CN112366746B - Method for preventing neutral line current of built low-voltage hydroelectric generating set from being too high - Google Patents
Method for preventing neutral line current of built low-voltage hydroelectric generating set from being too high Download PDFInfo
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- CN112366746B CN112366746B CN202011136866.7A CN202011136866A CN112366746B CN 112366746 B CN112366746 B CN 112366746B CN 202011136866 A CN202011136866 A CN 202011136866A CN 112366746 B CN112366746 B CN 112366746B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
Abstract
The invention discloses a method for preventing the neutral line current of a built low-voltage hydroelectric generating set from being excessive, which relates to the technical field of hydropower station power generation, and the method for installing a reactor on the neutral line well solves the problems of high neutral line current and serious heat generation of the low-voltage hydroelectric generating set; the built low-voltage hydroelectric generating set is ensured to be a neutral point direct grounding system, and the voltage deviation caused by the voltage rise of the outlet end of the generator is not more than 10% after the neutral point position occurs under the less adverse operation working condition. The specific scheme is as follows: the method comprises the following steps: and a reactor is connected in series between the neutral line outgoing line of the built low-voltage hydroelectric generating set and the 0.4kV side neutral line outgoing line sleeve of the step-up transformer. The built low-voltage water turbine generator set is still a neutral point direct grounding system, and the protection can be reliably disconnected when a single-phase grounding fault occurs, so that the generator is protected.
Description
Technical Field
The invention relates to the technical field of hydropower station power generation, in particular to a method for preventing the neutral line current of a built low-voltage hydroelectric generating set from being excessive.
Background
The low-pressure hydroelectric generating set has the advantages of simple structure, relatively low manufacturing cost and low requirements on factory building civil engineering, and is widely applied to rural small hydropower stations.
However, in the existing using equipment, the three-phase symmetry of the generator is often poor, and the neutral point potential U of the generator is shown N After the generator neutral point is connected to the low-voltage side neutral point of the step-up transformer through the cable line, the neutral line loop impedance is very low (X) because the distance between the generator neutral point and the transformer neutral point is very short (about ten meters), the section of the connecting neutral line cable wire is very large (the specification requires that the section of the neutral line wire is 1/3-1/2 greater than the section of the phase line, and no switch can be installed on the specified zero line, no fuse is installed, no open circuit is allowed) N Approximately 0) such that the current I is not large although the magnitude of the asymmetric electromotive force is not large N The values are very large, sometimes reaching hundreds of amperes. Two 500kW low-voltage sets shown in FIG. 1, the neutral line passes through two 185mm lines 2 The copper core cable is fed in parallel through a distance of about 15m to the low voltage side of the transformer and the neutral current reaches about 650A after commissioning. The thermal effect of the large neutral line current causes severe heating at the low-voltage side neutral line sleeve of the transformer, at the zero line busbar of the generator control screen and at the whole grounding foundation, a burnt odor can be smelled far away, and the parts feel very hot by touching with hands after power failure, so that owners are not dared to run. This problem is encountered in many power stations for synergistic capacity expansion using such low-pressure units, and help articles for power stations are also frequently found on the net.
Many people consider that the unbalance is caused by harmonic waves and actually exists, and a series of adverse reactions caused by the neutral line current thermal effect can be eliminated only by not connecting a generator neutral line with a low-voltage side neutral point of a transformer, and even some domestic journal of small hydropower is published with papers on recommending a method for canceling the neutral line. The present invention illustrates that the elimination of the neutral line (zero line) for a low pressure hydro-generator is erroneous. The low-voltage set specified by national regulations after the neutral connection is canceled adopts a neutral point direct grounding system to become a neutral point ungrounded system, once a point grounding fault occurs on a lead-out wire, the phase voltage of a user terminal is theoretically changed into line voltage from the original phase voltage which is increased by ∈3 times, and large-area overvoltage damage is caused to all user household appliances in the same 0.4/0.23KV power supply area, thereby causing electric shock accidents of people and livestock. See fig. 5; if the load of the user terminal runs asymmetrically, three-phase current cannot be balanced through a neutral line, neutral point potential displacement occurs in the generator, so that three-phase voltage imbalance is caused, and the voltage of some phases is very low, so that the output of the electric equipment of the user terminal is seriously insufficient; some of the phase voltages rise very high above the rated voltage, potentially causing dangerous overvoltage injuries to the user, see fig. 4; when a single-phase grounding fault occurs in the system, the grounding current cannot form a loop through a neutral line, and the current protection can be refused to operate, so that the generator set cannot be effectively protected.
