CN104483534A - Intelligent monitoring alarm for grounding current of transformer core - Google Patents

Abstract

The transformer core grounding current intelligent monitoring alarm includes a current transformer, the current transformer has a central hole, and the current transformer also includes a core grounding wire passing through the central hole and a secondary transformer for mutual inductance with the core grounding wire. side coil; and a detection circuit for collecting the secondary side coil current; the current detection circuit includes an induction current amplifier connected to the secondary side coil, an A/D converter connected to the output end of the induction current amplifier, and an A/D A single-chip processing system connected to the converter; the single-chip processing system is connected to the communication interface, and also includes a clock oscillator and a storage unit connected to the single-chip processing system. The invention performs mutual inductance isolated sampling and amplification on the ground wire current, greatly improves the test accuracy and test reliability, directly gives the judgment result and transmits it to the monitoring center through the communication interface, and realizes unattended and online real-time detection and judgment.

Description

Transformer core grounding current intelligent monitoring alarm

technical field

The invention belongs to the field of power electronics, and relates to a transformer ground wire current detection technology, in particular to an intelligent monitoring and alarm device for transformer core ground current.

Background technique

In the transformer structure, there is a certain parasitic capacitance between the coil and the iron core, and between the iron core and the box. When the power transformer is in normal operation, an uneven electric field is generated around the charged coil. The floating potential of the ground causes the iron core and the coil to achieve breakdown insulation, resulting in partial discharge, etc. Therefore, it is necessary to release the normal induced electromotive force, so that they are all at zero potential, so it is necessary to design and complete a little reliability grounding.

However, due to the uneven magnetic flux density of the iron core, the magnetic circuit close to the inner frame of the iron core is short and the magnetic resistance is small, and the magnetic circuit close to the outer frame of the iron core is long and the magnetic resistance is large, so when more than two points are grounded, a potential difference will be caused , Two-point and multi-point potential differences will form a loop with each other, resulting in a circulating current. The circulating current may range from milliamps to tens of amperes, and cause eddy current heating in the iron core, damage the insulation layer of the silicon steel sheet, and even affect the coil insulation, increase the oil temperature, and cause methane and acetylene to exceed the standard, resulting in transformer accidents.

From the above conclusion: the iron core must be grounded at one point, but it is absolutely not allowed to be grounded at two or more points. In order to achieve the aforementioned grounding requirements, the transformer is equipped with a ground wire connection method as shown in Figure 1: as can be seen from a in Figure 1, the transformer 1 leads the iron core wire 3 from the transformer body through the conduit 2, and connects it to Underground, to achieve a protective effect of a little grounding. However, when there are two or more grounding faults, it cannot be automatically notified, but most of them are shown in b of Figure 1, and the grounding current is measured regularly or irregularly by manually holding the clamp meter 4, according to DL/T 596-199 "Guidelines for Preventive Testing of Electric Power Equipment" stipulates that when the insulation of the iron core is normal, the grounding current is not greater than 0.1A, which is the basis for discrimination. If it exceeds the standard value of 0.1A, it means that there is a problem. At the same time, the larger the exceeding data, the more problems are indicated. First, there are two or more points of grounding.

The transformer core is grounded and manually tested. Not only is the method primitive and backward, but more importantly, problems cannot be found in time. Especially in the situation where unattended substations have been widely used today, the chances of patrol inspection are greatly reduced, and it is more difficult to timely and accurately detect If a fault is found, it will delay the time to deal with the accident, and even cause the situation to expand.

Contents of the invention

In order to overcome the shortcomings of the existing transformer core grounding wire current detection method that requires manned manual testing, is difficult to find faults in a timely and accurate manner, and may delay the timing of accident handling, the invention discloses an intelligent monitoring and alarming method for transformer core grounding current device.

The transformer iron core grounding current intelligent monitoring alarm of the present invention is used to measure the current of the transformer iron core grounding wire, including a current transformer, the current transformer has a central hole, and the current transformer also includes a wire that passes through the central hole Iron core grounding wire and secondary side coil with mutual inductance with the iron core grounding wire;

And a detection circuit for collecting the secondary side coil current; the current detection circuit includes an induction current amplifier connected to the secondary side coil, an A/D converter connected to the output end of the induction current amplifier, and an A/D converter connected A single-chip processing system; the single-chip processing system is connected with the communication interface, and also includes a clock oscillator and a storage unit connected with the single-chip processing system.

