CN1917109A - Method for turning on/off capacitive current of lightning arrester connected in parallel between AC filter and breaker - Google Patents

Abstract

The disclosed technical scheme connects arrester to two ends of breaker in parallel in order to restrict recovery voltage at two ends being disconnected of breaker when operation is executed for cutting off capacitive current. The invention carries out description by using data in the invention as example that ac circuit breaker in converter station turns ac filter etc. reactive compensation equipment on/off. The invention is applicable to capacitive current form breaker, idle aerial line or idle cable etc when voltage is lower 500kV. The invention selects parameter of arrester connected in parallel reasonably, and restricts recovery voltage effectively. Advantages are: acceptable level of energy consumption, feasible layout for arrester, easy of implementation, preponderant performance and economy.

Description

The capacity current of AC filter and breaker lightning arrester connected in parallel cut-offs method

Technical field

The present invention relates to the method that limiting circuit breaker cut-offs fracture recovery voltage at two ends being disconnected under the capacity current.

Background technology

Circuit breaker cut-offs capacity current and produces transient recovery voltage, and the cooperation and the capacity current size of circuit breaker being cut-off speed have higher requirements, and manufacturing brings difficulty to circuit breaker, at present breaking capacity of breaker is tested very difficult.DC transmission system exists comparatively serious operating mode to need AC filter and breaker (big group/group) to cut-off under over-voltage condition, and measure in the past comprises the fracture of the medium recovery strength that improves between the firm timesharing contact of circuit breaker, the high step voltage of outfit or installs lightning arrester over the ground at the circuit breaker two ends.

When cut-offfing capacity currents such as reactive-load compensation equipment, unloaded overhead wire or non-loaded cable when AC circuit breaker, what flow through in the circuit breaker is only hundreds of amperes small magnitude capacitive current of numerical value.When cut-offfing little electric current, clearance between open contacts is still short when arc extinction, and this moment, recovery voltage was high, therefore very easily caused arc reignition, just might produce the overvoltage of danger.Little capacitance current cut-off become the harshest condition of cut-offfing of extra high voltage circuit breaker it

One, be subjected to people's great attention.

Fig. 1 analyzes used equivalent electric circuit when cutting off capacitor C.

U=U among the figure _MaxSin ω t flows through the current i=I in loop _MaxCos ω t is (in the formula $I_{\max }=\frac{U_{\max }}{Z},$

$Z=(\mathrm{\ωL}-\frac{1}{\mathrm{\ωC}})\≅\frac{1}{\mathrm{\ωC}})$

At t ₁Constantly, the i zero passage, circuit breaker cut-offs, and the last instantaneous voltage value of C this moment is $U_{\mathrm{ce}}=I_{\max }\·\frac{1}{\mathrm{\ωC}}\≅U_{\max },$ The last voltage of L is approximately zero, so the constant U of voltage on the capacitor C _Ce=U _MaxConstant, but supply voltage arrives t still by the power frequency variation through half cycle ₂Constantly, supply voltage reaches reverse maximum, and at this moment, magnitude of voltage is between contact:

u _j=-U _Max-u _C0=-2U _Max, at t ₂Constantly, dielectric strength is less than or equal to 2U between contact _Max, gap breakdown then, arc reignition produces the higher-order of oscillation by distributed constant in the line, forms high-frequency current:

I=-2U _Maxω ₀C sin ω ₀T is (from t ₂Constantly begin), voltage is on the capacitor C:

$u_c=\frac{1}{C}\∫\mathrm{idt}=2U_{\max }\cos {\mathrm{\ω}}_{0}t-U_{\max }=U_{\max }(2\cos {\mathrm{\ω}}_{0}t-1)$

In the formula: ${\mathrm{\ω}}_0=\frac{1}{\sqrt{\mathrm{LC}}}$ (loop natural frequency)

At t ₂Constantly, process

Time, the high-frequency current zero passage, this moment, high-frequency current was cut off, and then voltage is on the electric capacity:

u _c＝U _max(2cosπ-1)＝-3U _max

The last magnitude of voltage of C this moment remains unchanged, and supply voltage reaches U through half-wave again _Max, t then ₃Voltage is 4U between contact constantly _Max, the gap punctures again restrikes, and then produce the higher-order of oscillation again, and after the oscillating current zero passage, electric current cuts off again, and 5U may appear in voltage on electric capacity _MaxSo when cutting off capacitance load, it is weak more that circuit breaker cuts off current capacity, being easy to generate bang more and wearing and restrike, superpotential multiple is high more.

