Brochure · EN — Siemens Energy brochure (2023) presenting the 3AP1 DTC (Dead Tank Compact) hybrid high-voltage switchgear for 145 kV and 245 kV. The DTC combines the proven self-compression interrupter of the AIS 3AP circuit breaker with SF6-insulated GIS components (8DN9 disconnector/earthing switch) in one compact module, cutting substation footprint by roughly 40 % versus a conventional dead-tank H-layout. Covers the modular component options (bushings, CTs, VTs, cable connections, high-speed earthing switch), drive variants of the disconnector/earthing switch, full IEC ratings for both voltage levels (up to 63 kA / 4000 A at 245 kV), and accessories such as the Voltage Detection System (VDS) and SIVIS stationary/mobile camera systems for position monitoring.
Circuit breakers are the central element of both air-insulated (AIS) and gas-insulated (GIS) switchgear. The DTC (Dead Tank Compact) circuit breaker applies a hybrid concept that combines the best of both worlds: a dead tank circuit breaker fitted with additional substation functions, configured to the individual substation requirements. It is available for rated voltages of 145 kV and 245 kV.
The core components are adopted from the established high-voltage circuit breaker, disconnector, and GIS product families: the self-compression arc-quenching interrupter unit of the AIS 3AP circuit breaker, the stored-energy spring drive mechanism, the SF6-insulated disconnector/earthing switch from the GIS type 8DN9, and an outdoor earthing switch from the Ruhrtal-designed range of disconnectors.
Because the components are compact and can be used flexibly, different layouts can be created with minimal engineering effort, and the level of encapsulation and module design can be adjusted to the substation layout and the operator's project budget. Reference installations include Spain (145 kV), Germany (145 kV), and China (245 kV).
Safety: according to CIGRE analyses, gas-insulated components are four times more reliable than air-insulated components. Separating gas compartments (e.g. between circuit breaker and disconnector) further increases switchgear availability. Deliveries of more than 1,200 DTC circuit breakers to over 30 countries back the concept.
Investment security: the 3AP1 DTC offers proven SF6 gas-insulated and air-insulated components that can be combined in new ways, optimized investment matched to individual substation layouts, gas-insulated components with the highest possible availability at minimum maintenance effort, suitability for confined spaces and extreme environmental conditions (e.g. low-temperature applications), and easy installation and commissioning.
Flexibility: configurations include a circuit breaker with one- or three-pole operating mechanism; disconnector, earthing switch, and high-speed earthing switch; current transformer, voltage transformer, and voltage detection system; cable connections at various positions; porcelain or composite bushings; additional gas-compartment separation with SF6 density monitor on request; double breaker modules for ultra-compact substation designs; and stand-alone components such as a disconnector module with voltage transformer.
Space efficiency: an H-layout of a conventional 145 kV AIS using 5 dead tanks compares to a DTC solution with 5 DTC switching modules at a space reduction of approximately 40 %.
A modular platform concept is applied across the high-voltage circuit breaker range, including the Dead Tank Compact. The main modular elements are the operating mechanism, control system, kinematic chain, and insulator designs. Possible components of the 3AP1 DTC are: bushing, current transformer, circuit breaker with self-compression principle, three-position disconnector/earthing switch, voltage transformer, cable connection assembly, and high-speed earthing switch.
Bushings: the switchgear connects to overhead lines or busbars via SF6-insulated bushings containing a fixed conductor and shield electrode. For both 145 kV and 245 kV the insulator is available in porcelain or composite (epoxy-impregnated fiberglass tube with silicone rubber sheds); variants with outdoor earthing switches use porcelain bushings.
Current transformer: conventional CT types; the housing accepts ring-type cores in many combinations with different ratings, for measuring and protection. The CT can be located at various positions, e.g. between the circuit breaker and the disconnector/earthing switch — equivalent to CT placement in air-insulated switchgear.
Circuit breaker: uses the self-compression arc-quenching principle, in which the arc energy itself interrupts the fault current so the operating mechanism does not have to supply that energy. Interrupter unit and stored-energy spring drive come from the established 3AP circuit-breaker family; one- or three-pole operation is available.
Three-position disconnector/earthing switch: based on GIS component designs, with movable contacts, shafts, and levers proven in long service; the motor drive is an established GIS-range component.
Voltage transformers: inductive VTs lower the operating voltage to values suitable for measuring instruments and protection equipment; per-pole implementation allows individual measurement of each phase. The separate gas compartment is monitored by an additional density monitor.
Cable connections: as an alternative to bushings, an SF6-insulated cable connection assembly is available, delivered with cable terminals according to IEC.
High-speed earthing switch: an additional spring snap mechanism provides fault-making capacity, so an overhead line can be earthed without using the circuit breaker. It can be mounted at the disconnector/earthing switch or at the cross-connection module, with separate operating mechanisms connected to the spring snap mechanism by coupling rods.
