SDV7-AR arc-resistant and SDV7 non-arc-resistant, outdoor, distribution circuit breakers
Rated short-time withstand current up to 40 kA
Rated continuous current up to 3,000 A
Lightning impulse (BIL) up to 200 kV
Outdoor, distribution, medium-voltage circuit breakers
The type SDV7 family is the latest generation of the successful type SDV product line.
Ratings have been expanded, along with introduction of an option for a magnetic-actuator operator, as an alternate to the standard stored-energy operator. An option for arc-resistant construction, tested to ANSI/IEEE C37.20.7 requirements for accessibility type 2B, is also available.
The magnetic actuator is adapted to the basic high-voltage support structure of the type SDV7 stored-energy operator version. The magnetic-actuator design has been qualified with full short-circuit tests to the same performance levels as with the stored-energy operator design.
The type 3AH35-MA magnetic actuator operator employs long-life, rare-earth permanent magnets to provide the
closing force needed for the worst-case closing and latching duty, in combination with the basic kinematic structure
used with the entire type SDV7 family for opening operations. The magnetic actuator employs an electronic
controller to provide power to close the circuit breaker, as well as to supply the energy to open the circuit breaker.
The type 3AH35-SE stored-energy operator is derived from the highly reliable type 3AH family of operators, with over
30 years of design heritage.
With over 10,000 type SDV circuit breakers and 350,000 type 3AH operators in service, you can rely on Siemens products to meet your distribution system demands.
The type SDV7 family now includes an option for arc-resistant construction. The arc-resistant enclosure has been
tested for conditions of internal arcing in accordance with ANSI/IEEE C37.20.7, for accessibility type 2B. The arc-resistant
design shares the same footprint dimensions as the non-arc-resistant design, for ease in application.
The design of the type SDV7 features significant reduction in enclosure size; and, consequently, in the overall footprint. The type SDV7 product line encompasses the voltage groups 15.5 kV, 27.6 kV and 38.0 kV. Each group is specifically designed to optimize space and material for the voltage class while retaining common features across the entire product line.
The heart of the medium-voltage circuit breaker is the time-proven Siemens vacuum interrupter. Siemens vacuum interrupters use chrome-copper contact material, which keeps the chopping current to five amperes or less and thereby keeps overvoltages to a minimum.
The contact configuration employs axial-magnetic field geometry to maintain the arc in diffuse mode and minimize contact erosion, and provide a capability of up to 100 full-rated fault interruptions (depending on rating) before replacement is necessary.
A contact-wear indicator is provided to directly determine the wear of the contacts within the vacuum interrupter.
Watch the video below to learn more about the SDV7 outdoor distribution medium-voltage circuit breaker family.
- Extended capacitor switching (optional)
- Tested for out-of-phase switching ratings (ANSI/IEEE C37.09)
- Large relay and control compartment
- Stainless steel exterior hardware
- Porcelain dry-type bushings with extended creep
- Highly reliable vacuum interrupters – MTTF over 53,000 years
- Pair with Siemens protective relays to match any typical application
- Moderate and high seismic qualification (Zones 1-4) available
- Meets or exceeds the latest ANSI, IEEE and NEMA standards
- ANSI/IEEE “rain tested” enclosure (ANSI/IEEE C37.20.2).
Medium-voltage SDV7 family outdoor distribution circuit breakers available as:
- Standard: non-arc-resistant enclosure
- Optional: arc-resistant, accessibility type 2B, tested to ANSI/IEEE C37.20.7.
Medium-voltage SDV7 distribution circuit breaker family includes:
- SDV7-SE: SDV7 non-arc-resistant with stored-energy operator
- SDV7-MA: SDV7 non-arc-resistant with magnetic-actuator operator
- SDV7-SE-AR: SDV7-AR arc-resistant with stored-energy operator
- SDV7-MA-AR: SDV7-AR arc-resistant with magnetic-actuator operator.
Stored-energy operator 3AH35-SE for types SDV7 and SDV7-AR circuit breakers
Type 3AH35-SE stored-energy operator
The type 3AH35-SE circuit breaker operator is a durable and reliable stored-energy mechanism. This operator is designed to perform up to 10,000 operations before overhaul, and the basic operator in the 3A family has a mean time before failure (MTBF) of over 23,000 years (as of 2014).
The type 3A operator family has over 1,000,000 units in service worldwide in vacuum circuit breakers. Over 120,000 type 3AH3 operators are in service.
Improvements in the operator have been incorporated to enhance service life and simplify maintenance. Newer lubricants and alternative bearing materials have been selected to reduce the chance for interaction between the lubricants and the metals to ensure long service life. Mounting provisions for devices, such as the opening latch, closing latch and similar items, are designed for one-person removal and installation.
Reusable spring clips are used for pivot pins, avoiding the need for special removal tools or a supply of special
purpose retainers during maintenance.
The spring charging mechanism is a gear-drive design. Compared to a ratchet-and-pawl mechanism, the type
3AH35 operator is quieter and exhibits longer mechanical life.