Because contact pitch is ever-increasing in interrupting process, therefore, dielectric strength constantly increases, and when medium recovery strength gathered way above voltage, re-breakdown phenomenon was ended, and cut off fully.So, to split outage and hold load, general overvoltage can not surpass 3U _Max(in fact, the randomness of be subjected to the restriction of circuit breaker fracture insulation recovery intensity and circuit breaker blow-out, restriking, and the existence of leakage or various losses, overvoltage will be lower than the numerical value of above-mentioned analysis)

When cutting the capacitor group, during the arc current zero passage, recovery voltage reaches peak value, possibility blow-out this moment, also may restrike between fracture because the medium recovery strength of circuit breaker is not enough, the back overvoltage of repeatedly restriking is by 3,5,7 times of risings (theoretical value) owing to gathering of energy, thereby threaten apparatus insulated, quickened the aging build-up effect of capacitor insulation, and the danger that causes switch to be blasted has been arranged.Canada has paper once to report many switch faults that cause because of restriking.

The test of capacitor group can be cut by 800A by at present domestic laboratory (Xi Gaosuo), if carry out the test of bigger electric current, has difficulties.Problem mainly is:

1, the testing transformer off-capacity of synthesis loop;

The overvoltage that causes when 2, testing is had higher requirement to test loop equipment.

Flat high electricly once tested at KEMA is cut-off the recovery overvoltage of surveying 1050kV under the situation of 500A capacity current.

When cutting off capacitance load, if opening velocity improves, can increase the speed that contact draws back, can improve the dielectric strength between contact, reducing takes place to thump wears, and in this occasion, can transfer opening velocity higher.

During the DC transmission system operation, be that rectifier or inverter all will consume certain reactive power.Usually, when rated load operation, the reactive power of converter consumption can reach 40%～60% of specified transmission power, so current conversion station need drop into a large amount of reactive power compensation capacity.The capacitive reactive power compensation equipment of current conversion station installing comprises: alternating current filter and shunt capacitor, usually they are divided into some groups, according to the direct current power size of carrying, by AC circuit breaker suitable switching filter group or capacitor group, realize control to the current conversion station reactive power.General current conversion station has several even tens groups, includes them in several big group by certain compound mode, is linked in the alternating-current field string, is controlled by the alternating-current field switch.Under normal circumstances, organizing switch greatly will disconnect after all minor group switches disconnects.Thereby the AC filter and breaker of DC converter station is faced with same technical problem.But, also exist some self characteristics:

One, because the type of alternating current filter has 11/13 or 12/24 inferior double-tuned filter of the filtering feature frequency in the needs of filtering, DC converter station, also have from background harmonics and uncharacteristic harmonics and consider, adopt 3 subharmonic filters, also have Shunt Capacitor Unit.During the operation of various capacitive reactive power compensation equipment filters, the voltage on the high-voltage capacitor is incomplete same, and the voltage on 3 filter capacities is higher relatively.Simultaneously, it is not only the power frequency amount that the AC harmonic that produces during DC operation makes in the electric current flow through filter, and it is abundant also to contain a large amount of harmonic waves, and there is serious distortion in circuit breaker drop-out current waveform.

Its two, under bipolar emergency outage, on ac bus higher power-frequency overvoltage can appear before reactive-load compensation equipment withdraws from, overvoltage is more serious under weak pattern system condition.Under the fault in ac transmission system condition, after fault clearance, the weak pattern system may cause system resonance down because electric network composition changes, and this is the most serious situation that should consider.

They are three years old, big group of alternating current filter is different with the capacity current level that the group filter need disconnect, and for domestic DC converter station, the little pool-size of the maximum reactive power compensation of 500kV current conversion station at present is the flat station of political affairs alternating current filter 220Mvar, under rated voltage, capacity current is 242A; Pool-size is the shunt capacitor that the alternating current filter of two groups of 220Mvar adds one group of 190Mvar the most greatly, 630Mvar altogether, the about 693A of running current under the rated voltage.

Therefore alternating current filter group circuit breaker and big group circuit breaker cut-off recovery voltage in capacity current and the interrupting process become to circuit breaker important require index.Because the recovery voltage when cut-offfing capacity current is difficult to carry out verification experimental verification before equipment dispatches from the factory preceding, field adjustable, according to the result of computational analysis, often adopt following method:

1) improves medium recovery strength between the firm timesharing contact of circuit breaker, restrike avoiding.This is that the superpotential essential measure of capacitive load is cut-off in restriction, extra high voltage circuit breaker has accomplished that basically cut-offfing nonloaded line does not restrike, but the circuit breaker that capacitor cut-offs in 35kV and following system has the generation of restriking also the time, and the characteristic of cut-offfing capacitive load also needs further to improve.

2) the circuit breaker fracture of the high electric pressure of employing as the back-to-back DC engineering 330kV of Lingbao City top-cross stream filter and breaker, has just all adopted the fracture of 500kV circuit breaker.

