Product Brochure Generator Circuit-Breaker HVR-EBCB For hydro or pump storage power plant
Introduction General The braking switch serves the purpose of electrical braking a machine in a hydro or pumped storage power plant after it has been disconnected from the system. Electrical braking is attractive because it allows to substantially reduce the wear of the mechanical braking system and hence to increase the maintenance intervals and to decrease the associated costs. Electrical braking typically sets in at 50% to 60% of the rated speed of the machine and mechanical braking is then applied only at 10% or less of the rated speed. In order to electrically brake a machine a short-circuit is applied to its terminals by closing the braking switch. Arrangement of the Braking Switch The braking switch is mounted in a cubicle and connected to the generator main busbar between the terminals of the generator and the generator circuit-breaker. Sequence of the Electrical Braking of a Machine The sequence of the electrical braking of a machine in a hydro or pumped storage power plant is as follows: The input of mechanical power to the turbine is interrupted. The generator is disconnected from the system by opening the generator circuit breaker. The speed of the machine is reduced due to the friction of the runner in water or air (depending of the type of the turbine). The generator is de-excitated; depending on the degree of de-excitation the residual voltage at the generator terminals typically lies between 5% and 25% of the rated voltage. At about 50% to 60% of the rated speed of the machine the braking switch is closed and hence a short-circuit is applied to the terminals of the generator. The residual voltage and the subtransient reactance of the generator thereby determine the making current. The generator is excitated again so that the necessary braking current of the generator is flowing in the circuit, thereby electrical braking takes place. At 10% or less of the rated speed mechanical braking is also applied and the machine finally comes to a complete standstill. After reaching the standstill position the excitation current is reduced to zero and the braking switch is opened (without current). Note: a braking switch is not intended for protection purposes; therefore no protection signals shall be wired to the opening coils of the braking switch. 2 HVR-EBCB ABB
Technical Data Generator circuit-breaker type HVR-EBCB (Braking Switch) General Type of circuit breaker Installation Service conditions HVR-63 Installation Indoor Rated maximum voltage kv 24 Rated continuous current 1) A rms up to 8000 Current carrying capability for 10 min. 2) A rms up to 16000 Rated insulation level Rated power frequency withstand voltage to earth and across circuit-breaker/switch contacts kv rms 60 Rated lightning impulse withstand voltage to earth and across circuit-breaker/switch contacts kv peak 125 Circuit-breaker Rated peak withstand current ka peak 190 Rated short-time withstand current ka, 3s 63 Rated short-circuit making current ka peak 190 Duty cycle for intermittent duty C - 10min - O - 30min - C - 10min - O or C - 5min - O - 15min - C - 5min - O Duty cycle for short-circuit currents CO - 30min -CO Maintenance intervals time based 20 Years mechanical 10000 CO Operating mechanism Type Number of stored operations Hydro-Mechanical Spring Operating Mechanism CO Degree of protection (IEC 60529) Operating mechanism of braking switch IP 54 Cubicle (enclosure) IP 41 Standards General IEC 62271-1 Braking switch (circuit-breaker) IEEE Std C37.013 Cubicle (enclosure) IEC 62271-200 Remarks: 1) Standard maximum rating of HVR-63 in open-air installation: for application in enclosure as braking switch, the given short-time duty shall apply. 2) Short-time duty: final duty cycle has to be defined based on actual braking specification. ABB HVR-EBCB 3
Dimension Drawing HVR-EBCB 300 *) 3800 300 *) N(1300) N(1300) 1500 *) 1865 Ø900 450 *) 2257 3750 *) 500 *) 755 4400 *) N = Phase distance *) min. space required for erection and maintenance 4 HVR-EBCB ABB
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