Description

Technical Specifications

Main Features and Advantages

IGBT-based high-speed chopping with adjustable frequency.​ The NBRA-656C​ uses industrial-grade IGBTs as the switching element — not the lower-grade GTO or bipolar transistors found on economy brake units — and switches at a default 4 kHz chopping frequency that is adjustable to tune acoustic noise and resistor ripple-current. The ≤2 ms response time from bus-overvoltage detection to first IGBT on-pulse matters in high-inertia decels: a 2000 kg hoist load dropping at 2 m/s can regenerate several hundred kW into the DC bus for a fraction of a second; if the chopper lags, the bus overshoots and the drive trips, the mechanical brake slams on, and you get rope jerk. The NBRA-656C​ keeps the bus pinned to the threshold window (e.g., 780 V on / 750 V off in 400 V mode) across the whole 60-second peak window.Voltage-class jumper and wide auto-adapt range.​ A frequent cause of “why won’t my chopper fire” calls is the internal voltage-selection jumper: the NBRA-656C​ must be jumpered to match the supply class — 230 V, 400 V, or 500 V. The jumper sets the overvoltage threshold (the “maximum limit” per ABB docs = 1.21 × 1.35 × U1max, where U1max = 415 V for 400 V selection, 500 V for 500 V selection). If a 400 V supply is jumpered to 500 V, the threshold sits ~780-800 V, but the bus on a 400 V drive only climbs to ~720-740 V under regen, never hits the threshold, and the chopper never fires — the drive then trips on overvoltage while the chopper sits idle. The NBRA-656C‘s jumper is the first thing to check on commissioning, and the second thing after any drive replacement.Full protection suite with relay fault output.​ The onboard NBRC control board monitors four fault classes and drops the relay if any trigger: (1) brake resistor or resistor cable shorted, (2) IGBT shorted, (3) control board failure, (4) enable input lost. The relay is a form-C (NO/NC) changeover, so the cabinet can wire it to the drive’s fault-tree or to a PLC DI — when the NBRA-656C​ disables itself (resistor disconnected from DC bus), the relay releases and the fault propagates upstream. One caveat ABB documents clearly: the chopper cannot clear a short-circuit current itself — the IGBT will fail if the resistor shorts and the drive’s own DC-fuse / breaker doesn’t clear. This is why the resistor cable must be short (≤10 m), shielded, and both-end grounded — a long unshielded run invites inductive kick and common-mode that fools the current sense.Parallel fiber-sync for power scaling.​ A single NBRA-656C​ tops out at 88.4 kW peak / 9 kW continuous — adequate for a single 30-55 kW hoist drive or a 75 kW centrifuge, but undersized for a 200 kW downhill conveyor or a multi-motor winding deck. The module includes a fiber-sync port that lets two or more NBRA-656C​ units parallel their enable/gating so they share the braking current proportionally. This avoids the “one big chopper” procurement constraint and lets plants scale: start with one NBRA-656C​ on a 55 kW hoist, add a second later when the hoist is upsized to 110 kW, re-use the first unit, fiber-sync them, done. The SAFUR resistor bank also scales — ABB offers multiple NBRC resistor elements that the NBRA-656C​ can drive in parallel strings.Mechanical fit for ACS800 cabinet integration.​ ABB designed the NBRA-656C​ footprint (145 × 157 × 177.5 mm) to drop into the designated brake-chopper bay of an ACS800 cabinet — wall-mount version of the drive has pre-drilled positions, and the DC+/DC- and R+/R- terminals land on the ACS800’s internal bus and resistor feeder without custom fabrication. Clearances are called out in the HW manual: ≥26 mm above, ≥51 mm to each side, to keep forced-air path open. For retrofit onto non-ABB drives, the NBRA-656C​ mounts on the cabinet wall near the DC bus bars, with DC+/DC- landed onto the drive’s DC-link terminals (many drives expose these as P+/N- studs even if they don’t document brake-chopper support). The 2.9 kg mass and IP20 rating mean it lives inside the cabinet, not exposed — the cabinet’s own enclosure (IP21/IP41/IP54) provides the environmental seal.SAFUR resistor ecosystem compatibility.​ ABB markets the SAFUR braking-resistor family (NBRC-xxx part numbers) as the matched load for the NBRA-656C​ — the resistor’s thermal inertia, ohmic value steps (2.7 / 4 / 6 Ω minimums per voltage class), and 2400 kJ energy rating align with the chopper’s 60s/10min cycle. Using a non-SAFUR resistor is permissible (minimum ohms must be respected or the IGBT overcurrents), but the SAFUR’s mechanical form factor and thermal-contact switch (wired to the NBRA-656C​ enable input) give a “designed together” commissioning path — the resistor’s thermostat opens the enable if the resistor overheats from consecutive heavy decels, the chopper stops switching, the bus rises, the drive trips — graceful degradation instead of a burned resistor.

