Generating Unit Maintenance Classification
The generator of the possibility of failure and normal working state, according to the generating unit capacity to selectively install the following protection:
1.Longitudinal differential protection: for stator winding and lead-out wire interphase short circuit protection.
2. Transverse differential protection for stator winding phase: interturn short circuit protection. Only when a stator winding
two and above the parallel branch to form two or three neutral point leading-out terminals, it installs this kind of protection.
3. Single phase grounding fault protection for generator stator windings: single-phase grounding protection.
4. Excitation loop grounding protection: for the excitation circuit grounding fault protection.
5. Low excitation, loss of field protection: in order to prevent large generator underexcitation ( excitation current is less than the static stability limit corresponding to the excitation current ) or loss of excitation ( excitation current is zero ), from the system to absorb a large amount of reactive power of system adverse effects, 100MW and above the capacity of the generator are installed in this protection.
6. Overload protection: generator long time exceeds the rated load acting on the signal protection. Generator stator only equipped with overload protection; large generator are respectively provided with stator overload and excitation winding overload protection.
7. Stator winding over current protection: when the generator longitudinal differential protection and short circuit, short circuit protection circuit breaker components or reject action, such as external short circuit protection of the reserve, also used as longitudinal differential protection backup protection.
8. Stator winding over-voltage protection: to prevent sudden rejection to the full load caused by the stator winding voltage, water turbine generator and turbine generator are installed in over voltage protection, small turbine generator are usually not equipped with over voltage protection.
9. Negative sequence current protection: power system short-circuit or asymmetrical three-phase load unbalanced (such as electric locomotives, electric arc furnace load proportion is too large ), will make the rotor end, retaining ring inner surface current density large parts of overheating, causing the rotor to local burns, therefore should be installed with a negative sequence current protection.
10. Out of step protection for large generator: response and system oscillation of out of step protection.
11. Reverse power protection: when the steam turbine main steam valve closed by mistake, or machine furnace protection action to close the main valve and the generator outlet circuit breaker without tripping, from power system active power caused by the absorption of steam turbine accident, so large units to be equipped with a reverse power relay a reverse power protection, for the protection of steam turbine.
