What are the types of shielded isolation transformers?

Shielded Isolation Transformers with Single Electrostatic Shield

This is the simplest type of shielded transformer with one grounded shield extending from top to bottom between the primary and secondary windings. This will typically supply 60dB of common mode noise attenuation from 100Hz through 1MHz. Up to 100dB of TMNA and 40dB at 1000kHz of CMNA can be obtained with effective close coupling and low capacitance.

Shielded Isolation Transformer with Double Electrostatic Shields

This has two grounded shields extending top to bottom between the primary and secondary windings and between the secondary windings and the core. This will typically supply 60-80dB of common mode noise attenuation from 100Hz through 1MHz.

Shielded Isolation Transformer with Triple Electrostatic Shields

This has three grounded shields extending top to bottom between the primary and secondary windings and between the secondary windings and core and covering the outer winding. Little benefit is gained by having the third shield. This will typically supply 65-80dB of common mode noise attenuation from 100Hz through 1MHz.

Note that recent testing may indicate that electrostatic shields have little to no benefit in typical applications where the secondary is grounded.