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The scaling behaviour of vortex-glass superconductivity is studied, by measuring the resistive transition as well as the I-V curve under a variety of magnetic fields, in a series of V doped YBa2Cu307_y samples with different grain sizes. The equilibrium phase boundary line between the normal and superconducting phases in the H-T plane obtained by fitting the resistive transition is consistent with that obtained by the I-V curve measurements. As the magnetic field is lower than a certain value, Hs, the scaling exponents are magnetic-field independent, but at H = H s, they begin to increase with the magnetic field and gradually get saturation. The switch field, Hs, decreases with decreasing the grain size in the samples. The results show that the magnetic-field-dependent scaling behaviour of the I-V curve observed in weak-link containing systems originates from the transition of a "weak" vortex-glass state to a "strong" vortex-glass state.