CN111208420B - Generator grounding switch state detection method and system based on signal injection - Google Patents

Generator grounding switch state detection method and system based on signal injection Download PDF

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Publication number
CN111208420B
CN111208420B CN202010117994.0A CN202010117994A CN111208420B CN 111208420 B CN111208420 B CN 111208420B CN 202010117994 A CN202010117994 A CN 202010117994A CN 111208420 B CN111208420 B CN 111208420B
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grounding
generator
low
disconnecting link
frequency current
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CN111208420A (en
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陈佳胜
王光
郭自刚
姬生飞
王凯
李华忠
陈俊
张琦雪
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NR Electric Co Ltd
NR Engineering Co Ltd
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NR Engineering Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/327—Testing of circuit interrupters, switches or circuit-breakers
    • G01R31/3271—Testing of circuit interrupters, switches or circuit-breakers of high voltage or medium voltage devices
    • G01R31/3275—Fault detection or status indication

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Abstract

The invention discloses a generator grounding switch state detection method and system based on signal injection, which are used for identifying the actual state of a generator grounding switch. In engineering practice, a generator grounding switch is a three-phase linkage mechanism, and an auxiliary contact cannot reflect the real state of a certain phase due to mechanical reasons because the certain phase is not switched in place, so that safety accidents are easily caused; or detecting corresponding low-frequency voltage on the PT open triangular winding at the machine end so as to judge whether the grounding knife switch is in place or not. According to the invention, through detection and analysis of the electric quantity of the generator and combination of the auxiliary contact position of the grounding disconnecting link, the states of all phases of the grounding disconnecting link of the generator are indirectly detected, the accuracy of state identification of the grounding disconnecting link of the generator is improved, and the operation reliability of a primary system of the generator is improved.

Description

Generator grounding switch state detection method and system based on signal injection
Technical Field
The invention relates to state monitoring of switch equipment at a generator end of a power plant, in particular to a method and a system for detecting the state of a generator grounding disconnecting link based on signal injection.
Background
In recent years, the condition of faults that the grounding knife switch of the generator is not in place in opening and closing is frequently generated in a hydropower station, the contradiction of closing with the grounding knife (ground wire) still exists, and the damage of the faults is great.
In 2014, when a certain 500kV bus of a certain hydropower station is powered on, the B phase and the C phase of a certain ground cutter are not actually switched off, so that the protection action is tripped. In 2015, when a certain 500kV transformer of a certain hydropower station is empty and charged, the protection action trips because the B phase of the grounding switch is not actually switched off. Generally, a contact of the grounding disconnecting link is arranged in a switch air chamber, and the opening and closing position of the grounding disconnecting link cannot be observed by naked eyes. The position can only be determined by means of the auxiliary contacts of the switch operating mechanism, but this has proved to be unreliable in the above-mentioned case.
The generator grounding knife switch is a three-phase linkage mechanism, and only one pair of auxiliary contacts is used for indicating the three-phase position of the generator grounding knife switch; the three-phase linkage mechanism appears on site for many times, because fatigue fracture produces the non-full-phase working condition, and certain looks switch does not divide and shut in place actually, but the auxiliary contact point instruction earthing switch has already been operated and has been accomplished, and operation operating personnel receives the error message and can't in time handle, threatens generating set safe operation, easily causes the accident.
Although power systems are typically configured with a complete differential protection scheme, such faults may be timely reflected in being removed. However, in consideration of the great harm of such faults, it is still necessary to avoid such operations by accurately identifying the states of the phases of the grounding switch through a perfect technical means.
Therefore, the invention provides a generator grounding switch state detection method and system based on signal injection, which can accurately identify the states of all phases of the grounding switch by detecting the low-frequency current on a grounding loop and the low-frequency voltage on a terminal PT and combining with the auxiliary contact of the grounding switch, thereby avoiding various safety accidents and improving the one-time system operation reliability of the generator.
Disclosure of Invention
The purpose of the invention is: the method and the system for detecting the state of the generator grounding disconnecting link based on signal injection are provided, and can accurately identify the state of each phase of the grounding disconnecting link by detecting the low-frequency current on a grounding loop and the low-frequency voltage on a terminal PT and combining with an auxiliary contact of the grounding disconnecting link, thereby avoiding the occurrence of a switching-on accident with the grounding switch and improving the operation reliability of a primary system of a generator.
