CN220190473U

CN220190473U - Novel capacitor series compensation device

Info

Publication number: CN220190473U
Application number: CN202321687239.1U
Authority: CN
Inventors: 齐进
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-06-29
Filing date: 2023-06-29
Publication date: 2023-12-15
Anticipated expiration: 2033-06-29

Abstract

The utility model relates to the field of voltage quality control of a transmission network and a distribution network, in particular to a novel capacitor series compensation device, which is connected with a switching operation switch, a power supply and sensing unit, an overvoltage protection unit, a capacitor bank C and a controller on a transmission line and a distribution line. Compared with the traditional capacitor series compensation device, the utility model innovates the overvoltage protection method of the capacitor bank, and adopts the autotransformer BK and the bypass breaker CB to replace the traditional discharge gap, zinc oxide voltage limiter, discharge damping equipment, power electronic switch or quick breaker. In addition, the third winding N3 of the autotransformer BK is used as a discharging coil of the voltage transformer and the capacitor bank, and is used for monitoring the internal fault of the capacitor bank in the normal working state of the power grid, limiting the discharging current of the capacitor bank and inhibiting the high-frequency oscillation of the capacitor bank when the bypass circuit breaker CB is switched on in the series compensation load side short circuit state.

Description

Novel capacitor series compensation device

Technical Field

The utility model relates to the field of voltage quality control of power transmission networks and distribution networks, in particular to a novel capacitor series compensation device which is suitable for alternating current transmission and distribution networks with the voltage of 750kV or below.

Background

Due to the development of extra-high voltage transmission of a power system, a capacitor series compensation device is required to improve the transmission capacity and stability of a long transmission line; at present, a high-capacity step-down transformer with high short-circuit impedance is mostly adopted, so that voltage fluctuation of a next-stage power grid is large, and frequent adjustment and accompanying reactive power crossing of a main transformer on-load tap changer can be avoided by adopting capacitor series compensation; the distribution network feeder circuit with longer transmission distance also has the requirement of adopting a capacitor series compensation device to compensate the reactive voltage loss.

In the power system, the overvoltage protection system of the traditional high-voltage, extra-high-voltage or distribution network-level capacitor series compensation device is very complex. For example, CN109066714A, CN109066720A, CN203536971U, CN204271652U, CN104882881a and the like and national standard GB/T6115.2-2017 (protection device for series capacitor group of part 2 of series capacitor for power system) describe series compensation devices, and it is indicated that the overvoltage protection system generally includes a trigger conduction bypass gap, a discharge current limiting damping device, a zinc oxide voltage limiter, a bypass switch (fast switching device, contactor or thyristor assembly) and the like.

When a short circuit fault occurs at the load end of the series compensation line, the transient power frequency overvoltage which is several times of the normal operation voltage at the two ends of the series compensation capacitor bank is required to be limited, the duration of the power frequency overvoltage can reach several seconds, the capacity requirement on the zinc oxide voltage limiter MOV in the overvoltage protector is very high, and even if a plurality of groups of metal oxide valve plates are operated in parallel, the series compensation capacitor bank can only last for tens of milliseconds, so that a discharge gap and a quick closing breaker or a power electronic switch are also required to be simultaneously configured.

Because the resistance of the metal oxide valve plates in the zinc oxide voltage limiter MOV has the negative temperature coefficient characteristic, current sharing is very difficult when a plurality of groups of valve plates are connected in parallel, the consistency requirement of the plurality of groups of valve plates on the resistance characteristic of the valve plates is very high, so that the quality control of the MOV is difficult, and the manufacturing cost and the operation failure rate are very high. That is, even for short support times of tens of milliseconds, MOVs are not ideal mains frequency overvoltage limiters.

The discharge gap is severely ablated under the action of power frequency overvoltage, so that the operation and maintenance cost is increased; meanwhile, outdoor climate conditions can obviously influence the discharge characteristics of the discharge gap, so that the overvoltage protection characteristics of the discharge gap are unstable.