The three-phase balance of a plurality of low-voltage hydroelectric generating sets constructed at present is relative, and the three-phase imbalance is absolute; even if the three-phase unbalance degree of the machine set produced by a manufacturer reaches the requirement of less than 5%U N Even if a little higher three-phase unbalance is required to reach 1%U e The unbalanced voltage for the 0.4kV unit will also reach 4V. The main contradiction is that the connecting cable between the neutral point of the unit and the neutral point of the low-voltage side of the transformer has a large section of the lead because of a short distance, and the connecting DC resistance is found to be corresponding to 370mm from a cable manual 2 The cable is 0.043 ohm/km, the connection length is 15m, and the direct current resistance is only 0.00065 ohm; considering that the inductance of an alternating current loop is 0.4 ohm/km, the inductance of the same 15m length is 0.006 ohm, and the total reactance of the loop is 0.006 ohm when the direct current resistance is ignored according to an analysis method of electric equipment for the convenience and simplification of research problems. It is this connecting loop total reactance is too small, and according to ohm's law, the loop current is: i=u N /X N Approximately 4/0.006 approximately 700A. It can be seen that the main reason for the excessive neutral loop current is unbalanced voltage, and the neutral wire is short, large in section and too small in inductive reactance.
Disclosure of Invention
In order to solve the technical problems, the method for installing the reactor on the neutral line well solves the problems of high neutral line current and serious heat generation of the low-voltage water turbine generator set; the low-voltage hydroelectric generating set also maintains a neutral point direct grounding system, and also solves the problem that the voltage deviation caused by the voltage rise of the outlet end of the generator is not more than 10% after the neutral point positioning occurs under the unfavorable operating condition. The above problems; the electric calculation can be obtained theoretically, the actual manufacturing of the reactor is not complex, an iron core is provided with an opening (the unsaturation of a magnetic circuit is ensured), a coil is provided with a tapped reactor, the price of the engineering with the unsaturated iron core and five groups of tapped reactors is about 300 yuan, the volume is about 20cm high, the square is 15cm, the weight is about 3-4 kg, the reactor is directly arranged in a power generator bus to main transformer low-voltage side power supply screen, and the reactor is connected in series between a zero line bus and a transformer low-voltage side neutral point connecting cable, so that the technical difficulty is avoided.
The technical aim of the invention is realized by the following technical scheme:
a method for preventing the neutral line current of a built low-voltage hydroelectric generating set from being excessive comprises the following steps:
and a reactor is connected in series between the neutral line outgoing line of the built low-voltage hydroelectric generating set and the 0.4kV side neutral line outgoing line sleeve of the step-up transformer.
As a preferable mode, the reactance value determining method of the reactor includes the steps of:
s1: the reactor is connected in series into a circuit of the voltage hydroelectric generating set and is positioned between a neutral line outgoing line of the low-voltage hydroelectric generating set and a neutral line outgoing line sleeve at the 0.4kV side of the step-up transformer;
s2: starting up and boosting the power generator set, and connecting the power generator set with the power generator set to increase the load to the rated load;
s3: continuously measuring the temperature of a low-voltage side sleeve and a connecting cable head of the primary step-up transformer, a zero line busbar of a generator control screen is led out to the neutral point connecting cable head of the transformer, a low-voltage neutral point sleeve outgoing line and a neutral point busbar cable outgoing line of the generator screen until the temperature rises stably, acquiring a stable value interval, and judging whether the neutral line current is normal;
s4: when the neutral line current is abnormal, the ammeter is used for actually measuring the connection current led out from the neutral line busbar of the control panel of the generator to the neutral point of the transformer, and further confirmation is carried out;
s5: making neutral lineThe reactor ensures that the unbalanced voltage of the generator does not exceed 1% ue, and the unbalanced current of the neutral line does not exceed 1.5% of rated line current after the generator is connected in series with the neutral line reactor; when the phase load is in an asymmetric running state of 80%, after unbalanced voltage generated by the neutral line reactor is added to the phase voltage, the phase voltage deviation of the user side is not more than +/-10% ue; solving and calculating reactance value X of neutral line reactor N ；
S6: and (3) connecting the reactor obtained in the step (S5) into a circuit, and carrying out the step (S3) again until the neutral line current is normal.
As a preferable scheme, in the S3 process, when the neutral line current is in a normal interval, the temperature stabilizing value interval is 25-40 ℃.
