Siemens 3AH5, 3AH3, 3AH4 and SION 3AE Vacuum Breakers

Short answer

The 3AH family are the Siemens medium-voltage vacuum circuit breakers: the 3AH5 is the standard type from 12 to 36 kV, the 3AH3 covers 7.2 to 40.5 kV with breaking currents up to 72 kA, the 3AH4 is built for very frequent switching, and there are versions for generator switching. The SION 3AE5 is the compact vacuum breaker up to 36 kV and 40 kA. All use a spring-operated mechanism with a charging motor.

What it is and where it is used

The Siemens 3AH are vacuum circuit breakers for medium voltage. The types include the 3AH5, the standard type; the 3AH3, for high short-circuit currents; the 3AH4, for very frequent switching; and the 3AH1, an earlier generation still found in installed switchgear. Alongside them is the SION 3AE5, of compact design. Siemens also publishes a catalog of 3AH vacuum breakers for generator switching.

They are installed in medium-voltage switchgear such as NXAIR, in distribution substations, industry, mining, power plants and solar plants, on feeder, transformer, motor and capacitor bank circuits. For the operating principle, see medium-voltage vacuum circuit breaker.

Variants: 3AH5, 3AH3, 3AH4, 3AH1, generator 3AH and SION 3AE5

Model	Application	Main difference according to Siemens
3AH5	Standard type	12 to 36 kV; at 36 kV, 25 kA and 2000 A
3AH3	High short-circuit power	7.2 to 40.5 kV, up to 72 kA
3AH4	Very frequent switching	Up to 40.5 kV; at 36 kV, 40 kA
Generator 3AH	Generator switching	Own catalog of vacuum breakers for generators
3AH1	Earlier generation	Found in existing switchgear
SION 3AE5	Compact, primary and secondary distribution	Up to 36 kV and 40 kA

The combinations of voltage, rated current and breaking current change by order number; the nameplate and the catalog for each version govern.

Main features

Vacuum interruption in sealed bottles, with no gas to monitor; see vacuum integrity test.
Spring-operated mechanism with a charging motor: the closing spring is charged, closing charges the opening springs, and the open-close-open sequence stays stored. The 3AH5 catalog states charging in under 15 s and classes E2, M2 and C2. See circuit breaker operating mechanism.
Releases: closing coil, shunt trip, current-transformer-operated release and undervoltage release, depending on the order. See trip and close coils.
Anti-pumping built into the control; see anti-pumping circuit.
Fixed or withdrawable-truck mounting, depending on the switchgear.

What each catalog states

Each type has its own catalog and scope. The data below are what Siemens publishes in them (3AH5, 2017 edition; 3AH3, 2018; 3AH4, 2025 edition; SION 3AE5, 2020); a specific order number may have different values.

3AH5: voltage levels of 12, 17.5, 24 and 36 kV, rated currents from 800 to 2500 A and breaking currents from 13.1 up to 31.5 kA at 12 kV. The vacuum interrupters are air-insulated and remain accessible, which allows the external insulation to be cleaned in harsh environments. A manually operated spring mechanism, a manual stored-energy mechanism and a motor-charged stored-energy mechanism are available.
3AH3: from 7.2 to 36 kV (40.5 kV according to the catalog text), with rated currents up to 6300 A and breaking currents up to 72 kA. Its catalog includes the 3AH37 and 3AH38, for high current and for generators.
3AH4: from 12 to 40.5 kV, designed for a very high number of operations: depending on the application, Siemens states 30,000, 45,000, 90,000 or 120,000 cycles. Its catalog gives arc furnaces as an example, which can require more than 100 operations a day.
SION 3AE5: the HG 11.02 catalog (2020) presents it from 7.2 to 24 kV, as a modular device for fixed mounting or on a withdrawable element, for new switchgear and for retrofitting existing switchgear. The Siemens product page lists a wider range, up to 36 kV, 40 kA and 4000 A.

