Differential protection is a power system protection mechanism that detects and isolates malfunctioning parts or equipment, such as
• Generators,
• Motors, and
• Transformers,
inside a predetermined protected zone.
Typically, it operates on the basis of constantly contrasting the current entering (or) leaving the protected zone (or) equipment.
A basic differential protection mechanism is illustrated below.
The concept is simple: under normal (or) external fault conditions, the current entering & leaving a protected zone is balanced, and no action is required.
However, if an internal fault happens, the differential relay detects the mismatch immediately, providing for fast and precise isolation.
A thorough grasp of these operating conditions is essential for dependable transformer, generator, & motor safety, particularly as grids get smarter and more complex.
In the most basic kind of differential protection, 2 CTs are utilized to defend a piece of equipment.
Assume that both CTs are identical, meaning that they have the same turn ratio and other features, and that they will supply the same secondary current if primary remains constant.
Both CTs are connected to a differential relay, such that no current flows through the relay’s operational coil when there is no fault.
During a fault, however, if there is a substantial variation in current, an amount of current will flow through the operational coil, activating the relay and sending a trip signal to the circuit breaker to isolate the protected zone.