CN111030143A - Three-phase unbalanced system capacitance current test correction method - Google Patents

Three-phase unbalanced system capacitance current test correction method Download PDF

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CN111030143A
CN111030143A CN201911291999.9A CN201911291999A CN111030143A CN 111030143 A CN111030143 A CN 111030143A CN 201911291999 A CN201911291999 A CN 201911291999A CN 111030143 A CN111030143 A CN 111030143A
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voltage
neutral point
suppression coil
grounding transformer
arc suppression
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崔巨勇
金鑫
李冠华
孔剑虹
王诗清
张新宇
耿莉娜
李胜川
韩洪刚
韦德福
朱义东
马一菱
刘芮彤
段方维
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State Grid Corp of China SGCC
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0084—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring voltage only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/28—Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G01R29/16—Measuring asymmetry of polyphase networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

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Abstract

The invention belongs to the technical field of capacitance current testing of a 10kV power distribution system, and particularly relates to a method for testing and correcting capacitance current of a three-phase unbalanced system, which comprises the following steps: setting the gear of a grounding transformer, the gear of an arc suppression coil and the resistance value of a damping resistor in the set; according to the actual operation condition of the system, adjusting three phases of the grounding transformer to different gears, and improving the sensitivity of the arc suppression coil to the grounding fault; recalculating the three-phase unbalance, the detuning degree and the damping rate of the system through the actual gear of the grounding transformer; the capacitive current level of the system is indirectly derived from the result of the recalculation. The invention can realize the correction of the neutral point displacement voltage of the arc suppression coil in a system connected by using the grounding transformer so as to accurately measure the capacitance current value of the system. On the basis of accurately measuring the capacitance current value of the system, the detuning degree of the arc suppression coil is corrected, the condition that the system is under compensation or over compensation is avoided, and the system is guaranteed to effectively extinguish fault arcs when ground faults occur.

Description

Three-phase unbalanced system capacitance current test correction method
Technical Field
The invention belongs to the technical field of capacitance current testing of a 10kV power distribution system, and particularly relates to a method for testing and correcting capacitance current of a three-phase unbalanced system, in particular to a method for testing and correcting capacitance current of a 10kV power distribution system in three-phase unbalanced state through a grounding transformer and an arc suppression coil grounding system.
Background
At present, a 10kV power distribution system mostly adopts a grounding mode that a neutral point is not grounded or an arc suppression coil passes through. With the development of national economy, the power supply radius of a power distribution system is larger and larger, and the line length is also increased continuously, so that the capacitance current level of the system is increased rapidly. Under the operating condition of a neutral point ungrounded mode, the current at a single-phase grounding fault point on the line cannot be compensated, and the fault line cannot be cut off in time for ensuring the reliability of power supply, so that the personal safety of nearby personnel is threatened. In view of the potential for fault currents that can cause repeated restrike of the arc to cause equipment damage by overvoltages in non-faulted phases, and the safety issues of personnel near the fault point, power distribution systems often employ neutral crowbar coils to compensate for the fault current and limit the overvoltage levels in the system.
The 10kV distribution system transformer windings are mostly connected in an angle shape without leading out a neutral point, if an arc suppression coil is deployed in the system to compensate the capacitance current of a single-phase ground fault, a grounding transformer needs to be connected to an outlet or a bus of the transformer, and then an arc suppression coil compensation device is connected to the neutral point of the grounding transformer. The compensation of the arc suppression coil is mainly judged by the displacement voltage of the neutral point, and when the displacement voltage is higher than a threshold value, the compensation is started. The capacitance current level of the single-phase earth fault in the system is related to the earth resistance, if the earth resistance value is large, the starting voltage of the arc suppression coil can not be reached, and the system can not compensate the fault current. Therefore, the unbalance degree of the system is properly changed, the sensitivity of the arc suppression coil to the grounding fault is improved, and the adaptability of the system to high-resistance grounding can be improved. The method influences the calculation of the system unbalance degree and the detuning degree by the complete set of equipment, indirectly causes the inaccurate evaluation of the equipment on the capacitance current level, and can cause the conditions that the system compensation is insufficient or the compensation degree is too high to effectively quench the arc.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for testing and correcting the capacitance current of a three-phase unbalanced system, and aims to solve the problem of correcting the test result of the capacitance current when a grounding transformer is connected in a staggered manner in the grounding mode of a grounding transformer and an arc suppression coil of the existing 10kV system, enable the setting of the detuning degree of the arc suppression coil to better meet the requirement of actual operation, and avoid the phenomenon that the arc cannot be extinguished or the system resonates due to the unreasonable setting of the detuning degree when a fault occurs.
