CN-122017366-A - Method for measuring bus capacitance of low-current grounding system

Abstract

The invention discloses a novel high-efficiency method for measuring bus capacitance of a low-current grounding system, and relates to the technical field of power system measurement. According to the method, under the condition that the arc suppression coil is normally connected into the system, accurate measurement of the bus grounding capacitance is realized by additionally adding a group of measurement capacitance and short-circuit current measurement links and combining an improved mathematical model. Compared with the traditional detection method, the novel method does not need to pull open a knife switch of the arc suppression coil or operate other primary high-voltage equipment during measurement, avoids an operation ticket application flow which is required to be executed because of operating the primary equipment, remarkably improves the measurement efficiency, is suitable for quick general investigation and daily operation and maintenance of a transformer substation, and is beneficial to guaranteeing safe and stable operation of a power grid.

Inventors

• YANG JUN

Assignees

• 电子科技大学

Dates

Publication Date

20260512

Application Date

20260302

Claims (4)

1. 1. The system comprises a bus capacitor C 0 , a three-phase unbalanced potential E p , an arc suppression coil Z formed by a resistor R and an inductor L, and an arc suppression coil knife switch K, and is characterized in that the bus capacitor C 0 is measured and calculated by controlling only an input switch of an external circuit through an external short-circuit measurement ammeter T, external measurement capacitors C1 and C2 and a corresponding input switch K 0 、K 1 、K 2 , and the external measurement capacitors C1 and C2, the short-circuit measurement ammeter T and the arc suppression coil Z are connected in parallel, and the measurement steps are as follows: When the arc suppression coil knife switch K is always in a closed state, the neutral point grounding voltage U 0 ;K 0 is measured when all the arc suppression coil knife switch K 0 、K 1 、K 2 is opened, the short-circuit current I d ;K 1 is measured when the arc suppression coil knife switch K 1 、K 2 is opened, the first grounding voltage U 1 ,K 0 is measured when the arc suppression coil knife switch K 0 、K 2 is opened, the second grounding voltage U 2 is measured when the arc suppression coil knife switch K 1 、K 2 is closed, and then a mathematical model is established to solve the bus capacitor C 0 .
2. 2. The method for measuring the bus capacitance of the low-current grounding system according to claim 1, wherein the arc suppression coil impedance under normal operation is reduced to a pure resistor R when the bus capacitance C 0 is solved by establishing a mathematical model, and inductance components are ignored.
3. 3. The method for measuring the bus capacitance of the low-current grounding system according to claim 1, wherein the establishing a mathematical model to solve the bus capacitance C 0 is specifically as follows: the relation between the equivalent resistance R of the arc suppression coil and the capacitance X 0 of the bus capacitor C 0 is obtained by using the capacitance X0 of the bus capacitor as an unknown number and is shown in the following formula: ; the expression of U 1 、U 2 is as follows: ; ; Wherein, the For the angular frequency of the grid frequency, bringing R into the expression of U 1 、U 2 yields two nonlinear equations containing only X 0 , and the right part of the expression is represented in simplified form by f (X 0 ): U 1 =f 1 (X 0 ); U 2 =f 2 (X 0 ); Wherein f 1 () is a U 1 calculation equation and f 2 () is a U 2 calculation equation; Two residual functions are defined: F 1 (X 0 )=U 1 -f 1 (X 0 ); F 1 (X 0 )=U 2 -f 2 (X 0 ); X 0 , which enables the residual equation F 1 =F 2 =0, is a solution to the residual function, and the value of C 0 can be calculated by obtaining X 0 .
4. 4. The method for measuring the bus capacitance of the low-current grounding system according to claim 1, wherein an equivalent circuit of the measuring method is specifically that one end of a resistor R, an inductor L, an external measuring capacitor C 1 、C 2 , an arc suppression coil disconnecting link K and an ammeter T is grounded, the other ends of the resistor R and the inductor L are connected with the other end of the arc suppression coil disconnecting link K, the other ends of the ammeter T and the external measuring capacitor C 1 、C 2 are respectively connected with one end of an input switch K 0 、K 1 、K 2 , and the other end of the input switch K 0 、K 1 、K 2 is grounded.

