CN101951221B - Twelve pulsating commutation transformer and method and circuit for removing residual magnetism thereof - Google Patents

Abstract

The invention discloses a twelve-pulse converter transformer and its method and circuit for removing residual magnetism. The principle of the method is to sequentially feed in direct current in the forward and reverse direction according to the wiring in the direct current resistance test, and gradually reduce and shrink The hysteresis loop of the iron core achieves the purpose of eliminating the residual magnetism. The invention can ensure the reliable operation of the converter transformer and realize the long-term safe and stable operation of the high-voltage direct current transmission system. The method has the advantages of simple implementation, reliable demagnetization, and prevention of protection malfunctions.

Description

A twelve-pulse converter transformer and its method and circuit for removing residual magnetism

technical field

The invention relates to a transformer, in particular to a twelve-pulse converter transformer, a method for removing residual magnetism thereof, and a high-voltage direct current transmission system using the twelve-pulse converter transformer. the

Background technique

Due to its unique advantages, such as: long distance, high power, asynchronous networking, fast power adjustment, power flow controllability, transmission economy, etc., HVDC transmission is more and more widely used. the

In order to reduce the harmonic components of the system, different connection methods of transformer windings are used to provide two sets of three-phase symmetrical commutation with equal amplitude and 30° phase difference (fundamental electrical angle) for two series-connected converters Voltage to achieve twelve-pulse commutation. the

分别为T1、T2换流变压器网侧、阀侧电流互感器二次侧的电流，如图1所示。  Figure 1 shows the wiring of the twelve-pulse converter transformer. In order to reflect the internal phase-to-phase short-circuit faults, grid-side single-phase ground short-circuit and inter-turn layer short-circuit faults of the twelve-pulse converter transformer (referred to as: converter transformer), it is often used Large difference ratio differential protection, the protection range of this protection is the T1 and T2 converter transformers in Figure 1, and its action equation is that the differential current I _OP is greater than a certain floating threshold value, and the calculation formula of the differential current I _OP is

are the currents on the grid side of the T1 and T2 converter transformers and the secondary side of the valve side current transformer, as shown in Figure 1.

Due to the influence of high-voltage test and other factors, the residual magnetism of Y/Y and Y/Δ converter transformers is different. When the switch 1 or switch 2 is turned on to charge the twelve-pulse converter transformer at the same time, the protection range may be The differential current of the differential protection (large difference protection) of the Y/Y and Y/Δ two groups of transformers is a symmetrical inrush current, and the excitation inrush current decays slowly. The differential current of the large difference protection is close to an odd symmetrical waveform, and the non-periodic component is small. The even-order harmonic content is small, and the protection will malfunction, resulting in the unavailability of some high-voltage direct current transmission systems and the reduction of transmission power. the

There are two main methods to prevent malfunction of the protection when the twelve-pulse converter transformer is charging:

1) Adopt synchronous closing device

Make the three phases of the converter transformer open and close at 90°, optimize the charging condition of the converter transformer, and eliminate the generation of excessive excitation inrush current from the source as much as possible. the

The disadvantage of this method: since the generation of symmetrical inrush current is not only related to the closing angle of the converter transformer, but also related to the residual magnetism of the Y/Y and Y/Δ converter transformers, and the synchronous closing device does not distinguish between Y The magnitude of the residual magnetism of the /Y and Y/Δ converter transformers is only fixed at 90°, which cannot solve the symmetrical inrush problem caused by the difference in the residual magnetism of the Y/Y and Y/Δ converter transformers. the

2) Improve the excitation inrush current blocking scheme in the software

When the transformer is charged, the excitation inrush current of a certain phase may no longer deviate from one side of the time axis and become a symmetrical inrush current, but the other two phases are still asymmetrical inrush currents that deviate from the time axis side. Asymmetric inrush current still contains a large number of aperiodic components, and its inrush current characteristics are obvious. Therefore, when any phase is detected to have excitation inrush current characteristics, it will block the differential protection of the three phases, thereby preventing the protection from malfunctioning. the

