CN105719815B - A kind of coupling transformer type dc circuit breaker hollow pulse transformer and its parameter acquiring method - Google Patents

Abstract

The invention provides an air-core pulse transformer for a coupling transformer-type DC circuit breaker and a parameter acquisition method thereof. The air-core pulse transformer includes a primary winding, a secondary winding, a high-voltage end of the primary winding, a low-voltage end of the primary winding, and a secondary winding. High-voltage end, low-voltage end of secondary winding, inter-turn insulating film of secondary winding, inter-turn insulating film of primary winding, main insulating film and insulating support frame; secondary winding is wound radially along the insulating support frame, and secondary winding has radial The inter-turn insulation of the secondary winding is realized by the inter-turn insulating film of the secondary winding; the low-voltage end of the secondary winding and the low-voltage end of the primary winding are insulated by the main insulating film; the primary winding is wound on the main insulating film In addition, the inter-turn insulation of the primary winding is realized by the inter-turn insulating film of the primary winding.

Description

An air-core pulse transformer for coupling transformer type DC circuit breaker and its parameter acquisition take method

technical field

The invention belongs to the technical field of high-voltage electrical appliances and pulse power, and more specifically relates to an air-core pulse transformer for a coupling transformer-type DC circuit breaker and a parameter acquisition method thereof.

Background technique

As one of the main equipment in DC transmission system, DC circuit breaker plays a vital role in the construction of large-scale DC power grid. Compared with the passive self-excited oscillation type and active pre-charging type DC circuit breaker, the coupling transformer type DC circuit breaker can not only ensure the rapid formation of zero-crossing point to complete the rapid breaking of the fault current, but also avoid the difficulty of using it to meet the requirements of no malfunction and failure at the same time. Non-refusal high-voltage closing switch.

In the coupling transformer type DC circuit breaker, the pulse transformer is mainly used to provide a high-frequency pulse current with an amplitude of tens of kiloamperes in the opposite direction to the fault current. Compared with the core-type pulse transformer, the air-core transformer directly relies on the tight coupling between the primary and secondary windings to transfer energy, so there is no problem of core saturation, avoiding the hysteresis effect and eddy current loss, and is suitable for high-power applications. However, compared with commonly used air-core pulse transformers, since the high and low voltage terminal potentials of the secondary winding of the pulse transformer are both the bus voltage when the DC circuit breaker is normally connected to the grid, the air-core pulse transformer for the coupling transformer type DC circuit breaker not only needs to withstand Due to the higher turn-to-turn insulation, it is also necessary to withstand the larger insulation between the primary and secondary windings.

Contents of the invention

Aiming at the defects of the prior art, the object of the present invention is to provide an air-core pulse transformer for a coupling transformer-type DC circuit breaker and its parameter acquisition method, aiming at solving the problem that the air-core pulse transformer for a coupling-transformer type DC circuit breaker needs to withstand the DC bus voltage. The level of main insulation between primary and secondary windings, and the method of obtaining specific parameters of this type of pulse transformer.

The invention provides an air-core pulse transformer for a coupling transformer type DC circuit breaker, which includes a primary winding, a secondary winding, a high voltage end of the primary winding, a low voltage end of the primary winding, a high voltage end of the secondary winding, a low voltage end of the secondary winding, The inter-turn insulating film of the secondary winding, the inter-turn insulating film of the primary winding, the main insulating film, and the insulating support frame; the secondary winding is wound radially along the insulating support frame, and the secondary winding has a radial voltage gradient , and the inter-turn insulation of the secondary winding is realized by the inter-turn insulating film of the secondary winding; the low-voltage end of the secondary winding and the low-voltage end of the primary winding are insulated by the main insulating film; The primary winding is wound outside the main insulating film, and the inter-turn insulation of the primary winding is realized by the inter-turn insulating film of the primary winding.

Among them, when the coupling transformer type DC circuit breaker is normally connected to the grid, the potentials of the high-voltage end of the secondary winding and the low-voltage end of the secondary winding are both the bus voltage.

Among them, the parameters of the air-core pulse transformer include the number of turns of the primary and secondary windings, the inductance of the primary and secondary windings, the capacitance of the primary and secondary windings, the outer diameter of the support frame, the width of the copper strip, and the thickness of the copper strip.

