BS EN 50522-2010 pdf download.Earthing of power installations exceeding 1 KV a. c.
6.1 Transferred potential from High voltage systems to Low voltage systems
6.1.1 HIgh and low voltage earthlng systems
Where high and low voltage earthing systems exist in proximity to each other and do not form a global earthing system, part of the EPR from the HV system can be applied on the LV system. Two practices are presently used:
a) interconnection of all HV with LV earthing systems;
b) separation of HV from LV earthing systems.
In either case, the relevant requirements concerning step, touch and transfer potentials specified below
shall be complied with within a substation and at a LV installation supplied from that substation.
NOTE Interconnectkn is preferred when pract,cab.ee.
6.1.2 LV supply only within HVsubstations
Where the LV system is totally confined within the area covered by the HV earthing system both earthing systems shall be Interconnected, even if there is no global earthing system.
6.1.3 L Vsupply leaving or coming to HVsubstations
Full compliance is ensured if the earthing system of the HV installation is part of a global earthing system or connected to a multi-earthed HV neutral conductor in a balanced system. If there is no global earthing system the minimum requirements of Table 2 shall be used to identify those situations where interconnection of earthing systems with low voltage supply outside the high voltage installation is feasible.
If high voltage and low voltage earthing systems are separate, the method of separating earth electrodes shall be chosen such that no danger to persons or equipment can occur in the low voltage installation. This means that step, touch and transfer potentials and stress voltage in the LV installation caused by a high voltage fault are within the appropriate limits.
NOTE For installations wffh rated voltages below 50 kV a distance of 20 m between separated earttiing systems has been used in many cases. For certain soil structures other values may be appropriate.
6.1.4 L Vin the proximity of HVsubstation
Special consideration should be given to LV systems which are located in the zone of influence of the HV substation earthing system.
For industrial and commercial installations a common earthing system can be used. Due to the close proximity of equipment it is not possible to separate earthing systems.
7.1 Installation of earth electrodes and earthing conductors
An earthing system is generally composed of several horizontal, vertical or inclined electrodes, buried or
driven into the soil by force.
The use of chemicals to reduce soil resistivity is not recommended.
Horizontal earth electrodes are preferably buried at a depth of 0,5 m to 1 m below ground level. This gives sufficient mechanical protection. It is recommended that the earth electrode is situated below the frost line.
In the case of vertical driven rods, the top of each rod will usually be situated below ground level. Vertical or inchned driven rods are particularly advantageous when the soil resistivity decreases with depth.
Metal frameworks, earthed in accordance with this standard, which form a construction unit, may be used as an earthing conductor to earth parts which are directly fixed to this framework. Consequently, the whole framework shall have a sufficiently conductive cross-section and the joints shall be conductively and mechanically reliable. Precautions shall be taken to avoid part of the framework becoming disconnected from the earthing system when temporary dismantling takes place, Large frameworks shall be connected to the earthing system in a sufficient number of points.
Where construction work involves an existing earthing system, protective measures shall be taken to ensure the safety of persons during fault conditions,
General installation details can be found in Annex K.
7.2 Lightning and transients
Lightning and switching operations are sources of high and low frequency currents arid voltages. Surges typically occur when switching long cable sections, operating GIS disconnectors or carrying out back-to- back capacitor switching. Successful attenuation requires sufficient electrode density at injection points to deal with high frequency currents, together with an earthing system of sufficient extent to deaf with low frequency currents. The HV earthing system shall form part of the lightning protection system and additional earthing conductors may be required at injection points.
Relevant electromagnetic compatibility and lightning standards shall be used to address specific aspects related to the transient performance of the earthing system and its components.
When an industrial or commercial installation includes more than one building or location, the earthing system of each shall be interconnected. Since during surges such as lightning strokes, there will be a large difference in potential between the earthing systems of each building and location in spite of the interconnection, measures shall be taken to prevent damage to sensitive equipment connected between different buildings or locations. Where possible, non-metallic media, such as fibre optic cable, should be used for the exchange of low-level signals between such locations.BS EN 50522-2010 pdf download.