CN115513913A - Line differential protection tripping method and system suitable for new energy access - Google Patents
Line differential protection tripping method and system suitable for new energy access Download PDFInfo
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- CN115513913A CN115513913A CN202211008181.3A CN202211008181A CN115513913A CN 115513913 A CN115513913 A CN 115513913A CN 202211008181 A CN202211008181 A CN 202211008181A CN 115513913 A CN115513913 A CN 115513913A
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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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
Abstract
The invention discloses a line differential protection tripping method and a system suitable for new energy access, which comprise the following steps: on the basis of the basic criterion of the current differential protection of the conventional line, the following supplementary criteria are added: the absolute value of the sum of the current vectors at two sides of the line differential protection is larger than k 1 The absolute value of the sum of the current vectors on both sides is greater than k 2 Absolute value of difference between two-side current vectors, sum of absolute values of two-side current vectors being less than k 3 Double secondary current rating, both side voltages being less than k 4 A multiple of a secondary voltage rating; k is a radical of 1 、k 2 、k 3 、k 4 The motion coefficient, the brake coefficient, the current coefficient and the voltage coefficient are respectively. The invention can effectively solve the problem that when new energy is accessed into a power grid through the flexible direct current converter station,when the grid-connected AC line has a fault, the operation sensitivity of the conventional line differential protection is insufficient.
Description
Technical Field
The invention belongs to the technical field of electric power systems, and relates to a line differential protection tripping method and system suitable for new energy access.
Background
Wind power, photovoltaic and other new energy enrichment areas are mostly far away from a load center, and the alternating current power grid is relatively weak and needs to be accessed from the tail end of the regional power grid through long-distance power transmission. The new energy has the characteristics of non-continuity, instability and the like, and is connected to a power grid in a large scale, so that the voltage stability is difficult to meet the requirements of an alternating current power grid.
The flexible direct current transmission technology can stabilize the problems of fluctuation, intermittence and the like of renewable energy sources through flexible and quick adjusting capacity, realize large-scale tide adjustment and control and improve the reliability of grid-connected operation of renewable energy source power generation. At present, large-scale new energy is mainly accessed into a power grid through a flexible direct current converter station, and a new energy field station is connected with a grid-connected line of the flexible direct current converter station and is an alternating current transmission line.
The new energy station is generally an inverter type power supply, and in the period of power grid faults, in order to ensure that the inverter has low voltage ride through capability, the control link needs to carry out amplitude limiting on current, so that overcurrent of power electronic devices is avoided. The fault current generally does not exceed about 1.2 times the rated load current of the inverter. In addition, when the new energy station is in no-load, a grid-connected line breaks down, and the supplied fault current is very small. Therefore, the new energy access side of wind power and photovoltaic presents weak power characteristics.
When a grid-connected line fails, the new energy station enters a low-voltage ride through mode, and the flexible direct current converter station enters a current limiting mode due to voltage outer ring saturation. If the new energy station is in no-load state, the voltage of a fault point is determined by the current output by the flexible direct current converter station; if the new energy station has fault current output, the voltage of the fault point is determined by the sum of the currents output by the new energy station and the flexible direct current converter station. The capacities of the new energy station and the flexible direct current converter station are matched, the current amplitudes of the equivalent outputs of the new energy station and the flexible direct current converter station are close to each other, and the phase angle difference is influenced by the steady state before the fault and the transient state adjusting process of the fault. When a two-phase interphase or symmetrical short-circuit fault occurs, the phase angle difference of short-circuit current on two sides may exceed 90 degrees, and at this time, the sensitivity of the conventional line differential protection is reduced, and even the condition of failure occurs.
