Protection Grounding and Operation Grounding.

<...1. What is the difference between protection grounding and operation grounding?...>

Under British Standard 7671, none at all.

<...2. Earthmats are what type of grounding?...>

See the Wikipedia article on earthing for complete explanations of earthing systems.

<...3. How can steel penstocks work as protection grounding?...>

Under BS7671, they can't. If they need grounding then the earth system wiring provides it. Adding equipotential bonding can always be carried out, and does not need certification under part P of the UK's Building Regulations.

<...4. The resistivity of soil is very less than resisitivity of rock. If there is rock, then different systems should be adopted?...>

Under BS7671, there are a number of options particularly applicable to TT earthing. One of them is to add residual current circuit breakers [RCCBs] so as to provide a much lower tripping point for the high resistivity conenction to operate the RCCB, rather than waiting for the overload protection devices to clear a fault at a much higher current level. Another option is to increase the size and number of the earth connections. Another is to decrease the resistivity of the soil in the location of the earth system - if tipping seawater into it is impracticable, animal urine is a good substitute liquid according to reports.

i think for protective grounding, touch potential etc. must be taken care of, whereas in operation grounding, it is not necessary?

regards,

BS7671 is not a matter of opinion.

I think it is the other way round. For operation grounding, touch potential is important and for protective grounding, earth resistance should not exceed 1(one) Ohm.

rgds.

Good answer - hope he gets good marks.

1. Basically it is same. Protection grounding implies grounding system/ network that may be used exclusively for electrical protection system and Instrument systems. This is also referred to as Insulated Earthing. For example, transformer earthing is not bonded with main earthing network of the system. DCS and computer system demand insulated earthing. In this case earth resistance should not exceed one ohm. Operation grounding implies general earthing network which includes earthing of structures, vessels, columns, tanks, buildings etc. Here earth resistance may not exceed 10 ohms provided it conforms to requirements of step potential / touch potential.

2. It is a grid like structure which is laid at the time of foundation laying of an eqpt. cast in situ which is wholly bonded with earth. It is best suitable for a rocky terrain.

3. As per statutory regulations taps, water pipes and things like that should never be used for earthing purposes. Steel penstock lies in that category.

4. True, in case of soil with low resistivity rod, pipe, and even plate type electrodes are used by burying them deep vertically in ground using appropriate process to build the electrode pit. In case of rocky ground, plate electrodes are buried horizontally which are interconnected to obtain required earth resistance.

rgds