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scottmert
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Routine maintenance when performed 3-7 years is a cost effective way to determine equipment status.
False
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What is an important tool for detecting over heating and arcing?
DGA
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Describe Thermal Runaway:
Excessive contact wear and carbon buildup increases contact resistance, causing more coking and more heating.
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Every ____ degrees C increase in tempurature _________ the rate of decay of winding insulation.
7 Seven----Doubles
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The _______ causes more unplanned transformer outages and is considered the highest maintenance area on the transformer.
L T C ---Load tap changer
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A temperature differential alarm could indicate a major temperature differential problem, such as off step, broken springs, severe arcing, etc.
TRUE
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Under normal load, it is normal for the LTC to operate warmer than the main tank due to switching operations.
FALSE
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What is an overcurrent within normal current paths?
An Overload.
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To protect equipment from momentary overloads, the overcurrent device is designed to open the circuit quickly.
FALSE
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A ______ is a one-shot device designed to open when a dangerously large current flows, for instance when a _______ ________ occurs.
FUSE
Short circuit
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A current limiting fuse will open how quickly when subject to a high level fault?
1/2 cycle.
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Fuses and breakers can be used to open and close circuits manually or automatically.
FALSE
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Explain a fuse's time current curve:
The higher the fault current, the faster the fuse will open.
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What two current parameters define the current limiting range of an OCPD?
THRESHOLD CURRENT and MAX INTERRUPT RATING
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If set too low, for arc fault protection, the instantaneous setting on circuit can cause ________ tripping as loads attempt to ________.
NUISANCE
START
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On time-current curves, the vertical axis represents:
TIME IN SECONDS.
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Total Time to Clear (Tc) time equals:
(Tm) melting time + (Ta) arcing time.
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On molded case panel breakers, the open under overload is sensed by a _______ Element, while on power circuit breakers a ________ _______ is generally used.
THERMAL
MAGNETIC COIL
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The time between when a breaker senses overload and the contacts begin to move apart is know as the:
UNLATCHING TIME.
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Once a breaker unlatches what happens?
The circuit opens.
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Dual element fuses are also known as ______ ______ fuses, and are designed to prevent in-rush currents or temporary overloads from opening the circuit, but will melt under continuous overloads or short circuits.
Time Delay
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Number 1-9 in proper order, the sequence of events of an SMD power Fuse.
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Maximum load current at the fuse location is typically the total _________ __________ ___________ measured in ______.
Connected tranformer capacity
(measured in) K V A
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Two fuse characteristic curves are:
Minimum Melting Time and
Maximum Clearing Time
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When a down-stream interrupting device interrupts a fault, the sectionalizer counter will:
a) Reset count -wrong
b) Not count - correct
c) Count once - wrong
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Sectionalizers work with upstream, ___________ side protective devices such as reclosers and reclosing breakers.
Source
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Sectionalizers do not open ________ current, but counts it and opens during the ____ ________ interval of the upstream device
Fault
open voltage
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ANSI Device numbers for instantaneous and time overcurrent relays:
50
51
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The instantaneous overcurrent trip is used in a _______ _________ scheme to allow the PCB to open prior to the melting time of the fuse.
Fuse Saving
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PCB reclosing function is provided by the _____________ Relay, device number ______.
Reclosure
79
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The purpose of the time delay of reclosing is to allow ___________________________ and _______________________________.
PCB closing spring to recharge
The ionization gases to dissipate to prevent re-arcing of the gases.
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The acceptable voltage tolerance to our customers is _________ %.
+ or - 5 %
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Three influences on distribution feeder impedance /voltage are:
Capacitance
Inductance
Resistance
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Voltage and turns ratio are __________ proportional.
Directly
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A traditional transformer becomes an ________ -Transformer when their windings are connected to either aid or oppose one and anouther.
AUTO
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The low voltage windings are known as the ________ windings, and contain taps.
The high voltage winding is known as the regulated or _________ winding.
Series
Shunt
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The bridging _________ limits the circulating current caused by the contacts being at different positions.
Reactor
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The ____ _____ ________ allows the regulator to maintain a constant voltage at a remote load center.
Line
Drop
Compensator
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32-step regulation provides an overall full _____ % voltage regutation.
20 %
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