6 F 2 T 0 1 7 2
2.4 Phase Undercurrent Protection
The phase undercurrent protection is used to detect a decrease in current caused by a loss of load,
typically motor load.
The undercurrent element operates for current falling through the threshold level. However,
operation is blocked when the current falls below 4 % of CT secondary rating to discriminate the
loss of load from the feeder tripping by other protection.
Each phase has two independent undercurrent elements for tripping and alarming. The elements are
programmable for instantaneous or definite time delayed operation.
The undercurrent element operates on per phase basis, although tripping and alarming is three-
phase only.
The tripping and alarming outputs can be blocked by scheme switches or a binary input signal.
Scheme Logic
Figure 2.4.1 shows the scheme logic of the phase undercurrent protection.
Two undercurrent elements UC1 and UC2 output trip and alarm signals UC1 TRIP and UC2
ALARM through delayed pick-up timers TUC1 and TUC2.
Those protections can be disabled by the scheme switches [UC1EN] and [UC2EN] or binary input
signal UC BLOCK.
C
B
A
UC1
+
"ON"
[UC1EN]
0.00 - 300.00s
&
&
&
TUC1
t
0
t
0
t
0
UC1 TRIP
UC1-A TRIP
UC1-B TRIP
UC1-C TRIP
≥
1
UC BLOCK
1
C
B
A
UC2
+
"ON"
[UC2EN]
0.00 - 300.00s
&
&
&
TUC2
t
0
t
0
t
0
UC2 ALARM
UC2-A ALARM
UC2-B ALARM
UC2-C ALARM
≥
1
71
72
73
74
75
76
126
127
128
129
130
131
132
133
Figure 2.4.1 Undercurrent Protection Scheme Logic
Settings
The table below shows the setting elements necessary for the undercurrent protection and their
setting ranges.
34
Summary of Contents for GRE110
Page 183: ...6 F 2 T 0 1 7 2 Appendix B Signal List 184 ...
Page 191: ...6 F 2 T 0 1 7 2 Appendix C Event Record Items 192 ...
Page 196: ...6 F 2 T 0 1 7 2 Appendix D Binary Output Default Setting List 197 ...
Page 199: ...6 F 2 T 0 1 7 2 Appendix E Relay Menu Tree 200 ...
Page 210: ...6 F 2 T 0 1 7 2 Appendix F Case Outline 211 ...
Page 211: ...6 F 2 T 0 1 7 2 Case Outline for model 400 401 420 421 820 and 821 212 ...
Page 212: ...6 F 2 T 0 1 7 2 Case Outline for model 402 and 422 213 ...
Page 213: ...6 F 2 T 0 1 7 2 Appendix G Typical External Connection 214 ...
Page 245: ...6 F 2 T 0 1 7 2 Appendix J Return Repair Form 246 ...
Page 249: ...6 F 2 T 0 1 7 2 Customer Name Company Name Address Telephone No Facsimile No Signature 250 ...
Page 250: ...6 F 2 T 0 1 7 2 Appendix K Technical Data 251 ...
Page 256: ...6 F 2 T 0 1 7 2 Appendix L Symbols Used in Scheme Logic 257 ...
Page 259: ...6 F 2 T 0 1 7 2 Appendix M Modbus Interoperability 260 ...
Page 289: ...6 F 2 T 0 1 7 2 Appendix N IEC60870 5 103 Interoperability 290 ...
Page 296: ...6 F 2 T 0 1 7 2 Appendix O PLC Default setting 297 ...
Page 298: ...6 F 2 T 0 1 7 2 Appendix P Inverse Time Characteristics 299 ...
Page 304: ...6 F 2 T 0 1 7 2 Appendix Q IEC61850 Interoperability 305 ...