Asian Power

Protection Relay


Voltage Relay

The MRU4 is designed to protect electrical equipment against dangerous voltage and frequency fluctuations, and is used for busbar, generator and feeder protection.

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The voltage protection relay MRU4 provides precise and reliable protective functions and is very easy to operate. It is designed to protect electrical equipment from dangerous voltage fluctuations. For example protection against under voltages caused by mains shortcircuits, or overvoltages due to load shedding or failure of a generator voltage controller. Its compact design makes the MRU4 ideal for installation within the LV terminal compartments of compact SF6-insulated MV systems. The protection functions of the MRU4 have been adapted to comply with the requirements of the VDE AR N 4110:2018. The MRU4 is available in 48 variants, that cover all combinations of properties that you might need or not need for your application. Each variant is uniquely specified by a typecode of form MRU4-2xxxxx (i.e. 5 digits/letters following the ‘-2’). Check the Order Form (depicted below, or in the brochure DOK-FLY-MRU4-2E or in the user manual MRU4-3.6-EN-MAN) for a complete overview.


  • Comprehensive Frequency Protection Package
  • SI X Elements Voltage Protection
  • Sliding-mean-square Supervision
  • Adjustable FRT (LRVT )
  • Flexible Fourth Voltage measuring input
  • Synch Check
  • Two Elements Residual Voltage Protection
  • Six Elements Voltage Asymmetry Supervision
  • THD-protection Power Quality
  • Supervision
  • Recorders
  • PC Tools
  • Commissioning Support
  • Communication Options
  • Comprehensive measured values and statistics
  • Logic equations for protection
  • Time Synchronisation


Voltage Inputs

4 (0– 800 V) with automatic CT Disconnect

Digital Inputs

Switching thresholds adjustable via software

Power Supply

24 VDC – 270 VDC / 48 VAC – 230 VAC (-20/+10%)


All terminals plug type


Door Mounting

Type of enclosure (Front)


Dimensions of housing (W x H x D)

19“ Flush Mounting:
141.5 mm x 173 mm x 209 mm
5 .571 in. x 6.811 in. x 8.228 in
Door Mounting:
141.5 mm x 183 mm x 209 mm
5 .571 in. x 7.205 in. x 8.228 in

Weight (max. components)

approx. 2.4 kg

Product Certification

A Manufacturer’s Certificate of Origin, also known as a Manufacturer’s Statement of Origin, is a specified document certifying the country of origin.



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