TRANSFORMER FAULT CONDITION
A number of transformer faults conditions can rise practically in any time following some special situations.
- Earth faults
- Core faults
- Internal faults
- Phase to phase faults
- Tank faults
1 Earth faults
A fault on a transformer winding will result in currents that depend on the source, neutral grounding impedance, leakage reactance of the transformer, and the position of the fault in the windings. The winding connections also influence the magnitude of fault current.If the neutral is solidly grounded, the fault current is controlled by the leakage reactance, which depends on fault location.
The reactance decreases as the fault becomes closer to the neutral point. As a result, the fault current is highest for a fault close to the neutral point. In the case of a fault in a ∆-connected winding, the range of fault current is less than that for a Y-connected winding, with the actual value being controlled by the method of grounding used in the system.
2. Core faults
Core faults due to insulation breakdown can permit sufficient eddy-current to flow to cause overheating, which may reach a magnitude sufficient to damage the winding.
3. Interturn faults
Interturn faults occur due to winding flashovers caused by line surges. A short circuit of a few turns of the winding will give rise to high currents in the short-circuited loops, but the terminal currents will be low.
4. Phase-to-phase faults
Phase-to-phase faults are rare in occurrence but will result in substantial currents of magnitudes similar to earth faults.
5. Tank faults
Tank faults resulting in loss of oil reduce winding insulation as well as producing abnormal temperature rises.
source:http://electrical-engineering-portal.com/
