Because SF6 is strongly electronegative and has a large volume, it is easy to capture electrons and can absorb their energy to generate stable negative ions with low mobility. Its free path is short, making it difficult for collision dissociation to occur in the gap, greatly reducing the amount of electrons in the gap. Charged particles. Therefore, at one atmospheric pressure (1. 01X105Pa), the insulation capacity of SF6 is more than twice that of air. When the pressure is 3 atmospheric pressure, its insulation capacity is equivalent to that of transformer oil. (3) Arc extinguishing performance of SF6 gas. Under the action of arc, SF6 receives electrical energy and generates low- fluorine compounds. However, when the arc current crosses zero, the low-fluorine compounds rapidly re -synthesize SF6. Therefore, the arc gap medium strength recovers quickly, and the arc extinguishing ability of SF6 is equivalent to 100 times that of air under the same conditions. During operation, since the gas decomposed by SF6 under the action of arc is harmful, attention must be paid to sealing the gas and taking correct treatment methods to ensure safety.

Structural forms of SF6 circuit breakers. In terms of appearance and structure, SF6 circuit breakers can be divided into two categories: porcelain pillar type SF6 circuit breakers (referred to as GCB.P.) and floor-standing tank type SF6 circuit breakers (referred to as GCB.T.). Among them, the porcelain pillar type SF6 circuit breaker is currently the most widely used form. The porcelain pillar type SF6 circuit breaker is similar in structure to the outdoor oil-less circuit breaker. It has the advantages of good serialization, high single-break voltage, large breaking current, high operational reliability and low maintenance workload, but it cannot have built-in current. transformer, and has poor earthquake resistance. The floor-standing tank type SF6 circuit breaker is developed on the basis of the porcelain column SF6 circuit breaker. It has all the advantages of the porcelain column SF6 circuit breaker, and can have a built-in current transformer. The overall height of the product is low, and its earthquake resistance is relatively improved. But the cost is relatively expensive.

Structural principle of 220kV SF6 circuit breaker

A factory uses Swiss ABB high-voltage switchgear

ELFSP4-1 circuit breaker produced by Co., Ltd.,

With AHWA single-phase transmission operating mechanism.

The circuit breaker consists of three independent columns (phases).

A circuit breaker consists of three main parts.

In the insulating epoxy housing at the bottom is the mechanical operating part,

The upper part of the mechanism is connected with an insulating tie rod moving in a hollow insulating porcelain sleeve .

The upper part is the breaking device ( i.e. arc extinguishing chamber ). The rated current is 4000A.

arc extinguishing unit in each arc extinguishing chamber porcelain bottle is composed of upper,

It consists of the lower outlet flange and the upper and lower current channels and contact systems in the middle.

The injection chamber is on the lower current channel,

The contacts installed in the upper and lower current channels are of integrated construction.

Each phase circuit breaker is mounted on a separate hot-dip galvanized bracket.

The bracket consists of two welded frames connected together with brace irons .

The ELFSP4-1 circuit breaker is operated by the AHWA type hydraulic operating mechanism.

the mechanism chamber of the pole are connected through a tie rod system.

The basic structure is shown in Figure 6-1:

Among them, 1 represents the circuit breaker column, 2 represents the operating mechanism, and 3 represents the bracket.

Figure 6-1 Basic structure of a circuit breaker The circuit breaker works according to the principle of automatic compression. The compression cylinder is divided into two parts, an automatic compression chamber and a compression chamber. When the normal operating current is cut off, SF6 gas is pressed into the compression chamber, causing its pressure to increase. When arcing occurs , the gas in the compression chamber is ejected, extinguishing the arc when the current crosses zero. When the short-circuit current is cut off, the required arc extinguishing pressure is generated in the automatic compression chamber due to the heating of the arc. In this way, the energy of the arc can be used to increase the pressure of SF6, so that no additional energy is required to operate the mechanism. When closing, the pressure cylinder moves upward, the contacts contact each other, and the pressure cylinder is refilled with gas. Operating mechanism of high-voltage circuit breaker The operating system of the circuit breaker is a system used to close, open and maintain the circuit breaker closed. The action process of the operating system is actually to obtain kinetic energy from the operating components (closing components and opening components ), and then transfer the kinetic energy to the contacts through the arm and link mechanism to achieve opening and closing. The part of the operating system that is independent of the circuit breaker body is called the operating mechanism, and the rest of the part that transmits power is called the transmission mechanism. According to the different power sources required for circuit breaker operation, the operating mechanism can be divided into manual, hydraulic, electromagnetic, and spring operating mechanisms. A mechanism that requires manpower directly as closing power is called a manual operating mechanism. Obviously, its operating power is limited by manpower, the closing time is long, reclosing cannot be achieved, and it is only used on small-capacity circuit breakers. The mechanism that uses electromagnets to convert electrical energy into mechanical energy as closing power is called an electromagnetic operating mechanism. This type of operating mechanism is simple and reliable.

