CN111463760A - Zero-sequence disturbance line selection protection system for neutral ungrounded substation and application thereof - Google Patents
Zero-sequence disturbance line selection protection system for neutral ungrounded substation and application thereof Download PDFInfo
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- CN111463760A CN111463760A CN202010192470.8A CN202010192470A CN111463760A CN 111463760 A CN111463760 A CN 111463760A CN 202010192470 A CN202010192470 A CN 202010192470A CN 111463760 A CN111463760 A CN 111463760A
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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
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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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
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/263—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of measured values
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Abstract
The invention discloses a zero sequence disturbance line selection protection system for a neutral ungrounded substation and application thereof.A primary equipment unit is used for changing the outgoing line topology of the substation into grounding through a grounding transformer and a line selection resistor after a single-phase grounding fault occurs in the substation, enhancing the zero sequence current signal of a fault loop by adjusting the resistance value and the input time of the line selection resistor, reducing the overvoltage level of a fault line, and judging the fault line by using the zero sequence signal; the primary equipment unit is connected with a secondary equipment unit, and the secondary equipment unit is used for judging fault occurrence, controlling switching of the primary equipment, calculating and reporting a line selection result. According to the invention, the zero sequence current signal of the fault loop is enhanced by using the grounding transformer and the line selection resistor which are put into a transient state, so that the fault line is judged quickly and accurately; by adjusting the resistance value and the input time of the line selection resistor, the line selection accuracy is improved, and the overvoltage level of a fault line is reduced; the operation is automatically quitted after the fault is removed, and the existing circuit topology of the power distribution network is not influenced.
Description
Technical Field
The invention belongs to the technical field of distribution equipment, and particularly relates to a zero-sequence disturbance line selection protection system for a neutral ungrounded substation and application thereof.
Background
The substation in the power distribution network of the power system generally uses the outgoing line form and the magnitude of the capacitance current when a single-phase earth fault occurs as the judgment standard for selecting the neutral point grounding mode. If the outgoing line of a certain transformer substation is mainly an overhead line, the capacitance current does not exceed 10A, and the neutral point is usually selected not to be grounded. The advantage of selecting the neutral point not to be grounded is that when a single-phase grounding fault occurs, the heat effect caused by the low grounding capacitance current can be borne by the insulation of each element of the power grid, and the single-phase grounding fault can still operate for 1-4 hours in a fault state.
However, with the development of power distribution networks, such a mode of operation with faults may increase the probability of occurrence of secondary risks such as arc grounding overvoltage or ferromagnetic resonance overvoltage due to multiple reignitions of the arc, and thus pose a challenge to personnel and equipment safety. In order to further improve the operation safety of the power distribution network, a fault line must be quickly and accurately judged, and the fault line must be isolated, so that the safe and stable live operation of a normal line is ensured. However, the transient state line selection device generally configured in the existing neutral point ungrounded system has low line selection accuracy, and the transient state signal has the most obvious signal characteristic only at the moment of fault occurrence, and once line selection fails, a fault line is difficult to select again, so that manual line pulling and line selection are widely used in the actual work of a transformer substation.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a zero sequence disturbance line selection protection system for a neutral ungrounded substation and an application thereof, aiming at the defects in the prior art, wherein a zero sequence current signal of a fault loop is enhanced by using a grounding transformer and a line selection resistor which are put into transient state after a single-phase grounding fault occurs, and a fault line is rapidly and accurately judged by using the zero sequence signal. And the line selection accuracy can be further improved and the overvoltage level of a fault line can be reduced by adjusting the resistance value and the input time of the line selection resistor. After the fault line selection process is finished, the line selection protection system automatically quits operation, and the existing circuit topology of the power distribution network is not influenced.