The present invention also provides a method for obtaining parameters of the air-core pulse transformer based on the above-mentioned coupling transformer-type DC circuit breaker. The parameters of the air-core pulse transformer include the number of turns of the primary and secondary windings, the inductance of the primary and secondary windings, the primary , Sub-side capacitance, support frame outer diameter, copper strip width, copper strip thickness, including the following steps:

(1) Determine the first amplitude i _2max of the secondary side current i ₂ of the pulse transformer according to the maximum breaking current I _max , and obtain the first rising edge time of the secondary side current i ₂ of the pulse transformer

Where U _n is the DC bus voltage, I _n is the rated current, is the maximum fault current drop rate, T _p is the time for the vacuum break to open to the maximum distance; L ₀ is the inductance value of the smoothing reactor,

(2) by formula Obtain the value of ω ₂ , and then by Determine the value of a group of pulse transformer secondary inductance L ₂ and secondary capacitor C ₂ ; through the formula Obtain the value of the primary side inductance _L1 , then by and Determine the value of the original capacitor _C1 ;

in, U ₀ is the charging voltage of the primary capacitor, k is the coupling coefficient, k is greater than or equal to 0.8, and χ is the tuning degree;

(3) Obtain the frequencies f ₁ and f ₂ of the primary and secondary currents i ₁ and i ₂ , and obtain the thickness of the primary and secondary winding copper strips according to the frequencies of the primary and secondary currents and

Among them, ρ=1.72×10 ^-8 Ω/m, which is copper resistivity; μ ₀ =4π×10 ^-7 H/m, which is vacuum permeability;

(4) According to the fact that the secondary winding needs to withstand 1.5 to 2 times the bus voltage, the insulation material between turns of the secondary winding is selected with a withstand voltage value of U _N2 and a thickness of d ₂ , and the number of turns of the secondary winding N ₂ is obtained. Then select the inter-turn insulation material of the primary winding: the withstand voltage value is U _N1 (U _N1 ≤ U _N2 ), and the thickness is d ₁ ; the primary and secondary windings need to withstand about 1.5 times the bus voltage, and the main insulation material is selected : The withstand voltage is U _N and the thickness is d;

(5) Obtain the number of turns N ₁ of the primary winding, the outer diameter r of the support frame, and the width l of the winding from formula III to formula VIII; and obtain the stray resistance of the primary side of the transformer and secondary side stray resistance

Among them, formula III is Formula IV is Formula V is Formula VI is Formula VII is Formula VIII is in,

(6) According to the formula Obtain the second amplitude I ₂ of the current i ₂ and the second rising edge time t′ _rise , and make the first amplitude equal to the second amplitude by adjusting the value of U ₀ and C ₂ , and the obtained The first rising edge time is equal to the second rising edge time;

in, L _k1 and L _k2 are the stray inductances of the primary and secondary sides, which can be taken in microhenries.

Further, in step (6), the value of adjusting U ₀ and the value of C ₂ is specifically:

When I ₂ is greater than i _2max, reduce the value of U ₀ , and when I ₂ is less than i _2max, increase the value of U ₀ ;

When _t'rise is greater than _trise , reduce the value of _C2 , and when _t'rise is less than _trise , increase the value of _C2 .

Furthermore, the bus voltage U _n , rated current I _n , current drop rate The maximum breaking current I _max and the time T _p from the vacuum break to the maximum opening distance are transformed into the first amplitude i _2max ≥ I _max and the first rising edge time t _rise of the secondary side current of the coupling transformer; where, the formula X for Formula XI is Formula XII is Formula XIII is Formula XIV is

In the present invention, the influence of the main insulation between the primary and secondary windings of the pulse transformer is fully considered,

Among them, l ₁ is the length of the copper strip of the primary winding.

Through the above technical scheme conceived by the present invention, compared with the prior art, since the main insulating film is used for insulation between the low-voltage end of the secondary winding of the pulse transformer and the low-voltage end of the primary winding, the pulse transformer can obtain a durable DC bus The beneficial effect of the main insulation between the primary and secondary side windings of the voltage level; at the same time, because the pulse transformer parameter acquisition method proposed by the present invention fully considers the specific working conditions of the DC circuit breaker and the main insulation problem between the primary and secondary side windings of the transformer, Coupling transformer-type DC circuit breakers for different voltage levels can be obtained, and corresponding air-core pulse transformers can be designed on a scientific basis. It can also be used to calculate whether an air-core pulse transformer is suitable for a specific coupling transformer-type DC circuit breaker The beneficial effect of the device.

