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What is a Dynamic Check?
While switching a fdr pos out, you parallel but get no indication of parallel. At this point, your next step is to perform a power flow and then open the fdr pos CB and transfer the load. If it transfers successfully, reclose the CB and reparallel, then continue with fdr switching normally.
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What is the bandwidth the dept sets its regulators to?
2 Volts
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What is responsible for simulating customer voltage?
Line Drop Compensator.
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Bandwidth and time delay help prevent what?
Hunting.
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While performing your required checks, you find that your voltage is not within 4 volts, what do you do next?
Perform a power flow and recheck your steps, then contact your supervisor.
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Why is it important to check opposing discs open, before opening fdr bus discs (and having already checked cb open as a safe to do so)?
To ensure your buses are not in parallel.
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Why isn’t it safe to operate banks in parallel?
The potential for increased fault current.
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What are we verifying by visually checking the 4.8kV Transfer Bus?
No load is connected (no fdr discs closed to the tb) and no grounds (no debris or abnormalities).
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Why do you block the fdr pos cb AR on manual and ensure that the TBT CB AR is also blocked on manual?
To ensure that if a problem occurs while switching and a cb trips, it will not reclose.
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Why is it important to block regulators on neutral and what happens if they are not?
To make sure there is no difference in voltage/potential.
If there is, a circulating current can be created tripping the fdr cb and/or the tbt cb.
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Why is there a reactor on the fdr pos at gas style stations?
To limit fault current to regulators
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If work is to be done to a front or rear bus at a dept style station, what would your alternate source be for your fdrs?
The opposite bus or the transfer bus.
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Why would you use the 4.8kV Transfer Bus at a gas style station?
If work is to be done on the fdr pos or the reactor bus.
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What is a Clearance?
A statement from an LD or designated LD that the SPECIFIED circuit, circuit component, or equipment is disconnected from SPECIFIED sources of energy.
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What does the term disconnected mean?
That a visible air gap exist
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What is a Local Clearance?
Originate with an operator or trouble dispatcher and relates to equipment within the station, not under the system jurisdiction.
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What equipment is included in a local clearance?
All equipment under 600V, fdr pos equipment, and hydraulic pipelines
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When is a Clearance required?
Before any person contacts parts of normal energized high voltage equipment.
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If an authorized person holds clearances on two adjoining circuits, can they ask to have you operate equipment for them while the clearance is still out?
Yes, to test on the adjoining circuit only and the equipment must be restored prior to the authorized person turning in their clearances.
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What are the two opposing functions of a CB?
When closed, it must carry current without loss. When open, it must insulate without leakage.
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What is plasma?
An electrically conductive gas formed by ionization
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What is ionization?
The formation of one or more ions by adding or removing electrons from atoms or molecules.
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What is a plasma arc?
When contacts separate but current is still being carried, ionization occurs as well as temperature rises. At a specific point, metal of the contacts begins to melt and bridges the gap. This is a plasma arc.
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What would happen if an arc did not appear, and current were to be cut off instantaneous within a CB?
Large destruction overvoltage would be created. This is because the magnetic field collapses too fast.
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How many volts can an air gap of 1cm withstand (as an insulator) at normal atmospheric pressure and temperature?
30000v (30kv)
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How are arcs extinguished?
Oil, SF6, and air. Air is used to extinguish the highest currents (much like an air blast CB).
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What is the maximum temp of the capacity of nitrogen to conduct heat?
7000° C
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A single pair of air blast cb contacts can interrupt up to how many volts?
100kw, so multiple contacts are needed for several thousand volt circuits.
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What type of oil is used in OCB’s?
Mineral
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What’s the chief virtue of hydrogen? What’s its drawback?
Its high heat conductivity. Hazard for fire.
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Where can OCB’s be used?
4.8kV to 500kV.
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What does moisture and debris do to the oil in an OCB?
Reduces the insulation and dielectric strength of the oil.
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Can sulfurhexaflouride catch fire?
No. It is non-conbustible
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Is SF6 dangerous?
No, but it’s byproduct is.
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What are the contacts made of in a vacuum cb?
Copper-tungsten.
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Why does the dept maintain specific voltage?
Customer equipment and appliances are designed to operate most effectively at rated voltages
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What types of customer loads are there?
Heating loads: electric stoves, irons, heaters and toasters
Motor loads: vacuum cleaners, washing machines, fans, refrigerators and power tools
Electronic loads: television, computers and radios
Lighting loads
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A 10% decrease in voltage results in how much decrease in illumination output?
30%.
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What are the two major benefits of maintaining voltage to the power system?
Customer satisfaction and efficiency
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What is a load center?
A point on the feeder where the circuit branches out to several primary circuits
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What is voltage drop?
A decrease in voltage between the source and the load
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How can the dept deal with voltage drop?
Shorten the length of the feeder. Reduce the load. Compensate for the drop
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Why are step type regulators preferred within the dept?
They cost less.
Excitation is 1/3 that of an induction type so less voltage is used within itself.
The step type regulator can hold voltage within a band of =- 3/4v.
The percentage of regulation can be adjusted in the field.
Only a portion of the secondary winding is within the circuit so losses and heating is reduced, increasing the load carrying capacity.
Load current can be increased by 160%.
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What is another name for a voltage regulator?
Autotransformer
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What is meant by “load bonus” feature?
Less percentage of regulation which in turn allows more load to be carried (up to 160%).
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How do you determine kva?
Nominal voltage of circuit being supplied X maximum rated current X percentage of regulation, or kva=kv*a*%
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A change in regulation from 5% to 10% does what?
Cuts maximum load in half.
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How are regulators cooled?
They are self-cooled.
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How are regulators wired?
Open delta, where A and CØ is directly wired in and BØ is an average of the two.
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How many contacts in a step type regulator?
9 (8 plus a neutral)
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How many volts difference between steps?
60V (or 1-1/4% of 4.8kV)
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What are the movable coils called on an induction type regulator?
Rotor.
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What are the stationary coils called on an induction type regulator?
Stator.
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What two reasons are there to block the regulators on neutral?
Prevent arcing and circulating current.
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What does it mean when it is said that a regulator is self-contained?
The regulator power supply is also the supply to the regulator voltmeter. (so, when the power supply is off, there is no voltage indication)
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Why raise the step indicator on a regulator past neutral?
To check the free play and indicator operation.
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A regulator that is one step off neutral has the greatest amount of short circuit current, why?
It has the least amount of impedance.
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