The invention adopts the following technical scheme:
a zero-sequence disturbance line selection protection system for a neutral ungrounded substation comprises a primary equipment unit, wherein the primary equipment unit is used for changing the outgoing line topology of the substation into grounding through a grounding transformer and a line selection resistor after a single-phase grounding fault occurs in the substation, enhancing a zero-sequence current signal of a fault loop by adjusting the resistance value and the input time of the line selection resistor, reducing the overvoltage level of a fault line, and judging the fault line by using the zero-sequence signal; the primary equipment unit is connected with a secondary equipment unit, and the secondary equipment unit is used for judging fault occurrence, controlling switching of the primary equipment, calculating and reporting a line selection result.
Specifically, the primary equipment unit comprises an isolation disconnecting link K1, the common end of the isolation disconnecting link K1 is connected with an output bus of a main transformer of a transformer substation, and the normally open end is connected with a grounding transformer T, a circuit breaker K2 and a line selection resistor R2 in series in sequence and then connected with a grounding body G.
Further, two ends of the series structure of the circuit breaker K2 and the line selection resistor R2 are provided with an arrester R1 in parallel.
Furthermore, the insulation level of the lightning arrester R1 is the same as the level of the bus voltage, the heat capacity is 50-500kJ, and the selection range of the direct current 1mA operating voltage is 30-50% of the instantaneous maximum value of the bus phase voltage.
Further, the circuit breaker K2 works in a normally open mode, the secondary equipment unit controls the circuit breaker to be closed and opened through a cable L O2, the insulation level of the circuit breaker K2 is the same as the bus voltage level, and the closing and breaking current capacity is larger than 2000A.
The secondary equipment unit comprises a line selection computer PB, wherein the line selection computer PB is connected with a transformer substation bus voltage sensor through a zero sequence voltage signal line L U0, is respectively connected with a zero sequence current sensor of an ith bus outgoing line through a zero sequence current signal line L Ii, and is i1, 2 … n, is connected with an isolation disconnecting link K1 control end through an isolation disconnecting link control cable L O1, is connected with a breaker K2 control end through a breaker control cable L O2, and is connected with an upper communication server in a transformer substation through a communication line L m.
Furthermore, the number n of the zero-sequence current signal lines L I1-L In is the same as the number of bus outgoing lines, and the isolation disconnecting link control cable L O1 and the breaker control cable L O2 both adopt multi-core cables.
Another technical scheme of the invention is that the zero-sequence disturbance line selection protection system for the neutral ungrounded substation is applied to an n-way outgoing line substation, and is respectively externally connected with a bus M, a superior communication server CM, a zero-sequence voltage transformer PT, an outgoing line Zi, a breaker Si and a zero-sequence current transformer CTi (i is 1,2 … n);
the bus M is provided with n outgoing lines Zi in total, each outgoing line Zi is respectively connected with the bus M through a breaker Si, each outgoing line Zi is respectively provided with a zero sequence current transformer CTi, and the bus is provided with a zero sequence voltage transformer PT;
the line selection computer PB is connected with a zero sequence voltage transformer PT through a zero sequence voltage signal line L U0, is connected with a zero sequence current transformer CTi corresponding to the outgoing line Zi through a zero sequence current signal line L Ii, and is connected with an upper communication server CM in the transformer substation through a communication line L m.
Further, when the outgoing line Zi has a ground fault, zero-sequence voltage measured on the zero-sequence voltage transformer PT rises, and when the zero-sequence voltage rises to 30% of phase voltage, a fault line selection process is started by a line selection computer PB; the breaker K2 is opened after being closed for 300-1000 ms, the closing-opening operation is repeated for 1-2 times after the interval of 200-1000 ms, and then the breaker K2 is closed until the fault is removed; or the circuit breaker K2 is closed continuously until the fault is removed, and is not opened during the fault is removed; during the closing period of the circuit breaker K2, the line selection computer PB repeatedly searches for a fault line Zi and reports a line selection result to an upper-level communication server CM in the transformer substation; after receiving the fault line selection result, the communication server CM controls the corresponding breaker S to open the brake and cuts off the fault line;
after the fault is removed, when the line selection computer PB detects that the voltage on the zero sequence voltage transformer PT is recovered to be normal, the circuit breaker K2 is disconnected, and the system is recovered to the neutral point ungrounded state to operate.
