CN110598368B - Cable withstand voltage test structure design method - Google Patents
Cable withstand voltage test structure design method Download PDFInfo
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- CN110598368B CN110598368B CN201910989937.9A CN201910989937A CN110598368B CN 110598368 B CN110598368 B CN 110598368B CN 201910989937 A CN201910989937 A CN 201910989937A CN 110598368 B CN110598368 B CN 110598368B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1245—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of line insulators or spacers, e.g. ceramic overhead line cap insulators; of insulators in HV bushings
Abstract
A cable withstand voltage test structure design method adopts a plurality of post insulators, and the head end and the tail end of each post insulator are respectively connected with a metal bracket and a metal base of a reactor, so that the reactor is isolated from the base; and the insulating sleeve is in short connection with the reactor metal support, so that the insulating sleeve and the reactor metal support are equipotential. The design method of the post insulator comprises the following steps: 1) adopting an insulating support column as a support column insulator, 2) calculating the safe bearing strength of the insulating support column, 3) obtaining a relation curve between an external lightning flat average value and the height of the insulating support column through a support column height flashover voltage test, 4) selecting the height of the insulating support column, and 5) designing the discharge capacity of the insulating support column. The method is reasonable in design, improves the electrical safety performance, reduces the cost and solves the problem of height design of the supporting insulator under the condition that the use performance of the equipment is not influenced.
Description
Technical Field
The invention provides a height optimization design for an insulating support of a high-voltage reactor of a wire and cable, belonging to the field of voltage test methods and measurement.
Background
In recent years, with the economic development and the acceleration of electric power construction in China, the demand of high-voltage and ultrahigh-voltage cables is increased year by year, the cables are the products with the fastest demand in the varieties of electric power cables, and the cables become a new round of investment hotspots of domestic cable manufacturing enterprises. According to the product standard requirements, the factory test items of 110kV, 220kV and 500kV cables comprise: the test system comprises a partial discharge test, a 2.5U0 (a 500kV cable is 2U 0) voltage test and an electrical test of a nonmetal outer sheath, so that corresponding high-voltage cable factory test equipment is indispensable, and a 700-800 kV series resonance power frequency partial discharge test system is generally adopted at present.
The voltage input mode of the experimental system is as follows: 10kV power supply → high-voltage switch cabinet → double-shielded isolation transformer → voltage regulator → filter → exciting transformer → reactor. Wherein, the output of the exciting transformer is connected to the reactor by a 10kV or 35kV insulated lead wire, and the lead wire is connected from a high-voltage insulated bushing at the bottom of the reactor (as shown in figure 1). The air gap between the insulated lead wire and the reactor base is small. The reactor base is made of metal and is provided with a grounding end, and an air gap between the insulated lead and the reactor base is an insulated lead grounding gap.
Because the distance between the lead wire output from the exciting transformer to the reactor and the equipment base (grounding) is too close or almost in direct contact, the air gap is too small, when the exciting output voltage is higher, flashover discharge is easily generated between the lead wire and the equipment base (grounding), the impact is generated on the equipment by frequent flashover discharge, and the normal operation of the test is influenced.
In addition, when a high-voltage and ultrahigh-voltage short cable test is carried out, the electric field is homogenized by adopting a water terminal, so that the problem that the quality factor (Q value) is too small due to terminal discharge is avoided, and the requirement of the test voltage is met by increasing the excitation voltage. However, the excitation voltage is increased, so that external flashover is more easily caused, and the risk of breakdown of the insulating sleeve of the reactor is caused. Because the length of the sleeve terminal is only 8-9 cm, the safety distance is limited, when the output voltage of the excitation transformer is too high, the high-voltage insulating sleeve insulation breakdown event is easily caused, more seriously, because the reactor is filled with transformer oil (about 6500L), once the sleeve insulation is broken down, if measures are not taken timely, the leakage of the transformer oil in the reactor is easily caused, on one hand, the oil quantity is too large and the transformer oil is discharged once, when a laboratory is polluted, the hidden danger of fire is also caused, on the other hand, the follow-up maintenance, oil filling, vacuum pumping treatment and the like of the reactor are very difficult, and the result is not imaginable.
In theory, longer high-voltage insulating sleeves can be replaced to eliminate defects, but the distance between the bottom of the reactor and the ground and the distance of the sleeves extending into transformer oil in the reactor are fixed in an experimental system, so that the scheme is difficult to implement.
