For an untwisted affine Kac-Moody Lie algebra g̃, and a given positive integer level k, vertex operators x(z) = ∑ x(n)z−n−1, x ∈ g, generate a vertex operator algebra V . For the maximal root θ and a root vector xθ of the corresponding finite-dimensional g, the field xθ(z) k+1 generates all annihilating fields of level k standard g̃-modules. In this paper we study the kernel of the normal order p...