CN209803216U - Voltage transformer with high-voltage and low-voltage isolation - Google Patents

Voltage transformer with high-voltage and low-voltage isolation Download PDF

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Publication number
CN209803216U
CN209803216U CN201920314707.8U CN201920314707U CN209803216U CN 209803216 U CN209803216 U CN 209803216U CN 201920314707 U CN201920314707 U CN 201920314707U CN 209803216 U CN209803216 U CN 209803216U
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voltage
low
transformer
isolation
arm
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祝顺峰
唐福新
祝顺庆
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Zhejiang Horizon Instrument Transformers Co Ltd
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Zhejiang Horizon Instrument Transformers Co Ltd
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Abstract

The utility model discloses a voltage transformer with high voltage and low voltage isolation, which comprises three capacitive voltage dividers fixed on a mounting plate, wherein the three capacitive voltage dividers are connected with an adjusting unit and an isolation transformer in sequence; the three capacitive voltage dividers are identical in structure and are formed by connecting high-voltage arm impedance and low-voltage arm impedance in series; the device adopts a technical scheme completely different from the existing capacitance voltage-dividing voltage transformer on the current market, the high-voltage arm adopts a double-capacitor series structure, and silicon rubber is sprayed on the surface of the high-voltage arm, so that the electrical performance of the product is ensured; the product increases the secondary output voltage by reducing the low-voltage capacitance, is connected in series with the primary winding of the weak-signal low-voltage isolation transformer, and then realizes the output of the standard secondary signal by the secondary winding, so that the physical isolation exists on the high-voltage and low-voltage electric circuit, and the operation safety of the power grid is further effectively ensured.

