{"id":10559,"date":"2026-08-29T23:43:00","date_gmt":"2026-08-29T15:43:00","guid":{"rendered":"https:\/\/q8bbzjnpm5.wpdns.site\/?p=10559"},"modified":"2026-08-29T23:43:00","modified_gmt":"2026-08-29T15:43:00","slug":"how-to-calculate-kva-for-three-phase-power-subian-electric-has-the-answer","status":"publish","type":"post","link":"https:\/\/subian-electric.com\/ar\/news\/how-to-calculate-kva-for-three-phase-power-subian-electric-has-the-answer\/","title":{"rendered":"\u0643\u064a\u0641\u064a\u0629 \u062d\u0633\u0627\u0628 kVA \u0644\u0644\u0637\u0627\u0642\u0629 \u062b\u0644\u0627\u062b\u064a\u0629 \u0627\u0644\u0637\u0648\u0631\u061f \u0633\u0648\u0628\u064a\u0646 \u0627\u0644\u0643\u0647\u0631\u0628\u0627\u0626\u064a\u0629 \u0644\u062f\u064a\u0647\u0627 \u0627\u0644\u062c\u0648\u0627\u0628"},"content":{"rendered":"

A Zambian brewing company procured a transformer rated at 630 kVA for its new bottling facility after receiving information from an electrician stating that 630 is the standard number for that type of facility. Half a year afterward, it was discovered that the unit was running very hot every day, the voltage was dropping when the compressor bank was activated, and the utility company threatened the brewery with a demand penalty. In reality, the real demand figure measured properly was 380 kVA with a peak of 520 kVA \u2013 a 500 kVA unit would have been ideal in this case. The core mistake that the company makes is that it orders a transformer rating without calculating the actual kVA of the three phase load. This article will demonstrate how to calculate the kVA of three-phase power accurately with the help of a formula, power factor, real examples, and how to calculate the right transformer rating.<\/p>\n

In short, the kVA formula for three-phase power is kVA= (\u221a3 \u00d7 volts \u00d7 amps) \u00f7 1000. Take for example a 400 V line with 360 A current drew. That turns out to be (1.732 \u00d7 400 \u00d7 360) \u00f7 1000, which answers to 249.4 kVA. Therefore, a 250 kVA transformer should be used, but with 10-20% addition . To use kW to get to kVA it should be divided by the power factor : kVA = kW \u00f7 PF. When PF = 0.85, 200 kW = 235 kVA. As for single-phase distributions, kVA = (volts \u00d7 amps) \u00f7 1000.<\/p><\/blockquote>\n

\"How<\/p>\n

\n

The Three-Phase kVA Formula<\/h2>\n

The three-phase apparent power equation is key in transformer sizing : kVA = (\u221a3 \u00d7 V_L-L \u00d7 I_L)\/1000.<\/p>\n

VL-L refers to the line-to-line voltage in volts and IL refers to the line current in amps. The \u221a3 is a necessary part of the equation in three-phase systems, whereby voltages and phase currents are offset by 120\u00b0. The assumption about power is based on the fact that the required power is equal to the sum of three-phase power. Thus, three-phase equipment capable of producing a certain amperage is able to transmit the power equal to 1.732 of its single-phase counterparts.<\/p>\n

As an example, in the case of a 480 volts three-phase feeder with a current of 200 amps, the output power is equal to kVA = 1.732 \u00d7 480 \u00d7 200 \u00f71000 = 166.3 kVA. After adding a 15% safety margin, the resulting demand will be 191 kVA, or which is rounded to a 200-kVA transformer. The calculations will not differ for any other case, for example, for generator or feeder sizing.<\/p>\n

Single-Phase vs. Three-Phase Calculation<\/h2>\n

The result obtained by mixing these two up goes wrong by a factor of 1,732, capable enough to buy transformers rated two steps lower. The formula for single-phase omits the factor of \u221a3 :<\/p>\n

kVA (single-phase) = (V \u00d7 A) \u00f7 1000<\/p>\n\n\n\n\n\n\n\n\n
\u0627\u0644\u0646\u0638\u0627\u0645<\/th>\nFormula<\/th>\n\u0645\u062b\u0627\u0644<\/th>\n<\/tr>\n<\/thead>\n
Single-phase<\/td>\nkVA = (V \u00d7 A) \u00f7 1000<\/td>\n240 V, 100 A \u2192 24.0 kVA<\/td>\n<\/tr>\n
\u062b\u0644\u0627\u062b\u064a \u0627\u0644\u0637\u0648\u0631<\/td>\nkVA = (\u221a3 \u00d7 V \u00d7 A) \u00f7 1000<\/td>\n240 V, 100 A \u2192 41.6 kVA<\/td>\n<\/tr>\n
\u062b\u0644\u0627\u062b\u064a \u0627\u0644\u0637\u0648\u0631<\/td>\nkVA = (\u221a3 \u00d7 V \u00d7 A) \u00f7 1000<\/td>\n400 V, 200 A \u2192 138.6 kVA<\/td>\n<\/tr>\n
\u062b\u0644\u0627\u062b\u064a \u0627\u0644\u0637\u0648\u0631<\/td>\nkVA = (\u221a3 \u00d7 V \u00d7 A) \u00f7 1000<\/td>\n480 V, 200 A \u2192 166.3 kVA<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Notice the top two rows: same load of 240V, 100A gives 24kVA in single-phase, but 41.6 kVA if three-phase. If you are using a three-phase system, then use the three-phase formula because the single-phase result underestimates the transformer size by 42%.<\/p>\n

