CN105450007A - A power supply for transformer DC bias test - Google Patents

Abstract

The invention provides a power supply for a transformer direct-current magnetic bias test, which comprises: direct current branch circuit: the direct current is generated and injected into the high-voltage windings of the intermediate transformer and the tested transformer; alternating current branch circuit: the direct current branch circuit is connected in parallel and used for providing an alternating load current path for the intermediate transformer and the tested transformer and preventing the alternating load current of the intermediate transformer and the tested transformer from flowing into the direct current branch circuit; protecting a branch circuit: and the high voltage of the intermediate transformer and the tested transformer is applied to the direct current branch circuit to damage the direct current branch circuit when the alternating current branch circuit fails. The technical scheme provided by the invention can realize accurate adjustment of direct current test current and long-time stable development of a transformer direct current magnetic biasing test, and reliably complete the direct current magnetic biasing test of a single-phase or three-phase large-scale power transformer.

Description

A power supply for transformer DC bias test

technical field

The invention relates to a power supply, in particular to a power supply for a large-scale transformer DC bias test.

Background technique

With the continuous construction of EHV and UHV DC transmission projects, more and more power transformers are affected by DC bias. For the AC system where the neutral point of the transformer is grounded, the DC operation mode of the single pole ground loop will cause two substations at different DC potentials to form a loop through the transmission line, and DC current will enter the neutral point of the transformer and the transformer winding, causing the transformer to appear DC bias phenomenon. When the DC bias occurs in the transformer, it will affect the transformer in terms of excitation current distortion, noise increase, vibration intensification, local overheating of the iron core, etc., which seriously threatens the safe operation of the power transformer.

In recent years, a large number of ultra-high and ultra-high voltage large-scale power transformers have been put into operation, and it is urgent to master the DC bias tolerance of large-scale power transformers, so as to provide a reference for the DC bias control measures of the power grid. Applying a DC current to a power transformer to carry out a DC bias test is the most direct and effective means to study the DC bias tolerance of a large power transformer.

However, at present, there is no power supply for large-scale power transformer DC bias test at home and abroad. Most of them use multiple sets of batteries connected in series and parallel to generate DC current. The output current is not only small but also the current waveform is unstable. At the same time, there is a lack of test circuit protection devices, resulting in huge potential safety hazards in transformer DC bias tests.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the present invention provides a power supply for transformer DC bias test.

The technical solution provided by the present invention is: a power supply for transformer DC bias test, the improvement of which is that the power supply includes:

DC current branch: connected in series between the intermediate transformer and the high-voltage winding of the transformer under test, used to generate DC current and inject it into the high-voltage winding of the intermediate transformer and the transformer under test;

AC current branch: connected in parallel with the DC current branch, used to provide an AC load current path for the intermediate transformer and the transformer under test, and prevent the AC load current of the intermediate transformer and the transformer under test from flowing into the DC current branch;

Protection branch: connected in parallel with the DC current branch, used to protect the DC current branch and prevent the high voltage of the intermediate transformer and the tested transformer from being applied to the DC current branch when the AC current branch fails. On the current branch, the direct current branch is damaged.

Preferably, the direct current branch circuit includes a direct current generator unit, and the direct current generator unit includes:

AC voltage source: its output terminal is connected to the input terminal of the isolation transformer, and is used to output AC power to the isolation transformer;

Isolation transformer: its output terminal is connected to the input terminal of the rectification circuit, and is used to isolate and transform the AC output from the AC voltage source before outputting to the rectification circuit;

Rectifier circuit: its output terminal is connected to the input terminal of the filter circuit, which is used to convert the alternating current output by the isolation transformer into direct current and output it to the filter circuit;

Filtering circuit: its output end is connected to the input end of the DC amplifier circuit, and is used to filter the DC output from the rectifier circuit and output it to the DC amplifier circuit;

DC amplifier circuit: its output terminal is connected with the secondary filter capacitor C2, which is used to amplify the DC output from the filter circuit, and output the amplified DC power to the secondary filter capacitor C2;

Secondary filter capacitor C2: connected to the intermediate transformer and the high-voltage winding of the tested transformer, used to perform secondary filtering on the DC output from the DC amplifier circuit and then output smooth DC current to the intermediate transformer and the high-voltage winding of the tested transformer.

Further, a control switch and a fuse are connected in series between the output terminal of the AC voltage source and the input terminal of the isolation transformer.

