Bus Zone Protection: Bus Zone Protection includes, besides the bus itself the apparatus such as circuit breakers, disconnecting switches, instrument transformers and bus sectionalizing reactors, etc. Although bus zone faults are rare, experience shows that bus zone protection is highly desirable in large and important stations. Bus zone is more vulnerable to the effects of …
Motor Protection: Motor Protection – There is a wide range of motors in existence for various purposes. However, the fundamental problems affecting the choice of protection are independent of the type of motor and the type of load to which it is connected. The motors under discussion here are a.c. motors which include synchronous motors …
Direct Connected Generator Protection: Direct connected generators are normally of smaller ratings and a typical scheme of Direct Connected Generator Protection for a 30 MW generator is shown in Fig. (6.21). It consists of the following protections: Unbiased differential protection. Backup overcurrent protection. Negative phase sequence protection. Standby earth fault. In addition to these protections …
Prime Mover Protection: In the event of prime-mover failure the machine starts motoring meaning thereby that it draws electrical power from the system and drives the prime-mover. This condition imposes a balanced load on the system, which can be detected by a power relay with a directional characteristic, as Prime Mover Protection illustrated in Fig. …
Overload Protection Relay: Overload Protection Relay – Continuous balanced overloading of a machine causes overheating in the stator winding. An obvious solution to this is the application of overcurrent relays; but this is not usually provided because this discriminates by time, it must be arranged to discriminate with the slowest relay on the system which …
Unbalanced Loading Protection of Generator: Unbalanced Loading Protection of Generator – Whatever be the cause of the unbalance it is obvious that the negative phase sequence current will result in heating of the stator. In case of high-speed turbo-generators, the continuous current which can be carried is usually between 10 and 15% of the positive …
Loss of Excitation Protection: Two distinct effects of Loss of Excitation Protection are that the machine starts drawing magnetizing current of large magnitude from the system, and the slip frequency emfs induced in the rotor circuit; both of them cause overheating of the rotor. Loss of Excitation Protection can be detected by measuring the reactive …
Rotor Protection: Rotor Protection – As pointed earlier rotor windings may be damaged by earth faults or open circuits. Figure (6.16) shows a modern method of rotor earth-fault detection. The field is biased by a d.c. voltage which causes current to flow through the relay R for an earth fault anywhere on the field system. …
Stator Protection: Stator Protection – The type of stator faults likely to occur have been discussed already. The earth-fault current is usually limited by resistance in the neutral of the generator. Depending upon the amount of resistance in the neutral circuit of the generator the fault current may be limited to a value between 200A …
Generator Faults: Generator faults can be considered under the following heads. (a) Stator Faults: These include the following: Phase-to-earth faults. Phase-to-phase faults. Inter-turn faults. Most faults occur in the stator windings and their connections and majority of these are earth faults. Phase faults and inter-turn faults an less common, these usually develop into an earth …