The type 3AH35-SE stored-energy operator includes provisions for manual operation, such as during
maintenance. The closing spring can be manually charged with a spring-charging crank. The spring-charging crank
includes a coupling that automatically disengages in the event that the spring-charging motor begins to operate.
The operating mechanism also includes pushbuttons for manually closing or opening the circuit breaker. The
buttons are recessed to avoid inadvertent operation.
The estimated total mechanical endurance of the operator is 60,000 operations with overhaul and vacuum interrupter
replacement at 10,000 operation intervals.
The entire type SDV7 family, from 15.5 kV through 38.0 kV, uses the same basic type 3AH35 operating mechanism. The
operators differ only in elements related to the design voltage or interrupting rating of the circuit breaker.
The components that differ according to rating include: the main rotating shaft, contact pressure springs, closing
spring, opening spring and pushrods, as well as the high-voltage elements, such as the interrupter, standoff
insulators and similar items.
Magnetic-actuator operator 3AH35-MA for types SDV7 and SDV7-AR circuit breakers
Type 3AH35-MA magnetic-actuator operator
The type SDV7 distribution circuit breaker is available with a magnetic-actuator operator. The basic configuration of the circuit breaker is the same as for the stored-energy version, including the high-voltage elements and the vacuum interrupters, with only the operating mechanism replaced.
The type 3AH35-MA magnetic-actuator operator employs rare-earth magnets (neodymium-iron-boron) to maintain a stable CLOSED position, in combination with an electromagnetic coil structure to change from the OPEN position to the CLOSED position. The magnetic actuator
uses a single coil design, providing a stable OPEN and a stable CLOSED position without supplemental energy input.
The electronic controller provides a substantial current to the electromagnetic coil for closing operation, so that the electromagnetic force adds to the magnetic force provided by the rare-earth magnets.
For opening, only a modest electromagnetic force is needed, in the reverse direction, to offset the magnetic force provided by the rare-earth magnets. In effect, the electromagnetic force cancels the magnetic force during
The force for opening primarily is provided by the contact pressure springs on each phase (not shown) with an assist
from the opening spring. The opening spring is the same as used on the stored-energy version, and its primary function
is to provide the force to oppose the force of atmospheric pressure on the vacuum interrupter bellows, which would
otherwise cause the contacts of the open circuit breaker to close.
The field diagrams of the magnetic actuator illustrate the combined magnetic and electromagnetic field conditions in
the various circuit breaker positions.
Magnetic-actuator electronic controller
The operation of the magnetic actuator is controlled by an electronic module. The electronic module receives power
from a 24 Vdc power supply, stores energy in capacitors on several printed circuit boards, and provides a variety of functions, including:
- Closing, upon remote (or relay) command or from local pushbutton
- Opening, upon remote (or relay) command or from local pushbutton
- Capacitor control, including charging, monitoring, and periodic condition checking.
The electronic controller allows for circuit breaker reclosing according to the standard reclosing duty sequence in ANSI/
IEEE C37.04, O – 0.3 s – CO – 15 s – CO. The capacitors used to power circuit breaker opening and closing actions recharge following operations as follows:
- After a C operation ≈ 10 s
- After an O operation ≈ 2-5 s
- After a CO operation ≈ 12-15 s.
When first energized, the capacitors require approximately 35 s to obtain full charge.
The electronic controller is designed for harsh environments and long life. The estimated life of the electronic controller is approximately 20 years with an ambient environment outside the circuit breaker enclosure of 50 °C or less. In an environment less harsh than this, the expected life is well in excess of 20 years.
The capacitors used have a life expectancy of 45 years with an ambient environment at the capacitors of 70 °C (3% of total hours), 50 °C (40% of total hours), with the remaining 57% of total hours in an ambient of 40 °C or less. In an environment less harsh than this, the expected life is well in excess of 45 years.
The capacitor boards are generously sized, with energy storage above the level needed to operate the circuit breaker. In fact, the system is able to open and close the circuit breaker if as much as 20% of the capacitors are disabled.
The capacitors have reserve energy such that the circuit breaker can be electrically opened using the pushbuttons on the operator for at least 300 seconds after control power is lost.
The power supply for the electronics circuits accommodates a wide range of input voltages. The high-range power supply accepts any voltage in the range of 110 Vac to 240 Vac or 110 Vdc to 250 Vdc. The low-range power supply accepts voltage in the range of 28 Vdc to 56 Vdc.
Electrical close and open commands operate through binary inputs, with the high-range command input version requiring input of at least 68 Vac or 68 Vdc for operation, while the low-range command input version requires input of at least 17 Vac or 17 Vdc for operation.
The electronic controller includes monitoring and self-test functions, among which are these:
- Failure to close on command (after 100 ms)
- Excessive coil current
- Capability of capacitors
- Initial charging of capacitors on energization
- Periodic charging test cycle to verify energy storage capacity (performed weekly)
- Power supply (24 Vdc) failure
- Overcharging of capacitors (excess voltage)
- Coil circuit integrity
- Interlock check (lockout).
The electronic controller also maintains a log, which includes details of the last 32 operations and results of capacitor capability tests.
