Clause Requirement: The GB/T standard clearly defines the rated voltage levels for indoor high - voltage vacuum circuit - breakers. For example, common rated voltage levels may include 7.2 kV, 12 kV, 24 kV, 40.5 kV, etc. The rated voltage indicates the nominal voltage at which the circuit - breaker is designed to operate under normal conditions.
Interpretation and Significance: This clause is fundamental as it determines the application scope of the circuit - breaker. Different power systems operate at different voltage levels. A circuit - breaker must be selected with a rated voltage that matches the voltage of the power circuit it is intended to be used in. Using a circuit - breaker with an inappropriate rated voltage can lead to insulation breakdown, over - voltage damage, or inability to effectively perform its switching and protection functions. For instance, in a 10 kV power distribution system, a circuit - breaker with a rated voltage of 12 kV is typically selected to ensure normal operation and sufficient insulation margin.
Clause Requirement: The standard specifies the rated current values that indoor high - voltage vacuum circuit - breakers should be able to withstand continuously. Rated current values can range from several hundred amperes to several thousand amperes, such as 630 A, 1250 A, 2500 A, 4000 A, etc.
Interpretation and Significance: The rated current reflects the load - carrying capacity of the circuit - breaker. It is designed to meet the normal operating current requirements of the power circuit. When choosing a circuit - breaker, the rated current should be greater than the maximum continuous current that the circuit is expected to carry. If the rated current of the circuit - breaker is too small, it may overheat during operation, reducing the lifespan of the equipment and even causing serious accidents such as fire. For example, in a substation where the maximum load current is calculated to be 1000 A, a circuit - breaker with a rated current of at least 1250 A should be selected to ensure reliable operation.
Clause Requirement: In China, the standard requires that indoor high - voltage vacuum circuit - breakers are generally designed to operate at a rated frequency of 50 Hz.
Interpretation and Significance: The rated frequency is an important parameter related to the electrical characteristics of the power system. Power systems operate at a specific frequency, and the circuit - breaker needs to be compatible with this frequency. A mismatch in frequency can affect the performance of the circuit - breaker, such as the operation time of its electromagnetic components and the accuracy of its protection functions. Since most of China's power grids operate at 50 Hz, ensuring that the circuit - breaker is designed for this frequency is essential for seamless integration into the power system.
Clause Requirement: The GB/T standard stipulates minimum requirements for the insulation resistance of indoor high - voltage vacuum circuit - breakers. For example, between the main circuit and the ground, and between different phases of the main circuit, the insulation resistance should be measured using a specified insulation resistance tester, and the measured value should be no less than a certain value (usually several hundred megohms or even higher, depending on the rated voltage).
Interpretation and Significance: Insulation resistance is a key indicator of the insulation performance of the circuit - breaker. A high insulation resistance can effectively prevent electrical leakage between the live parts and the ground or between different phases, ensuring the safety of personnel and equipment. Regular measurement of insulation resistance during the operation and maintenance of the circuit - breaker can help detect early signs of insulation degradation. If the insulation resistance drops significantly, it may indicate problems such as insulation aging, moisture ingress, or contamination, and timely maintenance or replacement measures need to be taken to avoid potential electrical accidents.
Clause Requirement: There are two main types of withstand voltage requirements in the standard: power - frequency withstand voltage and lightning impulse withstand voltage. For different rated voltage levels, specific withstand voltage values are specified. For example, for a 12 kV rated voltage circuit - breaker, the power - frequency withstand voltage (1 minute) between the main circuit and the ground and between phases may be around 42 kV, and the lightning impulse withstand voltage (peak value) may be around 75 kV.
Interpretation and Significance: Power - frequency withstand voltage testing is used to simulate the long - term insulation stress that the circuit - breaker may withstand under normal operating voltage conditions and some over - voltage situations. Lightning impulse withstand voltage testing, on the other hand, is to assess the ability of the circuit - breaker to withstand the high - voltage surges caused by lightning strikes. Meeting these withstand voltage requirements ensures that the circuit - breaker can maintain its insulation integrity under various voltage stress conditions, preventing insulation breakdown and ensuring the reliable operation of the power system. In areas with frequent lightning activities, the lightning impulse withstand voltage performance of the circuit - breaker is particularly critical.
