How to Calculate Capacitor Bank Size for 500kW 10-Floor Commercial Building Design Stage

The discussion addresses the challenge of calculating the capacitor bank size for a 500 kW load in a 10-floor commercial building at the design stage, with limited detailed load information. It is emphasized that accurate capacitor bank sizing requires knowledge of individual loads, especially motors, as power factor varies with load operation. A common practical approach in the UAE involves estimating capacitor bank size based on total load and a target power factor (e.g., 0.95), using trigonometric relations to calculate reactive power (Q). One formula cited is Q = 0.387 × kW for three-phase systems. Another method assumes a worst-case power factor (e.g., 0.8) to calculate apparent power (S = P/PF) and reactive power (Q = √(S² - P²)), resulting in a capacitor bank size of approximately 375 kVAR for 500 kW load. Stepwise capacitor banks with incremental kVAR ratings (e.g., 5, 10, 20, 25, 50 kVAR) are recommended for flexibility. The use of automatic power factor regulators is noted to adjust capacitor steps dynamically. Additionally, suggestions include using centralized cooling systems to reduce variable loads and simplify power factor correction. Overall, the consensus is that while exact calculation is complex without detailed load data, estimation methods based on total load and assumed power factor are widely used in practice.
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