MAIN FEATURES OF DESIGN
 
'When simplicity makes sense' is the basis for the Norwin turbines in the 150 kW to 225 kW range. The origin of these turbines goes back 17 years, with the first prototype installed in 1984, and with not less that 365 turbines installed in Denmark, USA, Germany, and Sweden.
 
The design philosophy for these turbines has resulted in simple and robust turbines. Despite the small size compared to the current utility size turbines, they are still very cost-effective turbines. They are ideal for installation by customers who want a small but reliable power source to supplement the local utility, or for use in conjunction with a stand-alone system. This is why Norwin has kept these turbines in our program, while most manufacturers have retired this turbine size from their catalog. Site analysis, economic feasibility, and customer preference will determine the best size turbine(s) for the project.
 
Two Norwin turbine models are offered in this range. The first is the Norwin 24-STALL that is a stall regulated wind turbine with a rotor diameter of 24 m and available with generator sizes of 100 kW, 150 kW or 200 kW. The second is the slightly larger Norwin 29-STALL-225 kW that is also a stall regulated wind turbine with a rotor diameter of 29 m and a generator size of 225 kW.
 
A "stall control" power control system was chosen for these turbines. This is a simple mechanical power control system that allows us to keep the price affordable. Stall control is a passive way of limiting the power produced by the turbine during strong winds. When the wind rises above a certain speed, the blade starts to stall, and loses some of the lift that drives the rotor, and thus reduces the power output from the turbine. The stall control method lacks several of the advantages of the active stall regulation method (ASR) used in the larger size Norwin turbines but it is important to keep building and maintenance costs at a minimum for these smaller size Norwin turbines. The benefits from ASR are more apparent for the larger size turbines and can justify the additional installation and maintenance costs for those systems.
 
Following are some of the main features of design for the turbine:
 
A pleasure to behold inside and out!
 
Tower, nacelle, and blades are painted in the same unifying color. This is one of the reasons that the Norwin wind turbine creates such a striking, simple silhouette on the landscape. The interior has similar complementary virtues. An access door located at the base of the tower can be securely locked and provides entrance to the control unit. An aluminum ladder with safety railings mounted inside the tower leads to the nacelle. The interior is fully lit, and there are rest platforms along the way. Hatches allow for inspection of blade tips, without use of a lift or hoist. The tower is a tubular tower and stands as a smooth, unbroken conical column. The steel sections are bolted together from the inside, and all joints are welded using the submerged arc welding technique for maximum fatigue strength.
 
Nacelle: Elbowroom for two!
 
Norwin wind turbines put an end to cramped crawling on exterior ladders and bridges. You climb up through the tower and straight into the nacelle, whether the wind turbine is operating or not. The nacelle is spacious enough for two people to work at a time. There is interior lighting and standard service checks can be accomplished without opening the hatches. This allows work to continue regardless of the weather.
 
All by design!
 
The nacelle and the spinner are made of fiberglass and kept the same color as the blades and tower. This material creates both a harmonious visual transition out from the tower to the blades and also provides protection of the wind turbines’ machinery from the ravages of inhospitable weather conditions.
 
Rotor: Heart of the matter!
 
The rotor is responsible for capturing the wind’s energy. The rotor’s rpm is determined by its gear ratio. The gears designed and manufactured for Norwin have the ideal gear ratio for the relevant rotor diameter, generator size, and wind distribution. The Norwin wind turbine’s great effectiveness is partly based on the blades, which are of top quality. The blades are manufactured for Norwin by LM Glasfiber, one of the world’s largest producers of wind turbine blades. The fiberglass reinforced polyester used to make the blades yields superior strength and a smooth surface.
 
Safety brake
 
The blades have integrated air brakes, which are of the turnable tip type. The braking action occurs on the actual surface of the blades, where energy is captured. The blade brakes operate in reverse principle; the tip is fixed in the operational position by a hydraulic cylinder until the pressure is released. The tips are then forced into braking position by centrifugal force.
 
Energy from 4 m/s
 
Norwin wind turbines start producing a measurable amount of energy at a speed of 4 m/s (8.95 mph) because of a generator with an extremely high efficiency level at very low resistance.
 
Main frame: simple, solid T construction
 
NORWIN distinguishes itself from competitors largely because of the wind turbine’s main frame. In general, the wind turbine main frames are heavy, steel constructions lacking efficient transmission of forces. Beyond its heavy weight, it inhibits access to the nacelle. However, for this turbine NORWIN has built the main frame in a T-construction cast in SG iron. The main bearings are mounted in integrated surfaces of support at each end of the main tube, i.e. the main shaft is placed inside the tube. Force is transferred to the tower through three strong slide claws, creating an ideal distribution of forces, which allows for both a light and very rigid construction. The main frame is machined to produce exact surfaces of support for bearings, generator, yaw gears and slide claws. The simple construction provides direct access to the nacelle from the closed tower.
 
Yawing system: protection from battering conditions
 
A cogged ring is bolted to the exterior of the top of the tower. Attached to this are the three strong slide claws securing the main frame. They also maintain its horizontal position. The wear surfaces can easily and inexpensively be replaced, not requiring the main frame to be dismounted. The nacelle is secured by three hydraulic yaw brakes, when not yawing. This ensures that random and rough conditions will not affect the yaw gear. Before yawing begins, the brake is released. Yawing movement is activated by two identical yaw drives. Each consists of an electrical motor. A powerful gear turns a smaller pinion wheel, which, in turn, engages the large cogged ring. Yawing is initiated by a wind vane via the control system. A slight delay has been programmed to prevent sudden, minor shifts in wind direction from triggering yawing.
 
