Tan Delta

Tan Delta is an effective tool in determining the insulation condition of power cables using a VLF-TD System Tan Delta measures the resistive component of a cable system; a perfect cable is all capacitance and has no resistance. The resistive component is caused by voids in the insulation, electrical trees, water trees etc. The resistive element causes the voltage not to lead the current by 90 (something less) This is difference in angle (less than 1 ) is the loss angle. The tangent of this loss angle is the Tan Delta / or the tangent of the loss angle.

tan delta testing is usally carried out to check the healthiness of insulation.so this testing is usally carried out in cb ,ct, bushings etc ,for all these equipements one standard value will be there,for breakers this value will be 0.00073, if any devation in this value we have to suspect about it insulation healthyness.

Ideally an insulation (be it across a cable or a electrical switch gear) should be of infinite resistance. That is ideally if voltage is applied across insulation no current should pass through (considering resistive current only). Now there is another aspect of an insulation. An insulation is also a capacitor (two plates seperated by dielectric) and hence there must be some current (opf course ac current) that will flow if voltage is applied acroos insulation (this is capacitive current). Now the ration of the resistive current (which shoud ideally be zero) and the capacitive current is called loss tangent or tan delta and is measurable. So if tan delta is measured we are actually get an idea of the resistive current through the insulation. A high tan delta indicates high resistive current and that means insulation is detoriating.

tan angle is the ratio of resistance current and capacitive current ..it is used to estimate the life of insulation by comparing periodical tandelta value of the same insulation..pure insulation has only capacitive current but with the insulation deteriorationor cavity formation(may occur due ambient condition temp or cont. over current flow) resistance is added hence resistive current increase wich leads to increase in tandelta value.

Ideally an insulation (be it across a cable or a electrical switch gear) should be of infinite resistance. That is ideally if voltage is applied across insulation no current should pass through (considering resistive current only). Now there is another aspect of an insulation. An insulation is also a capacitor (two plates seperated by dielectric) and hence there must be some current (opf course ac current) that will flow if voltage is applied acroos insulation (this is capacitive current).& IDEAL CAPACITIVE CURRENT IS ALWAYS 90 DEG AHEAD THAN VOLTAGE AS PER R-C CIRCUIT VECTOR DIAGRAM.BUT DUE TO AGING EFFECT & DETORIATION OF INSULATION , CAPACITIVE CURRENT IS SLIGHTLY
LESS THAT 90 DEG & ONE ANGLE CREATED BET IDEAL CAPA. CURRENT & ABOVE SAID CURRENT IS CALLED TAN DELTA ANGLE. HENCE WE CLEARLY SAY THAT TAN DELTA IS the ration of the resistive current (which shoud ideally be zero) and the capacitive current is called loss tangent or tan delta and is measurable. So if tan delta is measured we are actually get an idea of the resistive current through the insulation. A high tan delta indicates high resistive current and that means insulation is detoriating.

n general for electrical component, Ten delta means that the tangent value of insulating material. what is tangent value of IM? it is nothing but the dissipation factor. what is dissipation factor? The ratio of Power/ Voltage-Ampear (W/VA). so finally in simple words Tan delta testing is nothing but to find out the health of insulation OR insulating material.The test can be performed on Cables, power TR's or any electrical component.