POWER ELECTRONICS

UNIT I: Thyristor Silicon controlled rectifier (SCR), construction and principle of operation, two-transistor analogy, static and dynamic characteristics, gate characteristics, ratings, series and parallel operation of SCRs, over voltage and over current protections, protection against high di/dt and high dv/dt, use of UJT for pulse generation. UNIT II: Phase Controlled Rectifiers Principle of phase control, performance parameters, single-phase half wave and full wave controlled rectifiers, mid point and bridge converters, full controlled converters, half controlled converters, comparison between full and half controlled converters, three-phase half wave and fully controlled bridge converter, three-phase semi-converter, effect and source inductance in single-phase and three-phase bridge converters, commutation or overlap angle, effect of overlap. UNIT III: DC To DC Conversion Principle of chopper operation, controlled strategies, step up chopper, step down chopper, chopper configuration, forced commuted chopper, voltage commutated chopper, current commuted chopper, Load commuted chopper, Jone’s chopper, Morgan chopper. UNIT IV: Inverter Classification of inverters, voltage source inverter, current source inverter, series resonant inverter, modified series resonant inverter, parallel inverter, bridge inverter, auxiliary commuted single-phase inverter, complementary commuted singe-phase inverter, and three-phase inverter, Cyclo-converters: basic principle of operation, step-up and step down single-phase to single-phase Cyclo-converter. UNIT V: Speed Control Of DC Motors Four-quadrant operation of series and shunt DC motors, constant HP and constant torque operation, various schemes of speed control (single converter, double converter, chopper), modern semiconductor devices, power transistors, power bipolar junction transistors, steady state characteristics, switching characteristics, switching limits, safe operating area, power MOSFET: steady state characteristics, switching limits, safe operating area, IGBT: steady state characteristics, safe operating area.

POWER SYSTEM PROTECTION & SWITCHGEAR

UNIT-I REALY: Terminology, Basic circuit, realy connection with trip circuit and circuit breaker, objectives of protection, types of relay, construction and operation of instantaneous over current realy. I.DM.T. Relay, directional Unit, differential relay, percentage differential relay, Buchholz relay, Generalized torque expression, logical construction of impedance reactance, MHO and Off-set MHO Relays using generalized torque expression. UNIT-II Protection of Alternators: Differential protection, Protection of stator against phases to ground fault, phase to phase faults, inter turn fault, protection against unbalanced loading, protection of rotor against ground fault, field failure, reverse power, back up protection, field suppression, protection of bus bars, frame leakage protection, differential protection. UNIT III Protection of transformers & Feeders: differential protection of transformers for different winding configurations, difficulties encountered in differential protection and their remedies, protection of feeders, protection of ring main and parallel feeders, protection of radial feeders by over current relays, distance relays and carrier current protection scheme. UNIT IV Static Relays: directional relay, impedance relay, admittance relay and admittance relay, amplitude comparator, phase comparator, duality between amplitude and phase comparators. UNIT V Circuit Breakers and Fuses: Arc formation, arc interruption and restriking voltage, current chopping, resistance switch, Air blast circuit breakers, minimum and bulk oil circuit breakers, SF6 and Vacuum Circuit breakers, circuit breakers rating, testing of CB, definitions of terms in fuses, HRC fuses.

POWER SYSTEM ANALYSIS

UNIT I: Symmetrical three-phase short circuit on power systems, calculation of interrupting capacity of circuit breakers, current limiting reactors, symmetrical components, synthesis of unbalanced phasors from symmetrical components, representation of phase variables voltage, current and power in terms of symmetrical components, sequence impedances of power system elements, sequence networks of power system elements, phase shift in star-delta transformer banks. UNIT II: Unsymmetrical Short Circuits Single line-to-ground, line-to-line, double-line-to-ground faults on unloaded alternators, unsymmetrical faults on power systems, fault through impedance, open conductor faults. UNIT III: Power System Stability The stability problem, steady-state stability, transient stability, Swing equation, Equal area criterion of stability, application of equal area criterion, step-by-step solution of the swing equation, factors affecting transient stability, UNIT IV: Load Flow Studies Formulation of bus admittance matrix, formulation of load-flow equations and their solution techniques, digital computer techniques, reactive power optimization. UNIT V: Automatic Generation & Voltage control Introduction, single area and two area load frequency control, and Economic dispatch control, optimal (two area) load frequency control, automatic voltage control, Tie-line bias control.