What is the purpose of a differential protection scheme in a WEC electrical system?

The purpose of a differential protection scheme in a Wave Energy Converter (WEC) electrical system is to quickly detect and isolate internal faults within a specific piece of equipment, such as a transformer or a generator. It operates on the principle of Kirchhoff's current law, which states that the sum of currents entering a node (a point in a circuit) must equal the sum of currents leaving it. A differential protection scheme compares the current entering the protected equipment with the current leaving it. Under normal operating conditions or during external faults (faults outside the protected zone), these currents should be equal (or have a known, predictable relationship accounting for transformer turns ratio). However, if an internal fault occurs within the protected equipment, such as a winding short circuit, the currents entering and leaving the equipment will no longer be equal. The differential relay, which is the heart of the protection scheme, detects this difference in current (the differential current) and immediately trips a circuit breaker to isolate the faulty equipment from the rest of the electrical system. This rapid isolation minimizes damage to the equipment, prevents the fault from spreading to other parts of the system, and improves overall system reliability. The differential protection scheme is highly sensitive and selective, meaning it can detect even small internal faults while remaining stable during external faults.