PGCIL Field Engineer & DT flashcards
PGCIL Field Engineer & DT · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Thevenin's theorem
- Any linear two-terminal network can be replaced by a single voltage source V_th in series with R_th, where V_th is the open-circuit voltage and R_th the equivalent resistance with sources de-energized.
- Maximum power transfer
- A load receives maximum power when its resistance equals the Thevenin resistance of the source network. At that point the source delivers only 50 percent efficiency.
- Series resonance condition
- In a series RLC circuit, resonance occurs at f = 1/(2π√(LC)). At this frequency inductive and capacitive reactances cancel, impedance is minimum and current is maximum.
- Power factor correction
- Capacitor kVAR needed to raise power factor from cos φ₁ to cos φ₂ equals P multiplied by (tan φ₁ minus tan φ₂), where P is the active power in kW.
- Per-unit impedance base
- Z_base equals V_base squared divided by S_base. Converting actual ohms to per-unit simplifies transformer networks because per-unit impedances stay unchanged across voltage levels.
- Symmetrical components
- Any unbalanced three-phase set is resolved into positive, negative and zero sequence sets. The operator a equals 1 at 120 degrees, and a² equals 1 at 240 degrees.
- Surge impedance loading
- SIL equals V_L squared divided by the surge impedance √(L/C). At SIL the line delivers natural power with flat voltage profile and no reactive compensation.
- Equal-area criterion
- Transient stability is maintained when the accelerating area equals the maximum possible decelerating area. The method applies to a single machine against an infinite bus.
- Distance relay zones
- Zone 1 covers about 80 percent of the protected line with no intentional delay. Zone 2 reaches about 120 percent with a delay, and Zone 3 provides remote backup.
- Mho relay characteristic
- The mho relay has a circular characteristic passing through the origin, making it inherently directional. It is widely used for long transmission line protection.
- Buchholz relay function
- A gas-operated relay fitted in the pipe between transformer tank and conservator. It detects incipient faults by gas accumulation and severe faults by oil surge.
- Restricted earth fault protection
- A differential scheme using a core-balance CT on the transformer neutral. It detects ground faults in the winding that produce current below normal overcurrent settings.
- Three-phase controlled rectifier
- Average output of a fully controlled three-phase bridge is 1.35 times line voltage times cos alpha, where alpha is the firing angle measured from natural commutation.
- Buck converter voltage ratio
- In continuous conduction, output voltage equals duty cycle D multiplied by input voltage. The inductor current ripple depends on switching frequency and inductance value.
- V/f control principle
- Keeping voltage proportional to frequency maintains constant air-gap flux in an induction motor. This gives nearly constant torque capability below rated base speed.
- Thyristor latching current
- The minimum anode current needed to keep a thyristor conducting immediately after the gate pulse is removed. It is higher than the holding current value.
- Transformer EMF equation
- RMS induced EMF equals 4.44 times frequency times turns times peak flux. Voltage per turn is identical on primary and secondary windings of the same core.
- Maximum efficiency load
- A transformer reaches maximum efficiency when copper loss equals iron loss. The load fraction at that point equals the square root of iron loss over full-load copper loss.
- Slip at maximum torque
- For an induction motor, slip at maximum torque equals rotor resistance divided by rotor standstill reactance. Maximum torque itself does not depend on rotor resistance.
- Synchronous speed formula
- Synchronous speed in rpm equals 120 times supply frequency divided by the number of poles. A four-pole machine on 50 Hz runs at 1500 rpm.
- Ferranti effect
- On a lightly loaded long transmission line, receiving-end voltage exceeds sending-end voltage because charging current through line inductance raises the voltage. Shunt reactors compensate.
- ABCD constants
- A two-port transmission network is described by sending voltage equals AV_r plus BI_r and sending current equals CV_r plus DI_r. For a symmetrical network AD minus BC equals one.
- Voltage regulation
- The rise in receiving-end voltage, expressed as a percentage of full-load value, when full load is removed while sending-end voltage remains constant.
- Sag formula
- For level supports with uniformly distributed load, sag equals weight per unit length times span squared divided by eight times tension. Sag rises with span squared.
- Wheatstone bridge balance
- The bridge is balanced when the ratio of two adjacent arms equals the ratio of the remaining two arms. At balance no current flows through the galvanometer.
- PMMC instrument response
- A permanent-magnet moving-coil meter responds to the average value of current and is inherently a DC instrument. A rectifier extends it to AC measurement.
- PID controller actions
- Proportional action responds to present error, integral action eliminates steady-state offset, and derivative action anticipates error trend to reduce overshoot.
- Strain gauge gauge factor
- Gauge factor equals the fractional change in resistance divided by the fractional change in length. Metal foil gauges typically have a factor near two.
- Successive percentage change
- Two successive changes of a percent and b percent produce a net change of a plus b plus ab divided by 100 percent. A rise then equal fall never returns to the original value.
- Syllogism validity rule
- A conclusion follows only if it is true in every possible Venn diagram consistent with the premises. A single counterexample diagram makes it invalid.
- Active to passive voice
- The object becomes the subject, the verb becomes a form of be plus past participle, and the original subject follows 'by' or is omitted when unimportant.
- Load despatch centres
- The National Load Despatch Centre coordinates national grid operation in India, while regional load despatch centres manage their regions under its overall supervision.