Description of drawings

Fig. 1 is a design flow chart of an air-core pulse transformer for a coupling transformer-type DC circuit breaker according to the present invention.

Fig. 2 is a schematic circuit diagram of an air-core pulse transformer for a coupling transformer-type DC circuit breaker according to the present invention.

Fig. 3 is a structural schematic diagram of an air-core pulse transformer for a coupling transformer-type DC circuit breaker according to the present invention.

Fig. 4 is a schematic circuit diagram of the coupling transformer type DC circuit breaker involved in the present invention.

In all the drawings, the same reference numerals are used to represent the same components or structures, wherein: 1 is the primary winding; 2 is the secondary winding; 3 is the high voltage end of the primary winding; 4 is the low voltage end of the primary winding; 5 is the high voltage end of the secondary winding; 6 is the low voltage end of the secondary winding; 7 is the inter-turn insulating film of the secondary winding; 8 is the inter-turn insulating film of the primary winding; 9 is the main insulating film; 10 is the insulating support frame; C ₁ C ₂ is the capacitance of the secondary side; L ₁ is the inductance of the primary side; L ₂ is the inductance of the secondary side; R _k1 is the stray resistance of the primary side; R _k2 is the stray resistance of the secondary side; L _k1 is the stray resistance of the primary side Scattered inductance; L _k2 is the stray inductance of the auxiliary side; M is the mutual inductance of the transformer; S is the closed switch.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The purpose of the present invention is to propose a design method for an air-core pulse transformer suitable for a coupling transformer type high-voltage DC circuit breaker, which can be used according to specific engineering requirements (including bus voltage, rated current, Current drop rate, maximum breaking current, time from vacuum fracture opening to maximum opening distance, etc.), design the important parameters of the pulse transformer that meet the requirements (including the number of turns of the primary and secondary windings, the inductance of the primary and secondary windings, and the capacitance of the primary and secondary windings) , the outer diameter of the support frame, the width and thickness of the copper strip, etc.).

The design method of the air-core pulse transformer for the coupling transformer type DC circuit breaker provided by the present invention comprises the following steps:

The first step is to determine the amplitude i _2max of the secondary side current i ₂ of the pulse transformer from the maximum breaking current I _max , select the value of the smoothing reactor L ₀ by the formula (1), and use the formula (2) to formula (5) Determine the rising edge time t _rise of i ₂ ; where,

U _n is the DC bus voltage, I _n is the rated current, is the maximum fault current drop rate, T _p is the time for the vacuum break to open to the maximum distance, L ₀ is the inductance value of the smoothing reactor, i(t=T _p ) is the value of fault current i at T _p , T ₀ is the time of fault current i from T _p to the first zero-crossing point, is the rising rate of i ₂ , T _rise is the minimum rising edge time of i ₂ ;

The second step preliminarily sets the charging voltage of the primary capacitor as U ₀ , the coupling coefficient as k (greater than or equal to 0.8), and the tuning degree as χ. Use formulas (6) and (7) to determine the primary inductance L ₁ and secondary inductance of the pulse transformer. square inductance L ₂ , primary side capacitance C ₁ and secondary side capacitance C ₂ . in,

In the third step, the frequencies f 1 and f 2 of the primary and secondary currents i ₁ and i ₂ are respectively obtained from the formula (8) and the rising edge time t _rise of the secondary current i ₂ in the first step, so as to determine the primary and secondary currents i ₁ and i ₂ Thickness σ ₁ and σ ₂ of winding copper strip; where,

The fourth step is that the secondary winding needs to withstand 1.5 to 2 times the bus voltage, and the inter-turn insulation material of the secondary winding is selected: the withstand voltage value is U _N2 , the thickness is d ₂ , and the number of turns of the secondary winding is determined by formula (9) N ₂ , and then select the inter-turn insulation material of the primary winding: the withstand voltage value is U _N1 (U _N1 ≤ U _N2 ), and the thickness is d ₁ . The primary and secondary windings need to withstand about 1.5 times the bus voltage, select the main insulation material: the withstand voltage value is U _N , the thickness is d,

