516LE008146B
Protection functions
4.2 Long Time Delay protection IEC 60255-151
It is possible to configure the calculation of the sentinel Energy Long Time Delay protection in
accordance with the requirements of the IEC 60255-151 standard.
The Long time delay overcurrent protection in accordance with the IEC 60255-151 standard is
designed to protect the cables, the busbars and the busbar trunking from current overloads. It
also allows selectivity to be improved with an upstream protection device.
One of the following four trip curves can be chosen, based on a calculation in accordance with
the requirements of the IEC 60255-151 standard.
• SI I
0.02t
: Standard Inverse Time curve
• VI It: Very Inverse Time curve
• EI I
2t
: Extremely Inverse Time curve
• HVF I
4t
: High Voltage Fuse curve
• The chosen curve is added to the existing Long time delay protection (default setting Thi,
thermal image).
The parameters of the four curves depend on Ir and tr.
Long time delay overcurrent protection in accordance with IEC 60255-151 is available in
profiles A and B of the dual settings. It is adjusted independently for profiles A and B.
Tripping time calculation
The tripping time depends on the current I compared to the threshold Ir and the time delay tr.
The tripping time is calculated using the following equation, in accordance with the IEC
60255-151 standard Appendix A:
The value of the coecients k, c and α for each tripping curve is indicated in the table below:
Trip curve k c α
SI I
0.02t
0.14 0 0.02
VI It 13.5 0 1
EI I
2t
80 0 2
HVF I
4t
80 0 4
Tripping time reduction
tr
Ir 6xIr
0
HVF
EI
Thi
VI
SI