Description

voltage transformer with high-voltage and low-voltage isolation
Technical Field
The utility model relates to a mutual-inductor specifically is a take voltage transformer of high pressure and low-voltage isolation.
Background
currently, on-pole FZW28-12 load switches and ZW20-12 circuit breakers are generally adopted in China, and in order to meet the requirement of intellectualization, intelligent switch control equipment (FTU) needs to be added. In order to provide zero sequence signals for the equipment and meet the requirement of miniaturization of the overall equipment, the original outdoor voltage transformer is changed into a voltage transformer based on a capacitance voltage division principle and is internally arranged in a pole-mounted switch (short-circuit device), which is a main improvement point of a secondary fusion overall design scheme, but the following problems exist.
1) The voltage transformer based on the domestic capacitance voltage division principle adopts a primary and secondary capacitance integrated structure and is integrally implanted into a box body, and the secondary voltage division capacitor is large in capacitance value and small in required volume, so that a domestic electronic capacitance element is basically adopted, the service life of the element is not matched with that of a switch, the element is arranged in an air chamber of the box body, once the element is damaged, the complexity of replacement, the consumed time and the consumed cost are unacceptable for the operation of a power grid;
2) The primary and secondary of the voltage transformer are in a series voltage division principle, physical isolation does not exist between the primary and secondary voltage transformers, and once breakdown occurs in a primary capacitor, the breakdown will definitely reach secondary equipment.
3) The box body of the domestic pole-mounted circuit breaker is of a square welding structure, so that the leakage risk of insulating gas is high; the pole load switch adopts a gas normal pressure design, the external creepage distance of the voltage transformer and the narrow space in the cabinet are a pair of spear bodies, and the key of the design is how to balance to ensure the safety of the product operation.
In summary, a voltage transformer with an electrically and physically isolated miniaturized capacitor voltage division principle is developed on the primary part and the secondary part, so that the operation safety of a product is ensured, the product can be quickly replaced, and the voltage transformer is necessary under the current trend of primary and secondary integration of a power grid.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to provide a take voltage transformer of high pressure and low-voltage isolation to solve the problem that proposes among the above-mentioned background art.
In order to achieve the above object, the utility model provides a following technical scheme:
a voltage transformer with high voltage and low voltage isolation comprises three capacitive voltage dividers fixed on a mounting plate, wherein the three capacitive voltage dividers are sequentially connected with an adjusting unit and an isolation transformer; the three capacitive voltage dividers are identical in structure and formed by serially connecting high-voltage arm impedance and low-voltage arm impedance, the high-voltage arm impedance is formed by serially connecting two high-voltage capacitors C1 with the same capacitance value with a small resistor R1, the tail ends of the high-voltage arm impedance groups of the three capacitive voltage dividers are directly serially connected with the same low-voltage arm impedance, the low-voltage arm impedance comprises a low-voltage capacitor C0 and a small resistor R0 which are sequentially connected in series, and the tail ends of the low-voltage arm impedance are grounded to form an electric path.
The adjusting unit, the isolation transformer and the low-voltage arm impedance are arranged in parallel.
as the preferred scheme of the utility model: silicon rubber is sprayed on the outer surface of the high-voltage capacitor C1; the low-voltage capacitor C0 is externally arranged.
Compared with the prior art, the beneficial effects of the utility model are that: the device adopts the technical scheme completely different from the existing capacitor voltage-dividing voltage transformer in the current market, the high-voltage arm adopts a double-capacitor series structure, and silicon rubber is sprayed on the surface of the high-voltage arm, so that the electrical performance of the product is ensured. Moreover, after the single capacitor is broken down, the product can continue to operate, and the situation that the high voltage of the product with the single high-voltage capacitor in the current market is broken down when the high-voltage capacitor is broken down, and the high voltage is leaked into the secondary capacitor, so that hidden dangers are brought to the operation of secondary equipment and the safety of personnel. The product increases the secondary output voltage by reducing the low-voltage capacitance, is connected in series with the primary winding of the weak-signal low-voltage isolation transformer, and then realizes the output of the standard secondary signal by the secondary winding, so that the physical isolation exists on the high-voltage and low-voltage electric circuit, and the operation safety of the power grid is further effectively ensured. The low-voltage-dividing capacitor is arranged externally, so that the detection, the maintenance and the replacement are more rapid and convenient.
Drawings
Fig. 1 is a schematic structural view of the present invention;
Fig. 2 is a schematic circuit diagram of the present invention.
In the figure, 1 is a mounting plate, 2 is a capacitive voltage divider, 3 is a regulating unit and 4 is an isolation transformer.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
in the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Example 1:
Referring to fig. 1-2, a voltage transformer with high voltage and low voltage isolation comprises three capacitive voltage dividers 2 fixed on a mounting plate 1, wherein the three capacitive voltage dividers 2 are sequentially connected with an adjusting unit 3 and an isolation transformer 4; the three capacitive voltage dividers 2 are identical in structure and are formed by serially connecting high-voltage arm impedance and low-voltage arm impedance, the high-voltage arm impedance is formed by serially connecting two high-voltage capacitors C1 with the same capacitance value with a small resistor R1, the tail ends of high-voltage arm impedance groups of the three capacitive voltage dividers 2 are directly serially connected with the same low-voltage arm impedance, the low-voltage arm impedance comprises a low-voltage capacitor C0 and a small resistor R0 which are sequentially serially connected, and the tail ends of the low-voltage arm impedance are grounded to form an electric path; when the device is applied to a pole load switch or a breaker, the high-voltage ends (A, B, C ends) of the three capacitive voltage dividers 2 are directly connected with the high-voltage incoming line of the pole load switch or the breaker.
the adjusting unit 3, the isolation transformer 4 and the low-voltage arm impedance are arranged in parallel, so that the short circuit of an electric path caused by the fault of a single element can be effectively avoided, and the high-voltage fault can be avoided.
In actual use, the high-voltage capacitance changes with temperature and directly influences measurement errors, so that the high-voltage arm impedance and the low-voltage arm impedance of the capacitive voltage divider 2 are manufactured by the same material and process. The high-voltage arm capacitor and the low-voltage arm capacitor are made of the same materials and processes, and the medium-small resistance in the high-voltage arm impedance and the medium-small resistance in the low-voltage arm impedance are made of the same material resistance, so that the temperature drift rates of the high-voltage arm impedance and the low-voltage arm impedance on the same capacitive voltage divider have better consistency.
Calculated in practical use due to the impedance Z of the A-phase high-voltage armAB phase high voltage arm impedance ZBAnd C-phase high-voltage arm impedance ZCAre equal in impedance value, i.e. ZA=ZB=ZC=Z1the double-capacitor structure is adopted, so the equivalent capacitance value of the high-voltage arm is C1/2,Omega is the grid frequency, C1Is a high-voltage arm capacitor, R1The resistance of the high-voltage arm is small. Common low voltage arm impedanceC0Is a low-voltage arm resistance capacitor, R0The low-voltage arm resistance is small. Then for the voltage at the first signal input of the regulating circuitComprises the following steps:
Namely, it is
As can be seen from the formula (2),Is the voltage output according to a certain proportion.
the voltage at the input of the isolation transformer 4 isThe output end of the transformer is in a tapped double-winding structure, the number of turns of a primary winding of the isolation transformer 4 is assumed to be N1, the number of turns between a secondary side da and a secondary side dn is assumed to be N2, and the rated voltage value is assumed to beThen the following voltage transfer relationship exists:
It can be found that:
It can be seen from formulas (2) and (3) that the voltage signal sensing ratio of the transformer is determined by the impedance value of the capacitive voltage divider 2 and the 3 turns ratio of the isolation transformer, so that the voltage dividing ratio formed by the impedance of the high-voltage arm and the impedance of the low-voltage arm and the turns ratio of the isolation transformer 4 can be respectively designed and selected, and then the signal fine tuning is performed through the adjusting unit, so that the zero sequence voltage signal can be accurately obtained.
In order to ensure that the output accuracy of the product in the high and low temperature environment meets the requirement, the high-voltage arm impedance and the low-voltage arm impedance of the capacitive voltage divider 2 are manufactured by adopting the same structure, the same material and the same manufacturing process, and the rated current flowing through the high-voltage arm impedance is not more than 1 mA.
The product is applied to the measurement of the zero sequence voltage of a three-phase power grid with the rated voltage of 10kV and the frequency of 50 Hz. When single-phase metal grounding occurs, the maximum rated measurement output voltage value of the zero-sequence voltage of the primary sensor is 6.5V, the rated load is not less than 5M omega, and the zero-sequence voltage measurement accuracy of the three-phase power grid can reach 0.5 level.
The advantages of this design are: the capacitive voltage divider 2 is of a double-capacitor series structure, on one hand, when the power frequency withstand voltage is 48kV, each capacitor C1 bears 24kV, and the requirement on the insulating capability of the capacitors is greatly reduced; on the other hand, when one capacitor breaks down, high voltage is applied to two ends of the other capacitor and can still operate, and the high voltage is effectively prevented from channeling twice along the path. The low-voltage output end is connected with the isolation transformer 4 in parallel, so that physical isolation is formed between the high-voltage equipment and the secondary equipment, and the operation safety of a power grid is further ensured. The low-voltage-dividing capacitor is arranged externally, so that the detection, the maintenance and the replacement are more rapid and convenient.
2) Through calculation and experimental verification, the principle of selecting the voltage division ratio of the capacitive voltage divider 2 is researched, so that the intensity of a secondary output signal is ensured to be enough to drive the isolation transformer, and the reliable electrical performance of the voltage divider is fully considered.
The product voltage ratio is 10000V/√ 3/6.5V/3, namely 2664.62 times, and the secondary output is 6.5V when the single-phase ground fails. Because the accuracy required by the technical parameters of the product is 3P level, when 0.02 times of rated voltage is input for one time, the Un value can be accurately output for the second time, and in order to ensure that the output end of the isolation transformer 4 can provide enough exciting current, the voltage ratio is set to be 10: 1, namely, in the case of single-phase earth fault, the rated voltage of the primary end is 6.5 × 10-65V. Therefore, the impedance ratio of the high-voltage arm to the low-voltage arm is 2664.62/10-266.462. Considering that the resistor R1 is only provided for limiting the discharge current of the capacitor and preventing the capacitor from being damaged, R1' is the function of balancing R1, for this reason, the resistance value is very small, when calculating the impedances of the high-voltage arm and the low-voltage arm, it is only necessary to calculate the capacitive reactance, and the capacitive reactance is inversely proportional to the capacitance value, for this reason,
considering that the power frequency withstand voltage is 48000V, the normal operation voltage is8.31 times of the total weight of the powder. The high-voltage capacitor is selected to use a ceramic flat silver electrode capacitor in consideration of the insulation level required to be achieved by the high-voltage capacitor and the long-term operation experience of a power system. Considering the limitation of the product application environment to the overall dimension, the final capacitance value of the high-voltage capacitor C1 is selected to be 350pF, at this time, the total capacitance value of the high-voltage arm is 175pF, and the secondary capacitance value is 93.261nF by calculation of formula (4).
3) Through research and development on the low-loss, high-precision and linearly-changed weak signal isolation transformer, the precision of a secondary output port of the isolation transformer is guaranteed to meet requirements.
Because the accuracy required by the technical parameters of the product is 3P level, the Un value can be accurately output twice when 0.02 times of rated voltage is input once, and therefore, the research and development of the low-loss, high-precision and linearly-variable weak signal isolation transformer is one of the technical difficulties of the product.
the output voltage of the da-dn end of the isolation transformer can be calculated according to Un:
Un=4.44fN2AcB*10-4
(5)
In the formula, f-rated frequency
n2-number of turns of secondary winding
Ac-effective area of iron core, cm2
b-magnetic density of iron core
Formula (5) shows that Un is in direct proportion to the number of turns of the secondary winding, the effective sectional area of the iron core and the magnetic density of the iron core, and in order to output accurately when the requirement of 0.02 x Un is met, the three parameters of the number of turns of the secondary winding, the effective sectional area of the iron core and the magnetic density of the iron core must be ensured to be large enough.
The number of turns of the secondary winding and the number of turns of the primary winding are in a relation of 1:10, the two windings are wound on the iron core column, the number of turns of the secondary winding is increased without limitation, and the 10-time proportion increase of the number of turns of the primary winding can cause the great increase of the winding space of the iron core, so that the volume of a product is enlarged, and meanwhile, the use amount of copper wires and iron core materials is increased, and the cost is increased. Through test verification, the secondary winding selects 1000 turns to be a numerical value with the relative balance of volume, cost and product performance.
The increase of the core sectional area Ac also increases the amount of core material and copper wire used, and increases the product volume and cost, and therefore, it is not preferable to increase the core sectional area without limitation. We can calculate the core cross-sectional area by:
As can be seen from equation (6), when f, N2, and Un are constant values, the magnetic density B of the core material is increased, and the core cross-sectional area can be reduced.
In addition, since the accurate output can be obtained at 0.02 × Un, for this purpose, the core material with high initial permeability is selected as much as possible, and in combination with the requirement of the B value, the item group refers to the magnetic property data of the typical material in the table below, and after many times of tests and material replacement, the permalloy is finally selected as the core material of the isolation transformer, and the appropriate core sectional area is calculated by the formula (6).
Example 2:
Compared with the embodiment 1, the difference is that the silicon rubber is sprayed on the outer surface of the high-voltage capacitor C1, so that the problem of gap discharge of the interface of the capacitor and the epoxy resin is effectively solved.
The low-voltage capacitor C0 is external, and detection, maintenance and replacement are more rapid and convenient.
It is obvious to a person skilled in the art that the invention is not restricted to details of the above-described exemplary embodiments, but that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims (5)

