At present earth-termination is used to discharge,reduce ground resistance in domestic earthing system.The traditional material largely used in earth-termination is steel angle and steel flat. Considering the strong corrosion of some certain condition site toward the earth-termination system, some power station use copper material instead of steel angle and steel flat in order to solve the corrosion problem,such as some alkali soils ,coastal land ,fishing&PV power station project.
The main factor that affects the grounding resistance is the soil resistivity. The soil resistivity changes with the change of environment. The grounding device is also changing in the soil.
The potential inconsistent of different parts in earthing system caused by lack of experience or working mistakes easy to cause accident during the construction of power station.Especially in PV power station,large area is occupied.The voltage caused by potential inconsistent is easy to cause damage and error operation for combiner-box , micro electronic devices inside inverter.
3.problem of device earthing：
Some electrical devices are without grounding system or poor grounding contact.The branch earthing conductor of electrical devices , not connected with earthing bus conductors,in series connection or through bracket, high residual voltage can be generated when the fault current is passed through,which will damage the devices.There will be too many welding joints in PV power station.Faults will occur in high probability if it is completely dependent on manual experience.
Flat steel is connected by traditional welding when it as earthing material.Because of manual operation of welding ,there are some problem with the joint like welding slag, undercut and porosity.When the fault current through the welding joint,it will cause instantaneous high temperature.The joint will break because of the welding problem,thereby cause the device charged and also easy to produce the counter attackof high pressure to the control line .
Due to insufficient survey for the local soil,underestimate the erosion rate of the local soil . The problem of the material,we can not only count the corrosion rate by yearly,also put galvanic corrosion into consideration.The welding joint is the most serious corrosion point because of the welding problem. Grounding for a long time in the underground operation ,Operating conditions are serious ,In particular, some of the PV power station grounding grid in some wet or acidic soil where the most likely to occur corrosion.
1、GB/T50065-2011 Code for Earthing Design of AC Electrical Device.
2、GB50057-2010design code for protection of structures against lightning.
3、GB 50169-2006 Code for Construction and Acceptance of Earth-termination For Electrical Equipment Installation Engineering.
4、GB50601-2010 Code for Construction and Acceptance of Structures Against Lightning.
5、GB50797-2012 Code for Design of PV Power Station.
6、GB 50794-2012 Code for Construction of PV Power Station.
7、GB/T50796-2012 Code for Acceptance of PV Power Project.
8、IEEE std 80-2000 Safety Guide for Earthing of AC Power Station.