High voltage circuit breakers and other high voltage electrical appliances

(I) Switching devices : Mainly used to close and disconnect normal circuits and accident circuits or to isolate high-voltage power supplies. According to their functions, they are divided into:

1) High-voltage circuit breaker: It can disconnect various load circuits under normal conditions, close and disconnect short-circuit currents under accident conditions, and can achieve the requirements of automatic reclosing. It is the most comprehensive electrical appliance in high-voltage circuits.

2) High-voltage fuse: commonly known as insurance, it can automatically disconnect the circuit when the current in the line exceeds a certain limit or a short circuit occurs. After the circuit is disconnected, the fuse must be manually replaced before it can be used again.

3) High-voltage load switch: It can only close and open various load circuits under normal working conditions but cannot open short-circuit current.

4) High-voltage isolating switch: used to isolate power supply or circuit. The isolating switch can only break very small current, such as the no-load current of a small-capacity transformer.

5) Grounding switch: To ensure personal safety when inspecting and repairing electrical equipment on high-voltage and extra-high-voltage lines, a grounding switch can be used for grounding. The grounding switch can also be used to artificially cause a ground short circuit in the power system to achieve the purpose of control and protection.

(2) Measuring electrical appliances : mainly include current transformers and voltage transformers.

1) Current transformer: used to measure the current of high-voltage lines for metering and relay protection.

2) Voltage transformer: used to measure the voltage of high-voltage lines for metering and relay protection.

(3) Current-limiting and voltage-limiting electrical appliances : mainly include lightning arresters and reactors.

1) Lightning arrester: used to limit overvoltage and protect various electrical equipment related to the power system from the hazards of atmospheric overvoltage and internal overvoltage.

2) Reactor: It is essentially an inductor coil used to limit short-circuit current in case of fault. What are the basic requirements for high-voltage electrical appliances? What are the performance parameters? The main requirements for high-voltage electrical appliances include: general electrical performance requirements, natural environment requirements, and other requirements.

General electrical performance requirements: High voltage in power systems

Electrical appliances should be able to withstand various voltages and currents for a long time without being damaged.

1) Voltage: The maximum working voltage that the insulation part of a high-voltage electrical appliance with a certain rated voltage can withstand for a long time, and it can withstand the effects of atmospheric overvoltage and internal overvoltage to a corresponding degree. The performance parameters that indicate this aspect are: maximum working voltage, power frequency test voltage, full-wave and carrier impulse voltage, and operating wave test voltage.

2) Current: When the conductive parts of high-voltage electrical appliances are subjected to working current for a long time, the temperature rise of each part shall not exceed the allowable value. When short-circuit current is passed, it shall not be damaged by the action of electromotive force, the temperature rise of each part shall not exceed the allowable temperature value during short circuit, and the contact shall not be welded or damaged. These performances are all related to the current size, and the parameters indicating this aspect are: rated current, dynamic stability current, thermal stability current, etc.

Requirements for the natural environment: High-voltage electrical appliances should be able to be reliably grounded under various surrounding environmental conditions.

Ambient temperature: The relevant standards for high-voltage electrical appliances stipulate that the ambient temperature for the use of products is -40 to +40°C. Too low a temperature will increase the viscosity of transformer oil, hydraulic oil and lubricating oil, affect the speed of switch opening and closing, liquefy sulfur hexafluoride gas, deteriorate the performance of sealing materials, cause oil and gas leakage, and make the electrical equipment unable to work properly. Too high a temperature may cause overheating of the conductive part and leakage of the sealant of the capacitor bushing, etc. This is especially true for outdoor products.

(IV) What are the functions of high voltage circuit breakers?

High voltage circuit breaker is the most important and complex electrical appliance in high voltage equipment. Its main functions are:

1) Under the specified conditions of use, various load currents (including no-load, full load and overload current) can be connected or disconnected.

2) Under the action of the relay protection device, the short-circuit current can be automatically cut off.

3) Automatic reclosing can be achieved under the control of an automatic device. A high voltage circuit breaker is a dual-function electrical appliance that can be controlled and protected. It has a complete arc extinguishing device, but no obvious disconnection point.

(V) Main technical parameters of high voltage circuit breaker:

1) Rated voltage: refers to the normal operating voltage that the circuit breaker can withstand. The rated voltage refers to the line voltage and is indicated on the nameplate. The rated voltage of the circuit breaker not only determines its insulation distance, but also determines the external dimensions of the circuit breaker to a considerable extent.