\"From<\/p>\n

From kW to kVA: The Power Factor Step<\/h2>\n

The information on nameplates is frequently given in terms of either kW or horsepower, but rarely as kVA. The common denominators are the power factor that is defined as the cosine of the angle between voltage and current and is usually estimated at 0.8\u20130.9 for engines and 0.95\u20131.0 for resistive loads and VFDs.<\/p>\n

kVA = kW \u00f7 power factor<\/p>\n

A 100 kW engine with 0.85 PF consumes 117.6 kVA. A strictly resistive heater of 100 kW consumes exactly 100 kVA. If you rely on the data of kW without accounting for the PF, kVA will be underestimated by 15\u201325% in the case of motors. Convert each load to be expressed in kVA first and then calculate the total \u2014 do not just sum up the kW values and divide because of differing behavior of loads that have different power factors.<\/p>\n\n\n\n\n\n\n\n\n\n
Power Factor<\/th>\nkVA per 100 kW<\/th>\nEffect on Sizing<\/th>\n<\/tr>\n<\/thead>\n
1.00 (resistive)<\/td>\n100<\/td>\n\u0644\u0627 \u0634\u064a\u0621<\/td>\n<\/tr>\n
0.95 (VFD \/ LED)<\/td>\n105<\/td>\n+5%<\/td>\n<\/tr>\n
0.90<\/td>\n111<\/td>\n+11%<\/td>\n<\/tr>\n
0.85 (typical motors)<\/td>\n118<\/td>\n+18%<\/td>\n<\/tr>\n
0.80<\/td>\n125<\/td>\n+25%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Worked Examples You Can Reuse<\/h2>\n

Example 1 \u2014 Motor load. There are three motors of 45 kW rating operating at 0.87 power factor along with a compressor with 30 kW rating installed at 0.82 power factor ! kVA ratings of the three motors = 45 \u00f7 0.87 = 51.7 kVA! Therefore, total kVA rating of three motors = 3 \u00d7 51.7 = 155.2 kVA! In the case of the compressor, its kVA = 30 \u00f7 0.82 = 36.6 kVA! Total running kVA = 191.8 kVA! Now applying diversity = 191.8 \u00d7 0.85 = 163 kVA! Further adding 15% for growth (i.e. 163 + (15% of 163) = 187.5 kVA! Recommended rating = 200 kVA (i.e. 250 kVA if there is certainty of expansion)!<\/p>\n

Example 2 \u2014 Measured load. Suppose we measure the load at 260 A on a three-phase feeder running at a voltage of 415 V and operating at a power factor of 0.88! So we can calculate kVA as follows: kVA = 1.732 \u00d7 415 \u00d7 260 \u00f7 1000 = 186.8! Now since we have calculated the kVA we can easily calculate the real power: real power = 186.8 \u00d7 0.88 = 164.4 kW! So the rating of transformer should be greater than equal to 186.8 kVA! With 15% margin, the rating of the transformer should be set at 215 kVA since the industry standard is 250 kVA!<\/p>\n

Example 3 \u2014 Combined load. Let\u2019s examine a cold store having power consumption of compressors of 60 kVA, lighting of 20 kVA, and of 15 kVA for offices altitude totaling to 95 kVA! Now applying diversity we get 0.85 \u00d7 95 = 80.8 kVA followed by growth of 20% as well which gets to result in a rating for the transformer of 100 kVA.<\/p>\n

In conclusion, it can be said that the same three steps were repeated in every case: convert to kVA, apply diversity, and add margin.<\/p>\n

Measuring Amps and Voltage Correctly<\/h2>\n

The principle of \u201cgarbage in, garbage out\u201d deserves to be highlighted; accuracy is dependent on the quality of data. Instead, it is necessary to use a true RMS clamp meter (instead of a cheap average responding one), as motor and electronic loading deforms the shape of the signal, and the average meter gives false readings due to its low input. Make measurements at a main breaker or switchboard, not in each phase (ideally for at least one full cycle of operation, but preferably for one week in total) in order to get an accurate measurement. Record all maximum line current in the phases, line-to-line voltage, and the power factor only if this data can be provided by the meter.<\/p>\n

Key fact: measure on the load side of the device, not on the nameplate side of it, as the nameplate value reflects the maximum (which is hardly going to be relevant in practice. Besides, be sure to check the actual service voltage, as a \u201c400 V\u201d system may actually operate at 420-430 V at the transformer output.<\/p>\n

Turning Your kVA Number into a Transformer Rating<\/h2>\n

Once the value of kVA required for the design is determined, the next standard capacity must be used. For IEC purposes, these include: 25, 50, 100, 160, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, and 2500 kVA. North America uses: 25, 37.5, 50, 75, 100, 150, 167, 250, 333, and 500 kVA. To determine the appropriate next rating, there are two rules to follow:<\/p>\n