3) adopt metal oxide arrester; bus and circuit breaker electric capacity side at AC filter and breaker all have protection of arrester over the ground; the protection of arrester level of circuit breaker filter side is than the slightly high grade of bus bar side; to avoid bearing operating energy, as dragon's fountain, station, Jing Zhou and the HP3 of Lingbao City alternating current filter.The capacitive side lightning arrester cooperates with the bus lightning arrester; the protection minor group switches is closely related by the energy of lightning arrester and the capacity of capacitor group, along with the increase of capacity of capacitor bank; require the through-current capability of lightning arrester also will increase, the lightning arrester parameter is determined by computational analysis usually.

From ruuning situation, these methods all can reach certain effect, but this several method can't solve all problems that cut-offs capacity current under the above-mentioned various situation fully, comprises cut-offfing of big capacity current etc., and the recovery voltage level when tolerance is cut-off to circuit breaker is higher.

Summary of the invention

The present invention proposes, employing directly limits the recovery overvoltage of cut-offfing in the capacity current process in the way of the direct lightning arrester connected in parallel in AC circuit breaker two ends, make and adopt conventional circuit breaker just can guarantee that under the most serious system condition of foregoing description, big group of current conversion station, group's capacitive apparatus all can disconnect reliably.

Description of drawings

Fig. 1 analyzes used equivalent electric circuit when cutting off capacitor C.

Fig. 2 is the figure that expression produces superpotential process when cut-offfing capacitor.

Fig. 3 is the figure of expression DC converter station filter type (is example with the dragon's fountain station).

Fig. 4 is a lightning arrester V-I characteristic curve schematic diagram.

Fig. 5 is the outline dimensional drawing of the 500kV bus lightning arrester of Langfang factory production.

Fig. 6 is the outline dimensional drawing of flat high 500kV circuit breaker.

Fig. 7 is recovery voltage and the energy consumption calculation result (kV, MJ) that circuit breaker cut-offs capacity current.

Embodiment

For DC transmission system; fracture the fault condition and the order of operation of maximum transient recovery voltage (TRV) occur and is when causing circuit breaker to cut-off; on twice 500kV side lines of sending end road, one postback living earth fault; this faulty line of tripping behind the 100ms; make the short circuit level of system after the fault reduce to minimum capacity of short circuit from the minimum capacity of short circuit of twice; the hypothesis converter is owing to any possible reason locking when removing fault; the control protection system is sent the signal of jumping filter/capacitor group in the time of locking; circuit breaker cut-offs behind about 50～60ms, and at this moment the circuit breaker recovery voltage at two ends being disconnected is exactly the maximum overvoltage that will study.Preferably consider that converter transformer is saturated this moment, produce 2～3 subharmonic, all the other compensation equipments and AC impedance can make the voltage on the bus higher at 2～3 subharmonic resonance, and the situation of examination is more serious.

When taking place to exchange external fault and subnormal voltage operation, basic layout strategy is the continuous operation that keeps direct current system, supposition converter locking when the fault clearance of alternating current circuit in the research, this is very conservative supposition, get rid of whole dc loads when it means fault clearance, make on change of current bus and the circuit breaker when shorted to earth fault (particularly single-phase) voltage ratio reality want high.

Adopt the PSCAD/EMTDC4.0 program, is example with the Three Gorges dragon's fountain to the political affairs straight flow, comparative analysis under the specified transmission power of DC bipolar, sending end weak pattern system condition, filter and breaker cut-offs one group of HP3 or 11/13 double tunning alternating current filter, cut-offs the recovery overvoltage level at circuit breaker two ends under three groups of alternating current filters and the energy consumption level of relevant lightning arrester.

The circuit breaker lightning arrester connected in parallel mainly is to be used for fracture recovery voltage at two ends being disconnected in the limiting circuit breaker disconnection process, and normal operation lightning arrester two ends is not down born voltage by the circuit breaker short circuit.After circuit breaker disconnects fully, what bore at the fracture two ends will be the ac bus voltage to earth, and promptly the ac bus voltage to earth is born at the lightning arrester two ends, therefore, the rated value of lightning arrester tentatively according to the identical selection of rated value of ac bus lightning arrester.Experience according to former engineering; when adopting the circuit breaker two ends respectively over the ground during the protection of arrester scheme; the protection level of circuit-breaker capacitor side lightning arrester is than the slightly high grade of bus bar side; in this research; the rated value of capacitor side lightning arrester is still chosen according to the rated value identical with the ac bus lightning arrester; should, under the situation of not considering the lightning arrester energy consumption is required, the superpotential effect of suppression capacitor can be more better.

The characteristic of ac bus lightning arrester is tentatively pressed the characteristic of ASEA XAP-A lightning arrester, and its V-I characteristic curve is illustrated in fig. 4 shown below.