The quick closing circuit breaker used as the power frequency overvoltage backup protection is not a conventional product, and needs special manufacture, and the severe requirement on closing time leads to the reduction of the working reliability and stability of the circuit breaker. The use of power switches can replace the circuit breakers described above, but this in turn will lead to a significant increase in technical complexity and overall cost.

In a word, the cost of the series compensation device is greatly increased and the reliability of the series compensation device is reduced by a discharge gap, a zinc oxide voltage limiter MOV and a circuit breaker or a power electronic switch with rapid closing characteristics, and the popularization and application of the series compensation in a power system are seriously affected by high cost and high failure rate. Therefore, there is a need to innovate the conventional overvoltage protection method to greatly improve the reliability of the capacitor series compensation device and reduce the cost.

Disclosure of Invention

Aiming at the problems in the prior art, the utility model provides a novel capacitor series compensation device.

The technical scheme adopted for solving the technical problems is as follows: the novel capacitor series compensation device consists of a switching operation switch, a power supply and sensing unit, an overvoltage protection unit, a capacitor bank C and a controller, wherein the switching operation switch, the power supply and sensing unit, the overvoltage protection unit, the capacitor bank C and the controller are connected to an electric transmission and distribution line.

Specifically, the switching operation switch includes a first disconnecting switch GK1, a second switch GK2 and a third disconnecting switch GK3, and the second switch GK2 may be a disconnecting switch or a conventional circuit breaker.

Specifically, the power supply and sensing unit comprises a voltage transformer TV 1), a voltage measurement winding TV2 and a current transformer CT);

the overvoltage protection unit comprises an autotransformer BK and a bypass breaker CB, the autotransformer BK is a specially-made saturated reactor, the iron core structure of the autotransformer BK is a split-phase closed iron core, each phase comprises a first winding N1, a second winding N2 and a third winding N3 for measurement, the tail end of the first winding N1 is connected with the head end of the second winding N2, the head end of the first winding N1 and the head end of the second winding N2 are homonymous ends, and the head end of the first winding N1 and the tail end of the second winding N2 are respectively connected with an inlet end and an outlet end of a capacitor bank C;

the bypass circuit breaker CB is a conventional circuit breaker connected in parallel with the second winding N2

The voltage measurement winding TV2 is the third winding N3 of the autotransformer BK.

Specifically, the capacitor bank C is a three-phase capacitor.

Specifically, the controller may be an intelligent control unit or an analog control unit.

The novel capacitor series compensation device is in three states in the operation process;

first, when the power grid is in a normal operation state:

the first isolating switch GK1 and the third isolating switch GK3 are in a closed state, and the second switch GK2 and the bypass breaker CB are in a brake-separating state;

the voltage Uc at two ends of the capacitor bank is less than or equal to Un, and Un is the rated voltage of the capacitor bank;

under the action of Uc voltage, the autotransformer BK works in the I section of the curve and is in an unsaturated state, namely in a high-impedance state, and exciting currents in the first winding N1 and the second winding N2 flow through the autotransformer BK are smaller than 1.0A;

at this time, the capacitor bank C will realize the automatic compensation of the line voltage according to the change of the load current;

second, series compensation load side short circuit state:

once the load side of the series compensation device has short-circuit fault, the line current Is suddenly increased to lead Uc to be higher than the rated voltage Un of the capacitor bank, at the moment, the current i flowing through the autotransformer BK Is synchronously increased along with the increase of Uc, when i Is increased to IS, the autotransformer BK enters a saturation region and works in a section II of a curve, namely a low-impedance state, at the moment, the voltage at the two ends of the capacitor bank C Is not linearly increased any more, but Is slowly increased at a relatively gentle speed until the voltage approaches to a saturation voltage Up1 corresponding to the maximum short-circuit current Imax of the line;

to ensure the safety of the capacitor bank, upl here should be significantly below the limit voltage Ulim that the capacitor bank can withstand;