Endurance classes E2, M2 and C2

The catalogs cite the IEC 62271-100 classes that each breaker meets. E2 indicates extended electrical endurance: the breaker does not require maintenance of its interrupting parts during its life, under the conditions of the standard. M2 indicates extended mechanical endurance, with 10,000 mechanical operations in the class. C2 indicates a very low probability of restrike when switching capacitive currents. The 3AH5 and 3AH3 state E2, M2 and C2; the 3AH4 states E2 and C2 and exceeds the M2 class by up to 12 times; the SION states C2, E2, M2 and S1. Class S1 of IEC 62271-100 corresponds to breakers used in a cable system.

For switching capacitor banks, the catalogs publish tables of capacitive breaking currents. At 12 kV, for example, the C2 class values are 10 A for an unloaded line, 25 A for cable, 400 A for a capacitor bank and 400 A for a back-to-back capacitor bank. The frequency of the inrush current is 4250 Hz. This matters when selecting the breaker for a capacitor bank (capacitor bank trips).

These classes are explained in E1 and E2 electrical endurance classes, M1 and M2 mechanical endurance classes and C1 and C2 classes for capacitive currents. For the generator version, see generator circuit breaker: classes G1 and G2.

Spring mechanism: sequence and timing

In the 3AH5, the closing spring, charged by hand or by motor, is latched; closing charges the opening springs and it recharges automatically, so the open-close-open sequence stays stored. Siemens declares a trip-free mechanism per IEC 62271-100: if an opening command arrives after closing has started, the contacts return to the open position and stay there even if the closing command is maintained.

The rated sequences in the 3AH5 tables at 12 kV are O-3 min-CO-3 min-CO, O-0.3 s-CO-3 min-CO and O-0.3 s-CO-15 s-CO; the short sequence O-0.3 s-CO-15 s-CO is the one required by high-speed auto-reclosing schemes. The times published in the 3AH5 catalog are: closing time under 65 ms, opening time with the first release under 55 ms, arcing time under 15 ms and total break time under 70 ms. The dead time is 300 ms and the electrical spring charging time is under 15 s. For the SION 3AE5, the catalog states closing of 60 ms maximum and opening of 30 ms maximum with the first release. These are catalog values; the value measured in the field is compared with the unit’s test report and with the tolerance set by the manufacturer (operating time test).

Declared maintenance and operating cycles

Siemens declares the 3AH5, 3AH3 and SION maintenance-free for 10,000 cycles under the normal conditions of IEC 62271-1, with no regreasing or readjustment. The SION catalog adds that 30,000 cycles can be reached with maintenance work. The 3AH4 catalog declares it maintenance-free up to 15,000 cycles; after that it sets a maintenance schedule, with regreasing every 15,000 cycles and replacement of the vacuum interrupters at 30,000 or 45,000 cycles, depending on the application. This changes the maintenance plan of a plant with frequent switching (medium-voltage circuit breaker maintenance): the breaker operation counter is a decision input, not a detail.

Installation conditions: temperature, altitude and environment

The 3AH5 is sized for the normal service conditions of IEC 62271-100, with rated current defined for 40 °C ambient air with the breaker in open air; inside a closed panel, the data of the switchgear manufacturer govern. It is suitable for the climatic classes of IEC 60721-3-3 3K4 (lower temperature limit of -5 °C), 3B1, 3M2, 3C2 and 3S2 (with the restriction of clean insulation). The withstand voltage values in the catalog are for altitudes up to 1000 m; above that they are corrected with the factor Ka of IEC 62271-1. The catalog gives an example: for a lightning impulse of 75 kV required at 2500 m, a minimum level of 90 kV is needed under reference conditions (75 kV x 1.2). A common mistake is to specify a breaker for a high-altitude substation without that adjustment, especially in mining and high-plateau projects.