Therefore, a circuit differential protection tripping method suitable for new energy access is needed.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a line differential protection tripping method and system suitable for new energy access, and solves the problem that when new energy is accessed into a power grid through a flexible direct current converter station and a grid-connected alternating current line fails, the action sensitivity of conventional line differential protection is insufficient.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a line differential protection tripping method suitable for new energy access is characterized in that the following supplement criteria are added on the basis of the current differential protection criteria of a conventional line: the absolute value of the sum of the current vectors at two sides of the line differential protection is larger than k 1 The absolute value of the sum of the current vectors on both sides is greater than k 2 Absolute value of difference between two-side current vectors, sum of absolute values of two-side current vectors being less than k 3 Twice rated value of secondary current, both side voltages being less than k 4 A multiple of a secondary voltage rating; k is a radical of formula 1 、k 2 、k 3 、k 4 Respectively is an action coefficient, a brake coefficient, a current coefficient and a voltage coefficient;
the current differential protection is characterized in that a supplementary criterion function is put into, all supplementary criteria are met at the same time, and the circuit is allowed to trip after the time delay t is confirmed.
The invention further comprises the following preferred embodiments:
preferably, the method comprises the steps of:
step 1: the current differential protection devices on two sides of the line differential protection collect three-phase current and three-phase voltage at the protection installation position on the side in real time and send the three-phase current and the three-phase voltage to the current differential protection device on the opposite side;
step 2: the current differential protection devices on the two sides respectively receive the three-phase current and the three-phase voltage collected on the opposite sides;
and step 3: judging whether the two-side protection is started or not, if so, entering a step 4, and otherwise, returning to the step 1;
and 4, step 4: respectively judging whether the two sides meet the criterion of the conventional circuit current differential protection action, if not, entering the step 5, otherwise, tripping the circuit differential protection;
and 5: judging whether the current differential protection device is put into a supplement criterion function, if so, entering a step 6, otherwise, returning to the step 1;
step 6: and (3) judging whether various supplement criteria of the current differential protection are met or not according to the three-phase current and the three-phase voltage of the current differential protection devices on the two sides, if so, performing circuit differential protection after the time delay t is confirmed, and otherwise, returning to the step 1.
Preferably, in the step 1, in the line differential protection system, it is assumed that an M side is a new energy station and is a wind power or photovoltaic inverter type power supply, an N side is a flexible direct current converter station, an MN grid-connected line is an alternating current transmission line, current differential protection devices are respectively installed on the M side and the N side, the current differential protection devices on the M side and the N side communicate with each other through a dedicated or multiplexed optical fiber, and the two side protections mutually transmit three-phase current, three-phase voltage, start, action, and jump position information;
the current differential protection device collects the three-phase current I at the protection installation position of the current differential protection device in real time A 、I B 、I C Three phase voltage U A 、U B 、U C 。
Preferably, in step 5, if the protection device puts in the control word of the supplement criterion, it indicates that the current differential protection device puts in the supplement criterion function.
Preferably, in step 6, the supplementary criterion of the current differential protection specifically includes:
wherein the content of the first and second substances,
for M side current, including M side three-phase current
That is, the corresponding supplementary criterion is A, B, C which is applicable to all three groups of phases;
I DZ Setting a constant value for current differential protection;
U M including M side phase voltage U MA 、U MB 、U MC And phase-to-phase voltage U MAB 、U MBC 、U MCA ；
U N Including N-side phase voltage U NA 、U NB 、U NC And phase-to-phase voltage U NAB 、U NBC 、U NCA ；
I n Is the secondary current rating;
U n is the secondary voltage rating.
Preferably, in step 6, the supplementary criterion is calculated using the current data and the voltage data at the same time.
Preferably, in step 6, if any one of the phases a, B, and C simultaneously satisfies each current supplement criterion condition, and any one of the phases a, B, C, AB, BC, and CA phase voltages on the M side and the N side satisfies each voltage supplement criterion condition, the current differential protection is activated.
Preferably, the phase voltage is used to discriminate U M 、U N Secondary voltage nominal value U in case of relevant supplementary criterion n 57.7V;
discriminating U by using interphase voltage M 、U N Secondary voltage nominal value U in case of relevant supplementary criterion n Is 100V.