As a preferable scheme, in the S4 process, the actual measurement method of the ammeter comprises the following steps: all neutral cables are clamped by a clamp ammeter to measure the current; under the condition that the clamp ammeter can not clamp all the neutral lead-out cables at one time, two clamp meters are used for clamping more than two cables respectively, and the actual current I of the neutral point is obtained by superposition of simultaneous readings N. The method comprises the steps of carrying out a first treatment on the surface of the Simultaneously and respectively measuring three line currents I by the same method x-x 。
As a preferable scheme, an opening is arranged in the middle of the iron core of the reactor. And the effect of the reactor is prevented from being influenced by the saturation of the iron core due to the large current of the reactor.
As a preferable scheme, the reactor sequentially comprises a reactor output end, a reactor coil tap socket, a reactor coil tap plug key board, a reactor unsaturated iron core and a reactor input end.
As a preferred solution, the reactor comprises 5 sets of taps. The resistance of the reactor can be finely adjusted, and the reactor is suitable for different current limiting requirements.
In summary, the invention has the following beneficial effects:
the low-voltage hydroelectric generating set adopts the reactor with the unsaturated reactor and the five groups of tap coils, so that the problem of serious heating caused by overlarge neutral line current at present of the low-voltage hydroelectric generating set is basically solved, and the neutral point displacement in the most unfavorable operation mode after the reactors are connected in series is also solved, wherein the outlet voltage deviation is not more than 10% Ue; the built low-voltage water turbine generator set is still a neutral point direct grounding system, and the protection can be reliably disconnected when a single-phase grounding fault occurs, so that the generator is protected; and the danger that the single-phase earth fault protection of the generator set becomes a neutral point ungrounded system due to the blind disconnection of the neutral line and the user side generates large-area overvoltage when the single-phase earth is grounded is avoided.
Drawings
Fig. 1 is an electrical main wiring diagram including a reactor in an embodiment of the invention;
fig. 2 is a schematic structural view of a reactor in an embodiment of the present invention;
fig. 3 is a diagram of an asymmetrical operating vector of a low voltage neutral line reactor in an embodiment of the invention;
FIG. 4 is a graph of the severely asymmetric operational vector of the low voltage neutral line reactor of the present invention;
fig. 5 is a diagram of the operational vectors of a neutral ungrounded system generating a single phase ground.
Detailed Description
The description and claims do not take the form of an element differentiated by name, but rather by functionality. As used throughout the specification and claims, the word "comprise" is an open-ended term, and thus should be interpreted to mean "include, but not limited to. By "substantially" is meant that within an acceptable error range, a person skilled in the art is able to solve the technical problem within a certain error range, substantially achieving the technical effect.
The terms of the directions of the present specification and the claims, such as up, down, left, right, etc., are used for further description, so that the present application is more convenient to understand, but are not limited to, and in different scenes, the terms of up, down, left, right, inside, outside, etc., are relative.
The present invention will be described in further detail with reference to the accompanying drawings.
Aiming at the problems that the excessive heating of the neutral line current of the existing low-voltage hydroelectric generating set is serious or even affects the operation seriously, the invention provides a method for solving the problems by adopting a series neutral line unsaturated reactor, and simultaneously solves the problems that when the asymmetric operation is less than 80% ie after the series reactor occurs, the voltage deviation of the generator terminal generated after the neutral point displacement is not more than 10% ue; because the neutral line reactor is adopted, the low-voltage water turbine generator set still keeps a neutral point direct grounding system (strictly speaking, a neutral point is grounded through a small impedance), and when single-phase grounding occurs, the large grounding current flowing between the grounding phase through the line grounding point and the neutral point can enable the phase overcurrent protection action to start tripping to protect the generator. The problem that when the generator is turned into a neutral point ungrounded system and single-phase grounding occurs due to the fact that the generator neutral line is disconnected, the grounding current cannot be effectively started to protect the tripping generator is avoided; meanwhile, the danger that once single-phase grounding occurs in a system with the neutral point of the generator not grounded, the phase voltage of the ungrounded phase rises to the phase voltage, so that a large-area user bears overvoltage is realized.
The invention is realized in the following way:
step one, wiring a hydropower station low-voltage hydroelectric generating set according to the figure 1;
step two, starting up and boosting, connecting the grid, and slowly carrying out load to the rated value;
step three, detecting the low-voltage side sleeve and the connecting cable head of the step-up transformer once every five minutes by using a gun type far infrared thermometer, leading out the zero line busbar of the generator control screen to the temperature of the connecting cable head of the transformer and recording, and particularly paying attention to the temperature of the leading-out wire of the low-voltage neutral point sleeve and the temperature of the cable leading-out wire of the neutral point busbar of the generator screen. This operation is continued for 2 to 3 hours until the temperature rise is stable and no longer increases. When the measured temperature is increased to 250-400 ℃ above the ambient temperature, the abnormal neutral line current can be judged, and the following measures are needed.
