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Northstar Wind Towers Technical Overview


Group Experience

Tower Dimensions

General Analysis

Connection Testing

Internals Overview

Terminology – 80m Tower






SINGLE PANEL pre-shipping









Team Experience

• Northstar Wind Towers is comprised of engineers, finance and business professionals with backgrounds in the wind industry and heavy manufacturing. • Our group has installed a 1.5 MW machine on a tower that employs similar connection methods. This turbine has been operating for close to 5 years. • A prototype version of that tower (different application) was installed 7 years ago with a 660kW turbine atop. This tower is also still in full operation.

Team Experience

• The Northstar tower has recently been certified by Germanischer Lloyd for a 2.5MW wind turbine.

Frequency • Cross sectional properties were calculated using ANSYS Professional Software • In order to accurately predict the system's Eigen frequencies additional masses are added to the beam model (platforms, fasteners, opening reinforcements, etc). • Rigid Foundation analysis assumes complete fixity at zero elevation. • Soft Foundation modeled as a single 2m tall beam with finite stiffness and does not contribute to the mass matrix. • Based on simulation, 80m and 100m tower is within acceptable loads envelope for the majority of utility scale wind turbine on the market today.

General Analysis Considerations

Nonlinear buckling analysis of bottom section

Nonlinear analysis for bottom and top flange strength checks

In house analysis capabilities •

ANSYS Professional NLS

Bolt Tension Considerations • Installation Method • Turn of the nut - yields pretensions average 26% over minimum specified • Tighten the bolt to “snug tight” = full effort of a man using an ordinary wrench then apply a further turn to the bolt (1/3 or 1/2 turn depending on the length of the bolt versus the thickness of the plies

• As the nut is turned, conditions in the bolt are initially elastic but local yielding in the threaded portion begins. As the bolt continues to elongate the bolt load versus elongation response flattens out – the pretension levels off • What about variation in “snug tight” • Has been tested, again because of the inelastic response, there is minor variation of resulting preload

• What about relaxation? • The design friction coefficient includes relaxation characteristics due to creep of coating – this is implicit in the creep test • For example, the primer we have specified has a static capacity of 0.59, but Eurocode only allows use of 0.50 in part due to bolt relaxation • Min preload is used for design calculations – as can be seen above, actual preloads are much higher • Investigations reveal 12% relaxation in hot dipped galvanized assemblies due to coating (zinc) thickness • Additionally considered with hole geometry correction factor of 0.85 for oversize holes

• What is the external load the bolt is subjected to? • The bolt will experience a load fluctuation based on the increase or decrease in thickness from tension compression stresses in the shell (Poisson effect) but does not directly experience the applied load from the turbine

Connection Testing Bolt Relaxation •

Bolt elongation monitored throughout test with ultrasonic bolt length device


Maximum relaxation found was 10%, minimum bolt load 19% above design bolt tension

Bolt Force Results 75.00 333

70.00 311

Bolt Force (kN)

Initial Bolt Tension Final Bolt Tension 65.00 289 Design Tension

Minimum Final Tension 19% above Design Tension

60.00 267

Average Initial Pretension

Average Final Tension 55.00 244

50.00 222 1




5 Bolt




Connection Testing Summary and Conclusions •

After 1-million cycles at ±75kN, none of the test assemblies showed any signs of slip, deformation, or breakage

After 2-million cycles at ±75kN lbs, no signs of any slip deformation, or breakage

After 10-million cycles at ±75kN lbs, no signs of any slip deformation, or breakage

All tested assemblies exceeded the proof compressive load of 315kN without any indications of slip or plastic deformation

Under tensile load after 1E6 fatigue cycles and compressive proof load, slip occurred in two assemblies at approximately 396kN and 405kN respectively

Under tensile load after 1E7 fatigue cycles, slip occurred in one assembly at approximately 440kN

Internals Package Overview

Design Considerations – Compatibility • Utilize as much of the current tower internal design as practical in translating to the Northstar design

– Safety • ISO 14122-1, 14122-2, 14122-3, 14122-4 • OSHA 29 CFR 1910, 1910.66 Fall Arrest, 1910.68 Service Lift • EN 50308

– Functionality • Tower Erection • O&M

– Cost • Common Design • Optimized the use of shared parts • Manufacturability – Burn & Bend

– Installation • Lightweight parts.

