AUTOMATIC LOAD SHARING OF DISTRIBUTION TRANSFORMERS USING INTELLIGENT CIRCUIT BREAKER CONTROL AND PERFORMANCE ANALYSIS IN MATLAB/SIMULINK

This paper has presented a comprehensive design, modelling, and simulation study of an Automatic Load Sharing (ALS) scheme for two parallel distribution transformers — T1 (150 kVA, 11kV/430V) and T2 (63 kVA, 11kV/430V) — in a three-phase 11kV distribution network using MATLAB/Simulink R2023b. The five-breaker circuit topology (Breakers 1–5) with programmable switching logic was modelled with component parameters conforming to IEC 60076-1 and IS 2026 standards. The following principal conclusions are drawn: •       Simulation Accuracy: The MATLAB/Simulink model reproduces the steady-state operating parameters with less than 1% error for primary voltage (10,999.63V vs. 11,000V theoretical), primary current (1.05A vs. 1.052A), input power (18,483.13W vs. 18,510W), and power factor (0.92 vs. 0.921) — confirming model validity and suitability for engineering design validation. •       Load Sharing Performance: Under normal operating conditions, T1 carries 38.2% and T2 carries 47.6% of their respective rated capacities. The ALS scheme successfully redistributes load during simulated overload events, maintaining both transformers within safe loading limits and bus voltages within ±1.21% of nominal 430V across all tested scenarios. •       Switching Speed: All five breakers operated within their specification response times (secondary breakers ≤ 50ms, primary breakers ≤ 80ms), with the complete load transfer sequence completing in under 120 ms — fast enough to prevent cumulative thermal damage to transformer windings during transient overload events. •       Transient Overvoltage: Bus coupler closing transients were limited to 1.08 per-unit — below the IEC 60255-27 recommended maximum of 1.15 pu — demonstrating safe load transfer without insulation stress. •       System Efficiency: System efficiency of 98.07% was maintained under normal loading conditions. Prevention of overloading via the ALS scheme avoids disproportionate copper loss increases, saving approximately 1,100 kWh/year and ₹7,700/year per installation in energy loss costs alone. •       Emergency Backup: In the T1-offline emergency scenario, T2 successfully supplies all load at 91% of its rating via the bus coupler, demonstrating viable backup capability within IEC 60354 continuous overloading limits.

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