Siemens 3AP1 FG, 3AP1 FI, 3AP2 and 3AP4 Circuit Breakers

Short answer

The Siemens Energy 3AP family covers live-tank SF6 high-voltage circuit breakers from 72.5 kV up to 1100 kV, with a stored-energy spring mechanism between 72.5 and 800 kV. The 3AP1 FG covers the lowest voltages, the 3AP1 FI and 3AP2 FI the intermediate and high ones, and the 3AP1 DT is the dead-tank version. The 3AV1 from the Blue line interrupts in vacuum, with no SF6.

What it is and where it is used

The 3AP family from Siemens Energy is its line of SF6 high-voltage circuit breakers. Its models include the Siemens 3AP1 FG, mostly at 145 kV, and the 3AP1 FI, 3AP2 FI and 3AP4. Siemens Energy states that the 3AP family goes up to 1100 kV and uses a stored-energy spring mechanism from 72.5 to 800 kV. The 3AP1 DT is the dead-tank version, and the SF6-free Blue line includes the 3AV1, which interrupts in vacuum.

They are installed in utility transmission and distribution substations, in power plants and in heavy-industry substations, at high and extra-high voltage. For the principle, see live-tank high-voltage circuit breaker.

Variants: 3AP1 FG, 3AP1 FI, 3AP2 FI, 3AP4, 3AP1 DT and 3AV1

Model	Application	Main difference
3AP1 FG	Live tank, lower HV voltages	Approximate range 72.5 to 145 kV in the Siemens service table
3AP1 FI	Live tank, HV	Up to about 245 kV in the Siemens service table
3AP2 FI	Live tank, HV and EHV	Approximately 300 to 550 kV in the Siemens service table
3AP4	Live tank, EHV	Extra-high voltage, up to 800 kV
3AP1 DT	Dead tank	Interrupter in a grounded tank, bushing CTs (dead-tank breaker)
3AV1 (Blue)	Live tank and dead tank	Vacuum interruption and clean-air insulation, no SF6
3AT2/3, 3AT4/5 and LPO	Earlier generations	Still in service; the LPO has a hydraulic operating mechanism

In the Siemens service table, the 3AT generation reaches 80 kA and 800 kV. The exact voltage, rated current and breaking capacity of each unit are read from the nameplate.

Main features

SF6 self-blast interruption, which uses the thermal energy of the arc and allows lower-energy spring mechanisms; see interrupter chamber.
Stored-energy spring mechanism from 72.5 to 800 kV, with a charging motor, closing and opening coils, and spring supervision by motor running time. See circuit breaker operating mechanism.
Three-pole or single-pole operation, depending on the application.
Optional closing resistors and a modular design at extra-high voltage; see extra-high-voltage circuit breaker.
Control cabinet that Siemens Energy offers in a basic variant, with an operation counter and auxiliary contacts, and in variants with more supervision.

Spring mechanism: what the manufacturer publishes

The Siemens 3AP1 DTC brochure (in English) describes the 3AP family mechanism as a stored-energy spring mechanism with the same principle for all types from 72.5 to 800 kV. It is viable at those voltages because the self-blast interrupter needs little operating energy. The closing and opening springs sit inside the mechanism, outside the SF6 compartments, so they can be accessed without touching the gas. The manufacturer declares 10,000 guaranteed operating cycles and a maintenance-free mechanism for 25 years or 6,000 operating cycles. These are catalog values for the mechanism; the maintenance plan of a specific breaker comes from its manual and its operation history.

For whoever maintains the equipment, the key point is that spring supervision and the operation counter are condition data. The motor charging time and the number of operations are recorded at every intervention and compared with those from commissioning: a sustained drift in charging time is an early warning before a closing failure.

The 3AP1 DTC: the hybrid dead-tank version

The 3AP1 DTC (Dead Tank Compact) is not a stand-alone breaker. Siemens offers it for 145 and 245 kV as a module that combines in one unit the dead-tank breaker, the three-position disconnector and earthing switch, the current and voltage transformers and the cable connection. It reuses the 3AP self-blast interrupter and the disconnector of the 8DN9 GIS type. According to the brochure:

Data	145 kV	245 kV
Rated current, up to	3,150 A	4,000 A
Short-circuit current, up to	40 kA	63 kA
Lightning impulse withstand	650 kV	1,050 kV
Rated break time	3 cycles	3 cycles
Temperature range	-55 to +55 °C	-55 to +55 °C

The rated operating sequence is O-0.3 s-CO-3 min-CO or CO-15 s-CO, and the manufacturer declares a leakage rate below 0.1 % per year. It supports single-pole or three-pole operation, porcelain or composite bushings, and compartment separation with a density monitor. This makes it a compact alternative between an open-air substation and a GIS; see hybrid substation.

