault detection device preferably includes an inductive power supply unit that supplies a test induced current to a current application device unit, a current measurement unit that measures current in the PO line of the current transformer in the states where the test induced current is not applied and in the states where the test induced current is applied, a signal processing unit that processes a signal detected by the current measurement unit, and a control and calculation unit that applies or releases inductive power to the inductive power supply unit and receives a signal processed by the signal processing unit, calculates the current fluctuation amount in the states where the test induced current is applied and not applied to the PO line, and determines whether an internal fault occurs in the current transformer.

In addition, it is desirable that the current application device and the current measurement device be in the form of a clamp that can be detachably attached to the secondary line of the current transformer so that they can be installed on an already installed current transformer.

In addition, the present invention provides a method for detecting an internal fault in a current transformer, including the steps of applying a test induction current to a P0 line forming a vector sum of U phase, V phase, and W phase on the secondary side of a current transformer between the current transformer and a power meter or a protection relay, and the steps of detecting whether an internal fault in the current transformer exists by measuring the current fluctuation amount in a state in which the test induction current is applied to the PO line and a state in which the test induction current is not applied.

The current transformer internal fault detection device of the inductive current application method of the present invention can detect an internal fault of a current transformer much more quickly and accurately than before by applying a test inductive current to the current transformer PO line in a live state and measuring the secondary current fluctuation amount. However, the effects of the present invention are not limited to such literal description, but include all that can be inferred by a person skilled in the art through the present invention.

Figures 1 and 2 are a conventional transformer tester in a live state.
Figure 3 is a schematic diagram of a conventional internal fault detection device for a current transformer using induced current.
Figures 4a and 4b are equivalent circuits of a current transformer in normal and fault states using an internal fault detection device of the current transformer using an induced current.
Fig. 5a is an example of a wiring diagram between a transformer and a power meter.
Figure 5b is a wiring diagram of a current transformer internal fault detection device using induced current according to one embodiment of the present invention.
Figure 6 is a schematic diagram of a current transformer internal fault detection device using induced current according to one embodiment of the present invention.
Figure 7 is a schematic diagram of a control and operation unit according to one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. The embodiments are provided to easily explain the present invention to those skilled in the art, and the present invention is not limited thereto. The terms used in this application are only used to describe embodiments, and terms such as “include” or “have” mean that a configuration, etc., exists, and “connection” means electrically connecting.

A transformer includes a current transformer, and the current transformer (1) used in this specification is a concept that includes a current transformer in addition to a pure current transformer itself.

FIG. 3 is a schematic diagram of a current transformer internal fault detection device using an induced current invented by the inventor of the present invention, FIG. 4a is an equivalent circuit diagram for a normal current transformer and an induced voltage source, and FIG. 4b is an equivalent circuit diagram for a current transformer and an induced voltage source having an internal fault.

Since the present invention also determines whether a current transformer is broken by using an induced current, in order to help understand the present invention, FIGS. 4a and 4b are described.

i ₁ represents the primary current, i ₂ represents the secondary current, i _m represents the exciting current, i _f represents the fault current, i _i represents the test induced current, Z _m represents the magnetizing impedance, Z _f represents the fault impedance, Z _b represents the usage burden impedance, and V _i represents the induced voltage induced by the current applying device (3).

If the transformer's load impedance (Z _b ) satisfies the rated load, the relative sizes of the magnetizing impedance (Z _m ) and the fault impedance (Z _f ) compared to the load impedance (Z _b ) are such that the magnetizing impedance (Z _m ) is very large, but the fault impedance (Z _f ) is very small.

If this point is explained in terms of the secondary current change pattern according to the test induced current input in the normal current transformer of Fig. 4a, the size of the test induced current (i _i ) applied to the secondary line of the current transformer by the current application device (3) is determined by the size of the induced voltage (V _i ), magnetizing impedance (Z _m ), and usage burden impedance (Z _b ).

