why the high tension cables gives a buzz sound?

There is something called Ionization.. this happens because of charges..

specifically speaking.. we need to know about corona..

CORONA ...

In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient (the strength of the electric field) exceeds a certain value, but conditions are insufficient to cause complete electrical breakdown or arcing.

A corona is a process by which a current, perhaps sustained, develops from an electrode with a high potential in a neutral fluid, usually air, by ionizing that fluid so as to create a plasma around the electrode. The ions generated eventually pass charge to nearby areas of lower potential, or recombine to form neutral gas molecules.Corona discharge usually involves two asymmetric electrodes; one highly curved (such as the tip of a needle, or a small diameter wire) and one of low curvature (such as a plate, or the ground). The high curvature ensures a high potential gradient around one electrode, for the generation of a plasma.

NOW COMES THE ANSWER TO YOUR QUESTION...

Coronas can generate audible and radio-frequency noise, particularly near electric power transmission lines. They also represent a power loss, and their action on atmospheric particulates, along with associated ozone and NOx production, can also be disadvantageous to human health where power lines run through built-up areas. Therefore, power transmission equipment is designed to minimise the formation of corona discharge.

Corona discharge is generally undesirable in:

* Electric power transmission, where it causes:

o Power loss

o Audible noise

o Electromagnetic interference

o Purple glow

o Ozone production

o Insulation damage

* Inside electrical components such as transformers, capacitors, electric motors and generators. Corona progressively damages the insulation inside these devices, leading to premature equipment failure. One form of attack is ozone cracking of elastomer items like O-rings.

* Situations where high voltages are in use, but ozone production is to be minimised

* Static electricity discharge

* Lightning

Power lines produce an audible sound or buzz because they are producing something called a corona discharge that is interacting with the surrounding air. The corona discharge is a side-effect of the electric field the power line generates by carrying electricity. The discharge can be greater, and the buzzing louder if there is increased moisture or pollutants in the air.

Electric Fields

Any medium that conducts an electric current will produce an electric field. This is true of electronic devices, power cords, and power lines. An electric field is similar to the more familiar magnetic field. In fact the two types of fields are deeply related because they are both generated by the electromagnetic force.

The movement of electrons through the power line is called current, the electrons themselves carry an electromagnetic charge. An electric field radiates perpendicular from the direction of the current. A power line is a very long cylinder so the field radiates in a cylindrical shape. The strength of the field drops off in inverse proportion to the radius. In other words, the electric field is strongest nearer the line and drops off dramatically farther away.

Interaction with the Air

The electric field contains enough electricity to ionize the air. Specifically, it will ionize oxygen and nitrogen in the air. This can produce a low energy plasma, the corona discharge. A plasma is a fourth state of matter (after solid, liquid, and gas). It is like a gas or liquid, but molecules are separated into atoms, and the outer electrons are stripped off and are freed into the plasma. In comparison, the sun is essentially a big ball of very hot plasma.

The current carried in the power line alternates direction, usually 60 times a second (60Hz). This propagates to the electrical field, affecting the plasma, and producing the audible vibration of air.

electricity travels over the surface of metal. that is why high tension power grid suspension cables are multi-strand. they also flex in the wind and sun without work-hardening and breaking.

because this massive amperage is racing down the length of these cables they will encounter imperfections on the surfaces in the form of crap, and dust, which will cause arcing. the uniform ticking is the sound of 60 cycles per second, first established by nicola tesla almost 100 years ago.

once in a while you will see a utility truck spraying the insulator hangers on these assemblies, to clean the dirt and particulates off, reducing the resistance in that section. they can do this without shorting the system to blackout, by using deoinized pure water. it has no minerals in it to conduct electricity. firemen are trained with caution not to spray through power lines with tap water, knowing the disastrous results of electrocution. there!

the sound is due to the corona discharge. Coronas can generate audible and radio-frequency noise, particularly near electric power transmission lines. They also represent a power loss, and their action on atmospheric particulates, along with associated ozone and NOx production, can also be disadvantageous to human health where power lines run through built-up areas. Therefore, power transmission equipment is designed to minimise the formation of corona discharge.