CN111208418A - Phase selection switching-on and switching-off state monitoring system and method for converter station alternating current filter - Google Patents
Phase selection switching-on and switching-off state monitoring system and method for converter station alternating current filter Download PDFInfo
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Abstract
The invention discloses a phase selection, opening and closing state monitoring system and method for an alternating current filter of a converter station, and relates to the field of power monitoring. The method meets any one or more than one of the following criteria, and outputs an alarm signal, wherein the criterion is one: a certain phase differential current in the three-phase differential current of the alternating current filter is larger than a set phase differential alarm threshold value; criterion two: the time difference between the starting moment and the voltage zero-crossing moment of the phase selection switching-on and switching-off device is greater than a set time difference alarm threshold value; criterion three: and when the selected reference voltages are in different phases, judging the closing sequence. The invention can pre-judge and select the fault of the phase opening and closing device in advance by analyzing the recorded wave in time when the filter is put into operation, thereby carrying out inspection treatment in time before the fault, avoiding power failure caused by failure of the filter input and improving the availability ratio of equipment.
Description
Technical Field
The invention relates to the field of power monitoring, in particular to a phase selection switching-on and switching-off state monitoring system and method for an alternating current filter of a converter station.
Background
In a converter station, it is common to limit the harmonic currents flowing into the ac system by means of ac filters installed on the ac busbars and to provide reactive compensation for the dc converter valves. With the change of the transmission power of the direct current transmission system, the reactive compensation required to be provided also changes correspondingly, so that the alternating current filter of the converter station needs to be switched on and off frequently, and each switching on and off can bring impact to the system and the capacitor. In order to reduce the impact caused by frequent switching on and off of the filter as much as possible, the common alternating current filter is provided with a phase selection switching-on and switching-off device, and the overcurrent and overvoltage in the transient process of switching-on and switching-off operation are greatly reduced by controlling the optimal switching-on and switching-off angle of the circuit breaker when the filter is switched on and off. At present, the phase selection switching-on and switching-off devices of various manufacturers in operation of a converter station have no self-checking function, and when the devices fail and optimal switching-on and switching-off control cannot be performed, an alarm prompt signal cannot be sent out, so that impact is brought to a system and a filter when the filter is switched in, even the filter is switched in failure to cause filter shutdown accidents, and meanwhile, the operation and maintenance cost of equipment maintenance units is also promoted.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for monitoring the phase selection switching-on and switching-off states of an alternating current filter of a converter station, which can be used for pre-judging the fault of a phase selection switching-on and switching-off device in advance by analyzing the wave recording when the filter is put into operation in time, so that the fault can be checked and processed in time before the fault, the power failure caused by the failure of the filter input can be avoided, and the availability of equipment can be improved.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a phase selection and switching-on and switching-off state monitoring system of an alternating current filter of a convertor station comprises a first acquisition unit, a second acquisition unit, a third acquisition unit, a first monitoring processing unit, a second monitoring processing unit, a third monitoring processing unit and an alarm output unit,
the first acquisition unit is used for acquiring three-phase differential current of the alternating current filter, the first monitoring processing unit is used for judging whether a certain phase difference current in the three-phase differential current of the alternating current filter is larger than a set phase difference alarm threshold value, and if so, an alarm signal is output through the alarm output unit;
the second acquisition unit is used for acquiring the starting time and the voltage zero-crossing time of the phase selection switching-on and switching-off device, the second monitoring processing unit is used for judging whether the time difference between the starting time and the voltage zero-crossing time of the phase selection switching-on and switching-off device is greater than a set time difference alarm threshold value, and if so, an alarm signal is output through the alarm output unit;
the third acquisition unit is used for acquiring a closing sequence of the selected phase opening and closing device, the third monitoring processing unit is used for judging the closing sequence of the selected phase opening and closing device, when an A-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not an A-phase-C-phase-B-phase, or when a B-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not a B-phase-A-phase-C-phase, or when a C-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not a C-phase-B-phase-A-phase, and an alarm signal is output.
The phase selection, switching on and switching off state monitoring system for the converter station alternating current filter is characterized in that the first acquisition unit acquires a certain phase difference current I of the filter according to the following methoddiff：
Wherein the content of the first and second substances,
and
the secondary side currents of the current transformers T1 and T3 of the filter, respectively.
