Electrical Reliability

What is SFRA Test? Frequency response analysis (often referred to as FRA or SFRA ) is a powerful and sensitive method for testing the mechanical integrity of transformer cores, windings, and press frames, in power transformers. The winding of transformer may be subjected to mechanical stresses during transportation, heavy short circuit faults, transient switching impulses and lightening impulses etc. These mechanical stresses may cause displacement of transformer windings from their position and may also cause deformation of these windings. SFRA Test can detect, winding deformation – axial & radial, like hoop buckling, tilting, spiraling displacements between high and low voltage windings partial winding collapse shorted or open turns faulty grounding of core or screens core movement broken clamping structures problematic internal connections How SFRA works? Transformers consist of multiple complex networks of capacitances and resistors that can generate a unique ...

To evaluate any asset or system with the RCM(Reliability Centered Maintenance) process Following seven questions are to be asked, What are the functions and associate performance standards of the system in present operating condition? How the system is failed to fulfill its functions? What are the causes for the failure of its functions.? What happen when its function failure occurred? In what way each failure matter or failure significance or consequences? What can be done to prevent or predict the failure? What happen if any proper proactive task cannot be found to prevent or predict the failure? Any team ask this basic Seven question to the system or the asset to be evaluated via RCM process for determination the maintenance requirement to be done easily. #RCM #realibility

The dielectric response is a unique characteristic of the particular insulation system. The increased moisture content of the insulation results in a changed dielectric model and, consequently, a changed dielectric response. By measuring the dielectric response of the equipment in a wide frequency range, the moisture content can be assessed and the insulation condition diagnosed. The test connections and modes are the same as used in a traditional transformer insulation power-factor test with the difference being the test is performed at a low voltage, up to 200 Vp-p, and the test is performed at frequencies from 1 kHz to 1μHz .  In this Figure the response curve for oil-impregnated paper. This curve shows a frequency vs. dissipation factor relationship. The higher frequencies display the moisture and aging of the cellulose. Moving from left to right the frequency is reduced and the oil conductivity properties are displayed. In the millihertz range, the ...

Testing of cable with conventional method is "DC hipod" testing.A considerable rise in premature failures was observed when polymeric cables (XLPE, EPR, etc.) were introduced into the electric grid and readily being tested with DC. This failure with DC hi-Pot testing is cause of trapped charge within the defects of Insulation due to intense charge migration via Unidirectional DC field When DC test completed and AC supply applied to the cable this charge lead to rapid generation of electrical tree and subsequent failure. VLF testing benefits Potential failures should happen during the actual test so that repairs can be made immediately because test time of VLF testing is more about 15 min to 60 min. Lower power and current requirement for testing which significantly reduced size/weight to allow for a very portable high voltage tester. Both benefits describes briefly as below, Under DC test, test object remain less time under voltage stress than VLF test...

Here I'm providing the equation for calculate restraining quantity in differential relay. %restrain= I diff setting + (I1 * CT1 error) + (I2 * CT2 error) I diff setting =Differential setting in relay(ex. 0.2Amp) I1 =Current injected in CT for 1 end relay for testing I2 =Current injected in CT for 2 end relay for testing Ct erro r=5%(if injected current <1) OR 15%(if Injected current >=1) During testing we found Ij1=Ij2, because generally same current is seen during fault bay both end relay Case-1 Injected current=1Amp,I differ setting=0.2( Assume CT error 15% when Injected current >=1) %restrain= I diff setting + (I1 * CT1 error) + (I2 * CT2 error)                    =0.2 +(1 * 0.15) + (1 * 0.15)                    =0.50   %restrain =50%(around) Cas...