Furthermore, when the circuit breaker K2 is closed, the grounding transformer T and the line selection resistor R2 are connected to a fault loop, resistive current is additionally introduced into the fault line Zi, the magnitude of the resistive current is approximately equal to the quotient of the resistances of the phase voltage and the line selection resistor R2, and the line selection computer PB judges the outgoing line with the ground fault by comparing the steady-state currents of the outgoing line zero sequence current transformers CTi.
Compared with the prior art, the invention has at least the following beneficial effects:
a zero-sequence disturbance line selection protection system for a neutral ungrounded substation can automatically input a grounding transformer T and a line selection resistor R2 by a line selection computer PB after a single-phase grounding fault occurs, enhance the zero-sequence signal of a fault loop, complete accurate fault line selection within a few seconds and limit the overvoltage level of a fault line. Compared with the existing transient state line selection device which is low in accuracy and is used for operators to refer to and the working mode of fault operation and manual line pulling and selection, the automatic operation level of the power grid can be greatly improved, and the operation safety of the power distribution network is improved.
Furthermore, the isolation switch K1 is used for putting in or cutting off the whole set of line selection protection system, and is convenient to overhaul and maintain.
Further, the lightning arrester R1 is used for lightning overvoltage protection of the whole set of line selection protection system, the thermal capacity of the lightning arrester R1 is 50-500kJ, and the lightning arrester R1 can not only resist lightning current, but also resist extra heat in multiple switching processes of the line selection resistor. The direct-current 1mA action voltage of the lightning arrester R1 is slightly higher than the setting value of zero-sequence voltage protection, so that the overvoltage protection function of the lightning arrester can not be triggered when the line selection protection system acts, and the lightning arrester works in a low impedance area only when higher overvoltage comes temporarily; the zero sequence voltage protection setting value is usually set to be 30% of the bus voltage, so that the direct current 1mA action voltage of the lightning arrester is set to be 30% -50% of the instantaneous maximum value of the bus phase voltage.
Furthermore, when a single-phase earth fault occurs and a fault line needs to be selected, and the circuit breaker K2 is closed, the circuit topology of the fault circuit is changed, resistive current is additionally introduced into the fault line, and the zero sequence current of the fault line is increased but the zero sequence current of the fault line is basically unchanged, so that the fault line is selected.
Furthermore, the isolating switch control cable L O1 and the breaker control cable L O2 are multicore cables, the isolating switch control cable L O1 and the breaker control cable L O2 can transmit opening and closing command signals and opening and closing state information feedback signals of the isolating switch K1 and the breaker K2 at the same time, the opening and closing state of the breaker K2 is accurately mastered by the line selection computer PB, the system stability can be improved, transient waveforms at the opening and closing moment of the breaker K2 are avoided, and the line selection accuracy is further improved.
The zero sequence disturbance line selection protection system for the transformer substation with the neutral point ungrounded is applied to the transformer substation with n outgoing lines, a line selection computer PB reports a line selection result to an upper-level communication server through a communication line L m, a comprehensive automation system in the transformer substation can cut off a fault line according to the result command, rapid fault isolation is achieved, and after the fault is cut off, a circuit breaker K2 is opened, and the system automatically recovers to the operation mode that the neutral point is ungrounded.
Furthermore, the switching time of the grounding transformer T and the line selection resistor R2 can be artificially controlled by the algorithm of the line selection computer PB, so that a transient signal at the fault occurrence time can be avoided, a fault line is calculated by using a steady signal, and the line selection accuracy is further improved; in the algorithm of the line selection computer PB, multiple switching at intervals of several seconds can be artificially set, and multiple line selection results are mutually verified, so that the line selection accuracy is further improved; when the circuit breaker K2 is closed, the line selection resistor R2 is connected in series in the fault branch circuit, and can limit the electric arc from reigniting for many times, thereby limiting the arc grounding overvoltage or the ferromagnetic resonance overvoltage.
