Your iPad will suffer no ill effects through being connected to its Power Adapter for extended periods. Your iPad will automatically regulate and optimise charging - and will not overcharge the battery.
When used in retail or kiosk applications - where external power is connected for extended periods of time - the iPad may automatically modify its charging strategy and limit battery charge to ~80% of maximum. This modified charging strategy is designed to reduce chemical ageing that might otherwise occur if 100% charge is maintained at all times.
Nominal 100% charging will be restored when a normal charge/discharge routine is restored.
More information about iPad’s battery management can be found here:
About iPad and iPhone Charge Management Feature – Apple Suppo