The phase selection, switching on and switching off state monitoring system for the converter station alternating current filter is characterized in that the second acquisition unit acquires the starting time t according to the following methodiAnd the voltage zero crossing time tu；
At the instant of streaming tiThe acquisition method comprises the following steps: acquiring switching-on and switching-off deflection time t from fault recording dataclsAt a previous time tkLet a time tkThe corresponding effective value of the fundamental current is IkThe requirement includes the time tkA plurality of successive fundamental current effective values I before the inner partkSecondary rated value I of current transformer not greater than set multipleNThen, t can be considered askI.e. the start moment tiNamely:
ti＝tk(Ik,Ik-1,Ik-2,…,Ik-9≤nIN)
voltage zero crossing time tuThe acquisition method comprises the following steps: let tp1And tp2Is the voltage zero crossing time tuFront and back two adjacent sampling points p1And p2At the corresponding time, the corresponding voltage sampling instantaneous value up1And up2Satisfies the following conditions:
up1·up2≤0
at the start of streaming time tiTaking a time window [ t ] with the length of one half of power frequency period as a referencei-T/4,ti+T/4]Multiplying two adjacent points of the instantaneous voltage value of each sampling point in the time window until two sampling points with the product less than or equal to 0 are found out, and determining the zero-crossing time t of the voltageuThe median of these two point-corresponding times can be taken, namely:
the phase selection switching-on/off state monitoring system for the converter station alternating current filter further comprises a third monitoring processing unit, a second monitoring processing unit and a third monitoring processing unit, wherein the third monitoring processing unit is used for judging the switching-on sequence of the phase selection switching-on/off device according to the following method: setting a reference voltage urefAs a voltage reference of the voltage zero-crossing point time, the discriminant of the closing sequence is as follows:
wherein, ti_A、ti_B、ti_CIs the three-phase starting time of the AC filter, uA、uB、uCIs the three-phase voltage of the ac filter.
A method for monitoring the phase selection and switching-on and switching-off states of an AC filter of a converter station comprises
Output alarm signal according to any one or more than one of the following criteria,
criterion one is as follows: a certain phase differential current in the three-phase differential current of the alternating current filter is larger than a set phase differential alarm threshold value;
criterion two: the time difference between the starting moment and the voltage zero-crossing moment of the phase selection switching-on and switching-off device is greater than a set time difference alarm threshold value;
criterion three: when the A phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not the A phase-C phase-B phase, or when the B phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not the B phase-A phase-C phase, or when the C phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not the C phase-B phase-A phase.
The method for monitoring the phase selection opening and closing state of the alternating current filter of the converter station further comprises the step that in the first criterion, a certain phase difference current I of the filterdiffComprises the following steps:
wherein the content of the first and second substances,
and
the secondary side currents of the current transformers T1 and T3 of the filter, respectively.
The method for monitoring the phase selection switching-on and switching-off states of the alternating current filter of the converter station further includes that in the second criterion, the starting time t isiThe acquisition method comprises the following steps: acquiring switching-on and switching-off deflection time t from fault recording dataclsAt a previous time tkLet a time tkThe corresponding effective value of the fundamental current is IkThe requirement includes the time tkA plurality of successive fundamental current effective values I before the inner partkSecondary rated value I of current transformer not greater than set multipleNThen, t can be considered askI.e. the start moment tiNamely:
ti＝tk(Ik,Ik-1,Ik-2,…,Ik-9≤nIN)
the method for monitoring the phase selection switching-on and switching-off states of the alternating current filter of the converter station further comprises a voltage zero-crossing time tuThe acquisition method comprises the following steps: let tp1And tp2Is the voltage zero crossing time tuFront and back two adjacent sampling points p1And p2At the corresponding time, the corresponding voltage sampling instantaneous value up1And up2Satisfies the following conditions:
up1·up2≤0
at the start of streaming time tiTaking a time window [ t ] with the length of one half of power frequency period as a referencei-T/4,ti+T/4]Multiplying two adjacent points of the instantaneous voltage value of each sampling point in the time window until two sampling points with the product less than or equal to 0 are found out, and determining the zero-crossing time t of the voltageuThe median of these two point-corresponding times can be taken, namely:
the method for monitoring the phase selection, switching on and switching off states of the alternating current filter of the converter station further comprises setting a reference voltage urefAs a voltage reference of the voltage zero-crossing point time, the discriminant of the closing sequence is as follows:
wherein, ti_A、ti_B、ti_CIs the three-phase starting time of the AC filter, uA、uB、uCIs the three-phase voltage of the ac filter.
