Thursday, March 18, 2010

Substation main earth bar pictures

You will find below a few pictures of HV electrical substation’s main earth bar. I took these pictures inside a Consumer HV room at one of my recent building projects.

Picture 1 – Location of the main earthing bar inside a HV Switchgear Room

Observe the location and position of the main earth bar in the HV room. At every electrical room of significant size, at least one main earth bar like this should be provided.

Picture 2 below shows a closer view of this earth bar.

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Picture 2 – HV Room’s main earth bar

The purpose of having the main bar is simple.

All earthing conductors inside the HV room would be connected to this bar. That is the reason you can see in Picture 2 a number of ready-made termination holes complete with bolts, nuts and spring washers.

Notice the main copper earthing tape mounted along the substation wall in Picture 1. This is the main equipotential earthing conductor for this electrical room.

It should run through all perimeter walls of the room at a height of approximately 12 inch from the substation’s finish floor level. That is why you can see that in Picture 2 the left-most and right-most terminals have been connected with a horizontal copper tape conductor.

An ideal installation would have the main equipotential conductor run in a ring around the perimeter walls and both conductor ends connects to the main earth bar at the left-most and right-most terminals.

However, in this case it was not in a ring at the time this picture was taken because there was an entrance door at the wall in front of the 11 KV switchgear. Picture 1 was taken at the rear.

Later the horizontal copper tapes were connected into a ring by running additional conductor above the entrance door.

What are the conductors connected to the main earth bar in Picture 2?

The horizontal tapes at the left and right are what I have explained above.

The other three conductors have been installed vertically down into the cable trench.

(NOTE: Notice that the cable trench has been filled with river sand. Many installations prefer to have cable trenches filled with sand to avoid problems with rates and snakes playing hide and seek inside the cable trench.

Once a while these live beings find their way into the electrical switchgears and cause many problems including short circuits and intermittent trippings.

I have come across many operational problems because of these reasons.

To overcome these problems, many operation engineers prefer to just have all substation cable trenches filled with river sand. Then the trench is finished with approximately one inch of lean concrete on top of the sand and level with the substation floor.

When they need to do some work in the trench, they just knock down and break the thin concrete and dig out the sand.

No doubt this is a messy way of doing things, but it seemed to have been a very practical solution to these sorts of problems.)

Back to the earth tapes run vertical down into the cable trench. Where are these tape conductors for?

From the right, the first vertical conductor is connected to the HV switchgear equipotential conductors.

The center vertical conductor is connected to the earth busbar inside the switchgear compartments.

The last vertical conductor, at the far left, is the connection to the earthing electrodes outside the HV room.

Picture 3 – Disconnecting earth terminals

Some of the readers may not notice that the earth bar in Picture 2 is actually a two-piece bar. The two separate pieces are much more visible in Picture 3 above.

Notice that there is just one terminal (other than the terminal for connecting the two bars) on the short piece, while there are six terminals on the longer bar.

This has been designed to be so. The terminal on the short bar is called “disconnecting terminal”. The whole assembly is purchased readily assembled by manufacturer.

Usually earth bar with one or two disconnecting terminals are readily available. If an electrical contractor needs more disconnecting terminals, then it need to be ordered and it would be fabricated as required by the project at hand.

The terminals on the shorter piece are intended for testing and trouble-shooting purposes. That is why the conductor to the grounding electrodes is often connected to the short piece.

However, so clients forbid the use of the disconnecting terminals altogether. These sorts of clients usually manage many separate electrical installations with separate local operation teams.

It is usually not always easy to ensure an adequate level of competency of each member of the local operation and maintenance teams.

An earth lead conductor connected to the disconnecting terminal may easily lead to a total absence of connection to the earth electrode.

This presents a very serious safety risk.

This lead to a policy of forbidding the use of the disconnecting terminals. Therefore, all their substations would have single-piece earth bars.

Picture 4 – HV switchgear body earth conductor

This photo gives a clearer view of the switchgear equipotential bonding conductor.

As you may be aware, the switchgear came in separate smaller panels and the individual panels are then connected and bolted together at site.

The switchgear body earth (another name for the enclosure equipotential bonding) conductors, as indicated in Picture 4, have also been installed and bolted to each individual panel.

Therefore, these individual lengths of body earth conductors are connected and bolted to each other at the construction site.

The short inter-connecting copper pieces and all accessories including bolt-and-nuts for making the complete connection are provided by the switchgear manufacturer and shipped together with the rest of the panels.

Picture 5 – Bolt, nut and spring washer

This may be obvious for most readers, but some beginners may be silently screaming for help. So I labeled these components for them since they are such critical components in the electrical grounding system.

Picture 6 – Earth bar insulator post

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