What is galloping?
Galloping is a phenomenon of low frequency, high amplitude wind induced vibration with a single or a few loops
per span. Galloping usually occurs in moderately strong, steady wind acting upon an asymmetrically iced conductor surface. Wind direction
causing the galloping has to be more than 45° to the line axis.
Wind and ice cause power lines to gallop. Depending upon the wind
direction and speed it can create uplift on the iced-up conductor. Consequently a galloping, or jumping, motion occurs. Power lines
can sway in high winds, but it's the combination of wind and ice that causes them to gallop more forcefully.
Watch Galloping In Action
What Controls galloping?
CIGRE 322 advises on the following three protection methods as countermeasures to galloping:
of ice or preventing its formation on conductors.
* Interfering with the galloping mechanisms to prevent galloping from building up
or from attaining high amplitudes.
* Making lines tolerant of galloping through ruggedness in design, provision of increased phase
clearances or controlling the mode of galloping with interphase ties.
Trying to control galloping in one particular span may not decrease
the likelihood of galloping, since galloping can get started in any span and travel forward and back. The objective should be to control
the galloping amplitude to within safe limits (< 5ft).
Decreasing galloping amplitude by a certain factor (i.e. 20%) will not provide
an adequate galloping solution. Generally a conductor will gallop up to 100% of sag. Dampers that merely decrease the amplitude by
a certain factor leave the conductor at risk for flash-over and outages.
How does twisting help control galloping?
All AR products
offer galloping control by twisting the conductor. This methodology operates on two key principles – acceleration and inertia.
has shown that twisting the conductor will arrest galloping rather than decrease galloping amplitude. Generally a conductor will gallop
up to 100% of sag and gallop down a percentage too. A twisting mechanism effectively controls galloping by interrupting the cycle
before it gets going. As the angle of wind attack creates galloping conditions, the gravitational force on the AR damper causes the
conductor to start twisting and effectively dumping off the aerodynamic lift. AR Products are not intended to decrease the amplitude
of galloping, rather all are designed to interrupt galloping so that higher amplitudes are not achieved.
What are the electrical impacts
(corona) of AR product technology?
When galloping control systems are used on low and medium voltage lines (115kV-230kV) corona is
not a factor. When voltages are higher (345kV, 500kV) the AR Products are corona protected. To further protect the conductor most
AR products are installed with line guards or Armor Rods.
What is the mechanism of ice shedding/how many galloping cycles occur?
are two different phenomena. Galloping is a steady state of large amplitude motion. Ice shedding is an intermittent phenomenon that
causes the conductor to jump when the ice falls from the conductor.
The mechanism of ice shedding - ice sheds in large chunks which
causes the span to jump or gallop. Ice shedding and its affects have negligible effect in causing galloping.
We have little data or
experimental evidence on the number of galloping cycles. Because the AR Twister is designed for a low frequency conductor, you get
only one cycle every 5-7 seconds depending upon the span length. AR Twister interrupts the conditions that lead to galloping so there
are no cycles to get underway.
What is the difference between galloping and Aeolian vibration?
Galloping is a low frequency, high
amplitude wind-induced motion of a single conductor. Aeolian vibration is a high frequency, low amplitude motion caused by smooth
laminar winds flowing across a cable. Uncontrolled galloping at high amplitudes can cause flashover and outages. Vibration that is
unchecked can cause wear and structural damage to structures, hardware and the conductor itself.
Is there any impact on Aeolian vibration
due to the use of AR Twisters?
Yes, AR Twisters are designed to control Aeolian vibration and galloping at the same time, by the same
unit. This is a key element of the damper.
How does the MOD2 Spacer Damper control vibration and galloping?
The MOD2 controls galloping
by the twisting mechanism in the clamps. The installation methodology is also a key factor in controlling high amplitude galloping.
When the conductor experiences high frequency vibration, the conductor moves against the clamp. The clamp itself creates an impact
with the steel hoop, thereby absorbing the transferred energy. In addition that motion creates movement of the coil springs, which
also impact the hoop, adding more energy dissipation. Such features of the design eliminates the need for the dogbone or any other
high frequency damper.
Which AR Products use a twisting mechanism?
Low Frequency Galloping Control Systems all deliver an initial
twist of the conductor at installation. These product solutions include WINDAMPER, AR Twisters, AR MOD2 Spacer Dampers, and AR Lightweight
High Frequency Vibration Control Systems offer control for Aeolian vibration. These product solutions include Sandamper,
AR Snubber, AR Ring Damper. AR Dual Dampers and AR Twisters control galloping in addition to Aeolian vibration.
What is the life cycle
cost of AR Products?
The average service life value of the AR Twister is 12-15 years or more. Many WINDAMPERS have been in service
for more than 30 years. If routine maintenance plans are followed for Sandampers, the service life value can be 25 years or more.
AR MOD2 Spacer Dampers have been in service for more than 12 years.
How do AR Products compare with Interphase Spacers?
The key difference
between interphase spacers and the AR product line is the clamp. For example, the AR Twister clamp is responsible for rotating the
conductor through large angles so that galloping never gets going. The interphase spacers are designed to keep the conductors separated
to avoid flashover. The net result of using the interphase spacer is that the two lines tend to gallop in synchrony. Side by Side
comparison AR Twister – Interphase Spacers.
How does the AR Twister compare with dog-bone dampers?
The AR Twister is a galloping control
damper that also protects the line from Aeolian vibration because of how it is installed. Dogbone dampers are designed to protect
the line from vibration and the damage caused by unchecked vibration (structural wear and tear). Donbone dampers do not mitigate galloping.
What is the decrease in galloping amplitude by AR Products?
In a publication issued by a CIGRE work group in 2005, it was reported
that during a field test by EPRI, the Windamper was reported to reduce galloping amplitude by 75%. When AR Products are installed
as a system across at least 10 consecutive spans it is possible to achieve a reduction in peak-to-peak galloping amplitude of more
Observed peak-to-peak amplitudes of galloping are often as great as the sag in the span and are sometimes greater, especially in short spans.