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SUBSTATION ELECTRICIAN
APPRENTICESHIP EXAM,QUESTIONS
WITH WELL VERIFIED ANSWERS.
Please list the 6 major categories of discussion for any tailboard. - ANSWER->a. Methods of emergency notification b. What is our job plan? c. What is energized? What is not? What are the clearance points? d. What are the hazards associated with the job? e. What are the assignments, groups or individuals? Special precautions, special equipment, PPE? g. Does everyone understand/ask questions? What are the major categories of a Substation Maintenance switching tailboard? - ANSWER->a. Methods of emergency notifications b. What is our switching assignment? c. How will we accomplish the switching? d. Have I verified equipment to be operational? e. What are the hazards involved/ PPE required? f. What are my clearance points? g. Are grounds installed? If so, where?
What are the basic safe work practices observed in a 230KV or 500KV receiving station? - ANSWER->Check in to station upon arrival, close and lock gate after entering. Maintain MAD for personnel and equipment as well as safe working clearances at all times 500KV- PTG 11'11"PTP 19'9"230KV- PTG 5'8"PTP 9'2"115KV- PTG 3'4" PTP 4'7" 69KV- PTG 2'11" PTP 3'9" PWalk down yard and visually inspect for damaged equipment or missing/broken grounds.tailboard with other crews in working in the same area. Maintain speed limits and follow roadways. What insulating mediums are used in EHV breakers? - ANSWER->SF6 gas, ultra-dry high pressure air, polymer, ceramics, air, epoxy, silicone What does a WIKA gauge measure? - ANSWER->WIKA is a brand. Usually, it is measuring gas pressure. What is the minimum % of gas density that SRP allows in an EHV breaker? - ANSWER->98% on all new breakers,98% on Palo Verde Breakers, 97% on all other voltage class breakers including older 500KV breakers. Is SF6 gas harmful and or a hazardous material? - ANSWER->Yes, it displaces oxygen and can create a toxic
Name the different types of operating mechanisms and explain the safety hazards associated with each. - ANSWER->Air Hazards include: pressurized containment vessel, air leaks are not visible, fittings, hoses, regulators and air tools need to be rated for the pressure to be applied, beware of moving parts, drain air pressure before performing maintenance. Hydraulic hazards: pressurized containment vessel, containment vessel has a nitrogen pre-charge pressure even after hydraulic pressure has been drained, hydraulic oil is flammable, beware of moving parts, drain hydraulic pressure before performing maintenance. Spring hazards: beware of moving parts, discharge spring pressure before performing maintenance, spring can be charged in both open and closed breaker positions. Describe the basic function of the SF6 trailer has? - ANSWER->It is used to evacuate, purify, store, consolidate and fill SF6 gas. How does an SF6 gas breaker quench an arc? - ANSWER-
Current interruption in a high-voltage circuit breaker is obtained by separating two contacts in a medium, such
as sulfur hexafluoride (SF6), having excellent dielectric and arc-quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity. SF6 gas is electronegative and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high-pressure flow of sulfur hexafluoride gas, and an arc is struck between them. The gas captures the conducting free electrons in the arc to form relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds up enough insulation strength to extinguish the arc. A gas blast applied to the arc must be able to cool it rapidly so that gas temperature between the contacts is reduced from 20,000 K to less than 2000 K in a few hundred microseconds, so that it is able to withstand the transient recovery voltage that is applied across the contacts after current interruption. What are a P1 and a P2 alarm and what is the procedure for clearing them? - ANSWER->P1 alarms are high priority and indicate the equipment is at risk. They must be attended to immediately. P2 alarms indicate a problem with equipment but do not require immediate attention.
Explain what 230KV and 500KV breakers are used for? - ANSWER->Protecting the transmission lines in an electrical event. Also for switching circuits in order to perform maintenance. Given an equipment number, i.e. PB748, explain what this number tells you. - ANSWER->PB is the substation name, 7 is the voltage class, 4 indicates the bay the equipment is in and 8 designates the position of the equipment in the bay. What is a C.T. and what is it used for? - ANSWER-
Current Transformer, it takes a high current and ratios it down to a usable level in SRP's protection and metering devices. There are bushing CTs on breakers, which are just another element of protection. They monitor what comes in and out to ensure there is no difference otherwise the breaker will trip the breaker and open the circuit. What is a P.T. and what is it used for? - ANSWER- Potential transformer, it takes a high voltage and ratios it down to a useable level to be used in SRP's protection and metering devices.