But DC is required to operate the power supply. In the spring operating mechanism, the driving energy is supplied by the closing spring with pre-stored energy. Before operating the circuit breaker, another low-power power supply first stores energy in the closing spring to make it in the ready closing state. This mechanism does not require It is a large-capacity energy device and therefore widely used. The mechanism that uses high-pressure compressed gas (nitrogen) as the energy source and hydraulic oil as the energy transfer medium is injected into the working cylinder with the piston to push the piston to perform work to close and open the circuit breaker. It is called a hydraulic operating mechanism. . There is also a mechanism that uses a pre-stored closing spring as the energy source and hydraulic oil as the medium for energy transmission, which is called a hydraulic spring operating mechanism. The structural principles of the operating mechanism will not be introduced in detail here. The operating mechanism used in the ELFSP4-1 circuit breaker is a hydraulic operating mechanism.

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The post Sulfur Hexafluoride Circuit Breaker (SF6 Gas Circuit Breaker) appeared first on ecielkpower.

GIS is the English abbreviation of Gas Insulated Switchgear. It is generally translated as gas insulated fully enclosed combined electrical appliances. SF6 gas is usually used as the insulating medium, including circuit breakers (CB), isolating switches (DS), grounding switches (ES, FES), busbars ( BUS), current transformer (CT), voltage transformer (VT), lightning arrester (LA) and other high-voltage components. At present, GIS equipment products cover the voltage level range of 72.5 kV to 1200 kV.

Figure 1 Typical structural composition of GIS equipment

Characteristics of GIS equipment

Since SF6 gas has excellent insulation properties, arc extinguishing properties and stability, GIS equipment has the advantages of small footprint, strong arc extinguishing capability, and high reliability. However, the insulation capability of SF6 gas is greatly affected by the uniformity of the electric field. When GIS Insulation abnormalities are likely to occur when sharp points or foreign objects are present inside.

GIS equipment adopts a fully enclosed structure, which brings the advantages of internal components not being disturbed by the environment, long maintenance cycle, less maintenance workload, and low electromagnetic interference. At the same time, it also has problems such as complicated single maintenance work and relatively poor detection methods. When the closed structure is eroded and damaged by the external environment, it will further cause a series of problems such as water intrusion and air leakage.

Figure 2 GIS equipment adopts a fully enclosed structure

Internal structure of GIS equipment

The GIS conductive circuit is composed of several components. According to the working method, it can generally be divided into: fixed contact (electrical contact fastened with fasteners such as screws is called fixed contact. Fixed contact has no relative movement during the working process. Such as the connection between the contact and the basin, etc.), contact Contact (electrical contact that can be separated during the working process is also called separable contact), sliding and rolling contact (during the working process, the contacts can slide or roll with each other, but the electrical contact that cannot be separated is called sliding and rolling contact .The middle contact of the switching appliance uses this kind of electrical contact).

Figure 3 Contacts of GIS equipment

GIS substation

No.1

GIS concept

Sulfur hexafluoride enclosed combined electrical appliances, internationally known as “Gas Insulated Switchgear” ( GIS for short), include primary equipment in a substation other than transformers, including circuit breakers, isolating switches, grounding switches, voltage Transformers, current transformers, arresters, busbars, cable terminals, incoming and outgoing line bushings, etc. are organically combined into a whole through optimized design.

In addition to GIS, there is also HGIS, which is designed for harsher environments. Compared with GIS, there are fewer busbars, busbar voltage transformers, arresters and other equipment, especially busbars, so it is more flexible to use.

No.2

GIS features

(1) Miniaturization: Using SF6 gas with excellent insulation properties as insulation and arc extinguishing medium, the size of the substation can be greatly reduced.

(2) High reliability: All live parts are sealed in inert SF6 gas, which improves the reliability of the substation.

(3) Good safety: The live parts are sealed in a grounded metal shell, so there is no risk of electric shock. SF6 gas is a non-combustible gas, so there is no fire hazard.

(4) Eliminate adverse effects on the outside: The live parts are enclosed with a metal shell to shield electromagnetic and static electricity, with low noise and strong anti-radio interference ability.

(5) Short installation cycle: The realization of miniaturization allows the complete machine to be assembled and tested in the factory and then delivered to the site in the form of units or intervals. Therefore, the on-site installation period can be shortened and reliability can be improved.

(6) Easy maintenance and short maintenance time: Because of its reasonable structural layout and advanced arc extinguishing system, the service life of the product is greatly improved, so the maintenance cycle is long and the maintenance workload is small. Moreover, due to its miniaturization and low height from the ground, it is easy to use daily. Easy to maintain.

No.3

GIS classification

GIS can be divided into two types: outdoor type and indoor type according to the installation location.

outdoor

Indoor

GIS can generally be divided into two forms: single-phase single-cylinder type and three-phase common-cylinder type. The 110kV voltage level and busbar can be made into a three-phase common cylinder type, and the 220kV and above adopt a single-phase single-cylinder type.

Single phase common cylinder type

Three-phase common cylinder type

No.4

Basic principles of operation

(1) Under normal circumstances, GIS equipment circuit breakers and isolating switches are mainly operated remotely. The “remote/local” switch of circuit breakers and isolating switches switches to the “remote” position.

(2) The GIS equipment grounding knife gate can only be operated on site. During operation, turn the “remote/local” switch of the partition knife /ground knife to “local”.

