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

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