Here we have given the short descriptions of some essential accessories of overhead transmission lines.
A suspension clamp is used to fit a conductor with a suspension string. A suspension clamp is made of an alloy of aluminum. The internal surface of the clamp should be smooth enough. Two ends of the clamp are wider than its middle. This design helps the clamp to hold the conductor in place properly. The suspension clamps are of different sizes for holding conductors of different diameters. Each of the clamps is also provided with two GI U bolts to keep the conductor tightly inside it.
Double Bolt Strain Clamp
To fix the end of a conductor the strain clamp is used. The clamp is also made of aluminum alloy. The strain clamp is used for both AAAC and ACSR conductors. To hold the conductor inside the clamp there are two GI U bolts provided. For different sizes of conductor different standard strain claims are available in the market.
Multi Bolt Strain Clamp
Constructionally this is similar to the double bolt strain clamp. For holding a very long spaned heavy conductor the clamp is of wavy shape. Instead of using only two u bolts, there are a significant number of u bolts provided in the clamp. The multi bolt strain clamp is also called the dead-end clamp.
Compression Type Dead End Clamp
For the conductor of a diameter of more than 14.16 mm, a compression type dead end clamp is used. This type of dead-end clamp is used for both AAAC and ACSR conductors. Presently it is always preferable to use compression type dead end clamp for all the conductors from dog to moose. For ACSR conductors there is an aluminum tube provided as the outer part of the clamp. For the steel strands of conductors, there is a steel tube provided as the inner part of the clamp.
The jumper terminal is to be fixed with nut bolts to the projected rectangular extension of the aluminum tube. There is a hole provided at the backside of the steel tube to fix it with the tension string fitting with the help of a nut bolt. There is only one aluminum tube provided in the compression type dead end clamp used for AAAC. The hole for fixing the dead-end clamp with the tension string with the help of the nut bolt is provided at the back of the tubular dead clamp itself. To compress the dead-end clamp on the conductor, a hydraulic press machine is used.
A repair sleeve is used to repair the minor damages on the strand layers of a conductor. A repair sleeve is always made of aluminum. The sleeve has two parts. One part can slide in other to form a complete tubular shape.
First, the damaged part of the conductor is covered by the repair sleeve and then it is compressed with a hydraulic press machine. Since no tensile force acts on the sleeve, a smaller size portable hydraulic press machine can be used for the purpose. The repair sleeves of different sizes are used for the conductors of different cross-sections.
Mid Span Compressor Joint
A mid-span compressor joint is used to join two pieces of conductors. For the conductors of a diameter of more than 14.16 mm MSCJ is used. The construction of this clamp is very simple. It is just like a tube. For AAAC there is only a simple aluminum tube of the required diameter.
For ACSR, there is an inner tube made of steel for holding steel strands. The outer tube is made of aluminum to hold the aluminum strands of the conductor. A heavy-duty hydraulic press machine preferably of 100 Ton or more than 100 Ton is used to compress the clamp. Because the tensile forces of the conductor directly act on the joint.
Parallel Grooves Clamp or PG Clamp
This is mainly a bolted type clamp and this clamp can not carry any tension so it is not used in the middle of the span of an overhead line. This clamp is mainly used in the non-tensional zone of the conductor. This clamp is mainly used in the jumper of a transmission line. A PG clamp is made of aluminum alloy. Different sizes of PG clamps are available in the market for different sizes of conductors. There are two parts in a PG clamp. One is the upper part and another is the lower part. The upper part and lower part are joined together with the help of nuts and bolts. The grooves are provided on the inner side of the parts.
Vibration of Overhead Conductors
Overhead conductors vibrate due to wind. This vibration is tangential vibration. The vibration travels to the ends of the conductor and returns. The frequency of the vibration is quite large. Due to the vibration, the conductor continuously goes up and down mainly at the point where the conductor is fitted with the clamps. It causes fatigue pressure at the fitting points. Therefore there is always a chance of snapping the conductor from those points.
The simplest and most effective method of saving a conductor from this vibration is using armor rods at the point of fixing of conductor with the clamps. A certain portion of the conductor is covered with the armor rods at the place of fixing the conductor with the clamp. It makes the diameter of the conductor larger at that place than the rest portion of the conductor. Consequently, the strength of the conductor increases at that portion. Therefore the chance of snapping of conductor reduces. For thin conductors, the aluminum tape is used to cover the conductor at the fixing portion to increase the diameter.
For damping the vibration of conductors, vibration dampers are used for long-span conductors. There are two weights fixed together with the help of stranded and twisted steel wire. The stranded and twisted steel wire gives flexibility to the weights with the help of its spring action. The vibration damper is fixed with the conductor with the help of its clamp at two ends of a span. Because of vibration dampers, the amplitude of the vibration wave reduces nearer to the suspension and tension clamps. Therefore the fatigue pressure of the conductor reduces. Ultimately the chance of snapping of conductor gets reduced.
For different sizes of conductors, different vibration dampers are available in the market. Depending on the span length and weight of the conductor, the vibration dampers are fitted at a specific location nearer to the suspension or tension clamps of an overhead transmission line. For conductors of diameter 275 mm to 650 mm the weight of the damper may be from 0.67 kg to 8 kg. Up to 365 meters span, one vibration damper is fitted at both ends of the span. For the span from 365 meters to 600 meters, two vibration dampers are fitted at both ends of the span.