Method of measurement of the imbalance power of an electrical facility or system which comprises: i) acquiring instantaneous values of voltage (v A, v B, v C) and current (i A, i B, i C) of each of the phases A, B, C of the electrical facility or system, and decomposing them into their components at fundamental frequency (v A1, v B1, v C1), (i A1, i B1, i C1); ii) obtaining effective values of voltage (V A1, V B1, V C1) and current (I A1, I B1, I C1) and angles of initial phase displacement ( φ A1, φ B1, φ C1) between voltage and current, for the fundamental frequency; iii) starting from these effective values for the fundamental frequency obtained in the previous step, obtaining active powers (P A, P B, P C) and reactive powers (Q A, Q B, Q C) for each one of the phases according to the following expression; P A = V A 1 ⋅ I A 1 ⋅ cos φ A 1 Q A = V A 1 ⋅ I A 1 ⋅ sin φ A 1 P B = V B 1 ⋅ I B 1 ⋅ cos φ B 1 Q B = V B 1 ⋅ I B 1 ⋅ sin φ B 1 P C = V C 1 ⋅ I C 1 ⋅ cos φ C 1 Q C = V C 1 ⋅ I C 1 ⋅ sin φ C 1 or alternatively, starting from said effective values for the fundamental frequency, obtaining effective values of positive sequence and fundamental frequency voltage (V A1+, V B1+, V C1+) and phase displacement angles ( φ A1+, φ B1+, φ C1+) between voltage and current for the fundamental frequency, and obtaining active powers (P A, P B, P C) and reactive powers (Q A, Q B, Q C) for each one of the phases according to the following expression: P A = V A 1 + ⋅ I A 1 ⋅ cos φ A 1 + Q A = V A 1 + ⋅ I A 1 ⋅ sin φ A 1 + P B = V B 1 + ⋅ I B 1 ⋅ cos φ B 1 + Q B = V B 1 + ⋅ I B 1 ⋅ sin φ B 1 +; and P C = V C 1 + ⋅ I C 1 ⋅ cos φ C 1 + Q C = V C 1 + ⋅ I C 1 ⋅ sin φ C 1 + characterized by iv) starting from the active and reactive powers, an imbalance power phasor ( A U) is obtained according to the following expression: A ̅ U = √ 2 p ⋅ | P A + a 2 P B + aP C | + q ̅ ⋅ | Q ̅ A + a 2 Q ̅ B + aQ C | where a = I |120° and p and q are orthogonal unit phasors. i) acquiring instantaneous values of voltage (v A, v B, v C) and current (i A, i B, i C) of each of the phases A, B, C of the electrical facility or system, and decomposing them into their components at fundamental frequency (v A1, v B1, v C1), (i A1, i B1, i C1); ii) obtaining effective values of voltage (V A1, V B1, V C1) and current (I A1, I B1, I C1) and angles of initial phase displacement ( φ A1, φ B1, φ C1) between voltage and current, for the fundamental frequency; iii) starting from these effective values for the fundamental frequency obtained in the previous step, obtaining active powers (P A, P B, P C) and reactive powers (Q A, Q B, Q C) for each one of the phases according to the following expression; P A = V A 1 ⋅ I A 1 ⋅ cos φ A 1 Q A = V A 1 ⋅ I A 1 ⋅ sin φ A 1 P B = V B 1 ⋅ I B 1 ⋅ cos φ B 1 Q B = V B 1 ⋅ I B 1 ⋅ sin φ B 1 P C = V C 1 ⋅ I C 1 ⋅ cos φ C 1 Q C = V C 1 ⋅ I C 1 ⋅ sin φ C 1 or alternatively, starting from said effective values for the fundamental frequency, obtaining effective values of positive sequence and fundamental frequency voltage (V A1+, V B1+, V C1+) and phase displacement angles ( φ A1+, φ B1+, φ C1+) between voltage and current for the fundamental frequency, and obtaining active powers (P A, P B, P C) and reactive powers (Q A, Q B, Q C) for each one of the phases according to the following expression: P A = V A 1 + ⋅ I A 1 ⋅ cos φ A 1 + Q A = V A 1 + ⋅ I A 1 ⋅ sin φ A 1 + P B = V B 1 + ⋅ I B 1 ⋅ cos φ B 1 + Q B = V B 1 + ⋅ I B 1 ⋅ sin φ B 1 +; and P C = V C 1 + ⋅ I C 1 ⋅ cos φ C 1 + Q C = V C 1 + ⋅ I C 1 ⋅ sin φ C 1 + characterized by iv) starting from the active and reactive powers, an imbalance power phasor ( A U) is obtained according to the following expression: A ̅ U = √ 2 p ⋅ | P A + a 2 P B + aP C | + q ̅ ⋅ | Q ̅ A + a 2 Q ̅ B + aQ C | where a = I |120° and p and q are orthogonal unit phasors.