CT does not have a primary winding but the line acts as primary over which we wound the secondary winding. So primary current is line current.

If CT is OC, then secondary current is 0 and there is no secondary flux to oppose primary flux due to which flux becomes very high and then very high emf is induced in secondary and cause residual magnetism in the core which will increase phase angle error.

PT is connected with line voltage and its load current in dependent on the burden. When we connect load on secondary the secondary current flows and this tends to reduce primary flux but transformer is constant flux device so primary draws extra current from source to compensate the secondary flux.