Table 1 Comparative analysis of current/voltage-based techniques for internal fault discrimination.
From: Condition monitoring and fault diagnosis of power transformer based on non-invasive measurement
Method | References | General features | Non‐invasive/ invasive | Sensorless/ Sensor | Online | Offline |
|---|---|---|---|---|---|---|
Differential relay | Low sensitivity | Non | Sensorless | ✓ | ✓ | |
Very simple and robust | ||||||
Mal-operation occurrence during operation | ||||||
Effect of CT saturation, magnetizing current and errors | ||||||
Negative sequence | Reasonable sensitivity (3%) | Non | Sensorless | ✓ | __ | |
Production of negative current in case of un-grounded faults | ||||||
Impact of CT saturation, magnetizing current and errors | ||||||
voltage transformer limitations | ||||||
each side of the transformer must be loaded | ||||||
Algorithms do not consider incipient nature | ||||||
Negative Sequence-Based Positive Impedance Method | Error in case of online computations | Non | Sensorless | ✓ | __ | |
Simple calculation process | ||||||
Reasonable sensitivity (2.5%) | ||||||
OLTC operation adaptation | ||||||
Still stable at 10% over-excitation | ||||||
In case of unbalanced load and source, the algorithm still stable | ||||||
localization the internal fault cannot be achieved | ||||||
Zero sequence | Errors due to using CT and VT | Non | Sensorless | ✓ | __ | |
Still stable in inrush current cases | ||||||
Needs calibration in delta winding connection | ||||||
The healthy condition data must be existed | ||||||
Valid for transformer bank only | ||||||
ΔV‐I locus diagram | Can deal with various faults | Non | Sensorless | ✓ | __ | |
Errors due to using CT and VT | ||||||
The healthy condition data must be existed | ||||||
Extended Park’s vector approach | Cannot acts well for unbalance load | Non | Sensorless | ✓ | __ | |
Cannot operate in transformer energization | ||||||
Measuring instruments error | ||||||
Can detect only 4% turns faults | ||||||
Magnetic Flux Test | Can detect the faulty phase | Non | Sensorless | __ | ✓ | |
The implementation for Y-connection for 3-phase transformer | ||||||
Cannot applied for five-leg core | ||||||
Error due to flux interception |