Preferably, k is 1 、k 2 、k 3 、k 4 The values are respectively 0.2, 0.15, 2.5 and 0.75;
t takes the value of 40ms.
The invention also provides a line differential protection tripping system suitable for new energy access, which comprises:
the signal acquisition module is used for acquiring three-phase current and three-phase voltage at the protection installation position of the local side in real time by the current differential protection devices at two sides of the line differential protection and sending the three-phase current and the three-phase voltage to the current differential protection device at the opposite side;
the signal receiving module is used for receiving the three-phase current and the three-phase voltage which are acquired by the opposite sides by the current differential protection devices on the two sides respectively;
the protection starting judging module is used for judging whether the protection on the two sides is started, if so, the protection enters the conventional differential protection action judging module, and if not, the protection returns to the signal acquisition module;
the conventional differential protection action judging module is used for respectively judging whether the two sides meet the conventional line current differential protection action criterion, if the two sides do not meet the criterion, the conventional differential protection action judging module enters a supplement criterion function input judging module, and if not, the line differential protection is tripped;
the supplementary criterion function input judging module is used for judging whether the current differential protection device is input with the supplementary criterion function, if so, the current differential protection device enters the supplementary differential protection action judging module, and if not, the current differential protection device returns to the signal acquisition module;
and the supplementary differential protection action judging module is used for judging whether various supplementary criteria of current differential protection are met or not according to the three-phase current and the three-phase voltage of the current differential protection devices on the two sides, if so, the circuit differential protection action is carried out after the delay t confirmation, and otherwise, the circuit differential protection action returns to the signal acquisition module.
Compared with the prior art, the invention has the beneficial effects that:
the invention is protected in the current differential of the conventional lineBased on basic criterion, adding action coefficient k 1 Coefficient of braking k 2 Coefficient of current k 3 Voltage coefficient k 4 Wherein the motion coefficient k 1 The coefficient of the differential current relative to the protection fixed value of the differential current is the smaller the value is, the more sensitive the action is; coefficient of braking k 2 The coefficient of the differential current relative to the braking current is the slope of the braking curve, and the smaller the value is, the more sensitive the action is; coefficient of current k 3 The ratio of the sum of the current modulus values of the two sides to the secondary rated current is used for judging how large the current of the two sides can be used for inputting the supplement criterion so as to prevent the supplement criterion from being input by mistake; voltage coefficient k 4 The ratio of the voltages at two sides to the secondary rated voltage is used for judging how much the voltage is reduced to determine that the system has a fault, and further preventing the supplement criterion from being input by mistake;
furthermore, considering that the action is sensitive, the action rejection can be prevented, but the risk of misoperation exists, therefore, after the supplement criterion meets the action condition, the differential protection can be operated to trip after the delay t is confirmed;
further, by setting k 1 、k 2 、k 3 、k 4 The value range and the preferred value of the coefficient and the time t are reliably input into supplement criteria, and the problem that the action sensitivity of the differential protection of the conventional circuit is insufficient when new energy is accessed into a power grid through a flexible direct current converter station and a grid-connected alternating current circuit fails can be effectively solved.
Drawings
FIG. 1 is a diagram illustrating the operation characteristics of a typical conventional current differential protection;
fig. 2 is a schematic wiring diagram of a line differential protection tripping method suitable for new energy access according to the present invention;
fig. 3 is a schematic flow chart illustrating steps of a line differential protection tripping method suitable for new energy access according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The embodiments described herein are only some embodiments of the invention, and not all embodiments. All other embodiments obtained by a person skilled in the art without any inventive step based on the spirit of the present invention are within the scope of the present invention.
The following technical terms used in the present invention are first explained or defined:
fig. 1 is a schematic diagram showing the operation characteristics of a typical conventional current differential protection. The current differential protection has a proportional braking characteristic, wherein I D Is a differential current, I B For braking current, I DZ The braking coefficient K is generally 0.6-0.8 for the current differential protection constant value, and the conventional differential protection acts when the action characteristic is met.
