Question 1 of 60Fuses, Isolators and Reactors
An HRC (High Rupturing Capacity) fuse, compared to a rewireable fuse, offers:
ASlower, less reliable operation
BFaster, more reliable operation and higher breaking capacity
CNo breaking capacity at all
DOnly domestic-scale application
Answer is hidden
Question 2 of 60Fuses, Isolators and Reactors
A fuse's time-current characteristic is generally:
ADirectly proportional (higher current = slower operation)
BInversely related (higher fault current causes faster operation)
CCompletely independent of current
DOnly valid at rated current
Answer is hidden
Question 3 of 60Fuses, Isolators and Reactors
An isolator (disconnector) is characterized by:
AThe ability to interrupt fault current safely
BProviding a visible open gap for isolation, with no fault-current interrupting capability
CBeing operated under full load routinely
DAutomatic operation during a fault
Answer is hidden
Question 4 of 60Fuses, Isolators and Reactors
The correct sequence for de-energizing a circuit using a circuit breaker and isolator is:
AOpen isolator first, then breaker
BOpen circuit breaker first, then isolator
COpen both simultaneously
DThe sequence does not matter
Answer is hidden
Question 5 of 60Fuses, Isolators and Reactors
An isolator must never be operated:
AWhen the circuit is de-energized
BUnder load, since it has no current-interrupting capability
CDuring scheduled maintenance
DIn outdoor substations
Answer is hidden
Question 6 of 60Fuses, Isolators and Reactors
A series (current-limiting) reactor is inserted into a power system to:
AIncrease fault current magnitude
BLimit fault current magnitude, reducing the required breaking capacity of switchgear
CAbsorb reactive power at line receiving ends
DProvide visible isolation
Answer is hidden
Question 7 of 60Fuses, Isolators and Reactors
A shunt reactor is typically connected:
AIn series with a feeder to limit fault current
BIn parallel, often at the receiving end of long transmission lines, to absorb excess reactive power
COnly inside a fuse assembly
DIn series with an isolator
Answer is hidden
Question 8 of 60Fuses, Isolators and Reactors
The Ferranti effect, which shunt reactors help mitigate, refers to:
AExcessive voltage rise at the receiving end of a lightly-loaded long transmission line
BA type of fuse failure
CIsolator arcing under load
DCircuit breaker overheating
Answer is hidden
Question 9 of 60Fuses, Isolators and Reactors
A drop-out (expulsion) fuse is characterized by:
ANo visual indication of operation
BThe fuse carrier visibly dropping/swinging out after operation, providing clear indication and isolation
CUse only in low-voltage domestic wiring
DBeing non-replaceable
Answer is hidden
Question 10 of 60Fuses, Isolators and Reactors
Common types of isolators used in outdoor substations include:
AOnly rewireable fuse types
BDouble-break and pantograph types
COnly HRC cartridge types
DOnly drop-out fuse types
Answer is hidden
Question 11 of 60Circuit Breakers
A vacuum circuit breaker (VCB) quenches the arc using:
AInsulating oil decomposition
BA high-vacuum interrupter with very high dielectric strength
COpen air only
DSF₆ gas
Answer is hidden
Question 12 of 60Circuit Breakers
A gas circuit breaker (GCB) typically uses which gas for arc quenching?
