In depth analysis and selection guide for SIEMENS 3AH3 vacuum circuit breaker technology

SIEMENS 3AH3 Vacuum Circuit Breaker: A High Reliability Medium Voltage Switching Solution for Industrial and Generator Applications

In the field of medium and high voltage distribution and power generation, the reliability, breaking capacity, and full lifecycle cost of circuit breakers are the core considerations. The Siemens 3AH3 series vacuum circuit breaker, as a proven and mature product, has established its leading position in the global market with its unique vacuum arc extinguishing technology, modular design, up to 10000 maintenance free operation cycles, and special certification for harsh generator applications. This article is based on Siemens' official technical catalog (HG 11.03, 2018), and comprehensively analyzes the 3AH3 series from the aspects of technical principles, product series, special applications, and selection and configuration.

Core structure and technological advantages: vacuum arc extinguishing and maintenance free design

The core design concept of 3AH3 vacuum circuit breaker revolves around high reliability and maintenance free. Its structure mainly consists of two parts: pole assembly and operating mechanism box, connected by post insulators.

Arc extinguishing medium: vacuum arc extinguishing chamber

Adopting vacuum switch technology that has been developed for over 40 years as the arc extinguishing principle. The vacuum arc extinguishing chamber, with its excellent dielectric recovery characteristics, can quickly and reliably disconnect short-circuit currents ranging from small capacitive/inductive currents to up to 72kA. The air insulated and easily accessible design of the arc extinguishing chamber makes it possible to clean insulation components in harsh environments.

Operating mechanism: Spring energy storage type

The operating mechanism is of the spring energy storage type. The closing spring can store energy electrically or manually, and lock it as energy storage after the energy storage is completed. During the closing operation, the spring energy is released to drive the moving contact to close, while the spring energy is stored for the opening (or contact pressure) to prepare for the next opening. The mechanism has a free tripping function that complies with the IEC 62271-100 standard, ensuring that even if the closing command continues, the opening command can immediately open the circuit breaker.

The key to the commitment of "maintenance free"

Siemens claims that 3AH3 is maintenance free throughout its entire lifecycle, provided that it is used under normal environmental conditions as specified in IEC 62271-1 and the operating cycle does not exceed 10000 times. This is due to:

Durable mechanical design and long-lasting vacuum arc extinguishing chamber.

No need for recalibration or adjustment, its characteristic parameters are not affected by the opening and closing frequency or long-term static state.

Strictly follow IEC durability levels such as E2, M2, C2, S1, etc.

Product series and core electrical parameters: covering a wide range of application scenarios

The 3AH3 series offers multiple sub series, covering a wide range of needs from general industrial to specialized power generation.

Series classification Main standards Rated voltage range Rated current range Rated short-circuit breaking current Typical applications

3AH3 (high current type) IEC 62271-100 7.2 kV -40.5 kV 1250 A -6300 A 31.5 kA -72 kA Industrial distribution, motor drive, substation

3AH37/3AH38 (generator type) IEC 62271-100 and IEC/IEEE 62271-37-013 17.5 kV, 24 kV 3150 A-12000 A (forced air cooling) up to 90 kA thermal/hydraulic/nuclear power generator outlet protection

Core parameter analysis:

Rated current and ambient temperature: The standard rated current is based on an ambient temperature of+40 ° C. When the ambient temperature decreases, the circuit breaker can carry higher currents, and the product catalog provides detailed derating curves.

Insulation level and altitude correction: Standard insulation parameters (lightning impulse withstand voltage, power frequency withstand voltage) are applicable for altitudes below 1000 meters. Beyond this altitude, the air density decreases and the insulation strength decreases. It is necessary to increase the insulation level of the equipment according to the correction factor (Ks).

Capacitive current breaking capacity: All circuit breakers meet the C2 level requirements of IEC 62271-100 and have the ability to break line charging current, cable charging current, and back-to-back capacitor banks. For example, at 7.2kV, the line charging current breaking capacity can reach 10A.

Specialized solution: Generator circuit breaker and "phase isolation" design

Siemens has launched specially certified generator circuit breakers for the special and harsh working conditions of power plants.

Special standard: IEC/IEEE 62271-37-013

The generator circuit breaker not only needs to pass the conventional type test of IEC 62271-100, but also must meet the additional requirements of IEC/IEEE 62271-37-013 standard. This standard mainly considers:

Generator side fault: The extremely high DC component may cause the current to have no zero crossing point, posing a serious challenge to the breaking capacity of the circuit breaker.