IEEE C57.149-2012 pdf download IEEE Guide for the Application and Interpretation of Frequency Response Analysis for Oil-Immersed Transformers
2. Definitions
For the purposes of this document, the following terms and definitions apply. The IEEE StandardsDictionary Online should be consulted for terms not defined in this clause.
Baseline measurement: Provide a set of Frequency Response Analysis (FRA) waveforms for futurecomparative purposes for investigative or diagnostic analysis
Capacitive inter-winding measurement: Performed over a wide range of frequencies between twoelectrically isolated windings. Voltage is injected into one end of a winding, the input, and the response, theoutput, is measured at another winding, with all other terminals floating.CL: Is defined as the low-voltage winding-to-ground insulation and includes the low-voltage terminals. Itis commonly used in the description of transformer insulation designations.
Frequency Response Analysis (FRA):sensitive diagnostic technique for detecting changes in theclectrical characteristics of power transforimer windings. Such changescan result from various types oflectrical or mechanical stresses (shipping damage, seismic forces, loss of clamping pressure, short circuitforces, insulation failure, etc.). The test is non-destructive and non-intrusive and can be used either as astand-alone tool to detect winding damage, or as a diagnostic tool to pinpoint damages detected in othertests (e.g., insulation power factor, dissolved gas analysis, or short circuit impedance tests). FRA consistsof measuring the admittance or impedance of the capacitive and inductive elements comprising thetransformer windings. The measurement is performed over a wide range of frequencies and the results arecompared with a reference “signature” or “fingerprint of the winding to make a diagnosis
Frequency Response Analysis (FRA) magnitude: The FRA magnitude is the signal amplituderelationship between the reference (input, Vin) and measured (output, Vout) signals. It is often representedas decibels: MAG(dB)= 20*logl0(Vout/Vin), and contains the effect of the characteristic impedance of themeasurement systemm.
Frequency Response Analysis (FRA) phase angle: The phase angle shift of the response relative to thatofthe injected signal.
Frequency Response Analysis (FRA) resonance frequency: The term FRA resonance frequency isgenerally used to describe FRA Magnitude maxima or minima appearing in the frequency responsefunction of a transformer, accompanied by a zero value appearing in the phase angle of the frequencyresponse function. In practice, a power transformer is represented by a complex, distributed RLC circuit.which may include several FRA Resonance Frequencies over a given frequency range. FRA Magnitudmaxima occur at frequencies where the inductive and capacitive reactive impedance elements comprisingthe equivalent circuit are equal in magnitude, thereby resulting in zero net reactive impedance oralternatively as an infinite net reactive impedance as viewed from the terminals. The number of FRAResonance Frequencies occurring over a given frequency range depends on the design and construction otthe transformer.
Frequency Response Analysis (FRA) transfer function: The FRA transfer function is a complexfunction of frequency consisting of FRA magnitude and FRA phase angle
Frequency displacement: Is the frequency shift of the recognizable areas of the Frequency ResponseAnalysis (FRA) wave shape, ost notably the resonant frequency points, between the amplitude or phaseangle measurement of the test specimen and the reference measurement.