The method for monitoring the phase selection, closing and opening states of the alternating current filter of the converter station further requires the time tk10 continuous fundamental current effective values I in inward forwardkNot more than 0.01 times of secondary rated value I of current transformerN。
The method for monitoring the phase selection switching-on and switching-off states of the alternating current filter of the converter station further comprises a voltage zero-crossing time tuIs no more than half the sampling interval.
Compared with the prior art, the invention has the beneficial effects that: the invention judges whether the phase selection switching-on and switching-off device of the filter is abnormal or not by analyzing the wave recording quantity when the filter is put into operation each time, thereby prejudging the fault trend of the phase selection switching-on and switching-off device in advance, and carrying out inspection treatment in advance when the phase selection switching-on and switching-off device is in an abnormal state, so as to avoid the failure of the filter when the phase selection switching-on and switching-off device is in failure, save the operation and maintenance cost, improve the reliability of the filter in switching-on and switching-off, shorten the shutdown time of one-time equipment and.
Drawings
FIG. 1 is a schematic diagram of a typical configuration of a current transformer of a filter bank;
FIG. 2 is a logic diagram of monitoring the state of the phase selection switching-on and switching-off device of the AC filter when the reference voltage is A;
FIG. 3 is a logic diagram of monitoring the state of the phase selection switching-on and switching-off device of the AC filter when the reference voltage is B;
FIG. 4 is a logic diagram of monitoring the state of the phase selection switching-on and switching-off device of the AC filter when the reference voltage is C;
FIG. 5 is a flowchart of a method according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and detailed description.
Example (b):
normally, circuit breakers in power systems are randomly switched on and off, with inrush currents and voltage fluctuations. The circuit breaker phase selection Switching technology (CS for short) refers to a technology that a moving contact and a stationary contact of a circuit breaker are switched at a specified phase angle of a system voltage waveform by a certain means, so that power equipment is switched into a power system under the condition of minimum impact on the power equipment and the system. The CS technology can greatly reduce over-current and over-voltage in the transient process of switching-on and switching-off operation, thereby prolonging the service life of the power equipment and improving the stability of the whole power system.
The phase selection and opening and closing device of the circuit breaker can influence the residual magnetism by controlling the opening phase of the circuit breaker, and the closing phase of the circuit breaker is controlled to enable the bias magnetism to be just offset with the residual magnetism, so that the comprehensive magnetic flux is close to the steady-state magnetic flux under the normal operation condition at the closing moment, saturation caused by magnetic flux superposition is avoided, and the size of the magnetizing inrush current is actively restrained. For a three-phase linkage mechanism breaker, the three-phase opening time-division brake angle is different by 120 degrees, the three-phase remanence polarities are different in size, but the three-phase closing angle is also different by 120 degrees, the three-phase magnetic bias polarities are also different, as long as the opening phase and the closing phase are the same, the magnetic bias and the remanence phases are just opposite to each other for a specific certain phase magnetic circuit, and the phases are mutually offset when being superposed, so that the effect of inhibiting the excitation surge current is achieved.
For capacitive loads such as no-load capacitors, filter banks and other power equipment, the essence of overvoltage and inrush current generated in the operation process of a circuit breaker is a transient physical phenomenon caused by voltage mutation at two ends of a capacitor, and switching-on should be completed sequentially near the voltage zero crossing point of each phase system to improve transient impact caused at the moment of operation. Therefore, when the capacitive load is charged, a large amount of transient imbalance electrical quantities, such as overvoltage and inrush current, are generated at the moment of connection, just at the voltage peak, so that the capacitive load should be applied at the voltage zero crossing point in order to achieve the minimum voltage difference when the capacitive load is applied.
Referring to fig. 1 to 5, a method for monitoring the phase selection switching-on/off state of an ac filter of a converter station is used for monitoring a phase selection switching-on/off device of a circuit breaker, and outputting an alarm signal according to any one or more of the following criteria.