(3) Under any circumstances, only program operations can be performed. The ” interlock release switch” on the HSBC cabinet must be in the ” interlock ” position, and its unlocking key is sealed together with the microcomputer anti-mistake locking key and used according to the same regulations.

No.5

Basic requirements for operation

(1) Indoor SF6 equipment rooms frequently entered by operating personnel: Ventilate at least once per shift for 15 minutes. The air exchange volume should be greater than 3-5 times the air volume. The exhaust outlet should be installed in the lower part of the room; operating personnel do not frequently enter. Access equipment areas: Ventilate for 15 minutes before entering.

(2) Under normal circumstances, the induced voltage on the shell and structure of the GIS during operation should not exceed 36V for parts that are easily accessible to operation and maintenance personnel.

Temperature rise: The parts that are easily accessible to operators should not exceed 30K; the parts that are easily accessible to operators but not accessible during operation should not exceed 40K; the individual parts that are not easily accessible to operators should not exceed 65K.

(3) SF6 switching equipment is inspected and inspected at least once a day, and unmanned substations are inspected in accordance with regulations. During the inspection, we mainly conduct visual inspections to see if there are any abnormalities in the equipment and keep records.

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The post Introduction to GIS (Gas Insulated Switchgear)equipment appeared first on ecielkpower.

In today’s high-voltage power systems, zinc oxide arresters play a vital role. Its practicality lies in its ability to effectively protect power equipment from damage caused by lightning overvoltage and operating overvoltage, thereby ensuring the stable operation of the power system.

Zinc oxide arrester is a special arrester that uses zinc oxide, a material with highly nonlinear resistance characteristics. Under normal voltage, the resistance of zinc oxide is extremely high, almost equivalent to that of an insulator. However, when the voltage exceeds a certain threshold, its resistance drops sharply, allowing current to pass through. This characteristic enables the zinc oxide arrester to quickly limit the overvoltage within a safe range when lightning overvoltage or operating overvoltage occurs, thereby protecting power equipment.

Another advantage of zinc oxide arresters is their extremely fast response. Its action time is less than microseconds, and overvoltage limitation can be completed almost instantly. This enables zinc oxide arresters to effectively prevent the impact of lightning overvoltage on power equipment, avoiding equipment damage and potential power outages.

In addition, zinc oxide arresters have stable performance and long life. Because its internal components use zinc oxide, a stable metal oxide, its performance is less affected by the environment and has a long service life. At the same time, zinc oxide arresters have low maintenance costs, reducing operating costs.

#CompositeInsulator#TransmissionLine#linepostinsulator#PinTypeInsulator #CrossArmInsulator#RubberInsulator#ElectricProduction #InsulationProduction #PowerStationProductions#lightingarrester #surgearrester #dropoutfusecutout #dropoutfuse #outdoorisolatingswitch #highvoltagefuse #polymerinsulator #porcelaininsulator #glassinsulator #highvoltagevacuumcircuitbreaker #vacuumcircuitbreaker #pininsulator #postinsulator #crossarminsulator#electricpower#МФЭС#VDNKh#ВДНХ#МЕЖДУНАРОДНЫЙФОРУМ#ЭЛЕКТРИЧЕСКИЕСЕТИ

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The post Practicality of zinc oxide surge arrester(lightning arrester) appeared first on ecielkpower.

In the power system, transmission lines are the components with the most failures. Therefore, how to improve the reliability of transmission lines is of great significance to the safe operation of the power system.

The nature of transmission line faults is that most of them are transient faults, accounting for about 80% to 90% of the total number of faults. Most of these transient faults are caused by insulator surface flashover caused by lightning, line discharge to tree branches, and line collision caused by strong winds. These faults are caused by objects such as birds, branches falling on the wires, and surface contamination of the insulator. After the circuit breaker is disconnected by the relay protection action, the fault point becomes free, the arc is extinguished, the insulation strength is restored, and the fault is eliminated by itself. At this time, if the circuit breaker of the transmission line is closed, the power supply can be restored, thereby reducing the power outage time and improving the reliability of the power supply. Of course, transmission lines also have a small number of permanent faults caused by downed poles, short wires, insulator breakdown or damage, etc. These faults still exist after the line is disconnected. At this time, if the circuit breaker is closed, the circuit breaker will be disconnected again by the relay protection action.

It can be seen from the nature of transmission line faults that the possibility of success is quite high if the line is disconnected and then reclosed. Although this closing can be done manually, the effect is not good due to the long power outage. Very significant. For this reason, an automatic reclosing device is used to put the cut line back into operation to replace our manual closing.

After the reclosing is installed on the line, the reclosing itself cannot determine whether the fault is instantaneous. Therefore, if the fault is instantaneous, the reclosing can succeed; if the fault is permanent, the relay protection will operate again to open the circuit after reclosing. The circuit breaker tripped and the re-closing failed. Operational practice shows that the success rate of line reclosing is about 60% to 90%. It can be seen that the benefits of using automatic reclosing are considerable.

