Tan delta is the insulation power factor & is equal to the ratio of power dissipated in the insulation in watts to the product of effective voltage & current in volt ampere when tested under sinusoidal voltage.

1. TAN DELTA TEST FOR POWER
TRANSFORMERS

2. TAN DELTA(INSULATION DISSIPATION FACTOR)
 Tan delta is the insulation power factor & is equal to
the ratio of power dissipated in the insulation in
watts to the product of effective voltage & current in
volt ampere when tested under sinusoidal voltage.

3. PROCEDURE
 All windings immersed in insulating liquid.
 All windings shortcircuited using bare braided
jumper such that jumper shall not be allowed to sag.
 All bushings in place.
 Temperature of winding & insulation liquid near to
the reference temperature(27 degree).
 All bushings cleaned properly.
 Transformer earthed properly.

4.  Neutral,star point of 3 phase winding connected to
other bushing of that winding by means of short
jumper.
 Tan delta is then tested between below
combinations,
a. HV to EARTH
b. LV to EARTH
c. HV to LV.

5. TEST SETUP
 TRANSFORMER SPECIFICATONS
RATING-100 MVA
VOLTAGE CLASS-33KV/220KV
Yyn-0
COOLING-OFAF
 INSTRUMENT MAKE-OMICRON
 APPLIED VOLTAGE-10KV

6. LV TO EARTH TESTING

7. HV TO EARTH TESTING

8. LV-HV TESTING

9. TAN-DELTA TEST RESULTS
WINDING TAN-DELTA
LV TO EARTH 0.4702
HV TO EARTH 0.4983
LV TO HV 0.2616