What procedures are followed for clearance cancellation and the re-energization of EHV equipment? - ANSWER-
Complete switching tailboard and have clearance and ground tracking form ready. Ensure equipment is ready to return to service, the breaker is in the open position, 43m is in the local position and control power is off, remove all shorts and grounds, clear the area of all people, tools and equipment. Person holding clearance calls PDO to cancel clearance and then follows PDO's switching instructions using 3 way communication to return the breaker to service. What is a hygrometer? - ANSWER->An instrument used to measure the moisture content of a gas or air. Explain some of the hazards possible while adding SF gas to energized equipment? - ANSWER->Wet gas, breaker tripping hazards, ruptured bushings, or ruptured discs. Total breaker failure is possible. Mismatched hose and tank pressures, breaker operation while filling. Before you add SF6 to a breaker, what test must be performed on a bottle? - ANSWER->Before SF6 is added to the breaker you must test the moisture, purity, and SO2 of the SF6 with a hygrometer.
Why must you never leave a disconnect closed on an open EHV breaker? - ANSWER->The grading capacitors across some of the contacts are not rated for continuous duty. With the contacts open, they could fail. A loss of the insulating medium could also cause a catastrophic breaker failure. Why do some EHV breakers have heaters on the SF storage tanks? - ANSWER->To keep the SF6 gas from liquefying if it gets too cold. On a pressure switch with an adjustable differential, which would you adjust first, the cutoff point, the pickup point, or the differential? - ANSWER->Set the differential first because this can change the pick-up and cut off points. Explain the SF6 differential alarm system on an EHV breaker? - ANSWER->It is an electrical control circuit designed to send an alarm, or block operation, or trip the breaker if the gas pressure on one pole varies too much from another pole. What is a pole disagreement scheme and what can cause a disagreement? - ANSWER->It is an electrical control circuit scheme designed to trip the breaker if all three
poles do not close simultaneously. It can be caused by timing issues, mechanical latching, bad coil, loss of dc, bent mechanism, incorrect spring pressures. What is a micro-ohm meter or ductor used for when performing maintenance on an EHV breaker? - ANSWER-
To measure the resistance across the closed electrical contacts, connections and conductors. using Ohms law. Takes a known current and measures the voltage drop to find the resistance in micro-ohms. E/I = R Explain how a micro-ohm meter or ductor operates. - ANSWER->Operation consists of passing a known current and a known voltage through a path to be check and measuring the voltage across that path. it uses Ohms Law to calculate the resistance value using E/I =R What is a timer used for in EHV breaker maintenance? - ANSWER->A timer measures the speed at which a breakers main contacts touch and drive mechanism operates. It can also measures the speed at which contactors, auxiliary switches, relays and closing resistors
operate. What should be done when you come upon an energized breaker with very little or no SF6 gas in its system? -
What is an un-loader valve? - ANSWER->A device that ensures a compressor starts with no pressure applied to it and it also removes accumulated moisture from the compressor. If an un-loader valve didn't unload, what would the compressor motor do when you started it? - ANSWER->It would overload the motor, It would either start with great difficulty, trip the overload protector and/or possibly burn up the motor. What precaution should be taken when Dobling an EHV breaker? - ANSWER->Conduct a tailboard and be working under a grounded clearance with the crew and the tester, install red barricade tape around the test area with a tag noting necessary information, keep all unauthorized people outside of the test area, use good communication with the tester, use proper PPE; hardhat, gloves, Fire Retardant clothing, safety glasses, boots, handheld safety trip button, and only a hot apprentice under supervision of a qualified electrical journeyman may handle the test leads. All leads are considered energized, don't lean on anything.