The use of automatic reclosing on transmission lines not only improves the reliability of power supply, but also improves the stability of parallel operation of the system and the transmission capacity of the line. It can also correct problems caused by poor structure of the circuit breaker itself, misoperation of relay protection and accidental collision . False trip. Automatic reclosing is widely used in power systems because of its low cost, reliable operation and great effect. However, the use of automatic reclosing will also have some adverse effects on the power system. For example, when reclosing occurs with a permanent fault, the system will be impacted by short-circuit current again, which may cause system oscillation; at the same time, the working conditions of the circuit breaker will deteriorate.

The reclosing of transmission lines can often be divided into single-phase reclosing, three-phase reclosing and comprehensive reclosing; or it can be divided into one-action reclosing and two-action reclosing; it can also be divided into single-side power reclosing and double-sided power reclosing. In addition, it can also be divided into mechanical, electrical and transistor reclosing .

automatic reclosing device should meet the following basic requirements:

1. Automatic reclosing can be started based on the principle that the position of the control switch does not correspond to the position of the circuit breaker.

2. When the circuit breaker is disconnected with a control switch or a remote control device, or when the circuit breaker is placed on a faulty line and is immediately disconnected by a protective device, the automatic reclosing shall not operate .

3. In any case, the number of automatic reclosing actions should comply with the predetermined regulations.

4. The automatic reclosing action should automatically reset.

5. Automatic reclosing should be able to accelerate the action of relay protection after reclosing. If necessary, it should also be able to accelerate its action before reclosing. When closing with a control switch, measures should be taken to accelerate the action of relay protection.

6. When the circuit breaker is in an abnormal state that does not allow automatic reclosing, the automatic reclosing should be blocked.

“Ten questions” about reclosing gates

What is the automatic reclosing device?

automatic reclosing device is a device that automatically switches the circuit breaker back on as needed after the circuit breaker trips due to line fault protection action.

2: Why should we install automatic reclosing device ?

About 90% of the faults on overhead transmission lines are transient faults. After the relay protection action cuts off the transmission line, the short-circuit current disappears and the insulation level of the air will return to the level before the fault. If the automatic The reclosing device can re-close the circuit breaker to immediately resume operation of the line, ensuring the safety and stability of the system.

What are the automatic reclosing methods?

1

Overall weight:

For single-phase faults, single-phase coincidence will cause three-phase jumps after coincidence with a permanent fault; for inter-phase faults, three phases will jump, and three-phase coincidence will cause three-phase jumps after coincidence with a permanent fault.

02

triple:

Any type of fault will jump three phases, three phases will jump after coincidence, and three phases will jump after coincidence permanent fault.

03

Single:

Single-phase fault, single-phase coincidence, three phases will jump after coincidence permanent fault. Phase-to-phase fault, three phases do not overlap after tripping.

04

Disable:

Any fault will jump three phases without overlapping.

Reclosing is divided into single reclosing and multiple reclosing. China basically adopts single reclosing. Circuit breaker reclosing of 110kV and below are three-phase reclosing. At voltages of 220kV and above, circuit breakers have phase-divided tripping . Therefore, there are single-phase reclosing, three-phase reclosing and comprehensive reclosing. Different operating conditions require different reclosing methods to be selectively adopted.

4: What are the starting methods of automatic reclosing?

01

The position does not correspond to the starting mode

After the trip relay operates (TWJ=1), it proves that the circuit breaker is in the off position. If the control switch is in the closed state at this time (KKJ=1), it means that the circuit breaker has been in the closed state before. The method of corresponding start reclosing is called position non-corresponding start reclosing.

This method can not only start reclosing after the circuit breaker is tripped by the protection, but can also start reclosing when the circuit breaker “stealthly trips”.

02

protection start

In most cases, the protection action first issues a tripping command and then the reclosing command is required to issue a closing command. Therefore, the reclosing can be started by the protection.

When the protection device issues a single-phase trip command and checks that there is no current in the phase line, or when a three-phase trip occurs and there is no current in all three-phase lines, reclosing is started. This starting method is implemented by the protection itself through internal software. Reclosing cannot be started when the circuit breaker accidentally trips using the protective start-reclosing method .

How to set the automatic reclosing action time

The reclosing time is the time from when the main contacts of the circuit breaker are disconnected and there is no flow in the line to when the reclosing device sends out the closing pulse.

⑴

The three-phase reclosing method is usually used on single-sided power lines. The reclosing time should be the power outage time plus the margin time minus the inherent closing time of the circuit breaker.

Among them, the power outage time is the arc extinguishing time and the short-circuit point de-dissociation time, while the inherent closing time is the period from the circuit breaker receiving the closing pulse to the circuit breaker main contact closing. This time is carried out simultaneously with the fault point de-dissociation time. , needs to be removed when calculating the reclosing time.

⑵

The longitudinal protection on the double-sided power line will instantly remove the fault within the entire length of the line. If there is only distance and zero-sequence protection that reflects the electrical quantities on one side, the protection action time on the opposite side will likely be longer than on this side . Reclosing must take into account the delay on the opposite side.

At the same time, when single-phase reclosing and comprehensive reclosing are used for bilateral power lines, the impact of latent current must also be considered if single-phase tripping of the line occurs .

Extension: A single-phase ground fault occurs on the line. The relay protection only disconnects the faulted phase from both sides of the line through the phase selection component . The non-faulty phase still continues to operate. The non-faulty two-phase voltage passes through the inter-phase capacitance and the other two-phase current passes through the interphase. Mutual inductance provides short-circuit current to the short-circuit point, so that a certain amount of current still passes through the arc channel at the fault point. This current is called latent current.

