In this paper, a new numerical algorithm for high-accurate computation of exact Carson formulas is developed. Carson formulas are used for computing of per-unit-length (pul) self and mutual impedances of infinitely long parallel conductors. The proposed algorithm is based on piecewise linear approximation of kernel function and analytical integrations of piecewise-linearized kernel function multiplied by the rest of two integrands. Using proposed numerical algorithm, high-accurate results with desired n-digit accuracy can be easily obtained. Results computed by two approximation methods are compared with high-accurate results computed by proposed numerical algorithm for power frequency.