CN113992082A - Combined de-excitation resistor circuit - Google Patents
Combined de-excitation resistor circuit Download PDFInfo
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- 230000005347 demagnetization Effects 0.000 claims abstract description 101
- 230000001629 suppression Effects 0.000 claims abstract description 75
- 230000005284 excitation Effects 0.000 claims abstract description 49
- 230000002441 reversible effect Effects 0.000 claims abstract description 31
- 238000004804 winding Methods 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims description 42
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical group [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 39
- 230000008569 process Effects 0.000 claims description 35
- 239000011787 zinc oxide Substances 0.000 claims description 17
- 238000010891 electric arc Methods 0.000 claims description 2
- 238000009413 insulation Methods 0.000 abstract description 5
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 23
- 229910010271 silicon carbide Inorganic materials 0.000 description 21
- 230000002829 reductive effect Effects 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 230000009471 action Effects 0.000 description 5
- 238000010791 quenching Methods 0.000 description 5
- 230000000171 quenching effect Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 230000000670 limiting effect Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 230000001960 triggered effect Effects 0.000 description 2
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000004870 electrical engineering Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003252 repetitive effect Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000001075 voltammogram Methods 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
- H02P9/12—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for demagnetising; for reducing effects of remanence; for preventing pole reversal
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/06—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric generators; for synchronous capacitors
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Abstract
The application aims at providing a combined demagnetization resistance circuit. The combined demagnetization resistance circuit comprises a first branch circuit and a second branch circuit which are connected in parallel: the first branch circuit comprises a linear resistor and a reverse thyristor which are connected in series, a second terminal of the linear resistor is electrically connected with a cathode end of the reverse thyristor, and an anode end of the reverse thyristor is electrically connected with a cathode end of the generator excitation winding; the second branch circuit comprises a nonlinear resistor and a one-way switch which are connected in series, a second terminal of the nonlinear resistor is electrically connected with a cathode end of the one-way switch, and an anode end of the one-way switch is electrically connected with a cathode end of the generator excitation winding; the first terminal of the linear resistor is connected with the first terminal of the non-linear resistor in parallel and is electrically connected with the positive terminal of the generator excitation winding. The field suppression resistor can effectively control field suppression reverse overvoltage level, ensure rotor insulation safety and give consideration to field suppression rapidity when large current under the most severe working condition is subjected to field suppression.
Description
Technical Field
The application relates to the technical field of electrical engineering, in particular to a combined demagnetization resistance circuit.
Background
A de-excitation device in a generator excitation system is the last defense line for ensuring the safe shutdown of a generator set after an accident. When the generator and the excitation system thereof have faults inside or outside, after the relay protection action tripping of the generator-transformer set is disconnected, a field-extinguishing switch in a field-extinguishing device of the excitation system is quickly opened, and an excitation power unit is interrupted by an excitation loop to output excitation power to an excitation winding of the generator; and simultaneously triggering the de-excitation resistor to be conducted, and transferring the energy stored in the excitation winding inductor to the de-excitation resistor for complete consumption.
Only in the fault process of the generator-transformer set and other related system equipment, the safety of the main equipment can be ensured through rapid and reliable de-excitation, and the de-excitation resistor plays a vital role in the safe operation of the generator set.
At present, the widely used field suppression resistors in the static excitation system of large and medium-sized generating sets in China comprise a linear resistor, a zinc oxide (ZnO) nonlinear resistor and a silicon carbide (SiC) nonlinear resistor, and different field suppression resistor selections can obviously influence the speed of a field suppression process and the reverse overvoltage level of field suppression. Typical current-voltage characteristics of the three types of field suppression resistors are shown in figure 1.
The linear resistor has high reliability and convenient maintenance and test, is easy to trigger and conduct, is favorable for reducing the burden of the arc contact of the field suppression switch, and can prolong the service life of the switch. Therefore, the linear resistor is generally used in the occasions with low requirements on the field-extinguishing speed or weak influence of the field-extinguishing speed of the field winding current on the field-extinguishing time inside the generator magnetic field. The current-voltage characteristic of the linear resistor is a linear straight line (as shown in a curve c in fig. 1), the voltage at two ends of the linear resistor has a completely linear relation with the flowing current, and the resistance value R is almost unchanged in the field suppression process. Under the most serious working conditions (such as short circuit at the generator end, no-load error forced excitation and the like), the reverse demagnetization voltage is the highest when the maximum demagnetization current flows. Therefore, the maximum demagnetization voltage must be ensured to be within a safe range (to prevent damage to rotor insulation), thereby greatly limiting the value range of the linear resistance; when the resistance value is small, the demagnetization time can be obviously prolonged, and the quick demagnetization in fault is not facilitated; meanwhile, in the de-excitation process, as de-excitation current is reduced, the voltage at two ends of the resistor is reduced, so that the current attenuation speed is further reduced, and the trailing phenomenon in the de-excitation process is obvious.