Current differential protection device: the main protection elements of the line protection device comprise split-phase current differential protection and zero-sequence current differential protection devices. The differential current and the braking current are calculated by means of the mutual transmission of information such as current, voltage, starting, action, jump position and the like of the optical fiber channels, and the differential protection action is carried out after the condition of the differential action is met. The differential protection of the split-phase current of the phase A, the phase B or the phase C is instantaneous action, and the zero-sequence current differential protection is delayed for 100ms action.
Differential current: the method comprises split-phase differential current and zero-sequence differential current. The split-phase differential current comprises an A-phase differential current, a B-phase differential current and a C-phase differential current. The differential current is the same-name phase current measured by the protection of the two sides of the line, and vector addition is carried out, and then the absolute value is taken.
Braking current: the brake system comprises split-phase brake current and zero-sequence brake current. The split-phase braking current comprises an A-phase braking current, a B-phase braking current and a C-phase braking current. And the braking current is vector subtraction of phase currents with the same name measured by protection on two sides of the line, and then an absolute value is taken.
Current differential protection constant: and setting a fixed value for the protection device. If the differential current is smaller than the constant value, the current differential protection can not be operated.
Protection starting: the protection starting element is used for monitoring whether the power system has a fault or not, opening the power supply of the protection tripping outlet relay and starting a protection fault processing program if the fault is confirmed. The protection starting element comprises current break variable starting, zero sequence auxiliary starting, static stability destruction starting, weak feed starting and the like. Any one of the startup elements opens the protection function after being actuated and self-holds the whole group of the device to return.
Fig. 2 is a wiring schematic diagram of a line differential protection tripping method suitable for new energy access, in fig. 2, an M side is a new energy station and is an inversion type power supply such as wind power or photovoltaic power, an N side is a flexible direct current converter station, an MN grid-connected line is an alternating current transmission line, current differential protection devices are respectively installed on the M side and the N side, current differential protection devices on the two sides communicate with each other through a special or multiplexing optical fiber, the protection devices on the two sides mutually transmit data such as three-phase current and three-phase voltage, and an F point is a fault in a grid-connected line generation area.
The invention is suitable for a line differential protection tripping method for new energy access, and adds the following supplement criteria on the basis of the current differential protection criterion of the conventional line: the absolute value of the sum of the current vectors at two sides of the line differential protection is larger than k 1 The absolute value of the sum of the current vectors on both sides is larger than k 2 The absolute value of the difference between the two side current vectors, the sum of the two side current vectors being less than k 3 Double secondary current rating, both side voltages being less than k 4 A multiple secondary voltage rating; k is a radical of 1 、k 2 、k 3 、k 4 Respectively is an action coefficient, a brake coefficient, a current coefficient and a voltage coefficient;
the current differential protection is characterized in that a supplementary criterion function is put into, all supplementary criteria are met at the same time, and the circuit is allowed to trip after the time delay t is confirmed.
Fig. 3 is a schematic flow chart of the steps of the line differential protection tripping method suitable for new energy access of the present invention, as shown in fig. 3, the method includes the following steps 1-6:
step 1: the current differential protection devices on the two sides acquire three-phase current and three-phase voltage at the protection installation position in real time.
Three-phase current I of current differential protection device real-time acquisition protection installation position A 、I B 、I C Three phase voltage U A 、U B 、U C And sent to the contralateral side.
The three-phase voltage acquired in the step 1 is used for supplementing the criterion U in the step 6 M <k 4 U n And U N <k 4 U n 。
For phase voltages, e.g. U N (U NA 、U NB 、U NC ) Obtaining the three-phase voltage collected in the step 1;
for interphase voltage U NAB 、U NBC 、U NCA It needs to be simply calculated based on the three-phase voltage collected in step 1, such as U NAB ＝U NA -U NB 。
Step 2: the current differential protection devices on the two sides receive three-phase current and three-phase voltage on the opposite sides.
