At 132 kV, we purchase the GIS with the sensors fitted, check them at commissioning, then have the option to install a permanent monitor down the track, or perform periodic online PD checks with a handheld meter.
I do recommend at least purchasing with the factory installed sensors, then if you don't install the monitor now, you can easily do it in the future. Monitoring equipment will no doubt come down in price, so even if it is not now, it may become economically viable to install.