The volt-ampere characteristic of a zinc oxide (ZnO) demagnetization resistor is a nonlinear curve (as shown by a curve b in fig. 1), and the volt-ampere characteristic expression is U ═ CIβWherein, C is the whole group of nonlinear resistance coefficient, beta is the nonlinear coefficient, which has strong nonlinear characteristic, and the nonlinear coefficient beta is generally 0.046, so that the voltage change at two ends of the demagnetization resistor is very small in a very wide through-flow range, namely, the voltage change at two ends of the demagnetization resistor is not large in the demagnetization process, the current is attenuated almost according to the linear law, and the rapid demagnetization under the fault is facilitated. When the maximum de-excitation current flows under the most serious working condition, the de-excitation back pressure is not greatly increased, the reverse de-excitation voltage is suitable for being controlled in a safety range, and the rotor insulation safety in the de-excitation process is facilitated. However, when the common small excitation current is used for de-excitation (such as de-excitation under no-load or load rated working condition), the requirement on the arc voltage when the de-excitation switch is disconnected is not reduced, and the load of the contact when the de-excitation switch is disconnected is heavier.
The volt-ampere characteristic of the silicon carbide (SiC) demagnetization resistor is also a nonlinear curve (as shown by a curve a in fig. 1), and the volt-ampere characteristic can be expressed as U ═ CIβThe nonlinear characteristic of the high-voltage direct current transformer is weak, the nonlinear coefficient beta is generally 0.3-0.4, and the voltage change of two ends of the high-voltage direct current transformer is obvious in a wide through-current range. Similarly, when the maximum demagnetization current under the most severe working conditions flows, the demagnetization back pressure is obviously increased (the increase degree is lower than the linear resistance and higher than the ZnO resistance), and the demagnetization back pressure is also required to be increasedEnsuring that the reverse de-excitation voltage does not exceed a safety range; after considering the de-excitation voltage level in large current, the de-excitation time is increased due to low de-excitation voltage in de-excitation of small exciting current. But the silicon carbide resistor is easy to trigger and conduct, and the load of the arc contact of the field suppression switch is reduced. Meanwhile, the silicon carbide resistor is in an open-circuit state after a fault, the device is high in safety, high in power density, small in size and compact in arrangement, and the silicon carbide resistor is widely applied to excitation systems of import manufacturers of many power plant generator sets in China.
It can be seen that the problems that the reverse demagnetization voltage is possibly higher when the large current is demagnetized under severe working conditions, the demagnetization time is longer when the small current is demagnetized, and the trailing phenomenon in the demagnetization process is obvious along with the current decrease mainly exist in the linear resistor as the demagnetization resistor, the problem that the linear resistor is not easy to trigger and conduct when the zinc oxide resistor is demagnetized under the small current exists in the zinc oxide resistor, and the problem that the reverse voltage is higher when the large current is demagnetized under severe working conditions also exists in the silicon carbide resistor as the demagnetization resistor.
In order to avoid the defects of the single resistor devices in the field suppression process and fully exert the respective excellent characteristics of the single resistor devices, the existing field suppression resistors need to be effectively combined, so that the field suppression reverse overvoltage level can be effectively controlled and the insulation safety of a rotor can be ensured when the large current under the most serious working condition is used for field suppression, and meanwhile, the field suppression switches are easy to trigger and conduct when the field suppression is carried out under the low current working condition, the current conversion burden of the field suppression switches is reduced, and the service lives of the switches are prolonged.
The combined demagnetization resistor volt-ampere characteristic is changed by adjusting the linear resistance value and the nonlinear resistance coefficient C, and the demagnetization voltage level and the demagnetization speed are adjusted, optimized and changed according to needs.
The above information disclosed in this background section is only for enhancement of understanding of the background of the application and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.
Disclosure of Invention
The application aims at providing a combined demagnetization resistor circuit, changes the volt-ampere characteristic of the combined demagnetization resistor by adjusting the linear resistance value and the nonlinear resistance coefficient C, and adjusts, optimizes and changes the demagnetization voltage level and the demagnetization speed as required.
