CN106872752A - A kind of capacitance type potential transformer - Google Patents

Abstract

A capacitive voltage transformer, comprising a coaxial series capacitive voltage divider and an electromagnetic unit, the capacitive voltage divider is composed of a top equalizing cover and a series connected three-layer coaxial capacitor in series, and the electromagnetic unit includes a compensating reactance The three-layer coaxial capacitor is provided in sequence from the inside to the outside: main capacitor (1), auxiliary capacitor for inner layer shielding (5), and inner layer annular shielding electrode (4) , Auxiliary capacitor (3) for outer layer shielding, composite insulating sleeve (7) and outer layer annular shielding electrode (2); the voltage measurement accuracy and fast response of the voltage transformer can meet the requirements from ultra-high voltage to ultra-high voltage The requirements for accurate measurement of power frequency AC voltage in the power grid; the voltage divider for measurement is in a good shielding state, not affected by stray parameters, the voltage division ratio is stable, and the measurement accuracy is high. It can be used as a standard transformer.

Description

A Capacitive Voltage Transformer

technical field

The invention relates to a power system transformer device, in particular to a capacitive voltage transformer with a double-layer equipotential shielding structure.

Background technique

With the application of 1000kV and above UHV transmission technology in power transmission projects, the requirement for accurate measurement of UHV grid voltage has been put forward. The existing power frequency high-voltage measurement devices widely used in power systems mainly include electromagnetic voltage transformers and capacitive voltage transformers, both of which are passive voltage measurement systems. These transformers can basically meet the requirements of 500kV and below. Voltage level voltage metering and relay protection requirements. The photoelectric voltage transformer and electronic voltage transformer belonging to the active voltage measurement system are still in the process of research and development and trial operation, and there are still problems such as voltage measurement accuracy, laser life, and system reliability that need to be further studied and solved. Meet the scale application.

Due to the difficulty of insulation, electromagnetic voltage transformers are rarely used in EHV/UHV grades. Due to its simple structure, high reliability and low cost, capacitive voltage transformer (CVT) is still the main equipment used in EHV/UHV grid voltage measurement. However, the existing CVT design is applied to the UHV power grid, and encounters the following technical difficulties:

1) Stray capacitance current affects measurement accuracy

Due to the stray capacitance between the high-voltage arm of the capacitor voltage divider and the surrounding grounding body or charged body, the traditional capacitive voltage transformer (CVT), under the action of high voltage, the stray capacitance current flows out or flows into the high-voltage arm, resulting in Voltage measurement error. This error increases as the voltage level increases. The test results show that the measurement error caused by the real stray current (including the capacitive current and the surface leakage current of the insulating sheath) of the capacitive voltage transformer of the 750kV power grid can be as high as 0.2%. Electric field simulation shows that for a 1000kV CVT, the capacitive current flowing from the high-voltage arm of the voltage divider into the ground can reach 20mA, which causes significant measurement errors. Usually, the measure of increasing the main capacitance of the voltage divider is adopted to reduce the influence of stray current, but even if the capacitance is increased to 10000pF, the accuracy level of UHV CVT is difficult to reach the standard of 0.1 level.

2) Difficulty in on-site verification

Existing CVT measurement errors are affected by stray capacitance and thus are related to the installation location. After on-site installation, CVTs with EHV/UHV voltage levels need to be tested on-site to correct the ratio difference and angle difference from the factory. It is not easy to carry out the field test of transformers in UHV substations. In addition to the difficulty of manufacturing UHV standard capacitors, the electromagnetic interference at the UHV substation site is also an important constraint factor for accurate on-site comparisons.

To sum up, the development of UHV power transmission puts forward an urgent need to improve the measurement accuracy of the existing CVT, improve the response characteristics, and eliminate field tests.

Chinese patent application No. 200710050439.5 discloses a fully shielded capacitive voltage transformer, which includes a capacitive voltage divider and an electromagnetic device placed in a sealed housing filled with an insulating medium, the medium and high voltage electrodes of the capacitor voltage divider and the housing The three are coaxial structures. Under the action of voltage, the electric field force generated between them is evenly distributed on the circumference and cancels each other out. The relative position between the electrodes will not shift, and the capacitance between the electrodes is extremely stable. The accuracy of the transformer. This patent adopts a fully shielded structure, so it has an excellent shielding effect, but it is precisely because of the use of full shielding measures that its volume will increase rapidly with the increase of the measured signal voltage level, limited by its own structure , It is not suitable for use in power engineering sites, let alone for the measurement of million volts of high voltage. This fully shielded voltage transformer is more suitable for use in high-voltage laboratories instead of standard capacitors.