And 3, step 3: judging whether the protection starting element is started or not, if the protection on the two sides is started, entering the step 4, and if not, returning to the step 1.
Both sides need to be judged to start and act, and for the judgment of starting, both sides are required to be started, and the simultaneous starting is not required. That is, when a fault occurs, the two-side protection starting elements may not be started at the same time, but the actions are judged after the two-side protection is started, so that incorrect actions under the conditions of secondary current loop disconnection and the like can be prevented.
And 4, step 4: respectively judging whether the two sides meet the criterion of the conventional circuit current differential protection action, if not, entering the step 5, otherwise, tripping the circuit differential protection;
and for action, the two sides are respectively judged, if the current differential protection of the conventional lines at the two sides does not act, the supplementary criterion is entered.
The action criterion of the conventional current differential protection is as follows:
wherein, I DZ Setting a constant value for current differential protection;
k is a braking coefficient and is generally 0.6-0.8.
And 5: and (4) checking whether the current differential protection is put into a supplement criterion function, if so, entering the step 6, otherwise, returning to the step 1.
The supplement criterion is only applied to the occasion that new energy is accessed into the power grid through the flexible direct current converter station, and if the protection device puts in control words of the supplement criterion, the supplement criterion function is effective. The circuit is used for solving the problem of insufficient action sensitivity of the conventional circuit differential protection.
And 6: judging whether various supplement criteria of current differential protection are met or not according to the three-phase current and the three-phase voltage of the current differential protection devices on the two sides, if so, performing circuit differential protection after time delay t confirmation, and otherwise, returning to the step 1;
the supplementary criteria of the current differential protection include:
wherein the content of the first and second substances,
for M side current, including three phase current
That is, the corresponding supplementary criterion is A, B, C which is applicable to all three groups of phases;
I DZ Setting a constant value for current differential protection according to a primary value of 600A-1000A generally;
U M is the M side phase voltage U MA 、U MB 、U MC And phase-to-phase voltage U MAB 、U MBC 、U MCA ；
U N Is N side phase voltage U NA 、U NB 、U NC And phase-to-phase voltage U NAB 、U NBC 、U NCA ；
In specific implementation, the M side and the N side do not need to be synchronously selected;
I n is the secondary current rating of 1A or 5A;
U n 57.7V or 100V for secondary voltage rating;
k 1 、k 2 、k 3 、k 4 are respectively coefficients;
and t is the delay time.
k 1 The motion coefficient is a coefficient of the differential current relative to a differential current protection fixed value, and the smaller the value is, the more sensitive the motion is; k is a radical of 2 The braking coefficient is the coefficient of the differential current relative to the braking current, and is the slope of a braking curve, and the smaller the value is, the more sensitive the action is; k is a radical of 3 The current coefficient is a ratio of the sum of the current modulus values of the two sides to the secondary rated current, and is used for judging how large the currents of the two sides can be input into the supplement criterion so as to prevent the supplement criterion from being input by mistake; k is a radical of 4 The voltage coefficient is the ratio of the voltages on two sides to the secondary rated voltage, and is used for judging how much the voltage is reduced to determine that the system has faults, so that the fault is further prevented from being input into a supplement criterion by mistake. The action sensitivity can prevent the action rejection, but the action rejection risk exists, so after the supplement criterion meets the action condition, the differential protection can act to trip after the delay t is confirmed. k is a radical of 1 、k 2 、k 3 、k 4 And t needs to limit a reasonable value range, so that a supplement criterion can be correctly input, and the correct action of the current differential protection is ensured.
