EN
The authors use coincidence degree theory to establish some new results on the existence of T-periodic solutions for the delay differential equation
x''(t) + a₁x'(t) + a₂(xⁿ(t))' + a₃x(t)+ a₄x(t-τ) + a₅xⁿ(t) + a₆xⁿ(t-τ) = f(t),
which appears in a model of a power system. These results are of practical significance.