LADWP Electric Station Operator – Circuit Breakers, Disconnects, Transformers Practice Test

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• Using multiple contacts and rapid opening times helps ______ the arc by reducing the cross sectional area of the arc or by lengthening it.
• Which statement best describes how LV line currents relate to HV line currents in a delta-wye transformer?
• The secondary voltage of distribution transformers is typically which of the following?
• Which category of switching includes actions such as isolating trouble and restoring service?
• What is the primary purpose of a circuit breaker in a power system?
• What are the typical steps in a substation switching procedure after de-energizing?
• If a second coil is placed in the field of the first coil that is connected to an AC source, the rising and collapsing magnetic field of the first coil will cut across the second coil and will induce an AC voltage in the second coil as well. This is known as ______ induction.
• __________ are designed to open, close, energize, de-energize, and interrupt normal and abnormal values of current flow in electrical circuits.
• The primary voltage of distribution transformers is typically what value?
• A great variety of operating conditions can be easily reproduced on the ______.
• Which statement best describes impedance grounding in electrical systems?
• Electrical ________ are installed in the path from the generator to the consumer to provide reliability, flexibility, and safeguards for the electrical power system.
• Which component provides a visual indication that a circuit is disconnected from energy sources?
• During switching a line, what is the recommended sequence for opening devices?
• What voltages are typical for the DWP Transmission System?
• A transformer whose secondary or output voltage is lower that its input or primary voltage is called a step-________ transformer.
• __________-ratio is the number of turns of wire in the primary winding compared to the number of turns in the secondary winding.
• In an ideal transformer with a turns ratio of 2:1 (Np:Ns), the secondary voltage is what fraction of the primary voltage under ideal conditions?
• Which statement describes definite-time overcurrent protection as opposed to inverse-time protection?
• Why is it important to coordinate breaker trip settings with the protection philosophy?
• The current that flows across the gap in air when contacts separate is called the ______.
• Transformer oil in good condition must withstand _____kV applied across two flat electrodes submerged in a sample of the oil without arcing.
• The mechanical linkage in a circuit breaker is often described as what component, also referred to as the actuating arm or lever?
• The ability of a substance to prevent the flow of electrical current is described as its __________ strength.
• What is the purpose of a mechanical interlock between a circuit breaker and a disconnect switch?
• What are standard practices for lockout/tagout (LOTO) when working on electric equipment?
• Disconnects through which current does not normally flow usually remain _________.
• What is the typical maintenance action for the operating mechanism of a circuit breaker?
• ______ switching is performed in substations to provide adequate capacity for customer load, provide an alternate source for customer load when equipment maintenance is required, and to search for 4.8kV grounds.
• What is the importance of proper working clearance around energized equipment?
• What is a bus-tie breaker and where is it used?
• Bank-in-Service caps are applied to closed bank CBs as blocking devices; what term describes this function?
• In per-unit impedance calculations, which expression correctly gives Isc (per unit) in terms of the base values?
• __________ are provided as a method of visually confirming that a circuit has been 'disconnected' from specified sources of electrical energy.
• How does a tap changer affect voltage regulation under varying load?
• The heat loss due to the friction of molecules during magnetization is called what?
• After a fault occurs, operators re-establish service by routing current to circuits that are not ______.
• How does a delta-wye transformer affect line currents and phase angles?
• Severe contamination of a dielectric medium can cause circuit breakers to __________ by allowing an arc to be sustained between the open contacts or the contacts and the grounded tank.
• Differentiate solidly grounded neutral and impedance-grounded neutral.
• What term describes the second category of switch function described alongside manipulation?
• What type of electrical component has no dielectric strength and allows current to flow in a circuit?
• Which statement correctly describes the insulation media and typical applications of oil-filled and dry-type transformers?
• If the source impedance increases, what happens to the short-circuit current at the bus?
• If a transformer has primary 80 turns and secondary 40 turns, the turns ratio is.
• When energizing large banks, __________ current can be considerable and may negatively affect customer service if not performed properly.
• Which device is used to energize or de-energize transformers and voltage regulators?
• When current flow in a coil causes an emf to be induced in itself, it is known as ______.
• Well-designed transformers are typically about what percent efficient?
• The heat from a fault current path across the surface of a bushing or insulator causes porcelain to ______.
• Larger transformers are about _____% efficient.
• What does the transformer vector group Dyn11 indicate about winding connections and phase displacement?
• The ________ operation of these electrical switches can pose a serious hazard to personnel, cause destruction of equipment, and cause unnecessary interruptions.
• In distribution stations, load transfer to a paralleled bank is achieved by opening the bank __________ side CB.
• Which gas is listed among dielectric media used in circuit breakers for interrupting power system currents?
• The losses due to hysteresis and eddy currents in the magnetic core are known as what?