Generator and high-current breakers

The generator 3AH3 (3AH37 and 3AH38) is tested, in addition to IEC 62271-100, according to IEC/IEEE 62271-37-013 (generator circuit breakers). That standard incorporates the conditions specific to a generator. Faults fed by the generator carry high DC components, with no current zero crossings. Faults fed by the grid carry higher rates of rise of the transient recovery voltage (TRV). The test voltage levels are also higher. The catalog shows 17.5 and 24 kV units with breaking currents of 50, 63 and 72 kA and rated currents from 3150 to 6300 A. It also shows a three-breaker solution in an isolated-phase design for breaking currents up to 90 kA and 12,000 A. That solution includes a 3AH36 (HB3) module of up to 12,500 A and 100 kA. Generator switching also calls for its own protection, such as reverse-power (32) tripping.

SION 3AE5 inside a switchgear panel

The SION is offered with contact arms and contacts for fixed mounting or on a withdrawable element. Siemens states that the module, with an earthing switch, forms almost the whole breaker compartment inside the panel and that the 3AE5 breakers up to 12 kV, 31.5 kA and 1250 A meet the DNVGL-CG-0339 classification for marine applications. The modules were tested according to IEC 62271-200, 62271-1 and 62271-102 (dielectric strength, temperature rise and switching capacity). The interlock of the withdrawable element prevents inserting it with the breaker closed (draw-out truck and panel interlocks).

Communications and integration

The breaker does not communicate by itself: position, spring charged and trip signals reach the panel relay through auxiliary contacts, and from there SCADA over IEC 61850, DNP3 or Modbus. Siemens offers auxiliary contact blocks of different sizes depending on the version. Auxiliary contacts and panel details are covered in medium-voltage switchgear.

Frequently asked technical questions

Manuals for the 3AH3 and 3AH4: Siemens publishes one catalog per type (for example, HG 11.05 for the 3AH5, HG 11.03 for the 3AH3 and HG 11.04 for the 3AH4) and operation manuals per version.
The 3AH does not close: it is usually the uncharged spring, the closing coil, the undervoltage release without supply, the truck interlock or the anti-pumping function.
Interrupter wear: it is monitored with timing, contact resistance and the vacuum integrity test.
Replacing an old 3AH1: the new breaker must fit the panel or require an adapter kit; review the whole panel and the control circuits.
3AH5 or SION 3AE5 for a new panel: it depends on the switchgear, the voltage and the breaking current; the switchgear manufacturer defines which breaker it accepts.

How we help

At Tiza Group we do not sell circuit breakers. We test and commission Siemens 3AH and SION breakers and any other make: operating times, contact resistance, insulation, vacuum, coils and mechanism, and we verify the control and protection circuits of the panel. See circuit breaker testing within testing and commissioning. If you are going to modernize switchgear with old breakers, we design the change under engineering design and studies. Field work is done in Colombia, or elsewhere on request. Write to us through the contact page.

References

IEC 62271-100, high-voltage alternating-current circuit-breakers.
IEC/IEEE 62271-37-013, alternating-current generator circuit-breakers.
IEC 62271-200, metal-enclosed switchgear for 1 kV to 52 kV.
Siemens, catalogs HG 11.05 (3AH5, 2017), HG 11.03 (3AH3, 2018), HG 11.04 (3AH4, 2025 edition), HG 11.02 (SION 3AE5, 2020) and HG 11.10 (vacuum circuit breakers for generator switching).

Frequently asked questions

What is the difference between the Siemens 3AH5 and the 3AH3?

Both are Siemens vacuum circuit breakers with a spring-operated mechanism. The 3AH5 is the economical standard type from 12 to 36 kV; the 3AH3 covers 7.2 to 40.5 kV and reaches higher breaking currents, up to 72 kA according to its catalog, for applications with high short-circuit power.

What is the Siemens 3AH4 used for?

It is the Siemens vacuum circuit breaker for very frequent switching, up to 40.5 kV according to its catalog. It is used where the breaker opens and closes many times a day, a mechanical duty that a standard breaker is not designed to withstand.

What is the Siemens SION 3AE5?

It is a compact-design Siemens vacuum circuit breaker, up to 36 kV and 40 kA according to its catalog, for primary and secondary distribution switchgear. How it is mounted depends on the switchgear panel it is installed in.