in the process, the controller rapidly judges whether a short circuit occurs at the series compensation load side by monitoring the current in the current transformer CT, if the current exceeds a preset threshold value, the controller controls the bypass breaker CB to switch on so as to bypass the second winding N2 of the autotransformer BK, at the moment, only the first winding N1 is in an excitation state, and the autotransformer BK is pushed out of saturation and works in the section III of the curve because the number of turns of the first winding N1 is far smaller than that of the second winding N2;

the bypass breaker CB can be adopted to reduce the requirement of short-circuit current thermal stability of the second winding N2 by times, and finer wires can be adopted to wind, so that the manufacturing cost of the autotransformer BK is greatly reduced;

when the bypass circuit breaker CB is switched on, the first winding N1 is adopted to damp the discharge current of the capacitor bank C so as to eliminate possible impact damage to the capacitor and the circuit breaker;

third, a serial repair state:

firstly, placing a bypass breaker CB in a closing state, then closing a second switch GK2, and then opening a first isolating switch GK1 and a third isolating switch GK3;

the series compensation device is withdrawn from operation, and the series compensation device can be overhauled and maintained after the ground wire is hung.

The utility model has the beneficial effects that:

the novel capacitor series compensation device adopts the autotransformer BK and the bypass breaker CB to realize the power frequency overvoltage protection at the two ends of the capacitor bank C. The no-load saturation characteristic of the large-capacity autotransformer which is easy to manufacture is adopted to replace an expensive and high-failure-rate discharge gap, a zinc oxide voltage limiter MOV, a damping device and a quick breaker or a power electronic switch, and meanwhile, an electromagnetic voltage transformer which is usually connected in parallel at two ends of a capacitor and used for protecting a discharge coil and unbalanced voltage is omitted. The wiring is greatly simplified, the number of components is reduced, the power frequency overvoltage protection cost of the series compensation device is obviously reduced, and the reliability of product operation is greatly improved.

Drawings

The utility model will be further described with reference to the drawings and examples.

FIG. 1 is a schematic wiring diagram of a novel capacitor series compensation device provided by the utility model;

fig. 2 is a schematic diagram of power frequency overvoltage protection characteristics of an autotransformer BK in the novel capacitor series compensation device provided by the utility model.

In the figure: 1. a switching operation switch; 11. a first disconnecting switch GK1; 12. a second switch GK2; 13. a third disconnecting switch GK3; 2. a power supply and sensing unit; 21. a voltage transformer TV1; 22. a voltage measurement winding TV2; 23. a current transformer CT; 3. an overvoltage protection unit; 31. an autotransformer BK; 32. a bypass breaker CB; 4. a capacitor bank C; 5. and a controller.

Detailed Description

The utility model is further described in connection with the following detailed description in order to make the technical means, the creation characteristics, the achievement of the purpose and the effect of the utility model easy to understand.

As shown in fig. 1 and 2, the novel capacitor series compensation device of the utility model is composed of a switching operation switch 1, a power supply and sensing unit 2, an overvoltage protection unit 3, a capacitor bank C4 and a controller 5, wherein the switching operation switch 1, the power supply and sensing unit 2, the overvoltage protection unit 3 and the capacitor bank C4 are connected to an electric transmission and distribution line.

Specifically, the switching operation switch 1 includes a first disconnecting switch GK111, a second switch GK212, and a third disconnecting switch GK313, and the second switch GK212 may be a disconnecting switch or a conventional circuit breaker.

Specifically, the power supply and sensing unit 2 includes a voltage transformer TV121, a voltage measurement winding TV222, and a current transformer CT23;

the overvoltage protection unit 3 comprises an autotransformer BK31 and a bypass breaker CB32, the autotransformer BK31 is a specially-made saturated reactor, the iron core structure of the autotransformer is a split-phase closed iron core, each phase comprises a first winding N1, a second winding N2 and a third winding N3 for measurement, the tail end of the first winding N1 is connected with the head end of the second winding N2, the head end of the first winding N1 and the head end of the second winding N2 are homonymous ends, and the head end of the first winding N1 and the tail end of the second winding N2 are respectively connected with an inlet end and an outlet end of the capacitor bank C4;

the bypass circuit breaker CB32 is a conventional circuit breaker connected in parallel with the second winding N2

The voltage measurement winding TV222 is the third winding N3 of the autotransformer BK 31;

this winding can be used to monitor the voltage across the capacitor bank C4 during normal operation of the grid.

