- Device
- Requirements
- Calculation of the
- section
installation and removal procedure
device Made of flexible, copper cable, without braid, with clamp-type clamping devices with insulating handles for phase-to-phase and ground bus connection. There are both for three-phase devices, it is constructive to combine four earthing switches into one device, and separately to the ground bus and phase.
Looks like a portable grounding as on the photo:
The design of the clamps allows their installation with a special insulating rod. Combination of cores in a three-phase earthing rod is made by crimping or welding, a bolted connection is permissible, but the cores must be tinned with refractory solder in the crimping site. Simply soldering is not allowed, because short-circuit currents can heat up the connection and destroy the integrity of the device.
You can clearly see what a portable grounding is and how to use it correctly, you can in the video lesson below:
Requirements for the
The cable and the attachments of the portable device must withstand short-circuit current and dynamic loads. Clamps provide reliable contact, be heat resistant. The cross-section of conductors for installations up to 1000 volts is not less than 16 mm. Above 1000 volts, the conductors are not less than 25 mm.
At voltages above 6 kV, the core section will be 120 mm and above, which is not practical and difficult. Therefore, it is allowed to install several grounding lines side by side, summing up the required cross-section.
It is forbidden to use a conductor in insulation for earth conductors since the insulating layer makes it difficult to detect damage to the conductor cores in time and to reduce the design cross-section, which can lead to the burnout of the earthing switch.
Calculation of the section
The required cross-section of the core can be calculated using the simplified formula:
S =( Iust √tf) / 272
where:
- Iust - steady short-circuit current. A;
- tf is a dummy time, sec;
When calculating the ground for a single-voltage switchgear, tf takes the highest value of the operating time of the electrical protection relay. In networks with earthed neutral, the conductor cross-section is calculated by the short-circuit current of one phase.
Installation and removal procedure
The installation is carried out on the de-energized part of the busbars from the side with which the supply of voltage is possible. Before installing the pointer check the presence of current-carrying buses voltage, making sure in its absence, a portable grounding is installed. First of all, clamps are attached to the zero bus or grounded structure, and then alternately to phase ones. The installation of the clamps is carried out using an insulated rod, using protective equipment, dressing bots and mittens, as shown in the picture:
If the site on which the work is done is divided by switching devices, or produced with disassembly of tires, grounding is superimposed on both sides of the work siteto avoid voltage pick-up from a number of live busbars.
Installation of a portable grounding is made from the floor or ground, lifting on the ground not yet equipment is prohibited without a repeated voltage test. Remove the grounding in the reverse order. First, the clamps are removed from the busbars, then the conductor is removed from the grounded element or the zero bus. Remove the portable grounding is necessary with the help of an isolated rod and protective means. After removing the jumpers, it is forbidden to touch tires without protective means, since they can be stressed.
In the video examples below it is clearly demonstrated how to install a portable grounding:
Remember, the work in the electrical installations is carried out according to the permit-admission, accompanied by the supervisor, with instructions before starting work, in accordance with the current regulations on TB andrules of technical operation.
That's all I wanted to tell you about what a portable grounding is, how to install it and what requirements are imposed on the conductor section. We hope that the information was useful and understandable for you.
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