Built-in fast-discharge circuit for capacitors
The controller system design includes built-in means to discharge the capacitors if maintenance is to be performed.
There is no need for the user to provide jumper wires or loading resistors to discharge the capacitors – simply
disconnect the plug between the electronic controller board and the capacitor boards, and the discharge circuit is
automatically enabled, discharging the capacitors to a low level to enable maintenance. The NEC (NFPA 70) requires
discharge to below 50 Vdc within five minutes, but the system incorporated in the type SDV7-MA magnetic actuator design discharges to less than 5 Vdc in approximately 90 seconds.
When control power is initially energized, the controller executes a start-up routine, after which charging of the
When control power is first applied, a green LED on the power supply is illuminated.
The controller includes LEDs to indicate the energy status of the capacitor bank.
From complete discharge, approximately 25 seconds after control power is applied, a yellow LED lights, and
approximately 5 to 10 seconds later, the yellow LED goes off and a green LED illuminates. The LEDs indicate status as
- Green LED on power supply illuminated (visible with operator cover removed) indicates control power is available
- Green LED (adjacent to pushbuttons) illuminated indicates the operator is ready and is capable of Open-Close-Open sequence
- Yellow LED (adjacent to pushbuttons) illuminated indicates the operator is capable of an Open operation
- Red LED (adjacent to pushbuttons) illuminated indicates error and the energy is not sufficient for operation.
- The controller includes output terminals corresponding to the LEDs so that status can be monitored from remote locations.
External manual trip handle
An external manual trip handle is provided as standard on the type SDV7-MA and type SDV7-MA-AR with magnetic-actuator operator. The external manual trip handle requires only a modest force to operate it, and once the circuit breaker is opened, the handle can be padlocked to provide a lockout function and prevent closing of the circuit breaker either by electrical means or by manual means.
- 83 ms/five-cycle optional for stored-energy operator.
- TRV values are in accordance with ANSI/IEEE C37.06-2009 TRV peak value uc roughly equal to historic E2 value in ANSI/IEEE C37.06-2000. Value t3, time to voltage uc is approximately 1/1.138 times T2 value in ANSI/IEEE C37.06-2000.
- First value is full-wave impulse withstand circuit breaker open or closed. Second value is chopped-wave impulse withstand, applicable only with circuit breaker closed.
- Magnetic-actuator availability to be announced for these ratings. Consult factory.
TechTopics is a series of papers that discuss issues of interest to users or specifiers of electrical equipment.
- No. 02 - Loss of vacuum
- No. 03 - Vacuum vs. SF6
- No. 05 - Reclosing applications - minimum reclosing time
- No. 14 - X-radiation emissions by vacuum interrupters
- No. 24 - Checking integrity of vacuum interrupters
- No. 25 - Shunt reactor switching applications
- No. 26 - Ground bus ratings
- No. 27 - Standards for medium-voltage metal-clad switchgear
- No. 28 - Standards for outdoor high-voltage circuit breakers
- No. 29 - Derating factors for reclosing service
- No. 30 - Altitude correction factors
- No. 31 - Solar radiation correction factors
- No. 32 - Capacitor switching applications
- No. 35 - Transient recovery voltage
- No. 36 - Early “b” contacts
- No. 37 - Low current switching capabilities
- No. 38 - Harmonic filter application
- No. 41 - Circuit breakers or switches - application considerations
- No. 43 - Interposing relay requirements
- No. 44 - Anatomy of a short circuit
- No. 55 - Capacitor trip devices
- No. 56 - Switchgear outdoor enclosure type - Why isn’t it NEMA 3?
- No. 59 - Control power sources for switchgear
- No. 61 - Circuit breaker “standard duty cycle”
- No. 62 - A bit of history on circuit breaker standards
- No. 65 - Arc-furnace switching applications
- No. 66 - Clearances
- No. 67 - %dc component
- No. 77 - Residual voltage on load side of an open circuit breaker
- No. 78 - Personal protective equipment (PPE) required with metal-clad switchgear
- No. 79 - Working space required around electrical equipment
- No. 80 - Special tests - type SDV7 distribution circuit breaker gearbox lubrication
- No. 82 - Continuous current capability in ambient temperatures other than 40 °C
- No. 83 - Arc-resistant construction for outdoor distribution circuit breakers
- No. 91 - Current transformer relaying accuracies - IEEE compared to IEC
- No. 93 - Capacitor switching performance classes
- No. 94 - Circuit breaker interlocking and operating requirements
- No. 99 - Special tests - type SDV7 distribution circuit breaker gearbox lubrication
- No. 110 - Corrosion prevention effects on electrical equipment life
- No. 119 - Momentary ratings – peak or rms?
- No. 120 - High-potential testing – current doesn’t matter!
- No. 122 - Current transformer thermal-rating factor
- No. 126 - Testing of vacuum interrupters with dc test sets
- No. 129 - Interrupting capacity for system X/R ratios exceeding 17
- No. 130 - Reclosers or circuit breakers?
- Entire TechTopics catalog