Furthermore, when the circuit breaker K2 is closed, the substation outgoing line topology is changed to be grounded through the grounding transformer T and the line selection resistor R2, the input of the line selection resistor R2 additionally introduces resistive current of tens of amperes to thousands of amperes to a fault line, and zero-sequence current of a non-fault line is basically unchanged, so that the signal-to-noise ratio of effective information of line selection is enhanced by tens of amperes to thousands of times.
In conclusion, after a single-phase earth fault occurs, the zero-sequence current signal of a fault loop is enhanced by using the earth transformer and the line selection resistor which are put into the transient state, and the fault line is judged quickly and accurately by using the zero-sequence signal. And the line selection accuracy can be further improved and the overvoltage level of a fault line can be reduced by adjusting the resistance value and the input time of the line selection resistor. After the fault is removed, the line selection protection system automatically quits operation, and the existing circuit topology of the power distribution network is not influenced.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic structural view of example 1;
fig. 3 is a schematic structural diagram of embodiment 2.
Detailed Description
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Referring to fig. 1, the zero sequence disturbance line selection protection system for the non-grounded neutral transformer substation of the present invention includes a primary equipment unit and a secondary equipment unit.
The transformer substation is connected with the secondary equipment unit through the primary equipment unit, the primary equipment unit is used for changing the outgoing line topology of the transformer substation into the grounding through the grounding transformer and the line selection resistor after the single-phase grounding fault occurs, the zero-sequence current signal of the fault loop is enhanced by adjusting the resistance value and the input time of the line selection resistor, the overvoltage level of the fault line is reduced, and the fault line is judged quickly and accurately by using the zero-sequence signal; the secondary equipment unit is used for judging fault occurrence, controlling switching of the primary equipment, calculating and reporting a line selection result; after the fault line selection process is finished, the line selection protection system automatically quits operation, and the existing circuit topology of the power distribution network is not influenced.
The primary equipment unit comprises an isolation disconnecting link K1, a grounding transformer T, a circuit breaker K2, a line selection resistor R2 and a lightning arrester R1.
The common end of the isolation disconnecting link K1 is connected with an output bus of a main transformer of a transformer substation, the normally open end is connected with a grounding body G after being sequentially connected with a grounding transformer T, a circuit breaker K2 and a line selection resistor R2 in series, and two ends of the series structure of the circuit breaker K2 and the line selection resistor R2 are provided with lightning arresters R1 in parallel.
The secondary equipment unit comprises a line selection computer PB, a zero-sequence voltage signal line L U0, n zero-sequence current signal lines L I1-L In, an isolation disconnecting link control cable L O1, a breaker control cable L O2 and a communication line L m.
The line selection computer PB is connected with a substation bus voltage sensor through a zero-sequence voltage signal line L U0, connected with a zero-sequence current sensor of an ith line of a bus through a zero-sequence current signal line L Ii (i is 1 and 2 … n), connected with a control end of an isolation switch K1 through an isolation switch control cable L O1, connected with a control end of a breaker K2 through a breaker control cable L O2, and connected with an upper-level communication server in a substation through a communication line L m.
Preferably, the isolation switch K1 is a three-phase switch, the insulation level of which is the same as the bus voltage level, and the opening and closing of which is controlled locally or by the secondary equipment unit through a control cable L O1.
Preferably, the capacity of the grounding transformer T is 5-50 kVA.
Preferably, the circuit breaker K2 operates in a normally open mode, and is controlled to be closed and opened by the secondary equipment unit through a cable L O2, the insulation level of the circuit breaker is the same as the bus voltage level, and the off and on current capacity is more than 2000A.
Preferably, the line selection resistor R2 is a stainless steel resistor with a resistance value of 5-300 omega.
