Electrical Protection: Relays, Generators, and Power Systems, Study notes of Engineering

Download Electrical Protection: Relays, Generators, and Power Systems and more Study notes Engineering in PDF only on Docsity! Q: Relay and its types? Relay: Relay are electrical switches that open or close another circuit under certain conditions. Types of relay:  Electromagnetic relay  Solid state relay  Numerical relay Q: Overcurrent relay, types, application? Overcurrent relay: The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. Types of Overcurrent relay:  Instantaneous Overcurrent relay  Inverse time Overcurrent Relay  Definite Time Overcurrent Relay  Inverse Definite Time Overcurrent Relay  Very Inverse Definite Time Overcurrent Relay  Extremely Inverse Definite Time Overcurrent Relay  Instantaneous Overcurrent relay Application of Overcurrent relay: 1.Motor Protection:  Used against overloads and short-circuits in stator windings of motor.  Inverse time and instantaneous overcurrent phase and ground  Overcurrent relays used for motors above 1000 kW. 2.Transformer Protection:  Used only when the cost of overcurrent relays are not justified.  Extensively also at power-transformer locations for external-fault back-up protection. 3.Line Protection:  On some sub transmission lines where the cost of distance relaying cannot be justified.  primary ground-fault protection on most transmission lines where distance relays are used for phase faults.  For ground back-up protection on most lines having pilot relaying for primary protection. 4.Distribution Protection: Overcurrent relaying is very well suited to distribution system protection for the following reasons:  It is basically simple and inexpensive.  Very often the relays do not need to be directional and hence no PT supply is required.  It is possible to use a set of two O/C relays for protection against inter-phase faults and a separate Overcurrent relay for ground faults. Q: Generator and alternator? Basis for Comparison Alternator Generator Definition A machine that converts the mechanical energy into AC electrical power. A machine that changes mechanical energy into electrical energy (AC or DC). Current Induces alternating current Generate both AC & DC. Magnetic Field Rotating Stationary Input Supply Takes from stator. Takes from rotor. Armature Stationary Rotatory Output EMF Alternating Constant RPM (Rotation per minute) Wide Range Narrow Range Dead Battery Do not charge charge Output Higher Lower Switch gear and its role? Switch gear: