What is Generator differential protection?

Differential protection for a generator is mainly employed for the protection of stator windings of generator against earth faults and phase-to-phase faults. The stator winding faults are very dangerous, and it causes considerable damage to the generator. For the protection of stator winding of the generator, the differential protection system is used for clearing the fault in the shortest possible time for minimizing the extent of a damage.

Dear frnd,

Over view of Differential Relay:

While over-current, voltage, distance and directionality are powerful techniques, all of them involve some compromise between the objectives of reliability, security, speed, selectivity and economy. Differential protection is different. It is profoundly simple, inherently secure, highly reliable, fast, and reasonably economical. As a result, differential protection is the most important concept in protection. The concept is a direct extension of Kirchoff’s current law – the sum of all currents into a region must be zero. Current transformers are placed at each electrical terminal of the protected zone and wired together as indicated within the zone. For external faults, where fault current passes through both CTs as same ratio.

The zone, current circulates in the current transformer secondary without passing through the relay. If the fault is internal to the zone, then the currents introduced into the current transformer secondary oppose each other and are forced to flow through the relay. The basics of a differential application include:

• CT at each power connection to the protected zone
• All CT’s have the same rating
• Careful attention to assure proper ct connections
• Differential protection is primary protection: it cannot provide backup protection for remote zones

Internal Protection of Generator in case of Phase to Phase Short Circuit or phase to Groud Short Cases.

Mostly happen due to over Voltage and Over loading on Generator,

Breaking of insulation due to High volt or High current.

relais thermique st prévue pour la protection contre les défauts entre phases (courts-circuit)

over current protection, winding over heating of the stator wingings of a generator stator

In higher size generators the differential relay is provided to avoid unbalanced loads.The said relay is very vital for all huge generators.There are  six take off leads in generators Three to bus side and three to star point earthing side,between bus and between star side the cts of same size and same burdon is to be provided,when there will be any un balanced current devoloped the differential  protection relay will come in line and trip the generators.

with best regards,

Thiagarajan.E