Detailed characteristics of the external SCPD: Difference between revisions

From Electrical Installation Guide
Home > Overvoltage protection > Surge protection technical supplements > Detailed characteristics of the external SCPD
(content modified as per guide 2016)
(images modified as per guide 2016)
Line 2: Line 2:


__TOC__
__TOC__
== Current wave withstand  ==
== Current wave withstand  ==


Line 18: Line 17:
*to protect a SPD defined for Imax = 40 kA, the external SCPD to be chosen is either a MCB 40 A or a Fuse aM 125 A,
*to protect a SPD defined for Imax = 40 kA, the external SCPD to be chosen is either a MCB 40 A or a Fuse aM 125 A,


----
[[File:DB422521_EN.svg|none]]


[[File:Fig J50.jpg|none]]
'''''Fig. J53:''' Comparison of SCPDs voltage wave withstand capabilities for Imax = 20 kA and Imax = 40 kA''  
'''''Fig. J53:''' Comparison of SCPDs voltage wave withstand capabilities for Imax = 20 kA and Imax = 40 kA''  
----


== Installed Up voltage protection level ==
== Installed Up voltage protection level ==


In general:  
In general:  

Revision as of 00:17, 25 July 2016


Current wave withstand

The current wave withstand tests on external SCPDs show as follows:

  • For a given rating and technology (NH or cylindrical fuse), the current wave withstand capability is better with an aM type fuse (motor protection) than with a gG type fuse (general use).
  • For a given rating, the current wave withstand capability is better with a circuit breaker than with a fuse device.

Figure J53 below shows the results of the voltage wave withstand tests:

  • to protect a SPD defined for Imax = 20 kA, the external SCPD to be chosen is either a MCB 16 A or a Fuse aM 63 A,

Note: in this case, a Fuse gG 63 A is not suitable.

  • to protect a SPD defined for Imax = 40 kA, the external SCPD to be chosen is either a MCB 40 A or a Fuse aM 125 A,
DB422521 EN.svg

Fig. J53: Comparison of SCPDs voltage wave withstand capabilities for Imax = 20 kA and Imax = 40 kA

Installed Up voltage protection level

In general:

  • The voltage drop across the terminals of a circuit breaker is higher than that across the terminals of a fuse device. This is because the impedance of the circuit-breaker components (thermal and magnetic tripping devices) is higher than that of a fuse.However:
  • The difference between the voltage drops remains slight for current waves not exceeding 10 kA (95% of cases);
  • The installed Up voltage protection level also takes into account the cabling impedance. This can be high in the case of a fuse technology (protection device remote from the SPD) and low in the case of a circuit-breaker technology (circuit breaker close to, and even integrated into the SPD).

Note: The installed Up voltage protection level is the sum of the voltage drops:
  - in the SPD;
  - in the external SCPD;
  - in the equipment cabling

Protection from impedant short circuits

An impedant short circuit dissipates a lot of energy and should be eliminated very quickly to prevent damage to the installation and to the SPD.
Figure J54 compares the response time and the energy limitation of a protection system by a 63 A aM fuse and a 25 A circuit breaker.
These two protection systems have the same 8/20 µs current wave withstand capability (27 kA and 30 kA respectively).


Fig J51.jpg

Fig. J54: Comparison of time/current and energy limitations curves for a circuit breaker and a fuse having the same 8/20 µs current wave withstand capability


zh:外部短路保护器的详细特征

Share