Step four, actually measuring the connecting current led out to the neutral point of the transformer by using a clamp ammeter to measure the zero line busbar of the generator control screen, further confirming, taking attention to the fact that all neutral line cables are clamped by using the clamp ammeter, if the clamp ammeter cannot clamp all the neutral line leading-out cables at one time, more than two cables can be respectively clamped by using two clamp ammeters, and simultaneously reading and superposing to obtain the actual neutral pointCurrent I N A third party; simultaneously and respectively measuring three line currents I by the same method x-x 。
Step five, designing and manufacturing a neutral line reactor according to the requirement that the three-phase unbalanced voltage of the generator is not more than 1% ue and the neutral line electric unbalanced current is not more than 1.5% of the rated line current after the generator is connected in series with the neutral line reactor, wherein the diagram is shown in fig. 2; calculating the resistance value X of the neutral line reactor according to two-condition simultaneous solution of ensuring that the phase voltage deviation of a user side is not more than +/-10% Ue after unbalanced voltage generated by the neutral line reactor is added to the phase voltage when the asymmetric running state of 80% of one-phase load occurs N . The neutral line reactor is manufactured in a professional transformer factory, and is arranged in a generator control screen and connected between a neutral line of a neutral line busbar and a neutral line cable outgoing line in series.
Step six, testing the temperature of the point by using a pistol type far infrared thermometer on site after operation, wherein the temperature is greatly reduced, and no obvious temperature rise is felt by hands; the clamp ammeter is used for testing the point current, the current is reduced to about 10A, and the problem is completely solved.
The invention further aims to provide a safe and reliable method which solves the problem that the operation is seriously affected by the overlarge neutral line current of the low-voltage hydroelectric generating set, and ensures that the voltage deviation of the machine end generated by neutral point displacement is not more than 10% ue in a less-favorable asymmetric operation state after the neutral point is connected with the reactor in series; because the reactor is connected in series on the neutral line, the generator is kept to be a neutral point direct grounding system, and the grounding loop current can be reliably started to protect and disconnect the generator set when single-phase grounding faults occur; the system also ensures that the generator becomes a neutral point ungrounded system because the neutral line is dismantled due to too large neutral line current, thereby avoiding the problems of serious personal injury and serious danger of damage to the overvoltage of a large area user and the damage of a large amount of overvoltage of household appliances and current protection refusal caused by the fact that the ungrounded phase is raised to line voltage when single-phase grounding faults occur.
The invention is a novel practical system of the small hydropower station low-voltage set, which is suitable for hydropower stations in the current practical situation of the low-voltage hydroelectric generating set, has the advantages of high reliability, high safety, high efficiency, energy conservation, environmental protection, high investment saving, extremely simple and convenient use and practical effect.
The inductance between the neutral line of the generator led out to the neutral line point sleeve at the low-voltage side of the main transformer is properly increased, and the inductance of a loop to be connected in series is calculated to be 0.4Ω -0.3Ω according to the unbalanced voltage of 1%ue, namely 4V, and the neutral line current (namely unbalanced current) is not more than 1% -1.5% of rated current, namely 9.1-13.5A; in the embodiment, a single-phase reactor with an unsaturated iron core of 0.22 omega is purchased at a transformer manufacturer, five groups of taps can be arranged on a reactor coil for ensuring a certain adjustment range of the reactor, and the reactor can be flexibly adjusted on site, as shown in the accompanying drawings 1 and 2;
the neutral line current immediately drops to ten amperes of current after the series reactor, the heating value is greatly reduced compared with the original value, and the ideal heating reduction effect can be obtained. However, after such engineering measures are adopted, it should be verified that an asymmetric operation of 80% ie of one phase occurs in a relatively unfavorable state, the product of the unbalanced neutral line current flowing through the neutral line and the impedance of the neutral line reactor is the neutral point displacement value Un', and the phase voltage deviation caused by the neutral point displacement generated in the asymmetric operation mode is considered to be not more than 10% ue of the national prescribed value; the requirement that the neutral reactor meet both conditions is a fundamental principle of determining the impedance of the neutral reactor. When the three phases of the generator run asymmetrically (such as one-phase open circuit), the unbalanced current passing through the windings of the neutral line reactor is the broken phase current (absolute value), and the neutral line reactor may be damaged; and the neutral point generated by the unbalanced current on the reactor may cause a phase voltage deviation greater than 10% ue, the generator circuit breaker should be tripped by the zero sequence current protection action installed at the generator neutral point.