Chinese patent application No. ZL201010163455.7 discloses an equipotential shielded capacitive voltage transformer, which includes a capacitive voltage divider with an equipotential shielded double-layer coaxial capacitor assembly and a ferromagnetic resonance suppressor with no energy storage element and The electromagnetic unit of the intermediate transformer can meet the requirements of accurate measurement of power frequency AC voltage and fast and reliable action of relay protection from ultra-high voltage to ultra-high voltage power grid. Because the measuring main capacitor is in a good shielding state, the capacitance can be greatly reduced, thus the weight of the voltage divider can be greatly reduced, and the anti-seismic characteristics of the thin and tall voltage divider are also improved accordingly.

The object of the present invention is to reduce the coupling between the external stray capacitance and the voltage divider by adopting a double-layer equipotential shielding structure, reduce the current flowing out or flowing in from the main capacitance through the stray capacitance, and further improve the measurement accuracy; in addition, only Fewer shielding capacitors and lower capacitance are required to achieve the same measurement accuracy as the single-layer equipotential shielding CVT.

Contents of the invention

The capacitive voltage transformer with double-layer equipotential shielding structure designed by the present invention is mainly based on equipotential shielding technology, and its principle is as follows:

A series of ring-shaped coaxial shielding electrodes are arranged around the main capacitor of the high-voltage arm of the measuring voltage divider, and each layer of shielding electrodes is connected to an auxiliary shielding voltage divider. It can be proved that if the potential distribution of the ring electrode along the axis is consistent with the potential distribution of the main capacitance for measurement, the current flowing out or flowing in from the main capacitance through the stray capacitance can be completely blocked. The voltage distribution of the ring electrodes can be adjusted by parameter selection of the auxiliary shielding voltage divider. There is no electrical connection between the measuring divider system and the ring electrode and auxiliary shielding divider system. In this way, the capacitive current to the ground and the leakage current on the surface of the insulating sleeve are provided by the auxiliary shielding voltage divider without passing through the main capacitor for measurement, so that the measuring voltage divider is in a perfect shielding state, thereby ensuring the high precision of voltage measurement .

The invention provides a capacitive voltage transformer with a double-layer equipotential shielding structure, which includes a capacitive voltage divider and an electromagnetic unit. The capacitive voltage divider is connected in series with three layers of coaxial capacitors by a top equalizing cover from top to bottom. Layered coaxial capacitors are formed in series in sequence, and the electromagnetic unit includes a compensating reactor, an intermediate transformer, and a fast saturated damping reactor.

Further, the three-layer coaxial capacitor is coaxially arranged in sequence from the inside to the outside: main capacitor (1), auxiliary capacitor (5) for inner layer shielding, inner ring shielding electrode (4), auxiliary capacitor for outer layer shielding A capacitor (3), a composite insulating sleeve (7), and an outer annular shielding electrode (2).

Further, the main capacitor (1) is placed on the inner axis of the composite insulating sleeve (7), and the outer ring-shaped shielding electrode (2) and the inner ring-shaped shielding electrode (4) are coaxially arranged on the main capacitor (1) The outer edge of the upper and lower flanges, the diameter of the outer annular shielding electrode (2) is greater than the diameter of the inner annular shielding electrode (4).

Further, an auxiliary capacitor (3) for outer layer shielding is arranged along the inner wall circumference of the composite insulating sleeve (7), and the positive and negative electrodes of the auxiliary capacitor (3) for outer layer shielding are reliably connected to the outer annular shielding electrode; An auxiliary capacitor (5) for inner layer shielding is symmetrically arranged on the inside of the inner layer annular shielding electrode (4), and the positive and negative electrodes of the inner layer shielding auxiliary capacitor (5) are reliably connected to the inner layer annular shielding electrode,

Further, the main capacitor (1), the auxiliary capacitor for inner shielding (5) and the inner annular shielding electrode (4), the auxiliary capacitor for outer shielding (3) and the outer annular shielding electrode (2) There is no electrical connection between them, and good insulation is maintained by insulating material (6).

Further, the main circuit of the voltage transformer is: the main capacitor _C1 of the high-voltage arm is connected to the main capacitor C2 of the low _- voltage arm and then grounded G, the high voltage to be measured is connected to the transformer through the terminal V, and the measured signal obtained by voltage division F is grounded after the compensation reactor and the intermediate transformer connected in series, the secondary induction signal of the intermediate transformer is connected to the load for measurement, and the fast saturated damping reactor connected in parallel with the load is a ferromagnetic resonance suppressor.

