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Extended Protective Relaying

7.5 Undervoltage

If the amount of voltage on any phase goes below a speciﬁed

level, the trip unit can alarm or trip by setting the parameters

from the

Undervoltage

selection of the

Protective Relays

. To alarm, or to trip and alarm, on undervoltage:

1. From the

Protective Relays Menu

, select

Under Voltage.

The Alarm checkbox is highlighted, but alarming has not

yet been set.

2. To enable alarming, press the Up Arrow key, then press

Enter . If you have enabled alarming, a checkmark

appears and the pickup settings are highlighted.

3. Select a pickup value by pressing the Up or Down

Arrow keys until the value is at the desired level. The pos-

sible pickup values depend on the rating of the breaker;

see the table in the appendix,

Parameter Settings

. Press

Enter .

4. Then select a delay time by pressing the Up or Down

Arrow keys until the value is at the desired level. Possi-

ble time delay settings are 1, 2, 3, 4, 5, 7, 10 and 15 sec-

onds. Press Enter .

7.6 Voltage Unbalance

Voltage unbalance is a protective relay function that protects

against an unbalance in the line to line voltages. Each line-to-

line voltage is compared to the arithmetic average of the three

voltages. Tripping or alarming occurs when any voltage

exceeds the unbalance pickup for a period of time equal to the

delay time setting. To alarm, or to trip and alarm, on current

unbalance:

1. From the

Protective Relays Menu

, select

Voltage Unbal-

ance

. The Alarm checkbox is highlighted, but alarming

has not yet been set.

2. To enable alarming, press the Up Arrow key, then press

Enter . If you have enabled alarming, a checkmark

appears and the pickup settings are highlighted.

3. Select a pickup value by pressing the Up or Down

Arrow keys until the value is at the desired level. The pos-

sible pickup values depend on the rating of the breaker;

see the table in the appendix,

Parameter Settings

. Press

Enter .

4. Then select a delay time by pressing the Up or Down

Arrow keys until the value is at the desired level. Possi-

ble time delay settings are 1, 2, 3, 4, 5, 7, 10 and 15 sec-

onds. Press Enter .

If you want to

enable...

Then...

alarming only follow steps 2–4 and press Escape

. Then press Enter at the veriﬁ-

cation screen.

alarming and tripping follow steps 2–4, press Enter to

highlight the Trip checkbox, then

repeat the process you used in

steps 2–4 to set pickup and delay

values. After setting both the alarm

and trip values, press Escape .

Then press Enter at the veriﬁca-

tion screen.