Conductor galloping on power lines: what it is, when it occurs and what it means for poles

What it is and how it differs from vibration

By the definition in the PUE (Rules for the Arrangement of Electrical Installations, 2026 edition), galloping of conductors and ground wires is a steady periodic low-frequency oscillation in a span at 0.2–2 Hz, forming standing waves (sometimes combined with travelling waves) with from one to twenty half-waves and an amplitude of 0.3–5 m. One full cycle takes from half a second to five. The conductor moves in one big arc or several, and it can be seen from the ground without binoculars.

Galloping is often confused with vibration because both are «oscillation», but the nature and the consequences differ. Vibration is fast and small, galloping is slow and large.

When galloping occurs

Two things are needed at once: wind and an asymmetric conductor profile. A clean conductor is round and the air flows around it equally from all sides. When ice, rime or wet snow has built up on the windward side, the section takes a shape like a wing, and the airflow produces a lift force that changes as the conductor moves. If the rhythm of these changes matches one of the natural frequencies of the span, the swing grows.

The deposit does not have to be thick. Galloping is possible even when the ice is hardly visible from the ground. The wind has to be fairly steady and blow across the route.

Open plains, hilltops, sections on ridges and across valleys are riskier. Forest, dense buildings and a heavily broken relief shelter the conductor from the cross wind and reduce the probability; the PUE takes this into account in cl. 2.5.98 (see below).

Galloping lasts until the weather changes: the wind weakens or changes direction, the deposit falls off or melts. That may be hours, sometimes a day or more. How often such days occur on a given section is shown by observations: the PUE allows climatic values to be refined from long-term data of weather stations and network owners, including the frequency of conditions in which galloping may occur (cl. 2.5.30).

Galloping zones in Ukraine under the PUE

The PUE divides the territory into two zones by the average frequency and intensity of galloping (cl. 2.5.72, fig. 2.5.9). Zone 1 is moderate galloping, on average not more often than once in five years. Zone 2 is more often than once in five years, intense. On the map zone 1 covers the northern belt of the country (Polissia) and a small area in the west; the rest of the territory is zone 2.

The map may be refined from operating data. So for a particular route the zone is determined by the line design, not by an article on a website.

This map should not be confused with two other maps that also concern ice and wind.

Conductor spacing: what the PUE requires

Galloping is dangerous first of all because it brings the conductors together in the middle of the span, where the swing is greatest. So the standard solves the problem by geometry: it sets the spacing between conductors and the horizontal offset of the tiers, and does not put a dynamic component into the pole calculation (cl. 2.5.72).

For a horizontal arrangement of conductors the spacing in the span is calculated by the formula of cl. 2.5.97; it is covered in the article Span length of power lines. For mixed and vertical arrangements (cl. 2.5.98) the rules depend on the galloping zone.

• Suspension poles, sag of the design span up to 16 m, zone 1: the offset of adjacent tiers is taken from table 2.5.22. In ice zones 3–6 the spacing is also checked by formula (2.5.24) and the larger of the two values is taken.
• The same poles in zone 2: the offset is taken from table 2.5.23, without the additional ice check.
• Sag above 16 m: the spacing is calculated by formula (2.5.24): d = 1.0 + U/110 + 0.6·√f + 0.15·V. Here U is the line voltage, kV; f is the greatest sag at the highest temperature or under ice without wind for the design span, m; V is the vertical distance between the conductors, m.

The difference between the zones shows in the numbers of the two tables: with intense galloping the required offset is greater, in the rows chosen by 0.5–0.85 m.

A few rows from both tables are taken for illustration; the full tables for 35–330 kV are in the text of the PUE. The values depend on the vertical distance between conductors, which the design sets.

Tension poles, exceptions and protective measures

On tension poles of 35–750 kV lines the spacing between conductors is calculated by formulas (2.5.22) and (2.5.23), and the least offset of adjacent tiers is, as a rule, not taken below table 2.5.24. Here the galloping zones are no longer distinguished, but the ice zone is taken into account.

No horizontal offset is required on poles of 35–330 kV of all types if the vertical distance between conductors is greater than 0.8f + U/250 for single conductors and greater than f + U/250 for bundled phases. A conditional example: a 110 kV line, single conductors, f = 6 m: 0.8 · 6 + 110/250 = 4.8 + 0.44 = 5.24 m.

There are two more relaxations. If a section lies in zone 2 but is sheltered from cross winds by relief, forest, buildings or structures at least two thirds of the pole height, the zone with moderate galloping is recommended. And if anti-galloping measures are used on the line, the spacing may be taken by formulas (2.5.22) and (2.5.23), and the tier offset by table 2.5.24.

PUE table 2.5.24: least horizontal offset of conductors of adjacent tiers on tension poles.

Design measures against galloping

The PUE does not require the dynamic effects of galloping to be included in the pole calculation. Instead, where galloping may occur, it is dealt with by design measures (cl. 2.5.72). There are several, and they act at different levels.