Define contact wipe. - ANSWER->Contact wipe is the amount of travel of the moving contacts after they touch the stationary contacts. When you push a reset button on an overload relay, what happens? - ANSWER->You reset the bi-metallic strip to restore current path for the control circuit and the load. Also known as thermal overload for a motor or motor branch circuit. Name some of the alarms that might appear on an annunciator panel from an EHV breaker. - ANSWER->Low air, hydraulic, oil, or gas pressure; air, hydraulic, oil, or gas lock out; pole disagreement, motor trouble, extreme compressor operate, mechanism trouble. Explain the 52X-Y schemes in an EHV breaker. - ANSWER-
The 52X energizes the close coil, the 52Y energizes the 52X dropping out the close coil at a predetermined time. This prevents the breaker from pumping or giving multiple close commands. This is also referred to as an anti-pump scheme.
- 52xy is the anti-pump scheme that is used in the SRP electrical system.
Explain what grading capacitors and closing resistors do on an EHV breaker? - ANSWER->A closing resistor limits the in-rush of current across the contacts during operation. This helps to protect the current carrying path of the contacts. The grading capacitors equalize potential across multiple sets of contacts to avoid re-strike of an arc. This helps to protect the current carrying path of the main contacts. When they have multiple sets of contacts. What is the main purpose of an accumulator? - ANSWER-
An accumulator is used for the storage of energy in a hydraulic system. Accumulators usually are installed in hydraulic systems to store energy and to smooth out pulsations. Typically, a hydraulic system with an accumulator can use a smaller pump because the accumulator stores energy from the pump during periods of low demand. This energy is available for instantaneous use, released upon demand at a rate many times greater than what could be supplied by the pump alone. What is the "pre-charge" on an accumulator? - ANSWER- The initial gas pressure on the accumulator that when exceeded at a set level, the accumulator will function.
When the system pressure exceeds the pre-charge pressure, the nitrogen gas is squeezed, compresses and decreases in volume, letting hydraulic fluid into the accumulator. The accumulator's fluid volume increases until the system reaches its maximum pressure. When system pressure decreases, the nitrogen gas expands and forces the fluid out of the accumulator, providing power to the hydraulic system, until the system and accumulator pressures equalize. What is the difference between a bushing and an insulator? - ANSWER->The main difference is A bushing is a current carrying conductor that allows current to flow through an insulated grounded plane. An insulator is a material that does not easily allow electricity to pass through it. IE: Rubbers, glass, ceramic, air What is a contactor and how does it operate? - ANSWER-
A contactor is an electro-mechanical switch used in an electrical power circuit. Contactors are switching devices used to control power flow to any load.
A Seal-in circuit is a method of maintaining current flow after a momentary switch has been pressed and released. How many close coils are on an EHV breaker? - ANSWER-
1 How many trip coils are on an EHV breaker? - ANSWER- 2 Is it possible to wire a close/trip coil backwards? - ANSWER->Yes, current is designed to flow in one direction. It wil work in either direction, but work better in the correct position. What is the purpose of a surge arrestor in an EHV yard? - ANSWER->A surge arrestor protects equipment. It operates when the voltage spikes to a certain level which energizes internal varistors which then, when they all become energized during the voltage spike, shunt the excess voltage to ground. Can a surge arrestor be re-used after an operation? - ANSWER->After it has been tested and verified as operational, then yes.
What is the 43M switch used for on an EHV breaker - ANSWER->Maintenance control, local operation only, removes supervisory control, breaker indication, alarm indication, removes relaying, should be on equipment. What is a station service throw over switch? - ANSWER-
A station throw-over switch allows the source to be changed. What is the definition of density, and what is the relationship with SF6 in our breakers? - ANSWER->Mass per unit of volume. If we know the temperature and the molecular weight of the gas we are measuring we can calculate the density of the specific gas in a volume. The higher the density of the gas, the more pure the volume is in relation to the gas. What different types of capacitor banks for we use in 500KV and 230KV receiving station? - ANSWER->They are overhead capacitor banks. They can be found is series or parallel connections. What is a circuit switcher used for in EHV application, and can it interrupt a fault? - ANSWER->A circuit switcher, brings in and out capacitor banks under load. It is not used to interrupt faults.