In order to achieve the purpose, the invention adopts the technical scheme that:
a generator grounding switch state detection method based on signal injection comprises the following steps:
step 1: the injection power supply device injects a low-frequency current signal from the low-voltage side of the neutral point grounding transformer of the generator;
step 2: collecting the state of a grounding disconnecting link and three-phase current on a grounding circuit of the grounding disconnecting link, and separating three-phase low-frequency current signals; or simultaneously collecting three-phase current on a grounding circuit of the grounding disconnecting link and voltage signals at two ends of an opening triangular winding of a terminal voltage transformer, and separating three-phase low-frequency current signals and low-frequency voltage signals;
and step 3: whether the grounding knife switch is effectively closed is judged by adopting one of the following schemes:
scheme 1: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a first preset threshold value, the grounding disconnecting link is judged to be not closed effectively;
scheme 2: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not closed effectively;
whether the grounding disconnecting link is effectively disconnected is judged by adopting one of the following schemes:
scheme 3: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 4: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 5: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the amplitude of any phase of low-frequency current is detected to be larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not effectively disconnected.
In a further preferred scheme, the frequency of the low-frequency signal injected in step 1 may be 12.5Hz or 20Hz or a low-frequency signal with other frequencies, so as to be distinguished from the power-frequency signal;
in a further preferred embodiment, in step 2, a method combining hardware filtering and digital filtering is adopted to separate the low-frequency component for detection.
The specific calculation formula of the scheme 1 is shown as the formula (1):
Figure BDA0002392076990000031
when the formula (1) is satisfied, the grounding knife switch is judged to be not effectively closed, and the low-frequency current of a certain phase is smaller than a set threshold Ith1Indicating that the phase is not closed in place;
the specific calculation formula of the scheme 4 is shown as the formula (2):
Figure BDA0002392076990000032
when the formula (2) is satisfied, the grounding disconnecting link is judged to be not effectively disconnected, and the low-frequency current of a certain phase is larger than a set threshold Ith2Indicating that the phase is not broken in place;
wherein:
Figure BDA0002392076990000033
for three-phase low-frequency current amplitude, I, measured on the earth returnth1For threshold setting of current, Ith2Setting a value for a no-flow threshold; status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
The specific calculation formula of the scheme 3 is shown as the formula (3):
Figure BDA0002392076990000034
when the formula (3) is satisfied, judging that the grounding disconnecting link cannot be effectively disconnected;
wherein:
Figure BDA0002392076990000035
amplitude, U, of low-frequency voltage measured on terminal PT open-ended delta windingthIs a voltage threshold; status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
The specific calculation formula of the scheme 2 is shown as the formula (4):
Figure BDA0002392076990000041
when the formula (4) is satisfied, judging that the grounding disconnecting link cannot be effectively closed, and if the amplitude of the low-frequency current of a certain phase is smaller than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient k, indicating that the grounding disconnecting link is not closed in place;
the specific calculation formula of the scheme 5 is shown as the formula (5):
Figure BDA0002392076990000042
when the formula (5) is satisfied, judging that the grounding disconnecting link is not effectively disconnected, and if the amplitude of the low-frequency current of a certain phase is greater than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient, indicating that the grounding disconnecting link of the phase is not disconnected in place;
wherein:
Figure BDA0002392076990000043
the three-phase low-frequency current amplitude measured on the grounding loop;
Figure BDA0002392076990000044
the amplitude of the low-frequency current between BC, AC and AB phases measured on the grounding loop;
k is a fixed coefficient;
status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
Further, when the grounding disconnecting link is judged to be not closed effectively or not disconnected effectively, an alarm signal is sent out through a set time delay T1, the fixed value range of the time delay T1 is 0.1 s-30.0 s, and the default time is 10.0 s.