Criterion one is as follows: and a certain phase difference current in the three-phase differential current of the alternating current filter is larger than a set phase difference current alarm threshold value.
Criterion two: and the time difference between the starting moment of the phase selection switching-on and switching-off device and the voltage zero-crossing moment is greater than a set time difference alarm threshold value.
Criterion three: when the A-phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not A phase-C phase-B phase, when the B-phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not B phase-A phase-C phase, and when the C-phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not C phase-B phase-A phase.
For criterion one, a typical configuration of a filter bank current transformer is shown in fig. 1, the current transformer T1And T3Respectively of secondary side currents of
And
differential current expression of filter IdiffComprises the following steps:
filter with a filter element having a plurality of filter elementsThe differential currents of the three phases can be calculated by the above formula. Can set a differential current alarm threshold value IsetWhen satisfying Idiff＞IsetAn alarm signal is sent out when the alarm signal is received.
For criterion two, the starting moment of the filter branch current (namely the conducting moment of the filter branch) is set as tiThe zero-crossing time of the bus voltage of the filter is tuThen the difference Δ t between the two is | ti-tuI represents the time difference between the starting time and the voltage zero-crossing time, and if the switch is switched on at the voltage zero-crossing time, Δ t is equal to 0. Considering the error, inrush current bearing capacity and certain margin of the phase selection switching-on and switching-off device, a time difference alarm threshold value t can be setsetWhen Δ t > tsetAnd the closing time (namely the starting time) is not the voltage zero-crossing time, namely an alarm signal is sent out.
With respect to the start of streaming time tiBecause the transmission of the position signal of the circuit breaker has time delay and the switching-on process of the circuit breaker has a pre-breakdown process, the starting time tiGenerally, the time t is earlier than the opening displacement (0 → 1) of the breaker closing positioncls. Easily-obtained switching-on/off displacement moment t from fault recording dataclsAnd the effective value of the fundamental current at each sampling point, which can be considered as tclsTo start, consider tclsThe effective value of the fundamental current of each previous sampling point. Let tkThe effective value of the fundamental current corresponding to the moment is IkAnd the effective value of the fundamental current of 10 continuous points including the point is not more than 0.01 times IN(INIs the current transformer secondary rating), then t can be considered to bekI.e. the start moment tiNamely:
ti＝tk(Ik,Ik-1,Ik-2,…,Ik-9≤0.01IN)
with respect to the voltage zero-crossing time tuLet a tp1And tp2Is the voltage zero crossing time tuFront and back two adjacent sampling points p1And p2At the corresponding time, the corresponding voltage sampling instantaneous value up1And up2Satisfies the following conditions:
up1·up2≤0
in the above formula equal to 0 corresponds to tp1Or tp2This is exactly the case at the zero crossing. And for two adjacent sampling points near the zero crossing point of the non-voltage, the product of the instantaneous values of the voltage is always greater than 0. Therefore, the above-mentioned obtained t can be obtainediFor reference, a time window [ t ] of length one-half of the power frequency cycle (since the voltage zero crossing occurs once every one-half of the power frequency cycle) is takeni-T/4,ti+T/4]Multiplying two adjacent points of the instantaneous voltage value of each sampling point in the time window until two points which meet the condition that the product is less than or equal to 0 are found, and determining the zero-crossing time t of the voltageuThe median of these two point-corresponding times can be taken, namely:
considering tp1And tp2The time lengths from the real zero-crossing time are not necessarily equal, and t is calculated by the formulauWill have a certain error with the real zero-crossing time, the maximum value of the error can reach half of the sampling interval, namely Ts/2. The sampling rate of the fault recording device is generally large, and taking sampling 200 points per cycle as an example, the maximum error is TsT/2N 0.05ms, which translates to an electrical angle of 0.9 °, falling within the acceptable range.
Up to this point, the starting time t of each phaseiAnd the voltage zero crossing time tuCan be determined as described above, i.e. Δ t ═ t can be comparedi-tuI and tsetTo determine whether each phase is closing at a voltage zero crossing.
For criterion three, a reference voltage u needs to be set for the phase selection switching-on and switching-off devicerefAs the reference of the zero crossing point time of the voltage, when the selected reference voltages are in different phases, the closing sequence is also different, namely:
using the determined starting time tiThen, the discriminant of the closing sequence can be written as:
wherein, ti_A、ti_B、ti_CIs the starting time of the three phases, uA、uB、uCIs the three-phase voltage of the ac filter.