Further, the rectification circuit is a full-bridge rectification circuit composed of diodes;

The filter circuit includes an inductor L and a capacitor C1; the DC amplifier circuit includes a triode T;

One end of the inductance L is respectively connected to one end of the capacitor C1 and the collector of the triode T, and the other end is connected to the output end of the rectification circuit; the other end of the capacitor C1 is respectively connected to the other output of the rectification circuit end and one end of the secondary filter capacitor C2; the other end of the secondary filter capacitor C2 is connected to the emitter of the triode T;

The base of the triode T is connected to the portable computer through a 485 connection cable; the portable computer adjusts the output current of the direct current branch by controlling the current reference of the triode T.

Further, the direct current branch also includes an inductance unit connected in series with the direct current generator unit for reducing the AC load current flowing into the direct current branch; one end of the inductance unit is connected to one end of the secondary filter capacitor C2 The other end of the secondary filter capacitor C2 is connected to the high voltage winding of the intermediate transformer.

Further, the inductance unit is a dry-type reactor, and the dry-type reactor is composed of a silicon steel sheet core and a winding wound on the silicon steel sheet core; the allowable current of the inductance unit is the direct current 1.2 times the maximum output current of the branch.

Preferably, the AC current branch is a capacitor cabinet composed of several film capacitors connected in series and parallel; the voltage and current of the capacitor cabinet are measured with an electronic voltmeter and ammeter with a precision of 0.5 to monitor the capacitor in real time. Whether the cabinet is faulty; the allowable current of the capacitor cabinet is greater than 1.5 times the rated load current of the transformer under test.

Preferably, the protection branch includes a power supply, a switch controller, a fast switch, a zinc oxide valve group, and a current transformer; the zinc oxide valve group is connected in parallel with both ends of the fast switch; the power supply is connected and provides power to the switch controller, the current transformer detects the current flowing through the zinc oxide valve group, and sends the detected current value to the switch controller, and the switch controller according to the current value controls the turn-on or turn-off of the fast switch.

Preferably, the low-voltage winding of the intermediate transformer is connected to the output terminal of the generator, and its high-voltage winding is connected in parallel with the high-voltage winding of the tested transformer; the low-voltage winding of the tested transformer is open; the power supply is connected in series in the intermediate The transformer is connected in parallel with the high-voltage winding of the tested transformer.

Preferably, the low-voltage winding of the intermediate transformer is connected in parallel with the low-voltage winding of the tested transformer and then connected to the output end of the generator, and its high-voltage winding is connected in parallel with the high-voltage winding of the tested transformer and one end is grounded; the power supply is connected in series Between the grounded high voltage winding of the intermediate transformer and the grounded high voltage winding of the transformer under test.

Compared with the closest prior art, the present invention has following remarkable progress:

The present invention adopts the DC current branch, the AC current branch and the protection branch to form the transformer DC bias DC power supply system, which can achieve the purpose of separating the DC current and the AC load current of the transformer, and effectively protect the DC current generator unit . It can realize the precise adjustment of the DC test current and the long-term stable development of the DC bias test of the transformer. It can inject stable DC into the winding of the large transformer under the no-load and load conditions of the single-phase or three-phase large-scale transformer, and reliably complete the DC of the large-scale power transformer. Bias test.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the transformer DC bias test provided by the present invention;

Fig. 2 is the circuit schematic diagram of DC generator unit;

Fig. 3 is the circuit schematic diagram of protection branch;

Figure 4 is a schematic diagram of the DC bias test circuit under the no-load condition of the single-phase transformer;

Fig. 6 is a schematic diagram of a DC bias test circuit of a three-phase transformer under no-load conditions;

Fig. 5 is a schematic diagram of a DC bias test circuit under a single-phase transformer load condition;

Fig. 7 is a schematic diagram of a DC bias test circuit under the load condition of a three-phase transformer.

1-DC generator unit; 2-inductance unit; 3-capacitance unit; 4-loop protection unit; 5-DC current branch; 6-AC current branch; 7-protection branch; 8-control switch; 9 -fuse; 10-isolation transformer; 11-rectifier circuit; 12-inductor L; 13-transistor T; 14-capacitor C1; 15-485 connecting cable; 16-portable computer; 17-filter capacitor C2; ;19-Ammeter; 20-Switch controller; 21-Quick switch; 22-Current transformer; 23-Single-chip high-energy zinc oxide valve; 24-Zinc oxide valve group; 25-Generator; 26-Generator circuit Protection unit; 27-intermediate transformer; 28-tested transformer; 29-power supply.

detailed description

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

In order to thoroughly understand the embodiments of the present invention, the detailed structure will be set forth in the following description. Obviously, the practice of the embodiments of the invention is not limited to specific details familiar to those skilled in the art. Preferred embodiments of the present invention are described in detail below, however, the present invention may have other embodiments besides these detailed descriptions.