1) Maximum operating voltage: Because there is voltage loss on the transmission line, the rated voltage at the power supply end of the line will be higher than the rated voltage at the power receiving end of the line. In this way, the circuit breaker may work for a long time at a voltage higher than the rated voltage. Therefore, the maximum operating voltage of the circuit breaker is specified.

2) Rated current: refers to the maximum operating current that can be passed for a long time under the specified ambient temperature as indicated on the nameplate. The size of the rated current determines the degree of heating of the circuit breaker, and thus determines the cross-section and structure of the contacts and conductive parts of the circuit breaker.

3) Rated breaking current: refers to the maximum current that the circuit breaker can reliably cut off under rated voltage.

4) Rated current capacity: also known as rated interrupting capacity or breaking capacity. The rated interrupting capacity of a circuit breaker is related to the rated breaking current and the rated line voltage, that is, it is expressed as √3 times the product of the rated breaking current and the rated line voltage, SKN = √3UINIKN.

5) Dynamic stability current: refers to the maximum short-circuit current allowed to pass through the circuit breaker when it is in the closed position. It is also called the limit passing current. When the circuit breaker passes this short-circuit current, it will not suffer any mechanical damage due to the action of the electromotive force. The dynamic stability current indicates the ability of the circuit breaker to withstand electromotive force. The magnitude of this current is determined by the mechanical strength of the conductive part and the insulating part.

6) Thermal stability current: When short-circuit current passes through the circuit breaker, the conductive part will heat up, and the heat is proportional to the square of the current. Therefore, when the circuit breaker passes the short-circuit current, the contacts may be welded and damage the electrical appliances. Therefore, the circuit breaker stipulates the thermal stability current within a certain period of time. It is generally expressed in effective value. The thermal stability current indicates the ability of the circuit breaker to withstand the thermal effect of the short-circuit current.

7) Closing time: the period from when the closing signal is sent to when the contacts of the circuit breaker are just connected. The requirements for the closing time of the circuit breaker are not high, but it should be as stable as possible. The closing time of short-circuit breaker produced in my country is generally about 0.25s.

8) Opening time: refers to the period of time from the time when the opening coil is connected to the time when the three-phase arc of the circuit breaker is completely extinguished. The opening time includes the inherent opening time of the circuit breaker and the arc existence time. The inherent opening time refers to the period of time from the time when the opening coil is connected to the time when the contacts are just separated. The arc existence time refers to the period of time from the time when the contacts are separated to the time when the three-phase arc is completely extinguished. Based on the requirement of cutting off the short-circuit current, the shorter the opening time, the better, generally 0.6s.

9) Contact travel: refers to the distance traveled from the starting position to the ending position of the contact.

10) Contact overtravel: It means that after the moving and static contacts of the circuit breaker come into contact during the closing operation, the moving contact continues to move forward a certain distance, which is equal to the difference between the stroke and the two distances.

11) Opening speed: refers to the speed at which the moving contacts just separate during the opening process of the circuit breaker.

12) Closing speed: refers to the moving speed of the moving contact when the moving contact just touches during the closing process of the circuit breaker. In addition, there are other technical parameters such as three-phase synchronization, oil weight, total weight, and no-current interval time.

KYN Series:

Product model and meaning

Structural features 1. KYN indoor AC metal armored removable switchgear (hereinafter referred to as trolley-type cabinet) is designed and manufactured according to the "3-35KV AC metal-enclosed switchgear" and IEC298 "AC metal-enclosed switchgear and control equipment" standards. It can also meet the "five-protection" function requirements of the high-voltage switchgear proposed by the Ministry of Water Resources and Electric Power.

a. The circuit breaker trolley cannot be closed during the process of pushing or pulling out;

b. The circuit breaker trolley can only be closed or opened when it is in the test position or working position, and the trolley cannot be pulled out from the working position when the circuit breaker is closed;

c. The circuit breaker trolley can be moved from the test position to the working position only when the grounding switch is in the open position; the grounding switch can be opened and closed only when the circuit breaker trolley is in the test position or outside the cabinet;

d. When the grounding switch is in the open position, the rear door cannot be opened;

e. When the trolley is in the working position, the secondary plug is locked and cannot be unplugged.

"Five-protection locking" of high-voltage cabinet

1) Prevent accidental closing or opening of circuit breakers.

2) Prevent the disconnector from opening and closing under load.

3) Avoid hanging ground wires while they are powered.

4) Prevent closing the circuit breaker with ground wire.

5) Prevent accidental entry into live compartments.