UCI274G 1-Phase - Stamford | 175 kW

Model. The UCI274G 1-Phase is a Stamford UCI 4-pole alternator. Stamford designates the frame by the number in the model (274) and the core length by the letter that follows it (G). Within one frame the letter runs from short to long, and each step adds lamination stack and therefore output. It is wound for single-phase service at 50 Hz. Electrical rating. At 0.8 power factor lagging this machine is rated 175 kW, which is 218.8 kVA, delivered as single-phase at 230 V 50 Hz. At 230 V that is 951.1 A through the line and the neutral. This is the band where motor starting, not steady-state kW, usually sizes the machine: a direct-on-line motor of roughly 30% of the alternator kVA will pull the terminal voltage down by about 15% at start, which is normally acceptable, and anything larger needs a soft starter or a bigger frame. The 1500 rpm figure is synchronous speed, so there is no slip and no speed-dependent voltage droop. Frame and core. As built, this machine weighs 580 kg (1-bearing) / 598 kg (2-bearing), stator 225 kg, rotor 210.35 kg, crate 123 x 67 x 103 cm. The cooling circuit is 0.617 m3/s (1308 cfm) at UCI274, and the frame is steel frame, cast iron end shields. Single-phase winding. This is a single-phase machine, so the winding is laid out to produce one sinusoid across the output terminals rather than a three-phase set. Single-phase alternators of this size are almost always fitted with a capacitor or a compounded excitation arrangement to hold the voltage steady as the load swings, because the pulsating armature reaction of a single-phase load pulls the terminal voltage around far more than a balanced three-phase load does. The practical consequence for the buyer is that single-phase kVA and three-phase kVA of the same frame are not interchangeable: the single-phase machine is derated for the same iron, and the wiring, the circuit breaker and the cable all have to be sized on the single-phase current, which is roughly 1.7 times the three-phase current for the same kVA at the same voltage. 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, rotating rectifier, regulated by MX321 (+/-0.5%) or MX341 (+/-1.0%), holding steady-state voltage to +/-0.5% (MX321) / +/-1.0% (MX341). The MX321 and MX341 regulators are the two standard AVRs on this frame. MX321 holds +/-0.5% and adds three-phase sensing plus over-excitation and under-excitation limiting; MX341 holds +/-1.0% with single-phase sensing and is the cheaper option where the load is well behaved. Both are fed from a separate auxiliary winding, so the excitation supply does not collapse when the main output is shorted — which is what gives the machine its three-times-full-load fault current for ten seconds. Mechanical build. The frame is steel frame, cast iron end shields. Bearings are BALL.6315-2RS drive end / BALL.6310-2RS non-drive end (UCI274). Mounting is single bearing SAE flange or two bearing, IM 1201 / IM 1001. Maximum overspeed is 2250 rpm, and the machine is rated for 1000 m; derate 3% per 500 m above. The stator winding is double-layer concentric, and the rotor is balanced to better than BS6861 Part 1 Grade 2.5, which is what keeps vibration low enough for a set that will sit on a skid in a plant room. Derating for a dirty environment is 5% with an inlet filter fitted, 3% per 500 m above 1,000 m, and 3% per 5 degrees C above 40 degrees C ambient. Where it fits. Industrial plant and institutional standby: a hospital theatre block, a small data room, a food processing line, or a water treatment works. These jobs usually ask for a PMG or AREP excitation system so that the downstream protection can discriminate on a fault. On a single-phase machine of 175 kW the practical constraint is usually the downstream protection and the cable, not the alternator itself. Core stack position. The G core is stack position 5 of 6 in the UCI family, roughly 83% of the way along the family's lamination length range. It sits between the shorter F and the longer H. 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 UCI family is catalogued from 32 kW up to 1250 kW, and this page covers the 175 kW / 218.8 kVA point. The step below it is the UCI274G 3-Phase at 160 kW, 200 kVA. The step above it is the UCI274H 3-Phase at 176 kW, 220 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 Stamford designation is read as the family letters (UCI, UCDI, HCI, PI, LVSI), a three-digit frame number, a core letter, and an optional winding suffix. Here that gives UCI274G 1-Phase for the model, 274 for the frame, G for the core and single 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 UCI range is built on 3 frame sizes — 224, 274, 634 — and the 274 frame is number 2 of them. No other frame in this range carries exactly this rating, so the 274 is the only build at 175 kW and there is no cross-frame decision to make. What the nameplate means once it is wired in. At 175 kW and 218.8 kVA this machine pushes 951 A down each line on a 230 V single-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 1250 A frame device set to trip above 1189 A, and the run from the alternator terminals to the first panel should be 400 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 196 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 175 kW alternator is normally quoted against a 196 kW engine rather than a 175 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 51 L per hour; at 75 per cent load it drops to about 40 L per hour and at half load to about 28 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 274 frame UCI carries 11 distinct ratings, and this is number 9 of them at 175 kW. The step below is the UCI274G 3-Phase at 160 kW / 200 kVA, 15 kW under this one; the step above is the UCI274H 3-Phase at 176 kW / 220 kVA, 1 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 Stamford unit — Cummins Generator Technologies, built in United Kingdom. the Stamford mark is owned by Cummins Generator Technologies and the machines are built in their own plants. 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.