The invention also provides a generator grounding switch state detection system based on signal injection, which comprises an injection power supply device and a detection device;
the injection power supply device is used for injecting a low-frequency signal into the primary system of the generator through the grounded secondary side variable resistor;
the detection device comprises an acquisition unit, a filtering unit and a detection calculation unit;
the acquisition unit is used for acquiring the state of the generator grounding switch, acquiring the current of the switch grounding loop or simultaneously acquiring the current of the switch grounding loop and the voltage of the PT (potential transformer) opening triangular winding at the generator end and transmitting the current and the voltage to the filtering unit;
the filtering unit is used for filtering, calculating and processing the electric quantity signals received from the acquisition unit to obtain the amplitudes of low-frequency current and voltage;
the detection and calculation unit is configured to determine whether the grounding switch is effectively closed or turned off according to the state of the grounding switch, the low-frequency current, and the voltage semaphore, and specifically, determine whether the grounding switch is effectively closed by using one of the following schemes:
scheme 1: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a first preset threshold value, the grounding disconnecting link is judged to be not closed effectively;
scheme 2: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not closed effectively;
whether the grounding disconnecting link is effectively disconnected is judged by adopting one of the following schemes:
scheme 3: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 4: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 5: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the amplitude of any phase of low-frequency current is detected to be larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not effectively disconnected.
In a further preferred embodiment, the filtering unit separates the low-frequency component by a method combining hardware filtering and digital filtering.
In a further preferred scheme, the detection device further comprises an alarm unit: and when the grounding knife switch is judged to be not effectively closed or not effectively disconnected by the detection and calculation unit, an alarm signal is sent out through set time delay.
The invention has the beneficial effects that: by injecting low-frequency signals into the primary system of the generator and respectively detecting the low-frequency current and voltage signals at the disconnecting link grounding loop and the PT opening triangular winding at the generator end, the states of all phases of the grounding disconnecting link at the generator end are indirectly reflected, and when the disconnecting link is not in place, an alarm signal can be reliably sent out, so that safety accidents such as closing with an earth switch and the like are prevented, and the safety and reliability of the primary system of the generator can be effectively improved.
Drawings
FIG. 1 is a schematic diagram of the working principle of the detection system of the present invention.
Fig. 2 is a detection system embodiment 2 of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The invention designs a generator grounding switch state detection method and system based on signal injection. The specific implementation of the method and the working principle of the system are described by taking a certain hydropower station 700MW generator system as an example.
The electrical main wiring diagram and the wiring of the detection system are shown in figure 1. The neutral point of a certain 700MW hydroelectric generator is grounded through grounding, and the injection power supply device injects a low-frequency signal into a primary system of the generator through a grounded secondary side-variable resistor Rn. The detection device of the detection system acquires a disconnecting link position signal, a grounding loop current and a terminal PT opening triangular winding voltage through an acquisition unit, obtains low-frequency current and voltage signals through frequency separation processing of a filtering unit, obtains the amplitudes of the low-frequency current and voltage signals through a detection and calculation unit, obtains a signal whether the grounding disconnecting link is broken in place or not through comparison with a set value, gives an alarm signal through set time delay, and prompts an operator to execute corresponding inspection operation.
Example 1: the specific steps for implementing the state detection of the 700MW generator grounding disconnecting link are as follows:
s101: the injection power supply device injects a low-frequency current signal from the low-voltage side of the generator neutral grounding transformer.
The injection power supply should be able to operate properly and reliably during normal operation and shutdown of the generator.
S102: the detection device is connected with a generator grounding knife switch position contact signal JD.Status and the three-phase current amount of a knife switch grounding loop;
the detection device calculates the amplitude of the low-frequency component of the three-phase current of the disconnecting link grounding circuit in real time through the processing of the filtering unit.
S103: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a preset threshold value, the grounding disconnecting link is judged to be not closed effectively; as shown in formula 1:
Figure BDA0002392076990000071
when the formula (1) is satisfied, the grounding knife switch is judged to be not effectively closed, and the low-frequency current of a certain phase is smaller than a set threshold Ith1Indicating that the phase is not closed in place.
Wherein the content of the first and second substances,
Figure BDA0002392076990000072
for three-phase low-frequency current amplitude, I, measured on the earth returnth1Setting a value for the current threshold; status is the auxiliary contact of the generator end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
When the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected; such as (2)
Shown in the figure:
Figure BDA0002392076990000073
Ith2the no-flow threshold is fixed.