Its size is related to the parameters of the line. The higher the line voltage, the longer the line, the greater the load current, and the greater the latent current.

Due to the influence of latent current, the single-phase reclosing time is generally longer than the three-phase reclosing time to facilitate arc extinguishing.

Submersible current diagram

6: What is the “acceleration” of reclosing?

If a permanent fault occurs in the line, the system will be impacted by the fault again after reclosing, which is extremely detrimental to the stable operation of the system. The “acceleration” of reclosing can effectively reduce the impact of reclosing and permanent faults on the system. . Reclosing acceleration is divided into front acceleration and rear acceleration:

01

Acceleration before reclosing

When a fault occurs on the line, the protection close to the power supply side first acts non-selectively and instantaneously to trip, and then relies on reclosing to correct this non-selective action. After reclosing the faulty line, its action time limit is based on the stepped time limit. According to the time limit of characteristic matching, front acceleration is generally used in radiation lines with several series connections, and the reclosing device is only installed on a section of the line close to the power supply.

Although the first trip is fast, it may be a non-selective trip, causing the power outage to expand. Therefore, this acceleration method is only used on direct distribution lines for unimportant users.

02

Acceleration after reclosing

When a line fault occurs, the protection selectively removes the fault, and the reclosing circuit restores power supply after a single reclosing operation. If the reclosing occurs due to a permanent fault, the protection device will trip the circuit breaker without time limit and without selective action. This method is called post-reclosing acceleration.

7: What is the principle of reclosing charging and discharging?

In analog protection , resistors and capacitors are used to realize charging and discharging. When the reclosing device sends a closing command, the voltage on the capacitor is used to discharge the outlet relay, thereby completing the closing process of the circuit breaker. Only when the charging time exceeds 15 seconds is the voltage on the capacitor sufficient to cause the relay to operate.

There is a counter in the reclosing program in microcomputer protection, which simulates the charging and discharging of the capacitor by continuously counting and clearing the counter.

8: What are the conditions for reclosing charging and discharging?

In order to ensure that the reclosing can be reclosed normally and only once, reclosing is only allowed after charging is completed. The protection device can only allow reclosing to charge if the following conditions are met at the same time.

1) The reclosing pressure plate is in the input state;

2) All three-phase trip relays are active, that is, the circuit breaker is in the closed position;

3) There is no circuit breaker low pressure latching reclosing and other external latching reclosing inputs;

4) When using comprehensive reclosing or three-phase reclosing, there is no signal input for line TV disconnection. Line TV is used when three-phase tripping is used to detect line voltagelessness or to detect synchronized reclosing .

When reclosing is not allowed under normal operation or short-circuit fault operation, the discharge should be carried out immediately, the counter should be cleared, and the reclosing should be blocked. There are many discharge conditions for reclosing, which will not be described here .

9. Inspection conditions for automatic reclosing

There is no synchronization problem with reclosing in power side protection on single-sided power lines .

the single-phase reclosing method or the comprehensive reclosing method is used on a double-sided power line, the systems on both sides are always connected through the two normally operating phases after the single-phase tripping. At this time, there is no need to consider synchronization issues.

After a three-phase trip occurs on both sides of the power line, the systems on both sides may not have any connection. Synchronization issues need to be considered when closing the reclosing. In this case, the inspection conditions for reclosing are as follows:

01

Check the line for no voltage and check the synchronized reclosing

Both sides of the line are equipped with check line voltage-free and synchronous reclosing respectively. After the line is short-circuited and three-phase trips, the three phases have no voltage. Check that the line has no voltage and the reclosing side reaches the closing condition first. After the three-phase reclosing action time Then the closing command is issued, and then the synchronous reclosing side of the line is checked to find that there is voltage in the line and busbar and the synchronous closing conditions are met and the closing command is issued within the three-phase reclosing action time.

The check synchronization function can be enabled on the non-voltage side of the line, and the reclosing command can also be issued after the circuit breaker “stealthly trips”; while the no-voltage check function on the synchronization side of the line cannot be enabled, otherwise both sides may be closed at the same time. The gate causes asynchronous closing.

02

Check if the line has a pressure-retaining mother but no pressure, if the line has no pressure the mother-in-law has pressure, if the line has no pressure the mother has no pressure.

These three reclosing inspection methods have been added to the microcomputer protection used on 110kV lines and small ground current system lines below 110kV to adapt to the needs of different operating modes, and these three methods can also be used in combination.

03

for current in adjacent lines

This reclosing check condition is used on double circuit lines. When a circuit in a double-circuit line is short-circuited and the three phases on both sides are tripped, just check that there is current in the other circuit, indicating that the systems on both sides are still connected through the other circuit , and the closing conditions are met.

10: What are the special requirements for reclosing under 3/2 wiring?

When the 3/2 wiring mode line protection issues a tripping command, two circuit breakers must be tripped. The order of coincidence of the two circuit breakers is to close the side circuit breaker first and then the breaker. If the side circuit breaker fails to reclose and closes on the faulty line, the protection will trip the side circuit breaker again, and the circuit breaker will no longer reclose and a three-trip command will be issued.