The disadvantage of this method: when the 12-pulse converter transformer is charged, the current detected by the protection is the superposition of the excitation inrush current of the Y/Y and Y/Δ converter transformers, which is different from the excitation inrush current of the conventional transformer only for this group of transformers. Therefore, the characteristics of the asymmetric inrush current of the twelve-pulse converter transformer are different from those of the conventional transformer, and may form a three-phase symmetrical inrush current, resulting in no obvious excitation inrush current characteristics for the differential current of the three phases, resulting in a large difference Protection against misoperation. the

Therefore, the prior art still needs to be improved and developed. the

Contents of the invention

The purpose of the present invention is to provide a 12-pulse converter transformer, aiming to solve the problem that the 12-pulse converter transformer may form a three-phase symmetrical inrush current caused by residual magnetism when charging, resulting in no obvious excitation of the three-phase differential current Inrush current characteristics, thus causing the problem of misoperation of large difference protection. the

Technical scheme of the present invention is as follows:

A residual magnetization removal circuit of a twelve-pulse converter transformer, which includes a DC power supply, a variable resistor, a first DC ammeter, a second DC ammeter, a double-pole double-throw switch, a first switch, a second switch, a third switch and a fixed resistor; the DC power supply is connected in series with a variable resistor and a first DC ammeter to form an input circuit, the two ends of the input circuit are positively connected to the terminal A of the double-pole double-throw switch, and the input circuit is also reversely connected into the terminal B of the double-pole double-throw switch; the terminal C of the double-pole double-throw switch is connected to the transformer; the second DC ammeter, the fixed resistor and the first switch K1 are connected in sequence, and connected in parallel to the terminal C of the double-pole double-throw switch; the second switch is connected in parallel to the variable resistor, and the third switch is connected in parallel to the second DC ammeter. the

The residual magnetism removal circuit of the twelve-pulse converter transformer, wherein the converter transformer is a single-phase transformer, and when the single-phase transformer demagnetization test is performed, the terminal C of the double-pole double-throw switch is connected to Both ends of the α-phase high-voltage winding of the converter transformer. the

The residual magnetism removal circuit of the twelve-pulse converter transformer, wherein the converter transformer is a three-phase transformer, and the terminal C of the double-pole double-throw switch is respectively connected to the αβ terminal and the βγ terminal of the three-phase transformer. the

A method for removing residual magnetism of a 12-pulse converter transformer, wherein, according to the wiring during the DC resistance test, DC current is sequentially fed in forward and reverse directions, and gradually decreases to reduce the hysteresis loop of the iron core, so as to eliminate residual magnetism. Magnetic purpose, its specific steps include:

Step S100: disconnect the double pole double throw switch K and the first switch K1, close the third switch K3 and K2, enter the charging preparation stage of the tested converter, then connect the double pole double throw switch K to the terminal A, wait for the first The reading of a DC ammeter A1 reaches the expected value;

Step S200: close the first switch K1, open the second switch K2, enter the discharge preparation stage of the tested converter, then open the double-pole double-throw switch K and the third switch K3, and use the second DC ammeter A2 to monitor the discharge process, when the reading of the second DC ammeter A2 is close to zero, turn off the first switch K1, and the discharge process ends;

Step S300: Set the predicted value of the incoming direct current, and repeat steps S100 and S200. the

In the method for removing residual magnetism of a twelve-pulse converter transformer, the initial value of the estimated value in step S100 is 5A. the

The method for removing residual magnetism of a twelve-pulse converter transformer according to claim 4, characterized in that the specific setting method for setting the expected value of the incoming DC current in step S300 is: for each incoming DC current A reduction range is set for the current, and the reduction range can be set as 5-10% of the estimated value in step S100. the