When the formula (2) is satisfied, the grounding disconnecting link is judged to be not effectively disconnected, and the low-frequency current of a certain phase is larger than a set threshold Ith2Indicating that the phase is not broken in place.
Example 2: the specific steps for implementing the state detection of the 700MW generator grounding disconnecting link are as follows:
s201: the injection power supply device injects a low-frequency current signal from the low-voltage side of the generator neutral grounding transformer.
The injection power supply should be able to operate properly and reliably during normal operation and shutdown of the generator.
S202: the detection device is connected with a generator grounding knife switch position contact signal JD.Status and the three-phase current amount of a knife switch grounding loop;
the detection device calculates the amplitude of the low-frequency component of the three-phase current of the disconnecting link grounding circuit in real time through the processing of the filtering unit.
S203: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not closed effectively; as shown in formula (4):
in a shutdown state, the grounding knife switch is closed, and if the formula 4 is met, a certain phase is not closed in place;
Figure BDA0002392076990000081
when the formula (4) is satisfied, the grounding disconnecting link is judged to be not effectively closed, and the amplitude of the low-frequency current of a certain phase is smaller than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient k, so that the grounding disconnecting link is not closed in place.
When the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the amplitude of any phase of low-frequency current is detected to be larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not effectively disconnected. As shown in formula (5):
Figure BDA0002392076990000082
when the formula (5) is satisfied, judging that the grounding disconnecting link is not effectively disconnected, and if the amplitude of the low-frequency current of a certain phase is greater than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient, indicating that the grounding disconnecting link of the phase is not disconnected in place;
wherein:
Figure BDA0002392076990000083
the three-phase low-frequency current amplitude measured on the grounding loop;
Figure BDA0002392076990000084
the amplitude of the low-frequency current between BC, AC and AB phases measured on the grounding loop; k is a fixed coefficient; in this example, 0.8 is taken;
status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
By adopting the method, the low-frequency current of the grounding circuit of the generator grounding disconnecting link is detected, the grounding disconnecting link contact of the generator is combined, the phase states of the grounding disconnecting link of the generator can be monitored in real time, when the low-frequency current meets the relevant criterion, the grounding disconnecting link can be judged to be not in place, and an alarm signal is sent out after the set time delay, so that an operator is reminded of processing in time. In order to avoid various fault interferences of the system, the fixed value range of the delay is set to be 0.1 s-30.0 s, and the fixed value of the delay is set to be 10.0s in this embodiment.
Example 3: the specific steps for implementing the state detection of the 700MW generator grounding disconnecting link are as follows:
s301: the injection power supply device injects a low-frequency current signal from the low-voltage side of the generator neutral grounding transformer.
The injection power supply should be able to operate properly and reliably during normal operation and shutdown of the generator.
S302: and the detection device is connected with a generator grounding knife switch position contact signal JD.
The detection device calculates the amplitude of the three-phase current of the disconnecting link grounding loop and the amplitude of the low-frequency component of the triangular voltage of the PT opening at the machine terminal in real time through the processing of the filtering unit.
S303: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a preset threshold value, the grounding disconnecting link is judged to be not closed effectively; as shown in formula 1:
Figure BDA0002392076990000091
when the formula (1) is satisfied, the grounding knife switch is judged to be not effectively closed, and the low-frequency current of a certain phase is smaller than a set threshold Ith1Indicating that the phase is not closed in place.
Wherein the content of the first and second substances,
Figure BDA0002392076990000092
for three-phase low-frequency current amplitude, I, measured on the earth returnth1Setting a value for the current threshold; status is the auxiliary contact of the generator end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
When the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected; as shown in formula (3):
Figure BDA0002392076990000101
when the formula (3) is satisfied, judging that the grounding disconnecting link cannot be effectively disconnected;
wherein the content of the first and second substances,
Figure BDA0002392076990000102
amplitude, U, of low-frequency voltage measured on terminal PT open-ended delta windingthIs a voltage threshold; status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 1 when the grounding switch is disconnected and 0 when the grounding switch is closed.
