Reverse power flow in electrical distribution networks poses a significant safety and operational hazard, particularly in systems where customer-side backup sources such as diesel generators, solar photovoltaic arrays, and battery energy storage systems are connected to the low-voltage distribution network. When a grid fault occurs and backup generation activates, uncontrolled reverse power flow can energise dead sections of the distribution network, endangering maintenance personnel, causing damage to distribution transformers, and producing out-of-synchronism fault currents that exceed equipment ratings. Anti-islanding conditions arising from solar overproduction present an additional class of reverse power hazard that conventional overcurrent protection alone cannot address.

This project presents the design, implementation, and demonstration of an interactive simulation platform for reverse power protection in a grid-connected backup power system. The simulated system models a complete distribution network topology comprising an 11 kV utility grid supply, a step-down distribution transformer, an 11 kV high-voltage busbar, a 415V/220V low-voltage busbar, an automatic transfer switch, customer loads, and dual backup sources consisting of a diesel generator and a solar-plus-battery system. Reverse power protection is implemented via a wattmetric reverse power relay installed at the distribution board of each distribution transformer, consistent with established protection coordination practice.

The simulation platform was developed in two complementary environments. A browser-based interactive simulation provides animated single-line diagram visualisation with particle-flow representation of power direction, real-time status telemetry, and an event log with timestamped protection operations. A MATLAB graphical user interface implementation provides the same functionality within an engineering analysis environment suitable for academic instruction and professional demonstration. Both implementations support four operational scenarios: normal grid-to-load power flow, grid fault with automatic transfer switch operation and backup source activation, backfeed attempt with reverse power relay trip and grid isolation, and solar overproduction triggering anti-islanding protection.

The detection methodology implemented is the wattmetric method, in which the relay continuously computes real power P = V · I · cos φ using voltage transformer and current transformer inputs. When the phase angle between voltage and current exceeds 90 degrees, the cosine term becomes negative, yielding a negative real power measurement that indicates reverse power flow. An interactive phasor diagram enables the user to vary the current phase angle continuously and observe the transition from forward power through the reactive power boundary to reverse power, with relay pickup threshold and time delay settings adjustable in real time.

The simulation demonstrates that the reverse power relay provides reliable discrimination between legitimate backup power delivery to customer loads and hazardous backfeed conditions, without nuisance tripping during reactive load switching or motor starting transients. Results confirm that correct placement of the reverse power relay at the distribution transformer distribution board, combined with appropriate pickup threshold settings of three to ten percent of rated power and a time delay of 0.1 to 2.0 seconds, provides effective protection of the distribution network under all simulated fault conditions.

The platform serves as both an engineering design reference and a pedagogical tool, bridging the gap between theoretical relay protection principles and practical distribution system protection scheme implementation.