CN210693452U - Neutral point grounding control device of medium-voltage power grid - Google Patents
Neutral point grounding control device of medium-voltage power grid Download PDFInfo
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- CN210693452U CN210693452U CN201920909311.8U CN201920909311U CN210693452U CN 210693452 U CN210693452 U CN 210693452U CN 201920909311 U CN201920909311 U CN 201920909311U CN 210693452 U CN210693452 U CN 210693452U
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Abstract
The utility model discloses a medium voltage electric network neutral point grounding control device, including bus voltage transformer, grounding transformer, circuit zero sequence current transformer and controller, bus voltage transformer is connected with generating line and controller, grounding transformer is connected with generating line and arc suppression coil, be provided with the neutral point current transformer and the neutral point voltage transformer that are connected with the controller between grounding transformer and the arc suppression coil, be provided with the shunt between neutral point voltage transformer and the arc suppression coil, the shunt is connected with the resistor through the switch that is connected with the controller, the controller is connected with at least two branch lines through circuit zero sequence current transformer, the branch line with the generating line is connected; this application has synthesized the advantage of two kinds of ground connection modes of neutral point resonance ground connection and resistance ground connection, has both kept the advantage that resistance ground connection can accurate route selection, can reduce the earth connection residual current again, restricts the arc light ground connection overvoltage to can be according to the different situation of short-term ground fault or permanent ground fault, select suitable working method, ensured circuit safe operation promptly, improved the reliability of power supply again.
Description
The technical field is as follows:
the utility model relates to a power transmission and transformation field especially relates to a neutral point grounding control device of middling pressure electric wire netting.
Background art:
the neutral point grounding mode of the urban power distribution network is a complex comprehensive problem and is related to power supply reliability, personal safety, equipment safety and the like. However, the existing neutral point grounding mode has the following problems that the overvoltage limitation of the arc suppression coil grounding mode is insufficient, the grounding fault circuit is difficult to detect, the capacity of the arc suppression coil cannot keep up with the change of a power grid, and the arc suppression coil is easily in an under-compensated state, so that the grounding fault residual current is increased; series resonance overvoltage which may occur when the wire is broken; the small resistance ground connection mode, the single-phase ground connection of system emergence is just tripped out rapidly, has an influence to the power supply reliability, joins in marriage net structure, and mutual confession ability, equipment and automation level require highly, specifically do:
the grounding mode of the arc suppression coil has the advantages and disadvantages that:
the scale of the urban power grid is larger and larger, and particularly, the capacitance and current of the system are greatly increased due to the large use of cables in a power distribution network. When single-phase earth fault occurs, the arc light cannot be self-extinguished due to large capacitance current, and the safe operation of a power system is seriously threatened. The mode that the neutral point is grounded through the arc suppression coil is adopted, the inductive current of the arc suppression coil compensates the capacitance current of the power grid, the destructive effect of the grounding fault current is limited, and the grounding arc of the residual current is easy to extinguish. When the residual current zero crossing is extinguished, the initial speed and the amplitude of the fault phase recovery voltage can be reduced, the reignition of the grounding arc is avoided and the grounding arc is extinguished completely, and the probability of the fault caused by single-phase grounding is prevented or reduced. Effectively limits the destructive effect of ground current and electric arc electrodynamic force, thermal effect and the like on equipment and systems. The instantaneous earth fault disappears when the electric arc is extinguished, and the compensation power grid can recover normal operation when the fault disappears. In recent years, various automatic tracking arc suppression coil systems are developed and produced domestically, so that small residual current is ensured, and the arc suppression problem is basically solved.
Although the small current grounding can be realized by means of various principle methods, such as fundamental voltage, fundamental zero sequence current maximum principle, zero sequence current reactive power direction principle, zero sequence current active power direction principle, transient zero sequence voltage direction principle (first half-wave phase comparison principle), signal injection method, population ratio amplitude comparison method, harmonic current analysis method, residual current incremental method, wavelet analysis method and the like, the problem of difficult small current grounding line selection exists by using the arc suppression coil.