The fifth step is to determine the number of turns N ₁ of the primary side winding, the outer diameter r of the support frame, and the width l of the winding from formulas (10) to formulas (15), and then use formulas (16) to formulas (19) to calculate the primary and secondary sides of the transformer scattered resistors R _k1 and R _k2 ,

Among them, μ ₀ =4π×10 ^-7 H/m,

Among them, ρ=1.72×10 ^-8 Ω/m;

The sixth step is to obtain the amplitude I ₂ of the current i ₂ and the rising edge time t' _rise from the formula (20). If I ₂ is not equal to i _2max , adjust the value of U ₀ (if I ₂ is greater than i _2max , reduce the value of U ₀ , If I ₂ is less than i _2max , increase the value of U ₀ ), if t' _rise is not equal to t _rise , adjust the value of C ₂ (if t' _rise is greater than t rise, reduce the value of C ₂ , and if t' _rise is less than t _rise , increase _{C 2} value), until the value of U ₀ and C ₂ makes the waveform of current i ₂ meet the amplitude i _2max and rising edge time t _rise in the first step,

in, L _k1 is the stray inductance of the primary side, and L _k2 is the stray inductance of the secondary side.

The present invention proposes that as long as the application voltage level, rated current, fault current drop rate, maximum breaking current, and the time for the vacuum fracture to open to the maximum opening distance of the coupling transformer type DC circuit breaker are known, it can be provided according to the present invention The design step determines the key parameters of the air-core pulse transformer including the number of turns of the primary and secondary windings, the inductance of the primary and secondary windings, the capacitance of the primary and secondary sides, the outer diameter of the support frame, and the width and thickness of the copper strip.

In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:

(1) Insulation film insulation is used between the low-voltage end of the primary winding and the low-voltage end of the secondary winding, so that the air-core pulse transformer can withstand the main insulation between the primary and secondary windings of the DC bus voltage level.

(2) The design method proposed by the present invention can not only design and manufacture corresponding air-core pulse transformers for coupling transformer-type DC circuit breakers of different voltage levels on a scientific basis, but also can be used for calculation and inspection of a certain air-core pulse transformer Whether it is suitable for a specific coupling transformer type DC circuit breaker.

In the air-core pulse transformer for coupling transformer type DC circuit breaker proposed by the present invention, its secondary winding 2 is radially wound along the insulating support frame 10, and there is a radial voltage gradient in the secondary winding 2, and the inter-turn insulating film 7 of the secondary winding insulation. Since the potential of the high voltage terminal 5 of the secondary winding and the low voltage terminal 6 of the secondary winding is the bus voltage when the coupling transformer type DC circuit breaker is normally connected to the grid, the potentials of the low voltage terminal 6 of the secondary winding and the low voltage terminal 4 of the primary winding are connected by the main The insulating film 9 is insulating. The primary side winding 1 is wound outside the main insulating film 9 , and the inter-turn insulation of the primary side winding is borne by the inter-turn insulating film 8 of the primary side winding.

In order to further illustrate the air-core pulse transformer for coupling transformer-type DC circuit breaker provided by the embodiment of the present invention and its parameter acquisition method, it is further elaborated from a theoretical point of view as follows:

Suppose the DC bus voltage is U _n , the rated current is I _n , the maximum breaking current is I _max , and the maximum fault current drop rate is The time for the vacuum break to open to the maximum opening distance is T _p . In order for the DC circuit breaker to break the fault current normally, the reverse current, that is, the secondary current i ₂ of the pulse transformer, needs to meet two conditions:

①The first amplitude of i ₂ needs to be greater than I _max , which is taken as i _2max .

② In order to make the fault current not exceed the maximum breaking current I _max of the circuit breaker, the smoothing reactor L ₀ needs to meet:

(Formula 1)

When the closed switch S is closed, the fault current i is:

(Formula 2)

The time of fault current _i from T _p to the first zero-crossing point is:

(Formula 3)

The reverse current, that is, the rising rate of the pulse transformer secondary current i ₂ is:

(Formula 4)

The rising edge time of pulse transformer secondary current i ₂ is:

(Formula 5)

Therefore, the rising edge time of i ₂ needs to be greater than T _rise , which is taken as t _rise .