Preferably, the insulation level of the lightning arrester R1 is the same as the bus voltage level, the heat capacity is 50-500kJ, the direct current 1mA operating voltage selection range is 30-50% of the instantaneous maximum value of the bus phase voltage, and the direct current 1mA operating voltage selection range is higher than the setting value of zero sequence voltage protection.
Preferably, the line selection computer PB is configured with signal input, output and communication interfaces corresponding to the cables, and a line selection algorithm with line selection resistors R2 put in at intervals or put in continuously is built in, so that digital-to-analog conversion and analysis of input voltage and current signals, switching of the autonomous control circuit breaker K2, and output and report line selection results can be realized.
Preferably, the zero-sequence voltage signal line L U0 and the zero-sequence current signal line L I1-L In are both 1-4 mm2The number n of the conducting wires, namely the zero-sequence current signal wires L I1-L In, is the same as the number of the bus outgoing lines, and the conducting wires are used for transmitting analog signals of voltage and current.
Preferably, the isolating switch control cable L O1 and the breaker control cable L O2 both use multi-core cables.
Preferably, the communication line L m is an ethernet line, an optical fiber communication line, or a serial communication line, and is used for reporting a line selection result to a superior communication server.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Referring to fig. 2, the zero-sequence disturbance line selection protection system for the neutral ungrounded substation is applied to an n-way outgoing line substation, which has 12 outgoing lines, and is externally connected with a bus M, a superior communication server CM, a zero-sequence voltage transformer PT, an outgoing line Zi, a breaker Si, and a zero-sequence current transformer CTi (i is 1,2 … 12), respectively.
Each outgoing line Zi is connected with a bus M through a breaker Si, each outgoing line Zi is provided with a zero sequence current transformer CTi, the bus M is provided with a zero sequence voltage transformer PT, a line selection computer PB is connected with the zero sequence voltage transformers PT through a zero sequence voltage signal line L U0, and is connected with the zero sequence current transformer CTi corresponding to the outgoing line Zi through a zero sequence current signal line L Ii (i is 1,2 … 12), and is connected with an upper level communication server CM in a transformer substation through a communication line L M.
The voltage class of the bus is 10kV, the capacity of the grounding transformer T is 5kVA, the breaking current capacity of the breaker K2 is 2000A, the resistance value of the line selection resistor R2 is 300 omega, the thermal capacity of the arrester R1 is 500kJ, the direct current 1mA operating voltage is 2.5kV, and the sections of the zero-sequence voltage signal line L U0 and the zero-sequence current signal line L Ii are 1mm2The isolation disconnecting link control cable L O1 and the breaker control cable L O2 are four-core cables, the communication line L m is a serial communication line, and the line selection computer PB is configured with a line selection algorithm that line selection resistors R2 are put in at intervals.
When an outgoing line Z6 has a ground fault, zero sequence voltage measured on a zero sequence voltage transformer PT rises, and when the zero sequence voltage rises to 30% of phase voltage, a fault line selection process is started by a line selection computer PB; the route selection computer PB commands the circuit breaker K2 to close 300ms before opening.
In 300ms, the grounding transformer T and the line selection resistor R2 are connected to a fault loop, a 20A resistive current is additionally introduced into the fault line Z6, while the zero-sequence currents of other lines are basically unchanged, the line selection computer PB finds that the zero-sequence current transformer CT6 corresponding to the outgoing line Z6 is obviously larger than other outgoing lines by comparing the magnitudes of the steady-state currents of the zero-sequence current transformers CT1 to CT12, and judges that the outgoing line Z6 has a ground fault.
After 200ms, the line selection computer PB commands the breaker K2 to close again and then open after 300ms, the steps are repeated, and if the result is that the line Z6 is judged to have the ground fault, the line selection result is reported to an upper communication server CM in the transformer substation.