Description

Method for measuring bus capacitance of low-current grounding system Technical Field The invention relates to the technical field of power system measurement, in particular to a method for measuring the capacitance of a bus to the ground in a low-current grounding system, which has the greatest advantage that the accurate measurement of the capacitance of the bus can be realized without pulling a knife switch of an arc suppression coil during measurement compared with the existing neutral point externally-added capacitance method. Background In the power system, a system in which the neutral point is not grounded or grounded via high impedance is called a low current grounding system. The primary equipment such as transformers, buses, lines and the like in the system has distributed capacitance to the ground, namely bus capacitance. When a single-phase earth fault occurs, the capacitor will generate an earth fault current. If the fault current is too large (usually > 5A), an arc suppression coil is required to be arranged for compensation. As the load of the power grid increases, the bus capacitance value changes, so that the bus capacitance value needs to be measured regularly to check and adjust the compensation parameters of the arc suppression coil. At present, methods for measuring the bus capacitance to the ground of a small-current grounding system in electric power comprise an inter-frequency signal injection method and a neutral point additional capacitance method. The operating principle of the pilot frequency signal injection method is that a constant current signal with a special frequency (such as 5Hz, 20Hz, 75Hz and the like, commonly called as pilot frequency) different from the power frequency (50 Hz) is injected into the system, and the three-phase total capacitance of the system can be calculated by accurately measuring the pilot frequency voltage response generated by the injection point because the impedance characteristic of the system to the pilot frequency signal is mainly determined by the capacitance to the ground. The principle of operation of the neutral point plus capacitance method is that in a small current grounding system, as the three-phase to ground capacitance is not fully balanced, a tiny asymmetric voltage (usually very small) exists at the neutral point itself. When an additional capacitor of known capacity is temporarily inserted between the system neutral point and ground, the system neutral point changes significantly to ground potential, i.e. the (zero sequence voltage). By accurately measuring the zero sequence voltage values before and after the additional capacitance is added, the total capacitance of the three phases of the system relative to the ground can be calculated Both of the above methods have in common that they require a single plant operation on the high voltage plant. The different-frequency signal injection method needs to exit the bus PT, temporarily short-circuit the high-voltage side harmonic elimination resistor and then put into operation the bus PT. And simultaneously, pulling open the knife switch of the arc suppression coil. The neutral point externally-added capacitance method needs to pull open the arc suppression coil knife switch before operation. All of the above operations require high voltage equipment for power outage operation. In the power system, when the primary equipment operation or power failure is involved, strict power failure application and work ticket permission procedures must be performed, which is time-consuming and uncontrollable. When a scene of carrying out quick census test on a large number of power stations is met, the measuring method can greatly limit the working efficiency of equipment measurement due to the influence of external factors such as power failure application, work ticket permission flow and the like. Therefore, a method for accurately measuring the bus capacitance under the normal operating condition of the primary equipment (normal connection of the bus PT, the arc suppression coil and the harmonic elimination resistor) is needed, so that the testing flow is simplified, the working efficiency is improved, and the safe and economical operation of a power grid is ensured. Disclosure of Invention The invention aims to overcome the defect that primary equipment (an arc suppression coil knife switch is pulled open) is required to be operated to measure the bus capacitance in the prior art, and provides an efficient and accurate external capacitance measuring method. According to the method, under the working condition that the arc suppression coil is normally connected into the system, uninterrupted measurement of the bus capacitor is realized by improving a measuring circuit and a calculation model. In order to solve the technical problems, the specific technical scheme of the invention is as follows: The system comprises a bus capacitor C 0, a three-phase unbalanced potential E p, an arc suppression