Disclosure of Invention
In order to solve the above defects in the prior art, the invention provides 1 a cable withstand voltage test structure design method, which is characterized in that a plurality of post insulators are adopted, and the head end and the tail end of each post insulator are respectively connected with a metal bracket and a metal base of a reactor, so that the reactor is isolated from the base; the insulating sleeve is in short connection with the reactor metal support, so that the insulating sleeve and the reactor metal support are equipotential;
the design method of the post insulator comprises the following steps:
(1) Insulating struts (e.g. epoxy fiber tube insulating struts) are used as post insulators:
at least 3 insulating support columns are adopted for supporting, and all the support columns are uniformly distributed at the bottom of the reactor support;
an epoxy fiber tube insulating support column is taken as an example, the outer diameter D of the support column is 180mm, and the inner diameter D is 140mm;
(2) Calculating the safe pressure-bearing strength of the insulating support:
calculating the load bearing of a single insulating support column according to the total weight of the reactor; acquiring the number of the required insulation struts according to the physical characteristics of the insulation struts;
(3) Obtaining a relation curve between the external lightning flat average value and the height of the insulating support column by a support column height flashover voltage test:
the design factors of the height of the support column comprise the stability of the equipment and no external flash, the higher the support column is, the worse the stability of the equipment is, the shorter the support column is, the smaller the insulation distance is, and the higher the probability of the external flash is; the method for determining the optimal height of the support column is to perform a power frequency external flashover voltage test on the support insulator, and the test method comprises the following steps:
3.1 For an insulating pillar with a certain height, the bottom of the insulating pillar is grounded; a copper wire is wound around the insulating support column at a position h1 away from the bottom of the insulating support column and is fastened tightly;
3.2 Copper wire is connected with a high-voltage end, power frequency voltage is applied, the voltage is gradually increased until flashover along the surface of the insulating support column is generated, flashover voltage U1 is recorded, and the process is repeated for n times; calculating an external lightning flattening average value: u shape Mean value of external lightning flattening ＝(U1+U3+U2……Un)/n
Here, n is a natural number.
3.3 Increasing the height of the copper wire, repeating the step 3.2) at h2, applying voltage to perform a flashover test, recording a flashover voltage U2, and repeating for n times; and calculating the average value of the external lightning flattening.
3.4 ) repeating step 3.2) at h3, h4, h5, … … hn in sequence to obtain U3, U4, U5, … … U n; respectively calculating and calculating the external lightning flattening average value;
the relation curve between the external lightning flat average value and the height of the insulating support column is as follows: h1, h2, h3, h4, h5 and … … hn are insulation distances, and coordinate curves are drawn in a two-dimensional coordinate system according to the insulation distances and corresponding external lightning flat average values;
here, the more the natural number n is, the better, but from the economical and perspective, 5 points may be adopted, that is, n is 5.
4) Height selection of insulating support
Maximum withstand voltage U of insulating support m ，U m ≥1.2U 0 (ii) a Maximum input voltage U of reactor 0 ，U 0 Also is the excitation variable output voltage;
in the relation curve between the external average lightning mean value and the height of the insulating pillar, the external average lightning mean value is equal to U m Selecting the corresponding height of the insulating support;
5) Design requirements for discharge capacity of insulating pillars
Input voltage U 0 At the highest, a partial discharge test is performed, requiring no discharge at this time that exceeds the test system's stated sensitivity.
The method has reasonable design, improves the electrical safety performance, reduces the cost and solves the problem of height design of the supporting insulator under the condition of not influencing the service performance (voltage, partial discharge and the like) of the equipment.
Drawings
FIG. 1 is a schematic diagram of an experimental layout of the prior art;
FIG. 2 is a schematic diagram of a test layout using a post insulator scheme;
FIG. 3 is a schematic diagram of the flashover test structure of step 3) of the method;
FIG. 4 is a schematic diagram of the experimental set-up of step 5) of the method;
FIG. 5 is a schematic axial cross-sectional view of a single insulating strut of this example;
in the figure: the reactor comprises a reactor 1, an exciting transformer 2, a reactor metal support 3, a metal base 4, a high-voltage bushing 5, an insulating support 6, a copper wire 7, a copper strip grounding 8 at the bottom of the insulating support, a high-voltage terminal 9 and a grounding terminal 10.
