Repeated Shoot-Out on Red Phase of a 33kV Single Core PLWS Armoured Cable

Hi all, i need your urgent advice/solution to this problem. Firstly this cable (3no) is terminated to the primary side of a 2.5mva trafo feeding a 50mld water treatment plant. During operations the feeder tripped on over-current. Fault investigated and found out that the j&p fuse dropped on the red phase, Amoured cable terminated to the red phase on trafo primary side had a blow-out on the Raychem termination,also the out-going 11kv cable from the end box of the fused extension of the rmu was also burnt.Cable injection tests were carried out and results ok despite the fact that water was found between the steel wire Armour and the outer pvc of the Armoured cable,insulation readings are in the tetra range! Cable ends re-terminated using raychem kits,a set of new 50A fuses were fused on the j&p,system put on potential and ok.

Secondly,after 4 days the problem re-occurred and the blow-out was on the red phase of trafo primary! However, no fuse dropped- only tripping of the 33kv feeder at the transmitting station thus isolating our feeder.

What could cause this re-occurrence? Is this cable bad? or is there something we are not seeing? Ambient temp. at location is 37degC,Nominal plant loading is 1.4mva,rmu over-current setting is 100A.

Thanks in advance. R4ROTY