In addition, the transformer's usage burden impedance (Z _b ) is generally less than 1Ω (based on 25VA) considering the rated burden conditions of the current transformer, while the magnetizing impedance (Z _m ) is several MΩ, which is very large compared to the usage burden impedance (Z _b ) (Z _m >>Z _b ).

The magnitude of the induced voltage (V _i ) applied to the secondary line of the current transformer using the current application device (3) is a microvoltage, the test induced current (i _i ) in a normal current transformer is small, and the secondary current (i ₂ ) of the current transformer does not change much (while the magnetizing impedance (Z _m ) is very large, the magnitude of the induced voltage (V _i ) is a microvoltage).

However, in the case of an internal fault current transformer, a fault impedance (Z _f ) that is considerably smaller than the magnetizing impedance (Z _m ) is synthesized (Z _m >>Z _f ), as shown in Fig. 4b, so that the effect of the magnetizing impedance (Z _m ) disappears (in the equation below, Z _m //Z _f indicates that Z _m and Z _f are connected in parallel, and since Z _m is very large, Z _f remains), and the test induced current (i _i ) is determined by the sizes of the fault impedance (Z _f ) and the usage burden impedance (Z _b ).

And considering that the fault impedance (Z _f ) is much smaller than the service impedance (Z _b ) (Z _b >Z _f ), even if a microvoltage is applied, a large test induced current (i _i ) is generated, and accordingly, the secondary current of the current transformer (i ₂ ) fluctuates greatly.

Based on this, the current application device (3) is installed on the secondary line between the secondary terminal of the current transformer and the protection relay or power meter (2) to perform the function of applying the test induced current. The current measurement device (4) is for measuring the size of the secondary current of the current transformer that changes according to the application of the test induced current, and measures the current in the normal use state before the application of the test induced current and after the application of the test induced current, respectively.

Meanwhile, the signal processing unit (20) of Figs. 6 and 7 converts the analog current signal transmitted from the current measuring device unit (4) into a digital signal and provides it to the control and operation unit (30). The signal processing unit (20) is used to remove noise included in the signal and extract the signal of the required bandwidth while converting the analog signal into a digital signal.

As illustrated in FIG. 7, the control and operation unit (30) includes an application control unit (31) that controls power to be applied or released for applying an induced current to the inductive power supply unit (10), an operation unit (32) that calculates the secondary current variation before and after the test induced current application from a signal transmitted from the signal processing unit (20), and a judgment unit (33) that determines an internal fault in the current transformer based on the secondary current size variation.

The judgment unit (33) that determines the internal fault of the current transformer calculates the amount of change in the secondary current before and after the application of the test induced current as shown in the following formula. That is, since the secondary current (i ₂ ) changes in the fault state due to the test induced current (i _i ), the amount of change is calculated. I ₂ is the current size (rms value) before the application of the test induced current, and I ₂ ' is the current size (rms value) after the application of the test induced current.

And by comparing this with a preset threshold value, it determines whether there is an internal fault in the current transformer, and when a fault is detected, the test result is displayed on the display unit (40). In addition, even if the primary current flows low and the secondary current also flows low, the present invention applies a test induction current to the secondary line of the current transformer, so that it is possible to determine an internal fault in the current transformer.

Based on this, if the present invention is further explained using FIGS. 5a and 5b, the current transformer internal fault detection device (5) of the present invention is not installed in each of the U, V, and W phases of the current transformer, but is installed in the P0 line where the U, V, and W phases of the current transformer are combined by vector addition between the current transformer (1) and the power meter or protection relay (2).

It includes a current application device (3) that applies a test induced current, a current measurement device (4) that measures the current amount in a normal use state before the test induced current is applied and in a state when the test induced current is applied, and a configuration that detects whether there is an internal fault in a current transformer (1) based on the amount of change in the measured secondary current, and calculates the amount of change in the current size before and after the application of the test induced current.