In order to realize the purpose of the invention, the invention is realized by adopting the following technical scheme:
a method for testing and correcting the capacitance current of a three-phase unbalanced system is characterized by comprising the following steps: the method comprises the following steps:
step 1: according to the capacitance current level estimated value, adjusting the gear of the arc suppression coil, the resistance values of the damping resistor and the gear of the grounding transformer;
step 2: measuring the displacement voltage of the neutral point of the system under the working condition according to a voltage transformer of the complete device;
and step 3: adjusting the gears of different phases of the grounding transformer to meet the operation requirement, and measuring the displacement voltage of the neutral point of the system;
and 4, step 4: after the complete equipment is connected into the system, adjusting the gear and the damping resistance value of the arc suppression coil, and measuring the shift voltage of the neutral point;
and 5: and (4) calculating the damping rate and the detuning degree of the system according to the neutral point displacement voltage obtained by measuring in the step (4), and indirectly calculating the capacitance current value of the system.
The capacitance current level estimation in step 1 comprises: estimating the value range of the capacitance current according to the structure of the system network frame; and setting the gear of the arc suppression coil, the gear of the grounding transformer and the damping resistance value by combining the condition of the selected equipment, wherein the gears of the grounding transformer are consistent in three phases.
The step 2 of measuring the shift voltage of the system neutral point under the working condition comprises the following steps: the neutral point displacement voltage at this time is the component of the rest part after the zero sequence impedance voltage division of the grounding transformer.
Further, the step 2 of measuring the displacement voltage of the neutral point of the system under the working condition according to the voltage transformer of the complete device comprises the following steps; obtaining the relation between the neutral point displacement voltage and the three-phase unbalance degree and the detuning degree of the system according to the formulas (1) to (3):
Figure BDA0002319432100000021
in the formula:
Figure BDA0002319432100000022
for shifting the voltage of the neutral point of the earthed transformer, LarcFor the inductance of the arc suppression coil at the current position, R is the resistance value of the damping resistor, UunFor system unbalance voltage, ZjSingle-phase zero-sequence impedance of the grounding transformer; when the three-phase gears of the grounding transformer are consistent, the equivalent impedance is ZjAnd 3, omega is the angular frequency of the system, and j is a constant.
Figure BDA0002319432100000031
Figure BDA0002319432100000032
In the formula: v is the detuning degree of the arc-suppression coil, ICIs the system capacitance current, ILIs the compensation current of the arc suppression coil,
Figure BDA0002319432100000034
for shifting the voltage of the neutral point of the earthed transformer, LarcR is the resistance value of the damping resistor, and is the inductance of the arc suppression coil at the current position.
Further, the step 3 in the step 2 is to adjust the gears of different phases of the grounding transformer by adopting a measure of differential configuration of the gears of the grounding transformer, that is, the three-phase winding of the grounding transformer is adjusted to different gears, so that the unbalance of the system is enlarged.
Further, in step 3, adjusting the gears of different phases of the grounding transformer to meet the operation requirement, and measuring the shift voltage of the neutral point of the system includes:
when the zero-sequence impedances of the grounding transformers in equation (1) are not equal, equation (1) becomes:
Figure BDA0002319432100000033
in the formula of UA、UB、UCIs a three-phase voltage, ZA、ZB、ZCIn order to adjust the three-phase zero-sequence impedance of the grounding transformer,
Figure BDA0002319432100000035
for shifting the voltage of the neutral point of the earthed transformer, LarcR is the resistance value of the damping resistor, and is the inductance of the arc suppression coil at the current position.
Further, in the step 4, the adjustment of the gear and the damping resistance value of the arc suppression coil is performed by obtaining the relationship between the neutral point displacement voltage of the grounding transformer and the system unbalance degree according to the previous steps, considering the influence factors caused by the zero sequence impedances of different gears of the grounding transformer during calculation, and adjusting the gear and the damping resistance value of the arc suppression coil to measure the displacement voltage.