When a permanent single-phase earth fault exists in a10 kV part of the system, the value of a short-circuit current flowing through a fault line is close to the value of a capacitance current flowing through a normal line due to the fact that the capacitance current in the fault line is offset by the inductance current generated by the arc suppression coil, and therefore judgment is difficult. Although microcomputer type low-current grounding line selection devices are available in recent years, a general complete set of automatic compensation arc suppression coil device has a quick single-phase grounding line selection function at the same time. The line selection principle generally adopts the comprehensive modes of zero-sequence current, zero-sequence power direction, fifth harmonic, audio signal injection method and the like, but the line selection accuracy is mostly between 70% and 90%, the wrong selection probability is high, and the power supply reliability is influenced.
The advantages and disadvantages of the low resistance grounding mode are as follows:
the neutral point is grounded through a small resistor, so that overvoltage in the system can be effectively inhibited, and the system equipment is low in overvoltage bearing level and short in time. The insulation level of the equipment can be properly reduced, the service life of the system equipment is prolonged, and good economic benefits are achieved; in addition, the application of the zinc oxide arrester MOA with excellent volt-second characteristics is facilitated, and the lightning overvoltage level is reduced.
When the system has single-phase earth fault, the fault line is immediately cut off, and the relay protection selectivity is good. However, because the instantaneous single-phase earth fault cannot be distinguished from the permanent single-phase earth fault, the instantaneous single-phase earth fault is also tripped, and the power supply reliability is influenced. The grounding of a small resistor causes the instantaneous grounding which occupies the majority of the grounding to trip, causes power failure and seriously influences the grounding reliability. Meanwhile, by adopting the mode, the switch equipment with good performance, the standby power supply and other conditions need to be provided, otherwise, tripping and power failure are frequent, the power supply reliability is poor, and the maintenance workload of the switch is increased. For an overhead line power grid, this approach will create electromagnetic interference on the communication lines.
The utility model has the following contents:
the utility model discloses the technical problem that will solve is: the medium-voltage power grid neutral point grounding control device overcomes the defects of the prior art, and integrates the advantages of two grounding modes of neutral point resonance grounding and resistance grounding by connecting resistors in parallel at the arc suppression coil on the basis of the existing adoption of arc suppression coil grounding, thereby ensuring the safe operation of circuits and improving the reliability of power supply.
The technical scheme of the utility model is that: the utility model provides a medium voltage electric wire netting neutral point earthing control device, includes busbar potential transformer, grounding transformer, circuit zero sequence current transformer, busbar potential transformer and bus with the controller is connected, grounding transformer is connected with bus and arc suppression coil, be provided with between grounding transformer and the arc suppression coil with neutral point potential transformer and neutral point potential transformer that the controller is connected, the controller passes through circuit zero sequence current transformer and is connected with two at least branches, the branch line with the bus connection, neutral point potential transformer with be provided with the branch road between the arc suppression coil, the branch road is connected with the resistor through the switch of being connected with the controller.
Further, the arc suppression coil and the resistor are both grounded, the arc suppression coil is a capacitance-adjustable arc suppression coil or a turn-adjustable arc suppression coil, and the resistor is an adjustable resistor.
Further, the adjustable resistors are a medium resistance and a small resistance.
Further, the controller is connected with the power supply board, the switching value input board, the analog quantity signal board, the switching value output board and the communication port.
Furthermore, the grounding transformer is a Z-shaped grounding transformer, and a control switch is arranged between the grounding transformer and the bus.
The utility model has the advantages that:
1. the utility model discloses on the basis of current neutral point through arc suppression coil resonance ground connection mode, at parallelly connected median resistance of arc suppression coil and small value resistance, the advantage of two kinds of ground connection modes of neutral point resonance ground connection and resistance ground connection has both been kept resistance ground connection can accurate route selection, can reduce the ground point residual current again, restriction arc light ground connection overvoltage, and can be according to the different situation that is short-term ground connection fault or permanent ground connection fault, select suitable working method, the safe operation of circuit has been ensured promptly, the reliability of power supply has been improved again.
2. The utility model discloses when the restriction overvoltage, distinguish transient fault and permanent trouble, realize the ground connection route selection of permanent trouble, full play well resistance suppression overvoltage promptly, arc suppression coil reduces advantages such as fault point grounding current, arc extinguishing, has utilized the good advantage of relay protection selectivity that little resistance grounding mode had again, amputates permanent ground fault fast to improve power supply reliability, security, economic nature.