FIGS. 2 to 4 are schematic diagrams of monitoring logic of the present invention when A, B, C phases are taken as reference voltages, respectively, wherein Idiff_A、Idiff_B、Idiff_CThree-phase differential currents of filter subgroups, ti_A、ti_B、ti_CIs the starting time of the three phases, tu_A、tu_B、tu_CIs the voltage zero-crossing time of the three phases, IsetFor differential current alarm threshold, tsetAnd the time difference alarm threshold value is obtained.
a. Referring to FIG. 2, the reference voltage is phase A, i.e., uref＝uAThe closing sequence is A → C → B, and the logic expression of the alarm signal is as follows:
(Idiff_A＞Iset)||(Idiff_B＞Iset)||(Idiff_C＞Iset)||(ΔtA＞tset)||(ΔtB＞tset)||(ΔtC＞tset)||！(ti_A＜ti_C＜ti_B)
b. referring to FIG. 3, the reference voltage is phase B, i.e., uref＝uBIf the switching-on sequence is B → A → C, the logic expression for sending out the alarm signal is:
(Idiff_A＞Iset)||(Idiff_B＞Iset)||(Idiff_C＞Iset)||(ΔtA＞tset)||(ΔtB＞tset)||(ΔtC＞tset)||！(ti_B＜ti_A＜ti_C)
c. referring to FIG. 4, the reference voltage is C phase, i.e., uref＝uCIf the sequence of closing is C → B → A, an alarm is givenThe logical expression of the signal is:
(Idiff_A＞Iset)||(Idiff_B＞Iset)||(Idiff_C＞Iset)||(ΔtA＞tset)||(ΔtB＞tset)||(ΔtC＞tset)||！(ti_C＜ti_B＜ti_A)
the invention judges whether the phase selection switching-on and switching-off device of the filter is abnormal or not by analyzing the wave recording quantity when the filter is put into operation each time, thereby prejudging the fault trend of the phase selection switching-on and switching-off device in advance, and carrying out inspection treatment in advance when the phase selection switching-on and switching-off device is in an abnormal state, so as to avoid the failure of the filter when the phase selection switching-on and switching-off device is in failure, save the operation and maintenance cost, improve the reliability of the filter in switching-on and switching-off, shorten the shutdown time of one-time equipment and.
Meanwhile, the invention also provides a system for monitoring the phase selection, opening and closing states of the AC filter of the converter station, which comprises a first acquisition unit, a second acquisition unit, a third acquisition unit, a first monitoring processing unit, a second monitoring processing unit, a third monitoring processing unit and an alarm output unit,
the first acquisition unit is used for acquiring three-phase differential current of the alternating current filter, the first monitoring processing unit is used for judging whether a certain phase difference current in the three-phase differential current of the alternating current filter is larger than a set phase difference alarm threshold value, and if so, an alarm signal is output through the alarm output unit;
the second acquisition unit is used for acquiring the starting time and the voltage zero-crossing time of the phase selection switching-on and switching-off device, the second monitoring processing unit is used for judging whether the time difference between the starting time and the voltage zero-crossing time of the phase selection switching-on and switching-off device is greater than a set time difference alarm threshold value, and if so, an alarm signal is output through the alarm output unit;
the third acquisition unit is used for acquiring a closing sequence of the selected phase opening and closing device, the third monitoring processing unit is used for judging the closing sequence of the selected phase opening and closing device, when an A-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not an A-phase-C-phase-B-phase, or when a B-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not a B-phase-A-phase-C-phase, or when a C-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not a C-phase-B-phase-A-phase, and an alarm signal is output.
Further, the first acquisition unit obtains a certain phase difference current I of the filter according to the following methoddiff：
Wherein the content of the first and second substances,
and
the secondary side currents of the current transformers T1 and T3 of the filter, respectively.
