In an apparatus protection perspective, generators constitute a special class of power network equipment because faults are very rare but can be highly destructive and therefore very costly when they occur. If for most utilities, generation integrity must be preserved by avoiding erroneous tripping, removing a generator in case of a serious fault is also a primary if not an absolute requirement. Furthermore, protection has to be provided for out-of-range operation normally not found in other types of equipment such as overvoltage, over-excitation, limited frequency or speed range, etc.
It should be borne in mind that, similar to all protective schemes, there is to a certain extent a “philosophical approach” to generator protection and all utilities and all protective engineers do not have the same approach. For instance, some functions like over-excitation, backup impedance elements, loss-of- synchronism, and even protection against inadvertent energization may not be applied by some organizations and engineers. It should be said, however, that with the digital multifunction generator protective packages presently available, a complete and extensive range of functions exists within the same “relay”: and economic reasons for not installing an additional protective element is a tendency which must disappear.
The nature of the prime mover will have some definite impact on the protective functions implemented into the system. For instance, little or no concern at all will emerge when dealing with the abnormal frequency operation of hydraulic generators. On the contrary, protection against under-frequency operation of steam turbines is a primary concern.
The sensitivity of the motoring protection (the capacity to measure very low levels of negative real power) becomes an issue when dealing with both hydro and steam turbines. Finally, the nature of the prime mover will have an impact on the generator tripping scheme. When delayed tripping has no detrimental effect on the generator, it is common practice to implement sequential tripping with steam turbines.
It should be borne in mind that, similar to all protective schemes, there is to a certain extent a “philosophical approach” to generator protection and all utilities and all protective engineers do not have the same approach. For instance, some functions like over-excitation, backup impedance elements, loss-of- synchronism, and even protection against inadvertent energization may not be applied by some organizations and engineers. It should be said, however, that with the digital multifunction generator protective packages presently available, a complete and extensive range of functions exists within the same “relay”: and economic reasons for not installing an additional protective element is a tendency which must disappear.
The nature of the prime mover will have some definite impact on the protective functions implemented into the system. For instance, little or no concern at all will emerge when dealing with the abnormal frequency operation of hydraulic generators. On the contrary, protection against under-frequency operation of steam turbines is a primary concern.
The sensitivity of the motoring protection (the capacity to measure very low levels of negative real power) becomes an issue when dealing with both hydro and steam turbines. Finally, the nature of the prime mover will have an impact on the generator tripping scheme. When delayed tripping has no detrimental effect on the generator, it is common practice to implement sequential tripping with steam turbines.
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