The current application device part (3) and the current measurement device part (4) installed on the PO line of the current transformer (1) may be installed in a fixed form for the purpose of applying the test induced current and measuring the current, or may be installed in a type of clamp that can be detachably attached to the PO line. In this case, there is a significant advantage in that the internal fault of the current transformer can be tested without dismantling or separating the line of the current transformer that has already been installed.

In addition, the current transformer internal fault detection device (5) also includes, as in the past, an inductive power supply unit (10) connected to a current application device unit (3), a signal processing unit (20) connected to a current measurement device unit (4), a control and calculation unit (30), a display unit (40), a power supply unit (50), etc.

Fig. 5a is a wiring diagram commonly used between a current transformer and a power meter. Terminals 1S, P1, 2S, P2, 3S, P3, P0, 3L, 2L, and 1L are connected to the current transformer, and terminals 1S (U phase), 2S (V phase), 3S (W phase), P0, 3L (W phase), 2L (V phase), and 1L (U phase) are connected to the current transformer of each phase, and among these, P0, 3L, 2L, and 1L are connected to each other.

In the past, by applying an induced current to each of 1S (U phase), 2S (V phase), and 3S (W phase), a fault in the U phase, V phase, and W phase, and thereby a fault in the current transformer, was detected. However, the present invention detects a fault in the current transformer by applying an induced current to the PO phase, which is the sum of 1L, 2L, and 3L of the U phase, V phase, and W phase.

That is, the present invention can be said to detect an internal fault in a current transformer by including a step of applying a test induced current to a P0 line forming a vector sum of U phase, V phase, and W phase at the secondary side of a current transformer between the current transformer and a power meter or a protection relay, and a step of detecting whether an internal fault in the current transformer exists by measuring the current fluctuation amount in a state in which the test induced current is applied to the PO line and a state in which the test induced current is not applied.

The present invention conducts tests on a P0 wire to which current transformers 1L, 2L, and 3L of U-phase, V-phase, and W-phase are commonly tied, so it has the advantage of being able to significantly reduce measurement time by determining whether or not the current transformer is broken with just one measurement.

In order to determine which of the U, V, and W phases has a fault, a test must be conducted for each phase. Considering that if a fault occurs in any one of the U, V, and W phases, the current transformer must be replaced to ensure measurement accuracy, the present invention can be said to be significantly effective in reducing the measurement time.

In addition, the PO current is the vector sum of the currents of the transformer 1S (U phase), 2S (V phase), and 3S (W phase), and the present invention is smaller than the secondary current of the transformer, so even if the same induced current is applied, the fluctuation of the P0 current is greater than the fluctuation of the secondary current of the transformer, making it easy to determine a fault, which is a significant advantage qualitatively different from the prior art.

For example, if a current of about 3A flows through phases U, V, and W in a normal state and a fault occurs in phase W, 1.8A flows. If an induced current of 1A is applied to phase W, making it 2.8A, the fluctuation range of 1.8A and 2.8A is relatively small, so it may not be easy to calculate the fluctuation amount.

Considering that the current flowing through a current transformer fluctuates to some extent up and down even under normal conditions, it is difficult to accurately determine that the current transformer is faulty when the fluctuation is relatively small, and additional inspection may be necessary for an accurate determination.

However, if a fault occurs in phase W, and currents of 3A, 3A, and 1.8A flow in phase U, phase V, and phase W, approximately 1.2A will flow in the PO line as a result of the three vector sums. When an induced current of 1A, the same as before, is applied to become 2.2A, the relative fluctuation range is greater than when an induced current was applied to phase W previously, so it is possible to determine whether or not the current transformer is faulty much more accurately than before.

In other words, the current flowing in PO is smaller than the secondary currents of the U, V, and W phases of the current transformer, so even if the same induced current is applied to the U, V, and W phases, the current fluctuation is relatively large, so it has the advantage of being easy and accurate to determine a fault.