The method for removing the residual magnetism of the twelve-pulse converter transformer, wherein, in step S300, the specific setting method for setting the expected value of the incoming DC current is: setting a reduction range for each incoming DC current , the reduction is 5-10% of the initial estimated value. the

A twelve-pulse converter transformer, wherein the twelve-pulse converter transformer includes the residual magnetism removal circuit described in claims 1 to 3. the

Beneficial effects of the present invention: the present invention stipulates the connection mode of the direct resistance test and the magnitude and direction of the DC measurement current, and performs DC demagnetization work on the twelve-pulse converter transformer after the high-voltage test, and gradually reduces the demagnetization according to the setting Direction-changing DC current is applied multiple times to achieve the effect of removing residual magnetism, ensuring the safe and stable operation of the converter station, and avoiding the oil test after the protection malfunction occurs, ensuring the reliable operation of the converter transformer and realizing Long-term safe and stable operation of HVDC transmission system. The method has the advantages of simple implementation, reliable demagnetization and prevention of protection malfunctions. the

Description of drawings

Fig. 1 is the wiring diagram of the existing twelve-pulse converter transformer;

Figure 2 is the equivalent circuit diagram of the twelve-pulse converter transformer before empty charging;

Fig. 3 is the DC demagnetization wiring diagram of the twelve-pulse converter transformer provided by the embodiment of the present invention;

Fig. 4 is a flowchart of a DC demagnetization method for a twelve-pulse converter transformer provided by an embodiment of the present invention. the

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear and definite, the present invention will be further described in detail below with reference to the accompanying drawings and examples. the

The equivalent circuit diagram of the twelve-pulse converter transformer before empty charging is shown in Figure 2, _T1 is the star angle transformer, T2 is the star transformer, and K is the switch. L _1m , L _1σ , R _lσ1 , L _2m , L _2σ , R _2σ are T ₁ , T ₂ excitation inductance, primary and secondary side leakage inductance, coil resistance, respectively, and Ls, Rs are system inductance and resistance. Assume the system power supply voltage Us(θ)=Umsin(θ), i ₁ and i ₂ are the currents on both sides of the transformer respectively, and the reference direction is that the bus points to the transformer; i _s is the current from the system, and the reference direction is that the system points to the bus. Φ ₁ and Φ ₂ are the core flux linkages of T ₁ and T ₂ .

When K is closed, the magnetic flux of T ₁ and T ₂ satisfies:

$\frac{{\mathrm{<span\; class="notranslate">\; d\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\frac{{\mathrm{<span\; class="notranslate">\; d\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

一个周波内积分近似为0，则有：  Obviously, there are i ₁ =0 and i ₂ =0 before switching on, and both sides of the equation are integrated at the same time, and the change of magnetic flux within one cycle is considered. Since the inrush current i ₁ , i ₂ , and i _s are approximate periodic functions,

The integral within one cycle is approximately 0, then:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Since the excitation inrush currents i ₁ and i ₂ have discontinuous angles and are biased to one side of the time axis, i ₁ and i ₂ contain aperiodic components. Let i _1f and i _2f be the aperiodic components of i ₁ and i ₂ respectively average value. From the formula (3-4), the magnetic flux of the two transformers in one cycle can be obtained:

φ _1(2π) ＝φ ₁₍₀₎ -2πR _s (i _1f +i _2f )-2πR _1σ i _1f ................................... .........(5)

φ _2(2π) ＝φ ₂₍₀₎ -2πR _s (i _1f +i _2f )-2πR _2σ i _2f ................................... .........(6)

Subtract formula (6) from formula (5), and consider the two sets of transformers R _1σ ≈ R _2σ in parallel, get:

φ _1(2π) -φ _2(2π) ＝φ ₁₍₀₎ -φ ₂₍₀₎ -2πR _1σ i _1f +2πR _2σ i _2f .......... .....(7)

≈φ ₁₍₀₎ -φ ₂₍₀₎ -2πR _1σ (i _1f -i _2f )