Specifically, the end point of the secondary side coil is grounded, and the induction current amplifier includes a rectifier diode, a filter capacitor, a comparator, and a reference voltage generator; an input terminal, the filter capacitor is connected between the cathode of the rectifier diode and ground, and the output terminal of the reference voltage generator is connected to the inverting input terminal of the comparator;

It also includes a working point voltage setting circuit, the working point voltage setting circuit is a first voltage dividing resistor string connected in series between the DC power supply terminal of the induction current amplifier and the ground; the voltage dividing of the first voltage dividing resistor string Node connected to the rectifier diode cathode.

Further, the reference voltage generator is a second voltage-dividing resistor string connected in series between the DC power supply terminal of the sense current amplifier and the ground, and the output terminal of the voltage-dividing node reference voltage generator.

Further, a positive feedback resistor string is connected between the output terminal of the comparator and the negative pole of the rectifier diode, and the positive feedback resistor string is composed of a first positive feedback resistor and a second positive feedback resistor connected in series, wherein the first positive feedback resistor The resistor is connected to the output terminal of the comparator, and the second positive feedback resistor is connected to the cathode of the rectifier diode;

The resistance value of the first positive feedback resistor is greater than that of the second positive feedback resistor, and the intermediate node between the first positive feedback resistor and the second positive feedback resistor is connected to the non-inverting input terminal of the comparator.

Preferably, the induction current amplifier further includes a power supply circuit, the power supply circuit includes a power supply transformer and a three-terminal voltage stabilizer, the primary side of the power supply transformer is connected to the mains grid, and the starting point and end point of the secondary side are respectively connected to a rectifier diode The positive pole and the negative poles of the two rectifier diodes are connected together and connected to the input terminal of the three-terminal voltage regulator, and a grounded center tap is also connected on the secondary side; the first output terminal of the three-terminal voltage regulator is used as the power supply circuit DC positive output terminal, the second output terminal of the three-terminal regulator is grounded.

Further, a first filter capacitor is connected between the input terminal of the three-terminal voltage regulator and the ground, a second filter capacitor is connected between the first output terminal of the three-terminal voltage regulator and the ground, and the first filter capacitor is connected between the first output terminal of the three-terminal voltage regulator and the ground. The filtering frequency of the first filter capacitor is lower than that of the second filter capacitor.

Further, an indicating branch is also included, and the indicating branch includes a light-emitting diode and a current-limiting resistor connected in series between the direct current output terminal and the ground.

Preferably, the A/D converter is MAX125.

Preferably, it also includes a host PC and a keyboard input unit connected to the single-chip processing system.

Specifically, the detection transformer is BH-066 type.

Adopting the transformer iron core grounding current intelligent monitoring alarm of the present invention, the transformer grounding line current is isolated, sampled and amplified by mutual inductance, which greatly improves the test accuracy and test reliability, and at the same time introduces a single-chip processing system to perform calculation, processing and judgment on the collected signals , directly give the judgment result and transmit it to the monitoring center through the communication interface, realizing unattended and online real-time detection and judgment.

Description of drawings

Fig. 1 is the schematic diagram of the detection method of transformer iron core ground current in the prior art;

Fig. 2 is the structure schematic diagram of the real-time monitoring alarm of the transformer iron core ground current of the present invention;

Fig. 3 is a schematic diagram of a specific embodiment of the inductive current amplifier of the present invention;

FIG. 4 is a schematic flow chart of the current detection and judgment process in the present invention.

Detailed ways

The specific embodiment of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The transformer iron core grounding current intelligent monitoring alarm of the present invention is used to measure the current of the transformer iron core grounding wire, including a current transformer, the current transformer has a central hole, and the current transformer also includes a wire that passes through the central hole Iron core grounding wire and secondary side coil with mutual inductance with the iron core grounding wire;

And a detection circuit for collecting the secondary side coil current; the current detection circuit includes an induction current amplifier connected to the secondary side coil, an A/D converter connected to the output end of the induction current amplifier, and an A/D converter connected A single-chip processing system; the single-chip processing system is connected with the communication interface, and also includes a clock oscillator and a storage unit connected with the single-chip processing system.

The secondary side coil usually surrounds the iron core grounding wire in a spiral shape. When the grounding wire has an abnormal current, according to the principle of electromagnetic induction, the abnormal current of the iron core grounding wire is induced by the secondary side coil to generate an induced current signal. The induced current signal Input to the sense current amplifier in the current sense circuit

As shown in Figure 2, a schematic structural diagram of a specific embodiment of the present invention is provided. What is sent from the current detection circuit at the front end is an analog signal, so it is necessary to use the A/D converter to do analog/digital signal conversion (A/D conversion), the A/D conversion device model used can be MAX125, after the A/D conversion is completed, the data bus and address bus are sent to the single-chip processing system, through the address bus and data bus, the analog circuit and the manual setting of the keyboard are received Double signal, enter the working state, through the cooperation of software and hardware, compare, judge, calculate and store to determine whether the multi-point grounding of the transformer core occurs.

