Fast Speed Ratio - A speed ratio of melting
characteristics from 6-8 (refer to Speed Ratio). Fast Speed Ratio - A speed ratio of melting
characteristics from 6-8 (refer to Speed Ratio).
Fault Current - The current from the connected
power system that flows in a short circuit.
Fault Indicator
- A device which indicates fault current by sensing the magnetic
field caused by current flowing through the conductor. Once the
current is above the fault indicator's current rating, the fault
indicator will trip.
Ferroresonance
- A phenomenon characterized by overvoltages and very irregular
wave shapes which are potentially damaging to a transformer. It
typically occurs when there is no ground on the system except
through the transformer connected line to ground. It is always
associated with the excitation of one or more saturable inductors
through capacitance in series with the inductor. When one or two
phases are disconnected from the source by single-pole fault
clearing or switching, it is possible for the transformer
windings connected to the open phases to be excited through the
system capacitances to ground and between phases.
Flashover
- A disruptive discharge around or over the surface of an
insulator.
Flicker
- Impression of fluctuating brightness or color, occurring when
the frequency of the observed variation lies between a few hertz
and the fusion frequencies of the images.
Fluctuation
- A surge dip in voltage amplitude, often caused by load
switching or fault clearing.
Follow
Current - The current which flows through an arrester, caused
by the power frequency voltage across it, during and after the
passage of surge current.
Form
4C Control - Microprocessor-based electronic recloser
control.
F-O-W
Sparkover - Front-Of-Wave Sparkover; the voltage on the font
of an impulse wave at which a gapped arrester sparks over.
Frequency
- On ac circuits, the designated number of times per second that
polarity alternates from positive to negative and back again,
expressed in Hertz (Hz)
Front-Of-Wave
Sparkover - Refer to F-O-W Sparkover.
Fulgurite
- tunnel-like structure formed when a current-limiting fuse
operates; glass-like structure formed by the temperature of a
high voltage arc when a current-limiting fuse operates; the fused
silica sand that remains after prolonged abnormal current flow.
Fuse - A device that will
heat up, melt and electrically open the circuit after a period of
prolonged abnormal current flow.
Fuse
Arcing Time - The amount of time required of the fuse to
extinguish the arc and clear the circuit; the specific amount of
time required for an interrupter to clear a circuit after its
fusible element has melted.
Fuse,
Buttonhead - A relatively common type of expulsion fuse
utilized in open or enclosed cutouts; the name given to the upper
assembly of a distribution fuse link which is then used in a
reusable fuseholder for outdoor cutout applications.
Fuse
Canister - Dry well full range current-limiting fuse holder -
loadbreak and non-loadbreak. Fuses are mounted in an oil tight
canister which extends into the tank beneath the oil. Accessible
from the high voltage compartment, the fuse is air insulated.
Fuse,
Cartridge - Expulsion type fuse with either current sensing
or dual (current and oil temperature) sensing elements mounted
internally under-oil. Used to remove an apparatus from the
primary circuit in the event of a current fault. Cartridge fuses
have limited interrupting ratings.
Fuse
Clearing Time - The total time required for the fuse to melt
and clear the circuit; melting time plus arching time.
Fuse,
Clip-Mounted - A full range current-limiting fuse mounted in
clips in the high voltage compartment.
Fuse,
Current Sensing - An expulsion fuse having elements whose
characteristics are not affected by elevated oil temperatures; a
fuse having elements that are made of copper, tin or silver that
will react to current flow only.
Fuse,
Dual Sensing - An expulsion transformer fuse having elements
that are sensitive to fault current, load current and temperature
(top oil); a fuse that senses the top oil temperature of a
transformer in addition to the temperature from the current flow;
a fuse that can monitor the aging effects of elevated transformer
hot spot temperatures regardless of cause; sometimes know as
"load" sensing.
Fuse,
Electric - An overcurrent protective device with a circuit
opening fusible part that is heated and severed by the passage of
overcurrent through it.
Fuse,
Expulsion - A replaceable one-shot current interrupting
device having definite time current characteristics; a device
which has a metal melting element and uses the principles of
heated fibers releasing de-ionizing gases, and alternating
current passing through a zero reference periodically for arc
extinction.
Fuse
Link - The (metal) fusible element in an expulsion cutout;
the composite construction of materials that house the fusible
element.
Fuse
Maximum Interrupting Current - That upper current level that
a fuse can successfully clear with assured reliability; the
maximum current at a specified maximum design voltage that a fuse
if required to clear as specified by the manufacturer.
Fuse
Maximum Operating voltage - The maximum voltage that a fuse
can properly operate at with assured clearing.
Fusing
Melting Time - The amount of time required to melt a fusible
element at a specific current.
Fuse
Minimum Interrupting Current - That lower limit of current
that up0on melting a fuse can be assured of successfully
clearing; a term generally associated with back-up
current-limiting fuses indication the lower limit of current that
the fuse can clear upon melting.
Fuse,
Open-Link - An outdoor expulsion fuse for use in an open-link
cutout; a one-shot fuse that is usually suspended between two
spring arms which hold the link in tension; a "flipper"
fuse.
Fuse,
(silver) Sand - An abbreviated name for a type of
current-limiting fuse that has silver for its element and sand as
its surrounding media (refer to Current-Limiting Fuse).
Fuse
Spider - The element support material used in a
current-limiting fuse of various compositions and design.
Fuse,
Type D - Refer to D-Link.
Fuse,
Type K - A specific type of expulsion fuse available in
button and open-link configurations. The "K"
designation refers to specific time current characteristics,
defined by ANSI, allowing customers to purchase fuses from more
than one manufacturer without adversely affecting the overall
operation of the system.
Fuse,
Type N - Expulsion fuse links having time current
characteristics unique to and defined by individual fuse
manufacturers. Since the characteristics are unique, various
manufacturers' products cannot be interchangeably used on a
distribution system without adversely affecting its operation. In
addition to type "N", other links that fall into this
category are Type H, Type Q, Type QA, Type KS, Type 200, etc.
Fuse,
Type T - A specific type of expulsion fuse available in
button and open-link configurations. The "T"
designation refers to specific time current characteristics as
defined by ANSI. In reference to the type "K" links,
the type "T" links are time delayed or retarded in
operating characteristics.
Fuse,
Weak Link - A coined name for the cartridge fuse. The name is
take from the thought that the fuse would be the weakest link in
a chain causing the fuse to open the circuit before equipment is
damaged.