Optimising Prefix Sum
The solution looks good, my suggestions:

Generators: the function itertools.accumulate returns a generator which doesn't create the whole list in memory, but calling list on it does create the actual list in memory. This is probably why you get the runtime error. Changing Operations from:
def Operations(size, Array):

    values = [0] * (size+2)
    for a,b,k in Array:
        values[a] += k
        values[b+1] -= k

    values = list(accumulate(values))

    Result = max(values)
    return Result

To:
def Operations(size, Array):
    values = [0] * (size + 2)
    for a, b, k in Array:
        values[a] += k
        values[b + 1] -= k
    return max(accumulate(values))

solves the problem and all tests pass.
PEP 8: function names should be lowercase, with words separated by underscores as necessary to improve readability. Variable names follow the same convention as function names. More info. The function name is probably given by HackerRank, but the variable names Array and Result should be lowercase.

FYI, this is my old review on the same problem.