Further, the second acquisition unit obtains the starting time t according to the following methodiAnd the voltage zero crossing time tu；
At the instant of streaming tiThe acquisition method comprises the following steps: acquiring switching-on and switching-off deflection time t from fault recording dataclsAt a previous time tkLet a time tkThe corresponding effective value of the fundamental current is IkThe requirement includes the time tkA plurality of successive fundamental current effective values I before the inner partkSecondary rated value I of current transformer not greater than set multipleNThen, t can be considered askI.e. the start moment tiNamely:
ti＝tk(Ik,Ik-1,Ik-2,…,Ik-9≤nIN)
voltage zero crossing time tuThe acquisition method comprises the following steps: let tp1And tp2Is the voltage zero crossing time tuFront and back two adjacent sampling points p1And p2At the corresponding time, the corresponding voltage sampling instantaneous value up1And up2Satisfies the following conditions:
up1·up2≤0
at the start of streaming time tiTaking a time window [ t ] with the length of one half of power frequency period as a referencei-T/4,ti+T/4]Multiplying two adjacent points of the instantaneous voltage value of each sampling point in the time window until two sampling points with the product less than or equal to 0 are found out, and determining the zero-crossing time t of the voltageuThe median of these two point-corresponding times can be taken, namely:
further, the third monitoring processing unit judges the switching-on sequence of the phase selection switching-on and switching-off device according to the following method: setting a reference voltage urefAs a voltage reference of the voltage zero-crossing point time, the discriminant of the closing sequence is as follows:
wherein, ti_A、ti_B、ti_CIs the three-phase starting time of the AC filter, uA、uB、uCIs the three-phase voltage of the ac filter.
The device judges whether the phase selection switching-on and switching-off device of the filter group has abnormity or not by collecting the electric quantity which is easily acquired by the alternating current filter, thereby prejudging the fault trend of the phase selection switching-on and switching-off device in advance, and when the phase selection switching-on and switching-off device has abnormal state, checking and processing are carried out in advance, so that the filter input failure is caused when the fault occurs, the operation and maintenance cost is saved, the reliability of the filter input and output is improved, the outage time of primary equipment is shortened, and the equipment availability is improved.
The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.
Claims (10)
1. A phase selection switching-on and switching-off state monitoring system of an alternating current filter of a converter station is characterized by comprising a first acquisition unit, a second acquisition unit, a third acquisition unit, a first monitoring processing unit, a second monitoring processing unit, a third monitoring processing unit and an alarm output unit,
the first acquisition unit is used for acquiring three-phase differential current of the alternating current filter, the first monitoring processing unit is used for judging whether a certain phase difference current in the three-phase differential current of the alternating current filter is larger than a set phase difference alarm threshold value, and if so, an alarm signal is output through the alarm output unit;
the second acquisition unit is used for acquiring the starting time and the voltage zero-crossing time of the phase selection switching-on and switching-off device, the second monitoring processing unit is used for judging whether the time difference between the starting time and the voltage zero-crossing time of the phase selection switching-on and switching-off device is greater than a set time difference alarm threshold value, and if so, an alarm signal is output through the alarm output unit;
the third acquisition unit is used for acquiring a closing sequence of the selected phase opening and closing device, the third monitoring processing unit is used for judging the closing sequence of the selected phase opening and closing device, when an A-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not an A-phase-C-phase-B-phase, or when a B-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not a B-phase-A-phase-C-phase, or when a C-phase voltage of the alternating current filter is used as a reference voltage at a voltage zero crossing point moment, the selected phase opening and closing sequence is not a C-phase-B-phase-A-phase, and an alarm signal is output.
2. The system for monitoring the phase selection, opening and closing states of the ac filter of the converter station according to claim 1, wherein the first acquisition unit obtains a certain phase difference current I of the filter according to the following methoddiff：
Wherein the content of the first and second substances,
and
the secondary side currents of the current transformers T1 and T3 of the filter, respectively.