• ________ are usually operated manually by the use of levers, cranks, and "hook-sticks poles."
• The energy transfer between windings without direct electrical connection relies on what type of coupling?
• ______ transformers are used to step voltage down to a safe value, typically 120 volts.
• Back emf or counter emf is also referred to as what kind of voltage?
• __________ are not designed to interrupt current flow, open or close circuits, or energize and de-energize circuits other than short sections.
• ________ switching operations include insolate trouble, restoration, 4.8kV Ground Search, etc.
• Which statement about transformer protection and vector groups is accurate?
• What is the primary purpose of a sectionalizer in a distribution network?
• __________ are usually made of insulating porcelain.
• What is the purpose of a neutral grounding resistor (NGR) in an impedance-grounded system?
• How do you compute transformer impedance in per unit on a chosen base?
• Dirt contamination can reduce the interrupting capabilities by reducing the dielectric strength when moisture is present. Which statement best reflects this effect?
• The losses due to resistance of the windings are called what?
• What is a relay coordination study and its purpose?
• Which formula correctly expresses the symmetrical three-phase fault current in terms of line-to-line voltage and equivalent impedance?
• Laminating the core with thin sheets of silicon steel reduces which type of loss?
• During abnormal conditions, current often exceeds the normal limitation of these devices by as much as _____ to _____ times their normal rating.
• Visual disconnection is usually necessary to create __________ working conditions for repair and maintenance crews.
• __________ switching performed by Operators is usually in response to power outages and abnormal conditions such as overloads.
• The ability of a substance to resist electrical current flow is described as its Dielectric strength.
• What is differential protection and what does it monitor?
• Operators, among others, are charged with the responsibility of providing good __________ service. This means no unplanned service interruptions to customer load.
• High temperature limits the what carrying capacity of transformers?
• What does transformer impedance percentage indicate for fault levels?
• The act of connecting two circuits together so that current can simultaneously flow through both of them is known as __________.
• Which statement correctly differentiates a fused disconnect from a non-fused disconnect?
• What equipment is typically used to implement ground fault protection on feeders and buses?
• Transformer ratios of 400:1 are typically used in ______ transformers, depending on installation and equipment needs.
• A circuit that is not affected by a fault is described as ______.
• In LADWP practice, what is the difference between a circuit breaker and a disconnect switch?
• A simple power transformer essentially consists of two ______.
• Which statement distinguishes a three-phase fault from a single-line-to-ground fault in terms of current path?
• What is the vector group of a transformer, and why is it important for connections?
• Which device provides energy transfer between isolated circuits using magnetic coupling?
• Which dielectric medium has a relatively high dielectric strength and is used in many low voltage applications such as home light switches?
• What is the primary role of distribution transformers?
• Which combination of PPE is typically required for arc flash protection?
• Station ______ transformers are the distribution transformers for substations, providing single-phase power for lighting and three-phase power for equipment.
• When outages occur, operators re-route current flow to circuits that are not ______.
• Circulating currents that cause unwanted heating in a transformer are called what?
• __________ are used to energize or de-energize short sections of conductor such as leads connecting a circuit breaker to its associated disconnects.
• How does a tap changer affect transformer voltage regulation under varying load?
• Which device is used to step down high currents to relay/meter levels for protection and metering?
• The current that continues to flow across the opening contacts of a switch (or across any opening in a circuit) is known as an ______.
• Fault currents are described as currents that, if not controlled, can cause widespread outages.
• A certain amount of current flows when a bank is first energized. This current is known as __________ current.
• ______ are hook-stick operated and gang-operated.
• If the base apparent power Sbase is doubled while the voltage base remains the same and Zactual unchanged, how does Zpu change?
• Which component's surface is involved in porcelain fragmentation due to fault currents?
• Which instrument is used to measure insulation resistance in transformers during testing?
• The amount of __________ delivered by the secondary winding is less than the amount supplied to the primary winding.
• Good operators plan ahead by preparing __________ plans.
• Electrical current may flow across the contacts of how many electrical switches before it reaches the consumer?
• Which type of transformer is used to step voltage down to a safe value, typically 120 volts?
• Much stronger ________ fields are obtained if the wire is wound into a coil with many turns of wire.
• Which type of transformer is used to step down current to a safe value, a maximum of 5 amps?
• ______ transformers are used to step down current to a safe value, a maximum of 5 amps.
• What is the per-unit system primarily used for in protection and relay coordination?
• During surface faults, porcelain fragmentation is observed on the surface of a ______ or insulator.
• What is tested in a turn ratio test for a transformer, and what indicates a correct result?
• Which device may share winding and potentially have no isolation between circuits?
• A megger test on transformer windings is typically used to assess what?
• How do you verify proper phase rotation when connecting a transformer bank?
• Why is visual disconnection important for repair and maintenance crews?
