consider a circular loop (a particle accelator). Suppose any particle moves their with speed ≈ c. Now let the radius be such that it completes loop in 1 sec. Therfore velocity at any postion in the loop is c with direction tangent to it. So consider two point A & B where they are at 90 degree to each other. So Δv = √2*c. Therfore acceleration in Δv/Δt = √2*c/0.25 (Since it had only travelled one-quatar of loop). Therfore acceleration is 4*1.44*c > c. So is it a violation of special relativity or such process is not possible or special relativity allows acceleration to be greater than c. Time & radius is given from electron's frame. Thank you!