On-line Monitoring Device and Method for the Insulation of Impulse Capacitors Inside Generator Outlet Circuit Breakers

Abstract

The present invention relates to an on-line monitoring device and method for the insulation of impulse capacitors in generator outlet circuit breakers. It ingeniously separates the capacitor housing from the ground through insulating pads and connects them with soft copper wires, facilitating the collection of the current passing through the capacitor. It directly uses the PT inside the GCB, providing reliable reference data for the operation of the equipment, reducing the risk of unplanned shutdown of the equipment, and enabling on-line monitoring of the insulation between the poles of the impulse capacitor enclosed inside the GCB that cannot be directly observed through capacitance testing. It provides big data support and reference for the operation, inspection and maintenance of power plants. At the same time, when an unplanned outage occurs in a power generation enterprise, it can quickly and accurately judge whether the tripping is caused by the insulation of the impulse capacitor, helping the power generation enterprise quickly investigate the cause of the tripping and complete the unit grid connection operation in the shortest time, reducing the power consumption assessment of the power generation enterprise by the power grid dispatching department.

Description

Technical Field

[0001] The present invention relates to an on-line monitoring device and method for the inter-pole insulation of impulse capacitors, in particular to an on-line monitoring device and method for the inter-pole insulation of impulse capacitors in a generator outlet circuit breaker (hereinafter referred to as GCB). Background Art

[0002] At present, with the proposal of the national energy industry's carbon peak and carbon neutrality goals, the proportion of the installed capacity of traditional thermal power plants has shown a downward trend. The single-unit capacity of in-service thermal power plants (including nuclear power plants, the same below) is basically above 600MW; the single-unit capacity of large hydropower stations in the traditional clean energy industry is also about 700MW. In-service generating units should face the future to enable existing power generation methods to better adapt to the future intelligent society, energy revolution and innovation. The GCB is installed between the generator outlet and the main transformer and can perform unit grid connection or disconnection operations; during maintenance, the main transformer can be used as a start-up and standby transformer. At the same time, when a fault occurs on the generator side, the GCB operates to isolate the fault point from the system, avoiding the switching of the plant power supply accident, simplifying the control and protection wiring of the plant power supply, and reducing the complexity of the protection action interlock. When a fault occurs in the main transformer, the GCB can be quickly disconnected, so that the generator, transformer and high-voltage auxiliary transformer are within their respective independent protection scopes. The GCB bears a very high load current during operation and must also have the ability to interrupt a very large rated short-circuit current. During the interruption process, a very high arc acts between the breaker contacts of its arc extinguishing chamber, and the contacts are in a conducting state. After the arc extinguishes at the AC zero point of the short-circuit current, the recovery of the insulation dielectric strength between the contacts must be able to withstand the action of the recovery voltage to complete a successful interruption. In order to improve the interruption performance of the GCB, impulse capacitors are usually installed on both sides of its contacts to improve the transient recovery voltage (i.e., TRV) between the contacts after the current zero point. At the same time, as a part of the isolated-phase enclosed bus, the impulse capacitor is connected between the bus and the enclosure. When a single-point ground fault occurs, it is very difficult to detect a single-phase ground fault caused by the inter-pole insulation fault of the impulse capacitor only through insulation resistance testing. Due to its special structure, the impulse capacitor, together with the lightning arrester, voltage transformer, disconnecting switch, arc extinguishing chamber, etc., is enclosed and installed in the housing, and its insulation performance is difficult to visually detect or test by means such as infrared imaging. The impulse capacitor mainly adopts an oil film structure. When inter-pole insulation aging and oil leakage occur, it is very difficult to find problems in the first place, and it is necessary to open the cover plate for item-by-item inspection. At present, only preventive tests are carried out for testing, but the insufficient operation hours of the unit have caused the equipment to be overdue for repair. There is a lack of an intuitive and effective method for judging the inter-pole insulation performance of the impulse capacitor in the GCB. Therefore, its improvement and innovation are imperative. Summary of the Invention

[0003] In view of the above situation, to overcome the defects of the prior art, the object of the present invention is to provide an on-line monitoring device and method for the insulation of impulse capacitors in a generator outlet circuit breaker, which can effectively solve the problem that the insulation performance of impulse capacitors in the GCB cannot be monitored on-line.

