Woodward MRU3-11D Voltage Relay – Three-Phase ANSI 27/59/47 Protection

Application Scenarios

In a petrochemical facility’s catalytic cracking unit in southern China, the medium-voltage switchgear associated with the main air blower frequently experienced voltage protection false trips. The site had numerous variable frequency drive devices, causing severe harmonic pollution in the power grid. The existing voltage relays could not effectively distinguish between real faults and harmonic interference, leading to frequent unplanned shutdowns with substantial production losses each time.

After evaluation, the technical team adopted the MRU3-11D to replace the existing voltage protection relays. The module‘s discrete Fourier filtering function enabled accurate extraction of fundamental voltage components, effectively suppressing false signals caused by harmonics. Following the retrofit, the voltage protection system’s false trip rate significantly decreased, with no harmonic interference-induced false trips occurring over six months of subsequent operation. Meanwhile, the MRU3-11D‘s sequence component monitoring function (positive/negative/zero sequence voltage) provided operators with a more comprehensive view of grid health status, helping to proactively identify a potential phase imbalance issue.

Parameters