NPE32-2S4 - Mecc Alte

Model. The NPE32-2S4 is a Mecc Alte NPE32 4-pole alternator. Mecc Alte reads the model as series NPE32, frame 32 and winding 2S. The trailing 4 is the pole count. Within a frame the winding letter S, M or L sets the stack length, so S is the shortest core and L the longest. It is wound for three-phase service at 50 Hz. Electrical rating. At 0.8 power factor lagging this machine is rated 32 kW, which is 40 kVA, delivered as three-phase at 400 V 50 Hz. At 400 V line-to-line that is 57.7 A per line. Small frames like this are sensitive to load power factor: running them well below 0.8 PF pushes the field current up and the stator current up at the same kW, so the nameplate kVA is the number to design to. The 1500 rpm figure is synchronous speed, so there is no slip and no speed-dependent voltage droop. Frame and core. The 32 frame carries the 2S core. Frame size fixes the stator bore and the shaft centre height; the core length fixes how much active iron sits in that bore, and therefore how much output the machine can make at a given temperature rise. The exact finished weight and outline drawing depend on the winding and the coupling, so they are confirmed on the certified datasheet issued with the order. The cooling circuit is direct air cooled, and the frame is steel frame, aluminium or cast iron end shields, C45 steel shaft. Three-phase winding. This is a three-phase machine with a 12 re-connectable winding brought out to 12 re-connectable terminals, so it can be reconnected on site for the usual voltage pairs — 380/220 V, 400/230 V, 415/240 V, 440/254 V and 480/277 V on the 50 Hz build, and the 60 Hz pairs on the 60 Hz build. Reconnection is done on the link board inside the terminal box, not by rewinding, which is why one machine can serve a 380 V job and a 480 V job. The 2/3 pitch, skewed stator slots design is what keeps the fifth and seventh space harmonics down without skewing the stator, and it is the reason the line-to-line waveform stays within the distortion limits the standards ask for. Four-pole build. A four-pole machine turns at 1500 rpm on 50 Hz and 1800 rpm on 60 Hz. That is the standard choice for generator sets from a few tens of kVA up to the low megawatt range, because the lower rotor speed gives a longer bearing life, a quieter fan, a higher subtransient reactance that is easier to coordinate with downstream protection, and a rotor that can carry a substantial damper cage for parallel operation. The trade is weight: a four-pole machine of a given kVA is roughly twice the mass of a two-pole one. Excitation and voltage regulation. The excitation system is self-excited, brushless, regulated by DER1 / M2K, holding steady-state voltage to +/-1.0%. Mecc Alte uses the M2K or DER1 regulator on this frame, fed from an auxiliary winding in the stator. The machine is self-excited and brushless, with the armature rotating and a damping cage on the rotor, so there are no slip rings and no brushes to service. The stator slots are skewed and the winding is short pitched, which is how the waveform is kept clean without an oversized frame. Mechanical build. The frame is steel frame, aluminium or cast iron end shields, C45 steel shaft. Bearings are permanently lubricated sealed ball bearings. Mounting is single or two bearing, SAE flange adaptable. Maximum overspeed is 2250 rpm, and the machine is rated for 0-1000 m. The shaft is C45 carbon steel, the end shields are aluminium or cast iron depending on frame, and the fan is splined to the shaft rather than keyed. Impregnation is polyester resin on the rotating parts and a vacuum process on the stator. The radial force the frame is designed to take is about 5,200 N on this size. Where it fits. Light commercial duty: a retail unit, a small workshop, a guesthouse, or a farm with an irrigation pump. Loads are mostly resistive and lightly inductive, so a standard shunt-excited machine copes without a PMG. On a three-phase machine of 32 kW the practical constraint is usually the downstream protection and the cable, not the alternator itself. Core stack position. The 2S core is stack position 2 of 9 in the NPE32 family, roughly 22% of the way along the family's lamination length range. It sits between the shorter 1S and the longer 3S. Short-stack builds like this one are picked when the set has to fit a compact canopy or a tight skid: the frame carries the rating with the least iron and the shortest overall length, at the cost of a slightly higher flux density in the teeth and a little more excitation current at part load. Reading the model code. A Mecc Alte designation is read as the ECP or NPE series, a frame digit, a stack letter (S, M or L), and a winding number. Here that gives NPE32-2S4 for the model, 32 for the frame, 2S for the core and three for the phase count, so the code on the nameplate and the code on this page match one for one. Quoting the full code rather than just the frame matters on this family, because the same frame number is built in several core lengths and the winding changes with the voltage. Frame position. The NPE32 range is built on 1 frame sizes — 32 — and the 32 frame is number 1 of them. No other frame in this range carries exactly this rating, so the 32 is the only build at 32 kW and there is no cross-frame decision to make. What the nameplate means once it is wired in. At 32 kW and 40 kVA this machine pushes 58 A down each line on a 400 V three-phase supply. That current, not the kVA figure, is what the switchgear and the cable have to survive, so the outgoing breaker should be a 100 A frame device set to trip above 72 A, and the run from the alternator terminals to the first panel should be 25 mm2 copper per phase for a normal 25 to 30 m span. Longer runs, aluminium conductors or tray-installed cable all move that number up, and the volt drop at full load is what decides it in the end. On the mechanical side the prime mover has to deliver about 35.8 kW at the coupling. The usual 1.10 to 1.15 margin over the alternator rating covers the fan, the excitation loss and the governor droop, and it is the reason a 32 kW alternator is normally quoted against a 35.8 kW engine rather than a 32 kW one. Fuel burn follows the electrical load almost linearly in this range. At a realistic 0.29 L per kWh for a modern common-rail set, running this alternator at full rating takes roughly 9 L per hour; at 75 per cent load it drops to about 7 L per hour and at half load to about 5 L per hour, because the fixed losses stay put while the variable ones fall away. Quote the breaker frame, the cable size and the engine rating together with the alternator, because a set that is right on paper and undersized on the cable is the most common way a good alternator gets blamed for a bad installation. Supply. Supplied as a genuine Mecc Alte unit — Mecc Alte S.p.A., built in Italy. ECP and NPE ranges are built in Italy. Each alternator ships with the routine test certificate, the winding connection diagram, and the AVR commissioning sheet. Export packing is seaworthy plywood on a pallet sized to the frame, and the machine is strapped and shrink-wrapped inside it. Tell us the engine make and model, the coupling arrangement (single or two bearing), the voltage and frequency, and whether you need a PMG, and we will confirm the build before it leaves the works.