The overall structure of the transformer DC bias test power supply provided by the present invention is as shown in Figure 1: the power supply 29 includes:

DC current branch 5: connected in series with the high-voltage winding of the intermediate transformer 27 and the tested transformer 28, used to generate a direct current, and inject it into the high-voltage winding of the intermediate transformer 27 and the tested transformer 28;

AC current branch 6: connected in parallel with the DC current branch 5, for providing an AC load current path for the intermediate transformer 27 and the tested transformer 28, preventing the AC load current of the intermediate transformer 27 and the tested transformer 28 from flowing into the The direct current branch 5;

Protection branch 7: connected in parallel with the DC current branch 5, used to protect the DC current branch 5, and prevent the high voltage between the intermediate transformer 27 and the tested transformer 28 when the AC current branch 6 fails. A voltage is applied to the direct current branch 5 and damages the direct current branch 5 .

The direct current branch 5 comprises a direct current generator unit 1, and the direct current generator unit 1 comprises:

AC voltage source: a 330V AC voltage source, which provides power for the DC generator unit 1, and its output terminal is connected to the input terminal of the isolation transformer 10 for outputting AC power to the isolation transformer 10;

Isolation transformer 10: its output terminal is connected to the input terminal of rectification circuit 11, and is used for isolating and transforming the AC output from the AC voltage source before outputting to the rectification circuit 11;

Rectifier circuit 11: its output end is connected to the input end of the filter circuit, and is used to convert the alternating current output by the isolation transformer 10 into direct current and output it to the filter circuit;

Filter circuit: its output end is connected to the input end of the DC amplifier circuit, and is used to filter the DC output from the rectifier circuit 11 and output it to the DC amplifier circuit;

DC amplifier circuit: its output terminal is connected with the secondary filter capacitor C217, used to amplify the DC output from the filter circuit, and output the amplified DC power to the secondary filter capacitor C217;

Secondary filter capacitor C217: connected to the intermediate transformer 27 and the high-voltage winding of the tested transformer 28, used to perform secondary filtering on the DC output from the DC amplifier circuit and then output smooth DC current to the intermediate transformer 27 and the high-voltage winding of the tested transformer 28 .

A control switch 8 and a fuse 9 are connected in series between the output terminal of the AC voltage source and the input terminal of the isolation transformer 10 . The AC voltage source outputs 330V AC power and inputs it into the isolation transformer 10 through the control switch 8 and the fuse 9 .

The rectification circuit 11 is a full-bridge rectification circuit 11 composed of diodes;

The filter circuit includes an inductor L12 and a capacitor C114; the DC amplifier circuit includes a triode T13;

One end of the inductor L12 is respectively connected to one end of the capacitor C114 and the collector of the triode T13, and the other end is connected to the output end of the rectifier circuit 11; the other end of the capacitor C114 is connected to the other end of the rectifier circuit 11 respectively. An output terminal and one end of the secondary filter capacitor C217; the other end of the secondary filter capacitor C217 is connected to the emitter of the triode T13;

The base of the triode T13 is connected to the portable computer 16 through a 485 connection cable 15; the portable computer 16 adjusts the output current of the direct current branch 5 by controlling the current reference of the triode T13.

The voltage and output current at both ends of the DC generating unit are monitored and displayed by an electronic voltmeter 18 and an ammeter 19 with a precision of 0.5 grade.

The direct current branch 5 also includes an inductance unit 2 connected in series with the direct current generator unit 1 for reducing the AC load current flowing into the direct current branch 5; one end of the inductance unit 2 is connected to the secondary filter capacitor One end of C217 is connected, and the other end is connected with the high-voltage winding of the tested transformer 28; the other end of the secondary filter capacitor C217 is connected with the other high-voltage winding of the intermediate transformer 27.

The inductance unit 2 is a dry-type reactor, and the dry-type reactor is composed of a silicon steel sheet iron core and a winding wound on the silicon steel sheet iron core; its capacity is large enough to ensure that the inductance unit 2 passes through the DC current for a long time to generate 1.2 times the maximum output DC current of the converter unit. The inductance unit 2 uses an electronic voltmeter 18 and an ammeter 19 with a precision of 0.5 to display the AC voltage at both ends of the inductance unit 2 and the passing AC current, so as to monitor whether the inductance unit 2 fails in real time. The AC current branch 6 is a capacitor cabinet composed of several film capacitors connected in series and parallel; the voltage and current of the capacitor cabinet are measured by an electronic voltmeter 18 and an ammeter 19 with an accuracy of 0.5 to monitor the capacitor in real time. Whether the cabinet is faulty;

The impedance of the capacitive unit 3 is at least 2 orders of magnitude smaller than that of the inductive unit 2 , and its long-term allowable flow is greater than 1.5 times the rated load current of the tested transformer 28 .