Through simulation test, k is determined 1 、k 2 、k 3 、k 4 The value range of t is as follows:
k 1 the value range is 0.1-0.3 for the action coefficient, namely the minimum value is primary current 60A, the minimum unbalanced current and the transmission error can be avoided, and the preferred value is 0.2, namely primary currentWhen the current is 120A, the differential current when the characteristics of the current transformers on the two sides are seriously inconsistent can be further avoided;
k 2 the value range of the braking coefficient is 0.1-0.2, the optimal value is 0.15, the sensitive fault phase selection capability can be ensured, and the phase selection error in the case of an outside fault can be prevented;
k 3 the current coefficient is in a value range of 2-3, the optimal value is 2.5, and the current coefficient is consistent with the characteristic that the fault current provided by the new energy station and the flexible direct current converter station is small, so that the mistaken input of a supplement criterion is prevented;
k 4 the value range of the voltage coefficient is 0.5-0.9, the optimal value is 0.75, the voltage coefficient can be judged to be reduced due to the fault of the system, and the supplement criterion is prevented from being input by mistake when the system operates normally;
t is delay time, the value range is 30-50 ms, the preferred value is 40ms, and for a weak feed line, when a fault occurs outside a power supply side area, differential protection misoperation caused by transient capacitance current discharge of the line can be prevented.
The first 3 terms in the supplement criterion are the current supplement criterion, and the last 2 terms are the voltage supplement criterion.
The supplementary criterion is calculated using data at the same time.
If the current differential protection action is carried out, any phase of A phase, B phase and C phase is required to simultaneously meet various current supplement criterion conditions. Only one phase current meets the split-phase current differential protection action condition, and for a single-phase mode, single trip is protected, and the phase trips; and if the two-phase or three-phase current meets the split-phase current differential protection action condition, three jumps are protected. And secondly, any phase of the A phase, the B phase, the C phase, the AB phase, the BC phase and the CA phase voltage on the M side and the N side is required to meet the condition of each voltage supplement criterion.
In specific implementation, 3 current formulas in 5 supplementary criteria are simultaneously satisfied; the 2 expressions of the voltage are satisfied between the first 10ms and the last 10ms when the current is satisfied simultaneously. And after the supplement criterion meets the condition, the current differential protection can act to trip after the time delay t is confirmed.
Specifically, if the phase voltage A phase, the phase B phase or the phase C phase meets various voltage supplement criterion conditions,U n the secondary voltage rating is 57.7V;
if the AB phase, BC phase or CA phase of interphase voltage meets the criteria of each voltage supplement, U n The secondary voltage rating is 100V;
secondary current rating I n Is 1A or 5A, and is determined by the CT model selected on site.
The invention relates to a line differential protection tripping system suitable for new energy access, which comprises:
the signal acquisition module is used for acquiring three-phase current and three-phase voltage at the protection installation position of the local side in real time by the current differential protection devices at the two sides of the line differential protection and sending the three-phase current and the three-phase voltage to the current differential protection device at the opposite side;
the signal receiving module is used for the current differential protection devices on the two sides to respectively receive the three-phase current and the three-phase voltage collected on the opposite side;
the protection starting judging module is used for judging whether the protection on the two sides is started, if so, the protection enters the conventional differential protection action judging module, and if not, the protection returns to the signal acquisition module;
the conventional differential protection action judging module is used for respectively judging whether the two sides meet the conventional line current differential protection action criterion, if the two sides do not meet the criterion, the conventional differential protection action judging module enters a supplement criterion function input judging module, and if not, the line differential protection is tripped;
a supplementary criterion function input judging module used for judging whether the current differential protection device is input with a supplementary criterion function, if so, entering a supplementary differential protection action judging module, otherwise, returning to the signal acquisition module;
and the supplementary differential protection action judging module is used for judging whether various supplementary criteria of current differential protection are met or not according to the three-phase current and the three-phase voltage of the current differential protection devices on the two sides, if so, the circuit differential protection action is carried out after the delay t confirmation, and otherwise, the circuit differential protection action returns to the signal acquisition module.