3. The utility model discloses the resistance effect of median resistance and small value resistance is the complete difference, and the purpose of parallelly connected median resistance is overvoltage level when in order to restrict system fault, and the small resistance that drops into at last is for accurately selecting lines, therefore resistance between them also is inequality.
4. The utility model discloses the main objective of small-value resistance can utilize the ground connection route selection of small-value resistance, accurately selects out the trouble circuit fast, guarantees the reliability of power supply.
5. The utility model discloses the parallelly connected median resistance of neutral point's main objective can suppress the system overvoltage, and further follow two aspects of restriction intermittent type nature arc ground connection overvoltage and restriction resonance overvoltage are suppressed.
Description of the drawings:
fig. 1 is a schematic structural diagram of a medium-voltage grid neutral point grounding control device.
Fig. 2 is an equivalent circuit diagram of a neutral point connected with a resistor in parallel with an arc suppression coil.
The specific implementation mode is as follows:
example (b): see fig. 1 and 2.
In fig. 1, T is a Z-type grounding transformer for providing a system neutral point; l is a turn-adjusting arc suppression coil and is used for compensating the capacitance current of the power grid; rnThe adjustable resistor is used for suppressing overvoltage and selecting a line due to ground fault; PT0The neutral point voltage transformer is used for acquiring neutral point displacement voltage; CT0The current transformer is a neutral point current transformer and is used for obtaining neutral point current; PT is a bus voltage transformer and is used for acquiring bus voltage and opening triangular voltage; CT1、CT2、…、CTnIs a zero sequence current transformer of the line.
A neutral point grounding control device of a medium-voltage power grid comprises a bus voltage transformer PT, a grounding transformer T and a line zero sequence current transformer CT, wherein the bus voltage transformer PT is connected with a bus and a controller, the grounding transformer T is connected with the bus and an arc suppression coil, and a neutral point current transformer CT connected with the controller is arranged between the grounding transformer T and the arc suppression coil0And neutral point potential transformer PT0The controller is connected with at least two branch lines through a circuit zero sequence current transformer CT, the branch lines are connected with the bus, a shunt circuit is arranged between the neutral point voltage transformer and the arc suppression coil, and the shunt circuit passes through a switch PT connected with the controller0Connected to a resistor.
Furthermore, the arc suppression coil and the resistor are both grounded, the arc suppression coil is a capacitance-adjustable arc suppression coil or a turn-adjustable arc suppression coil L, and the resistor is an adjustable resistor Rn。
Further, the adjustable resistor Rn has a medium resistance and a small resistance (R1 and R2 in fig. 2).
Further, the controller is connected with the power supply board, the switching value input board, the analog quantity signal board, the switching value output board and the communication port.
Furthermore, the grounding transformer T is a Z-shaped grounding transformer, and a control switch is arranged between the grounding transformer T and the bus.
The controller of the application is realized by a WZXC arc extinction voltage limiting grounding compensation and line selection device in the prior art, and an embedded PC104 industrial personal computer (PCM-3350) of Taiwan Mohua company is adopted as a main processor of a mainboard of the controller.
According to the method, when the 10KV power grid has a ground fault, the control device can accurately and reliably act according to the working principle and the working process of the scheme that the neutral point is connected with the resistors in parallel through the arc suppression coils; the automatic tracking compensation and grounding line selection are mainly used for arc suppression coils.
The automatic tracking compensation control of the arc suppression coil mainly realizes that the capacitance current of a system is measured in real time when a power grid normally operates, and correspondingly adjusts the gear of the arc suppression coil to ensure that the arc suppression coil always operates close to a resonance point.
When a permanent earth fault occurs in a10 KV power grid, a small resistor is put into the grounding line selection and is connected with an arc suppression coil in parallel, and zero sequence loop parameters are changed to perform fault line selection.