[0004] The technical solution solved by the present invention is as follows:

[0005] An on-line monitoring device for the insulation of impulse capacitors in a generator outlet circuit breaker, including a GCB, the GCB includes a housing and an impulse capacitor and a voltage transformer installed in the housing. It is characterized in that both the impulse capacitor and the voltage transformer are installed upside down on the cover plate of the GCB housing. An insulating spacer is provided between the installation hanger of the impulse capacitor and the cover plate of the GCB housing, and is fixed by pressing with insulating bolts. The installation hanger of the impulse capacitor and the cover plate of the GCB housing are short-circuited by a flexible metal busbar. A current transformer for collecting current signals is installed at the grounding end of the outer shell of the impulse capacitor. At the same time, voltage signals are taken from the secondary winding of the voltage transformer inside the GCB housing. The on-line insulation monitoring device also includes a signal processing device;

[0006] The signal processing device calculates the real-time capacitance C through the real-time collected current signal and voltage signal x and compares the real-time capacitance C x with the nameplate rated value Cn, and monitors the insulation condition of the impulse capacitor in the generator outlet circuit breaker on-line through the capacitance change amount △C.

[0007] Preferably, the signal processing device includes a controller, an AD converter, an alarm, a power supply and a key. The signal output ends of the current transformer and the voltage transformer are connected to the signal input end of the AD converter. The output end of the AD converter is connected to the input end of the controller. The output end of the controller is respectively connected to the input ends of the display and the alarm.

[0008] An on-line monitoring method for the inter-electrode insulation of impulse capacitors in a generator outlet circuit breaker based on the above on-line monitoring device includes the following steps:

[0009] Step 1: Install the on-line monitoring device

[0010] During the shutdown and maintenance of the power plant, install the on-line monitoring device, and measure the voltage transformer ratio k1 by applying the operating voltage of the external system.

[0011] The on-line monitoring device includes a GCB. The GCB includes a housing and a shunt capacitor and a voltage transformer installed in the housing. It is characterized in that both the shunt capacitor and the voltage transformer are installed upside down on the cover plate of the GCB housing. An insulating spacer is provided between the mounting hanger of the shunt capacitor and the cover plate of the GCB housing and is fixed by tightening with insulating bolts. The mounting hanger of the shunt capacitor and the cover plate of the GCB housing are short-circuited by a flexible metal busbar. A current transformer for collecting current signals is installed at the grounding end of the outer shell of the shunt capacitor. At the same time, a voltage signal is taken from the secondary winding of the voltage transformer inside the GCB housing. The on-line monitoring device also includes a signal processing device;

[0012] The current signal collected by the current transformer is led out to the input end through a current signal lead-out bushing provided on the GCB housing; the voltage signal collected by the voltage transformer is led out to the input end of the signal processing device through a voltage signal lead-out bushing provided on the GCB housing;

[0013] The signal processing device includes a controller, an AD converter, an alarm, a power supply and a key. The signal output ends of the current transformer and the voltage transformer are connected to the signal input end of the AD converter. The output end of the AD converter is connected to the input end of the controller. The output end of the controller is respectively connected to the input ends of a display and an alarm;

[0014] Step two: On-line monitoring

[0015] When the GCB operates normally, the current transformer collects the current I in real time ax , and the voltage transformer collects the secondary voltage U in real time 1a1n . The signal processing device sequentially calculates the apparent power S, the reactive power Q, the system capacitive reactance X c , and the capacitance value C of the shunt capacitor x according to the following formulas:

[0016] S = k1×U 1a1n ×I ax

[0017] Q≈S, regarded as Q = S

[0018] Xc = k1×U 1a1n ÷I ax

[0019] C x = 1÷(2×π×f×Xc)

