Motor protection

Motor Protection – Reyrolle 7SR17

Reyrolle 7SR17

The Reyrolle 7SR17 Rho is a numeric protection relay with four current inputs and optionally three voltage inputs. The relay is applied to motors and their connections providing an integrated protection system.

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Features & functions

Motor protection Reyrolle 7SR17


The relay is typically used as a stand-alone device but can be supplied with an external unit to interface with remote temperature detectors embedded in the motor or installed on auxiliary equipment. 

The Reyrolle 7SR17 Rho relay includes thermal protection optimised for motor applications and motor starting supervision algorithms. Several other protections are also provided and are selectable as required so that a solution appropriate to the installation can be achieved. 

The Reyrolle 7SR17 Rho is housed in an E4 case. 

Full user configurability and integrate logic allows the optimal configuration of relay input and output functionality.


  • Optional RTD inputs

  • Cold load settings

  • Eight settings groups

  • Password protection

  • Self-monitoring

  • Circuit breaker trip counter

  • Fault, event and waveform records

Bruce Watson presents the motor protection devices Reyrolle 7SR105 and Reyrolle 7SR17


Protection functions

  • Stall protection (14)

  • Under/over voltage (27/59)

  • Power/power factor (32/55)

  • Undercurrent (37)

  • Current unbalance protection (46)

  • Phase reversal (46Ph Rev)

  • Voltage unbalance (47)

  • Start protection (48/66)

  • Motor thermal overload (49R)

  • Directional overcurrent (67)

  • Directional earth fault (67G/67N)

  • Backspin protection (81B)

  • Under/over frequency (81)

  • High impedance REF (87REF)

  • Temperature inputs (via comms port) (RTD)

Supervision functions

  • Circuit breaker fail (50BF)

  • CT supervision (60CTS)

  • VT supervision (60VTS)

  • Trip circuit supervision (74T/CCS)

Monitoring functions

  • Instrumentation