There is a clock oscillator inside the device to generate clock signals such as year, month, day, hour, minute, second, etc. Its purpose is not only to travel time, but also to record the time of fault occurrence, which is convenient for accident analysis and handling. The model of the crystal clock oscillator used may specifically be DS12887, and the storage unit is used to store the initial parameter storage for judgment and record the judgment result.

Although the present invention is based on the purpose of being unattended, input devices such as a keyboard and a mouse can still be provided to facilitate inspection staff to set judgment parameters and command operations. By setting the keyboard receiving processor, the keyboard can also input the monitored grounding line, sensor number, voltage threshold value, alarm start value, time correction, communication protocol, etc.; it can also be combined with the LCD liquid crystal display for the monitored grounding line number, grounding current Viewing and querying of value, failure time, etc. The type of receiving processor used may be JCDL8279.

The processing results made by the single-chip processing system, through the communication interface, select different signal interfaces and communication protocols according to the communication protocol and baud rate adapted to the site, such as RS232, RS485 interface, etc., to transmit the signal to the system network, so that the centralized control center Supervisors and relevant leaders can also understand and master the grounding situation of the transformer core in a remote place, and make timely analysis and investigation of accidents to ensure the safe and stable operation of the entire transformer.

You can also set up a local display, and send the processing results to the LCD screen of the machine in parallel to display an alarm. You can also set up a host computer, and another signal is sent to the host computer for classification, arrangement, and tabulation in a wider range and with greater functions. , storage and other processing.

As shown in Figure 4, the flow diagram of the current judging process of the present invention is provided. When the work starts, at first the initial processing such as zeroing and reset is performed on the monitoring system; a series of signals and data are input from the keyboard, including

1) The serial number of the monitored transformer, that is, the core grounding wire (the device is suitable for monitoring multiple main transformers);

2) Inspection cycle, in order to avoid instantaneous impact and subtract signal operation time, etc., to confirm the authenticity and continuity of the fault, for example, set the inspection cycle to 10 seconds.

3) Test and set the initial current I0. Under normal circumstances, the ground current should be less than the set value, for example, I0=0.1A, and store the threshold value of 0.1A in the storage unit.

When the parameter setting is completed, the data conversion process is automatically performed inside the single-chip microcomputer; at the same time, the digital signal measured by the current detection circuit and converted by A/D is sent to the single-chip processing system for comparison and judgment.

Normally, the measured current signal is close to 0, which must be lower than the initial current value I0 set by the benchmark. At this time, it is judged as the "No" state shown in Figure 4, and the cycle test is continued, that is, the next inspection cycle is repeated.

When the iron core of the monitored transformer is grounded at two or more points, a grounding current will be generated, and the collected signal will be sent to the single-chip processing system for comparison and judgment. At this time, it is judged as the "yes" state shown in Figure 4.

On the one hand, the output alarm signal is recorded and stored by the storage unit when the fault occurred, the transformer number, etc.; on the other hand, the signal is uploaded to the monitoring center through the communication interface, and can also be uploaded to the local display screen or used as a display alarm.

Current transformer can select existing mature model for use, and according to the concrete application situation of the present invention, grounding current may reach tens of amperes, preferably use the 0.5 grade that Shanghai switch factory produces, the BH-0.66 type current transformer of 75/5 ampere, The current transformer has high detection accuracy and small size, and is suitable for being installed in a position that is easy to fix and observe in the path of the grounding wire of the transformer.

The function of the induction current amplifier is to detect the induction current that occurs on the secondary side and output a judgment signal. As shown in Figure 3, a specific implementation of the induction current amplifier is provided, the terminal of the secondary side coil is grounded, and the induction current The current amplifier includes a rectifier diode D3, a filter capacitor C3, a comparator IC1, and a reference voltage generator; the positive and negative poles of the rectifier diode are respectively connected to the starting point of the secondary side coil and the non-inverting input terminal of the comparator, and the filter capacitor is connected to the negative pole of the rectifier diode and the ground, the output terminal of the reference voltage generator is connected to the inverting input terminal of the comparator; it also includes a working point voltage setting circuit, and the working point voltage setting circuit is connected in series with the DC power supply terminal of the induction current amplifier and the ground The first voltage-dividing resistor string between them; the voltage-dividing node of the first voltage-dividing resistor string is connected to the cathode of the rectifier diode.