Preferably, the reactor coil is provided with five groups of taps, and different taps are selected so that the reactor can be more suitable for units with different capacities and different unbalance degrees of three phases of the unit.
As the optimized reactor is provided with the unsaturated iron core, the situation that the current of the central point changes under various different symmetrical units and various asymmetrical operation conditions can be ensured, the open iron core ensures that the magnetic circuit is not saturated, so that the resistance of the reactor is ensured not to be influenced by the decrease of the saturated reactance value of the iron core along with the increase of the current, and the linearity of the reactance performance of the reactor is ensured.
As engineering practical application, the method can effectively solve the problem of overlarge neutral line current of a plurality of low-voltage units, so that the produced and installed low-voltage generator units can operate in parallel, and the phase voltage deviation can be ensured not to exceed +/-10 Ue when 80% asymmetric load is carried; however, in the actual process, as the neutral line reactor is arranged, the reactor inevitably generates neutral point displacement during asymmetric operation, the method can only normally operate when 80% asymmetric load is ensured, and overvoltage caused by the displacement of the neutral point during three-phase severe asymmetric (extremely asymmetric operation is one-phase open circuit) operation cannot be ensured, and at the moment, the generator set needs to be disconnected when the zero sequence current is matched for protecting the asymmetric load of more than 80% or the one-phase open circuit.
If the generator and the system are in grid-connected operation, the symmetry of the general power system is good, so that unbalanced current on a neutral line is small; however, if a large asymmetric operation mode occurs in the isolated power grid system, a large unbalanced current flows through the neutral line, and although the three-phase voltage unbalance degree can be ensured to be not more than +/-10% ue through the calculation, the unbalanced current is all required to pass through the unsaturated reactor, so that the lead section of the unsaturated reactor is required to be properly enlarged when the unsaturated reactor is manufactured, and the lead section of the winding coil of the reactor is selected by adopting the neutral line unbalance current not to be more than 15% -20% of rated current.
Further, when the three-phase unbalance degree exceeds 80% in the operation of an isolated power grid, unbalanced current of the three-phase unbalance degree can cause overload of a reactor coil to burn out, in order to solve the problem that the occurrence probability is not large but loss is caused, three current transformers configured at a neutral point of a generator can be connected into a zero-sequence current filter, zero-sequence overcurrent protection (or inverse time-limit zero-sequence overcurrent protection) is introduced, and when the asymmetry degree exceeds more than 80%, the three-phase unbalance degree acts to trip an outlet breaker of the generator, so that the safety of equipment is ensured.
It is particularly emphasized that the invention is a remedy for the low-voltage hydroelectric generating set with the truly overlarge neutral point current which is already produced and installed, and the forced requirement on symmetry in the manufacturing process of the low-voltage hydroelectric generating set cannot be relaxed, especially the three-phase serious unbalance of the motor itself caused by serious uneven air gap of a motor tooth slot and the like because the unit manufacturing enterprises cannot adopt larger iron core magnetic flux density and winding current density to cause the saturation of a magnetic circuit and serious heating of a winding for saving investment, or the production process is rough. The method of the invention cannot be excessively relied upon to reduce the requirement for three-phase symmetry of the generator.
The engineering measures for reducing the heating caused by the neutral line current are safe and reliable, and the implementation method is simple and easy to implement.
The method for reducing the neutral line current of the low-voltage set neutral line reactor can greatly reduce the neutral line current, thereby greatly reducing the extremely high additional temperature rise caused by the neutral line current thermal effect; the huge difficulty that the neutral line cannot operate due to the excessively high temperature is thoroughly solved.
In the method for reducing the neutral line current of the low-voltage set neutral line reactor, the neutral line current is not more than 1.5 percent of rated line current (the neutral point unbalanced current is not more than 5 percent of rated line current required by national standards), and the method is not more than 1.5 percent of rated line current and is superior to the national standards); in the case of a less asymmetrical operation with a phase-shift of 80% of the nominal load, the neutral point is displaced, so that the phase voltage offset caused by the neutral point displacement does not exceed the national standard of + -10% ue. When the three-phase asymmetric operation of the generator is greater than 80% of one phase, the neutral line reactor is possibly damaged by the overlarge unbalanced current passing through the neutral line reactor winding, and the phase voltage deviation caused by the neutral point displacement generated by the unbalanced current on the reactor is possibly greater than the national standard of +/-10% ue, the generator breaker should be tripped by utilizing the zero sequence current protection action installed at the neutral point of the generator. See fig. 1.