Preliminarily set the precharge voltage of C ₁ as U ₀ , the coupling coefficient as k (greater than or equal to 0.8), ignore the influence of pulse transformer stray parameters R _k1 , R _k2 , L _k1 , and L _k2 , the primary and secondary circuit currents can be obtained Expressions for i ₁ and i ₂ :

(Formula 6)

(Formula 7)

in,

Preliminarily set a tuning degree χ, its expression is:

(Formula 8)

From (Equation 8), the expression of h, h ₁ , h ₂ with respect to ω ₂ can be obtained:

(Formula 9)

(Formula 10)

(Formula 11)

Deriving (Equation 7) yields (Equation 12):

(Formula 12)

According to the requirements of condition ②, substitute t _rise into (Formula 12) to obtain the value of ω ₂ (take the minimum solution to ensure that i ₂ obtains the first peak value at the moment of t _rise ). Then substitute _ω2 into Determine a set of C ₂ and L ₂ values. According to the requirements of condition ①, the value of L ₁ can be obtained by substituting U ₀ , k, i _2max , t _rise and L ₂ into (Formula 7), and then by and (Equation 8) determine the value of _C1 .

Define four times the rising edge time of the primary and secondary currents i ₁ and i ₂ as the periods of i ₁ and i ₂ , then the frequencies f ₁ and f 2 of i ₁ and i ₂ can be obtained from (Formula 6) and condition _② respectively. Substitute f ₁ and f ₂ into (Equation 13) to find the skin depth σ ₁ and σ ₂ of the primary and secondary windings. In order to reduce the influence of stray resistance, the thickness of the primary and secondary winding copper strips is selected as the corresponding skin depth σ ₁ and σ ₂ .

(Formula 13)

Wherein, σ is skin depth; ρ=1.72×10 ^-8 Ω/m, copper resistivity; μ ₀ =4π×10 ^-7 H/m, vacuum magnetic permeability.

After the circuit breaker is disconnected, both ends of the secondary side capacitor C ₂ will withstand an overvoltage U _C2 whose amplitude is greater than the bus voltage U _n . If the arc reignites in the vacuum circuit breaker, the secondary winding needs to withstand about 1.5 to 2 times the bus voltage, and the inter-turn insulating material of the secondary winding should be selected: the withstand voltage value is U _N2 and the thickness is d ₂ . Determine the number of turns N ₂ of the secondary winding according to (Formula 14).

(Formula 14)

Both ends of C ₂ need to withstand the overvoltage U _C2 , since the reverse discharge branch is connected in parallel with both ends of the primary capacitor C ₁ , the withstand voltage at both ends of C ₁ is the precharge voltage U ₀ , so the primary winding turns The withstand voltage value of the inter-turn insulating material is less than U _N2 , and the inter-turn insulating material of the primary winding is selected: the withstand voltage value is U _N1 and the thickness is d ₁ .

When the DC circuit breaker is normally connected to the grid, the potentials of the high and low voltage terminals of the secondary winding of the pulse transformer are close to the bus voltage U _n , and the low voltage terminal of the primary winding is directly grounded, so the primary and secondary windings must withstand the bus voltage. Consider the insulation margin of about 50%, and select the insulating material between the low-voltage end of the primary winding and the low-voltage end of the secondary winding: the withstand voltage value is U _N and the thickness is d.

Substituting L ₁ , L ₂ , k and N ₂ into (Equation 15) ~ (Equation 20) can obtain the relevant parameters of the pulse transformer: the number of turns of the primary winding N ₁ , the outer diameter of the support frame r, and the winding width l.

(Formula 15)

(Formula 16)

(Formula 17)

(Formula 18)

(Formula 19)

(Formula 20)

The length of the secondary winding of the transformer is:

(Formula 21)

The secondary winding resistance is:

(Formula 22)

The length of the primary winding of the transformer is:

(Formula 23)

The primary winding resistance is:

(Formula 24)

Due to the inhomogeneity of the current distribution, the actual winding resistances R _k1 and R _k2 are 10 to 100 times the theoretically calculated value (related to the current frequency). The influence of stray inductance L _k1 and L _k2 on i ₂ is not great, and its value can be in microhenry level. Considering the effects of R _k1 , R _k2 , L _k1 , and L _k2 , the secondary current i ₂ can be expressed as:

(Formula 25)

in,

From (Formula 25), the amplitude I ₂ of current i ₂ and the rising edge time t' _rise can be obtained. If the amplitude I ₂ of i ₂ does not meet the condition ①, then adjust the value of U ₀ (if I ₂ is too large, reduce U ₀ The value of I ₂ is too small to increase the value of U ₀ ), if the rising edge time t' _rise of i ₂ does not meet the condition ②, then adjust the value of C ₂ (t' _rise is too large to reduce the value of C ₂ , t' _rise is too large to reduce the value of C ₂ ), so the basic parameters of the entire air-core pulse transformer have been determined. So far, the theoretical derivation of the present invention has been completed.

From the above analysis, the design steps of the band-wound air-core transformer in the coupling transformer type DC circuit breaker involved in the present invention can be given:

Step (1) Determine the amplitude i _2max of the secondary side current i ₂ of the pulse transformer from the maximum breaking current I _max , select the value of the smoothing reactor L ₀ by (formula 1), and then use (formula 2)～(formula 5) Determine the rising edge time t _rise of _i2 ;

Step (2) Preliminarily set the charging voltage of the primary capacitor as U ₀ , the coupling coefficient as k (0.8 is acceptable), the tuning degree as χ, and the primary inductance L of the pulse transformer is determined by (Formula 7) and (Formula 12) _1. Secondary side inductance L ₂ , primary side capacitance C ₁ , secondary side capacitance C ₂ ;

Step (3) Calculate the frequencies f 1 and _{f 2} of the primary and secondary currents i ₁ and i ₂ respectively from (Formula 6) and the rising edge time t _rise of the secondary current i ₂ in step (1), thereby determining the primary Thickness σ ₁ and σ ₂ of the secondary winding copper strip;

Step (4) The secondary winding needs to withstand 1.5 to 2 times the bus voltage, select the inter-turn insulation material of the secondary winding: the withstand voltage value is U _N2 , the thickness is d ₂ , and use (Formula 14) to determine the secondary winding turns N ₂ , and then select the inter-turn insulation material of the primary winding: the withstand voltage value is U _N1 (U _N1 ≤ U _N2 ), and the thickness is d ₁ . The primary and secondary windings need to withstand about 1.5 times the bus voltage, and the main insulation material is selected: the withstand voltage value is U _N , and the thickness is d;

Step (5) From (Formula 15) to (Formula 20), determine the number of primary winding turns N ₁ , the outer diameter of the support frame r, and the winding width l, and then use (Formula 21) to (Formula 24) to calculate the primary and secondary sides of the transformer Stray resistances R _k1 and R _k2 ;

Step (6) Obtain the amplitude I ₂ of current i ₂ and the rising edge time t' _rise from (Formula 25). If I ₂ is not equal to i _2max , adjust the value of U ₀ (I ₂ is too large to reduce the value of U ₀ , I ₂ is too small to increase the value of U ₀ ), if t' _rise is not equal to t _rise , adjust the value of C ₂ (t' _rise is too large to reduce the value of C ₂ , t' _rise is too small to increase the value of C ₂ ) , until the values of U ₀ and C ₂ make the waveform of current i ₂ meet the amplitude i _2max and rising edge time t _rise in step (1).

After step (6) is completed, the air-core pulse transformer for coupling transformer type DC circuit breaker including the number of turns of the primary and secondary windings, the inductance of the primary and secondary windings, the capacitance of the primary and secondary sides, the outer diameter of the support frame, the width and thickness of the copper strip, etc. is completed. key parameter design.

In order to further illustrate an air-core pulse transformer for a coupling transformer-type DC circuit breaker and its parameter acquisition method provided by the embodiment of the present invention, a design example of an air-core pulse transformer for a coupling-transformer type DC circuit breaker is given here:

The coupling transformer type DC circuit breaker is applied to the DC transmission system with bus voltage U _n of 320kV and rated current I _n of 3kA. The DC circuit breaker uses a vacuum circuit breaker as the main fracture, and the maximum breaking current I _max is 15kA. In order to ensure the normal arc extinguishing of the vacuum fracture, the fault current drop rate after the vacuum circuit breaker is disconnected It needs to be less than 100A/μs, and the time T _p for the vacuum break to open to the maximum opening distance is 3ms.

