LSA 50S4 3-Phase - Leroy Somer | 900 kW

Model. The LSA 50S4 3-Phase is a Leroy Somer LSA 4-pole alternator. In Leroy Somer's LSA nomenclature 50 is the frame and S4 is the core length: the frame fixes the stator bore and shaft centre height, and the core code fixes how much active iron is stacked into that bore. This one uses the short core, stack position 4 within that family. A longer core in the same frame buys more output at the same temperature rise, which is why the same frame number appears across a spread of ratings. It is wound for three-phase service at 50 Hz. Electrical rating. At 0.8 power factor lagging this machine is rated 900 kW, which is 1125 kVA, delivered as three-phase at 400 V 50 Hz. At 400 V line-to-line that is 1623.8 A per line. Ratings in this band are usually specified with a 1.25 service factor margin over the prime kW of the driving engine, so the alternator is not the limiting item when the set is asked to carry a block load. The 1500 rpm figure is synchronous speed, so there is no slip and no speed-dependent voltage droop. Frame and core. The 50 frame carries the S4 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, IC01, 0.9 m3/s at 47.2 frame, and the frame is steel frame with cast iron end shields. Three-phase winding. This is a three-phase machine with a 6 or 12 re-connectable winding brought out to 6 or 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 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 SHUNT (R250) standard; AREP (R450 / D510C) or PMG optional, regulated by R250 shunt / R450 AREP / D510C AREP, holding steady-state voltage to +/-0.5%. Leroy Somer builds the LSA around three excitation levels. Plain SHUNT excitation with the R250 regulator is the default and is entirely adequate for a single set carrying a stable load. AREP — the Auxiliary winding, Regulated, Excitation, Protection arrangement, run through the R450 or D510C regulator — adds a separate auxiliary stator winding that keeps the excitation supply independent of the main output voltage, so the machine sustains about 300% of full load current into a short circuit for up to ten seconds. That is what lets a downstream breaker clear a fault selectively. PMG excitation goes one step further with a permanent magnet pilot exciter and is normally specified where the load is heavily non-linear or where the set has to ride through a sustained fault. Mechanical build. The frame is steel frame with cast iron end shields. Bearings are permanently lubricated ball bearings. Mounting is IM 1201 (single bearing, SAE flange + drive discs) or IM 1001 (two bearing, SAE flange + keyed shaft). Maximum overspeed is 2250 rpm, and the machine is rated for 1000 m without derating. The rotor is dynamically balanced to ISO 1940 and IEC 60034-14. The single-bearing arrangement couples through a SAE flange and drive discs, so the alternator rotor is carried partly by the engine flywheel housing; the two-bearing arrangement carries its own shaft extension and takes a conventional coupling. Where it fits. Utility-scale standby and heavy process plant. At this rating the alternator is normally specified with a PMG and a digital AVR, and the specification usually calls out reactive capability, fault current, and parallel operation with the grid rather than just kW. On a three-phase machine of 900 kW the practical constraint is usually the downstream protection and the cable, not the alternator itself. Core stack position. The S4 core is stack position 1 of 5 in the LSA family, roughly 20% of the way along the family's lamination length range. It is the shortest stack the LSA family is built with. 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. Where it sits in the range. The LSA family is catalogued from 6.4 kW up to 1680 kW, and this page covers the 900 kW / 1125 kVA point. The step below it is the LSA 49.1M75 3-Phase at 800 kW, 1000 kVA. The step above it is the LSA 50M6 3-Phase at 1312 kW, 1640 kVA. If your load sits between two steps, take the higher one and let the engine run at part load rather than pushing the smaller machine to its limit on a hot afternoon. Reading the model code. A Leroy Somer designation is read as the LSA or TAL series, the frame size, and the core stack code (VS, S, M, L or VL plus a stack number). Here that gives LSA 50S4 3-Phase for the model, 50 for the frame, S4 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 LSA range is built on 2 frame sizes — 40, 50 — and the 50 frame is number 2 of them. The same 900 kW rating is also catalogued on the 49.1 frame as the LSA 49.1L9 3-Phase. The 49.1 is the smaller of the two, so it is shorter and lighter and is the one to quote when the skid or the canopy is the limiting dimension. The 50 carries the same rating with more iron around it, which shows up as lower flux density, a cooler core and more headroom when site ambient runs above 40 C. What the nameplate means once it is wired in. At 900 kW and 1125 kVA this machine pushes 1624 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 2500 A frame device set to trip above 2030 A, and the run from the alternator terminals to the first panel should be 630 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 1008 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 900 kW alternator is normally quoted against a 1008 kW engine rather than a 900 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 261 L per hour; at 75 per cent load it drops to about 204 L per hour and at half load to about 144 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. Where this rating sits in the frame ladder. Within the 50 frame LSA carries 5 distinct ratings, and this is number 1 of them at 900 kW. This is the smallest rating the 50 frame carries; the step above is the LSA 50M6 3-Phase at 1312 kW / 1640 kVA, 412 kW over it. Every step inside one frame is one more lamination stack length. The shaft, the bearings, the foot pattern, the terminal box and the AVR are the same part across the whole ladder, and only the core length and the winding change. That is why the price gap between two neighbouring steps is small while the gap between the last step of one frame and the first step of the next is large. It also sets the value-engineering rule: dropping one core size inside the frame saves money and axial length but eats the margin to the load, while stepping up one size costs far less than jumping to the next frame and buying a bigger skid, a bigger breaker and a bigger cable with it. Supply. Supplied as a genuine Leroy Somer unit — Nidec Industrial Solutions, built in France. LSA and TAL ranges are built in Europe and carry a European certificate of origin. 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.