Turbinator Spørsmål & Svar
Dette er en liste over vanlig stilte tekniske spørsmål om Turbinator. Vi svarer gjerne på andre spørsmål - ta kontakt!
Turbine questions
Q: What standard diameters is the turbine supplied at?
A: We will standardize on a number of diameters in order to reduce the number of variants on the mechanical housing.
Q: How many blades does the turbine have?
A: In order to cover the announced range of head / flow we use different runner wheel / blade geometries. The numbers of blades are four, five six or eight depending on runner wheel geometry. For each generic runner wheel we have data enabling us to select the blade pitch (which will be fixed) ensuring a good efficiency.
Q: What are the intake screening requirements? (Minimum bar spacing)
A: The trash rack bar spacing is dependent upon the blade opening, which will vary depending on blade opening and configuration. As a starting point, 100 mm open distance between bars could be assumed – to be confirmed once the turbine blade characteristics are known.
In some site configurations there could in addition be a risk of rocks rolling along the stream bottom which could pass through the trash rack and down the penstock. In such cases a rock trap or other means to stop rocks from entering the flow conduit upstream of the trash rack should be considered. This is typically a consideration for a canal or stream inlet, not for sites with a reservoir.
Q: What is the specific speed of the turbine for maximum efficiency?
A: By choosing the appropriate runner wheel and blade pitch we can cover the necessary range of speeds for our working range.
The Turbinator needs site a Speed number larger than approximately 0.6.
The Speed number is calculated as:
where
w=105 can be used for an initial estimation
Q = flow [m3/s]
H = Net head [m]
g = 9.81 m/s2
Q: Can the Turbinator be supplied at a range of specific speeds (by revising the blade fixed pitch for example) or just one arrangement?
A: Yes, the Turbinator wheel will be configured independently for each site, with (fixed) blade pitch according to site flow and head data.
Q: What are the cavitation characteristics of the Turbinator?
A: As part of the design/configuration of the runner wheel to the site, the maximum suction height (Hs) is calculated. The calculation method is based on knowledge of each individual runner wheel geometry. Suction height Hs is defined as the maximum distance from the highest point of the runner wheel downstream edge down to the tailrace water level, and is an important parameter for a given site in order to avoid potentially damaging cavitation. Increased need for suction height for a given site can to some extent be accommodated by design selections.
Q: What is the maximum turbine setting (above tailrace water level)?
A: The maximum achievable suction height (Hs) will vary depending on head (H) and flow (Q) for the given site, but also on the rotational speed. Hs = 2-4 meters is usually achievable, please contact us for an feasibility evaluation should you have a site that requires high suction height.
Q: Draft tube details (cone angle and maximum length?
A: The design of a good draft tube is not really linked to the Turbinator design, but a specific area of competence "on the side". The draft tube shall be shaped in such a way as to reduce the water speed in order to limit the overall head loss, which is especially important on low head turbines. The Turbinator can be installed at any angle, meaning that a simple diffusor type draft tube can be used (without bend). Optimum diffusor designs was studied in the 1950-70's, and we will propose diffusor / draft tube angle and length based on that knowledge.
Q: What is the runaway speed (this should be shown on the performance graph)?
A: Due to low inertia in the construction, the turbine will in case of i.e. grid loss go to runaway within seconds. The runaway speed will be below but close to two times the nominal speed.
Generator questions
Q: As a PMG there are no exciter windings and therefore no possibility of AVR?
A: Correct.
Q: Is the Turbinator designed for fixed speed operation? Can a variable speed drive controller be used to operate the set at different speeds?
A: The set has its optimum at a certain speed, head and flow. The Turbinator can be delivered inverter-driven with variable speed.
Q: Will Power Factor correction be needed?
A: With fixed speed where the load is more or less constant, it is designed to have a PF of around 1 at full load. With inverter / variable speed the frequency converter will do the PF-correction.
Q: How many arrangements of generator pole-pairs are possible?
A: Since the generator is wrapped around the runner it gets a relatively large diameter, so it will be impractical to make direct drive generator (50Hz, bound to synchronous speeds) with pole-pair numbers less than 3 (preferable 4). With variable speed converter we can choose frequency, speed and pole number more freely.
Q: What material is used for the permanent magnets?
A: Neodymium Iron Boron magnets (NdFeB)
Q: IP rating of the generator?
A: The generator is completely sealed and submersible (IP68).
Q: IP rating of the generator termination box?
A:The terminationbox is a part of the generator and has the same IP-rating (IP68)
Q: How is the Turbinator water cooled?
A: The rotor is cooled through the rotor yoke and the runner (small losses) while the stator is sealed and filled with biodegradable oil. The stator is cooled passively through the house (partly to air, mainly to the water running through the machine acting as an efficient heat sink).