Tracking Index Apparatus
Breakdown of any insulating material generally occurs either through its volume or over its surface, or in both ways.

Surface failures may arise from flashover, or from progressive degradation of the insulation surfaces by small, localised sparks. Such sparks are the result of breaking up of a surface film of conducting contaminant on the insulation by the heat of a leakage current passing through it.

Rapid breaks in the leakage current produce an over-voltage at the site of the discontinuity and an electric spark is caused. Repeated sparks at any one point may lead to setting up of a carbon track between points at different potentials. This process is known as tracking.

Insulating parts retaining live parts in position shall have adequate resistance to tracking if they are exposed to excessive deposition of moisture or dirt in normal use.

The PROLIFIC Tracking Index Apparatus is designed to test resistance to tracking of insulating materials other than ceramics. The apparatus consists of two brass electrodes of specified dimensions with an arrangement to place them on the surface of the test specimen exerting a specified load on it, and suitable means to apply a specified test voltage across them. A conducting liquid dropping device is provided to wet the surface between the electrodes with a solution of ammonium chloride, with drops of specified size falling at specified time intervals.

The electrode assembly and dropping device are fitted in a sheet metal chamber having an acrylic door for viewing the test set up. A micro-switch cuts off supply to the electrodes whenever the door is opened. An exhaust fan is provided to remove water vapour and other gases produced during the test.

The test chamber is placed on the side of a sheet metal control panel which houses various voltage and current controlling elements, besides switches, indicators, drop counter, etc.

The control panel has an auto-transformer (variac) to vary the voltage across the electrode, a rheostat to adjust the resistance in the circuit to limit the current to 1 ampere with the electrodes short circuited, an over-current relay for tripping the circuit when the current exceeds the specified value, and a drop counting circuit with an electronic digital counter to count the number of drops falling. It also has a voltmeter, an ammeter, and various switches and indicators. A thermal relay is provided to trip off the supply to the electrodes and to activate an audio-visual alarm as soon as the breakdown of the insulation occurs.

The apparatus is supplied with two sets of brass electrodes. Platinum electrodes can also be supplied against specific demand.

The standard model of the apparatus is designed to determine tracking index of up to 300 volts. Special models for determining tracking index of up to 600 volts or up to 1200 volts can also be offered against specific requirements.