+/- 0.2% is the recomended figure. Preferably synchronise when the generator is <0.2% fast. We synchronise several machines within this tolerance. Protection settings are +0.5Hz/0.5secs for over frequency and -2.0Hz/0.5secs for under frquency during parallel operation.
If it is a higher voltage cable, the semiconducting screen is used for voltage stress relief to reduce the effect of cable insulation imperfections. The semiconducting varnish or extruded layer is in contact with a copper tape for earth fault current carrying capacity.
