⎯
361
⎯
6
F
2
S
0
8
3
5
Implementation of Thermal Model to IEC60255-8
Heating by overload current and cooling by dissipation of an electrical system follow exponential time
constants. The thermal characteristics of the electrical system can be shown by equation (1).
θ
=
I
I
e
AOL
t
2
2
1
100
−
⎛
⎝⎜
⎞
⎠⎟
×
−
τ
%
(1)
where:
θ
= thermal state of the system as a percentage of allowable thermal capacity,
I = applied load current,
I
AOL
= allowable overload current of the system,
τ
= thermal time constant of the system.
The thermal state
θ
is expressed as a percentage of the thermal capacity of the protected system, where
0% represents the cold state and 100% represents the thermal limit, that is the point at which no further
temperature rise can be safely tolerated and the system should be disconnected. The thermal limit for any
given electrical plant is fixed by the thermal setting I
AOL
. The relay gives a trip output when
θ
= 100%.
If current I is applied to a cold system, then
θ
will rise exponentially from 0% to (I
2
/I
AOL
2
×
100%), with time
constant
τ
, as in Figure P-2. If
θ
= 100%, then the allowable thermal capacity of the system has been reached.
Figure P-2
A thermal overload protection relay can be designed to model this function, giving tripping times
according to the IEC60255-8 ‘Hot’ and ‘Cold’ curves.
t =
τ
·
Ln
I
I
I
AOL
2
2
2
−
⎡
⎣
⎢
⎤
⎦
⎥
(1) ····· Cold curve
t =
τ
·
Ln
I
I
I
I
P
AOL
2
2
2
2
−
−
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
(2) ····· Hot curve
where:
I
P
= prior load current.
θ
(%)
t (s)
100%
%
100
1
2
2
×
−
=
⎟
⎠
⎞
⎜
⎝
⎛
−
τ
θ
t
AOL
e
I
I
%
100
2
2
×
AOL
I
I
Summary of Contents for GRL100-101A
Page 223: ... 222 6 F 2 S 0 8 3 5 ...
Page 228: ... 227 6 F 2 S 0 8 3 5 Appendix B Signal List ...
Page 256: ... 255 6 F 2 S 0 8 3 5 Appendix C Variable Timer List ...
Page 258: ... 257 6 F 2 S 0 8 3 5 Appendix D Binary Output Default Setting List ...
Page 269: ... 268 6 F 2 S 0 8 3 5 ...
Page 270: ... 269 6 F 2 S 0 8 3 5 Appendix E Details of Relay Menu ...
Page 279: ... 278 6 F 2 S 0 8 3 5 ...
Page 288: ... 287 6 F 2 S 0 8 3 5 Appendix G Typical External Connection ...
Page 326: ... 325 6 F 2 S 0 8 3 5 Appendix J Return Repair Form ...
Page 330: ... 329 6 F 2 S 0 8 3 5 Customer Name Company Name Address Telephone No Facsimile No Signature ...
Page 331: ... 330 6 F 2 S 0 8 3 5 ...
Page 332: ... 331 6 F 2 S 0 8 3 5 Appendix K Technical Data ...
Page 343: ... 342 6 F 2 S 0 8 3 5 ...
Page 344: ... 343 6 F 2 S 0 8 3 5 Appendix L Symbols Used in Scheme Logic ...
Page 347: ... 346 6 F 2 S 0 8 3 5 ...
Page 348: ... 347 6 F 2 S 0 8 3 5 Appendix M Multi phase Autoreclose ...
Page 351: ... 350 6 F 2 S 0 8 3 5 ...
Page 352: ... 351 6 F 2 S 0 8 3 5 Appendix N Data Transmission Format ...
Page 358: ... 357 6 F 2 S 0 8 3 5 Appendix O Example of DIF and DIFG Setting ...
Page 364: ... 363 6 F 2 S 0 8 3 5 Appendix Q IEC60870 5 103 Interoperability ...
Page 377: ... 376 6 F 2 S 0 8 3 5 ...
Page 378: ... 377 6 F 2 S 0 8 3 5 Appendix R Failed Module Tracing and Replacement ...
Page 384: ... 383 6 F 2 S 0 8 3 5 Appendix S PLC Setting Sample ...
Page 386: ... 385 6 F 2 S 0 8 3 5 Appendix T Ordering ...
Page 392: ......