FIG. 2 shows: t is a grounding transformer; XL is a turn-adjusting arc suppression coil; r1 is median resistance; r2 is a small resistance; r3 is a damping resistor; K1-K4 are vacuum switches; s1 is an isolation knife switch; L1-Ln is 10KV outgoing line 1-n; XC 1-XCn is the capacitance reactance of the ground distributed capacitance of 10KV outgoing lines 1-n; r 1-rn is the insulation resistance distributed to the ground of 10KV outgoing lines 1-n; AHL 1-AHLn is a zero sequence current transformer of 10KV outgoing lines 1-n; AHR1 is a current transformer installed in the middle resistance R1 loop; AHR2 is a current transformer installed in the loop of the small value resistor R2; AHR3 is a current transformer installed in an arc suppression coil XL loop;
as shown in fig. 2, the automatic tracking arc suppression coil is connected to the neutral point on the high-voltage side of the grounding transformer in the same manner as the neutral point is connected to the arc suppression coil through the arc suppression coil resonance grounding, except that the medium resistance R1 and the small resistance R2 are connected in parallel to the arc suppression coil.
When the power grid normally operates, the arc suppression coil and the medium resistance are connected in parallel and normally switched, the arc suppression coil adopts a preset turn-adjusting type arc suppression coil, the controller measures the capacitance current of the system through the mutual inductor in real time, and correspondingly adjusts the gear position of the arc suppression coil to ensure that the arc suppression coil always operates close to a resonance point.
And when a single-phase earth fault occurs, the arc suppression coil does not need to be adjusted, and zero delay is compensated.
The function of compensating capacitive fault current and slowing down the rising speed of fault phase recovery voltage is exerted by the arc suppression coil, and overvoltage is suppressed by the parallel median resistor.
After a period of time, if single-phase grounding exists continuously, cutting off the parallel median resistance, fully playing the role of the arc suppression coil in compensating fault current, extinguishing the electric arc by the residual current smaller than 10A after compensation, and if the electric arc is extinguished and the grounding disappears, putting the parallel median resistance again, and recovering the normal operation of the system by using the damping function of the parallel median resistance; if the grounding does not disappear, the permanent grounding fault of the power grid is considered to occur, a small resistor is put into the power grid and is connected with the arc suppression coil in parallel, the zero sequence loop parameter is changed, and the fault line selection is carried out by utilizing a zero sequence protection or line selection device.
It is described in further detail as: the neutral point is connected with the middle resistor in parallel through the arc suppression coil under the normal working condition in a grounding mode of combining the arc suppression coil and the resistor. After the single-phase earth fault occurs, overvoltage is suppressed through the median resistance.
Starting timing from the occurrence of the single-phase earth fault, and if the system earth disappears within the time T1 (0.5s-2s), not switching the parallel resistor; if the fault does not disappear, the control device trips the vacuum switch K1 to cut off the median resistance, and the arc extinction coil compensates the median resistance, so that the purpose of arc extinction is achieved.
Starting timing from the removal of the median resistance, and in T2 (settable) time, if the system is grounded and disappears, closing a vacuum switch K1 by the control device, and putting the median resistance again to restore the system to the operating state of the median resistance with the arc suppression coils connected in parallel; if the ground is not lost and a permanent ground fault is considered to occur, the vacuum switch K2 is turned on and a small resistance is applied.
The timing is started from the input of the small resistor, and the small resistor grounding line selection after parallel connection is utilized within the time T3 (which can be set), because the zero sequence current signal difference between the grounding line and the normal line is quite obvious within the input time of the parallel resistor, the line selection device can accurately select the fault line aiming at metallic and low-resistance grounding faults, and the zero sequence protection device can also rapidly cut off the fault line. When T3 time is up, the small resistor must be cut off, and the control device trips the vacuum switch K2 to cut off the small resistor.
Starting timing from the removal of the small resistor, and in the T4 time (which can be set), if the ground fault disappears, putting the parallel median resistor again, and recovering the system to the operation mode that the arc suppression coil is connected with the median resistor in parallel; after the time T4 expires, if the ground fault does not disappear, the vacuum switch K2 is closed, and the small resistor is turned on for the second time.