[0020] (There is no discharge resistor inside the shunt capacitor. The power loss of the system is mainly reactive power loss, and the active power loss P is ignored)

[0021] And the obtained data is stored and the C x -t data curve is plotted;

[0022] The signal processing device compares the capacitance value C of the impulse capacitor measured in real time x with the rated capacitance value C on the nameplate n through the following formula for differential comparison calculation to obtain the capacitance change ΔC:

[0023] ΔC = (C x - C n ) ÷ C n × 100%

[0024] The insulation condition of the impulse capacitor in the generator outlet circuit breaker is judged by the following criteria:

[0025] a. When the capacitance change ΔC is within [-5%, +10%], it is judged that the current is in the initial state and the main insulation of the impulse capacitor is good;

[0026] b. When the capacitance change ΔC is within (-∞, -5%), it is judged that the main insulation of the impulse capacitor has failed (such as open circuit in the series section of the capacitor core, etc.), and a fault alarm signal is sent on the display interface of the display, and at the same time the alarm goes off;

[0027] c. When the capacitance change ΔC is within (+10%, +∞), it is judged that the main insulation of the impulse capacitor has deteriorated (such as serious breakdown of the capacitor core, moisture ingress in the oil film insulation, etc.), and a deterioration alarm signal is sent on the display interface of the display, and at the same time the alarm goes off.

[0028] Inside the impulse capacitor, several capacitor cores are composed in a series-parallel structure. The electrodes of the capacitor core are made of aluminum foil, the dielectric between the electrodes is made of polypropylene film, and benzyltoluene is impregnated (for filling and insulation). When the insulation of the dielectric between the electrodes deteriorates, the dielectric constant changes, which in turn affects the capacitance of the capacitor core, and the capacitance of the impulse capacitor changes accordingly; short circuits and open circuits in the series and parallel connections of different capacitor cores will also affect the capacitance of the impulse capacitor. Therefore, the on-line monitoring method of the present invention obtains the real-time capacitance C of the impulse capacitor by collecting the PT secondary voltage signal in the GCB and the current signal at the grounding end of the impulse capacitor, and through signal calculation by the processor x and compares the real-time capacitance C x with the rated value Cn on the nameplate, and on-line monitors the insulation condition of the impulse capacitor in the generator outlet circuit breaker through the capacitance change ΔC.

[0029] Compared with the prior art, the on-line monitoring device of the present invention has a novel and unique structure, which is simple and reasonable, easy to produce and operate, and can be modified on the basis of the existing GCB. It provides reliable reference data for the operation of the equipment, reduces the risk of unplanned shutdown of the equipment, and can realize on-line monitoring of the inter-pole insulation of the impulse capacitor enclosed inside the GCB through capacitance testing. It can provide big data support and reference for the operation, inspection and maintenance of power plants. As a device inside the GCB, the insulation of the impulse capacitor is easily overlooked. At the same time, when an unplanned outage occurs in a power generation enterprise, it can quickly and accurately judge whether the tripping is caused by the insulation of the impulse capacitor, which helps the power generation enterprise quickly investigate the cause of the tripping and complete the unit grid connection operation in the shortest time, reducing the power consumption assessment of the power generation enterprise by the power grid dispatching department. Thus, it indirectly generates income for the power generation enterprise. The innovation of the present invention in on-line monitoring of the insulation state of the impulse capacitor inside the GCB cleverly separates the capacitor shell from the ground through an insulating pad and connects them through a soft copper wire, which is convenient for collecting the current passing through the capacitor and directly uses the PT inside the GCB, reducing the cost. It is convenient to use and has good effects. It is an innovation in the method of on-line monitoring of the insulation of the impulse capacitor inside the generator outlet circuit breaker, and has good social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the electrical schematic diagram of the present invention (in the figure, C1 and C2 are the impulse capacitors on both sides of the arc extinguishing chamber of the GCB, and all the devices within the dotted line box constitute the GCB).

[0031] Figure 2 is the cross-sectional view at the impulse capacitor of the GCB of the present invention.

[0032] Figure 3 is the structural schematic diagram of the on-line monitoring device of the present invention.