In addition, most distribution transformers are in the form of △-Y, and most of the loads connected to Y are unbalanced loads. Even in this case, the current in the P0 line of the transformer is theoretically 0A, and even when actually measured, it has a small size of several mA. A device that measures internal faults, etc., should not judge a normally operating device as faulty as much as it should detect a fault, but if the current in the P0 line is used, there is a significant advantage in that a normally operating transformer is not judged as faulty when the load changes.

Moreover, the conventional method of applying an induced current to the secondary of a current transformer as described above can judge a normally operating device as broken due to a load that momentarily fluctuates up to several A. On the other hand, in the case of a normally operating current transformer, the current of the P0 line has a small value close to several mA even if the load current of each phase fluctuates up to several A, and the fluctuation value is also very small. Therefore, when using the present invention, there is an advantage in that the probability of incorrectly judging a normally operating current transformer as broken is extremely low.

In addition, the present invention may include an alarm device that generates a signal when there is an abnormality in the transformer, an alarm control unit for driving the same, and a communication unit for connecting the transformer internal fault detection device (5) to an external device.

In addition, the transformer internal fault detection test can be performed manually by the user's operation of the test button, or automatically according to a set cycle, and can be performed continuously without affecting normal operation.

As described above, the current transformer internal fault detection device (5) is installed in the line between the current transformer (1) and the protection relay or power meter (2), but it can also be installed between the current transformer (1) and the terminal block of the current transformer, or between the current transformer and the TTB (Test Terminal Bed) terminal block, and it can also be built into the protection relay, power meter, terminal block, etc.

Although the present invention has been described above, the present invention is not limited to the disclosed embodiments and the attached drawings, and various modifications may be made by those skilled in the art within a scope that does not depart from the technical idea of the present invention. In addition, the technical ideas described in the embodiments of the present invention may be implemented independently, or two or more may be implemented in combination with each other.

1: Current transformer (voltage transformer) 2: Protection relay or power meter
3: Current application device section 4: Current measurement device section
5: Transformer internal fault detection device 10: Inductive power supply unit
20: Signal processing unit 30: Control and operation unit
40: Display section 50: Power supply section

Claims (4)

It is installed on the P0 line, which forms the vector sum of U phase, V phase, and W phase, on the secondary side of the current transformer between the current transformer (1) and the power meter or protection relay (2).
A current transformer internal fault detection device characterized in that it can detect whether there is an internal fault in a current transformer (1) by measuring the current fluctuation amount in a state in which a test induced current is applied to the PO line and a state in which a test induced current is not applied, including a current application device (3) that applies a test induced current to the PO line. In claim 1,
The above transformer internal fault detection device is,
An induction power supply unit (10) that supplies a test induction current to the above current application device unit (3);
A current measuring unit (4) that measures current in the PO line of the above current transformer (1) in the state where no test induced current is applied and in the state where the test induced current is applied; a signal processing unit (20) that processes a signal detected by the current measuring unit (4);
A current transformer internal fault detection device characterized by including a control and calculation unit (40) that applies or releases inductive power to the inductive power supply unit (10) and receives a signal processed by the signal processing unit (20) to calculate the current fluctuation amount in the state of applying and not applying a test inductive current to the PO line to determine whether there is an internal fault in the current transformer. In claim 2,
The current application device (3) and the current measurement unit (4) are characterized by being in the form of a clamp that can be attached to the secondary line of the current transformer. A step of applying a test induced current to the P0 line, which forms a vector sum of the U phase, V phase, and W phase, on the secondary side of the current transformer between the current transformer (1) and the power meter or protection relay (2).
A method for detecting an internal fault in a current transformer, characterized by including a step of detecting whether there is an internal fault in a current transformer (1) by measuring the amount of current fluctuation in a state in which a test induction current is applied to the PO line and a state in which the test induction current is not applied.