Step (1) According to the above engineering application conditions of DC circuit breaker, the pulse transformer secondary side current i ₂ needs to meet:

①The first amplitude i _2max of i ₂ needs to be greater than 15kA, so take i _2max = 20kA.

② It can be seen from (Formula 1) that L ₀ must be greater than 80mH, which is taken as 100mH, and then from (Formula 2) to (Formula 5), the rising edge time of i ₂ must be greater than 194μs, and tri _rise = 250μs.

Step (2) takes U ₀ =100kV, k=0.8, χ=0.97. Substitute t _rise =250 μs into (Formula 12) to obtain ω ₂ =0.0027×10 ⁶ rad/s. according to Determine a set of C ₂ and L ₂ values: C ₂ =4mF, L ₂ =34.29μH. Substitute U ₀ , k, i _2max , t _rise and L ₂ into (Formula 7) to get L ₁ =1619.17μH, and then by C ₁ =90.04μF can be obtained.

Step (3) Calculate the frequencies f ₁ and f ₂ of the primary and secondary currents i ₁ and i ₂ from (formula 6) and condition ② in step (1), both of which are about 1000 Hz, and determine the thickness of the primary and secondary winding copper strips σ ₁ and σ ₂ are both 2.09mm.

Step (4) The interlayer insulation of the secondary winding needs to withstand a high voltage of about 640kV. The polyester film (DMD) with a thickness _d2 of 0.35mm and a withstand voltage U _N2 of 16kV is used as the interlayer insulation of the secondary winding. Formula 14) shows that the number of turns N ₂ of the secondary winding is 38 turns. The turn-to-turn insulation of the primary winding is insulated with a DMD insulation film with a thickness _d1 of 0.34mm and a withstand voltage U _N1 of 13.6kV. Between the primary side low-voltage terminal and the secondary side low-voltage terminal, it is necessary to withstand about 1.5 times the bus voltage. 38 turns of DMD insulation with a withstand voltage of 12kV and a thickness of 0.25mm are used. The total insulation thickness d is 9.5mm.

Step (5) From (Formula 15)～(Formula 20), obtain the number of turns of the primary winding N ₁ =108, the outer diameter of the support frame r=76mm, and the winding width l=2306mm, use (Formula 21)～(Formula 24) to calculate The primary and secondary stray resistances of the transformer are R _k1 =0.45mΩ and R _k2 =0.11mΩ.

Step (6) Considering a certain margin, R _k1 and R _k2 are taken as 45mΩ and 11mΩ respectively. From (Formula 25), the amplitude I ₂ of the current i ₂ is 128kV, and the rising edge time _t'rise is 230μs. Adjusting U ₀ to 15kV and C ₂ to 5.5mF can make the waveform of the current i ₂ satisfy the step ( 1) The amplitude of 20kA and the rising edge of 250μs, so far the design is completed.

Therefore, to design the aforementioned air-core pulse transformer used in a 320kV coupling transformer type DC circuit breaker, the primary winding inductance L ₁ is 1619.17μH, the secondary winding inductance L ₂ is 34.29μH, and the primary capacitance C ₁ is 90.04μF. The charging voltage U ₀ is 15kV, the secondary capacitor C ₂ is 5.5mF, the outer diameter r of the designed transformer support frame is 76mm, the winding width is 2306mm, the primary winding turns N ₁ are 108 turns, and the secondary winding turns N ₂ is 38 turns.

The design method of the air-core pulse transformer for the coupling transformer-type DC circuit breaker proposed by the present invention can scientifically and rationally design the corresponding air-core pulse transformer step by step under the condition of known engineering technical requirements.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (4)

1. A parameter obtaining method of an air-core pulse transformer for a coupling transformer type direct current breaker is characterized in that the air-core pulse transformer for the coupling transformer type direct current breaker comprises the following steps: the winding comprises a primary winding (1), a secondary winding (2), a primary winding high-voltage end (3), a primary winding low-voltage end (4), a secondary winding high-voltage end (5), a secondary winding low-voltage end (6), a secondary winding inter-turn insulating film (7), a primary winding inter-turn insulating film (8), a main insulating film (9) and an insulating support frame (10); the secondary winding (2) is wound along the radial direction of the insulating support frame (10), the secondary winding (2) has a radial voltage gradient, and the turn-to-turn insulation of the secondary winding (2) is realized by the turn-to-turn insulating film (7) of the secondary winding; the low-voltage end (6) of the secondary winding and the low-voltage end (4) of the primary winding are insulated by the main insulating film (9); the primary winding (1) is wound outside the main insulating film (9), and the turn-to-turn insulation of the primary winding (1) is realized by the turn-to-turn insulating film (8) of the primary winding; the parameter acquisition method comprises the following steps:

