42
6
F
2
S
0
7
8
9
2.11.6 Thermal Overload Element THR
Thermal overload element THR has a characteristic based on thermal replica according to IEC
60255-8 standards (see Appendix N), which evaluates the phase current (A-phase) of CT
secondary circuits. Figure 2.11.4 shows the characteristic of THR element. The element has trip
and alarm stages.
Trip stage:
t =
Ln
I
2
Ip
2
I
2
(k
I
B
)
2
Alarm stage:
t =
Ln
(I
2
Ip
2
)
(1
T
A/
)
I
2
(k
I
B
)
2
where
t :
operating time
: thermal time constant
I :
load current
k
I
B
: allowable overload current as specified in IEC 60255-8 (refer to Appendix N)
I
B
: basic current of transformer (rated current)
k : constant (allowable overload current / IB)
Ip : prior load current before the overload occurs
T
A : time for alarm
(Alarming time = t (operating time)
TA (setting time))
Ln
: natural logarithm
Figure 2.11.5 shows the thermal curve for a range of time constant settings under cold state when
the prior load current Ip is zero.
Trip
I
Alarm
0
K
IB
t
TA
TA
Figure 2.11.4 Characteristic of Thermal Overload Element
Summary of Contents for GRT100 Series
Page 142: ... 141 6 F 2 S 0 7 8 9 Appendix A Block Diagram ...
Page 144: ... 143 6 F 2 S 0 7 8 9 Appendix B Signal List ...
Page 159: ... 158 6 F 2 S 0 7 8 9 ...
Page 160: ... 159 6 F 2 S 0 7 8 9 Appendix C Variable Timer List ...
Page 162: ... 161 6 F 2 S 0 7 8 9 Appendix D Binary Output Default Setting List ...
Page 165: ... 164 6 F 2 S 0 7 8 9 ...
Page 166: ... 165 6 F 2 S 0 7 8 9 Appendix E Details of Relay Menu and LCD and Button Operation ...
Page 174: ... 173 6 F 2 S 0 7 8 9 Appendix F Case Outline Flush Mount Type Rack Mount Type ...
Page 179: ... 178 6 F 2 S 0 7 8 9 ...
Page 180: ... 179 6 F 2 S 0 7 8 9 Appendix G External Connections ...
Page 185: ... 184 6 F 2 S 0 7 8 9 ...
Page 200: ... 199 6 F 2 S 0 7 8 9 ...
Page 201: ... 200 6 F 2 S 0 7 8 9 Appendix J Return Repair Form ...
Page 205: ... 204 6 F 2 S 0 7 8 9 Customer Name Company Name Address Telephone No Facsimile No Signature ...
Page 206: ... 205 6 F 2 S 0 7 8 9 ...
Page 207: ... 206 6 F 2 S 0 7 8 9 Appendix K Technical Data ...
Page 220: ... 219 6 F 2 S 0 7 8 9 ...
Page 221: ... 220 6 F 2 S 0 7 8 9 Appendix M Symbols Used in Scheme Logic ...
Page 224: ... 223 6 F 2 S 0 7 8 9 ...
Page 225: ... 224 6 F 2 S 0 7 8 9 Appendix N Implementation of Thermal Model to IEC60255 8 ...
Page 228: ... 227 6 F 2 S 0 7 8 9 ...
Page 229: ... 228 6 F 2 S 0 7 8 9 Appendix O IEC60870 5 103 Interoperability and Troubleshooting ...
Page 241: ... 240 6 F 2 S 0 7 8 9 Appendix P Modbus Interoperability ...
Page 255: ... 254 6 F 2 S 0 7 8 9 ...
Page 256: ... 255 6 F 2 S 0 7 8 9 Appendix Q Inverse Time Characteristics ...
Page 259: ... 258 6 F 2 S 0 7 8 9 ...
Page 260: ... 259 6 F 2 S 0 7 8 9 Appendix R Failed Module Tracing and Replacement ...
Page 266: ... 265 6 F 2 S 0 7 8 9 Appendix S Ordering ...
Page 269: ... 268 6 F 2 S 0 7 8 9 3 1 Oct 2 2017 Republished under spin off company ...
Page 270: ......