1. the voltage transformer with the high-voltage and low-voltage isolation function is characterized by comprising three capacitive voltage dividers (2) fixed on a mounting plate (1), wherein the three capacitive voltage dividers (2) are sequentially connected with an adjusting unit (3) and an isolation transformer (4); the three capacitive voltage dividers (2) are identical in structure and are formed by connecting high-voltage arm impedances and low-voltage arm impedances in series, the high-voltage arm impedances are formed by connecting two high-voltage capacitors C1 with the same capacitance value in series with a small resistor R1, the tail ends of high-voltage arm impedance groups of the three capacitive voltage dividers (2) are directly connected with the same low-voltage arm impedance in series, and the tail ends of the low-voltage arm impedances are grounded to form an electric path.
2. The voltage transformer of claim 1, wherein the low-voltage arm impedance comprises a low-voltage capacitor C0 and a small resistor R0 connected in series.
3. The voltage transformer with high and low voltage isolation according to claim 1 or 2, characterized in that the regulating unit (3), the isolation transformer (4) and the low voltage arm impedance are arranged in parallel.
4. The voltage transformer with high voltage and low voltage isolation as claimed in claim 1 or 2, wherein the outer surface of the high voltage capacitor C1 is coated with silicone rubber.
5. The voltage transformer with high voltage and low voltage isolation as claimed in claim 2, wherein said low voltage capacitor C0 is external.
CN201920314707.8U 2019-03-13 2019-03-13 Voltage transformer with high-voltage and low-voltage isolation Active CN209803216U (en)

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Application Number Priority Date Filing Date Title
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Publication Number Publication Date
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