It can be seen from the above formula that if the initial conditions of T1 and T2 are not much different, Φ ₁₍₀₎ and Φ ₂₍₀₎ are the same, and when i _1f and i _2f are the same, Φ _1(2л) and Φ _2(2л) are also the same, The inrush current characteristics of the 12-pulse converter transformer are similar to those of the single converter transformer. However, if the absolute value of Φ ₁₍₀₎ - Φ ₂₍₀₎ is relatively large before the 12-pulse 2-group converter switch is turned on, it can be known from formula (7) that Φ ₁ = Φ ₂ , there must be a Φ ₁₍₀₎ -Φ ₂₍₀₎ attenuation process, and this attenuation process is only related to R _1σ and R _2σ , and has nothing to do with the system impedance.

The reasons for forming a large Φ ₁₍₀₎ -Φ ₂₍₀₎ are: the residual magnetism is inconsistent before charging (such as after the DC resistance test); or the steady-state DC current flows from the neutral point after the transformer is closed, and there is DC biased and inconsistent.

In order to realize the object of the present invention, it is first necessary to reduce the residual magnetism before the first charging of the converter transformer, and ensure that the direction of the residual magnetism of the twelve-pulse converter transformer is the same. the

Because the iron core of the transformer is a ferromagnetic material with high magnetic permeability, the iron core material has hysteresis characteristics. When a magnetic field is generated on the ferromagnetic material and the excitation source that generates the magnetic field is removed, a certain magnetic field will still remain in the iron core. The residual magnetism of the transformer is generally generated by the switch opening and the DC resistance test. the

When the transformer is switched off, since there is a 120° phase angle among the three-phase voltages of the system, when the switch cuts off the power supply, there will be a certain voltage in each phase due to the phase difference, so there will also be a certain residual magnetism in the transformer core. The residual magnetism formed by this situation is generally smaller than the rated magnetic flux of the transformer. For general high-voltage DC converters, the excitation current is about 1A during normal operation. When the converter is rated for excitation, the magnetic flux of the iron core is basically close to the saturation inflection point. the

When testing the DC resistance of the converter, the current generally used in the field is 5A. In order to speed up the measurement speed under certain construction conditions, a larger DC current is used for measurement. Therefore, during the DC resistance test, the magnetic field in the transformer core is generally saturated, so after measuring the DC resistance, the residual magnetism in the transformer core is relatively large. Judging from the residual magnetism produced by the above two situations, the residual magnetism produced by the winding DC resistance measurement is much more serious. This brings great hidden danger to the first charging of the converter transformer. the

In order to solve the above problems, a small-capacity DC power supply can be used to measure the DC resistance of the converter transformer, so as to reduce the residual magnetism on the winding as much as possible. Under the premise of ensuring the measurement accuracy of the DC resistance of the winding, the grid-side DC resistance measurement is first carried out with a 2.5A DC power supply. If the measurement accuracy cannot be guaranteed, the measurement current can be increased to 5A. In the operation instructions of the direct resistance test, the wiring mode of all converter transformer direct resistance tests must be consistent with the direction of the DC measurement current to prevent the formation of residual magnetism in the opposite direction. After the measurement, demagnetize the converter transformer. the

Figure 3 shows the wiring diagram of the DC demagnetization circuit, which is connected to the transformer during the demagnetization test after the high-voltage test of the converter transformer, and removed after the DC demagnetization. The demagnetization circuit includes a DC power supply E, a variable resistor R1, a first DC ammeter A1, a second DC ammeter A2, a double pole double throw switch K, a first switch K1, a second switch K2, a third switch K3 and Fixed resistor R. The two ends of the DC power supply E are connected in series with the variable resistor R1 and the first DC ammeter A1 to form an input circuit, the two ends of the input circuit are forwardly connected to the terminal A of the double-pole double-throw switch K, and the input circuit is reverse to the terminal B of the double pole double throw switch K. The terminal C of the double pole double throw switch K is connected to a transformer. The second DC ammeter A2, the fixed resistor R and the first switch K1 are connected in sequence, and then connected in parallel to the terminal C of the double pole double throw switch K. The second switch K2 is connected in parallel to the variable resistor R1, and the third switch K3 is connected in parallel to the second DC ammeter A2. the