Further, when the damping rate and the detuning degree of the system are calculated in step 5, the sum of the zero sequence impedances of the arc suppression coil and the grounding transformer is regarded as the inductive reactance generating the compensation current, and then the corrected zero sequence voltage value of the system needs to be used.
Further, in step 5, the neutral point displacement voltage obtained through measurement according to the above process, the damping rate and the detuning degree of the system are calculated, and the capacitance current value of the system is indirectly obtained, the relationship between the neutral point displacement voltage of the grounding transformer and the zero sequence voltage of the system is obtained according to the formula (4), and the damping rate and the detuning degree of the system are calculated, so that the capacitance current value of the system is indirectly obtained.
Further, in step 5, the calculating of the damping rate and the detuning degree of the system according to the neutral point displacement voltage obtained through the measurement in the above process and the indirectly obtaining the capacitance current value of the system specifically include:
the damping rate, the degree of detuning, etc. of the computing system are estimated according to equation (5):
Figure BDA0002319432100000041
in the formula:
Figure BDA0002319432100000042
for shifting the voltage of the neutral point of the earthed transformer, UunThe voltage is the unbalanced voltage of the system, v is the detuning degree of the arc suppression coil, and d is the damping rate of the system; and calculating the capacitance current value of the system according to the detuning degree of the system and the gear of the current arc suppression coil, and setting the detuning degree according to the corrected zero sequence voltage value of the system.
The invention has the following beneficial effects and advantages:
the correction method can realize the correction of the neutral point displacement voltage of the arc suppression coil in a system connected by using the grounding transformer so as to accurately measure the capacitance current value of the system.
The correction method can correct the detuning degree of the arc suppression coil on the basis of accurately measuring the capacitance current value of the system, avoid the condition that the system is under compensation or over compensation, and ensure that the system can effectively extinguish the fault arc when the ground fault occurs.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments of the present invention will be briefly described below. Wherein the drawings are only for purposes of illustrating some embodiments of the invention and are not to be construed as limiting the invention to all embodiments thereof.
FIG. 1 is a schematic diagram of the system of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention relates to a method for testing and correcting the capacitance current of a three-phase unbalanced system, which specifically comprises the following steps:
step 1: according to the capacitance current level estimated value, adjusting the gear of the arc suppression coil, the resistance values of the damping resistor and the gear of the grounding transformer;
the estimated value of the capacitance current level in step 1 can estimate an approximate value range of the capacitance current according to the structure of the system network frame. And setting the gear of the arc suppression coil, the gear of the grounding transformer and the damping resistance value by combining the condition of the selected equipment, wherein the gears of the grounding transformer are consistent in three phases.
Step 2: measuring the displacement voltage of the neutral point of the system under the working condition according to a voltage transformer of the complete device;
and 2, measuring the system neutral point displacement voltage under the working condition, wherein the neutral point displacement voltage at the moment is not all zero-sequence voltage caused by system unbalance, but is the component of the rest part after partial voltage is divided by zero-sequence impedance of the grounding transformer.
The relation between the neutral point displacement voltage and the three-phase unbalance degree and the detuning degree of the system at the moment can be obtained according to the formulas (1) to (3):
Figure BDA0002319432100000051
in the formula:
Figure BDA0002319432100000054
for shifting the voltage of the neutral point of the earthed transformer, LarcFor the inductance of the arc suppression coil at the current position, R is the resistance value of the damping resistor, UunFor system unbalance voltage, ZjIs single-phase zero-sequence impedance of the grounding transformer. When the three-phase gears of the grounding transformer are consistent, the equivalent impedance is ZjAnd 3, omega is the angular frequency of the system, and j is a constant.
Figure BDA0002319432100000052
Figure BDA0002319432100000053
In the formula: v is the detuning degree of the arc-suppression coil, ICIs the system capacitance current, ILIs the compensation current of the arc suppression coil,
Figure BDA0002319432100000055
for shifting the voltage of the neutral point of the earthed transformer, LarcR is the resistance value of the damping resistor, and is the inductance of the arc suppression coil at the current position.
And step 3: adjusting the gears of different phases of the grounding transformer to meet the operation requirement, and measuring the displacement voltage of the neutral point of the system;
and in the step 3, different phases of gears of the grounding transformer are adjusted. In order to improve the sensitivity of the arc suppression coil to the ground fault, a measure of differential configuration of the gears of the grounding transformer is often adopted, namely, the three-phase winding of the grounding transformer is adjusted to different gears, so that the unbalance degree of the system is enlarged, and the compensation of the arc suppression coil is facilitated.