The characteristic of this lightning arrester should be worse than the characteristic of present lightning arrester, and therefore, result of calculation should be too conservative.

Compared following three kinds of situations:

1) except that bus (filter bus) lightning arrester, there are not other protection of arrester;

2) the filter and breaker two ends are respectively by protection of arrester over the ground;

3) the direct lightning arrester connected in parallel in filter and breaker two ends;

Result of calculation sees Table 1.By table 1 as seen; three kinds of protection schemes for research; under single-phase and three-phase fault; employing all can reduce the overvoltage level and the bus lightning arrester energy consumption level at circuit breaker fracture two ends effectively in the scheme of lightning arrester two ends lightning arrester connected in parallel; especially under single-phase fault; it is remarkable to reduce superpotential effect; recovery overvoltage when situation 1 and 2 is cut-off group and big group reactive-load compensation equipment under single-phase and three-phase fault situation is all above 1200kV; and adopt under the scheme of circuit breaker lightning arrester connected in parallel; the fracture recovery voltage can be limited in below the 800kV; and for the energy consumption requirement of lightning arrester connected in parallel, maximum is no more than 2MJ.

Through getting in touch with Langfang lightning arrester factory, the 75mm that Langfang factory is produced and the 500kV of 100mm diameter exchange the lightning arrester, and the energy absorption capability of single-column (be respectively 6.3MJ and greater than 10MJ) all can satisfy the energy consumption requirement under the serious condition in the table 1.The 500kV bus single-column lightning arrester overall dimension of Langfang factory is considered according to the creepage ratio distance under the filthy condition of secondary, as shown in Figure 5.

Exchange double break mouth circuit breaker for 500kV, lightning arrester connected in parallel can be made two joint series connection, in parallel with two fractures respectively, the flat high 500kV double break mouth goat's horn circuit breaker air clearance that Fig. 6 shows reaches 5500mm, on size, have enough spaces and be installed in parallel lightning arrester (the lightning arrester 5094mm of Langfang factory).

Because lightning arrester will be installed in the circuit breaker two ends, will be horizontal mounting means therefore, but not vertical mode adopt the magnetic overcoat, pollution flashover and the wet probability that dodges are less than vertical mode, and the requirement of creepage distance is little.

For the requirement of weight, if the magnetosheath formula can't meet the demands (nearly weighing 1000kg), also can consider to adopt composite sheath, on the one hand can weight reduction, on the other hand, consider that from the external insulation of lightning arrester lightning arrester length can also shorten.

The conclusion that draws is:

1, cut-offfing capacity current is a burden for circuit breaker.

2, compare with present other protected modes, AC filter and breaker two ends lightning arrester connected in parallel can play the effect that reduces circuit breaker fracture two ends recovery voltage level when cut-offfing capacity current better.

3, lightning arrester is chosen according to 500kV ac bus lightning arrester rated voltage, and energy consumption level is within the energy absorption capability of present single-column lightning arrester technical merit.

4, because the lightning arrester level is installed,, can consider to adopt composite sheath if magnetic overcoat weight is bigger than normal.

5, need do further to analyze to the influence and the economic index of switch safety to circuit breaker lightning arrester connected in parallel scheme.

6, for extra-high voltage direct-current, reactive compensation capacity is huge, and the protection scheme of circuit breaker two ends lightning arrester connected in parallel will guarantee that breaker safe disconnects significant reliably to the definite of the big pool-size of reactive power compensation with under serious operating mode.

Claims (7)

1. a method of cut-offfing capacity current adopts circuit breaker to carry out and cut-offs operation, it is characterized in that: at circuit breaker two ends lightning arrester connected in parallel.

2. the method for claim 1, it is characterized in that: described capacity current can be the capacity current of reactive-load compensation equipment, unloaded overhead wire or non-loaded cable.

3. method as claimed in claim 2 is characterized in that: described reactive-load compensation equipment is alternating current filter or shunt capacitor.

4. as the described method of one of claim 1～3, it is characterized in that: at described circuit breaker is when exchanging double break mouth circuit breaker, and lightning arrester connected in parallel is made two joint series connection, is connected in parallel on respectively on two fractures; When described circuit breaker is the single break circuit breaker, lightning arrester is directly parallel in the circuit breaker two ends.

5. method as claimed in claim 4 is characterized in that: the overcoat of circuit breaker lightning arrester connected in parallel can be magnetosheath or composite sheath.

6. method as claimed in claim 5 is characterized in that: described method is used for the AC circuit breaker of 500KV and following each electric pressure.

7. the method for claim 1, it is characterized in that: described method is used for the circuit breaker of DC transmission system reactive-load compensation equipment.

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