Compared with the prior art, the invention has the beneficial effects that:
the invention adds a basic action coefficient k based on the basic criterion of the conventional line current differential protection 1 Coefficient of braking k 2 Coefficient of current k 3 Voltage coefficient k 4 Wherein the motion coefficient k 1 The coefficient of the differential current relative to the protection fixed value of the differential current is the smaller the value is, the more sensitive the action is; coefficient of braking k 2 The coefficient of the differential current relative to the braking current is the slope of the braking curve, and the smaller the value is, the more sensitive the action is; coefficient of current k 3 The ratio of the sum of the current modulus values of the two sides to the secondary rated current is used for judging how large the current of the two sides can be used for inputting the supplement criterion so as to prevent the supplement criterion from being input by mistake; voltage coefficient k 4 The ratio of the voltages at two sides to the secondary rated voltage is used for judging how much the voltage is reduced to determine that the system has a fault, and further preventing the supplement criterion from being input by mistake;
furthermore, considering that the action is sensitive, the action rejection can be prevented, but the risk of misoperation exists, therefore, after the supplement criterion meets the action condition, the differential protection can be operated to trip after the delay t is confirmed;
further, by setting k 1 、k 2 、k 3 、k 4 The value range and the preferred value of the coefficient and the time t are reliably input into supplement criteria, and the problem that the action sensitivity of the differential protection of the conventional circuit is insufficient when new energy is accessed into a power grid through a flexible direct current converter station and a grid-connected alternating current circuit fails can be effectively solved.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (10)
1. A line differential protection tripping method suitable for new energy access is characterized by comprising the following steps:
current differential in conventional linesOn the basis of the protection criterion, the following supplementary criteria are added: the absolute value of the sum of the current vectors at two sides of the line differential protection is larger than k 1 The absolute value of the sum of the current vectors on both sides is larger than k 2 Absolute value of difference between two-side current vectors, sum of absolute values of two-side current vectors being less than k 3 Double secondary current rating, both side voltages being less than k 4 A multiple of a secondary voltage rating; k is a radical of 1 、k 2 、k 3 、k 4 Respectively is an action coefficient, a brake coefficient, a current coefficient and a voltage coefficient;
the current differential protection is characterized in that a supplementary criterion function is put into, each supplementary criterion is met at the same time, and the circuit is allowed to trip after the confirmation of the delay t.
2. The line differential protection tripping method suitable for new energy access according to claim 1, characterized in that:
the method comprises the following steps:
step 1: the current differential protection devices on two sides of the line differential protection acquire three-phase current and three-phase voltage at the protection installation position of the current differential protection device in real time and send the three-phase current and the three-phase voltage to the current differential protection device on the opposite side;
step 2: the current differential protection devices on the two sides respectively receive the three-phase current and the three-phase voltage collected on the opposite sides;
and 3, step 3: judging whether the two-side protection is started or not, if so, entering a step 4, and otherwise, returning to the step 1;
and 4, step 4: respectively judging whether the two sides meet the criterion of the conventional circuit current differential protection action, if not, entering the step 5, otherwise, tripping the circuit differential protection;
and 5: judging whether the current differential protection device is put into a supplement criterion function, if so, entering a step 6, otherwise, returning to the step 1;
step 6: and (3) judging whether each supplement criterion of the current differential protection is met or not according to the three-phase current and the three-phase voltage of the current differential protection devices on the two sides, if so, performing line differential protection after the delay t is confirmed, and otherwise, returning to the step 1.
3. The line differential protection tripping method suitable for new energy access according to claim 2, characterized in that:
in the step 1, in a line differential protection system, an M side is assumed to be a new energy station and is a wind power or photovoltaic inverter type power supply, an N side is assumed to be a flexible direct current converter station, an MN grid-connected line is an alternating current transmission line, current differential protection devices are respectively installed on the M side and the N side, the current differential protection devices on the M side and the N side are communicated through a special or multiplexing optical fiber, and two sides are protected to mutually transmit three-phase current, three-phase voltage, starting, action and jump position information;
the current differential protection device collects the three-phase current I at the protection installation position of the current differential protection device in real time A 、I B 、I C Three phase voltage U A 、U B 、U C 。
4. The line differential protection tripping method suitable for new energy access according to claim 2, characterized in that:
in step 5, if the protection device inputs the control word of the supplement criterion, it indicates that the current differential protection device inputs the supplement criterion function.
