740RSL4046 3-Phase - Marathon | 1250 kW

Model. The 740RSL4046 3-Phase is a Marathon RSL 4-pole alternator. Marathon reads the model as frame 740 followed by the RSL family code and the winding number 4046. The frame sets the mechanical envelope and the family code sets whether the machine is wound for single-phase or three-phase service. It is wound for three-phase service at 60 Hz. Electrical rating. At 0.8 power factor lagging this machine is rated 1250 kW, which is 1562.5 kVA, delivered as three-phase at 480 V 60 Hz. At 480 V line-to-line that is 1879.4 A per line. At this rating the machine is normally ordered with a PMG excitation system rather than plain shunt excitation, because the fault current available from a permanent magnet pilot exciter is what lets the downstream protection discriminate properly on a set this size. The 1800 rpm figure is synchronous speed, so there is no slip and no speed-dependent voltage droop. Frame and core. The 740 frame carries the 4046 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, and the frame is rolled steel frame, cast iron end brackets. 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 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 with SE350E AVR, regulated by SE350E standard / PM500 / DVR2400 with PMG, holding steady-state voltage to +/-1.0%. Marathon fits the SE350E as the standard regulator on the smaller frames, with the PM500 and the DVR2400 available where a PMG is specified. On the Mariner and harsh-duty builds the excitation stator is fully encapsulated and the rotating rectifier is a heavy-duty assembly with a 300% diode margin and sealed welded stud terminations, which is the difference between a machine that survives a damp boat hold and one that does not. Mechanical build. The frame is rolled steel frame, cast iron end brackets. Bearings are sealed for life ball bearings. Mounting is single bearing SAE flange or two bearing. Maximum overspeed is 2250 rpm, and the machine is rated for 1000 m. On the 280 to 430 frames the machine ships with twelve leads and a link board as standard, and the minimum inlet clearance is six inches. On the 570 frame and above the terminal box is mounted on top with the link board inside it, and a selenium surge suppressor is fitted as standard from the 360 frame up. Harsh-duty builds get multiple dip-and-bake cycles on the main stator. 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 1250 kW the practical constraint is usually the downstream protection and the cable, not the alternator itself. Core stack position. The 4046 core is stack position 26 of 33 in the RSL family, roughly 79% of the way along the family's lamination length range. It sits between the shorter 4045 and the longer 4048. Long-stack builds carry the rating in the frame with the lowest flux density of the family. The extra iron costs length and weight, and buys a cooler-running core, lower magnetising current, better part-load efficiency and more margin for site ambient above 40 C or for a non-standard voltage. Where it sits in the range. The RSL family is catalogued from 160 kW up to 2300 kW, and this page covers the 1250 kW / 1562.5 kVA point. The step below it is the 575RSL4044 3-Phase at 1100 kW, 1375 kVA. The step above it is the 742RSL4049 3-Phase at 1300 kW, 1625 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 Marathon designation is read as the frame number, the winding family (PSL, CSL, CSA, RSL, FSL or FDL), and a four-digit winding code. Here that gives 740RSL4046 3-Phase for the model, 740 for the frame, 4046 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 RSL range is built on 12 frame sizes — 431, 432, 433, 572, 573, 574, 575, 740, 741, 742, 743, 744 — and the 740 frame is number 8 of them. No other frame in this range carries exactly this rating, so the 740 is the only build at 1250 kW and there is no cross-frame decision to make. Lead count and reconnectable voltages. This 740RSL4046 3-Phase leaves the factory with 10 leads brought out to the terminal box. Ten leads means two reconnectable groups only: 240Y/480Y and 208Y/416Y. The six winding sections are jumpered for one of those two at installation, and the machine then runs at that voltage for the rest of its life unless the links are physically moved. The ten-lead build is what to quote when the site voltage is already fixed and documented, because it carries the full rating with fewer terminal studs, a shorter link bar set and a smaller terminal box than the twelve-lead version. What each jumper setting actually delivers. With ten leads only two settings exist, and the kVA available is not the same on both. 240Y/480Y gives about 1250 kW / 1562.5 kVA on this frame — 480 V line-to-line, 277 V line-to-neutral, the usual North American commercial supply. 208Y/416Y gives about 1100 kW / 1375 kVA on this frame — 416 V line-to-line, 240 V line-to-neutral, the usual Canadian and older industrial supply. Quote the voltage group you actually intend to run, not just the frame rating: a machine ordered for 480 V and then rejumpered to 416 V will not deliver the nameplate kW at the lower voltage without exceeding its temperature rise. What the nameplate means once it is wired in. At 1250 kW and 1562.5 kVA this machine pushes 1879 A down each line on a 480 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 2349 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 1400 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 1250 kW alternator is normally quoted against a 1400 kW engine rather than a 1250 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 362 L per hour; at 75 per cent load it drops to about 283 L per hour and at half load to about 199 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 Marathon unit — Regal Rexnord, built in United States. Marathon alternators are built by Regal Rexnord in the United States. 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.