• Phase arrangement. In ice zones 4–6 and for lines above 330 kV the phases are recommended to be placed horizontally or in a triangle, with the middle phase above or below the outer ones; on 35–110 kV lines (except covered-conductor lines) with several tiers, preference is given to offsetting the conductors of adjacent tiers horizontally (cl. 2.5.95).
• Interphase insulating spacers in the span in the schemes «conductor – conductor», «phase – phase», «phase – ground wire», «conductor – ground wire» (cl. 2.5.90). They do not damp the motion, they keep the conductors from approaching.
• Anti-galloping devices on the conductors themselves. The PUE mentions protective means and allows relaxations of spacing for them, but does not describe their design. In practice these are dampers of different operating principles, selected separately for single and bundled phases; the type, mass and spacing are set by the line design.
• Ice melting. For lines with bare conductors in areas with an ice load above 20 N/m (ice zones 5 and 6), with frequent ice or rime together with strong winds, and in areas with frequent and intense galloping, the PUE recommends providing for ice melting on conductors and ground wires (cl. 2.5.22). This requirement does not apply to covered-conductor lines.

All this is a decision of the line design and the power company. For the pole they matter because part of them (the phase scheme and tier offset) is carried by the pole geometry itself.

What this means for the pole and crossarm

The standard does not require the pole to be calculated for galloping dynamics, but that does not mean galloping does not touch the pole. The design cases (wind, ice, broken conductor) set static loads, while during galloping the insulator string, clamps and crossarm take many cycles of alternating force. On the joints this acts as fatigue loading, not as a single shock.

The shape of the pole head itself depends on the galloping zone and the conductor scheme: the vertical distance between crossarm tiers, their reach and offset. So the galloping zone and conductor spacing belong to the input data for pole design, not to later refinements. We make our multi-sided poles for 6–10 kV, 35 kV, 110 kV and 220 kV lines to the customer’s drawings or develop KM and KMD drawings for the specified geometry.

In joints that carry alternating load the most vulnerable places are the crossarm-to-shaft connection, the lugs for insulator strings, and flange and bolted joints. So in the shop we check welds by visual inspection and ultrasonic testing, and supply the bolted connections with fasteners as the design requires. How this is built on a multi-sided pole is described in the articles on joints of a multi-sided pole and acceptance of multi-sided poles; on bolt tightening torque see Bolt tightening torque.

If the line runs in zone 2 and the design sets an additional load from galloping, we take it from the brief: the PUE gives no standard values for galloping dynamics, and we will not invent them ourselves.

What to send for pole design in an intense galloping zone

Besides the usual set (voltage class, conductor grade and section, number of circuits, wind and ice zone), such lines need data that is not in a standard brief:

• the galloping zone from fig. 2.5.9, refined from operating experience if there is any;
• the arrangement of conductors and ground wires, the vertical distances between tiers, the horizontal offset and the sag of the design span;
• whether interphase spacers, dampers or ice melting are provided: if so, their mass and attachment points;
• additional loads from galloping, if the line design sets them, with the design case stated.

The rest (pole type, height, foundation) is selected in the usual way, see the section on power line poles.

What to inspect on the pole after galloping

If the line tripped during ice and wind, or a line walker saw large swings of the conductors, the pole is inspected out of turn afterwards. The procedure and scope are set by the operating documents of the line owner; below is what it makes sense to look at on the steel structure itself.

• Bolts and nuts: in the crossarm attachment, on flange joints and on anchors. Look for loosened tightening, turned nuts, missing lock nuts and washers.
• Welds of crossarms and lugs for insulator strings: cracks, especially at the weld root, in the stiffener zone and at flanges.
• Crossarms: residual bends, a change of position relative to the horizontal, cracks in the parent metal.
• Lugs, shackles and insulator brackets: wear, elongated holes, marks of rubbing.
• Shaft or lattice: local dents, bent members, deviation of the pole from the vertical along and across the line.
• Foundation and anchor bolts: cracks and chips in the concrete around the bolts, new settlement, exposed reinforcement.
• Zinc coating: rubbed-through areas in places of friction and suspension points.

Inspection does not replace calculation. If residual deformation, cracks or sheared bolts are found, the pole is judged by the results of a technical survey and a verification calculation; the method and the list of defects are given in the article Condition assessment of steel overhead line poles. Technical survey of structures is our service. The condition of conductors, fittings, spacers and dampers is assessed by the line operating service.

What we do and what we do not

We make poles and crossarms, develop KM and KMD drawings and carry out technical surveys of steel structures. Pole erection is carried out by a licensed partner construction company under its work execution plan.

We do not design lines, do not choose the anti-galloping scheme, do not install spacers and dampers on conductors and do not maintain conductors. These are the tasks of the design organisation and the power company. General requirements for power line poles are collected in the article on requirements for power line poles; loads are covered in Loads on overhead lines and power line poles.

Standards and validity

All numbers and clauses in this article are taken from the Rules for the Arrangement of Electrical Installations (PUE), 2026 edition, chapter 2.5: the definitions of conductor vibration and galloping, cl. 2.5.22, 2.5.29, 2.5.30, 2.5.72 (fig. 2.5.9), 2.5.90, 2.5.94–2.5.98, 2.5.100, tables 2.5.22–2.5.24. The PUE came into force on 05.06.2026 and replaced the previous edition. For a project, the table values should be taken from the text in force.

Operation and inspection of lines of 35 kV and above is described by SOU-N EE 20.502:2007 «Overhead power lines of 35 kV and above. Operating instructions».

The validity and edition of each document must be checked before it is used in a project.