MPPSC SES Electrical key terms

In a linear bilateral network with several independent sources, the response in any branch equals the algebraic sum of the responses caused by each source acting alone, with all other independent voltage sources short-circuited and current sources open-circuited.

Any linear two-terminal network can be replaced at a pair of terminals by a single voltage source equal to the open-circuit voltage in series with a resistance equal to the equivalent resistance seen looking back with all independent sources deactivated.

A source delivers maximum power to a load when the load resistance equals the internal (Thevenin) resistance of the source; the efficiency at that condition is only 50 percent for a resistive source.

In a linear bilateral network, if a voltage source in one branch produces a current in another branch, the same source placed in the second branch produces the same current in the first, provided the network is unchanged.

The frequency at which a series RLC circuit's inductive and capacitive reactances cancel, leaving impedance purely resistive and current maximum; for series resonance it equals one divided by two pi times the square root of LC.

A dimensionless measure of a resonant circuit's selectivity, equal to resonant frequency divided by bandwidth, or for a series coil to inductive reactance divided by resistance; higher values give sharper resonance.

The cosine of the phase angle between sinusoidal voltage and current at a terminal, equal to real power divided by apparent power; a low value means large reactive current for the same useful power.

The tendency of alternating current to concentrate near the surface of a conductor as frequency rises, increasing effective resistance; it is why high-frequency and high-voltage conductors may be stranded or hollow.

A method that resolves an unbalanced three-phase set of phasors into three balanced sets: positive sequence, negative sequence and zero sequence, allowing unbalanced faults and loads to be analysed with per-sequence impedances.

The maximum short-circuit apparent power, usually expressed in MVA or kA at rated voltage, that a network can deliver at a point; switchgear and busbars must be rated to withstand it.

The impedance offered to the zero-sequence component of currents, which flow in phase in all three lines and return through earth or a neutral; it depends strongly on transformer winding connections and earthing.

The rise of receiving-end voltage above sending-end voltage on a lightly loaded or open-circuited long alternating-current line, caused by the line's capacitive charging current flowing through its series inductance.

The load at which a lossless line's reactive generation exactly balances its reactive absorption, equal to the square of line voltage divided by surge impedance; around this loading the voltage profile stays flat.

Ionisation of air around a high-voltage conductor when surface voltage gradient exceeds breakdown strength, producing hiss, ozone, radio interference and power loss; reduced by larger conductor diameter or bundled conductors.

The shortest path along the external surface of an insulator between two conductive parts; it must be long enough to prevent surface flashover under pollution and moisture at the applied voltage.

The standardised peak voltage, usually a 1.2/50 microsecond lightning impulse, that insulation must withstand without flashover or puncture; it coordinates insulation levels across a power system.

The total impedance, expressed in volt-amperes at rated secondary current, connected to a current transformer's secondary; exceeding the rated burden causes ratio and phase errors and possible saturation.

A scheme that compares currents entering and leaving a protected zone, such as a transformer or generator winding, and trips when their difference exceeds a setting, giving fast and selective internal-fault clearance.

An overcurrent relay that operates only when fault current exceeds a setting and flows in a chosen direction, allowing coordination in meshed or multiple-source networks where plain overcurrent grading fails.

The fractional difference between synchronous speed and actual rotor speed of an induction machine, expressed as a per-unit or percentage value; it is positive in motoring and negative in generating.

The curve relating electromagnetic torque of an induction motor to slip, showing a stable low-slip region, a maximum (breakdown) torque at a critical slip, and reduced torque at high slip during starting.

The large current drawn by a motor at standstill, typically five to eight times rated current for a squirrel-cage induction motor, which causes voltage dips and dictates starting method choice.

The effective reactance of a synchronous machine armature winding under steady-state conditions, used with excitation voltage to compute power-angle and terminal characteristics in stability studies.

The change in secondary terminal voltage of a transformer or generator from no load to full load at a stated power factor, expressed as a fraction or percentage of rated voltage.

A device that alters the turns ratio of a transformer by selecting winding taps, usually off-circuit manually or on-load automatically, to hold secondary voltage within limits as load varies.

A feedback circuit that locks the phase of a voltage-controlled oscillator to a reference signal, used for frequency synthesis, clock recovery and grid synchronisation in power converters.

A switching technique that controls the average output voltage of a converter by varying the width of fixed-frequency pulses, shifting unwanted harmonics to higher frequencies that are easier to filter.

The process by which current transfers from one switching device or thyristor to another in a converter; natural commutation uses supply voltage while forced commutation needs auxiliary circuitry.

The fraction of each switching period for which a switch or pulse train is on, equal to on-time divided by period; it sets the voltage conversion ratio in choppers and switching regulators.

A sampling theorem stating that a signal must be sampled at more than twice its highest frequency component to allow reconstruction without aliasing; it also underlies stability analysis of feedback loops.

A discrete-time transform that converts a sequence of samples into a function of a complex variable, enabling analysis of difference equations, digital filters and sampled control systems.

A plot of the closed-loop poles of a feedback system as a gain parameter varies, showing how damping and stability change and guiding compensator design.

A pair of magnitude and phase versus frequency curves for a system's sinusoidal transfer function, drawn on logarithmic frequency axes, used to read gain margin and phase margin.

The ability of equipment to operate without causing or suffering unacceptable electromagnetic disturbance, addressed by shielding, filtering, earthing and limiting emission and susceptibility levels.

A transducer exploiting the transverse voltage produced when current flows through a conductor in a magnetic field, used to measure current, position and speed without direct electrical contact.

A high-input-impedance differential amplifier, usually built from three op-amps, that amplifies small signals riding on large common-mode voltages; it is standard for bridge and sensor conditioning.

An analogue-to-digital converter that determines output bits one at a time from most significant to least, comparing the input against a digital-to-analogue converter output; it offers good speed at moderate resolution.

The selection of insulation strengths and protective device levels so that insulation withstands expected overvoltages with adequate margin, balancing reliability against cost across the system.

The electrical energy used per unit of output, such as kWh per tonne or per kilometre, used to compare traction and heating methods and to judge efficiency of utilisation.

A braking method in which traction motors act as generators, returning energy to the supply or an energy store instead of dissipating it as heat; effective only above a minimum speed.

The ratio of luminous flux emitted by a lamp to the electrical power it consumes, expressed in lumens per watt; it is the key figure of merit when comparing illumination sources.

A situation in which a public servant's private interest or relationship could improperly influence official decisions; it must be disclosed and avoided rather than merely managed privately.

Strict adherence to transparency, fairness and documented evaluation in purchasing, ensuring specifications are not tailored to favoured bidders and that bid information stays confidential until opening.

Consistent honesty and adherence to moral principles in official conduct, including refusing bribes, resisting undue pressure and reporting wrongdoing even when doing so is personally costly.