Standards and data requested for a 3AP breaker

IEC 62271-100 defines the service conditions and the type tests; the rated values (voltage, current, breaking capacity, operating sequence) are the ones a breaker must declare on its nameplate.
The O-0.3 s-CO-3 min-CO sequence (or the 15 s one) is the typical rated sequence for fast reclosing; on networks that reclose, confirm that the breaker’s sequence matches the reclosing scheme.
Rated break time of 2 or 3 cycles: this is a breaker figure, not a relay figure; the actual times are measured at commissioning. See operating time test.

Points to watch in commissioning and maintenance

SF6 density. The manufacturer uses one monitor per compartment; the first-level alarm and the lockout are confirmed against its temperature curve, not against the absolute value.
Single-pole operation. If the order is single-pole, pole discrepancy is supervised and trips: test that the discrepancy circuit acts within the set time and that the 62BF relay respects the single-pole logic.
Contact resistance and timing. These are the condition reference of the breaker; the commissioning values are saved as the baseline for future interventions.
Cabinet heaters. In cold or humid climates, the heaters and their thermostat prevent condensation that damages the operating mechanism; this is a frequent cause of control failures in old cabinets.

Communications and integration

The breaker does not communicate by itself: position, spring charged, SF6 density and alarms reach the relay or the bay controller through auxiliary contacts, and reach SCADA over IEC 61850 or DNP3. Siemens Energy also offers breaker monitoring systems. See circuit breaker auxiliary contacts and circuit breaker control cabinet.

Frequent technical questions

Which manual applies to the 3AP1 FG 145? The manual depends on the mechanism, the cabinet and the accessories of the order; request it with the serial number.
Motor alarm that does not clear: running-time supervision warns if the motor takes too long to charge the spring; check the supply, the motor protection and the limit switch.
Low SF6 density: check the density monitor and locate the leak before topping up the gas.
3AT or LPO in service: these are earlier generations; their major maintenance and spare parts availability are checked with the manufacturer, and replacement is often worth evaluating.
3AP1 FG or 3AV1 for a new project: it depends on the utility’s policy on SF6 and on the rated values; Siemens Energy offers both lines.

How we help

At Tiza Group we do not sell circuit breakers. We test and commission Siemens 3AP breakers and those of any brand: operating times, contact resistance, travel, coils, mechanism and SF6 gas analysis, and we verify the bay control and protection circuits. This fieldwork is done in Colombia, or elsewhere on request. See circuit breaker testing within testing and commissioning. If you are going to replace a 3AT or an LPO, we design the change remotely, worldwide, under engineering design and studies. Write to us through the contact page.

References

IEC 62271-100, high-voltage alternating-current circuit-breakers.
IEEE C37.04, rating structure for high-voltage circuit breakers.
Siemens Energy, brochure 3AP1 DTC for 145 kV and 245 kV, with spring mechanism data and DTC rated values.
Siemens Energy, high-voltage circuit breakers page and brochure High-Voltage Circuit Breakers from 72.5 kV up to 1100 kV.
Siemens, brochure Live-tank breaker parts and service (2017), with the range table of the 3AP and 3AT families.

Frequently asked questions

What is the difference between the Siemens 3AP1 FG and the 3AP1 FI?

Both are live-tank breakers from the 3AP family. In the Siemens service table, the 3AP1 FG covers the lowest voltages, roughly 72.5 to 145 kV, and the 3AP1 FI goes up to about 245 kV. The nameplate gives the exact voltage and breaking capacity.

Where can I find the manual for the Siemens 3AP1 FG 145?

The operation and maintenance manual ships with each breaker and depends on the mechanism and the accessories. Siemens Energy also publishes product brochures; request the documentation using the serial number.

Is the 3AP1 DT a dead-tank breaker?

Yes. DT indicates the dead-tank version, in which the interrupter sits inside a grounded tank and the current transformers are mounted on the bushings. Siemens Energy has 3AP1 DT brochures, including a low-temperature version.