Consider the table given :

Constructional feature	Machine type	Mitigation
P. Damper bars	S. Induction motor	X. Hunting
Q. Skewed rotor slots	T. Transformer	Y. Magnetic locking
R. Compensating winding	U. Synchronous machine	Z. Armature reaction
	V. DC machine

The correct combination that relates the constructional feature, machine type and mitigation is

The correct combination that relates the constructional feature, machine type, and mitigation is P-U-X, Q-S-Y, R-V-Z.

Let us analyze and match each combination step-by-step:

1. Damper bars (P) ⇒ Synchronous machine (U) ⇒ Hunting (X)
In synchronous machines, sudden variations in load can cause the rotor to oscillate about its equilibrium position. This phenomenon is known as hunting. To mitigate or damp out these oscillations, damper bars are placed in the rotor pole faces of the synchronous machine. When hunting occurs, relative motion is set up between the rotating magnetic field and the damper winding, which induces currents in the damper bars. According to Lenz's law, these induced currents oppose the relative motion (oscillations), thereby mitigating hunting.
Thus, the correct match is P - U - X.

2. Skewed rotor slots (Q) ⇒ Induction motor (S) ⇒ Magnetic locking (Y)
In squirrel cage induction motors, if the number of rotor slots is equal to or an integral multiple of the stator slots, the rotor teeth can align exactly with the stator teeth. This causes a strong magnetic attraction between them, resulting in the rotor failing to start, a phenomenon known as magnetic locking (cogging). To prevent or mitigate magnetic locking, the rotor slots of the induction motor are skewed (made slightly angular relative to the shaft).
Thus, the correct match is Q - S - Y.

3. Compensating winding (R) ⇒ DC machine (V) ⇒ Armature reaction (Z)
In DC machines carrying heavy loads, armature reaction occurs due to the magnetic field produced by the armature current, which distorts and weakens the main field flux (specifically at the pole tips). To neutralize the cross-magnetizing effect of the armature reaction in the interpolar region under the pole faces, a compensating winding is placed in slots on the pole faces of the DC machine.
Thus, the correct match is R - V - Z.

Combining these matches, we get:
P-U-X, Q-S-Y, R-V-Z