Platform Elevations 80 meter example

• •

Total of 6 platforms including the base platform. Ladder & Service lift are located centrally in the tower. This allows for open unrestricted access to all bolts during tower erection. The base platform through the C platform are shipped as palletized bundles to be assembled on site with its corresponding section. Platforms D & E are fully assembled in the manufacturing facility. (D & E Sections ship complete)

Internals Package Overview Typical Patform • • •

0.1875” Diamond Tread Plate Common cross section allows streamlined manufacturing operations All platforms to be assembled on site fit on a flatbed trailer along with one A Section Panel

Service Lift / H 200 SL - L Product Photos

Looking Up: Top access from service lift Looking Down: Bottom access from service lift

Images: courtesy of Hailo LLC

Transportation Overview

Northstar Wind Towers Transportation Overview

1) Design Goals 2) Panel Transportation System

3) Cost a) 80 meter b) 100 meter

Primary Design Goals Bundling Frames Utilization of custom designed bundling frames allow for the safe and efficient transportation and offloading of the lower tower section components. Bundling frames enable the lower tower components to remain intact and together as loaded at the factory and can be offloaded onto common cribbing materials as site conditions require. Elements of the bundling frames work in conjunction with the assembly jig components to supplement panel alignment and enable an efficient onsite assembly process.

Standard Trailers Transportation of the modules or panels can be done on readily available standard flatbed and double-drop trailers.

Panel Transportation System (80m) The tower will arrive on site via a total of 7 standard flatbed trailers and 2 expandable double drop trailers. Custom covers (tarpaulins) and pre-assembled internals not shown.

Transportation Cost Comparison 80m

Northstar Wind Towers Field Assembly & Tower Erect Overview

Northstar Wind Towers Field Assembly & Tower Erect Overview

1) Foundation 2) Site Layout

3) Section Assembly 4) Tower Erect 5) Costing Summary

6) Component Return

Foundation Foundation Design • Northstar has solicited Engineer’s Budgetary Estimates for three different foundation types (Barr - Inverted T / P&H - Pier / P&H - Rock/Soil Anchor) for a generic foundation. • All of the foundation estimates for the Northstar 80m foundation designs are on par with the cost estimates received for the conventional tubular tower foundation currently in use. • The estimates for the 100m tower are significantly lower for the Northstar tower as there is no need for embedment rings.

Site Layout (80m)

REQUIREMENTS A relatively flat area conducive to assembly of the tower sections is required. It is not anticipated that any special requirements beyond that associated with normal turbine and rotor assembly and installation will be required for NMT field assembly.

Generic Site Layout Option

Section Assembly The bundling frames are interlocking and fit into a simple fixture that forms the base of the field assembly jig.

Assembly Jig and Panels at the jobsite. Pre-assembled internals components not shown.

Section Assembly INTERNALS ASSEMBLY Internals assembly of the platforms and other internals components for the lower tower sections will take place in conjunction with the section assembly process. Top of ‘A’ Section Platform

Northstar will pre-assemble in the factory as much of the tower internals as is practical. Some of these preassembled items could include ladders, buss-bar, cabling and related support brackets.

Tower Erect GENERAL • Erecting the NMT tower is accomplished in generally the same manner as the erection of a conventional tower. Sections are lifted and swung into place, then fastened to the section below. • Instead of a flange to flange connection, the NMT utilizes a horizontal splice (friction) connection. • Oversize holes, stringent manufacturing tolerances and CNC drilling technology help to ensure that field alignment of the section-to-section connections can be accomplished in a timely, efficient and repeatable manner. • Bolt alignment in the NMT requires a somewhat more organized methodology, but in the end, the installation crew is still just inserting and tightening bolts.

Field Assembly & Tower Erect


Bundling Frames Section Support Carriages Lifting Fixtures Assembly Jig Brackets Shipping Covers (Tarps)

Northstar Wind Towers Program Overview

1) Intellectual Property 2) Prototype

3) Conclusion

Intellectual Property

We anticipate that the patent office will eventually require the IP to be broken into two or three separate patents, but rather than try to decide where to draw the lines ourselves, we will let the USPO make the specific determinations.

Patents will include manufacturing methods, transportation rigging, pre-assembly configuration, outside nut retention and various details of the internals configuration.

Conclusion Benefit Summary

• End-users and developers are the entities with the competitive advantages using the Northstar tower. Lower cost and more flexibility. • Northstar has already developed over 1,000MW of demand for customers in North America & Eurasia. • Northstar Wind Towers is confident that we can provide any developer with the best all-around solution to your tower needs now and in the future…

Conclusion Benefit Summary For larger turbines (2MW+) on taller towers (100m+), Northstar’s modular tower design with increased base diameters provides substantial advantages over conventional tubular tower designs: • Optimized steel efficiency - reduce weight by 25-35% • Greatly reduced transportation costs - reduced by 70%

• Cost-effective access to 100m+ hub-heights - reduced COE • Minimal O&M training and low lifetime O&M costs • Increased manufacturing capacity and through-put • Fully enclosed personnel access with regularly spaced platforms and personnel lift compatibility • Aesthetics – virtually no difference in appearance from conventionally accepted norm

NWT presentation  

Modular towers are the future of wind energy

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