ANitrogen
BSulfur hexafluoride (SF₆)
COxygen
DHydrogen
Answer is hidden
Question 13 of 60Circuit Breakers
An oil circuit breaker (OCB) quenches the arc via:
AA vacuum interrupter
BDecomposition of insulating oil, generating hydrogen gas that cools/deionizes the arc
CSF₆ gas
DOpen air with arc chutes
Answer is hidden
Question 14 of 60Circuit Breakers
The rated breaking capacity of a circuit breaker refers to:
AIts continuous current carrying capability
BThe maximum fault current it can safely interrupt
CIts physical size
DIts rated voltage only
Answer is hidden
Question 15 of 60Circuit Breakers
The rated making capacity of a circuit breaker refers to:
AIts interrupting time only
BThe maximum current (including asymmetrical/DC offset) it can safely close onto
CIts insulation resistance
DIts continuous voltage rating
Answer is hidden
Question 16 of 60Circuit Breakers
A type test on a circuit breaker is:
APerformed on every manufactured unit
BPerformed once on a design, e.g. a short-circuit/breaking capacity test
COnly a visual inspection
DNot required for HV breakers
Answer is hidden
Question 17 of 60Circuit Breakers
An MCB (Miniature Circuit Breaker) is typically used for:
AMain distribution of large industrial loads
BFinal circuit protection in domestic/light commercial installations
CHigh-voltage transmission line protection only
DSF₆ gas insulated substations only
Answer is hidden
Question 18 of 60Circuit Breakers
An MCCB (Moulded Case Circuit Breaker), compared to an MCB, generally offers:
ALower current rating and no adjustable trip settings
BHigher current rating, often with adjustable trip settings
CUse only in domestic wiring
DNo overload protection capability
Answer is hidden
Question 19 of 60Circuit Breakers
Circuit breaker selection is primarily based on:
AColor and physical appearance only
BSystem voltage, fault level, continuous current rating, and required operating speed
CManufacturer brand name only
DOnly the installation location's altitude
Answer is hidden
Question 20 of 60Circuit Breakers
Operating (interrupting) time of a circuit breaker includes:
AOnly the mechanical breaker operating time
BBoth relay operating time and breaker mechanical operating time, from fault inception to arc extinction
COnly the time to reset the breaker
DTime unrelated to protection relays
Answer is hidden
Question 21 of 60Protective Relays
An IDMT (Inverse Definite Minimum Time) overcurrent relay is characterized by:
AConstant operating time regardless of fault current
BOperating time that decreases as fault current increases
COperation only at exactly rated current
DNo time delay under any condition
Answer is hidden
Question 22 of 60Protective Relays
An earth fault relay is specifically designed to detect:
AOnly three-phase balanced faults
BCurrent flowing to earth, typically via residual/zero-sequence current sensing
CUndervoltage conditions only
DOnly overload conditions
Answer is hidden
Question 23 of 60Protective Relays
An undervoltage relay operates when:
ACurrent exceeds a threshold
BSystem voltage falls below a preset threshold
CFrequency exceeds a threshold
DThe system is fully de-energized only
Answer is hidden
Question 24 of 60Protective Relays
A contactor differs from a circuit breaker in that a contactor:
ACan safely interrupt fault currents
BIs used for frequent switching of loads under normal conditions, not fault interruption
CProvides a visible isolation gap like an isolator
DHas no electrical control mechanism
Answer is hidden
Question 25 of 60Protective Relays
Differential protection operates based on the principle that: internal fault
AVoltage always equals current
BCurrent entering and leaving a protected zone balances under normal conditions, with imbalance indicating an
CImpedance is proportional to distance
DTime delay increases with fault severity
Answer is hidden
Question 26 of 60Protective Relays
A key advantage of differential protection is:
ASlow but highly sensitive operation
BFast, highly selective operation limited strictly to the protected zone
CApplicability only to overhead lines
DRequiring no current transformers
Answer is hidden
Question 27 of 60Protective Relays
Distance protection determines fault location by measuring:
AOnly the fault current magnitude
BImpedance between the relay location and the fault point
COnly the system frequency
DOnly the fault duration
Answer is hidden
Question 28 of 60Protective Relays
Distance protection is most widely used for protecting:
ASmall domestic circuits
BTransmission lines, using graded zones (Zone 1, 2, 3) for backup protection
COnly low-voltage motor circuits
DOnly lighting circuits
Answer is hidden
Question 29 of 60Protective Relays