According to an aspect of the application, a combined demagnetization resistance circuit comprises a first branch circuit and a second branch circuit connected in parallel, wherein:
the first branch circuit comprises a linear resistor and a reverse thyristor which are connected in series, a second terminal of the linear resistor is electrically connected with a cathode end of the reverse thyristor, and an anode end of the reverse thyristor is electrically connected with a cathode end of a generator excitation winding;
the second branch circuit comprises a nonlinear resistor and a one-way switch which are connected in series, a second terminal of the nonlinear resistor is electrically connected with a cathode end of the one-way switch, and an anode end of the one-way switch is electrically connected with a cathode end of the generator excitation winding;
and the first terminal of the linear resistor is connected with the first terminal of the nonlinear resistor in parallel and is electrically connected with the positive terminal of the generator excitation winding.
According to some embodiments, the relationship between the initial total current flowing through the field suppression resistor and the initial voltage across the field suppression resistor satisfies:
r is the total resistance value of the linear resistor, C is the overall resistance coefficient of the nonlinear resistor, beta is the nonlinear coefficient of the nonlinear resistor, and Im1Is the initial total current, U, flowing through the field suppression resistor under the first field suppression conditionm1Is the initial voltage, I, across the demagnetization resistor under the first demagnetization conditionm2Is the initial total current U flowing through the demagnetization resistor under the second demagnetization working conditionm2The initial voltage at the two ends of the demagnetization resistor under the second demagnetization working condition.
According to some embodiments, the initial total current flowing through the field suppression resistor is generator excitation current which triggers the field suppression switch to trip, triggers the field suppression resistor to be conducted, extinguishes an arc flowing through the field suppression switch, and completely flows through the field suppression resistor;
and the initial voltage at the two ends of the de-excitation resistor is the voltage at the two ends of the de-excitation resistor corresponding to the initial total current flowing through the de-excitation resistor.
According to some embodiments, the nominal configuration capacity of the linear resistor is determined as:
umfor instantaneous value of voltage i across said demagnetization resistor during demagnetization1For a field-suppression current flowing through the first branch circuit, t0Is the moment when the de-excitation resistor is conducted at the beginning of the de-excitation process, teAnd K is a margin coefficient at the moment of finishing the demagnetization process.
According to some embodiments, the end time of the demagnetization process is a total demagnetization current imA time less than 1% of the initial total current of the field suppression resistor.
According to some embodiments, the nominal configuration capacity of the non-linear resistor is determined as:
i2is a field suppression current flowing through the second branch circuit.
According to some embodiments, further comprising: and the jumper is electrically connected with the reverse thyristor and controls the reverse thyristor to be started.
According to some embodiments, the unidirectional switch is a diode or a second inverse thyristor.
According to some embodiments, the jumper is electrically connected to the second triac to control the second triac to turn on.
According to some embodiments, the linear resistance comprises a single linear resistance or a series-parallel combination of a plurality of linear resistances.
According to some embodiments, the non-linear resistance comprises a single non-linear resistance or a series-parallel combination of a plurality of non-linear resistances.
According to some embodiments, the nonlinear resistance is a zinc oxide resistance.
According to an aspect of the application, an excitation system is proposed, comprising a combined field suppression resistor circuit as described in any one of the preceding.
According to an aspect of the application, a generator set is proposed, comprising an excitation system as described hereinbefore.
Technical solutions according to some embodiments of the present application may have one or more of the following benefits:
(1) the voltage-current characteristic difference of the linear resistor and the nonlinear resistor in different current sections is utilized to carry out parameter selection on the linear resistor and the nonlinear resistor, and the parallel connection combination is carried out to obtain the deexcitation resistor, so that the reverse overvoltage level of deexcitation can be effectively controlled when large current is deexcitation under the severe fault working condition, the insulation safety of a rotor in the deexcitation process is ensured, and the back pressure level of the deexcitation resistor in the deexcitation process is favorably maintained to ensure the rapidity of the deexcitation process.
(2) When the switch is de-energized under a low-current working condition (no-load or load rated working condition), the linear resistor consumes energy, is easy to trigger and conduct, is beneficial to arc quenching of the de-energized switch contact, reduces the switch commutation burden and prolongs the service life of the switch.