If the fault lines judged twice by the line selection computer PB are inconsistent due to some reason, the circuit breaker K2 is commanded to close again for 300ms and then is disconnected, a third line selection judgment is performed, the same result obtained twice in the third time is taken as a final fault line selection result, and the final fault line selection result is reported to the communication server CM.
After the line selection process is completed, the circuit breaker K2 is commanded to close again, and the line selection resistor R2 is put into use to limit the overvoltage level of the fault line. After receiving the fault line selection result, the communication server CM may directly control the corresponding breaker S6 to open the brake, cut off the fault line, or notify the staff to perform subsequent processing.
After the fault is removed, the line selection computer PB detects that the voltage on the zero sequence voltage transformer PT is recovered to be normal, the circuit breaker K2 is commanded to be disconnected, and the system is recovered to the neutral point ungrounded state to operate.
In the normal working or fault line selection process of the system, the leakage current is very small due to very low voltage at two ends of the arrester R1, the arrester R1 works in a high-resistance state, and the circuit topology can be ignored.
If the bus M is struck by lightning, under the action of lightning overvoltage, the lightning arrester R1 works in a low-resistance area with nonlinear characteristics, lightning impulse current is conducted, the lightning overvoltage at two ends of the lightning arrester R1 is limited, and a line selection system and other devices of a transformer substation are protected.
As can be seen from embodiment 1, after a single-phase ground fault occurs, the line selection computer PB switches in the line selection resistor R2 for multiple times, so that a resistive current of 20A is additionally introduced to the fault line, and the signal-to-noise ratio of effective information of line selection is improved; the investment time is 300ms each time, transient signals are avoided, and the line selection results are mutually verified after multiple switching and line selection, so that the accurate and reliable line selection results are ensured by the technical measures. After the line selection completion result is reported, the line selection resistor R2 is kept to be put into use, and the overvoltage level of the fault line is limited.
Example 2
Referring to fig. 3, the substation has 8 outgoing lines, the connection mode is the same as that of embodiment 1, the grade of the bus voltage is 35kV, the capacity of the grounding transformer T is 50kVA, the breaking current capacity of the circuit breaker K2 is 10kA, the resistance value of the line selection resistor R2 is 5 Ω, the thermal capacity of the lightning arrester R1 is 50kJ, the action voltage of the direct current 1mA is 9kV, and the cross sections of the zero-sequence voltage signal line L U0 and the zero-sequence current signal line L Ii are 4mm2The isolation disconnecting link control cable L O1 and the breaker control cable L O2 are six-core cables, the communication line L m is an ethernet line, and the line selection computer PB configures a line selection algorithm for the continuous input of the line selection resistor R2.
When the outgoing line Z6 has a ground fault, the zero sequence voltage measured on the zero sequence voltage transformer PT rises, and when the zero sequence voltage rises to 30% of the phase voltage, the line selection computer PB starts a fault line selection process.
The line selection computer PB instructs the circuit breaker K2 to close, the grounding transformer T and the line selection resistor R2 are connected into a fault loop, 4000A resistive current is additionally introduced into a fault line Z6, zero-sequence current of other lines is basically unchanged, the line selection computer PB finds that the zero-sequence current transformer CT6 corresponding to the outgoing line Z6 is obviously larger than other outgoing lines by comparing the magnitude of steady-state current of the zero-sequence current transformers CT 1-CT 8, judges that the outgoing line Z6 has a grounding fault, and reports a line selection result to a superior communication server CM in a transformer substation.
And after receiving the fault line selection result, the communication server CM directly controls the corresponding breaker S6 to open the brake, cut off the fault line or inform the staff of carrying out subsequent processing. After the fault is removed, the line selection computer PB detects that the voltage on the zero sequence voltage transformer PT is recovered to be normal, the circuit breaker K2 is commanded to be disconnected, and the system is recovered to the neutral point ungrounded state to operate.