It can be seen from Fig. 3 that the two terminals S1 and S2 of the ground wire of the current transformer core pass through the current transformer core and the secondary side coil, and output the collected ground current signal at the terminals S3 and S4 of the secondary side coil. It is half-wave rectified by the rectifier diode D3 and filtered by the filter capacitor C3 to cooperate with the work of the subsequent circuit in the form of DC.

Since the current signal is collected from the secondary side coil end, it is converted into a voltage signal through the resistor R3 to the ground, so as to conform to the structural principle of the integrated op amp to work mainly on voltage. The two voltage-dividing resistors R2 and R3 of the first voltage-dividing resistor string also have the purpose of generating a DC operating point by dividing the power supply voltage to adapt to the input voltage operating range of the comparator, for example, the power supply voltage is 12V, the input voltage of the comparator IC1 If the working range is in the range of 2-8V, the ratio of R2 and R3 can be set so that the DC voltage value of the voltage dividing node is around 4V.

As shown in Figure 3 , the reference voltage generator can be a second voltage-dividing resistor string connected in series between the DC power supply terminal of the sense current amplifier and the ground, consisting of voltage-dividing resistors R5 and R6 connected in series, and the voltage-dividing nodes are R5 and R6 The common terminal of the reference voltage generator is used as the output terminal.

A preferred embodiment is that a positive feedback resistor string is connected between the output terminal of the comparator and the negative pole of the rectifier diode, and the positive feedback resistor string is composed of a first positive feedback resistor R7 and a second positive feedback resistor R4 connected in series, wherein The first positive feedback resistor is connected to the output terminal of the comparator, and the second positive feedback resistor is connected to the rectifier diode; the resistance value of the first positive feedback resistor is greater than that of the second positive feedback resistor, and the intermediate node of the first positive feedback resistor and the second positive feedback resistor is connected for comparison non-inverting input terminal.

The function of the positive feedback resistor string is to increase the amplification factor of the voltage signal. Example settings:

R4＝10kΩ, R7＝100kΩ, then the amplification gain:

Comparator voltage magnification A=1+R7/R4=1+100/10=11 times.

Taking the BH-0.66 type current transformer as an example, the relationship between the primary and secondary current transformation ratios is 1:15. For a small grounding current—such as 1A, after the 1:15 transformation ratio of the current transformer, the secondary The stage has current:

1÷15＝0.067A

In the voltage conversion through the resistor current, even if it is 1:1, it can only have 0.067V, so it is difficult to promote the subsequent circuit. But after adding the amplification gain, there are:

0.067×11=0.74V, that is, the output terminal OUT of the comparator produces a voltage value of 0.74V, which is entirely possible to produce logic effects, which can drive subsequent circuits or further A/D sampling.

The induction current amplifier can be powered by a DC battery, but in order to avoid frequent replacement of the battery and reduce costs, the commercial power connected to the transformer can also be directly converted into direct current and used as the power supply for the induction current amplifier. The invention provides a power supply for the induction current amplifier circuit, the power supply circuit includes a power supply transformer B and a three-terminal voltage stabilizer WY1, the primary side of the power supply transformer is connected to the mains grid, the starting point and the end point of the secondary side are respectively connected to the anode of a rectifier diode, and two rectifier diodes D1 and D2 The negative poles are connected together and connected to the input terminal of the three-terminal voltage regulator, and the secondary side is also connected to a grounded center tap; the first output terminal of the three-terminal voltage regulator is used as the DC positive output terminal of the power supply circuit, The second output terminal of the three-terminal voltage regulator is grounded.

As shown in Figure 3, the 220v AC mains is introduced from the AC terminal, and reaches the primary side of the power supply transformer B through the switch K1 and the fuse BX. Through the setting of the middle tap, the equivalent alternating voltage can be output on the secondary side. After full-wave rectification by rectifier diodes D1 and D2, the DC power is output through the three-terminal voltage stabilizer WY1, thereby completing AC and DC conversion.