By adopting the method, the low-frequency component of the triangular zero-sequence voltage of the PT opening at the generator end and the low-frequency component of the current of the grounding loop are detected, the grounding disconnecting link contact of the generator is combined, the states of all phases of the grounding disconnecting link of the generator can be monitored in real time, when the low-frequency current and the voltage meet the relevant criteria, the grounding disconnecting link can be judged to be not effectively switched on and off, and an alarm signal is sent out after the set time delay, so that an operator is reminded of timely processing.
Example 4: the specific steps for implementing the state detection of the 700MW generator grounding disconnecting link are as follows:
s401: the injection power supply device injects a low-frequency current signal from the low-voltage side of the generator neutral grounding transformer.
The injection power supply should be able to operate properly and reliably during normal operation and shutdown of the generator.
S402: and the detection device is connected with a generator grounding knife switch position contact signal JD.
The detection device calculates the amplitude of the three-phase current of the disconnecting link grounding loop and the amplitude of the triangular zero-sequence voltage low-frequency component of the PT opening at the machine end in real time through the processing of the filtering unit.
S403: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a preset threshold value, the grounding disconnecting link is judged to be not closed effectively; or if the amplitude of any phase of low-frequency current is smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, judging that the grounding disconnecting link is not closed effectively; as shown in formulas (1) and (4):
Figure BDA0002392076990000103
Figure BDA0002392076990000111
wherein the content of the first and second substances,
Figure BDA0002392076990000112
for three-phase low-frequency current amplitude, I, measured on the earth returnth1Setting a value for the current threshold; status is an auxiliary contact of the generator end grounding disconnecting link, the value of the auxiliary contact is 0 when the grounding disconnecting link is disconnected, and the value of the auxiliary contact is 1 when the grounding disconnecting link is closed;
Figure BDA0002392076990000113
the amplitude of the low-frequency current between BC, AC and AB phases measured on the grounding loop; k is a fixed coefficient; in this example, 0.8 is taken; .
When the formula (1) or (4) is satisfied, the grounding knife switch is judged to be not effectively closed, and the low-frequency current of a certain phase is smaller than a set threshold Ith1Or the amplitude of the low-frequency current of one phase is smaller than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient k, and the phase is not closed in place.
When the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected; or if the amplitude of any phase of low-frequency current is larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, judging that the grounding disconnecting link is not effectively disconnected; or, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected. As shown in formulas (2), (3) and (5):
Figure BDA0002392076990000114
Figure BDA0002392076990000115
Figure BDA0002392076990000116
wherein:
Figure BDA0002392076990000117
for three-phase low-frequency current amplitude, I, measured on the earth returnth2Setting a value for a no-flow threshold;
Figure BDA0002392076990000121
the amplitude of the low-frequency current between BC, AC and AB phases measured on the grounding loop; k is a fixation systemCounting; in this example, 0.8 is taken;
Figure BDA0002392076990000122
amplitude, U, of low-frequency voltage measured on terminal PT open-ended delta windingthIs a voltage threshold; status is the auxiliary contact of the generator end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
When the formula (2), (3) or (5) is satisfied, the grounding disconnecting link is judged to be not effectively disconnected, wherein the low-frequency current of a certain phase is greater than a set threshold Ith2Or the amplitude of the low-frequency current of one phase is larger than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient, and the phase is not broken in place.
By adopting the method, the low-frequency current of the grounding circuit of the generator grounding disconnecting link and the low-frequency component of the triangular zero sequence voltage of the PT opening at the generator end are detected, the grounding disconnecting link contact of the generator is combined, the states of all phases of the grounding disconnecting link of the generator can be monitored in real time, when the low-frequency current and the triangular low-frequency zero sequence voltage of the PT opening at the generator end meet relevant criteria, the grounding disconnecting link can be judged to be not in place, and an alarm signal is sent out after set time delay to remind operating personnel to process in time.
