Limitation Curves
Introduction
The limiting capacity of a device is its aptitude to let through a current, during a short-circuit, that is less than the prospective short-circuit current.
The exceptional limiting capacity of TeSys GV5 / GV6 devices is due to the rotating double-break technique (very rapid natural repulsion of contacts and the appearance of two arc voltages in-series with a very steep wave front).
Ics = 100% Icu
The exceptional limiting capacity of TeSys GV5 / GV6 devices greatly reduces the forces created by faults in devices.
The result is a major increase in breaking performance.
In particular, the service breaking capacity Ics is equal to 100% of Icu.
The Icu value, defined by IEC/EN 60947-2 standard, is guaranteed by tests comprising the following steps:
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Break the circuit three times consecutively with a fault current equal to 100% of Icu
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Check that the device continues to function normally, that is:
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It conducts the rated current without abnormal temperature rise.
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Protection functions perform within the limits specified by the standard.
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Suitability for isolation is not impaired.
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Longer Service Life of Electrical Installations
Current-limiting devices greatly reduce the negative effects of short-circuits on installations.
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Thermal effects: Reduced temperature rise in conductors, therefore longer service life for cables.
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Mechanical effects: Reduces electrodynamic forces, therefore less risk of electrical contacts, or busbar being deformed or broken.
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Electromagnetic effects: Reduction in disturbances for measuring devices located near electric circuits.
Economy by Means of Cascading
Cascading is a technique directly derived from current limiting.
Devices with breaking capacities less than the prospective short-circuit current may be installed downstream of a limiting device.
The breaking capacity is reinforced by the limiting capacity of the upstream device.
It follows that substantial savings can be made on downstream equipment and enclosures.
Current and Energy Limiting Curves
The limiting capacity of a device is expressed by two curves which are a function of the prospective short-circuit current (the current which would flow if no protection devices were installed):
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The actual peak current (limited current)
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Thermal stress (A²s), that is, the energy dissipated by the short-circuit in a condition with a resistance of 1 Ω.
Maximum Permissible Cable Stresses
The tables below indicate the maximum permissible thermal stresses for cables depending on their insulation, conductor (Cu or Al), and their cross-sectional area (CSA). CSA values are given in mm² and thermal stresses in A²s.
|
CSA |
Conductor |
1.5 mm² (16 AWG) |
2.5 mm² (14 AWG) |
4 mm² (12 AWG) |
6 mm² (10 AWG) |
10 mm² (8 AWG) |
|---|---|---|---|---|---|---|
|
PVC |
Cu |
2.97x104 |
8.26x104 |
2.12x105 |
4.76x105 |
1.32x106 |
|
Al |
– |
– |
– |
– |
5.41x105 |
|
|
PRC |
Cu |
4.1x104 |
1.39x105 |
2.92x105 |
6.56x105 |
1.82x106 |
|
Al |
– |
– |
– |
– |
7.52x105 |
|
CSA |
Conductor |
16 mm² (6 AWG) |
25 mm² (4 AWG) |
35 mm² (2 AWG) |
50 mm² (1 AWG) |
|---|---|---|---|---|---|
|
PVC |
Cu |
3.4x106 |
8.26x106 |
1.62x107 |
3.31x107 |
|
Al |
1.39x106 |
3.38x106 |
6.64x106 |
1.35x107 |
|
|
PRC |
Cu |
4.69x106 |
1.39x107 |
2.23x107 |
4.56x107 |
|
Al |
1.93x106 |
4.7x106 |
9.23x106 |
1.88x107 |
Current-limiting Curves
The following example shows a current-limiting curve of TeSys GV5 / GV6 devices on 400/440 Vac networks.
1 GV5P150F/H
2 GV5P220F/H
3 GV6P320F/H
4 GV6P500F/H
Energy-limiting Curves
The following example shows a energy-limiting curve of TeSys GV5 / GV6 devices on 400/440 Vac networks.
1 GV5P150F/H
2 GV5P220F/H
3 GV6P320F/H
4 GV6P500F/H