• Before closing a breaker to re-energize a line, which checks should be verified?
• Why is arc-flash safety critical when operating high-voltage equipment?
• Which current flows when a bank is first energized, not during steady-state operation?
• A transformer whose secondary or output voltage is higher that its input or primary voltage is called a step-________ transformer.
• What is the Department's Subtransmission System voltage?
• Distribution transformers can be configured as which of the following options?
• Which contaminant, especially when moisture is present, can destroy the interrupting capabilities of a dielectric medium?
• What is ground fault protection and where is it typically applied?
• Transformer ratios of 400:1 are typically used in instrument transformers. Which type of transformer is described?
• Improper operation of electrical switches can pose what type of risk?
• The operating time, from fully open to fully closed, in many large CBs, is often less than __________ seconds?
• Which device is used to perform switching operations on high voltage circuits to control power delivery?
• How does inverse-time overcurrent protection differ from definite-time overcurrent protection?
• Alternating current is easier to interrupt than direct current because periodically (120 times per second in a 60Hz circuit) the current value becomes ______.
• What is the purpose of a transformer bushing test?
• Which statement best describes how an impedance relay decides to trip?
• How is symmetrical short-circuit current at a bus typically calculated?
• ________ circuits use auxiliary devices that direct the operation of the CB.
• A measure of the ability of a substance to conduct magnetic lines of force is called ______.
• Which statement best describes the core material used in transformers?
• When there is no physical or electrical connection between the two coils yet energy is transferred from one coil to the other. The coils are said to be ______ coupled.
• In distribution stations, what equipment steps down 34.5 kV to 4.8 kV?
• In an ideal transformer with a turns ratio of 1:2 (Np:Ns), the secondary voltage is what fraction of the primary voltage under ideal conditions?
• Which of the following is not listed as a benefit of placing automatic switches in the power system?
• Operators use electrical switches to perform routine, automatic, and ______ switching operations on the electrical system.
• What is an impedance relay and what does it protect?
• What is a Buchholz relay and what fault does it detect?
• What is the function of a sectionalizer in a distribution network?
• Bank-in-Service caps are __________ devices that are applied to the control handles of closed bank CBs.
• Instrument transformers are used for measurement of electrical quantities and for control purposes. Which statement best describes their use?
• What property of air determines its ability to withstand high voltages before breakdown between conductors?
• Which banks step down transmission system voltage from 138 kV or 230 kV to 34.5 kV?
• An ideal __________ is one in which all the lines of force produced by the primary winding inductively link every turn of the secondary winding.
• One of the primary tasks of the Electric Station Operator is to perform which operation on high voltage circuits?
• In a 60 Hz circuit, how many times per second does the current cross zero?
• ________ must never be used to interrupt current flow in circuit.
• Which protection scheme is designed to trip all three phases together for a three-phase fault?
• Which of the following is a common cause of transformer overheating in operation?
• Why is the transformer vector group important for protection coordination?
• Disconnects are used to energize or de-energize short sections of conductor such as leads connecting a circuit breaker to its associated disconnects. Which term describes the portion connected to the circuit breaker?
• Which component connects generators to the DWP Transmission System and typically steps up voltage from 18 kV to transmission levels of 138 kV or 230 kV?
• After a fault, what action helps restore electrical service?
• The mechanical indicator used at the CB to indicate the status of the breaker is called the __________.
• In a transformer, adding more turns to the winding primarily increases which parameter related to magnetic linkage?
• The electrical function of switches falls into two categories: ___________ of relatively high values of current and voltage under load and the switching of circuits to provide a visual confirmation of de-energization.
• Which method helps cool the arc by using multiple contacts and fast opening times?
• Large three-phase power transformers are generally referred to as what?
• What device allows the transfer of electric energy between two circuits that are completely insulated from each other through magnetic induction?
• This is the insulating mechanism that occupies the space between the open contacts of a CB and prevents the flow of current through the device while the contacts are in the open position.
• Some of the materials used in __________ that have sufficient dielectric strength to interrupt power system currents include insulating oils, pressurized inert gases, sulfur hexafluoride gas, and vacuum chambers?
• Air has a high ______ value so this current flow creates heat.
• A ________-shaped coil allows a much stronger field to be created than a flat coil does.
• In a transformer, what quantity is stepped down when voltage is stepped up?
• Which action best describes restoring service after a fault by using alternate paths?
• Localized areas of greater heat are called __________?
• What is the function of a differential relay in a transformer bank?
• Disconnects that do not normally carry current are typically kept in which state to prevent unintended energization?
• Short-term, limited outages are intentionally caused to isolate circuits to clear a ______.
• Large-bank energization requires attention because magnetizing current can affect what aspect of service?
• Core losses in a transformer are composed of which two types of losses?
• The heat caused by iron and copper losses shortens the service life of what materials used in transformer windings?
