Figure 6 - uploaded by Mirko Palazzo
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Typical single line diagram of a generator circuit-breaker system 1 Generator circuit-breaker 2 Line disconnect switch 3 Earthing switch 4 Starting switch for SFC connection 5 Manual short-circuiting connection (only with generator side earthing switch) (by removal of cover)
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... for the present study simulations referring to such a fault conditions have been performed. The wave-shape of the out-of-phase current in case of δ 0 = 90° is depicted in Figure 60. The results show that the fault current resulting from out-of- phase synchronising can impose extremely severe interrupt- ing conditions if the generator circuit-breaker closes when the voltage across its contacts in one pole is at its maximum value and the arc-voltage of the circuit-breaker is not high enough to force current to zero before the condition of δ = 0 is reached. ...
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... The main aim of all power companies is to achieve the highest plant availability whilst having the lowest possible cost. The method to connect the high-voltage (HV) grid and the power supply to auxiliaries affects the power plant availability significantly [1]. ...
... Compared with the unit connection structure, the GCB's layout not only simplifies power operational procedures but also improves protection of both generator and unit transformers. Meanwhile, GCBs increase power plant availability [1]. Due to the above advantages, increasing numbers of the power plant have GCBs, which significantly reduced both time and expense for installation and commissioning. ...
... Hence, the GCB is an economical and efficient solution for protecting generators and transformers [2]. With improved arc-extinguishing capability, the modern GCB has achieved 57 kA rated current (2000 MW generating units) and 210 kA fault current [1]. Furthermore, with the developing scale of renewable energy such as offshore wind farms, HV direct current (HVDC) has gained great attention due to its advantage of longdistance transmission. ...
The AC and DC dielectric properties of hydrofluoroethers (HFE) [C 3 F 7 OCH 3 ] and fluorinated ketone (FK) [C 2 F 5 C(O)CF(CF 3 ) 2 ] have been characterised by dielectric spectroscopy and DC conductivity at different temperatures. Results show that DC conductivity and imaginary permittivity of both fluids are positively correlated with increasing temperature. However, the real permittivity decreases with increasing temperature. The breakdown voltages of HFE and FK at 295 K are ∼10 kV mm ⁻¹ . Reducing temperature is an effective method to increase the breakdown voltage of the FK coolant, but the breakdown voltage of HFE is less temperature dependent. Finally, as expected repeated breakdown had no significant effect on the AC dielectric strength of both liquids.