5. The line differential protection tripping method suitable for new energy access according to claim 2, characterized in that:
in step 6, the supplementary criterion of the current differential protection specifically includes:
wherein the content of the first and second substances,
for M side current, including M side three-phase current
Namely, the corresponding supplementary criterion is A, B, C which is applicable to all three groups of phases;
I DZ Setting a constant value for current differential protection;
U M including M side phase voltage U MA 、U MB 、U MC And phase-to-phase voltage U MAB 、U MBC 、U MCA ；
U N Including N-side phase voltage U NA 、U NB 、U NC And phase-to-phase voltage U NAB 、U NBC 、U NCA ；
I n Is the secondary current rating;
U n is the secondary voltage rating.
6. The line differential protection tripping method suitable for new energy access according to claim 5, characterized in that:
in step 6, the supplement criterion is calculated using the current data and the voltage data at the same time.
7. The line differential protection tripping method suitable for new energy access according to claim 5, characterized in that:
in step 6, if any phase among the phases a, B and C simultaneously satisfies each current supplement criterion condition, and any phase among the phases a, B, C, AB, BC and CA phase voltages on the M and N sides satisfies each voltage supplement criterion condition, the current differential protection is performed.
8. The line differential protection tripping method suitable for new energy access according to claim 5, characterized in that:
discriminating U using phase voltages M 、U N Secondary voltage nominal value U in case of relevant supplementary criterion n 57.7V;
discriminating U by using interphase voltage M 、U N Secondary voltage nominal value U in case of relevant supplementary criterion n Is 100V.
9. The line differential protection tripping method suitable for new energy access according to claim 5, characterized in that:
k 1 、k 2 、k 3 、k 4 the values are respectively 0.2, 0.15, 2.5 and 0.75;
t takes the value of 40ms.
10. A line differential protection trip system adapted for new energy access, the system comprising:
the signal acquisition module is used for acquiring three-phase current and three-phase voltage at the protection installation position of the local side in real time by the current differential protection devices at two sides of the line differential protection and sending the three-phase current and the three-phase voltage to the current differential protection device at the opposite side;
the signal receiving module is used for receiving the three-phase current and the three-phase voltage which are acquired by the opposite sides by the current differential protection devices on the two sides respectively;
the protection starting judging module is used for judging whether the protection at the two sides is started, if so, entering the conventional differential protection action judging module, and if not, returning to the signal acquisition module;
the conventional differential protection action judging module is used for respectively judging whether the two sides meet the conventional line current differential protection action criterion, if the two sides do not meet the criterion, the conventional differential protection action judging module enters a supplement criterion function input judging module, and if not, the line differential protection is tripped;
the supplementary criterion function input judging module is used for judging whether the current differential protection device is input with the supplementary criterion function, if so, the current differential protection device enters the supplementary differential protection action judging module, and if not, the current differential protection device returns to the signal acquisition module;
and the supplementary differential protection action judging module is used for judging whether various supplementary criteria of current differential protection are met or not according to the three-phase current and the three-phase voltage of the current differential protection devices on the two sides, if so, the circuit differential protection action is carried out after the delay t confirmation, and otherwise, the circuit differential protection action returns to the signal acquisition module.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117410947A (en) * | 2023-12-14 | 2024-01-16 | 国网天津市电力公司电力科学研究院 | Differential protection method for new energy station grid-connected line |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117410947A (en) * | 2023-12-14 | 2024-01-16 | 国网天津市电力公司电力科学研究院 | Differential protection method for new energy station grid-connected line |
| CN117410947B (en) * | 2023-12-14 | 2024-04-12 | 国网天津市电力公司电力科学研究院 | Differential protection method for new energy station grid-connected line |
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