Disconnection and earthing are achieved by combining disconnector/earthing switches, additional earthing switches, and high-speed earthing switches. When the respective part of the system is switched off and isolated, the isolation-distance requirements for safe working conditions and earthing are met. Additional rupture discs and filter attachments increase safety and lifetime during operation, and optional inspection windows allow monitoring of the switching positions.
Because the unit is designed as a three-position device, the disconnector and earthing switch functions are mechanically interlocked. The additional earthing switch or the high-speed earthing switch can be operated independently of the disconnector/earthing combination, and in the unlikely event of a technical failure each operating mechanism can be operated manually. Four build variants exist: disconnector only; disconnector + earthing switch; disconnector earthing switch with additional earthing switch; and disconnector earthing switch with high-speed earthing switch.
Advantages: the drive variant can be defined per substation requirement or design; the disconnector/earthing switch can be mounted at different positions of the DTC module; a position indicator at the operating mechanism monitors the disconnector/earthing switch position; and an integrated high-speed earthing switch increases the fault-making capacity of the DTC.
The application chart positions the DTC 145 kV variant at rated voltages up to 145 kV with breaking currents up to 40 kA, and the DTC 245 kV variant at rated voltages up to 245 kV with breaking currents up to 63 kA. All values are in accordance with IEC; other values are available on request.
| Technical data | Unit | 3AP1 DTC 145 | 3AP1 DTC 245 |
|---|---|---|---|
| Rated voltage | kV | 145 | 245 |
| Rated short-duration power-frequency withstand voltage | kV | 275 | 460 |
| Rated lightning impulse withstand voltage/min | kV | 650 | 1050 |
| Rated normal current, up to | A | 3150 | 4000 |
| Rated short-time withstand current (1 s – 3 s), up to | kA (rms) | 40 | 63 |
| Rated short-circuit breaking current, up to | kA | 40 | 63 |
| Number of interrupter units per pole | – | 1 | 1 |
| Temperature range | °C | -55 up to +55 | -55 up to +55 |
| Rated operating sequence | – | O-0.3 s-CO-3 min-CO or CO-15 s-CO | O-0.3 s-CO-3 min-CO or CO-15 s-CO |
| Rated break time | – | 3 cycles | 3 cycles |
| Rated frequency | Hz | 50 or 60 | 50 or 60 |
| Maintenance after | – | 25 years | 25 years |
The Voltage Detection System is an intelligent accessory of the DTC component portfolio. It is an economic alternative to a voltage transformer when voltage values do not need to be measured, offers high reliability through an optical interface, guarantees a high safety level via an integrated surge arrester protecting electronics and staff, and enables simple integration of switching-error protection — for example blocking closure of the earthing switch under live conditions.
Up to three VDS systems can be integrated in the outgoing units to monitor the voltage. The three sensor attachments are mounted directly on the housing of the disconnector and earthing switch element. A splash-proof housing and surge arrester ensure long service life; the electrode decouples a capacitive current proportional to the high-voltage connection and is mounted on a cover with a gas-tight bushing. The measured-signal converter transforms the capacitive current into an optical signal, supplying an output from a minimum threshold current of 5 µA, corresponding to a primary-side voltage in the range of 10 % and 35 % UR/√3.
The control cabinet unit evaluates the signals from all three phases; the voltage condition is displayed via LEDs on the front of the unit and made available by relay outputs. An electrical interlocking device can then prevent the disconnector and earthing switch from switching while voltage is applied. The optical fiber transmission link eliminates external interference so the voltage condition is always displayed correctly.
SIVIS camera systems make it possible to quickly check the disconnector, earthing switch, and high-speed earthing switch positions of the 3AP1 DTC during maintenance, complementing the pre-existing position indicators on the operating mechanisms. Both a stationary and a mobile camera system are available.
Stationary camera: up to 6 cameras per pole (up to 18 cameras total) are mounted directly on the inspection windows of the disconnector and earthing switch modules, with cable connection to the control system in the control cabinet, rotary selector switches to switch between camera images, and an LCD display in the control cabinet for visualization. It provides simple, at-any-time visual monitoring of up to 18 positions, and integrated galvanic separation on the camera control board protects the switchgear's secondary equipment.
Mobile camera: a telescope bar allows hazard-free placement at hard-to-reach locations for contactless monitoring of the switching position inside the disconnector/earthing unit, with a universal USB interface to a laptop PC, shipment in a robust carrying case including documentation and software, and an optional adapter for the 245 kV compact switchgear. It can be attached to every inspection window of the 3AP1 DTC, is applicable in assembly, maintenance, and test switching, and is easy to use in four steps: connect the camera via laptop USB, start the operating software, place the telescope bar onto the inspection window, and optimize the picture in the software if necessary.
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