Dead-bands

A voltage dead-band of 0.02 pu is used to provide hysteresis and helps to prevent a voltage value that is fluctuating around a pickup threshold from causing excessive events for example pickup/reset.

With the default Normal Phase to Earth setting of 6300 V, the dead band would be 0.02 x 6300 = 126 V.

This dead-band will affect the minimum/maximum range of values for threshold settings. For example, the maximum value for the Under Voltage Pickup setting would be the Normal Voltage Low setting – 0.02 pu.

The dead-bands also affect the normal voltage range depending on whether the measured voltage is normal or abnormal.

When the voltage is in the Normal voltage range the high and low thresholds are:

High: Voltage is greater than the Normal Voltage High setting + the dead-band.
Low: Voltage is less than the Normal Voltage Low setting – the dead-band.

When the voltage is outside the Normal voltage range the normal thresholds are:

Normal: Voltage

Is less than or equal to the Normal Voltage High setting.

Greater than or equal to the Normal Voltage Low setting.

UOV Protection can be configured with the following settings:

Table 54 UOV Protection settings

Under Voltage Protection
Setting	Description
Under Voltage Protection	On or Off
Under Voltage Mode	Trip or Alarm (Only applicable when Under Voltage Protection is On).
Under Voltage Pickup	The voltage expressed as a per unit value at which an Under Voltage pickup will occur. Range: 0.50 per unit – (Normal Voltage Low setting -0.02 per unit). Default: 0.9 per unit
Under Voltage Definite Time	The time that an under voltage condition will take to cause an alarm or trip depending on the UV mode setting. (Only applicable when the Curve setting is Definite Time). Range: 0.01...300.00 s. Default: 1.0 s
Under Voltage Phase Logic	The phase logic that applies to Under Voltage protection. Range: AND/OR/Average. Default: AND
Under Voltage Excess Sequences At	The number of Under Voltage trip/close sequences that can occur within a given time before Under Voltage protection is turned Off. Range: Off, 1...20 Default: Off
Excess Sequences In	The time in which the number of UV trip/close sequences configured in Excess Sequences A must occur for UV protection to be turned Off. (Only applicable when Excess Sequences At is not Off).
Over Voltage Protection
Over Voltage Protection	On or Off
Over Voltage Mode	Trip or Alarm (Only applicable when Over Voltage Protection is On).
Over Voltage Pickup	The voltage expressed as a per unit value at which an Over Voltage pickup will occur. Range (Normal Voltage High setting + 0.02 per unit) - 2.00 per unit Default 1.1 per unit
Over Voltage Definite Time	The time that an over voltage condition will take to cause an alarm or trip depending on the OV mode setting. (Only applicable when the Curve setting is Definite Time). Range: 0.01...300.00 s. Default: 1.0 s
Over Voltage Phase Logic	The phase logic that applies to Over Voltage protection. Range: AND/OR/Average. Default: AND
Over Voltage Excess Sequences At	The number of Over Voltage trip/close sequences that can occur within a given time before Over Voltage protection is turned Off. Range: Off, 1...20 Default: Off
Excess Sequences In	The time in which the number of OV trip/close sequences configured in Excess Sequences At must occur for OV protection to be turned Off. (Only applicable when Excess Sequences At is not Off).
UOV Protection
Normal Voltage Low	The voltage expressed as a per unit value below which it is considered to be below the normal voltage range. Range: Under Voltage Pickup + 0.02 per unit – 1.00 per unit Default: 0.95 per unit.
Normal Voltage High	The voltage expressed as a per unit value above which it is considered to be above the normal voltage range. Range: 1.00 per unit - Over Voltage Pickup - 0.02 per unit. Default: 1.05 per unit.
Nominal Phase to Earth	Defines the nominal phase to earth system voltage. This is a critical setting as it is used to derive the per unit values configured for other settings. Range: 2000...25,000 V Default: 6,300 V
Recovery Time Out	The time period allocated for the recovery of the voltage to within the Normal System Voltage range after an Under or Over Voltage trip. (Only applicable if Normal Voltage Close is On). Range: Off, 1...1440 minutes. Default: Off
Normal Voltage Close	This setting determines whether the switchgear must automatically reclose following a UOV trip if the source voltage returns to within normal limits within a set time. Range: On/Off Default: Off
Normal Voltage Close After	The time that the source voltage must have returned to and stayed within the UOV Normal Voltage thresholds (plus dead-bands) before an automatic Normal Voltage Close takes place. (Only applicable if Normal Voltage Close is On). Range: 1...1000 s or 1 s - ((Recovery Time Out setting/60) – 1) s – When Recovery Time Out is On. Default: 10 s
Curve	This setting is used to select the Voltage – Time curve. Range: Definite Time, User Curve 1 to 5. Default: Definite Time.
Fault Reset	The time it takes for a UOV alarm to reset after the voltage returns to normal (± the dead-band) following a UOV pickup. Range: 0...10,000 ms Default: 50 ms