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Voltage-Restrained Overcurrent (ANSI 51V)

Generator back-up overload relay whose pickup scales with measured bus voltage. Pickup_applied = Pickup_base · (V_actual / V_rated)^n.

ElectricalProtection
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Formula, assumptions, and limits

Ipickup=Ipickup,base(VVrated)nI_\text{pickup} = I_\text{pickup,base} \cdot \left(\frac{V}{V_\text{rated}}\right)^n
SymbolMeaningUnit
Ipickup,baseI_\text{pickup,base}Pickup at rated voltageA
VVMeasured voltageV
VratedV_\text{rated}Rated voltageV
nnRestraint exponent

Source: IEEE C37.2 - Standard for protective device function numbers

In short

Generator back-up overload relay whose pickup scales with measured bus voltage.

Learn the theory Marine Electrical Generation and Distribution