Power transformer diagnostics is an integral element of preventive maintenance, whose purpose is to determine the condition of main transformer parts: windings, core, bushings, insulation system, and tap changer.
On-site diagnostics – basic scope:
- measurement of insulation resistance
- measurement of C & tanδ of windings
- measurement of C & tanδ of bushings
- low voltage measurement of no-load current
- measurement of the voltage ratio
- measurement of winding resistance
- measurement of leakage inductance (Lx)
On-site diagnostics – enhanced scope = basic scope + additional measurements:
- frequency response analysis (FRA)
- measurement of transformer insulation polarisation spectrum – RVM method
- dielectric response analysis (PDC & FDS method)
Special diagnostic methods
Special diagnostic methods are used to determine causes and locations of transformer faults/failures, or as a part of special investigations:
- PD testing – Acoustic Emission (AE) method
- OLTC diagnostics:
- dynamic resistance measurement
- measuring of resistance with 100 A (R vs. I characteristics
PD acoustic emission detection
This method is used to locate discharges (PD), bad contacts, or localized hot regions in transformers (> 200⁰C). Acoustics Emission (AE) method enables:
- location the source of potential problem on-site
- assess the option for its elimination,
- assess risks of running problematic transformers.
The accuracy of acoustic detection is equal to the size of a soccerball – approx ±15 cm. PD acoustic detection method is not susceptible to electrical interference, which makes it applicable to transformers in service. PD can be detected at an early stage (∼500 pC). The transformer is on-line during preparation and measurement.
Application of AE method:
- when a potential problem is detected by another diagnostic method
- as a reference measurement (acoustics fingerprint)
Instrument transformer diagnostics
- measurement of insulation resistance
- measurement of C & tanδ of insulation
- PD measurement (acoustic method)
- accuracy class measurement
BROCHURE: Power and Instrument Transformer Diagnostics