(3) By combining the two resistors, the SiC resistor characteristic is well fitted, the defect of the SiC resistor is overcome, the silicon carbide field suppression resistor is effectively replaced on the original occasion of using the imported silicon carbide field suppression resistor, and the problem of supply risk of the imported silicon carbide devices can be effectively solved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
The above and other objects, features and advantages of the present application will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings. The drawings described below are for illustrative purposes only of certain embodiments of the present application and are not intended to limit the present application.
FIG. 1 shows a typical voltammogram of three resistors ZnO, SiC and R;
FIG. 2 illustrates a combined field suppression resistor circuit diagram of an exemplary embodiment;
FIG. 3 illustrates yet another embodiment of an exemplary combined field suppression resistor circuit diagram;
fig. 4 shows a combined demagnetization resistance current-voltage characteristic and SiC resistance current-voltage characteristic of an exemplary embodiment.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The same reference numerals denote the same or similar parts in the drawings, and thus, a repetitive description thereof will be omitted.
The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the embodiments of the disclosure can be practiced without one or more of the specific details, or with other means, components, materials, devices, or the like. In such cases, well-known structures, methods, devices, implementations, materials, or operations are not shown or described in detail.
The flow charts shown in the drawings are merely illustrative and do not necessarily include all of the contents and operations/steps, nor do they necessarily have to be performed in the order described. For example, some operations/steps may be decomposed, and some operations/steps may be combined or partially combined, so that the actual execution sequence may be changed according to the actual situation.
The terms "first," "second," and the like in the description and claims of the present application and in the above-described drawings are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
It will be appreciated by those skilled in the art that the drawings are merely schematic representations of exemplary embodiments, and that the blocks or processes shown in the drawings are not necessarily required to practice the present application and are, therefore, not intended to limit the scope of the present application.
Embodiments of apparatus of the present application are described below that may be used to perform embodiments of the methods of the present application. For details not disclosed in the embodiments of the apparatus of the present application, reference is made to the embodiments of the method of the present application.
Fig. 2 shows a combined field suppression resistor circuit diagram of an exemplary embodiment.
As shown in fig. 2, the combined demagnetization resistor circuit comprises two branch circuits connected in parallel; the first branch comprises a linear resistor element R and an inverted thyristor element S1 which are connected in series, wherein the 2 end of the linear resistor R is connected with the cathode of the thyristor element S1, and the anode of the thyristor element S1 is connected with the negative end of the generator excitation winding; the second branch comprises a nonlinear resistor such as a zinc oxide (ZnO) element FR and a reverse diode element D1 which are connected in series, wherein the 2 end of the nonlinear resistor FR is connected with the cathode of the diode element D1, and the anode of the diode element D1 is also connected with the negative end of the generator excitation winding; and the 1 end of the first branch linear resistor R is directly connected with the 1 end of the second branch zinc oxide resistor FR and is connected with the positive end of the generator excitation winding.
According to an exemplary embodiment, a jumper connects the trigger terminals of thyristor element S1. The jumper detects the voltage across the loop. When the voltage reaches or exceeds a set voltage threshold Uth, a trigger pulse is sent out, the thyristor element S1 is triggered to be conducted, and therefore the linear resistor R and the nonlinear de-excitation resistor FR are communicated with the generator rotor on an electric loop to form a loop, and the stored energy of the rotor is absorbed.
According to an exemplary embodiment, prior to the jumper firing, thyristor element S1 is non-conductive, so the loop in which linear field suppression resistor R is located is not in communication with the generator rotor (equivalent to an open circuit).
According to some embodiments, when the magnetic quenching switch is tripped, an arc voltage generated by tripping of the magnetic quenching switch is superposed with an output voltage of the rectifier bridge to form a reverse voltage um, and when the jumper detects that the voltage is greater than a set threshold value Uth, the thyristor element S1 is triggered, so that the thyristor element S1 is turned on, the linear resistor R is connected into a loop and connected with the rotor in parallel, and then the rotor current is transferred into the linear resistor R and the non-linear resistor FR to absorb the energy of the rotor. Thyristor element S1 is turned on until the current through linear resistor R reaches 0A.
According to some embodiments, the initial total current through the degaussing resistor and the initial voltage across the degaussing resistor are determined for two typical degaussing conditions, including the initial total current I through the degaussing resistor for the first degaussing condition, according to the relevant industry specificationsm1And an initial voltage U across the demagnetization resistorm1And an initial total current I flowing through the quenching resistor under a second quenching conditionm2And an initial voltage U across the demagnetization resistorm2(ii) a The initial total current flowing through the field suppression resistor refers to the fact that the field suppression switch is tripped to trigger the field suppression resistor to be conducted, an electric arc flowing through the field suppression switch is extinguished, and at the moment, the generator exciting current completely flows through the field suppression resistor; the initial voltage at the two ends of the demagnetization resistor refers to the voltage at the two ends of the demagnetization resistor corresponding to the current flowing through the initial total current.