Independent main shaft and bearing supports!
 
The wind turbine has an independent main shaft and bearings. In contrast to a construction with an integrated main shaft, bearing and gears, side loads from the rotor are not transferred to the gearbox. Thereby, the gearbox is free to absorb the torque from the rotor only, making it a more simple construction. The main shaft is forged and made of special chrome-nickelmolybdenum steel. It is mounted in the main frame with two strong, double spherical roller bearings. The bearings have low-friction labyrinth seals with no sliding parts and require neither maintenance nor replacement. When lubricating, fresh grease is forced into the bearings’ center hence, the new grease forces the old out. Periodic dismantling and cleaning is not necessary.
 
The Gearbox
 
NORWIN wind turbines employ specially designed gears. As optimal productivity depends on the gear ratio, NORWIN uses no ordinary industrial gear but only those especially designed for NORWIN turbines by the leading gear manufacturers with knowledge in this field. The NORWIN gearbox is a powerful, 3-stage hollow shaft gear mounted directly onto the main shaft. This ensures automatic centering.
 
The torque is transferred from the main shaft by means of a shrink disc. Concentrations of tension that typically arise with standard torque and groove connections are avoided thus the standard risk of fatigue breaks. NORWIN mounts the shrink disc on the side of the gearbox facing the main shaft. In this position, there is no danger of slippage or wear and tear on the shaft where it enters the gearbox. The gearbox’s torque rod has link bearings at both ends. The gears’ motions are absorbed without slack or internal tensions on the rod. The bearings are tightened with labyrinth seals. Pressure lubrication of the gear reduces the amount of oil in the gearbox. The oil pump is powered by an electric motor. By running the oil pump before start, the rotor can run freely at low rpm and still be well lubricated, even after a stand still period.
 
The induction generator
 
The closed asynchronous induction generator is a component that has proven its value and stability in thousand of turbines all over the world in all types of environmental conditions. Cooling is accomplished on the outer surface, meaning that the windings are not exposed to humidity and contamination from the cooling air. The generator is equipped with heating elements, if necessary, as a further prevention against humidity build up during standstill. Overload protection is provided using two separate systems for monitoring the temperature in the windings. A double, flexible clutch has been mounted between the generator shaft and the gearbox’s high-speed shaft. This protects both the bearings in the gearbox and in the generator against transmission torque peaks, and small misalignments of the gear and generator shafts.
 
Doubly-secured brake system!
 
Apart from the aerodynamic braking system (the turnable blade tips), the turbine is equipped with a second safety brake: the mechanical disk brake. This brake is able to brake down the turbine even in case of a malfunction in the aerodynamic brake (a very unlikely situation). The brake is a precaution for keeping the high standard for personal safety, where it is vital that the turbine can be brought to a complete standstill quickly. A cast steel brake disc has been placed on the high-speed shaft of the gearbox. The braking takes place with two symmetrically placed calipers of the fail-safe type. This means that they have a reverse action, i.e. hydraulic pressure inhibits – rather than activates the brakes. A break-down in the hydraulic system will thus activate the brake and not lead to a brake failure. Since a full emergency braking eats a certain portion of the gearbox lifetime, it is unwise to use the full emergency breaking torque each time the turbine brakes. For this reason, the brake is equipped with a soft brake device for use in all non-critical braking situations. The function is that the brake torque increases slowly and only to the necessary level. This is normally around 60% of the maximum torque. In case of i.e. grid failure or emergency button stop, the brake will immediately supply full torque.
 
Electronic supervision of operation and production!
 
Norwin does not regard delivery, assembly and installation of a wind turbine as a complete product supply. We ensure that our wind turbines also deliver the optimal energy production with reliable operation. This occurs via our optional remote monitoring system with direct contact to each Norwin wind turbine. A computer is connected via the telephone network. Surveillance and remote control of the wind turbine can be communicated through the telephone connection. Norwin’s computerized surveillance is an extra service, contracted on an individual basis, and ensures maximum security, productivity and longevity.
 
Electronic surveillance of four types:
 
The main controller of the turbine is placed at the bottom of the tower for easy access. It generally performs four types of electronic surveillance:

• Control of the wind turbine operation
• Safety and security surveillance
• Registration of the turbine’s operational data
• Optimization of the turbines energy production

Electronic control of the turbine’s operation comprises yawing the turbine according to wind direction, start up (if necessary) by means of a motor when the wind-speed is sufficient, and cut-in and cutout of the generator. Cut-in and cut-out of the generator is accomplished using thyristors which ensure a gradual connection to and from the grid (Soft cut-in). Safety surveillance will monitor possible faults in the turbine or non-favorable conditions and will, if necessary, bring the turbine to a standstill. The wind turbine will start up automatically when proper conditions have been restored, such as after a grid failure has been corrected. When faults require service, e.g. worn brakes, the turbine will not be able to start up until the fault has been corrected.
 
Safety concept
 
The safety concept is based on the fail-safe principle. Two separate rotor brake systems are used: a mechanical brake disc and turnable blade tips. They can each be operated by two independent safety-chains. The first safety chain is the main controller, and the second is a directly wired chain that will only look at a few critical parameters. The purpose of the second chain is to secure the turbine even if the main controller goes down. If one of the safety-chains is interrupted, an emergency stop takes place by activating both mechanical and air brakes immediately. The directly wired safety system is activated in case of failure of the electronic system. It activates the rotor brakes by switching off the hydraulic valve and the emergency system of the control unit. It works in cases of grid failure, nacelle vibration, over-speed (10% over rated speed, measured on the main shaft), or pushing an emergency stop button.