In the DC degaussing circuit provided by the embodiment of the present invention, the DC power supply E is a 12V storage battery; the tissue range of the variable resistor R1 is 0-100 ohms; the first DC ammeter and the second DC ammeter A1 , The measurement range of A2 is 5-10 amperes; when the double-pole double-throw switch K is hit on the terminal A, the demagnetization circuit is in the positive input state; the double-pole double-throw switch K is hit on the terminal B , the demagnetization circuit is in reverse input state. The resistance value of the fixed resistor R is 200 ohms. the

Using the DC demagnetization method, according to the wiring during the DC resistance test, the DC current is passed in the forward and reverse directions in turn, and gradually decreases to reduce the hysteresis loop of the core to achieve the purpose of eliminating residual magnetism. the

For example, if the converter transformer is a single-phase transformer, when the α-phase demagnetization test is performed, a DC current is passed through both ends of the high-voltage winding of the tested α-phase transformer (α-phase bushing to the neutral end bushing), as shown in Figure 3 If the converter transformer is a three-phase transformer, direct current can be passed through the αβ and βγ terminals respectively. The direction of the direct current is opposite to the direction when testing the direct current resistance of the winding. For example, after first passing in a DC current of 5A, close K1, disconnect K, and wait for the number of the second DC ammeter A2 to drop to "zero"; then pass in a DC current of 4.7A in the opposite direction, close K1, disconnect K, and wait The number of the second DC ammeter A2 drops to "zero"; the size of the current that is passed in each time decreases to 5-6% of the initial amplitude, and so on, until the current value of the first ammeter is below 0.05A, the DC demagnetization The step ends, and the demagnetization work is completed. the

Referring to Fig. 4, the specific operation steps of described remanence removal method are as follows:

Step S100: disconnect the double pole double throw switch K and the first switch K1, close the third switch K3 and K2, enter the charging preparation stage of the tested converter, then connect the double pole double throw switch K to the terminal A, wait for the first The reading of a DC ammeter A1 reaches the expected value;

When charging for the first time, the estimated value is the initial estimated value, which can be adjusted accordingly according to the DC resistance test current of the preventive test procedure of the converter, for example, the expected value of the 500kV converter is 5A. the

Step S200: close the first switch K1, open the second switch K2, enter the discharge preparation stage of the tested converter, then open the double-pole double-throw switch K and the third switch K3, and use the second DC ammeter A2 to monitor the discharge process, when the reading of the second DC ammeter A2 is close to zero, turn off the first switch K1, and the discharge process ends;

Step S300: Set the predicted value of the incoming direct current, and repeat steps S100 and S200. the

A reduction range is set for the input direct current, and the reduction range can be set to reduce the expected value in step S100 by about 5-10%, which is a dynamic value; it can also be set as a fixed value, For example, set it at 5-10% of the initial estimated value. If the estimated value in the previous step is 5A, the estimated value in this step can be set to 4.7A. the

The time of the DC demagnetization test, that is, the number of times to repeat step S100 and step S200 mainly depends on the test current measured by the winding DC resistance and the step amplitude of DC reduction each time. The specific time needs to be determined according to the DC charging time of different transformers. The demagnetization time after the test is about 2-3 times of the DC resistance measurement time. the

The invention stipulates the connection mode of the direct resistance test and the magnitude and direction of the DC measurement current, and performs the DC demagnetization work on the twelve-pulse converter transformer after the high-voltage test, and gradually reduces the demagnetization and reversing DC current according to the setting. After the first application, the effect of removing residual magnetism is achieved, which ensures the safe and stable operation of the converter station, and also avoids the oil test after the protection malfunction occurs, ensures the reliable operation of the converter transformer, and realizes the long-term maintenance of the high-voltage direct current transmission system. Safe and stable operation. The method has the advantages of simple implementation, reliable demagnetization and prevention of protection malfunctions. the