If the line selection resistor R2 is connected in series, the arc reignition possibly occurs at the fault point, and the generated arc grounding overvoltage can reach 4 times of normal voltage; or ferromagnetic resonance is generated, and the voltage transformer and the lightning arrester in the system are easily burnt out.
After the circuit breaker K2 is closed, the line selection resistor R2 is connected in series in the faulty branch, greatly limiting the overvoltage level. In the process, because the resistance value of the line selection resistor R2 is small, the introduced zero-sequence current is large, zero-sequence protection in the fault outgoing line Z6 can be triggered, the breaker S6 is directly disconnected, other outgoing lines are recovered to be normal, if the line selection computer PB detects that the voltage on the zero-sequence voltage transformer PT is automatically recovered to be normal, the breaker K2 is commanded to be disconnected, and the system is recovered to the neutral point ungrounded state to operate.
It can be seen from embodiment 2 that, after a single-phase ground fault occurs, the line selection computer PB additionally introduces 4000A of resistive current to the fault line through the input line selection resistor R2, and since the current value is large, it is possible to directly trigger zero-sequence protection of the fault outgoing line, thereby realizing rapid fault isolation. If the zero sequence protection is not triggered, the signal-to-noise ratio of effective line selection information is also improved thousands of times, and an accurate and reliable line selection result is ensured. After the fault occurs, the line selection resistor R2 is continuously switched on, and the overvoltage level of the fault line is limited.
In summary, according to the zero-sequence disturbance line selection protection system for the non-grounded neutral transformer substation and the application thereof, after a single-phase ground fault occurs, the zero-sequence current signal of a fault loop is enhanced by using the grounding transformer and the line selection resistor which are put into transient state, and the fault line is judged quickly and accurately by using the zero-sequence signal. And the line selection accuracy can be further improved and the overvoltage level of a fault line can be reduced by adjusting the resistance value and the input time of the line selection resistor. After the fault line selection process is finished, the line selection protection system automatically quits operation, and the existing circuit topology of the power distribution network is not influenced.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A zero-sequence disturbance line selection protection system for a neutral point ungrounded substation is characterized by comprising a primary equipment unit, wherein the primary equipment unit is used for changing the outgoing line topology of the substation into grounding through a grounding transformer and a line selection resistor after a single-phase grounding fault occurs in the substation, enhancing a zero-sequence current signal of a fault loop by adjusting the resistance value and the input time of the line selection resistor, reducing the overvoltage level of a fault line, and judging the fault line by using the zero-sequence signal; the primary equipment unit is connected with a secondary equipment unit, and the secondary equipment unit is used for judging fault occurrence, controlling switching of the primary equipment, calculating and reporting a line selection result.
2. The zero-sequence disturbance route selection protection system for the neutral ungrounded substation according to claim 1, wherein the primary equipment unit comprises an isolation switch K1, a common end of the isolation switch K1 is connected with an output bus of a main transformer of the substation, and a normally open end is connected with a grounding body G after being sequentially connected with a grounding transformer T, a circuit breaker K2 and a route selection resistor R2 in series.
3. The zero-sequence disturbance line selection protection system for the neutral ungrounded substation according to claim 2, characterized in that two ends of a series structure of a circuit breaker K2 and a line selection resistor R2 are provided with a lightning arrester R1 in parallel.
4. The zero-sequence disturbance line selection protection system for the neutral ungrounded substation according to claim 3, characterized in that the insulation level of the lightning arrester R1 is the same as the bus voltage level, the heat capacity is 50-500kJ, and the direct current 1mA operating voltage selection range is 30% -50% of the instantaneous maximum value of the bus phase voltage.
5. The zero-sequence disturbance route selection protection system for the neutral ungrounded substation as claimed in claim 2, wherein a breaker K2 works in a normally open mode, the closing and the opening are controlled by a secondary equipment unit through a cable L O2, the insulation level of the breaker K2 is the same as the bus voltage level, and the closing and breaking current capacity is more than 2000A.