(1) according to the maximum breaking current I_maxDetermining secondary current i of pulse transformer₂Of a first amplitude i_2maxAnd obtaining the secondary current i of the pulse transformer₂First rising edge time of

Wherein, U_nIs a DC bus voltage, I_nFor the purpose of the rated current, the current,for maximum fault current reduction rate, T_pThe time for the vacuum fracture to be pulled open to the maximum opening distance; l is₀Is the inductance value of the smoothing reactor,

(2) according to the formula Andto obtain omega₂Then C is added₂、ω₂Substitution intoL can be determined₂Taking the value of (A); according to the formulaObtaining the original square inductance L₁Is then represented by the formulaAndobtaining the original square capacitance C₁A value of (d);

wherein, U₀Is an original square capacitor C₁K is a coupling coefficient, k is greater than or equal to 0.8, and χ is a set tuning degree;

(3) obtaining the primary current i₁Frequency f of₁And secondary current i₂Frequency f of₂And obtaining the thickness of the copper strip of the primary winding according to the frequency of the primary and secondary currentsThickness of copper strip of secondary winding

Where ρ is 1.72 × 10^-8Ω/m, copper resistivity; mu.s₀＝4π×10^-7H/m, vacuum magnetic permeability;

(4) selecting the withstand voltage value U of the turn-to-turn insulating material of the secondary winding according to the condition that the secondary winding needs to withstand 1.5-2 times of bus voltage_N2And a thickness d₂According to the formulaObtaining the number of turns N of the secondary square winding₂；

(5) Obtaining the number of turns N of the primary square winding according to formulas III to VIII₁The outer diameter r of the support frame and the width l of the winding; and obtain the primary stray resistance of the transformerAnd secondary stray resistanceWherein i is the number of turns of the primary winding, and j is the number of turns of the secondary winding;

wherein formula III isFormula IV isFormula V isFormula VI isFormula VII isFormula VIII isWherein,k is a coupling coefficient; u shape_N1Is the voltage withstanding value of turn-to-turn insulation material of the primary winding, U_N1≤U_N2；d₁The thickness of the turn-to-turn insulating material of the primary winding; d is the thickness of the main insulating material;

(6) according to the formulaObtain a current i₂Of a second amplitude value I₂And a second rising edge time t'_riseAnd by adjusting U₀Value of (A) and C₂Such that the first amplitude is equal to the second amplitude and the first rising edge time is equal to the second rising edgeA (c) is added;

wherein,L_k1and L_k2The stray inductances of the primary and secondary squares are microhenry levels.

2. The parameter acquisition method according to claim 1, wherein in step (6), U is adjusted₀Value of (A) and C₂The values of (a) are specifically:

when I is₂Greater than i_2maxTime-reduced U₀When a value of (A) is₂Is less than i_2maxIncrease U by time₀A value of (d);

when t'_riseGreater than t_riseDecrease in time C₂Value of when t'_riseLess than t_riseIncrease in time C₂The value of (c).

3. The parameter acquisition method of claim 1, wherein the formula X to formula XIV are used to convert the bus voltage U of the dc breaker into the bus voltage U_nRated current I_nCurrent reduction rateMaximum on-off current I_maxAnd the time T of the vacuum fracture opening to the maximum opening distance_pConverted into a first amplitude i of a secondary current of the counter-coupled transformer_2max≥I_maxAnd a first rising edge time t_rise；

Wherein, the formula X isFormula XI isFormula XII isFormula XIII isFormula XIV is

4. The parameter acquisition method according to claim 1, wherein when the coupling transformer type dc circuit breaker is normally in a grid-connected operation, the high-voltage end (5) of the secondary winding and the low-voltage end (6) of the secondary winding are at the same potential as the dc bus.