1.5. Placement of surge arresters - general comments

Correct placement of surge arresters in a power line has crucial meaning for correct operation of the designed surge protection system.
As it was mentioned before, at the organizaton of surge protection systems of high-power-generating machinery, the arresters are put in the following places:
a.   outside the construction site, in oV lightning protection zone, on the input of power cables to devices ( most frequently these are arresters of class II, sometimes class I);
b.   in places of power line going through the wall of the building (depending on the lightning threat , these are arresters of class I or II) - in cable connection, grounded in the shortest way to the grounding device;
c.   inside the construction site:

  • in local switchboards (depending on the level of lightning threat, these are arresters of class II or III);
  • near protected devices ( most frequently, these are arresters of class III, sometimes- class II, from the point of view of too weak rated current of arresters of  class III, which is 16 A only).

1.6. Short circuit resistance of arresters

Short arrestes should be protected from short circuit current consequences. Its configuration (parallel connection relatively to clamps of the protected circuit) means that any action of surge arrester causes flowing of short circuit current in the protected line. Due to this, the manufacturer should claim, when and what safety device should be used sequentially with the arrester in order to provide corresponding resistance to short circuit current of the schme safety device- surge arrester.
Defining the need to use additional protection of surge arrester sequentially connected by the dafety device, it is reasonable to compare values of rated currents  IF1 of phase safety devices of the protected circuit with acceptable current value IDOP,  which may flow in surge arrester circuit (recommended by the manufacturer). Depending on results of such comparison, it is reasonable to use the scheme:

  • IF1 ≤ IDOP -  without any additional protective safety device (fig.1.3.a),
  • IF1 > IDOP -  containing an additional safety device F2, sequentially connected with surge arresters (fig.1.3.b).

1.7.  Schemes of surge arresters connection

Depending on the grounding system of electrical supply network, one type of surge arresters connection is used, as shown in fig. 1.4, 1.5 or 1.6.

In TT network system there is a possibility to apply 4 typical surge arresters or the so-called system 3+1 (3 surge arresters + 1 N-PE arrester). Such connection systems refer to surge arresters of classes I and II.

In case of using class I arresters, it is necessary to use systems with additional safety devices, connected sequentially with arresters. Application of safety devices is not obligatory, if the following conditions, described in section 1.6. are fulfilled.

Schemes of surge arresters connection-1

Системы соединений ограничителей перенапряжений класса I – Schemes of class I surge arresters
Для систем питания TN- for TN power system

Schemes of surge arresters connection-2

Системы соединений ограничителей перенапряжений класса I – Schemes of class I surge arresters
Для систем питания TN- for TT and IT power system



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