According to some embodiments, the relationship between the initial total current flowing through the demagnetization resistor and the initial voltage across the demagnetization resistor is obtained according to the relationship between the total current of the demagnetization resistor and the branch current as follows:
and obtaining the R value and the C value by simultaneous calculation of the formula. Wherein, R is the total resistance value of the linear resistance element; c is the integral resistance coefficient of the zinc oxide nonlinear resistor, beta is the nonlinear coefficient of the nonlinear resistor, and the zinc oxide resistor is generally 0.046.
According to some embodiments, the energy capacity of the linear resistance R and the non-linear resistance FR is determined. Various typical de-excitation working conditions are simulated, including no-load error forced excitation of the generator, short circuit at the generator end, disconnection and trip under a load rated working condition and the like. According to the maximum energy values respectively absorbed by the linear resistance element R and the nonlinear resistance element FR in the process of different demagnetization working conditions, multiplying the maximum energy values by a margin coefficient K to be used as the nominal capacity configuration. The nominal arrangement capacity Sr of the linear resistive element R and the nominal arrangement capacity Sfr of the zinc oxide nonlinear resistive element FR are calculated as follows:
wherein u ismFor instantaneous value of voltage across the demagnetization resistor in the demagnetization process, i1For the de-excitation current flowing through the first branch i2Is the de-excitation current flowing through the second branch; t is t0At the moment when the de-excitation resistor is switched on at the beginning of the de-excitation process, teFor the end time of the de-excitation process, the de-excitation total current i is takenmThe moment less than 1% of the initial total current of the demagnetization resistor is considered to be the end of the demagnetization process; k is margin coefficient, and is 1.2-1.4.
According to some embodiments, the linear resistance element R may adopt a single linear resistor or a series-parallel combination of a plurality of linear resistors, the total resistance value R satisfies the above formula, and the total capacity Sr satisfies the above formula; the zinc oxide nonlinear resistance element FR can adopt series-parallel combination of a plurality of zinc oxide nonlinear resistors, the overall resistance coefficient C meets the above formula, and the total capacity Sfr meets the above formula.
The application is further explained by taking a certain 300MW thermal power generating unit excitation system as an example. In the embodiment, the generator set adopts a self-shunt excitation mode, and the main parameters of the generator set are shown in the following table:
| serial number | Name (R) | Numerical value | |
| 1. | Rated | 300MW | |
| 2. | Rated power factor | 0.85 | |
| 3. | Rated stator voltage | 20kV | |
| 4. | Rated stator current | 10.190kA | |
| 5. | No-load rated exciting current | 750A | |
| 6. | No-load rated excitation voltage | 150V | |
| 7. | Load rated exciting current Ifn | 2203A | |
| 8. | Load rated field voltage Ufn | 463V |
According to an example embodiment, a structure of a combined demagnetization resistance circuit is determined, which is formed by connecting two branch circuits in parallel: the first branch is formed by connecting a linear resistor element R and an inverted thyristor element S1 in series, wherein the 2 end of the linear resistor R is connected with the cathode of the thyristor element S1, and the anode of the thyristor element S1 is connected with the negative electrode of the excitation winding of the generator; the second branch is formed by connecting a nonlinear resistor zinc oxide (ZnO) element FR and a reverse diode element D2 in series, wherein the 2 end of the nonlinear resistor FR is connected with the cathode of the diode element D2, and the anode of the diode element D2 is also connected with the negative end of the generator excitation winding; and the 1 end of the first branch linear resistor R and the 1 end of the second branch zinc oxide resistor FR are directly connected and connected with the anode of the generator excitation winding.