Clause Requirement: The GB/T standard defines the rated short - circuit breaking current values for indoor high - voltage vacuum circuit - breakers. These values vary according to different rated voltage levels and application scenarios, and can range from tens of kilo - amperes to hundreds of kilo - amperes, such as 20 kA, 25 kA, 31.5 kA, 40 kA, etc.
Interpretation and Significance: The rated short - circuit breaking current is a crucial parameter that reflects the ability of the circuit - breaker to cut off short - circuit currents. When a short - circuit occurs in the power system, a large - current fault will be generated. The circuit - breaker needs to quickly and reliably cut off this short - circuit current to protect the power system and equipment from damage. A circuit - breaker with an insufficient rated short - circuit breaking current may fail to cut off the short - circuit current, resulting in serious consequences such as equipment burnout, fire, and even large - scale power outages. Therefore, accurately selecting a circuit - breaker with an appropriate rated short - circuit breaking current according to the short - circuit current level of the power system is essential for ensuring the safety and stability of the power system.
Clause Requirement: The standard also specifies the rated short - circuit closing current, which is the maximum short - circuit current that the circuit - breaker can safely close when it is in a normal open state. The value of the rated short - circuit closing current is related to the rated short - circuit breaking current and is usually expressed as a certain multiple (such as 2.5 times) of the peak value of the rated short - circuit breaking current.
Interpretation and Significance: The ability to close into a short - circuit current is also an important aspect of the circuit - breaker's performance. In some cases, such as when the power system needs to be re - energized after a fault or during certain switching operations, the circuit - breaker may need to close into a short - circuit current. If the circuit - breaker cannot close into the short - circuit current safely, it may cause severe arcing, damage to the contacts, and even failure of the circuit - breaker. The rated short - circuit closing current requirement in the standard ensures that the circuit - breaker has the necessary mechanical and electrical strength to withstand the impact of closing into a short - circuit current, thereby ensuring the normal operation of the power system during such critical operations.
Clause Requirement: The GB/T standard stipulates the minimum mechanical life of indoor high - voltage vacuum circuit - breakers. For example, the mechanical life of a general - purpose circuit - breaker may be required to reach 10,000 to 20,000 operations. During this mechanical life cycle, the circuit - breaker should be able to perform normal opening and closing operations without significant mechanical failures.
Interpretation and Significance: Mechanical life reflects the durability of the circuit - breaker's mechanical structure. A long mechanical life means that the circuit - breaker can be used for a long time without frequent mechanical maintenance or replacement, which is beneficial to reducing the operation and maintenance costs of the power system. In actual operation, the circuit - breaker may need to perform opening and closing operations frequently due to power - grid switching, fault protection, etc. If the mechanical life is too short, it will not only affect the normal operation of the power system but also increase the overall cost of power supply. Therefore, manufacturers need to optimize the mechanical design and manufacturing process of the circuit - breaker to meet the mechanical life requirements specified in the standard.
Clause Requirement: The standard also has requirements for the opening and closing operating times of indoor high - voltage vacuum circuit - breakers. For example, the opening time should be within a certain range (such as 20 - 50 milliseconds), and the closing time should also meet specific time limits (such as 50 - 80 milliseconds).
Interpretation and Significance: The operating time of the circuit - breaker is directly related to the speed of its protection action. In case of a fault in the power system, the circuit - breaker needs to open quickly to cut off the fault current and minimize the impact of the fault on the power system. A too - long opening time may lead to more serious equipment damage and power - grid instability. Similarly, a proper closing time is also important for ensuring the smooth connection of the power circuit during normal switching operations. Precise control of the operating time is achieved through the design and adjustment of the circuit - breaker's mechanical and electrical control systems, which is crucial for the reliable operation of the power system.