It should be understood that the application of the present invention is not limited to the above examples, and those skilled in the art can make improvements or transformations according to the above descriptions, and all these improvements and transformations should belong to the protection scope of the appended claims of the present invention. the

Claims (8)

1. A remanence removal circuit of a twelve-pulse converter transformer, characterized in that it comprises a DC power supply, a variable resistor, a first DC ammeter A1, a second DC ammeter, a double-pole double-throw switch K, a first switch K1, the second switch, the third switch K3 and a fixed resistor; the DC power supply is connected in series with the variable resistor and the first DC ammeter A1 to form an input circuit, and the two ends of the input circuit are positively connected to the double pole double throw switch K Terminal A, the input circuit is also reversely connected to the terminal B of the double-pole double-throw switch K; the terminal C of the double-pole double-throw switch K is connected to the transformer; the second DC ammeter, fixed resistor and The first switch K1 is connected in sequence and is connected in parallel to the terminal C of the double-pole double-throw switch K; the second switch is connected in parallel to the variable resistor, and the third switch K3 is connected in parallel to the second DC ammeter superior. 2. The residual magnetism removal circuit of a twelve-pulse converter transformer according to claim 1, wherein the converter transformer is a single-phase transformer, and when the single-phase transformer demagnetization test is carried out, the double pole Terminal C of the double-throw switch K is connected to both ends of the α-phase high-voltage winding of the converter transformer. 3. The residual magnetism removal circuit of a twelve-pulse converter transformer according to claim 1, wherein the converter transformer is a three-phase transformer, and the terminals C of the double-pole double-throw switch K are connected to three phases respectively. The αβ and βγ terminals of the phase transformer. 4. A method for removing residual magnetism of a twelve-pulse converter transformer, characterized in that the method is applied to the residual magnetism removing circuit as claimed in any one of claims 1-3, and the winding of the converter transformer that needs to eliminate residual magnetism At both ends, direct current is passed in forward and reverse directions in turn, and gradually decreases to reduce the hysteresis loop of the core to achieve the purpose of eliminating residual magnetism. The specific steps include: Step S100: Turn off the double pole double throw switch K and the first switch K1, close the third switch K3 and the second switch K2, enter the charging preparation stage of the tested converter, and then connect the double pole double throw switch K to the terminal A , waiting for the reading of the first DC ammeter A1 to reach the expected value; Step S200: close the first switch K1, open the second switch K2, enter the discharge preparation stage of the tested converter, then open the double-pole double-throw switch K and the third switch K3, and use the second DC ammeter A2 to monitor the discharge process, when the reading of the second DC ammeter A2 is close to zero, the first switch K1 is turned off, and the discharge process ends; Step S300: Set the predicted value of the incoming direct current, and repeat steps S100 and S200. 5 . The method for removing residual magnetism of a twelve-pulse converter transformer according to claim 4 , wherein the initial value of the predicted value in step S100 is 5A. 6. The method for removing residual magnetism of a twelve-pulse converter transformer according to claim 4, characterized in that, in step S300, the specific setting method for setting the expected value of the incoming DC current is as follows: A reduction range is set for the DC current, and the reduction range can be set as 5-10% of the estimated value in step S100. 7. The method for removing residual magnetism of a twelve-pulse converter transformer according to claim 5, characterized in that, in step S300, the specific setting method for setting the expected value of the incoming DC current is as follows: The DC current setting a reduction amplitude, the reduction is 5-10 % of the initial estimated value. 8. A twelve-pulse converter transformer, characterized in that the twelve-pulse converter transformer includes the residual magnetism removal circuit according to any one of claims 1 to 3.

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