According to the requirement of DL/T843, the overvoltage of the rotor in de-excitation should not exceed 60% of the amplitude of the voltage of the power frequency withstand voltage test of the rotor (according to the unit parameters, namely 6 times of the rated voltage of the rotor), and should be lower than the overvoltage protection action voltage of the rotor. Considering that the maximum demagnetization initial current can reach 3-4 times of rated excitation current when three phases at the machine end are suddenly short-circuited under rated load, the initial total current flowing through the demagnetization resistor under the first demagnetization working condition is considered according to 4 times of Ifn, and meanwhile, the initial voltage Um1 at the two ends of the demagnetization resistor is determined to be not more than 5Ufn (less than 6 times of the rated voltage of the rotor). Considering the maximum initial current of demagnetization as the rated excitation current Ifn when the train is de-magnetized under the rated load condition of the thermal power generating unit, and not pursuing too fast demagnetization speed for the thermal power generating unit, the initial total current passing through the demagnetization resistor under the second demagnetization condition is considered by 1 time Ifn, and meanwhile, the initial voltage Um2 at two ends of the demagnetization resistor is determined to be 2 Ufn.
According to an exemplary embodiment, the relationship between the initial total current of the demagnetizing resistors and the initial voltage across the demagnetizing resistors is obtained from the voltage values of the demagnetizing initial currents at the two demagnetizing operating points, as shown in the following formula (7), and R-0.420336 and C-1594.67 are obtained by simultaneous calculation and solution of the formula. That is, the total resistance of the linear resistance elements is 0.420336ohm, which is about 2 times the thermal resistance of the rotor; the voltage across the zinc oxide nonlinear resistor when a current of 1A flows through the whole resistor was 1594.67V.
Under the parameter configuration, if the field suppression switch is de-energized under the no-load rated working condition of the unit or the field suppression switch is de-energized under the load rated working condition, the linear resistor R mainly bears the field suppression energy consumption task, and the current flowing through the nonlinear resistor FR is very small; meanwhile, the linear resistor is easy to trigger and conduct, the field suppression voltage at two ends of the resistor is not high, and the purposes of reducing the current conversion burden of the field suppression switch and prolonging the service life of the switch are achieved. And when the initial current of the demagnetization reaches 4Ifn under the most serious fault working condition, the shunting action of the FR nonlinear resistor effectively controls the maximum reverse overvoltage value of the demagnetization to be not more than 5Ufn, and meanwhile, the conduction of the FR nonlinear resistor maintains the level of the demagnetization back pressure in the demagnetization process so as to ensure the rapidity of the demagnetization process.
According to the embodiment, various typical de-excitation working conditions are simulated, including the error forced excitation of the generator in no-load, the sudden short circuit at the generator end under the rated load of the generator, the disconnection and trip of the rated working condition of the load and the like, and the relay protection action time and the de-excitation switch trip time are considered. According to the maximum energy values respectively absorbed by the linear resistance element R and the nonlinear resistance element FR in the whole process under different demagnetization working conditions, multiplying the maximum energy values by a margin coefficient K to obtain a capacity configuration value, wherein the margin coefficient K is generally 1.2-1.4.
The invention is further explained by taking an excitation system of a certain 300MW hydroelectric generating set as an example. In this example, the generator set still adopts a self-shunt excitation mode, and the main parameters of the generator set are shown in the following table:
according to an example embodiment, a structure of a combined demagnetization resistance circuit is determined, which is formed by connecting two branch circuits in parallel: the first branch is formed by connecting a linear resistor element R and an inverted thyristor element S1 in series, wherein the 2 end of the linear resistor R is connected with the cathode of the thyristor element S1, and the anode of the thyristor element S1 is connected with the negative electrode of the excitation winding of the generator; the second branch is formed by connecting a nonlinear resistor zinc oxide (ZnO) element FR and a reverse diode element D2 in series, wherein the 2 end of the nonlinear resistor FR is connected with the cathode of the diode element D2, and the anode of the diode element D2 is also connected with the negative end of the generator excitation winding; and the 1 end of the first branch linear resistor R and the 1 end of the second branch zinc oxide resistor FR are directly connected and connected with the anode of the generator excitation winding.
According to the exemplary embodiment, according to the requirement of DL/T583, the field winding reverse voltage during de-excitation is preferably controlled to be not lower than 30% of the winding-to-ground withstand voltage test voltage during factory test (according to the above unit parameter, i.e. 3 times of the rated rotor voltage), and not higher than 50% of the winding-to-ground withstand voltage test voltage during factory test (according to the above unit parameter, i.e. 5 times of the rated rotor voltage). In addition, the excitation system originally adopts an imported SiC field suppression resistor, and the combined field suppression resistor characteristic is considered to be matched with the original SiC resistance characteristic as much as possible when the field suppression resistor is reconstructed. The nonlinear volt-ampere characteristic of the original SiC field suppression resistor is shown as the following formula. The nonlinear index of SiC is 0.4.