[0033] Figure 4 is the cross-sectional view at the voltage transformer of the GCB of the present invention.

[0034] Figure 5 is the circuit principle block diagram of the signal processing device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The following further details the specific embodiments of the present invention with reference to the accompanying drawings.

[0036] By Figures 1-5Provided is an on-line monitoring device for the inter-electrode insulation of impulse capacitors in a generator outlet circuit breaker according to the present invention. The circuit breaker includes a GCB, which comprises a housing and an impulse capacitor 5 and a voltage transformer 8 installed in the housing. The impulse capacitor 5 and the voltage transformer 8 are both installed upside down on the cover plate 1 of the GCB housing. An insulating spacer 3 is provided between the mounting hanger 2 of the impulse capacitor 5 and the cover plate 1 of the GCB housing, and is fixed by pressing with an insulating bolt 4. The mounting hanger 2 of the impulse capacitor 5 and the cover plate 1 of the GCB housing are short-circuited by a flexible metal bus 6. A current transformer 7 for collecting current signals is installed at the grounding end of the outer shell of the impulse capacitor 5. At the same time, a voltage signal is taken from the secondary winding of the voltage transformer 8 inside the GCB housing. The on-line insulation monitoring device further includes a signal processing device;

[0037] The signal processing device calculates the real-time capacitance C through the real-time current signal and voltage signal collected in real time x and compares the real-time capacitance C x with the nameplate rated value Cn, and online monitors the insulation condition of the impulse capacitor in the generator outlet circuit breaker through the capacitance change ΔC.

[0038] To ensure the use effect, one terminal of the flexible metal bus 6 is pressed and contacted with the mounting hanger 2 by an insulating bolt 4, and the other terminal is contacted and installed on the cover plate 1 of the GCB housing. The input end of the current transformer 7 is connected to the flexible metal bus 6.

[0039] The current signal collected by the current transformer 7 is led out to the input end through a current signal lead-out bushing provided on the GCB housing; the voltage signal collected by the voltage transformer 8 is led out to the input end of the signal processing device through a voltage signal lead-out bushing provided on the GCB housing.

[0040] Small round holes (such as Figure 4 shown as 1a and 1n in the figure) are provided on the outer walls at both ends of the GCB arc extinguishing chamber break for leading out voltage and current signals. After the installation bushings are led out, they are sealed with fireproof mud to prevent foreign objects from falling in or small animals from entering. The signal wire uses a shielded cable to prevent interference caused by strong electric fields to signal measurement, and the signal wire is arranged closely along the GCB outer shell, maintaining a sufficient insulation distance from the high-voltage energized part of the GCB. The impulse capacitor and the voltage transformer are arranged in a horizontal straight line in three phases of U, V, and W. One impulse capacitor is installed on each side of the GCB, and there are three phases of U, V, and W in total, so 6 sets of signal acquisition structures are required.

[0041] The signal processing device includes a controller, an AD converter, an alarm, a power supply and a key. The signal output ends of the current transformer 7 and the voltage transformer 8 are connected to the signal input end of the AD converter, the output end of the AD converter is connected to the input end of the controller, and the output end of the controller is respectively connected to the input ends of the display and the alarm.

[0042] The button is connected to the controller for inputting relevant instructions, the power supply is used to supply power to each component, and the AD converter is used for signal conversion; the controller can multiply the measured voltage by the transformation ratio of the voltage transformer to obtain the current relative ground voltage of the system operation; combined with the measured current of the impulse capacitor, the apparent power S and the reactive power Q are obtained through power analysis and calculation, and then the current capacitive reactance is obtained. The controller can identify the current system frequency f through the measured voltage, as well as the calculated apparent power S, reactive power Q, and the capacitance value C of the impulse capacitor x The display is used to display the measured voltage U 1a1n and current I ax and frequency f. The signal processing device has the functions of setting rated values and alarm values. When the real-time capacitance Cx exceeds the deviation, the controller can prompt an alarm signal on the display interface, and at the same time, the alarm sounds. This controller is a prior art, such as a single-chip microcomputer controller of model MCS-80960, etc.

