GE UR Series L90 Instruction Manual page 353

5 SETTINGS
The following examples explain how the restraining signal is created for maximum sensitivity and security. These examples
clarify the operating principle and provide guidance for testing of the element.
EXAMPLE 1: EXTERNAL SINGLE-LINE-TO-GROUND FAULT
Given the following inputs: IA = 1 pu 0°, IB = 0, IC = 0, and IG = 1 pu180°
The relay calculates the following values:
1


Igd = 0, IR0 abs 3 -- -
=

3
The restraining signal is twice the fault current. This gives extra margin should the phase or neutral CT saturate.
EXAMPLE 2: EXTERNAL HIGH-CURRENT SLG FAULT
Given the following inputs: IA = 10 pu 0°, IB = 0, IC = 0, and IG = 10 pu –180°
The relay calculates the following values:
1

 -- -
Igd = 0, IR0 abs 3
=

3
EXAMPLE 3: EXTERNAL HIGH-CURRENT THREE-PHASE SYMMETRICAL FAULT
Given the following inputs: IA = 10 pu 0°, IB = 10 pu –120°, IC = 10 pu 120°, and IG = 0 pu
The relay calculates the following values:
 
Igd = 0, IR0 abs 3 0
=
EXAMPLE 4: INTERNAL LOW-CURRENT SINGLE-LINE-TO-GROUND FAULT UNDER FULL LOAD
Given the following inputs: IA = 1.10 pu 0°, IB = 1.0 pu –120°, IC = 1.0 pu 120°, and IG = 0.05 pu 0°
The relay calculates the following values:
I_0 = 0.033 pu 0°, I_2 = 0.033 pu 0°, and I_1 = 1.033 pu 0°
Igd = abs(3  0.0333 + 0.05) = 0.15 pu, IR0 = abs(3  0.033 – (0.05)) = 0.05 pu, IR2 = 3  0.033 = 0.10 pu,
IR1 = 1.033 / 8 = 0.1292 pu, and Igr = 0.1292 pu
Despite very low fault current level the differential current is above 100% of the restraining current.
EXAMPLE 5: INTERNAL LOW-CURRENT, HIGH-LOAD SINGLE-LINE-TO-GROUND FAULT WITH NO FEED FROM
THE GROUND
Given the following inputs: IA = 1.10 pu 0°, IB = 1.0 pu –120°, IC = 1.0 pu 120°, and IG = 0.0 pu 0°
The relay calculates the following values:
I_0 = 0.033 pu 0°, I_2 = 0.033 pu 0°, and I_1 = 1.033 pu 0°
Igd = abs(3  0.0333 + 0.0) = 0.10 pu, IR0 = abs(3  0.033 – (0.0)) = 0.10 pu, IR2 = 3  0.033 = 0.10 pu,
IR1 = 1.033 / 8 = 0.1292 pu, and Igr = 0.1292 pu
Despite very low fault current level the differential current is above 75% of the restraining current.
EXAMPLE 6: INTERNAL HIGH-CURRENT SINGLE-LINE-TO-GROUND FAULT WITH NO FEED FROM THE GROUND
Given the following inputs: IA = 10 pu 0°, IB = 0 pu, IC = 0 pu, and IG = 0 pu
The relay calculates the following values:
I_0 = 3.3 pu 0°, I_2 = 3.3 pu 0°, and I_1 = 3.3 pu 0°
Igd = abs(3  3.3 + 0.0) = 10 pu, IR0 = abs(3  3.3 – (0.0)) = 10 pu, IR2 = 3  3.3 = 10 pu, IR1 = 3  (3.33 – 3.33) = 0
pu, and Igr = 10 pu
The differential current is 100% of the restraining current.
GE Multilin
1

–   
1 2 pu , IR2 3 -- -
– = =

3

–   
10 20 pu , IR2 3
– = =

0    
0 pu , IR2 3 0
– = = =
L90 Line Current Differential System
1 3 
1 pu , IR1 0.042 pu
--------- -
= = =
8
10
10 ----- - 10

----- - 
10 pu , IR1 3
= = –

3
3
10
 

0 pu , IR1 3 ----- - 0
= – =
 
3
5.6 GROUPED ELEMENTS
, and Igr = 2 pu

----- - 0 , and Igr = 20 pu.
=

3
10 pu , and Igr = 10 pu.
5-215
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