The three-terminal voltage regulator can choose W7812, the first filter capacitor C1 can be connected between the input terminal of the three-terminal voltage regulator and the ground for low-frequency filtering, and the first output terminal of the three-terminal voltage regulator and the ground The second filter capacitor C2 is connected for medium and high frequency filtering, C1 can choose an electrolytic capacitor, and C2 can choose a polyester capacitor for low and medium high frequency filtering respectively. Among them, the low-frequency filter capacitor C1 is set between the input terminal of the three-terminal voltage regulator and the ground. Since the voltage at the input terminal is converted from the 50 Hz mains power supply and contains a lot of low-frequency noise, the capacitance of C1 is relatively large, which can reach hundreds of microfarads or thousands of microfarads. After the rectification and clipping and the three-terminal voltage regulator, the three-terminal voltage regulator may generate medium and high-frequency noise with a frequency much higher than the 50 Hz frequency of the mains, so the value of the C2 capacitor is small, in microfarads or nanofarads Law level, used to filter out medium and high frequency noise.

An indicating branch can also be provided, including a light-emitting diode Fg1 and a current-limiting resistor R1. When the power supply terminal has a DC voltage, the light-emitting diode lights up to indicate normal operation.

The foregoing are various preferred embodiments of the present invention. If the preferred implementations in each preferred embodiment are not obviously self-contradictory or based on a certain preferred implementation, each preferred implementation can be used in any superposition and combination. The above examples and the specific parameters in the examples are only for clearly expressing the inventor's invention verification process, and are not used to limit the scope of patent protection of the present invention. The scope of patent protection of the present invention is still subject to its claims. The equivalent structural changes made in the specification and drawings of the present invention should be included in the protection scope of the present invention in the same way.

Claims (10)

1. transformer iron core grounding current intellectual monitoring alarm, for measuring transformer iron core grounding line current, it is characterized in that, comprise current transformer, described current transformer has center pit, and described current transformer also comprises through the iron core grounding line of center pit and the second siding ring with the mutual inductance of iron core grounding line;

And gather the testing circuit of second siding ring electric current; Described current detection circuit comprises the induction current amplifier be connected with second siding ring, the A/D converter be connected with induction current amplifier out, and the scm managing system be connected with A/D converter; Described scm managing system is connected with communication interface, also comprises the clock oscillator and storage unit that are connected with scm managing system.

2. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 1, it is characterized in that, described second siding ring terminal ground connection, described induction current amplifier comprises commutation diode, filter capacitor, comparer, reference voltage generator; Described commutation diode positive and negative electrode is connecting secondary lateral coil starting point and comparer in-phase input end respectively, and described filter capacitor is connected between commutation diode negative pole and ground, and described reference voltage generator output terminal connects comparer inverting input;

Also comprise quiescent potential initialization circuit, described quiescent potential initialization circuit is the first divider resistance string be connected between the DC power supply terminal of induction current amplifier and ground; The divider node of described first divider resistance string connects commutation diode negative pole.

3. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 2, it is characterized in that, described reference voltage generator is the second divider resistance string be connected between the DC power supply terminal of induction current amplifier and ground, the output terminal of divider node reference voltage generator.

4. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 2, it is characterized in that, positive feedback resistor string is connected with between the output terminal of described comparer and the negative pole of commutation diode, described positive feedback resistor string is composed in series by the first positive feedback resistor and the second positive feedback resistor, wherein the first positive feedback resistor connects comparator output terminal, and the second positive feedback resistor connects commutation diode negative pole;

First positive feedback resistor resistance is greater than the second positive feedback resistor, and the first positive feedback resistor is connected comparer in-phase input end with the intermediate node of the second positive feedback resistor.

5. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 1, it is characterized in that, described induction current amplifier also comprises power circuit, described power circuit comprises supply transformer and three terminal regulator, described supply transformer primary side is connected with utility grid, secondary side starting point and terminal are connected a commutation diode positive pole respectively, two commutation diode negative poles link together and connect three terminal regulator input end, described secondary side are also connected with the centre tap of ground connection; First output terminal of described three terminal regulator as the direct current forward output terminal of power circuit, the second output head grounding of three terminal regulator.

6. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 5, it is characterized in that, the first filter capacitor is connected with between the input end of described three terminal regulator and ground, be connected with the second filter capacitor between first output terminal of described three terminal regulator and ground, described first filter capacitor frequency filtering is less than the second filter capacitor.

7. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 5, is characterized in that, also comprise instruction branch road, and described instruction branch road comprises and is connected on light emitting diode between direct current forward output terminal and ground and current-limiting resistance.

8. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 1, it is characterized in that, described A/D converter is MAX125.

9. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 1, is characterized in that, also comprise the upper PC and key input unit that are connected with scm managing system.

10. transformer iron core grounding current intellectual monitoring alarm as claimed in claim 1, it is characterized in that, described detection mutual inductor is BH-066 type.