[0043] An on-line insulation monitoring method for impulse capacitors in a generator outlet circuit breaker based on the above on-line monitoring device, comprising the following steps:

[0044] Step 1: Install the on-line monitoring device

[0045] During the power plant shutdown for maintenance, install the on-line monitoring device, and measure the transformation ratio k1 of the voltage transformer by applying the system operating voltage externally;

[0046] The on-line monitoring device includes a GCB. The GCB includes a housing and an impulse capacitor 5 and a voltage transformer 8 installed in the housing. It is characterized in that both the impulse capacitor 5 and the voltage transformer 8 are installed upside down on the cover plate 1 of the GCB housing. An insulating spacer 3 is provided between the mounting hanger 2 of the impulse capacitor 5 and the cover plate 1 of the GCB housing, and is fixed by pressing with an insulating bolt 4. The mounting hanger 2 of the impulse capacitor 5 and the cover plate 1 of the GCB housing are short-circuited by a flexible metal bus 6. A current transformer 7 for collecting current signals is installed at the grounding end of the outer shell of the impulse capacitor 5. At the same time, a voltage signal is taken from the secondary winding of the voltage transformer 8 inside the GCB housing. The on-line monitoring device also includes a signal processing device;

[0047] The current signal collected by the current transformer 7 is led out to the input end through a current signal lead-out bushing provided on the GCB housing; the voltage signal collected by the voltage transformer 8 is led out to the input end of the signal processing device through a voltage signal lead-out bushing provided on the GCB housing;

[0048] The signal processing device includes a controller, an AD converter, an alarm, a power supply and a button. The signal output ends of a current transformer 7 and a voltage transformer 8 are connected to the signal input end of the AD converter. The output end of the AD converter is connected to the input end of the controller. The output end of the controller is respectively connected to the input ends of a display and an alarm;

[0049] Step 2: Online monitoring

[0050] The GCB operates normally, and the current transformer real-time collects current I ax , and the voltage transformer real-time collects secondary voltage U 1a1n , and the signal processing device sequentially calculates the apparent power S, the reactive power Q, and the system capacitive reactance X according to the following formula c , the capacitance value C of the impulse capacitor x :

[0051] S = k1 × U 1a1n × I ax

[0052] Q ≈ S, regarded as Q = S

[0053] Xc = k1 × U 1a1n ÷ I ax

[0054] C x = 1÷(2×π×f×Xc)

[0055] And store the obtained data and draw the C x -t data curve;

[0056] The signal processing device compares the capacitance value C of the impulse capacitor measured in real time x with the rated capacitance value C on the nameplate n through the following formula for difference comparison calculation to obtain the capacitance change ΔC:

[0057] ΔC = (C x - C n )÷ C n × 100%

[0058] Judge the insulation condition of the impulse capacitor in the generator outlet circuit breaker through the following criteria:

[0059] a. When the capacitance change ΔC is within [-5%, +10%], it is determined that the current is in the initial state and the main insulation of the impulse capacitor is good;

[0060] b. When the capacitance change ΔC is within (-∞, -5%), it is determined that the main insulation of the impulse capacitor has failed (such as the series section of the capacitor core is open circuit, etc.), and a fault alarm signal is sent on the display interface of the display, and at the same time the alarm gives an alarm;

[0061] c. When the change in capacitance ΔC is within the range of (+10%, +∞), it is determined that the main insulation of the impulse capacitor has deteriorated (such as serious breakdown of the capacitor core, moisture ingress in the oil film insulation, etc.). A deterioration alarm signal is sent on the display interface of the monitor, and at the same time, the alarm goes off.

