To my knowledge Ex-e concept/ design is approved for Zone 1 & Div 1 operation.
Do you have any written statement or any standard showing that otherwise?
Ex e refers to "increased safety due to a lack of arcs, sparks, or sufficiently hot surfaces". In some medium voltage machines ("medium" being anywhere from 1 to 10 kV), the air gap may be small enough that during specific transient events, a spark will develop between stator and rotor steel which could - in a Zone 1 environment - ignite a flammable gas mixture inside the machine enclosure. This does not occur with a lower (i.e. < 1 kV) rating because there is insufficient energy to cross the gap.
Note that both altitude (due to decreased gas density) and humidity - and the presence of conductive contaminants - may all affect the voltage level at which the phenomenon occurs.
As Kiribanda pointed out - there are a lot of machines out there operating in Zone 1 environments that utilize voltages up to 13.8 kV. Enclosures may differ from their low voltage relatives, and maybe different precautions in terms of preventing the ingress of combustible gas.
Converting energy to motion for more than half a century
Also the HP/ kW ratings of Ex e motors are little lower than a Ex n motors due to the inherent limitations of Ex e design concept.
But still it is good for Zone 1 applications.
All machines are well insulated for their rated voltage. I don't see how the MV machines could create a spark across the air gap. PD across the stator slot walls (in poorly made machines may be) but definitely not across the air gap.
In some MV generators we’ve seen surface PD between end arms in the end winding region due to inadequate “vent spacing”, I would assume that would not be ideal for explosive environments.
