Routine maintenance when performed 3-7 years is a cost effective way to determine equipment status.
False
What is an important tool for detecting over heating and arcing?
DGA
Describe Thermal Runaway:
Excessive contact wear and carbon buildup increases contact resistance, causing more coking and more heating.
Every ____ degrees C increase in tempurature _________ the rate of decay of winding insulation.
7 Seven----Doubles
The _______ causes more unplanned transformer outages and is considered the highest maintenance area on the transformer.
L T C ---Load tap changer
A temperature differential alarm could indicate a major temperature differential problem, such as off step, broken springs, severe arcing, etc.
TRUE
Under normal load, it is normal for the LTC to operate warmer than the main tank due to switching operations.
FALSE
What is an overcurrent within normal current paths?
An Overload.
To protect equipment from momentary overloads, the overcurrent device is designed to open the circuit quickly.
FALSE
A ______ is a one-shot device designed to open when a dangerously large current flows, for instance when a _______ ________ occurs.
FUSE
Short circuit
A current limiting fuse will open how quickly when subject to a high level fault?
1/2 cycle.
Fuses and breakers can be used to open and close circuits manually or automatically.
FALSE
Explain a fuse's time current curve:
The higher the fault current, the faster the fuse will open.
What two current parameters define the current limiting range of an OCPD?
THRESHOLD CURRENT and MAX INTERRUPT RATING
If set too low, for arc fault protection, the instantaneous setting on circuit can cause ________ tripping as loads attempt to ________.
NUISANCE
START
On time-current curves, the vertical axis represents:
TIME IN SECONDS.
Total Time to Clear (Tc) time equals:
(Tm) melting time + (Ta) arcing time.
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
The time between when a breaker senses overload and the contacts begin to move apart is know as the:
UNLATCHING TIME.
Once a breaker unlatches what happens?
The circuit opens.
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
Number 1-9 in proper order, the sequence of events of an SMD power Fuse.
5
7
9
1
3
6
8
2
4
Maximum load current at the fuse location is typically the total _________ __________ ___________ measured in ______.
Connected tranformer capacity
(measured in) K V A
Two fuse characteristic curves are:
Minimum Melting Time and
Maximum Clearing Time
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
Sectionalizers work with upstream, ___________ side protective devices such as reclosers and reclosing breakers.
Source
Sectionalizers do not open ________ current, but counts it and opens during the ____ ________ interval of the upstream device
Fault
open voltage
ANSI Device numbers for instantaneous and time overcurrent relays:
50
51
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
PCB reclosing function is provided by the _____________ Relay, device number ______.
Reclosure
79
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.
The acceptable voltage tolerance to our customers is _________ %.
+ or - 5 %
Three influences on distribution feeder impedance /voltage are:
Capacitance
Inductance
Resistance
Voltage and turns ratio are __________ proportional.
Directly
A traditional transformer becomes an ________ -Transformer when their windings are connected to either aid or oppose one and anouther.
AUTO
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
The bridging _________ limits the circulating current caused by the contacts being at different positions.
Reactor
The ____ _____ ________ allows the regulator to maintain a constant voltage at a remote load center.
Line
Drop
Compensator
32-step regulation provides an overall full _____ % voltage regutation.
