Introduction: Matching a 150-500kVA SBW voltage stabilizer to factory loads depends on three site measurements: actual incoming voltage swing, true load current, and the output accuracy your equipment needs.
If you manage plant electrical maintenance, quotation talks often begin with a simple question: what kVA do you need? A high estimate wastes budget on a frame you never fully load. Sizing only from normal running current can lead to nuisance trips when a large motor starts. The practical approach is to log voltage at the incoming panel through a full production week, build a load schedule that separates continuous loads from motor starting duty, and estimate capacity additions for the next year or two. That site data gives an industrial voltage stabilizer supplier a clear basis for quotation and lets an SBW voltage stabilizer manufacturer confirm the correct frame size.
Three-phase 380V is a nominal figure. Industrial distribution standards include tolerance bands because voltage moves in real installations. At a factory, it moves for local reasons: a large compressor starting, welding equipment, a neighboring plant sharing the same feeder, or a long utility run with limited margin. The SBW input window is three-phase AC 380V ±15%, about 323V to 437V per phase, and the unit holds output at AC 380V ±2% across that band. A logger on the incoming panel for five to seven days, including the heaviest shift, gives you the numbers that matter: highest phase voltage, lowest phase voltage, when each occurs, and whether the dip is slow daily drift or a fast sag that recovers within a cycle or two. Record no-load and full-load values, because a panel reading 400V at rest may fall to 350V when the largest press starts. Note the speed of change as well. The SBW responds in 2 seconds when the input changes within 10V. That suits daily drift and gradual sag. For overvoltage, undervoltage, phase loss, short circuit, and overload, the unit provides alarms and protective actions. Deep, repeated sags during grid faults may call for a conversation with your utility, and the alarm log can support that discussion. IEC 60044-7 provides background on industrial 380V distribution voltage and tolerance, while IEC TR 61000-5-1 explains dynamic voltage sag effects on industrial equipment. Your own site log remains the deciding record.
Capacity is where many factory quotations need a second pass. Adding nameplate kilowatts and converting to kVA produces a number that fits a resistive load bank but fails in a plant full of motors. Two loads with the same running current can demand very different frame sizes if one starts direct-on-line and the other ramps up on a drive. The 150-500kVA range gives you room to match the frame to actual starting duty. Work through the two steps below to fix a frame size that matches how your plant runs.
Build the load schedule in two passes. First, continuous load: sum the running kW of all equipment that operates at the same time, divide by the power factor to get kVA, then add lighting, HVAC, and control loads on the same panel. Second, mark every direct-on-line motor. A motor drawing 140A running can pull five to seven times that for the first second, roughly 700A to 980A. The stabilizer must ride through that starting current without nuisance tripping, and that ride-through requirement sets the frame size. IEC 60034-18-34 explains how motors behave under steady-state and transient voltage variation, which is why undervoltage during starting stresses a motor more than the same dip at full speed. Size on your worst realistic starting sequence, and check whether two large motors can ever start together. That single question often changes the answer.
Two allowances keep a correctly sized frame from becoming undersized later. First, headroom: 20-25% above measured running load covers a new line, a larger chiller, or a motor upgrade. The 150-500kVA range lets you keep that future load inside one unit's capacity rather than adding a second cabinet. Second, feeder drop. The stabilizer holds AC 380V ±2% at its output terminals, but a 200m feeder across a large hall loses several volts at full current. A drive at the far end then sees less than the terminal accuracy suggests. Record feeder lengths, conductor sizes, and the intended installation point. Placing the unit at the main panel rather than at the end of a long run keeps that voltage drop out of the regulation loop.
±2% on a 380V output is about ±7.6V per phase. Compare that figure against what your equipment tolerates rather than against the nameplate voltage. Drives, CNC controls, and instruments can react to sustained deviation, so check their input tolerance and use ±7.6V as the reference. Efficiency of ≥98% affects heat and operating cost. At 300kVA, a 2% loss is roughly 6kW of heat released inside the electrical room. Ventilation or cooling must remove it, and the loss appears on the electricity bill for every hour the unit runs. Include the number of hours per day the stabilizer actually operates. The parameter list for an accurate quotation should include: your incoming voltage log with high, low, and timing; a load schedule with continuous kVA and starting currents; feeder lengths and conductor sizes; the output accuracy your equipment needs; expected expansion; ambient conditions in the electrical room; and your operating preferences, including the overvoltage, undervoltage, phase loss, short circuit, and overload alarms the SBW includes, plus whether you want manual or automatic mode switching during maintenance. Feixiangda Power builds the SBW series across 150kVA to 500kVA and quotes from that list rather than from a single kVA figure. Standard units ship in 7-15 working days, custom configurations in 15-30 working days, and standard samples carry no MOQ. Every unit passes 100% factory inspection plus a mandatory 48-hour full-load aging test before dispatch, backed by CE compliance, an ISO 9001 quality system, a 12-month parts warranty, and 24/7 remote technical support.
Matching a stabilizer to a factory is a site exercise with three outputs: the voltage range your panel really delivers, the load current including motor starting duty, and the output accuracy your equipment needs, plus headroom for planned additions. Put those on one page with feeder details and ambient conditions. The quotation you receive will then be sized to your plant instead of an average. Share your site parameter list to get the frame size, protection settings, and lead time confirmed for your configuration.
A：Add the running kW of all equipment that operates together, divide by the power factor to get kVA, then treat the largest motor's starting current as a ride-through check rather than adding it to the running total. Size for the worst realistic starting sequence, add 20-25% headroom for expansion and feeder drop, and compare the result against the 150-500kVA range before requesting a quotation.
A：Record the highest and lowest phase voltage at the incoming panel over five to seven days, including your heaviest shift, and note when each occurs and how quickly the change happens. The SBW input window is 380V ±15%, so a week of readings shows whether your normal swing fits inside it. Include no-load and full-load values, since a panel sitting at 400V idle can fall to 350V under load.
A：It defines the correction speed for slow and moderate changes. A 2-second response suits the daily voltage drift and gradual sag that many motor-heavy plants see on the incoming supply, and it holds output at AC 380V ±2% while motors run. Faster events such as fault-level dips call for protective action, which the SBW provides through undervoltage, phase loss, short circuit, and overload alarms.