Specifically, the capacitor bank C4 is a three-phase capacitor;

when the capacitor bank 4 is put into operation, the bypass breaker CB32 is in a disconnected state, and the autotransformer BK31 is operated in a voltage transformer mode. When the series compensation line is short-circuited, after the power frequency overvoltage at the two ends of the capacitor bank C4 exceeds the saturation voltage of the autotransformer, the autotransformer works in a saturated reactance mode to limit the transient overvoltage at the two ends of the capacitor bank; after a preset time delay, the bypass breaker CB32 is switched on, and the short-circuit impedance of the autotransformer BK31 forms a current limiting reactor and a damping resistor to limit the discharge current of the capacitor and the high-frequency oscillation thereof.

Specifically, the controller 5 may be an intelligent control unit or an analog control unit.

The device adopts an autotransformer BK31 and a bypass breaker CB32 to realize the power frequency overvoltage protection at two ends of the capacitor bank C4. The autotransformer BK31 is composed of three windings N1, N2 and N3, wherein N1 and N2 are power frequency overvoltage protection windings, and N3 is a measurement winding for unbalanced voltage monitoring during internal faults of the capacitor. The bypass circuit breaker CB32 is a conventional circuit breaker, a quick circuit breaker is not needed, the quick circuit breaker is controlled by the controller 5, and the voltage transformer TV121 supplies power to the controller 5 and an operating mechanism of the bypass circuit breaker CB 32;

upl in fig. 2: the protection level is the maximum peak value of the power frequency voltage appearing at the two ends of the overvoltage protector during the fault of the power system;

ulim: limit peak value of transient overvoltage which can be born by two ends of the capacitor bank;

us: a saturation voltage starting value of the autotransformer when no-load;

is: saturated exciting current of the autotransformer when no load exists;

imax: a short-circuit fault current maximum value of a mounting point of the capacitor series compensation device;

i: normal operation without short circuit fault, no-load operation mode volt-ampere characteristic line segment of the autotransformer;

II: short circuit fault, saturation working mode volt-ampere characteristic line segment of autotransformer when no-load;

III: closing a bypass breaker, and shorting a voltage-ampere characteristic line segment of an autotransformer in a working mode;

p: the initial saturation point of the no-load excitation voltage of the autotransformer, OP is the V-A characteristic of the I section, namely the voltage transformer mode.

When the power grid is in a normal operation state:

the first disconnecting switch GK111 and the third disconnecting switch GK313 are in a closed state, and the second switch GK212 and the bypass breaker CB32 are in a disconnected state. The voltage Uc at two ends of the capacitor bank is less than or equal to Un, and Un is the rated voltage of the capacitor bank. Under the action of Uc voltage, the autotransformer BK31 works in the I section of the blue curve and is in an unsaturated state, namely in a high impedance state, and only small exciting current <10A flows through windings of the autotransformers BK31N1 and N2. At this time, the capacitor bank 4 will realize automatic compensation of the line voltage according to the change of the load current.

Series compensation load side short circuit state:

once the load side of the series compensation device has a short circuit fault, the line current increases sharply to cause Uc to be higher than the rated voltage Un of the capacitor bank 4, at this time, the current i flowing through the autotransformer BK31 also increases synchronously with the increase of Uc, when i increases to Is, the autotransformer BK31 enters a saturation region, and works in the section II of the curve in fig. 2, i.e. in a low impedance state, at this time, the voltage across the capacitor bank C4 does not increase linearly but increases slowly at a relatively gentle speed until approaching the saturation voltage Upl corresponding to the maximum short circuit current Imax of the line. To ensure the safety of the capacitor bank, upl should here be significantly below the limit voltage Ulim that the capacitor bank can withstand. In this process, the controller 5 rapidly determines whether a short circuit occurs on the series compensation load side by monitoring the current in the current transformer CT23, and if the current exceeds a preset threshold value, controls the bypass breaker CB32 to close to bypass the N2 winding of the autotransformer BK31, and only the N1 winding is in an excited state at this time, since the number of turns of the N1 winding is far smaller than that of the N2 winding, the autotransformer BK31 will push out of saturation, and works on the curve in fig. 2, i.e., the section III. The advantages of using bypass breaker CB32 are: the requirement of short-circuit current thermal stability of the N2 winding is reduced by times, and finer wires can be adopted for winding, so that the manufacturing cost of the autotransformer BK31 is greatly reduced. The advantages of using the N1 winding are that: when bypass circuit breaker CB32 is closed, the discharge current of capacitor bank C4 is damped to eliminate possible impact damage to the capacitor and circuit breaker.

String repair inspection state:

the operation steps are as follows: the bypass circuit breaker CB32 is put into a closed state, the second switch GK212 is then closed, and the first and third disconnectors GK111 and GK313 are then opened. So far, the series compensation device is out of operation, and the series compensation device can be overhauled and maintained after the ground wire is hung.

It can be seen that the use of autotransformer BK31 and bypass breaker CB32 achieves power frequency overvoltage protection across capacitor bank C4. The advantage is that the high-capacity autotransformer with high energy capacity, which is easier to manufacture, is used for replacing the expensive discharge gap, the zinc oxide voltage limiter MOV, the damping device and the quick breaker or the power electronic switch with the no-load saturation characteristic, and meanwhile, an electromagnetic voltage transformer which is usually connected in parallel at two ends of a capacitor and used for protecting a discharge coil and unbalanced voltage is omitted. The wiring is greatly simplified, the number of components is reduced, the power frequency overvoltage protection cost of the series compensation device is obviously reduced, and the reliability of product operation is greatly improved.

The foregoing has shown and described the basic principles, principal features and advantages of the utility model. It will be understood by those skilled in the art that the present utility model is not limited to the foregoing examples, and that the foregoing description and description are merely illustrative of the principles of this utility model, and various changes and modifications may be made without departing from the spirit and scope of the utility model, which is defined in the appended claims. The scope of the utility model is defined by the appended claims and equivalents thereof.

Claims

1. The novel capacitor series compensation device is characterized by comprising a switching operation switch (1), a power supply and sensing unit (2), an overvoltage protection unit (3), a capacitor bank C (4) and a controller (5), wherein the switching operation switch is connected to an electric transmission and distribution line.

2. The novel capacitor series compensation device of claim 1, wherein: the switching operation switch (1) comprises a first disconnecting switch GK1 (11), a second switch GK2 (12) and a third disconnecting switch GK3 (13), and the second switch GK2 (12) is a disconnecting switch or a conventional circuit breaker.

3. The novel capacitor series compensation device of claim 1, wherein: the power supply and sensing unit (2) comprises a voltage transformer TV1 (21), a voltage measurement winding TV2 (22) and a current transformer CT (23);

the overvoltage protection unit (3) comprises an autotransformer BK (31) and a bypass breaker CB (32), the autotransformer BK (31) is a specially-made saturated reactor, the iron core structure of the autotransformer BK is a split-phase closed iron core, each phase comprises a first winding N1, a second winding N2 and a third winding N3 for measurement, the tail end of the first winding N1 is connected with the head end of the second winding N2, the head end of the first winding N1 and the head end of the second winding N2 are homonymous ends, and the head end of the first winding N1 and the tail end of the second winding N2 are respectively connected with the wire inlet end and the wire outlet end of the capacitor bank C (4);

the bypass circuit breaker CB (32) is a conventional circuit breaker connected in parallel with the second winding N2

The voltage measurement winding TV2 (22) is the third winding N3 of the autotransformer BK (31).

4. The novel capacitor series compensation device of claim 1, wherein: the capacitor bank C (4) is a three-phase capacitor.

5. The novel capacitor series compensation device of claim 1, wherein: the controller (5) may be an intelligent control unit or an analog control unit.