In this wiring method, reclosing and circuit breaker failure protection are implemented in separate circuit breaker protection devices.

If the circuit breaker is closed first and then closes due to a permanent fault, then the circuit breaker is protected and tripped. If the circuit breaker fails at this time, a trip command will be issued to the circuit breakers on both sides, causing the adjacent operating interval to lose power.

If the side circuit breaker is closed first , it coincides with the permanent fault, and then the side circuit breaker is tripped for protection. At this time, the side circuit breaker fails, and a trip command will be issued to the circuit breaker and all circuit breakers on the bus. The bus will be powered off but will not affect all operating intervals. Send power normally.

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The post What is recloser(Vacuum Circuit Breaker)? appeared first on ecielkpower.

answer:

An insulator (commonly known as a porcelain bottle) is composed of a porcelain part and a hardware part, and the middle part is glued with cement adhesive. The porcelain part is to ensure that the insulator has good electrical insulation strength, and the metal parts are used to fix the insulator.

The role of the insulator has two aspects: one is to firmly support and fix the current -carrying conductor, and the other is to form a good insulation between the current-carrying conductor and the ground.

It should have sufficient dielectric strength and mechanical strength, and at the same time have sufficient resistance to the erosion of chemical impurities, and can adapt to changes in the surrounding atmospheric conditions, such as the influence of temperature and humidity changes on itself. The insulators used in substations and overhead lines include pin insulators, post insulators, porcelain cross-arm insulators and high-voltage wall bushings.

2. What is the creepage distance ? What is the leakage distance ?

answer:

Both creepage distance and leakage distance are specific parameters of external insulation. The discharge distance along the outer insulating surface is the leakage distance of electricity, also known as creepage distance, or creepage distance for short.

Leakage distance multiplied by the effective coefficient and then divided by the line voltage is the leakage distance , that is, λ=KL/U where: λ is the leakage distance ; K is the effective coefficient; L is the leakage distance; U is the line voltage.

3. What is creeping discharge?

answer:

many suspension and pin insulators, transformer bushings and wall bushings in the power system, and many of them are in the air. When the voltage of these devices reaches a certain value, the air on the surface of these porcelain devices will discharge . It is called discharge along the surface of solid medium, or surface discharge for short.

When the surface discharge penetrates between the two electrodes, a surface flashover is formed. The creeping discharge voltage is lower than that in the air . The surface discharge voltage is related to the uniformity of the electric field, the surface state of the solid medium and the meteorological conditions.

4. What is flashover? What is the cause of pollution flashover?

answer:

When the gas or liquid dielectric around the solid insulation is broken down, the phenomenon of discharge along the surface of the solid insulation is called flashover.

There are a lot of industrial pollution particles on the surface of porcelain insulators in dirty areas. When these pollution particles are wet, they will form a conductive liquid film on the porcelain surface, which will significantly reduce the withstand voltage of porcelain insulation, and the flashover voltage will become very low. This is The reason why porcelain insulation is extremely easy to flashover under dirty and wet conditions. Pollution and damp are the necessary conditions for pollution flashover, and porcelain insulation will not cause flashover if it is only dirty but not wet .

5. How to prevent pollution flashover of insulators in substations?

answer:

(1) Add basic insulation. For example, increase the number of insulators, increase the distance of discharge along the surface, and meet the leakage ratio specified by the pollution classification.

(2) Strengthen cleaning. Porcelain insulation in dirty areas must be cleaned regularly to keep the surface of the porcelain insulation clean and prevent pollution flashover. Charged water flushing is an effective means.

(3) Adopt dust-proof paint. When the effective leakage ratio of ceramic insulation in dirty areas cannot meet the requirements, and the cleaning workload needs to be reduced, methods such as coating silicone oil and ozokerite are often used to increase the pollution flashover voltage and prevent pollution flashover accidents.

(4) Semiconductor sleeve insulators and silicone rubber insulators are used.

6. Why is the surface of the porcelain insulator corrugated?

answer:

distance within the same effective height, and each of them can play the role of blocking the arc.

(2) In case of rainy days, it can block the water flow, and the sewage cannot flow directly from the upper part of the porcelain bottle to the lower part, so as to avoid becoming flying and causing confusion .

(3) When the dust falls on the corrugated porcelain insulator, the distribution is uneven, so the resistance strength of the porcelain bottle is guaranteed to a certain extent.

7. Under what circumstances are porcelain insulators easily damaged?

answer:

(1) The installation and use of porcelain insulators are unreasonable, such as the mechanical load exceeds the regulations, the voltage level does not meet the requirements, and the installation location is improper.

(2) Due to sudden cold and hot weather and external damage caused by hail.

(3) Flashover caused by thunderstorm and fog due to pollution of porcelain insulators.

(4) Short circuit of electrical equipment, damage to porcelain insulators caused by excessive electrical and mechanical stress.

