Most (all?) ac Variable Speed Drives used for web handling have a dc link. This dc voltage is chopped using pulse-width modulation to drive the motor. The dc voltage is rectified from three-phase ac input using a rectifier or inverter. The dc voltage is about 1.35 times the ac input voltage or 621 VDC for 460 VAC input.
The dc link voltage is smoothed with a large capacitor. A high-resistance ground is used to discharge the dc link voltage when power is removed. The discharge time varies depending on the time-constant of the capacitor and discharge resistor. The discharge time may be several minutes.
Please check the user manual for the expected discharge time. I find most manufacturers omit the discharge time from their documentation. Some vendors warn of the dc voltage hazard and indicate the electrician must monitor the voltage before servicing. Wear your insulated gloves to verify the dc voltage, as well as the ac voltage, is at zero before working on the drive electrics.
We need to make checking for voltage a habit.