[0062] Through actual application, the present invention has achieved good technical effects. In the laboratory, an external excitation transformer is used to generate a high voltage of 10 kV, which is applied to the high-voltage end of the impulse capacitor to simulate the operating state; the signal acquisition device for measuring the current signal is clamped to the grounded end of the outer shell of the impulse capacitor; the voltage signal is taken from the measuring winding of the excitation transformer (the transformer is also a special voltage transformer, and the measuring winding can be used as the secondary winding). Using different parallel combinations of several existing capacitors in the laboratory for simulation, the equipment is connected according to the device of the present invention, and numerical acquisition and on-line monitoring are carried out by the method of the present invention. The live test data in the laboratory are shown in Table 1 as follows:

[0063] Table 1 Simulated live test data of impulse capacitors in GCB

[0064]

[0065] For Condition 1 in the table, the rated capacitance of the impulse capacitor is 260 nF, and the measured value is 264.8 nF, corresponding to the impulse capacitor on the main transformer side. The value of ΔC is +1.85%, which falls within the range of [-5%, +10%], and the insulation state should be good.

[0066] For Condition 2 in the table, the rated capacitance of the impulse capacitor used is 132 nF, and the measured value is 131.2 nF, corresponding to the impulse capacitor on the generator side. The value of ΔC is -0.6%, which falls within the range of [-5%, +10%], and the insulation state should be good.

[0067] For Condition 3a in the table, the impulse capacitor corresponds to a parallel combination of 260 nF and 132 nF capacitors. The measured capacitance is 395.4 nF, simulating the insulation deterioration state of the capacitor. Compared with the 132 nF capacitor, the value of ΔC is +199.5%, which falls within the range of (+10%, +∞), and the insulation state should be deteriorated, which is consistent with the simulated deterioration state;

[0068] For Condition 3b in the table, the impulse capacitor corresponds to a parallel combination of 260 nF and 132 nF capacitors. The measured capacitance is 395.4 nF, simulating the insulation deterioration state of the capacitor. Compared with the 264 nF capacitor, the value of ΔC is +49.77%, which falls within the range of (+10%, +∞), and the insulation state should be deteriorated, which is consistent with the simulated deterioration state;

[0069] In the table, for operating condition 4, the rated capacitance of the impulse capacitor is 260 nF, and the measured value is 193.3 nF. Corresponding to the impulse capacitor on the main transformer side, the value of △C is -25.6%, falling within the range of (-∞, -5%), indicating that the insulation has failed. After disassembly, it was found that the connecting wire between the series segments inside the capacitor was burned.

[0070] During the operation of a 420 MW load of Unit 2 of a power generation enterprise in October 2021, the device of the present invention reported a capacitance deviation of +14.3%. After applying to the dispatcher for an emergency shutdown and inspection, it was found that the excitation transformer, voltage transformer, enclosed bus, etc. connected to the generator outlet were all in normal insulation. The fault location was initially judged to be on the GCB side, which was consistent with the device alarm. After opening the GCB cover plate, it was found that the impulse capacitor on the main transformer side had bulging and oil leakage phenomena, effectively verifying the method of this invention patent.

Claims

1. An on-line insulation monitoring device for impulse capacitors in a generator outlet circuit breaker, comprising a GCB, the GCB including a housing and an impulse capacitor (5) and a voltage transformer (8) installed in the housing, characterized in that, The impulse capacitor (5) and the voltage transformer (8) are both installed upside down on the cover plate (1) of the GCB housing. An insulating spacer (3) is provided between the mounting hanger (2) of the impulse capacitor (5) and the cover plate (1) of the GCB housing, and is fixed by tightening with insulating bolts (4). The mounting hanger (2) of the impulse capacitor (5) and the cover plate (1) of the GCB housing are short-circuited by a flexible metal busbar (6). A current transformer (7) for collecting current signals is installed at the grounding end of the outer shell of the impulse capacitor (5). At the same time, a voltage signal is taken from the secondary winding of the voltage transformer (8) inside the GCB housing. The insulation on-line monitoring device further includes a signal processing device; The signal processing device calculates the real-time capacitance C through the real-time collected current signal and voltage signal. x , and the real-time capacitance C x Compared with the nameplate rated value Cn, the capacitance change △C is used to monitor the insulation condition of the impulse capacitor in the generator output circuit breaker online; One terminal of the flexible metal busbar (6) is pressed and contacted on the mounting hanger (2) by an insulating bolt (4), and the other terminal is contacted and installed on the cover plate (1) of the GCB housing. The input end of the current transformer (7) is connected to the flexible metal busbar (6); The current signal collected by the current transformer (7) is led out to the input end through a current signal lead-out bushing provided on the GCB housing; the voltage signal collected by the voltage transformer (8) is led out to the input end of the signal processing device through a voltage signal lead-out bushing provided on the GCB housing; The signal processing device includes a controller, an AD converter, an alarm, a power supply and a key. The signal output ends of the current transformer (7) and the voltage transformer (8) are connected to the signal input end of the AD converter. The output end of the AD converter is connected to the input end of the controller. The output end of the controller is respectively connected to the input ends of a display and an alarm.