8. What are the consequences of cracks in insulator castings and glued parts?

answer :

in the iron valve flange and the glued layer, the sealing performance of the electrical appliances will be reduced, which may cause moisture ingress, water ingress and internal insulation damage to the oil-filled equipment. In severe cases, it may cause equipment explosion accidents. Cracks in the cast iron flange of the isolating switch or the busbar support insulator may cause the support to separate from the insulator , resulting in equipment operation failure, and may cause the insulator to collapse or fall, resulting in a short circuit accident.

9. Why is there one more piece of tension insulator string than the general line?

answer:

Operation experience proves that tension insulator strings are prone to deterioration due to heavy mechanical load, and the chances of zero-value insulator strings appearing are more than those of hanging strings, so the number of reserved insulators should be more than that of straight strings .

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1. Infrared diagnosis of internal defects

1.1 Infrared features of internal defects

The heating sources of composite insulators mainly include polarization loss, partial discharge, and leakage current. The former two are due to the excessive concentration of the electric field caused by the defect; the leakage current heating is mostly caused by the deterioration of the canopy of the insulator, and the leakage current is concentrated in the deteriorated part, and there is an obvious temperature difference with the surrounding area. Usually, the end of the air gap and carbonization channel will become a “hot spot” due to the existence of partial discharge, while the middle part of the carbonization channel is often at a lower temperature due to the weaker electric field.

Example 1: Wet ends

A 500kV line has multiple composite insulators with a temperature rise of 2-4K . The temperature rise test under AC and DC withstand voltages is carried out in the laboratory, and the applied voltage amplitude is equal to the maximum operating voltage amplitude ( 1.1Um/ ).

Features: When AC high voltage is applied, the temperature rise under high humidity is about 4-5K , which is significantly higher than that under low humidity. In the DC high voltage test, the temperature rise of the insulator is hardly observed; the difference in temperature rise under different humidity makes the on-site During detection, sometimes the temperature rise is high, and sometimes there is no temperature rise. (Reference: Influence of moisture on composite insulator sheath on abnormal temperature rise at the end)

Example 2: Carbonization channel

One of the double V- string composite insulators in a certain tower of a 500kV line was broken. There were many holes in the core rod of the broken insulator, and electric corrosion channels had been formed inside. The broken insulator A and the same batch of insulators B were placed under the operating voltage for infrared measurement. temperature.

Infrared temperature measurement of two insulators

▲Figure 1 Insulator A (fracture) infrared characteristic map

▲Figure 2 Infrared characteristic diagram of insulator B

The detection found that The middle temperature of insulator A is 14.8 ℃, which is higher than that of insulator B 12.9 ℃. During the test, it was found that the temperature of units 45-46 in the middle of insulator A ( the first unit at the low-voltage end is the first unit , and the junction point between the corroded and uncorroded mandrel between units 45-46 ) is higher than that of insulator B 1.9 ℃ 1 ) The temperatures of the high-voltage ends of insulators A and B are both around 15 ℃, with little difference.

Infrared signatures of insulators with galvanic channels:

①The boundary area between the high voltage end of the electro-corrosion channel and the intact mandrel is an area with obvious temperature rise;

②Compared with insulators without electro-corrosion channels, the temperature rise may not be high (only 1.9 °);

③The temperature difference between different positions of the insulator itself is more obvious;

(In fact, the B insulator also has internal defects and poor bonding)

1.2 Test Judgment

The judgment criteria for infrared diagnosis of composite insulators in operation on site is the appendix I.2 of the standard ” DL/T 664 Application Specifications for Infrared Diagnosis of Live Equipment”. When the temperature difference of composite insulators exceeds 0.5-1.0 K , attention should be paid.

Considering that on-site infrared detection is easily affected by external light reflection, angle, and focus definition, and the test error is difficult to control, many units (including China Electric Power Research Institute and provincial companies) currently relax the above criterion to 2.0K during on-site tests .

In order to assist the judgment, for suspicious insulators, multiple follow-up inspections should be carried out, and phase-to-phase comparisons should be carried out to assist judgment.

1.3 Test Notes

a. Avoid the influence of sunlight and other visible light

Since the composite insulator is a voltage-induced heating device, its temperature field test is easily affected by the external environment. When the sunlight and visible light are strong, it will cause the temperature difference between the sunny side and the back side of the insulator, and cause the temperature difference between the different sides of the mandrel. As shown in Figure 3, the outside sunlight was strong during the test on that day . At this time, the highest point of infrared temperature measurement was located on the surface of the shed with strong sunlight reflection. They are 27.9°C and 25.0°C respectively, and the temperature difference reaches 2.9 K. The temperature difference caused by sunlight is very likely to submerge the possible hot spots inside the mandrel, resulting in missed judgments. Therefore, when testing, it is best to carry out on a cloudy day.