The embodiment of the generator grounding switch state detection system based on signal injection comprises: an injection power supply device and a detection device;
the injection power supply device is used for injecting a low-frequency signal into the primary system of the generator through the grounded secondary side variable resistor;
the detection device comprises an acquisition unit, a filtering unit and a detection calculation unit;
the acquisition unit is used for acquiring the state of the generator grounding switch, acquiring the current of the switch grounding loop or simultaneously acquiring the current of the switch grounding loop and the voltage of the PT (potential transformer) opening triangular winding at the generator end and transmitting the current and the voltage to the filtering unit;
the filtering unit is used for filtering, calculating and processing the electric quantity signals received from the acquisition unit to obtain the amplitudes of low-frequency current and voltage;
the detection and calculation unit is configured to determine whether the grounding switch is effectively closed or turned off according to the state of the grounding switch, the low-frequency current, and the voltage semaphore, and specifically, determine whether the grounding switch is effectively closed by using one or more of the following schemes:
scheme 1: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a first preset threshold value, the grounding disconnecting link is judged to be not closed effectively;
scheme 2: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not closed effectively;
judging whether the grounding disconnecting link is effectively disconnected by adopting one or more of the following schemes:
scheme 3: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 4: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 5: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the amplitude of any phase of low-frequency current is detected to be larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not effectively disconnected.
The filtering unit separates low-frequency components by adopting a method of combining hardware filtering and digital filtering.
Another embodiment of the generator grounding switch state detection system based on signal injection as shown in fig. 2 is based on the above embodiment, and the detection device further comprises an alarm unit: and when the grounding knife switch is judged to be not effectively closed or not effectively disconnected by the detection and calculation unit, an alarm signal is sent out through set time delay.
The method and the system provided by the invention can solve the problems that the grounding knife switch contact of the generator is difficult to reflect the actual state of three phases, the accidents of closing with a grounding knife and the like cannot be avoided, and the safety and the reliability of the primary system operation of a power plant are improved.
The above embodiments are merely illustrative of the technical ideas of the present invention, and the technical ideas of the present invention can not be used to limit the scope of the present invention.

Claims (10)

1. A generator grounding switch state detection method based on signal injection is characterized in that: the method comprises the following steps:
step 1: the injection power supply device injects a low-frequency current signal from the low-voltage side of the neutral point grounding transformer of the generator; under the normal operation and shutdown states of the generator, the injection power supply can work normally and reliably;
step 2: collecting the state of a grounding disconnecting link and three-phase current on a grounding circuit of the grounding disconnecting link, and separating three-phase low-frequency current signals; or simultaneously collecting three-phase current on a grounding circuit of the grounding disconnecting link and voltage signals at two ends of an opening triangular winding of a terminal voltage transformer, and separating three-phase low-frequency current signals and low-frequency voltage signals;
and step 3: whether the grounding knife switch is effectively closed is judged by adopting one of the following schemes:
scheme 1: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a first preset threshold value, the grounding disconnecting link is judged to be not closed effectively;
scheme 2: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not closed effectively;
whether the grounding disconnecting link is effectively disconnected is judged by adopting one of the following schemes:
scheme 3: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 4: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 5: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the amplitude of any phase of low-frequency current is detected to be larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not effectively disconnected.
2. The method for detecting the state of the generator grounding switch based on the signal injection as claimed in claim 1, wherein: in the step 2, a method of combining hardware filtering and digital filtering is adopted to separate the low-frequency component for detection.
