BENDER VMD421H-D-3 voltage monitoring relay

The BENDER VMD421H-D-3 is a multi-functional voltage monitoring relay designed for use in 3(N)AC systems (three-phase AC systems, with or without a neutral conductor). It is a highly specialized industrial component from Bender, a German manufacturer known for electrical safety.

Here's a detailed breakdown of its features and functions:

Core Functionality:

• Comprehensive Voltage and Frequency Monitoring: The VMD421H-D-3 continuously monitors for:

• Undervoltage (<U) and Overvoltage (>U): Detects when voltage falls below or rises above set thresholds.

• Underfrequency (<f) and Overfrequency (>f): Detects when frequency falls below or rises above set thresholds.

• Window Discriminator Function: Allows monitoring of voltage and frequency between two defined threshold values.

• Asymmetry, Phase Failure, and Phase Sequence Monitoring: Crucial for protecting three-phase equipment:

• Asymmetry: Monitors for unbalanced voltages between phases.

• Phase Failure/Loss: Detects when one or more phases are lost.

• Phase Sequence: Ensures the correct rotation of phases, vital for motor protection.

• True RMS Measurement (AC+DC): Measures the true RMS value of the voltage, even with distorted waveforms, providing accurate readings.

Key Features:

• Digital LCD Display: Provides real-time readings of measured values and allows for on-board menu navigation for settings.

• Adjustable Parameters:

• Response Values: Individually adjustable thresholds for undervoltage, overvoltage, underfrequency, and overfrequency.

• Start-up Delay (t_s): Prevents nuisance tripping during system startup.

• Response Delay (t_on): Introduces a delay before an alarm is triggered, filtering out transient disturbances.

• Delay on Release (t_off): Sets a delay before the alarm clears after the fault is rectified.

• Switching Hysteresis: Prevents rapid switching when the measured value hovers around a threshold.

• Two Separate Alarm Relays: Equipped with two changeover contacts (K1, K2) for signaling alarms. These can be configured for normally open (N/O) or normally closed (N/C) operation.

• Selectable Fault Memory (Latching Mode):

• Latching Mode: If set, the device remains in an alarm state until manually reset, even after the fault clears.

• Non-Latching Mode: The alarm automatically clears when the fault is resolved.

• Non-Volatile Memory: Stores settings and the last alarm value, even in case of power loss.

• Integrated Energy Backup: Allows the device to operate without an external supply voltage (it's self-supplied by the monitored voltage).

• LED Indicators: "Power On," "Alarm 1," and "Alarm 2" LEDs provide visual status indication.

• Preset Function: An automatic function that sets basic parameters upon initial device connection.

• Password Protection: Prevents unauthorized changes to device settings.

• Continuous Self-Monitoring: Ensures the internal integrity and proper functioning of the device.

• Compact Design: Typically in a two-module enclosure (36 mm width) for DIN rail mounting.

• Terminal Type: "D-3" in the model number often indicates a spring terminal connection, offering secure and quick wiring. (Note: other variants with screw terminals exist, like VMD421H-D.)

Applications:

The BENDER VMD421H-D-3 is widely used in various industrial and electrical installations for critical monitoring and protection, including:

• Protection of voltage-sensitive machinery and electrical installations.

• Monitoring of standby and emergency power supply systems.

• Supply voltage monitoring for portable loads.

• Phase protection of three-phase motors against phase failure, open-circuits, and asymmetry.

• Transformer protection (recognizing asymmetrical loads).

• Switching machinery and equipment on/off at specific voltage levels.

In essence, the BENDER VMD421H-D-3 is a robust and versatile voltage monitoring relay that plays a critical role in ensuring the reliable and safe operation of three-phase electrical systems and the equipment connected to them.

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