Detailed Description
The invention is further illustrated by the following specific embodiments:
a cable withstand voltage test structure design method adopts a plurality of post insulators, and the head end and the tail end of each post insulator are respectively connected with a reactor support and a reactor base so as to isolate a reactor from the base; the insulating sleeve is in short connection with the reactor support, so that the insulating sleeve at the bottom of the reactor and the reactor support are at the same potential;
in this example:
the design method of the post insulator comprises the following steps:
(1) Adopting an epoxy fiber tube insulating support as a support insulator; the pipe diameter design of epoxy fiber pipe insulating support is:
8 support columns are adopted for supporting, the outer diameter D of each support column is 180mm, and the inner diameter D of each support column is 140mm; all the insulating supports are uniformly distributed at the bottom of the reactor (metal) support;
(2) Calculating the safe bearing strength of the insulating support column:
the total weight of the reactor in this example was calculated as 38t, and 8 insulating supports were used (the cross section of the single support is shown in FIG. 5)
Then a single strut bears the weight: 38t/8 ≈ 5t
Strut sectional area: s = pi/4 (D-D) 2 ＝8380.66m㎡
And (3) calculating the pressure bearing of the strut: sigma pressure =50000N/8380.66m square meter approximately equal to 6Mpa
The compressive strength of the epoxy fiber tube is not less than 110Mpa
Therefore, the pressure bearing of the strut is far satisfied;
(3) Obtaining a relation curve between the external lightning flat average value and the height of the insulating support column by a support column height flashover voltage test:
the design factors of the height of the support column comprise the stability of the equipment and no external flash, the higher the support column is, the worse the stability of the equipment is, the shorter the support column is, the smaller the insulation distance is, and the higher the probability of the external flash is; the method for determining the optimal height of the support column is to perform a power frequency external flashover voltage test on the support insulator, and the test method comprises the following steps:
3.1 For an insulating support column with a height of about 500mm, the bottom of the insulating support column is grounded; winding the insulating support column by using a copper wire at a position h1=200mm away from the bottom of the insulating support column and fastening the insulating support column;
3.2 ) connecting a copper wire with a high-voltage end, applying power frequency voltage, gradually increasing the voltage until flashover along the surface of the insulating support column is generated, recording flashover voltage U1, and repeating for 5 times; and calculating the average value of the external lightning flattening.
3.3 Increasing the height of the copper wire, repeating step 3.2) at h2=250mm, applying a voltage for a flashover test, and recording a flashover voltage U2 and repeating 5 times; and calculating the average value of the external lightning flattening.
3.4 ) repeating step 3.2) at h3=300mm, h4=350mm and h5=400mm in sequence, U3, U4, U5 can be obtained; and respectively calculating the external lightning flattening average values;
the external lightning flat average value is calculated according to the following table.
Power frequency external flashover voltage of supporting insulator
Room temperature: ____ ℃ relative humidity: ____%
And drawing a set of obtained data into a coordinate curve such as insulation distance and external lightning flat average value in a table.
4) Height selection of insulating support
Maximum withstand voltage U of insulating support m ，U m ≥1.2U 0 (ii) a Maximum input voltage U of reactor 0 ，U 0 Also is the excitation variable output voltage;
in the relation curve between the external average lightning mean value and the height of the insulating pillar, the external average lightning mean value is equal to U m Selecting the corresponding height of the insulating support;
5) Design requirements for discharge capacity of insulating pillars
Input voltage U 0 At the highest, a partial discharge test is performed, requiring no discharge at this time that exceeds the test system's stated sensitivity.
In the embodiment, a post insulator is adopted, two ends of the post insulator are respectively connected with a reactor metal support and a metal base through flanges, so that the reactor is isolated from the base, an insulating sleeve is in short circuit with the reactor metal support, the insulating sleeve at the bottom of the reactor is equal in potential to the reactor support, and the possibility of discharge breakdown of the insulating sleeve is avoided (see figure 2). However, no method for determining the height of the supporting insulator exists at present, and the height far greater than the safety margin is generally adopted, so that the whole equipment is higher, the center of gravity is moved upwards, the cost is increased, and the problems of difficult operation, limited space and the like are caused.
In this example, the diameter of the epoxy fiber tube insulating support column is designed as follows: considering equipment balance and subsequent maintenance convenience, 6-8 supporting columns are selected for supporting the original equipment base. Because of the huge reactor equipment, the height is about 8 meters generally, the diameter is about 2.5 meters, the outer diameter of the support is preferably 180mm, and the inner diameter is preferably 140mm.
In the column height flashover voltage test, the column height should be considered in the aspect of ensuring the stability of the equipment and no external flash, the column height and the equipment are in conflict with each other, the higher the column is, the worse the stability of the equipment is, and on the contrary, the shorter the column is, the smaller the insulation distance is, and the higher the probability of the external flash is. In order to find the optimal height, a power frequency external flashover voltage test needs to be carried out on the supporting insulator, an insulating support column with the height of about 500mm is selected in the test, and the bottom of the insulating support is connected with the ground through a copper belt.