U＝42.27×I0.4
According to the calculation of the formula, under the serious fault working condition of machine end short circuit, the demagnetization initial voltage at two ends of the SiC resistor is about 1500V according to the calculation that the demagnetization initial current is 3 times of rated exciting current, and the technical requirement of DL/T583 is met. When the rated load of the unit is disconnected and de-magnetized, the de-magnetized initial voltage at two ends of the SiC resistor is about 966.5V and about 3.22 times of the rated exciting voltage according to the fact that the de-magnetized initial current is 1 time of the rated exciting current, and the technical requirement of DL/T583 is met. In order to match the combined demagnetization resistance characteristic with the original SiC resistance characteristic as much as possible, considering that the initial total current flowing through the demagnetization resistor at the first demagnetization working point is 3 times Ifn, and determining that the initial voltage Um1 at the two ends of the demagnetization resistor at the moment is 1500V; and determining that the initial total current flowing through the demagnetization resistor under the second demagnetization working condition is 1 time Ifn, and determining that the initial voltage Um2 at two ends of the demagnetization resistor is 966.5V at the moment.
R-0.38664 and C-1028.93 are obtained by simultaneous calculation. That is, the total resistance of the linear resistance elements is 0.38664ohm, which is about 3.22 times the thermal resistance of the rotor; the voltage across the zinc oxide nonlinear resistor when a current of 1A flows through the whole resistor was 1028.93V.
According to the embodiment, under the parameter configuration, if the field suppression of the jump field suppression switch under the no-load rated working condition of the unit occurs or the field suppression of the disconnection jump field suppression switch under the load rated working condition occurs, the linear resistor R still bears the field suppression energy consumption task, and the current flowing in the nonlinear resistor FR is very small; meanwhile, the linear resistor is easy to trigger and conduct, the field suppression voltage at two ends of the resistor is not high, and the purposes of reducing the current conversion burden of the field suppression switch and prolonging the service life of the switch are achieved. And when the initial current of the demagnetization reaches 3Ifn under the most serious fault working condition, the shunting action of the FR nonlinear resistor effectively controls the maximum reverse overvoltage value of the demagnetization to be not more than 5Ufn, and meanwhile, the conduction of the FR nonlinear resistor maintains the level of the demagnetization back pressure in the demagnetization process so as to ensure the rapidity of the demagnetization process.
Fig. 3 illustrates yet another embodiment of an exemplary combined field suppression resistor circuit diagram.
Referring to fig. 3, fig. 3 differs from fig. 2 in that: in fig. 2, a diode D1 is connected in series with the nonlinear resistor FR, and in fig. 3, a thyristor element S2 is connected in series with the nonlinear resistor FR. And the jumper is connected to the trigger terminals of both thyristor element S1 and thyristor element S2.
According to an example embodiment, FR is a ZnO nonlinear resistance because of the nonlinear resistance. The current-voltage characteristic is a distinct non-linear curve, and when the voltage across the current is low, the current flowing through the current is small, for example, less than 1mA, and the current is called leakage current. When the system works normally, the nonlinear resistor FR can flow small leakage current, and the influence on the self characteristic and the power consumption heating is not large. However, if the system is operating normally, the leakage current flowing through the nonlinear resistor FR is relatively significant (for example, greater than 10mA), which may affect its own nonlinear characteristics for a long time and also increase the power consumption and heat generation of the resistor itself.
According to some embodiments, in the design of the excitation system, if the system works normally (the excitation system outputs a normal sawtooth wave rectification voltage), the reverse value of the rectification voltage is small, and the leakage current at two ends of the nonlinear resistor FR is small, a diode can be connected in series with the diode to ensure the unidirectional conduction of the current when the excitation is deactivated; if the reverse value of the rectified voltage is large and the leakage current at the two ends of the nonlinear resistor FR is large (close to or larger than 10mA) when the system works normally (the excitation system outputs the normal rectified voltage), the thyristor is required to be connected with the thyristor in series, the FR loop is completely blocked when the system is conducted normally, and the system is conducted through the jumper when the system is de-energized.
Fig. 4 shows a combined demagnetization resistance current-voltage characteristic and SiC resistance current-voltage characteristic of an exemplary embodiment.
As shown in fig. 4, for the combined volt-ampere characteristic curve of the demagnetization resistor and the volt-ampere characteristic curve of the SiC resistor, the combined demagnetization resistor circuit provided by the present application has the combined demagnetization resistor better matched with the original SiC resistor characteristic in the full demagnetization current range.
