First of all I'm sorry I didn't notice the first sentence of the o.p.:
"I find the following terms when referring to a turbogenerator(400MVA)data sheet."
So, as a turbogenerator has a cylindrical [not a salient pole] rotor and Xd=Xq.
Second, I translated wrong instead of "field leakage reactance " into "field losses reactance" so what I noted Xs it is actually Xla [armature-stator-leakage reactance].
I have to apologize for my bad English!
Stator leakage field is "a lost field" indeed, since it does not flow with the main flux but it remains in the air space as slot and open winding ends. This includes also the magnetic field harmonics[ as differential leakage].
The negative and zero sequence reactance are used in the connection with short-circuit case as in steady state balanced regime the generator only generate
positive sequence voltage and negative and zero sequence voltages are zero.
Nevertheless, negative sequence currents can arise whenever there is
any unbalance present in the system. Their effect is to
set up a field rotating in the opposite direction to the
main field generated by the rotor winding, so subjecting
the rotor to double frequency flux pulsations. This gives
rise to parasitic currents and heating.
If a machine is operating with an earthed neutral, a
system earth fault will give rise to zero sequence
currents in the machine. This reactance represents the
machine's contribution to the total impedance offered to
these currents. In practice it is generally low and often
outweighed by other impedances present in the circuit.
If Y point is grounded through impedance Zg , then 3*Zg
will have to be added to zero sequence impedance of generator.