3. The phase selection, opening and closing state monitoring system for AC filter of converter station according to claim 1, characterized in that the second acquisition unit obtains the starting time t according to the following methodiAnd the voltage zero crossing time tu；
At the instant of streaming tiThe acquisition method comprises the following steps: acquiring switching-on and switching-off deflection time t from fault recording dataclsAt a previous time tkLet a time tkThe corresponding effective value of the fundamental current is IkThe requirement includes the time tkA plurality of successive fundamental current effective values I before the inner partkSecondary rated value I of current transformer not greater than set multipleNThen, t can be considered askI.e. the start moment tiNamely:
ti＝tk(Ik,Ik-1,Ik-2,…,Ik-9≤nIN)
voltage zero crossing time tuThe acquisition method comprises the following steps: let tp1And tp2Is the voltage zero crossing time tuFront and back two adjacent sampling points p1And p2At the corresponding time, the corresponding voltage sampling instantaneous value up1And up2Satisfies the following conditions:
up1·up2≤0
at the start of streaming time tiTaking a time window [ t ] with the length of one half of power frequency period as a referencei-T/4,ti+T/4]Multiplying two adjacent points of the instantaneous voltage value of each sampling point in the time window until two sampling points with the product less than or equal to 0 are found out, and determining the zero-crossing time t of the voltageuThe median of these two point-corresponding times can be taken, namely:
4. the system for monitoring the phase selection, closing and opening state of the ac filter of the converter station according to claim 1, wherein the third monitoring and processing unit determines the closing sequence of the phase selection, closing and opening device according to the following method: setting a reference voltage urefAs a voltage reference of the voltage zero-crossing point time, the discriminant of the closing sequence is as follows:
switching-on sequence
Wherein, ti_A、ti_B、ti_CIs the three-phase starting time of the AC filter, uA、uB、uCIs the three-phase voltage of the ac filter.
5. A method for monitoring the phase selection opening and closing state of an AC filter of a converter station is characterized by comprising the following steps
Output alarm signal according to any one or more than one of the following criteria,
criterion one is as follows: a certain phase differential current in the three-phase differential current of the alternating current filter is larger than a set phase differential alarm threshold value;
criterion two: the time difference between the starting moment and the voltage zero-crossing moment of the phase selection switching-on and switching-off device is greater than a set time difference alarm threshold value;
criterion three: when the A phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not the A phase-C phase-B phase, or when the B phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not the B phase-A phase-C phase, or when the C phase voltage of the alternating current filter is used as the reference voltage at the voltage zero crossing point moment, the phase selection switching-on and switching-off sequence is not the C phase-B phase-A phase.
6. The method according to claim 5, characterized in that in criterion one, a certain phase difference current I of the filter is obtaineddiffComprises the following steps:
wherein the content of the first and second substances,
and
the secondary side currents of the current transformers T1 and T3 of the filter, respectively.
7. The method for monitoring the phase selection, opening and closing states of the AC filter of the converter station as recited in claim 5, characterized in that in the criterion two, the starting time tiThe acquisition method comprises the following steps: acquiring switching-on and switching-off deflection time t from fault recording dataclsAt a previous time tkLet a time tkThe corresponding effective value of the fundamental current is IkThe requirement includes the time tkA plurality of successive fundamental current effective values I before the inner partkSecondary rated value I of current transformer not greater than set multipleNThen, t can be considered askI.e. the start moment tiNamely:
ti＝tk(Ik,Ik-1,Ik-2,…,Ik-9≤nIN)
voltage zero crossing time tuThe acquisition method comprises the following steps: let tp1And tp2Is the voltage zero crossing time tuFront and back two adjacent sampling points p1And p2At the corresponding time, the corresponding voltage sampling instantaneous valueup1And up2Satisfies the following conditions:
up1·up2≤0
at the start of streaming time tiTaking a time window [ t ] with the length of one half of power frequency period as a referencei-T/4,ti+T/4]Multiplying two adjacent points of the instantaneous voltage value of each sampling point in the time window until two sampling points with the product less than or equal to 0 are found out, and determining the zero-crossing time t of the voltageuThe median of these two point-corresponding times can be taken, namely:
8. the method of claim 6, wherein a reference voltage u is set for monitoring the phase selection, closing and opening of the AC filter of the converter stationrefAs a voltage reference of the voltage zero-crossing point time, the discriminant of the closing sequence is as follows:
switching-on sequence
Wherein, ti_A、ti_B、ti_CIs the three-phase starting time of the AC filter, uA、uB、uCIs the three-phase voltage of the ac filter.
9. The method of claim 7, wherein the request includes a time tk10 continuous fundamental current effective values I in inward forwardkNot more than 0.01 times of secondary rated value I of current transformerN。
10. The method for monitoring the phase selection, opening and closing state of the AC filter of a converter station according to claim 7, characterized in that the voltage zero crossing time t isuIs no more than half the sampling interval.
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