And starting timing from the second time of putting the small resistor, and in the T5 time (which can be set), the small resistor after parallel connection is used for grounding and line selection again, so that a fault line can be accurately selected under the condition that the system is grounded with high impedance, and meanwhile, the zero sequence protection device can also rapidly cut off the fault line. When T5 time is up, the small resistor must be cut off, and the control device trips the vacuum switch K2 to cut off the small resistor.
Counting from the second cut of the small resistor, within time T6 (which may be set). If the ground fault disappears, the parallel median resistance is put into the system again, and the system is recovered to be the operation mode that the arc suppression coil is connected with the median resistance in parallel; if the ground fault does not disappear, the arc suppression coil operates and compensates independently all the time, an alarm signal is sent out at the same time, the parallel-connection median resistance is not put into use until the ground fault disappears, and the system is recovered to the operation mode that the arc suppression coil and the median resistance are connected in parallel.
Selection of median resistance:
when the arc is grounded, if R is takennWhen the neutral point displacement voltage is reduced to 4.32% in a half cycle, the system energy is almost completely leaked, so that the maximum voltage recovery value (not exceeding the phase voltage) on the phase with the ground fault is reduced, and the electric arc reignition does not cause high-amplitude overvoltage. For different systems, C0In a different sense, RnThe values of (A) are also different, and the upper limit is generally more than 100 omega, belonging to a high value range.
When the system is grounded in a single phase and the sound phase generates resonance, the generated resonance overvoltage multiple is
If order
When α is equal to 1, i.e. IR＝ICIn time, the resonant overvoltage of the healthy phase can be limited to below 2.8p.u. When I isR>1.5ICSince the effect of suppressing the resonance overvoltage is not obvious, I can be selectedRHas a value of (1-1.5) IC。
Selection of small-value resistance:
according to the IEEE standard, the standard of the fault current level of a low-resistance grounding mode is 100-1000A, according to the specific condition of China, the ground fault current level of 400-1000A is the low-resistance grounding mode, and the calculation principle of the neutral point resistance of the power grid is as follows
The maximum operating voltage of a10 kV power distribution network (mainly used for 10KV transmission lines in the application) is 12kV, then RnThe value range of (1) is 6.93-17.32 omega.
The power panel selects a C-35P switch power supply which mainly provides +5V, +12V and-12V working power supplies for the control device. The +24V power supply circuit required by the input and output of the switching value mainly adopts an S15-04 power supply transformer of Beijing Xin Chuang Square electronic Limited.
The analog signal input board is mainly used for acquiring required voltage and current signal quantities and finishing signal processing. The analog input is isolated from the site by precision PT and CT, and the digital input is isolated by optical coupler. The main collected voltage signals comprise bus PT voltage UBC, open triangle voltage, neutral point voltage U0 and arc suppression coil internal PT voltage. The mainly acquired current signals comprise zero sequence CT current of each outgoing line loop of 10KV, neutral point current I0, current IR1 in a middle resistance R1 loop, current IR2 in a small resistance R2 loop, current IXL in an arc suppression coil XL loop and the like.
The adopted voltage transformer and current transformer are both of Beijing innovative four-side electronics Limited company, the model of the voltage transformer is TV1013-1, and the model of the current transformer is TA 1016-2.
The analog signal to digital signal conversion chip is MAX125 chip of Meixin corporation.
The switching value input signals mainly collected by the switching value input plate are as follows: a median resistance loop switch K1 potential dividing auxiliary contact and a median resistance loop switch K1 potential closing auxiliary contact; a small value resistance loop switch K2 potential dividing auxiliary contact and a small value resistance loop switch K2 potential closing auxiliary contact; the damping resistance loop switch K4 is divided into an auxiliary contact and a damping resistance loop switch K4 is closed; auxiliary contacts for arc suppression coil gear signals and the like.
The +24V power supply required by the switching value input board and the switching value output board mainly adopts an S15-04 power transformer of Beijing New quad electronics Limited. The alternating current 220V power supply is directly changed into a 24V power supply, and finally the power supply is changed into a stable +24V direct current power supply for the switching value output relay through the filter circuit, the decoupling circuit and the rectifying circuit. The independent power supply loop is adopted to improve the power supply reliability and the anti-interference capability of the line selection device and ensure the reliable action of the relay when the vacuum switches connected in parallel are switched.