The present embodiment is only for explanation of the present invention and is not to be construed as limiting the present invention, and modifications to the present embodiment, which may not creatively contribute to the present invention as required by those skilled in the art after reading the present specification, are all protected by patent laws within the scope of claims of the present invention.
Claims (6)
1. A method for preventing an excessive current in a neutral line of a built low-voltage hydro-generator set, comprising the steps of:
a reactor is connected in series between a neutral line outgoing line of the built low-voltage hydroelectric generating set and a neutral line outgoing line sleeve at the 0.4kV side of the step-up transformer;
the reactance value determining method of the reactor comprises the following steps:
s1: the reactor is connected in series into a circuit of the voltage hydroelectric generating set and is positioned between a neutral line outgoing line of the low-voltage hydroelectric generating set and a neutral line outgoing line sleeve at the 0.4kV side of the step-up transformer;
s2: starting up and boosting the power generator set, and connecting the power generator set with the power generator set to increase the load to the rated load;
s3: continuously measuring the temperature of a low-voltage side sleeve and a connecting cable head of the primary step-up transformer, a zero line busbar of a generator control screen is led out to the neutral point connecting cable head of the transformer, a low-voltage neutral point sleeve outgoing line and a neutral point busbar cable outgoing line of the generator screen until the temperature rises stably, acquiring a stable value interval, and judging whether the neutral line current is normal;
s4: when the neutral line current is abnormal, the ammeter is used for actually measuring the connection current led out from the neutral line busbar of the control panel of the generator to the neutral point of the transformer, and further confirmation is carried out;
s5: manufacturing a neutral line reactor, so that the unbalanced voltage of the generator does not exceed 1% Ue, and the unbalanced current of the neutral line after being connected into the neutral line reactor in series does not exceed 1.5% of rated line current; when the phase load is in an asymmetric running state of 80%, after unbalanced voltage generated by the neutral line reactor is added to the phase voltage, the phase voltage deviation of the user side is not more than +/-10% ue; solving and calculating reactance value X of neutral line reactor N ；
S6: and (3) connecting the reactor obtained in the step (S5) into a circuit, and carrying out the step (S3) again until the neutral line current is normal.
2. The method for preventing excessive neutral line current of a built low-voltage hydro-generator set according to claim 1, wherein in the S3 process, when the neutral line current is in a normal range, the temperature stabilizing value range is 25-40 ℃.
3. The method for preventing the neutral line current of the built low-voltage hydroelectric generating set from being too high according to claim 1, wherein in the S4 process, the ammeter actual measurement method is as follows: all neutral cables are clamped by a clamp ammeter to measure the current; under the condition that the clamp ammeter can not clamp all the neutral lead-out cables at one time, two clamp meters are used for clamping more than two cables respectively, and the actual current I of the neutral point is obtained by superposition of simultaneous readings N The method comprises the steps of carrying out a first treatment on the surface of the Simultaneously and respectively measuring three line currents I by the same method x-x 。
4. A method of preventing excessive neutral line current in a built low voltage hydro-generator set as defined in claim 1, 2 or 3 wherein an opening is provided in the middle of the core of the reactor.
5. The method of claim 4, wherein the reactor comprises, in order, a reactor tap outlet, a reactor coil tap receptacle, a reactor coil tap key plate, a reactor unsaturated core, and a reactor inlet.
6. The method of preventing excessive neutral line current in an established low voltage hydro-generator set as defined by claim 5 wherein said reactor contains 5 sets of taps.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011136866.7A CN112366746B (en) | 2020-10-22 | 2020-10-22 | Method for preventing neutral line current of built low-voltage hydroelectric generating set from being too high |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011136866.7A CN112366746B (en) | 2020-10-22 | 2020-10-22 | Method for preventing neutral line current of built low-voltage hydroelectric generating set from being too high |
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| Publication Number | Publication Date |
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| CN112366746A CN112366746A (en) | 2021-02-12 |
| CN112366746B true CN112366746B (en) | 2023-07-21 |
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| CN202011136866.7A Active CN112366746B (en) | 2020-10-22 | 2020-10-22 | Method for preventing neutral line current of built low-voltage hydroelectric generating set from being too high |
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