2. An on-line insulation monitoring method for impulse capacitors inside a generator outlet circuit breaker based on the on-line monitoring device of claim 1, characterized in that, Including the following steps: Step 1: Install the on-line monitoring device During the power plant shutdown for maintenance, install the on-line monitoring device, and measure the voltage transformer ratio k1 by applying the operating voltage of the external system; The on-line monitoring device includes a GCB. The GCB includes a housing and an impulse capacitor (5) and a voltage transformer (8) installed in the housing. It is characterized in that the impulse capacitor (5) and the voltage transformer (8) are both installed upside down on the cover plate (1) of the GCB housing. An insulating spacer (3) is provided between the mounting hanger (2) of the impulse capacitor (5) and the cover plate (1) of the GCB housing, and is fixed by tightening with insulating bolts (4). The mounting hanger (2) of the impulse capacitor (5) and the cover plate (1) of the GCB housing are short-circuited by a flexible metal busbar (6). A current transformer (7) for collecting current signals is installed at the grounding end of the outer shell of the impulse capacitor (5). At the same time, a voltage signal is taken from the secondary winding of the voltage transformer (8) inside the GCB housing. The on-line monitoring device further includes a signal processing device; The current signal collected by the current transformer (7) is led out to the input end through a current signal lead-out bushing provided on the GCB housing; the voltage signal collected by the voltage transformer (8) is led out to the input end of the signal processing device through a voltage signal lead-out bushing provided on the GCB housing; The signal processing device includes a controller, an AD converter, an alarm, a power supply and a button. The signal output ends of a current transformer (7) and a voltage transformer (8) are connected to the signal input end of the AD converter. The output end of the AD converter is connected to the input end of the controller. The output end of the controller is respectively connected to the input ends of a display and an alarm; Step 2: Online monitoring The GCB operates normally, and the current transformer collects the current I in real time ax , and the voltage transformer collects the secondary voltage U in real time 1a1n , and the signal processing device sequentially calculates the apparent power S, reactive power Q, system capacitive reactance X according to the following formula c , the capacitance value C of the impulse capacitor x : S = k1×U 1a1n ×I ax Q = S Xc = k1 × U 1a1n ÷ I ax C x = 1 ÷ (2 × π × f × Xc) And store the obtained data and plot the C x -t data curve; The signal processing device compares the capacitance value C of the impact capacitor measured in real time x with the rated capacitance value C on the nameplate n through the following formula for differential comparison calculation to obtain the capacitance change ΔC: △C = (C x - C n ) ÷ C n × 100% The insulation condition of the impulse capacitor in the generator outlet circuit breaker is judged by the following criteria: a. When the capacitance change amount △C is within [-5%, +10%], it is judged that the current is in the initial state and the main insulation of the impulse capacitor is good; b. When the capacitance change amount △C is within (-∞, -5%), it is judged that the main insulation of the impulse capacitor has failed, and a fault alarm signal is sent on the display interface of the display, and the alarm also gives an alarm at the same time; c. When the capacitance change amount △C is within (+10%, +∞), it is judged that the main insulation of the impulse capacitor has deteriorated, and a deterioration alarm signal is sent on the display interface of the display, and the alarm also gives an alarm at the same time.

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