The switching value output signals mainly controlled by the switching value output board are as follows: a medium resistance loop switch K1 is opened, and a medium resistance loop switch K1 is closed; tripping off the small-value resistance loop switch K2 and closing the small-value resistance loop switch K2; a tripping damping resistance loop switch K4 and a closing damping resistance loop switch K4; controlling the arc suppression coil to shift up; controlling the arc suppression coil to shift down; alarming after the ground fault occurs; alarm when the device is in failure, etc.
The WZXC arc extinction voltage limiting grounding compensation and line selection device mainboard adopts an embedded PC104 industrial personal computer (PCM-3350) of Taiwan Mohua company as a main processor.
The working power supply required by the mainboard is provided by the power panel; the switching value input state is obtained from a switching value input board; controlling the action of each switch through a switching value output plate; the analog input board and an 80C196 singlechip are used for completing data sampling, data processing and the like together; the communication with the comprehensive automatic background is realized through a serial port; the device is provided with two serial interfaces of RS232 and RS232/485/422, and can be used for interfacing with telemechanical and comprehensive automatic equipment to remotely transmit data or remotely control.
The hardware is manufactured in a factory modularization mode and is connected through a fixed interface during installation.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent changes and modifications made by the technical spirit of the present invention to the above embodiments still fall within the scope of the technical solution of the present invention.
Claims (2)
1. The utility model provides a neutral point grounding control device of medium voltage electric network, includes busbar voltage transformer, grounding transformer, circuit zero sequence current transformer, characterized by: the bus voltage transformer is connected with a bus and a controller, the grounding transformer is connected with the bus and an arc suppression coil, a neutral point current transformer and a neutral point voltage transformer which are connected with the controller are arranged between the grounding transformer and the arc suppression coil, the controller is connected with at least two branch lines through a line zero sequence current transformer, the branch lines are connected with the bus, a shunt circuit is arranged between the neutral point voltage transformer and the arc suppression coil, and the shunt circuit is connected with a resistor through a switch connected with the controller;
the arc suppression coil and the resistor are both grounded, the arc suppression coil is a capacitance-adjustable arc suppression coil or a turn-adjustable arc suppression coil, and the resistor is an adjustable resistor;
the adjustable resistor is a medium value resistor and a small value resistor; AHR1 is a current transformer installed in the middle resistance R1 loop; AHR2 is a current transformer installed in the loop of the small value resistor R2; AHR3 is a current transformer installed in an arc suppression coil XL loop;
the controller is connected with the power panel, the switching value input panel, the analog quantity signal panel, the switching value output panel and the communication port.
2. A medium voltage network neutral grounding control apparatus as claimed in claim 1, wherein: the grounding transformer is a Z-shaped grounding transformer, and a control switch is arranged between the grounding transformer and the bus.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201920909311.8U CN210693452U (en) | 2019-06-17 | 2019-06-17 | Neutral point grounding control device of medium-voltage power grid |
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| CN201920909311.8U CN210693452U (en) | 2019-06-17 | 2019-06-17 | Neutral point grounding control device of medium-voltage power grid |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111614116A (en) * | 2020-06-18 | 2020-09-01 | 南方电网科学研究院有限责任公司 | Grounding method and device for flexible DC system |
| CN112103934A (en) * | 2020-08-19 | 2020-12-18 | 许继电气股份有限公司 | Resistor switching device and method in low-current line selection parallel connection |
| CN112165077A (en) * | 2020-10-29 | 2021-01-01 | 国网北京市电力公司 | Grounding device of microgrid, control method thereof, control device and grounding system |
-
2019
- 2019-06-17 CN CN201920909311.8U patent/CN210693452U/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111614116A (en) * | 2020-06-18 | 2020-09-01 | 南方电网科学研究院有限责任公司 | Grounding method and device for flexible DC system |
| CN112103934A (en) * | 2020-08-19 | 2020-12-18 | 许继电气股份有限公司 | Resistor switching device and method in low-current line selection parallel connection |
| CN112165077A (en) * | 2020-10-29 | 2021-01-01 | 国网北京市电力公司 | Grounding device of microgrid, control method thereof, control device and grounding system |
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