Further, the main capacitor _C1 of the high-voltage arm and the main capacitor C2 of the low _- voltage arm are composed of three layers of main capacitors (1) connected in series at the axis of the coaxial capacitor.

Further, the measuring voltage divider is composed of main capacitors (1) of multiple three-layer coaxial capacitors connected in series.

Further, the auxiliary shielding voltage divider is composed of a plurality of three-layer coaxial capacitors, the auxiliary capacitors for outer layer shielding (3) and the auxiliary capacitors for inner layer shielding (5) respectively connected in series.

Further, the auxiliary shielding voltage divider is directly grounded to form a double-layer equipotential shielding structure of the measuring voltage divider; the output end of the measuring voltage divider is connected to the inlet end of the primary winding of the intermediate transformer through a compensation reactor, and the primary winding of the intermediate transformer The outlet end is grounded; a fast saturated damping reactor is connected in parallel between the outlet end of the secondary winding of the intermediate transformer and the ground; at the same time, the outlet end of the intermediate transformer secondary winding is grounded through the load.

Compared with the closest prior art, the present invention has the following excellent effects:

(1) The voltage measurement accuracy and fast response of the capacitive voltage transformer of the present invention can meet the requirements for accurate measurement of power frequency AC voltage from ultra-high voltage to ultra-high voltage power grids;

(2) The voltage divider for measurement is in a good shielding state, not affected by stray parameters, the voltage division ratio is stable, and the measurement accuracy is high, so it can be used as a standard transformer;

(3) When used as a transformer for engineering site, no field test is required, the value of shielding capacitance and main capacitance is small, the overall weight of the equipment is light, and the mechanical properties such as wind resistance and earthquake resistance are good.

Description of drawings

Figure 1 is a schematic diagram of the appearance of a capacitive voltage transformer with a double-layer equipotential shielding structure.

Among them, A-top equalizing cover, B-three-layer coaxial capacitor, C-electromagnetic unit;

Figure 2 is a schematic cross-sectional view of a three-layer coaxial capacitor,

Among them, 1. The main capacitor for measurement, 2. The outer annular shielding electrode, 3. The auxiliary capacitor for outer shielding, 4. The inner annular shielding electrode, 5. The auxiliary capacitor for inner shielding, 6. Insulation material, 7. Composite insulation sleeve;

Figure 3 is a longitudinal sectional view of a three-layer coaxial capacitor assembly,

Fig. 4 is a main circuit diagram of a novel voltage transformer according to the present invention.

specific embodiment

The present invention will be further described below in conjunction with the accompanying drawings.

The invention is mainly composed of a capacitive voltage divider of a coaxial capacitor assembly with a double-layer equipotential shielding structure and a traditional electromagnetic unit.

As shown in Figure 1, it is a schematic diagram of the appearance of a capacitive voltage transformer with a double-layer equipotential shielding structure. The components and connections from top to bottom are: Part A is the top equalizing cover, and four parts B are connected in series below it. Part B is a three-layer coaxial capacitor, and then connected to part C electromagnetic unit.

As shown in Figure 2, it is a schematic cross-sectional view of a capacitor assembly with a double-layer equipotential shielding structure. The three-layer coaxial capacitor assembly of the equipotential shielding is the core assembly of the present invention, and its internal structure: place and measure the axis in the composite insulating sleeve 7 Using the main capacitor 1, set the coaxial outer layer annular shielding electrode 2 on the outer edge of the upper and lower flanges of the main capacitor, and arrange several auxiliary capacitors 3 for outer layer shielding symmetrically along the inner wall of the composite insulating sleeve. The layer ring shield is reliably connected, the inner layer ring shield electrode 4 is set between the electrode of the outer layer shield capacitor 3 and the electrode of the main capacitor 1, and several auxiliary capacitors 5 for inner layer shielding are arranged symmetrically along the inner side of the inner layer ring shield electrode. Capacitors, inner layer shielding capacitors and inner ring shielding electrodes, outer shielding capacitors and outer ring shielding electrodes are not allowed to have any electrical connection with each other, and gas insulating materials or foam insulating materials 6 are used to maintain the contact between the three Good insulation.

According to the requirements of the voltage level, a plurality of the above-mentioned three-layer coaxial capacitor components can be connected in series to form a capacitive voltage divider for equipotential shielding.