Earth fault protection is generally more sensitive than phase-overcurrent protection because:
AGround fault currents can be much smaller than phase fault currents
BGround faults never occur in practice
CPhase faults are always larger than any threshold
DEarth fault relays cannot detect small currents
Answer is hidden
Question 30 of 60Protective Relays
Overload protection, as distinct from short-circuit protection, typically involves:
AInstantaneous tripping with no delay
BTime-delayed tripping for moderate, sustained excess current
CNo relay involvement at all
DOnly voltage-based tripping
Answer is hidden
Question 31 of 60Lightning Protection
A direct lightning stroke refers to:
ALightning that strikes a line/equipment directly
BA nearby strike inducing a surge via electromagnetic coupling
CA strike that never affects power systems
DOnly strikes occurring underground
Answer is hidden
Question 32 of 60Lightning Protection
An induced (indirect) lightning stroke affects a power line by:
ADirect physical contact with the conductor
BInducing a voltage surge via electromagnetic coupling from a nearby strike, without direct contact
COnly affecting underground cables
DNever causing any overvoltage
Answer is hidden
Question 33 of 60Lightning Protection
A rod (spark) gap arrestor's main drawback is:
AExtremely precise breakdown voltage
BImprecise breakdown voltage and the risk of a follow-through power-frequency arc
CBeing a modern, gapless design
DZero leakage current under all conditions
Answer is hidden
Question 34 of 60Lightning Protection
A horn gap arrestor improves on a simple rod gap by:
AEliminating the air gap entirely
BUsing diverging horn-shaped electrodes that elongate and help self-extinguish the follow-through arc
CRequiring no ground connection
DOperating only at DC
Answer is hidden
Question 35 of 60Lightning Protection
A valve-type lightning arrestor combines a series gap with:
AA simple resistor of fixed (linear) value
BA non-linear resistor (valve element) that limits follow-through current
CNo resistive element at all
DA capacitor bank only
Answer is hidden
Question 36 of 60Lightning Protection
A metal oxide (ZnO) lightning arrestor is distinguished by:
ARequiring a series spark gap always
BBeing a gapless design using highly non-linear zinc oxide resistive elements
CHaving high resistance during a surge
DBeing an older, largely obsolete technology
Answer is hidden
Question 37 of 60Lightning Protection
The core function of a lightning arrestor is to:
AIncrease the surge voltage reaching equipment
BLimit surge voltage reaching protected equipment to a safe level by diverting surge current to ground
CPermanently connect the line to ground
DPrevent all current flow at all times
Answer is hidden
Question 38 of 60Lightning Protection
An overhead earth wire (shield wire) on a transmission line primarily functions to:
ACarry normal load current
BIntercept direct lightning strokes before they hit the phase conductors, conducting surge current to ground
CReplace the need for insulators
DIncrease line inductance intentionally
Answer is hidden
Question 39 of 60Lightning Protection
An overhead earth wire is positioned on a transmission tower:
ABelow the phase conductors
BAbove the phase conductors
CAt the same height as the phase conductors
DUnderground, parallel to the tower base
Answer is hidden
Question 40 of 60Lightning Protection
After a metal oxide arrestor conducts a surge to ground, its behavior at normal system voltage is to:
AContinue conducting heavily, like a short circuit
BReturn to a very high resistance state, presenting negligible leakage current
CPhysically disconnect from the circuit
DRequire manual resetting before normal operation
Answer is hidden
Question 41 of 60Earthing
A solidly earthed system's neutral is connected to earth:
AThrough a large resistor
BDirectly, with no intentional impedance
CThrough a reactor only
DNot connected at all
Answer is hidden
Question 42 of 60Earthing
A resistance earthed system limits ground fault current by:
AConnecting the neutral directly to earth
BEarthing the neutral through a resistor
CLeaving the neutral completely unearthed
DIncreasing system voltage
Answer is hidden
Question 43 of 60Earthing
In an unearthed (isolated neutral) system, a single ground fault typically produces:
AA very large fault current requiring immediate tripping
BOnly a small capacitive current, not necessarily requiring immediate tripping
CNo current flow at all
DImmediate equipment destruction
Answer is hidden
Question 44 of 60Earthing
Equipment earthing primarily protects against:
AOvervoltage from lightning strikes only
BDangerous touch voltage on equipment frames in the event of an insulation failure
CLoss of supply frequency
