Table 1 Summary of different techniques used for protection coordination of distribution systems without DER penetration

Curve fitting [1]

Time inverse operating characteristics are generated for various types of linear & non-liner functions relay time operating curves.

Only method was available at that time.

Poor accuracy

Graph theory [3, 5, 7]

Break point relays are identified

Proper selection of break point lead to converged solution of relay coordination problems.

Selection of break point is critical

Analytical method [16,17,18,19]

Gradient, lagrange multiplier and other classical problem formulation are formulating relay coordination problems.

Mostly applicable for radial distribution systems.

Requires large no. of iteration and initial guess is essential for convergence of the solution of problem.

Linear optimization Based Techniques [22, 23]

Relay coordination problem is formulated as linear programming problem.

Helpful for optimizing only TDS

PS are selected based on the experience of the designer/operator

Non-Linear optimization Based Techniques [30]

Relay coordination problem is formulated as non-linear programming problem

Both TDS and PS are selected optimally.

Since relay coordination problem are non-convex, therefore there is chance of local minima trap.

Hybrid optimization techniques [38, 40].

Both analytic and optimization method are applied.

Capable to solve the relay coordination problem for big interconnected systems and global optimal solution can be easily achieved.

Works for fixed network topology.

Fuzzy & neuro based optimization [55]

Concept of fuzzy and training of neurons is extended for protection coordination problems.

Effective protection coordination for different network pre-identified network topologies.

Fails for respond when new network topology comes in existence during operational conditions.