The VMD423 series three-phase voltage and frequency monitors the voltage and frequency of the public power grid feed points. At the feed point of medium voltage network, the output voltage and frequency are measured by the voltage transformer (100 V). When the threshold is reached, activate the alarm relay within the range of <= 80 ms (response value refer to the VDEW policy, Special power generation system in medium voltage grid "). Overvoltage (&gt U2), measuring the average over 10 minutes of the stage, will cause an alarm relay switch.