Norwin 225 kW - Main Features of Design

When simplicity makes sense’ is the keyword for the Norwin turbine 225 kW.

The origin of this turbine goes 17 years back, 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 this turbine has resulted in a both simple and robust turbine. Despite of the small size compared to the main stream size of turbines, it is still a very cost-effective turbine. It is ideally suited for installation by customers who only want to have a small but reliable power installation, or for use together with stand-alone system. This is naturally also the reason why Norwin has kept this turbine in our program, where most other manufacturers have decided not to produce this size of turbine any more.

The Norwin 29-STALL-225 kW is a stall regulated wind turbine with a rotor diameter of 29 m and a generator size of 225 kW.

For this size of turbine, it was decided to use the most mechanical simple type of power control system, which is stall control.

Stall control is a passive way of limiting the power from the turbine in strong winds. What happens is that when the wind rises above a certain speed, the blade starts to stall, and looses some of the lift that drives the rotor, and thus 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. However, for a turbine this size, it is important to keep building and maintenance costs at a minimum. Moreover, it is a fact that the benefits from ASR rise much more with size of turbine than the installation and maintenance costs for the system. This is why we use stall control on this size of Norwin turbines: ‘When simplicity makes sense’!

In the following, some of the main features of design for this turbine will be presented.

A pleasure to behold inside and out!
Tower, nacelle, and blades are painted in the same unifying color: This is one of the several reasons that the NORWIN wind turbine creates such a striking, simple silhouette in the landscape – with the beauty of a sculpture. The interior has other, complementary virtues. For instance, a door that can be locked securely so that no outsider has access to its control unit, which is located at the base of the tower.

An aluminum ladder with safety railings leads to the nacelle. The interior is fully lit, and there are rest platforms along the way. Hathes allow for inspction of blade tips, without use of a lift or hoist. The tower is a tube tower and it stands as a sooth, 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.

NORWIN wind turbines put an end to cramped crawling about on exterior ladders and bridges. Up through the tower and straight into the nacelle, whether the wind turbine is operating or not.

The nacelle is spacious enough for two to be working at a time. There is interior lighting and standard service checks can be accomplished without ever opening the hatches. Meaning that work can go on, whatever the weather.

All by design
Nacelle and the spinner are made of fiberglass and kept in the same color as the wings and tower. This material creates both a harmonious visual transition out from the tower to the wings and 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. Thus, no wind turbine is better than its rotor’s capabilities. The rotor’s rpm is determined by its gear ratio. With that in mind, the gears designed and manufactured for NORWIN has the ideal gear ratio for the relevant rotor diameter, generator size, and wind distribution factored into its design.

NORWIN wind turbine’s great effectiveness is partly based on its 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 meaning that the tip are fixed in the operational position by a hydraulic cylinder and are only activated when the pressure is released. By then, the tips will be forced into braking position by the centrifugal force.

Energy from 4 m/s
NORWIN wind turbines start producing energy already at a speed of 4 m/s, because of a generator with an extremely high efficiency level at very low resistance.

Main frame: simple, solid T-construction
NORWIN distinguishes itself from its competitors largely because of its wind turbine’s main frame. In general, the main frame is a heavy, steel construction lacking an efficient transmission of forces. Beyond its heavy weight, it inhibits access to the nacelle.

For this turbine NORWIN has however build 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, performing 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 form 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 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-nickel-molybdenum 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 – and 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 and 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.

Cooled sufficiently as it is in the NORWIN turbine,

The closed type generator is cooled on the outer surface, meaning that the windings are not exposed to humidity and contamination from the cooling air. As a further prevention against humidity during standstill, the generator is equipped with heating elements if necessary.

The generator is protected against overload 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 is in order to protect 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 further a condition for keeping the high standard for personal safety, where it is vital that the turbine in very short time can be brought to a complete standstill.

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 potion 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 and reliable operation.

This occurs via our optional remote monitoring system with direct contact to each NORWIN wind turbine. A computer screen is connected with the telephone network. All that might be necessary for surveillance and remote control of the wind turbine can be communicated through a telephone plug. NORWIN’s computerized surveillance is an extra service, contracted on an individual basis, which 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 conducts four types of:

• 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 (if necessary) by means of motor when the wind-speed is sufficient, and cut-in and cut-out of the generator.

The cut-in and cut-out procedures of the generator are carried out by means of 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, if necessary, bring the turbine to a standstill.

Should the wind turbine come to a standstill due to some unacceptable condition, it will start up automatically when proper conditions have been restored, e.g., after grid failure. When faults require service, e.g. worn brakes, the turbine will, naturally, not be able to start up again until the fault has been corrected.

Safety concept
The safety concept is based on the fail-safe principle. Two separate rotor brakes are used – a mechanical brake disc and turnable blade tips. They can be each released 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 some 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-switch-off takes place by activating both mechanical and air brakes immediately at the same time.

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 case of grid failure, nacelle vibration, over-speed (10% over rated speed, measured on the main shaft) or pushing an emergency stop button.