PowerLogic Knowledge Base Procedure
Phasor Diagram Verification - 4 wire system
Safety Precautions
•
•
•
Work on De-Energized Gear
NEVER short circuit the secondary of a PT
NEVER open circuit a CT
Use the shorting block to short circuit the leads of the CT before removing the
connection from the CM.
Procedure
1. Follow Phasor Diagram Data Reading procedure
2. Draw each of the vectors in the diagram or complete the Phasor Diagram Creator
spreadsheet, 4-wire Tab
Example:
200
4-Wire
Current
Phase A
Phase B
Phase C
Neutral
Voltage
Phase A-B
Phase B-C
Phase C-A
Phase A-N
Phase B-N
Phase C-N
150
Magnitud Register Angle
1078
79
1079 327.8
1080
81
1081
90.6
1082
72
1083 207.9
1084
1085
Register
100
50
0
1094
1096
1098
1088
1090
1092
210
207
207
1095
1097
1099
1089
1091
1093
-150
-100
-50
0
50
100
150
200
250
-50
0
120.8
240.1
-100
-150
Ia
Ib
Ic
Van
Vbn
Vcn
-200
3. Compare your diagram with the possible cases
Note
•
•
•
Voltage between Va and Vn is the 0 degree reference
ALL other phasors are referenced from these phasors
Examples shown are with ABC or positive phasor sequence convention. To use
negative sequence convention or ACB replace B by C and C by B in all diagrams.
Phasor_Diagram_Verification_4_wire.doc
 1999 Square D Company, All Rights Reserved
Rev:05/22/99
1 of 3
PowerLogic Knowledge Base Procedure
Possible Cases
Vcn
Vcn (120)
ABC or Positive
Sequence
Ic
Van (0)
Van
n
Ia
Ib
Vbn (240)
CCW
Phasor Sequence Convention
Vcn
Vbn
Unity PF
Vcn
Ic
Ic
Ia
Van
Ib
Van
Ia
Vbn
0.5 Lag PF Inductive Load
Phasor_Diagram_Verification_4_wire.doc
 1999 Square D Company, All Rights Reserved
Ib
Vbn
0.87 Lead PF Capacitive Load
Rev:05/22/99
2 of 3
PowerLogic Knowledge Base Procedure
4. Use the following rules to match your system to one of the possible cases
• To change phasor direction: revert polarity of PT/CT
Example:
200
The polarity of CT phase b is
reversed
150
Reversing the polarity of the
CT will correct the phasor with
a shift of 180 degrees
100
50
0
-150
-100
-50
0
50
100
150
200
250
-50
Ia
Ib
Ic
Vab
Vbc
Vca
-100
-150
-200
•
To change phases: swap
CT/PT
Example:
200
150
The leads from the CTs for
B and C phases were
swapped on the input
terminals of the circuit
monitor
100
50
0
-200
-100
0
100
200
300
-50
Swapping the phase B&C CT
leads on the current input
terminal of the circuit monitor
will correct this condition
-100
-150
-200
•
•
Ia
Ib
Ic
Vab
Vbc
Vca
Do one change at a time
Repeat Checking Meter Readings procedure after you finish changing connections
Phasor_Diagram_Verification_4_wire.doc
 1999 Square D Company, All Rights Reserved
Rev:05/22/99
3 of 3