• In station designs, circuits are placed in what configuration with disconnects?
• Which transformer type provides galvanic isolation between primary and secondary windings?
• In an ideal transformer with Np:Ns = 3:1, the secondary voltage is what fraction of the primary voltage?
• Automatic switches placed in the power system provide reliability, flexibility, and safeguards. Which term best describes the third benefit?
• How does a fused disconnect differ from a non-fused disconnect?
• What is the role of current transformers (CTs) in protection circuits?
• Disconnects, through which current normally flows, must remain ______ at all times.
• Portions of the mechanical linkages connected to movable contacts must be constructed of __________ materials to prevent energizing the CB components such as the tank and controls.
• What does the presence of gas in transformer oil indicate?
• ______ stations banks are configured with either one or two 4.8kV (low side) circuit breakers (CBs).
• Which factor primarily limits the current-carrying capacity of transformers at elevated temperatures?
• In a transformer with no moving parts, the losses arise from field excitation and the resistance of what component?
• ________ switching is for maintenance, construction, cleaning, testing, etc.
• What does Zbase represent in per-unit calculations?
• A special type of transformer is the ______ transformer, used for measurement of electrical quantities and for control purposes.
• What is the difference between an on-load tap changer (OLTC) and an off-load tap changer?
• Name two common transformer cooling methods and where they are used.
• When operating at voltages above 1000 V, which tool rules apply for contacting live parts?
• The size of an electric arc and destruction it can cause are directly proportional to the amount of ________ being interrupted.
• Small and medium sized __________ are self-cooled; that is, cooling takes place by direct radiation from the tank to the surrounding air.
• Distribution transformers provide power to which customers?
• Which banks are dedicated to individual lines?
• Dry, clean air normally has a ______ strength of about 10,000 volts per inch. This means that you would have to apply a voltage greater than 10,000 volts across conductors separated by one inch of air to establish current flow across the separated conductors.
• Transformers and voltage regulators must be energized and de-energized using __________.
• Which term describes the maximum fault current a circuit breaker can interrupt without damage at a given voltage?
• Proper procedure requires banks to always be energized from the __________ side.
• Which currents, if allowed to flow uncontrolled, would quickly cause widespread outages by destroying electrical equipment?
• If a transformer has higher impedance, what is the expected effect on fault current?
• What does "breaking capacity" of a circuit breaker mean?
• The outages that are short-term and limited are intended to isolate circuits to clear a ______.
• Failure of the mechanical __________ (sometimes referred to as the actuating arm or lever) can cause serious damage to the circuit breaker or may energize normally non-energized portions.
• Which devices are used to manipulate high values of current and voltage in circuits that are carrying current or will be carrying current following the operation?
• The rapid fragmentation of porcelain when a fault current travels along an insulator surface is known as a porcelain ______.
• ________ switching operations include automatic reclosers (ARs), Voltage Pickup Unit (VPUs), and Automatic Transfer Switching (ATSs).
• Which coil shape is identified as producing a stronger magnetic field compared to a flat coil?
• What is the term for the phenomenon where a changing current in one coil induces current in a nearby coil without a direct connection?
• In an ideal transformer, if Vs > Vp, the secondary current Is compared to the primary current Ip: it decreases.
• The placement of ___________ electrical switches in the power system makes it possible to limit both the duration and the extent of power outages.
• What is the operating principle of an SF6 gas circuit breaker?
• Which component in a circuit breaker is typically associated with porcelain construction?
• What is the primary purpose of the short-term outages used during fault conditions?
• A switching plan must include the name of the __________ being operated and the major steps required to perform the switching.
• Which type of steel, known for high permeability, is used for manufacturing transformer cores?
• What does the presence of gas in transformer oil typically indicate?
• What not only helps extend the life of transformers but also increases its current carrying capacity?
• Breaker-failure protection serves to protect the system by which means?
• Which property of silicon steel contributes to its suitability for transformer cores?
• What does it mean for a circuit breaker to operate in 3-pole mode?
• In a transformer, what happens to current when the voltage steps down?
• Station service transformers provide single-phase power for lighting and three-phase power for equipment. Which statement best describes their output?
• Which banks connect together buses of different voltages such as 138 kV and 230 kV?
• Which dielectric medium used in circuit breakers is described as vacuum chambers?
• In substation switching procedures, what is the purpose of issuing a permit before performing switching?
• If ______ currents are allowed to flow unchecked, they would cause widespread outages by destroying electrical equipment.
• In distribution stations, load is transferred to a paralleled bank by normally opening the bank __________ side CB or CBs.
• What is the primary purpose of insulating the laminated sheets in transformer cores?
• What is the purpose of a reclosing scheme in transmission protection?
• Which device may share winding and potentially have no electrical isolation between circuits?
• What is breaker-failure protection?