Free Expert Guides on Power Systems, Circuit Design & Electrical Troubleshooting

There are different contacts connected in series along a trip circuit of an electrical circuit breaker. There must be some situation when the circuit breaker should not trip even a faulty current passes through its power contacts. Such situations are low gas pressure in SF6 circuit breaker, low air pressure in pneumatic operated circuit breaker etc. In this situation the trip coil of the CB must not be energized to trip the CB. So there must be NO contacts associated with gas pressure and air pr

For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor. There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator. Due to such symmetrical distribution, when three phase power supply is applied to the stator winding, a rotating magnetic field is produced. This field rotates at synchronous speed. The rotor is created in induction motor mainly by n

There are different kinds of transformers such as two winding or three winding electrical power transformers, auto transformer, regulating transformers, earthing transformers, rectifier transformers etc. Different transformers demand different schemes of transformer protection depending upon their importance, winding connections, earthing methods and mode of operation etc.It is common practice to provide Buchholz relay protection to all 0.5 MVA and above transformers. While for all small size di

Before applying proper electrical protection system, it is necessary to have through knowledge of the conditions of electrical power system during faults. The knowledge of electrical fault condition is required to deploy proper different protective relays in different locations of electrical power system.Information regarding values of maximum and minimum fault currents, voltages under those faults in magnitude and phase relation with respect to the currents at different parts of power system, t

This portion of our website covers almost everything related to protection system in power system including standard lead and device numbers, mode of connections at terminal strips, color codes in multi-core cables, Dos and Don’ts in execution. It also covers principles of various power system protection relays and schemes including special power system protection schemes like differential relays, restricted earth fault protection, directional relays and distance relays etc. The details of trans

Over Current and Earth Fault Protection of TransformerBackup protection of electrical transformer is simple Over Current and Earth Fault protection are applied against external short circuit and excessive over loads. These over current and earth Fault relays may be of Inverse Definite Minimum Time (IDMT) or Definite Time type relays (DMT). Generally IDMT relays are connected to the in-feed side of the transformer.The over current relays can not distinguish between external short circuit, over lo

It is essential to protect high capacity transformers against external and internal electrical faults.External Faults in Power TransformerExternal Short Circuit of Power TransformerThe short – circuit may occur in two or three phases of electrical power system. The level of fault current is always high enough. It depends upon the voltage which has been short-circuited and upon the impedance of the circuit up to the fault point. The copper loss of the fault feeding transformer is abruptly increas

This is to be noted that, the star point or neutral point of stator winding of an alternator is grounded through an impedance to limit the ground fault current. Reduced ground fault current causes less damage to the stator core and winding during ground or earth fault. If the ground impedance is made quite high, the ground fault current may become even less than normal rated current of the generator. If so, the sensitivity of phase relays becomes low, even they may fail to trip during fault. For

The rotor of an alternator is wound by field winding. Any single earth fault occurring on the field winding or in the exciter circuit is not a big problem for the machine. But if more than one earth fault occur, there may be a chance of short circuiting between the faulty points on the winding. This short circuited portion of the winding may cause unbalance magnetic field and subsequently mechanical damage may occur in the bearing of the machine due to unbalanced rotation.Hence it is always esse

Inter turn stator winding fault can easily be detected by stator differential protection or stator earth fault protection. Hence, it is not very essential to provide special protection scheme for inter turn faults occurred in stator winding. This type of faults is generated if the insulation between conductors (with different potential) in the same slot is punctured. This type of fault rapidly changes to earth fault.The high voltage generator contains a large number of conductors per slot in the