When the height of the insulating support is selected, the highest input voltage U of the reactor in the test system 0 (i.e., excitation variable output voltage), the insulating support must withstand 1.2 times U, considering 1.2 times the safety margin of the electrical equipment 0 The voltage is output, the power frequency partial discharge test has long running time (at least half an hour per test), and the highest withstand voltage U of the insulating support is selected for the reasons of reduced insulating performance, dust and moisture in the air and the like after long-term use and aging m ≥1.2U 0 And selecting the post insulator with the proper height in the coordinate curve according to the highest withstand voltage.
When the discharge capacity of the insulating support is designed, the insulating support is used in a high-voltage cable power frequency partial discharge test occasion, and the partial discharge performance of the insulating support is considered under the condition of ensuring that the voltage resistance meets the requirement according to the use characteristics, so the highest input voltage U of the system is required to be carried out 0 Partial discharge test (fig. 4): at U 0 Without an amount of discharge that exceeds the declared sensitivity of the system.
The power frequency partial discharge test system adopted by the method meets the requirement of the highest test voltage.
Claims (2)
1. A cable withstand voltage test structure design method is characterized in that a plurality of post insulators are adopted, and the head end and the tail end of each post insulator are respectively connected with a reactor metal support and a metal base so as to isolate a reactor from the base; the insulating sleeve is in short circuit with the reactor metal support, so that the insulating sleeve and the reactor metal support are equipotential;
the design method of the post insulator comprises the following steps:
1) Adopting an epoxy fiber tube insulating support column as a support insulator:
at least 3 insulating support columns are adopted for supporting; all the support columns are uniformly distributed at the bottom of the reactor bracket;
2) Calculating the safe bearing strength of the insulating support column:
calculating the bearing requirement of a single insulating support column according to the total weight of the reactor and the number of the insulating support columns; judging whether the bearing capacity of the single insulating support meets the bearing requirement or not according to the bearing capacity of the single insulating support;
3) Obtaining a relation curve between the external lightning flat average value and the height of the insulating support column by a support column height flashover voltage test:
the design factors of the height of the support column comprise the stability of the equipment and no external flash, the higher the support column is, the worse the stability of the equipment is, the shorter the support column is, the smaller the insulation distance is, and the higher the probability of the external flash is; the method for determining the optimal height of the support column is to perform a power frequency external flashover voltage test on the support insulator, and the test method comprises the following steps:
3.1 For an insulating pillar with a certain height, the bottom of the insulating pillar is grounded; a copper wire is wound around the insulating support column at a position h1 away from the bottom of the insulating support column and is fastened tightly;
3.2 Copper wire is connected with a high-voltage end, power frequency voltage is applied, the voltage is gradually increased until flashover along the surface of the insulating support column is generated, flashover voltage U1 is recorded, and the process is repeated for n times; calculating an external lightning flat average value:
U mean value of external lightning flattening ＝(U1+U3+U2……Un)/n；
3.3 Increasing the height of the copper wire, repeating the step 3.2) at h2, applying voltage to carry out a flashover test, recording flashover voltage U2, and repeating for n times; calculating an external lightning flattening average value;
3.4 ) repeating step 3.2) at h3, h4, h5, … … ht in sequence to obtain U3, U4, U5, … … Ut; respectively calculating and calculating the external lightning flattening average value;
the relation curve between the external lightning flat average value and the height of the insulating support column is as follows: the ht is an insulation distance, and a coordinate curve is drawn in a two-dimensional coordinate system according to the insulation distance and a corresponding external lightning flat average value;
4) Height selection of insulating pillars
Maximum withstand voltage U of insulating support m ，U m ≥1.2U 0 (ii) a Maximum input voltage U of reactor 0 ，U 0 Also is the excitation variable output voltage;
in the relation curve between the external average lightning mean value and the height of the insulating pillar, the external average lightning mean value is equal to U m Selecting the corresponding height of the insulating support;
5) Design requirements for discharge capacity of insulating pillars
Input voltage U 0 At the highest, a partial discharge test is performed, requiring no discharge at this time that exceeds the test system's stated sensitivity.
2. The method for designing a cable withstand voltage test structure according to claim 1, wherein the insulating support is an epoxy fiber tube insulating support; the outer diameter D of the epoxy fiber tube insulation pillar is 180mm, and the inner diameter D is 140mm.
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