▲ Figure 3 The impact of sunlight

b. Reasonably set the test distance, reflectivity, wind speed and other parameters. The reflectivity should be set between 0.85 and 0.95. The test distance should be set reasonably when climbing the tower and testing under the tower (you can carry rangefinder, anemometer and other equipment to survey the test environment. parameter);

c. Try to choose the angle perpendicular to the insulator mandrel during the test, and pay attention to the focus at the same time. For the infrared photos that are too blurred, they should be discarded. The temperature rise should be determined by comparing the hot spot of the insulator mandrel with other farther positions of the mandrel, as shown in the figure below:

▲ Figure 4 Recommended shooting angles

d. Record the time, ambient humidity, and temperature during the test, and give infrared photos for subsequent analysis.

e. When it is found that the infrared photo test parameters are set incorrectly, the software of the general infrared instrument has the inversion function of the test image. Using the software to modify the test parameters and recalculate the temperature rise can reduce the error caused by incorrect test parameter settings to a certain extent. impact (but still less accurate than if the parameters were set correctly when actually testing).

f . When the tower is too high, the test distance is long, and the resolution of the infrared instrument is limited, so the temperature rise cannot be measured. The test distance can be increased by adding a focusing lens.

2. Ultraviolet diagnosis of internal defects

2.1 UV characteristics of internal defects

When corona is caused by defects such as carbonization channels and erosion of composite insulators, the corona can be observed by using an ultraviolet imager. The advantage of the ultraviolet method is that the detection distance is long, the detection sensitivity to corona is high, and it is beneficial to detect defects as soon as possible, and the detection sensitivity to continuity defects is higher than that of the infrared method. The disadvantage of the ultraviolet method is that the types of defects that can be detected are relatively limited. Not all defects generate stable coronas. For example, cracks on the surface of mandrels will only generate coronas after being damp, but at this time raindrops on the surface of insulators may also generate coronas. The ultraviolet method has certain requirements on the light and the detection position. The discharge image can only be obtained on the front of the discharge. Therefore, the ultraviolet method is mainly in an auxiliary position for the judgment of the local defects of the insulator, and is usually used in conjunction with the infrared method .

UV detection case:

A 500kV transmission line composite insulator found a temperature rise, and carried out infrared and ultraviolet tests at the same time, as shown in the figure below.

▲ Figure 5 UV spectrum of composite insulator with galvanic corrosion channels

The ultraviolet images of the composite insulator when the sheath is damaged, the sheath is cracked along the mandrel, and the end is creeping are shown in Figure 6-Figure 8.

▲ Figure 6 The ultraviolet spectrum of insulator partial sheath damage

▲ Figure 7  The ultraviolet spectrum of insulator partial sheath damage

▲ Figure 8 Severe contamination caused creepage on the surface of the end

UV characteristics of defective insulators:

①For the insulator with the mandrel broken, when the infrared and ultraviolet are detected at the same time, the area where the insulator has abnormal discharge is consistent with the area where the temperature rise exceeds the standard; ( if there is a temperature rise and ultraviolet discharge at the same time, the probability of defect is very high)

②The partial sheath is damaged, and there will be significant ultraviolet discharge at the end of the elongated crack of the sheath;

In addition, the end creepage caused by serious local pollution will also cause damage to the insulator sheath. For composite insulators, if the ultraviolet test finds that there is concentrated and stable discharge on the surface of the sheath, the possibility of damage to the sheath should be considered, and careful inspection is required. If the sheath is damaged, it should be replaced as soon as possible.

2.2 Test Judgment

UV test is based on the standard: ” DL/T 345-2010 Guidelines for the Application of Ultraviolet Diagnostic Technology for Live Equipment”;

Diagnosis methods include the judgment of the equipment itself and the comparison and judgment between three-phase equipment. Generally, when the discharge is severe, the value of ultraviolet photons is relatively large, which is easy to judge. Follow up detection and carry out phase-to-phase comparison.

2.3 Notes on testing

① Set a reasonable gain

When the gain setting is too low, the detection sensitivity is not enough, and if the setting is too high, it is easy to be interfered by external optical fibers. Generally, the gain is set to the maximum value when starting the test, and the gain is gradually adjusted according to the saturation of the number of photons;

② The wind speed should not be greater than 5m/s;

When the wind speed is too high, it will affect the number of UV photons observed;

③Avoid shielding and electromagnetic interference;

④ It is advisable to test at night or on cloudy days;

⑤Excessive pollution on the surface and loss of hydrophobicity of composite insulators will also produce ultraviolet signals, which need to be distinguished;

3. Summary

① For insulators suspected to have mandrel defects, infrared and ultraviolet inspections can be carried out at the same time. If there are temperature rise and ultraviolet discharge at the same time, the probability of defects is very high;

②Infrared testing needs to set reasonable parameters to ensure the clarity of the test image, otherwise the test results will have large deviations, and the effect of the tower test is significantly better than that of the tower test;

③For the electro-erosion channel, it is often the end of the electro-erosion channel that generates infrared and ultraviolet abnormal signals;

④The temperature rise caused by internal defects is not obvious at the initial stage, and often requires multiple follow-up tests and phase-to-phase comparisons for final confirmation;

⑤UV testing is more sensitive to mandrel damage defects, but mainly relies on infrared testing for internal defects.

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ü Better hydrophobicity

ü Better hydrophobicity migration performance
ü Better pollution resistance
ü Excellent electrical insulation properties
ü Excellent aging resistance
ü Excellent resistance to high temperature, stress
corrosive & acid attack
ü Better damping Performance
ü High tensile strength (＞1200Mpa)
ü Excellent creep resistance
ü Excellent anti-fatigue fracture properties
ü High mechanical strength
ü Small dispersion
ü Reliable sealing performance
between rods and end fitting

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