As shown in Figure 4, it is the main circuit of the UHV equipotential shielding capacitive voltage transformer designed according to the present invention, in which _C1 is the main capacitor of the high _- voltage arm, C2 is the main capacitor of the low-voltage arm, and Cs is the ground stray Capacitor, V point is the terminal connected to the measured high voltage, G point is the ground, F point is the measured signal obtained by voltage division, the signal is connected to the load for measurement after signal conditioning by the compensation reactor and intermediate transformer, and the The saturated damping reactor is connected in parallel with the load as a ferromagnetic resonance suppressor.

The capacitors in the inner layer of the three-layer coaxial capacitor assembly are connected in series to form the main capacitor C ₁ of the high-voltage arm and the main capacitor C ₂ of the low-voltage arm, and the main capacitor C ₂ of the low-voltage arm is grounded to form a measuring voltage divider; auxiliary shielding voltage divider for shielding After being connected in series step by step, it is directly grounded to form the equipotential shielding of the measuring voltage divider; the output end of the voltage divider is connected to the primary winding of the intermediate transformer through a compensating reactor; a fast saturated damping reactor is connected in parallel to the secondary of the intermediate transformer; to the load.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Modifications or equivalent replacements to the specific embodiments, any modification or equivalent replacement that does not depart from the spirit and scope of the present invention, shall be covered by the scope of the present claims.

Claims (9)

1. A capacitive voltage transformer, comprising a coaxial series capacitive voltage divider and an electromagnetic unit, is characterized in that the capacitive voltage divider is composed of a top equalizing cover and a series connected three-layer coaxial capacitor connected in series, so The electromagnetic unit includes compensation reactor, intermediate transformer and fast saturation damping reactor. 2. The voltage transformer according to claim 1, characterized in that, the three-layer coaxial capacitor is arranged from the inside to the outside: the main capacitor (1), the auxiliary capacitor (5) for inner layer shielding, the inner layer annular A shielding electrode (4), an auxiliary capacitor (3) for outer shielding, a composite insulating sleeve (7) and an outer annular shielding electrode (2). 3. The voltage transformer according to claim 2, characterized in that, the two ends of the main capacitor (1) are respectively provided with flanges for placing the outer annular shielding electrode (2) and the inner annular shielding electrode (4) , the diameter of the outer annular shielding electrode (2) is larger than the diameter of the inner annular shielding electrode (4). 4. The voltage transformer as claimed in claim 2, characterized in that, the positive pole and negative pole of the auxiliary capacitor (3) for outer layer shielding are reliably connected with the outer layer annular shielding electrode; the auxiliary capacitor for inner layer shielding ( 5) The anode and cathode of the electrode are reliably connected to the inner annular shielding electrode. 5. The voltage transformer according to claim 4, characterized in that, the main capacitor (1), the auxiliary capacitor (5) for inner layer shielding, the inner annular shielding electrode (4), and the auxiliary capacitor for outer layer shielding An insulating material (6) is provided between (3) and the outer annular shielding electrode (2). 6. The voltage transformer as claimed in claim ₁ , characterized in that, the main circuit of the voltage transformer is: the main capacitor C of the low voltage arm is respectively connected with the main capacitor C _of the high voltage arm and the ground, and the measured high voltage is passed through The terminal V is connected to the transformer, and the measured signal F obtained by voltage division is grounded after being connected in series with the compensation reactor and the intermediate transformer. The secondary induction signal of the intermediate transformer is connected to the load for measurement. The device is a ferromagnetic resonance suppressor. 7. The voltage transformer according to claim 2, characterized in that the measuring voltage divider is composed of main capacitors (1) of a plurality of three-layer coaxial capacitors connected in series. 8. The voltage transformer as claimed in claim 2, characterized in that, the auxiliary shielding voltage divider is composed of auxiliary capacitors (3) for outer layer shielding and auxiliary capacitors (5) for inner layer shielding of a plurality of three-layer coaxial capacitors. ) are respectively connected in series. 9. The voltage transformer as claimed in claim 8, wherein the auxiliary shielding voltage divider is directly grounded to form a double-layer equipotential shielding structure of the measuring voltage divider; the compensation reactor is respectively connected to the output of the measuring voltage divider The terminal is connected to the incoming terminal of the primary winding of the intermediate transformer, and the outgoing terminal of the primary winding of the intermediate transformer is grounded; the outgoing terminal of the secondary winding of the intermediate transformer is grounded through the load, and the parallel fast saturated damping reactor is connected in parallel with the load.