The protection branch 7 includes a power supply 29, a switch controller 20, a fast switch 21, a zinc oxide valve plate group 24, and a current transformer 22; the zinc oxide valve plate group 24 is connected in parallel with the two ends of the fast switch 21; The zinc oxide valve plate group 24 is composed of a single high-energy zinc oxide valve plate 23 connected in parallel in sequence; The current is greater than 1.5 times the rated load current of the tested transformer 28, and the conduction time of the fast switch 21 is less than 1/5 of the allowable conduction time of the zinc oxide valve plate group 24.

The switch controller 20 is powered by a 220V power supply 29 to drive the fast switch 21 to conduct. When the test power supply 29 system proposed by the present invention is used to carry out the DC bias test on a large transformer, if the capacitor unit 3 is open circuited during the test, the high voltage of the tested transformer 28 will all be applied to the DC generator unit 1 and the capacitor unit 3 , resulting in damage to the DC generator unit 1 and the capacitor unit 3 and causing personnel safety issues. The protection branch 7 can be turned on by the zinc oxide valve plate group 24 when the above-mentioned fault occurs, so that all the transformer load current passes through the zinc oxide valve plate group 24, and instantly reduces the voltage at both ends of the DC generator unit 1 to oxidize. The residual voltage of the zinc valve plate group 24 (the residual voltage of the zinc oxide valve plate group 24 is less than the maximum withstand voltage of the DC generator unit 1 ). Since the zinc oxide valve plate group 24 can only pass the transformer load current for a short time (the allowable flow time is usually less than 1s), the protection logic set by the protection branch 7 is that when the zinc oxide valve plate group 24 is turned on, the current transformer 22 detects the current signal, and transmits the current signal to the switch controller 20, and the switch controller 20 controls the fast switch 21 to turn on (the turn-on time of the fast switch 21 is usually less than 100ms). When the fast switch 21 is turned on, due to the small conduction resistance of the fast switch 21, the transformer load current will be transferred from the zinc oxide valve plate group 24 to the circuit of the fast switch 21 instantaneously, and the long-term flow of the transformer load current will be realized by the fast switch 21.

As shown in accompanying drawings 4 and 5, accompanying drawing 4 is a schematic diagram of a DC bias test under the no-load condition of a single-phase power transformer using the present invention, and accompanying drawing 5 is a schematic diagram of a three-phase power transformer under no-load condition using the present invention Schematic diagram of DC bias test. The low-voltage winding of described intermediate transformer 27 is connected with the output end of generator 25, and its high-voltage winding is connected in parallel with the high-voltage winding of described tested transformer 28; The low-voltage winding of described tested transformer 28 is open circuit; Described power supply 29 is connected in series The intermediate transformer 27 is connected in parallel with the high-voltage winding of the tested transformer 28, and a DC current is injected into the high-voltage windings of the two transformers to conduct a DC bias test of the transformer.

As shown in accompanying drawings 6 and 7, accompanying drawing 6 is a schematic diagram of a DC bias test under the load condition of a single-phase power transformer applied to the present invention, and accompanying drawing 7 is a DC bias test under the load condition of a three-phase power transformer implemented in the present invention. Schematic diagram of the magnetic test. The low-voltage winding of the intermediate transformer 27 is connected in parallel with the low-voltage winding of the tested transformer 28 and then connected with the output end of the generator 25, and its high-voltage winding is connected in parallel with the high-voltage winding of the tested transformer 28. One end is grounded; 29 is connected in series between the grounded high-voltage winding of the intermediate transformer 27 and the grounded high-voltage winding of the tested transformer 28, and injects DC current into the high-voltage windings of the two transformers to conduct a DC bias test of the transformers.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still implement the present invention Any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention is within the protection scope of the pending claims.

