Under Frequency

Default value

• Dropout: 5%

• Pickup: 20% of delta dropout

Range

Delta frequency : 2% –10% of rated frequency and could be 2–3–4–5–6–7–8–9–10%..

Differential

The differential between dropout and pickup is fixed on automatic HMI and this gap is set at 20% of the delta.

Sequence of events

• When a sensor detects a frequency below the set drop-out frequency for a period longer than the time delay, it deems the voltage is out of range.

• When the sensor detects a frequency at or above the pick-up point, it deems the frequency as acceptable.

Example of calculation on underfrequency of TransferPacT Automatic

For example, Fe= 50 Hz , Dropout 5%= 2.5 Hz,

Differential between dropout and pickup= 2.5 Hz * 20%= 0.5Hz

Underfrequency dropout is 50 Hz - 2.5 Hz= 47.5 Hz

Pickup = 47.5 Hz + 0.5 Hz= 48 Hz