DExcessive reactive power
Answer is hidden
Question 45 of 60Earthing
Touch potential refers to:
AThe voltage between two points on the ground one stride apart
BThe potential difference between an energized object and the ground surface at a point a person could touch
CThe total system voltage
DThe resistance of the earth electrode
Answer is hidden
Question 46 of 60Earthing
Step potential refers to:
AThe voltage between an equipment frame and the person touching it
BThe potential difference between two points on the ground surface separated by one stride
CThe system's rated voltage
DThe earth electrode's physical depth
Answer is hidden
Question 47 of 60Earthing
Earth electrode resistance should generally be kept:
AAs high as possible
BAs low as practicable, per relevant standards
CExactly equal to the system voltage
DIrrelevant to safety
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Question 48 of 60Earthing
A key precaution in earthing system maintenance is:
ANever testing earth resistance
BRegular testing/measurement of earth resistance and maintenance of connections
CUsing undersized conductors to save cost
DAvoiding bonding of metallic parts
Answer is hidden
Question 49 of 60Earthing
A key risk of prolonged operation with an unresolved ground fault in an unearthed system is:
AImmediate complete system shutdown
BA second ground fault occurring, potentially causing a severe phase-to-phase fault condition
CNo risk at all, since the system is isolated
DAutomatic self-correction of the fault
Answer is hidden
Question 50 of 60Earthing
Equipment earthing conductors should be sized to:
ACarry only the rated normal load current
BCarry the expected fault current without damage
CBe as thin as possible to save material
DMatch only the equipment's physical dimensions
Answer is hidden
Question 51 of 60Substations
A step-up substation is typically located:
AAt the final consumer's premises
BNear generating stations, raising voltage to transmission level
COnly at switching points with no transformers
DOnly underground
Answer is hidden
Question 52 of 60Substations
A switching substation is distinguished by:
AAlways changing voltage level via transformers
BInterconnecting/switching circuits without changing voltage level
CBeing used only for generation
DHaving no circuit breakers
Answer is hidden
Question 53 of 60Substations
A single bus bar arrangement's main drawback is:
AExcessive cost
BPoor reliability, since a bus fault or maintenance takes the entire substation out of service
CBeing usable only for EHV substations
DRequiring the most breakers of any arrangement
Answer is hidden
Question 54 of 60Substations
A ring main bus bar arrangement improves reliability because:
AEach circuit breaker is fed from only one direction
BEach circuit breaker is fed from two directions, so a single outage doesn't interrupt other circuits
CIt has no circuit breakers at all
DIt requires the fewest breakers of any scheme
Answer is hidden
Question 55 of 60Substations
A breaker-and-a-half arrangement is typically used in:
ASmall domestic substations
BImportant EHV substations requiring high reliability and flexibility
COnly switching substations with no transformers
DOnly indoor GIS substations
Answer is hidden
Question 56 of 60Substations
A tap changing transformer regulates voltage by:
AChanging the system frequency
BAdjusting the transformer's turns ratio via a tap changer
CAdding a series capacitor only
DDisconnecting the load
Answer is hidden
Question 57 of 60Substations
A booster transformer provides voltage regulation by:
AChanging the main transformer's core material
BInjecting an additional series (boost or buck) voltage into the line
CAbsorbing reactive power only
DActing purely as a step-down transformer
Answer is hidden
Question 58 of 60Substations
A static compensator (e.g. SVC or STATCOM), compared to a synchronous condenser, generally offers:
ASlower response due to mechanical rotation
BMuch faster reactive power response, being power-electronic based
CNo ability to regulate voltage
DOnly reactive power absorption, never injection
Answer is hidden
Question 59 of 60Substations
Substation earthing (grounding) design primarily aims to:
AMaximize step and touch potentials
BKeep step and touch potentials within safe limits for personnel during a fault
CEliminate the need for any earth connections
DIncrease the substation's operating voltage
Answer is hidden
Question 60 of 60Substations
Which of the following is classified as substation auxiliary equipment?
ACurrent transformers used for metering
BStation batteries/DC supply for protection and emergency lighting
CThe main power transformer
DThe transmission line conductors
Answer is hidden