Generator back-up overload relay whose pickup scales with measured bus voltage. Pickup_applied = Pickup_base · (V_actual / V_rated)^n.
Formula
$$ I_\text{pickup} = I_\text{pickup,base} \cdot \left(\frac{V}{V_\text{rated}}\right)^n $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $I_\text{pickup,base}$ | Pickup at rated voltage | A | relay setting |
| $V$ | Measured voltage | V | relay input |
| $V_\text{rated}$ | Rated voltage | V | generator nameplate |
| $n$ | Restraint exponent | - | linear or square |
Sources
- IEEE C37.2 - Standard for protective device function numbers.