The voltage relays of the VME421H series are designed to monitor the frequency, undervoltage, overvoltage and the voltage between two threshold values (window discriminator function) in both AC and DC systems. The voltages are measured as r.m.s. values. The measured value is continuously shown on the device’s LC display. The measured value leading to the activation of the alarm relays will be stored. Thanks to the VMD’s to adjustable response times, installation-specific characteristics, such as time delay specific start-up procedures, short-time voltage fluctuations, etc. can be configured for specific applications. Device version VME421H takes the supply voltage from the system being monitored and utilizes an internal energy backup.

Applications:

• Voltage and frequency monitoring of single-phase machines and electrical installations
• Earth fault monitoring in medium-voltage systems via voltage transformers
• Monitoring of battery systems
• Switching machinery and equipment on and off at a certain voltage level