A 100 kVA unit is not always a 100 kW unit. The gap between those two numbers is the output power factor, and it is one of the most common reasons a system that looked right on paper overloads at commissioning.<\/p>\n\n\n\n
kVA<\/strong> is apparent power: voltage times current. It sets how much current the inverter and cables have to carry. kW<\/strong> is real power: what the load actually consumes and turns into work and heat. It sets how hard the power stage and the battery have to work.<\/p>\n\n\n\n They are linked by power factor (PF):<\/p>\n\n\n\n kW = kVA \u00d7 PF<\/strong><\/p>\n<\/blockquote>\n\n\n\n The same nameplate kVA can deliver 25% more real power on a unit with output PF 1.0 than on one with 0.8. Comparing quotes on kVA alone hides that difference.<\/p>\n\n\n\n Check the load against each rating separately. Which one runs out first depends on the power factor of the load compared with the output power factor of the unit.<\/p>\n\n\n\n A 100 kVA unit with output PF 0.8 gives 80 kW. A server load of 85 kW at PF 0.99 draws about 86 kVA. It looks fine against the 100 kVA headline, but it is over the 80 kW limit by more than 6%.<\/p>\n\n\n\n A 100 kVA unit with output PF 1.0 gives 100 kW. A motor-heavy load of 80 kW at PF 0.7 draws about 114 kVA. There is plenty of real power to spare, but the current limit is exceeded.<\/p>\n\n\n\n Cable, breaker and busbar sizes follow kVA, because they carry current whatever the power factor. For a quick figure:<\/p>\n\n\n\n\n
Rating<\/th> Output PF<\/th> Real power available<\/th><\/tr><\/thead> 10 kVA<\/td> 1.0<\/td> 10 kW<\/td><\/tr> 10 kVA<\/td> 0.9<\/td> 9 kW<\/td><\/tr> 100 kVA<\/td> 0.8<\/td> 80 kW<\/td><\/tr> 100 kVA<\/td> 1.0<\/td> 100 kW<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n A load has to fit inside both ratings<\/h2>\n\n\n\n
Case 1: kW runs out first<\/h3>\n\n\n\n
Case 2: kVA runs out first<\/h3>\n\n\n\n
What this means for current<\/h2>\n\n\n\n
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