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					                               EARTHING EQUIPMENT

1.1. General

          Grounding of equipment is the connection to the land of one or more metal parts

   perkawatan systems, tools, machines which in normal circumstances does not carry the

   current. In the electric power system parts are metal pipes, cable protectors, the cabinet, the

   switch box, motor frame, transformer tanks, control cabinets and others.

          At the substation need to obtain a uniform potential in all parts of the structure and

   equipment to keep the operator or the person who was the installation area is located in the

   same potential and is not dangerous at all times.

          If there is accidental contact between the parts through which flows the metal frame

   of the equipment, metal frame becomes equal to the voltage-voltage systems. To avoid

   dangerous electric shock metal framework should be earthed via a low impedance.

   Grounding impedance should be small enough so that the tension that arises in the

   framework IZ frame equipment can be quite small and harmless.

1.2 Objectives of Equipment Grounding

Grounding equipment, as opposed to pengetanahan system, is pengetanahan piece of equipment

that does not pass on the normal work flow. The purpose of equipment grounding are:

A.) To limit the voltage between parts of equipment that does not flow through and between

   these sections to the ground to arrive at a price that is safe (not dangerous) for all operating

   conditions of normal or abnormal.

B.) This point grounding system is to obtain a smooth potential (uniform) in all parts of the

   structure and equipment, and also to keep the operator or person residing in the installation

   area is located at the same potential and is not dangerous at all times. By reaching the

   potential that is almost evenly at all points in this area pengetanahan system, the possibility

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        of a large potential difference at a distance that can be achieved by man during a short

        circuit to ground wire to be very reduced.

    C.) The second objective of pengetanahan this equipment is to obtain a small impedance / low

        from        the       road   behind      the    short     circuit   current     to       ground.

        Accidents in personnel occur during ground short circuit occurs. So when the ground short

        circuit current is forced to flow through a high impedance ground, this will cause a potential

        difference is large and dangerous. It can also cause an electrical arc and the magnitude of

        warming light enough combustible material.

Briefly the purpose of equipment grounding can be explained as follows:

1. Prevent a dangerous voltage electric shock to people in that area.

2. To enable the emergence of certain currents both magnitude and duration of soil disturbance in a

state   without      causing     a   fire   or   explosion   in   the   building   or   its     contents.

3. To improve the appearance of the system.

1.3 (voltage exposure)

        International Electrotechnical Commission (IEC) of the proposed allowable touch voltage as

a function of the length of disorders such as in table 6.1. Table 6.1 is usually used to voltage

consumer systems.

        The system works pengetanahan safety in the event of failure of insulation on the

equipment, then the large fault current I f from the point of interruption to the agency the tools, and

equipment from the body to the ground via the grounding resistance RE 2 , then there was a tap on

the body voltage for equipment I f  RE 2 .

In order for the requirements in table 6.1 above are met, then the prisoner RE 2 is given by:

        RE 2           ohh
                 k  In

           In    = nominal current of safety devices or safety devices melting in

                        ampere overcurrent

           k     = number of magnitude depending on the characteristics of safety


                 = 2,5 – 5         melt or fuse for safety

                 = 1,25 – 3,5 other safety

                              Table 6.1. Large and long maximum touch voltage

                             Touch Voltage Volt              Maximum Disconnection

                                   (RMS)                         Time (second)

                                     < 50                             

                                      50                              5,0

                                      75                              1,0

                                      90                              0,5

                                     110                              0,2

                                     150                              0,1

                                     220                             0,05

                                     280                             0,03

Impedance transformer is usually small to RE1 atau RE 2 , then the ground circuit current:

                 R ph
If 
       RE1  RE 2  Rsaluran / 3
         Figure 6.1. Dash ground on the equipment in a earthed neutral systems.

         REA          2,78 ohm ( k diambil = 3)
                 3 6

Misalkan diambil :

                     RE 2   = 2,5 ohm

                     RE1    = 2,0 ohm

                     Rsal   = kecil dan diabaikan

         E ph  220 Volt

Maka :

         If               48,9 amper
                2,5  2,0

Tegangan sentuh adalah :

         Es  48,9  2,5  122 ,25 Volt

So the touch voltages arising 122.25 Volt, 50 Volt finished higher. But if the fuses used meet the

standard requirements, then the current 48.9 amperes fuse will be broken in 0.1 seconds,

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