When the zero sequence impedances of the grounding transformers in the formula (1) are not equal, the formula (1) is changed into
Figure BDA0002319432100000061
In the formula of UA、UB、UCIs a three-phase voltage, ZA、ZB、ZCIn order to adjust the three-phase zero-sequence impedance of the grounding transformer,
Figure BDA0002319432100000063
for shifting the voltage of the neutral point of the earthed transformer, LarcR is the resistance value of the damping resistor, and is the inductance of the arc suppression coil at the current position.
And 4, step 4: after the complete equipment is connected into the system, adjusting the gear and the damping resistance value of the arc suppression coil, and measuring the shift voltage of the neutral point;
and 4, adjusting the gear and the damping resistance value of the arc suppression coil in the step 4, obtaining the relation between the neutral point displacement voltage of the grounding transformer and the system unbalance degree according to the previous steps, considering influence factors caused by zero-sequence impedance of different gears of the grounding transformer during calculation, and adjusting the gear and the damping resistance value of the arc suppression coil to measure the displacement voltage.
And 5: and (4) calculating the damping rate and the detuning degree of the system according to the neutral point displacement voltage obtained by the measurement in the process, and indirectly calculating the capacitance current value of the system.
When the damping rate and the detuning degree of the system are calculated in the step 5, the sum of the zero sequence impedances of the arc suppression coil and the grounding transformer is regarded as the inductive reactance generating the compensation current, and then the corrected zero sequence voltage value of the system needs to be used.
And (4) obtaining the relation between the neutral point displacement voltage of the grounding transformer and the zero sequence voltage of the system according to the formula (4), calculating the damping rate and the detuning degree of the system, and indirectly calculating the capacitance current value of the system. The damping rate, the degree of detuning, etc. of the computing system are estimated according to equation (5):
Figure BDA0002319432100000062
in the formula:
Figure BDA0002319432100000064
for shifting the voltage of the neutral point of the earthed transformer, UunThe voltage is unbalanced in the system, v is the detuning degree of the arc suppression coil, and d is the damping rate of the system. And calculating the capacitance current value of the system according to the detuning degree of the system and the gear of the current arc suppression coil, and setting the detuning degree according to the corrected zero sequence voltage value of the system.
Those of ordinary skill in the art will understand that:
the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these examples; within the idea of the invention, also features in the above embodiments or in different embodiments may be combined, steps may be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.
The embodiments of the invention are intended to embrace all such alternatives, modifications and variances that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, substitutions, improvements and the like that may be made without departing from the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (10)

1. A method for testing and correcting the capacitance current of a three-phase unbalanced system is characterized by comprising the following steps: the method comprises the following steps:
step 1: according to the capacitance current level estimated value, adjusting the gear of the arc suppression coil, the resistance values of the damping resistor and the gear of the grounding transformer;
step 2: measuring the displacement voltage of the neutral point of the system under the working condition according to a voltage transformer of the complete device;
and step 3: adjusting the gears of different phases of the grounding transformer to meet the operation requirement, and measuring the displacement voltage of the neutral point of the system;
and 4, step 4: after the complete equipment is connected into the system, adjusting the gear and the damping resistance value of the arc suppression coil, and measuring the shift voltage of the neutral point;
and 5: and (4) calculating the damping rate and the detuning degree of the system according to the neutral point displacement voltage obtained by measuring in the step (4), and indirectly calculating the capacitance current value of the system.
2. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: the capacitance current level estimation in step 1 comprises: estimating the value range of the capacitance current according to the structure of the system network frame; and setting the gear of the arc suppression coil, the gear of the grounding transformer and the damping resistance value by combining the condition of the selected equipment, wherein the gears of the grounding transformer are consistent in three phases.
3. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: the step 2 of measuring the shift voltage of the system neutral point under the working condition comprises the following steps: the neutral point displacement voltage at this time is the component of the rest part after the zero sequence impedance voltage division of the grounding transformer.
4. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: step 2, measuring the displacement voltage of the neutral point of the system under the working condition according to the voltage transformer of the complete device, which comprises the following steps; obtaining the relation between the neutral point displacement voltage and the three-phase unbalance degree and the detuning degree of the system according to the formulas (1) to (3):
Figure FDA0002319432090000011
in the formula:
Figure FDA0002319432090000012
for shifting the voltage of the neutral point of the earthed transformer, LarcFor the inductance of the arc suppression coil at the current position, R is the resistance value of the damping resistor, UunFor system unbalance voltage, ZjSingle-phase zero-sequence impedance of the grounding transformer; when the three-phase gears of the grounding transformer are consistent, the equivalent impedance is ZjAnd 3, omega is the angular frequency of the system, and j is a constant.
Figure FDA0002319432090000021
Figure FDA0002319432090000022
In the formula: v is the detuning degree of the arc-suppression coil, ICIs the system capacitance current, ILIs the compensation current of the arc suppression coil,
Figure FDA0002319432090000025
for shifting the voltage of the neutral point of the earthed transformer, LarcR is the resistance value of the damping resistor, and is the inductance of the arc suppression coil at the current position.
5. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: in the step 2, the adjustment of the gears of different phases of the grounding transformer in the step 3 is performed by adopting a measure of differential configuration of the gears of the grounding transformer, namely, the three-phase winding of the grounding transformer is adjusted to different gears, so that the unbalance of the system is enlarged.
6. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: in step 3, adjusting the gears of different phases of the grounding transformer to meet the operation requirement, and measuring the shift voltage of the neutral point of the system comprises:
when the zero-sequence impedances of the grounding transformers in equation (1) are not equal, equation (1) becomes:
Figure FDA0002319432090000023
in the formula of UA、UB、UCIs a three-phase voltage, ZA、ZB、ZCIn order to adjust the three-phase zero-sequence impedance of the grounding transformer,
Figure FDA0002319432090000024
for shifting the voltage of the neutral point of the earthed transformer, LarcR is the resistance value of the damping resistor, and is the inductance of the arc suppression coil at the current position.
7. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: and 4, adjusting the gear and the damping resistance value of the arc suppression coil in the step 4, namely obtaining the relation between the neutral point displacement voltage of the grounding transformer and the system unbalance degree according to the previous steps, considering influence factors caused by zero-sequence impedance of different gears of the grounding transformer during calculation, and adjusting the gear and the damping resistance value of the arc suppression coil to measure the displacement voltage.
8. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: and 5, when the damping rate and the detuning degree of the system are calculated in the step 5, the sum of the zero sequence impedances of the arc suppression coil and the grounding transformer is regarded as the inductive reactance generating the compensation current, and the corrected zero sequence voltage value of the system is required to be used at the moment.
9. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: in the step 5, the neutral point displacement voltage obtained through the measurement according to the process is calculated, the damping rate and the detuning degree of the system are calculated, and the capacitance current value of the system is indirectly calculated, wherein the relation between the neutral point displacement voltage of the grounding transformer and the zero sequence voltage of the system is obtained according to the formula (4), the damping rate and the detuning degree of the system are calculated, and the capacitance current value of the system is indirectly calculated.
10. The method for testing and correcting the capacitive current of the three-phase unbalanced system according to claim 1, wherein the method comprises the following steps: in step 5, calculating the damping rate and the detuning degree of the system according to the neutral point displacement voltage obtained by the measurement in the process, and indirectly calculating the capacitance current value of the system, specifically comprising:
the damping rate, the degree of detuning, etc. of the computing system are estimated according to equation (5):
Figure FDA0002319432090000031
in the formula:
Figure FDA0002319432090000032
for shifting the voltage of the neutral point of the earthed transformer, UunThe voltage is the unbalanced voltage of the system, v is the detuning degree of the arc suppression coil, and d is the damping rate of the system; and calculating the capacitance current value of the system according to the detuning degree of the system and the gear of the current arc suppression coil, and setting the detuning degree according to the corrected zero sequence voltage value of the system.
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CN112269049A (en) * 2020-10-14 2021-01-26 广西电网有限责任公司电力科学研究院 Method and system for measuring capacitance-to-ground current of power distribution network
CN113341202A (en) * 2021-06-09 2021-09-03 国网陕西省电力公司电力科学研究院 Method and system for detecting measurement precision of arc suppression coil capacitance current
CN114122996A (en) * 2021-11-25 2022-03-01 广东电网有限责任公司 Capacitor maintenance method and device and transformer voltage regulation early warning method and device

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