Claims (10)

1. A transformer DC bias test power supply, characterized in that: the power supply comprises: DC current branch: connected in series between the intermediate transformer and the high-voltage winding of the transformer under test, used to generate DC current and inject it into the high-voltage winding of the intermediate transformer and the transformer under test; AC current branch: connected in parallel with the DC current branch, used to provide an AC load current path for the intermediate transformer and the transformer under test, and prevent the AC load current of the intermediate transformer and the transformer under test from flowing into the DC current branch; Protection branch: connected in parallel with the DC current branch, used to protect the DC current branch and prevent the high voltage of the intermediate transformer and the tested transformer from being applied to the DC current branch when the AC current branch fails. On the current branch, the direct current branch is damaged. 2. A kind of power supply for transformer DC bias test according to claim 1, characterized in that: The direct current branch comprises a direct current generator unit comprising: AC voltage source: its output terminal is connected to the input terminal of the isolation transformer, and is used to output AC power to the isolation transformer; Isolation transformer: its output terminal is connected to the input terminal of the rectification circuit, and is used to isolate and transform the AC output from the AC voltage source before outputting to the rectification circuit; Rectifier circuit: its output terminal is connected to the input terminal of the filter circuit, which is used to convert the alternating current output by the isolation transformer into direct current and output it to the filter circuit; Filtering circuit: its output end is connected to the input end of the DC amplifier circuit, and is used to filter the DC output from the rectifier circuit and output it to the DC amplifier circuit; DC amplifier circuit: its output terminal is connected with the secondary filter capacitor C2, which is used to amplify the DC output from the filter circuit, and output the amplified DC power to the secondary filter capacitor C2; Secondary filter capacitor C2: connected to the intermediate transformer and the high-voltage winding of the tested transformer, used to perform secondary filtering on the DC output from the DC amplifier circuit and then output smooth DC current to the intermediate transformer and the high-voltage winding of the tested transformer. 3. A kind of power supply for transformer DC bias test according to claim 2, characterized in that: A control switch and a fuse are connected in series between the output terminal of the AC voltage source and the input terminal of the isolation transformer. 4. A kind of power supply for transformer DC bias test according to claim 2, characterized in that: The rectification circuit is a full-bridge rectification circuit composed of diodes; The filter circuit includes an inductor L and a capacitor C1; the DC amplifier circuit includes a triode T; One end of the inductance L is respectively connected to one end of the capacitor C1 and the collector of the triode T, and the other end is connected to the output end of the rectification circuit; the other end of the capacitor C1 is respectively connected to the other output of the rectification circuit end and one end of the secondary filter capacitor C2; the other end of the secondary filter capacitor C2 is connected to the emitter of the triode T; The base of the triode T is connected to the portable computer through a 485 connection cable; the portable computer adjusts the output current of the direct current branch by controlling the current reference of the triode T. 5. A kind of power supply for transformer DC bias test according to claim 2, characterized in that: The DC current branch also includes an inductance unit connected in series with the DC generator unit for reducing the AC load current flowing into the DC current branch; one end of the inductance unit is connected to one end of the secondary filter capacitor C2, Its other end is connected with the high-voltage winding of the transformer under test; the other end of the secondary filter capacitor C2 is connected with the high-voltage winding of the intermediate transformer. 6. The power supply for transformer DC bias test according to claim 5, characterized in that: The inductance unit is a dry-type reactor, and the dry-type reactor is composed of a silicon steel sheet core and a winding wound on the silicon steel sheet core; the allowable flow current of the inductance unit is the DC current branch 1.2 times the maximum output current. 7. The power supply for transformer DC bias test according to claim 1, characterized in that: The AC current branch is a capacitor cabinet composed of several film capacitors connected in series and parallel; the voltage and current of the capacitor cabinet are measured with an electronic voltmeter and ammeter with an accuracy of 0.5 to monitor in real time whether the capacitor cabinet has Fault; the allowable current of the capacitor cabinet is greater than 1.5 times the rated load current of the transformer under test. 8. A power supply for transformer DC bias test according to claim 1, characterized in that: The protection branch includes a power supply, a switch controller, a fast switch, a zinc oxide valve group, and a current transformer; the zinc oxide valve group is connected in parallel with both ends of the fast switch; the power supply is connected and provides power to the The switch controller, the current transformer detects the current flowing through the zinc oxide valve plate group, and sends the detected current value to the switch controller, and the switch controller controls the turn-on or turn-off of the fast switch described above. 9. A power supply for transformer DC bias test according to claim 1, characterized in that: The low-voltage winding of the intermediate transformer is connected to the output end of the generator, and its high-voltage winding is connected in parallel with the high-voltage winding of the tested transformer; the low-voltage winding of the tested transformer is open; the power supply is connected in series between the intermediate transformer and the In the parallel circuit of the high-voltage winding of the transformer under test. 10. A power supply for transformer DC bias test according to claim 1, characterized in that: The low-voltage winding of the intermediate transformer is connected in parallel with the low-voltage winding of the tested transformer and then connected to the output end of the generator, and its high-voltage winding is connected in parallel with the high-voltage winding of the tested transformer and one end is grounded; the power supply is connected in series to the Between the grounded high-voltage winding of the intermediate transformer and the grounded high-voltage winding of the transformer under test.