Application Field

The NBRA-656C​ is deployed wherever an ABB ACS600/ACS800/ACS850 (or any 230-500 V drive with DC-bus access) feeds a load that regenerates meaningful energy on deceleration, and where letting the bus climb to the drive’s overvoltage trip is unacceptable — either because the process can’t tolerate the trip (hoist safety chain, conveyor product loss) or because the drive’s built-in brake unit is undersized for the inertia. The textbook application is overhead cranes and hoists: a 30 kW hoist motor lowering a 5-ton load regenerates roughly 20-30 kW back into the DC bus; the drive’s internal brake unit (often 2-4 kW class) saturates in seconds, the bus climbs, the drive trips, the mechanical brake snaps on — bad for rope life and for load swing. Adding a NBRA-656C​ with a SAFUR resistor sized to 4 Ω (400 V class) or 6 Ω (500 V class) absorbs the regen, holds the bus at ~770-780 V, and the hoist decelerates smoothly under control. Multiple hoists in a steel-service center or a shipyard gantry will each carry their own NBRA-656C, and the parallel-fiber option lets a dual-hoist trolley share a resistor bank if the electricals design calls for it.Elevators and lifts are a second domain — traction machines with counterweight-regeneration on down-fast runs; the NBRA-656C​ sits in the machine-room cabinet alongside the ACS800, and the resistor often goes into a separate vented enclosure (resistor gets hot — 2400 kJ is a lot of joules). Metallurgy applications — reheating-furnace pusher decels, roller-table retraction, shear flywheel spins-down — use the NBRA-656C​ because the duty is frequent-start-stop with high inertia; the 60s/10min cycle rating matches the furnace’s batch cadence. Fan and pump retrofit “heavy reduction” cases — a centrifugal fan spun down from 1500 rpm under VFD control where the dampers are closed and the inertia of the impeller + hub is 10× the motor — also benefit; the built-in brake unit on a standard HVAC drive is sized for the fan’s normal decel ramp, not for an emergency-stop from full speed, and the NBRA-656C​ fills that gap without upsizing the whole drive.Conveyor systems — especially downhill aggregate conveyors, mine-belt conveyors with loaded downhill sections, and parcel-sortation spirals — regenerate continuously while the belt runs; the NBRA-656C​ can be set up in a “continuous light regen” mode (the 6-9 kW continuous rating) with a larger SAFUR resistor bank, and the chopper holds the bus while the drive operates in regen steady-state. Engine and dyno test benches are another fit: the load machine (motoring the test article) regenerates to the DC bus, the NBRA-656C​ dumps it to resistors so the drive doesn’t feed it back to the grid (or the grid connection doesn’t permit reverse power). Wind-turbine converter DC-bus stabilization (especially retrofit on older doubly-fed units) also appears in the application list — the NBRA-656C​ manages bus overvoltage during gusty decels where the grid-side converter can’t sink fast enough.Retrofit and spare strategy: because the NBRA-656C​ talks to the drive only through DC+/DC- and the enable/fault relay, it is drive-generic within the 230-500 V / 320-800 V DC envelope. A plant running a mix of ACS800-04 (cabinet) and ACS850 (machinery drive) and even some non-ABB 400 V drives can standardize one NBRA-656C​ spare for all — the only variable is the voltage jumper and the SAFUR resistor value. For plants with multiple hoists or cranes, stocking 1 NBRA-656C​ per 3-4 units, plus a spare SAFUR resistor stack, covers the majority of braking-related downtime scenarios.