3. The method for detecting the state of the generator grounding switch based on the signal injection as claimed in claim 1, wherein: the specific calculation formula of the scheme 1 is shown as the formula (1):
Figure FDA0003353353180000021
when the formula (1) is satisfied, the grounding knife switch is judged to be not effectively closed, and the low-frequency current of a certain phase is smaller than a set threshold Ith1Indicating that the phase is not closed in place;
the specific calculation formula of the scheme 4 is shown as the formula (2):
Figure FDA0003353353180000022
when the formula (2) is satisfied, the grounding disconnecting link is judged to be not effectively disconnected, and the low-frequency current of a certain phase is larger than a set threshold Ith2Indicating that the phase is not broken in place;
wherein:
Figure FDA0003353353180000023
for three-phase low-frequency current amplitude, I, measured on the earth returnth1For threshold setting of current, Ith2Setting a value for a no-flow threshold; status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
4. The method for detecting the state of the generator grounding switch based on the signal injection as claimed in claim 1, wherein: the specific calculation formula of the scheme 3 is shown as the formula (3):
Figure FDA0003353353180000024
when the formula (3) is satisfied, judging that the grounding disconnecting link cannot be effectively disconnected;
wherein:
Figure FDA0003353353180000025
amplitude, U, of low-frequency voltage measured on terminal PT open-ended delta windingthIs a voltage threshold; status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
5. The method for detecting the state of the generator grounding switch based on the signal injection as claimed in claim 1, wherein:
the specific calculation formula of the scheme 2 is shown as the formula (4):
Figure FDA0003353353180000031
when the formula (4) is satisfied, judging that the grounding disconnecting link cannot be effectively closed, and if the amplitude of the low-frequency current of a certain phase is smaller than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient k, indicating that the grounding disconnecting link is not closed in place;
the specific calculation formula of the scheme 5 is shown as the formula (5):
Figure FDA0003353353180000032
when the formula (5) is satisfied, judging that the grounding disconnecting link is not effectively disconnected, and if the amplitude of the low-frequency current of a certain phase is greater than the product of the amplitude of the low-frequency current between the other two phases and a set coefficient, indicating that the grounding disconnecting link of the phase is not disconnected in place;
wherein:
Figure FDA0003353353180000033
the three-phase low-frequency current amplitude measured on the grounding loop;
Figure FDA0003353353180000034
the amplitude of the low-frequency current between BC, AC and AB phases measured on the grounding loop;
k is a fixed coefficient;
status is the status flag bit of the auxiliary contact of the generator-end grounding switch, and the value is 0 when the grounding switch is disconnected and 1 when the grounding switch is closed.
6. The method for detecting the state of the generator grounding switch based on the signal injection as claimed in claim 1, wherein: further comprising the step 4: and when the grounding knife switch is judged to be not closed effectively or not disconnected effectively, an alarm signal is sent out through set time delay.
7. The method for detecting the state of the generator grounding switch based on the signal injection as claimed in claim 6, wherein: the fixed value range of the set time delay is 0.1 s-30.0 s.
8. The utility model provides a generator ground connection switch state detecting system based on signal injection which characterized by: comprises an injection power supply device and a detection device;
the injection power supply device is used for injecting a low-frequency signal into the primary system of the generator through the grounded secondary side variable resistor; under the normal operation and shutdown states of the generator, the injection power supply can work normally and reliably;
the detection device comprises an acquisition unit, a filtering unit and a detection calculation unit;
the acquisition unit is used for acquiring the state of the generator grounding switch, acquiring the current of the switch grounding loop or simultaneously acquiring the current of the switch grounding loop and the voltage of the PT (potential transformer) opening triangular winding at the generator end and transmitting the current and the voltage to the filtering unit;
the filtering unit is used for filtering, calculating and processing the electric quantity signals received from the acquisition unit to obtain the amplitudes of low-frequency current and voltage;
the detection and calculation unit is configured to determine whether the grounding switch is effectively closed or turned off according to the state of the grounding switch, the low-frequency current, and the voltage semaphore, and specifically, determine whether the grounding switch is effectively closed by using one of the following schemes:
scheme 1: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than a first preset threshold value, the grounding disconnecting link is judged to be not closed effectively;
scheme 2: when the generator is in a shutdown state and the grounding disconnecting link is in a closed position, if the amplitude of any phase of low-frequency current is detected to be smaller than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not closed effectively;
whether the grounding disconnecting link is effectively disconnected is judged by adopting one of the following schemes:
scheme 3: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the detected low-frequency voltage is lower than a set voltage threshold, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 4: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if any phase of low-frequency current is detected to be larger than a second preset threshold value, the grounding disconnecting link is judged to be not effectively disconnected;
scheme 5: when the generator is in a starting state and the grounding disconnecting link is in a disconnection state, if the amplitude of any phase of low-frequency current is detected to be larger than the product of the amplitude of the other two phases of low-frequency current and a set coefficient, the grounding disconnecting link is judged to be not effectively disconnected.
9. The generator grounding switch state detection system based on signal injection as claimed in claim 8, wherein: the filtering unit separates low-frequency components by adopting a method of combining hardware filtering and digital filtering.
10. The generator grounding switch state detection system based on signal injection as claimed in claim 8, wherein: the detection device further comprises an alarm unit: and when the grounding knife switch is judged to be not effectively closed or not effectively disconnected by the detection and calculation unit, an alarm signal is sent out through set time delay.
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