It should be clearly understood that this application describes how to make and use particular examples, but the application is not limited to any details of these examples. Rather, these principles can be applied to many other embodiments based on the teachings of the present disclosure.
Furthermore, it should be noted that the above-mentioned figures are only schematic illustrations of the processes involved in the method according to exemplary embodiments of the present application, and are not intended to be limiting. It will be readily understood that the processes shown in the above figures are not intended to indicate or limit the chronological order of the processes. In addition, it is also readily understood that these processes may be performed synchronously or asynchronously, e.g., in multiple modules.
Exemplary embodiments of the present application are specifically illustrated and described above. It is to be understood that the application is not limited to the details of construction, arrangement, or method of implementation described herein; on the contrary, the intention is to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (14)
1. A combined field suppression resistor circuit, comprising a first branch circuit and a second branch circuit connected in parallel, wherein:
the first branch circuit comprises a linear resistor and a reverse thyristor which are connected in series, a second terminal of the linear resistor is electrically connected with a cathode end of the reverse thyristor, and an anode end of the reverse thyristor is electrically connected with a cathode end of a generator excitation winding;
the second branch circuit comprises a nonlinear resistor and a one-way switch which are connected in series, a second terminal of the nonlinear resistor is electrically connected with a cathode end of the one-way switch, and an anode end of the one-way switch is electrically connected with a cathode end of the generator excitation winding;
and the first terminal of the linear resistor is connected with the first terminal of the nonlinear resistor in parallel and is electrically connected with the positive terminal of the generator excitation winding.
2. The combined demagnetization resistor circuit of claim 1, wherein a relationship between an initial total current flowing through the demagnetization resistor and an initial voltage across the demagnetization resistor satisfies:
r is the total resistance value of the linear resistor, C is the overall resistance coefficient of the nonlinear resistor, beta is the nonlinear coefficient of the nonlinear resistor, and Im1Is the initial total current, U, flowing through the field suppression resistor under the first field suppression conditionm1Is the initial voltage, I, across the demagnetization resistor under the first demagnetization conditionm2Is the initial total current U flowing through the demagnetization resistor under the second demagnetization working conditionm2Under the second de-excitation working conditionThe initial voltage across the terminals is blocked.
3. The combined demagnetization resistance circuit according to claim 2, wherein:
the initial total current flowing through the field suppression resistor is generator exciting current which is generated by triggering the field suppression switch to trip and leading the field suppression resistor to be conducted, extinguishing an electric arc flowing through the field suppression switch and completely flowing through the field suppression resistor;
and the initial voltage at the two ends of the de-excitation resistor is the voltage at the two ends of the de-excitation resistor corresponding to the initial total current flowing through the de-excitation resistor.
4. The combined field suppression resistor circuit of claim 1, wherein a nominal configuration capacity of the linear resistor is determined as:
umfor instantaneous value of voltage i across said demagnetization resistor during demagnetization1For a field-suppression current flowing through the first branch circuit, t0Is the moment when the de-excitation resistor is conducted at the beginning of the de-excitation process, teAnd K is a margin coefficient at the moment of finishing the demagnetization process.
5. The combined de-excitation resistor circuit as claimed in claim 4, wherein the de-excitation process is completed at a de-excitation total current imA time less than 1% of the initial total current of the field suppression resistor.
6. The combined field suppression resistor circuit of claim 1, wherein a nominal configuration capacity of the nonlinear resistor is determined as:
i2is a field suppression current flowing through the second branch circuit.
7. The combined demagnetization resistor circuit of claim 1, further comprising:
and the jumper is electrically connected with the reverse thyristor and controls the reverse thyristor to be started.
8. The combined field suppression resistor circuit according to claim 7, wherein the unidirectional switch is a diode or a second triac.
9. The combined de-excitation resistor circuit as claimed in claim 8, wherein the jumper is electrically connected to the second triac to control the second triac to turn on.
10. The combined field suppression resistor circuit according to claim 1, wherein the linear resistor comprises a single linear resistor or a series-parallel combination of multiple linear resistors.
11. The combined field suppression resistor circuit according to claim 1, wherein the non-linear resistor comprises a single non-linear resistor or a series-parallel combination of multiple non-linear resistors.
12. The combined de-excitation resistor circuit as recited in claim 1, wherein the non-linear resistor is a zinc oxide resistor.
13. Excitation system, characterized in that it comprises a combined field suppression resistance circuit according to any of claims 1-12.
14. A generator set comprising an excitation system according to claim 13.
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