6. The zero-sequence disturbance line selection protection system for the non-grounded neutral substation of claim 1 is characterized in that the secondary equipment unit comprises a line selection computer PB, the line selection computer PB is connected with a substation bus voltage sensor through a zero-sequence voltage signal line L U0, is connected with a zero-sequence current sensor of an ith line outgoing line of a bus through a zero-sequence current signal line L Ii, i is 1 and 2 … n, is connected with a control end of an isolation switch K1 through an isolation switch control cable L O1, is connected with a control end of a breaker K2 through a breaker control cable L O2, and is connected with an upper communication server in the substation through a communication line L m.
7. The zero-sequence disturbance line selection protection system for the neutral ungrounded substation as claimed In claim 6, wherein the number n of zero-sequence current signal lines L I1-L In is the same as the number of bus outgoing lines, and multi-core cables are adopted for both the isolation switch control cable L O1 and the breaker control cable L O2.
8. The application of the zero-sequence disturbance line selection protection system for the neutral ungrounded substation in the n-way outgoing line substation according to claim 1 is characterized in that the zero-sequence disturbance line selection protection system is respectively externally connected with a bus M, a superior communication server CM, a zero-sequence voltage transformer PT, an outgoing line Zi, a circuit breaker Si and a zero-sequence current transformer CTi (i is 1,2 … n);
the bus M is provided with n outgoing lines Zi in total, each outgoing line Zi is respectively connected with the bus M through a breaker Si, each outgoing line Zi is respectively provided with a zero sequence current transformer CTi, and the bus is provided with a zero sequence voltage transformer PT;
the line selection computer PB is connected with a zero sequence voltage transformer PT through a zero sequence voltage signal line L U0, is connected with a zero sequence current transformer CTi corresponding to the outgoing line Zi through a zero sequence current signal line L Ii, and is connected with an upper communication server CM in the transformer substation through a communication line L m.
9. The use according to claim 8, characterized in that when the outgoing line Zi has a ground fault, the zero sequence voltage measured on the zero sequence voltage transformer PT rises, and when the zero sequence voltage rises to 30% of the phase voltage, the line selection computer PB starts the fault line selection process; the breaker K2 is opened after being closed for 300-1000 ms, the closing-opening operation is repeated for 1-2 times after the interval of 200-1000 ms, and then the breaker K2 is closed until the fault is removed; or the circuit breaker K2 is closed continuously until the fault is removed, and is not opened during the fault is removed; during the closing period of the circuit breaker K2, the line selection computer PB repeatedly searches for a fault line Zi and reports a line selection result to an upper-level communication server CM in the transformer substation; after receiving the fault line selection result, the communication server CM controls the corresponding breaker S to open the brake and cuts off the fault line;
after the fault is removed, when the line selection computer PB detects that the voltage on the zero sequence voltage transformer PT is recovered to be normal, the circuit breaker K2 is disconnected, and the system is recovered to the neutral point ungrounded state to operate.
10. The application of claim 9, wherein when the circuit breaker K2 is closed, the grounding transformer T and the line selection resistor R2 are connected to a fault loop, the fault line Zi additionally introduces a resistive current, the resistive current is equal to the quotient of the phase voltage and the resistance of the line selection resistor R2, and the line selection computer PB determines the outgoing line with the ground fault by comparing the steady-state currents of the outgoing line zero-sequence current transformers CTi.
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| CN114221319A (en) * | 2021-11-25 | 2022-03-22 | 江苏三得力电气有限公司 | Independent dynamic resistance control device and control method for system not directly connected to ground |
| CN116780488A (en) * | 2023-08-16 | 2023-09-19 | 山西迎润新能源有限公司 | New energy power station grounding protection system, method, electronic equipment and storage medium |
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| CN114221319A (en) * | 2021-11-25 | 2022-03-22 | 江苏三得力电气有限公司 | Independent dynamic resistance control device and control method for system not directly connected to ground |
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