Generator I of hydropower station for the design a

2022-08-13
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Hydropower station generators designed and selected to protect circuit breakers (I)

generally, people habitually call generator sets with single unit capacity of 100mva and below as small and medium-sized generators. In view of the basic national policy of China's comprehensive utilization and development of energy, since the western development, especially in the southwest region, the construction of small and medium-sized hydropower generating units has sprung up, and the industrial structure has also reached a certain scale. With the development of market economy, it is a general trend to design and select the protection circuit breakers of small and medium-sized hydropower generators and change the tradition of using general-purpose circuit breakers as generator type circuit breakers in the past

1 comparison of technical performance between generator type circuit breaker and general-purpose circuit breaker

generator type circuit breaker and general-purpose circuit breaker are basically the same in terms of mechanical characteristics, insulation characteristics and electrical characteristics

if the short-circuit breaking current is expressed by the effective value of AC component and the percentage of DC component (dc%); The performance of the machine before your eyes is assessed by power frequency and lightning impulse withstand voltage level; The mechanical characteristics assessment items are also basically the same

the difference between generator type circuit breaker and general-purpose circuit breaker is that the former requires much more stringent technical parameters for some technical properties. Because the inductance value of the generator is relatively larger than that of the system, the DC component and attenuation time constant borne by the protective circuit breaker at the moment are much larger. GB/T stipulates that when the opening time of the circuit breaker is increased by 0.01s, we have reviewed 80% of the products, and the DC component (dc%) is about 68%, and the attenuation time constant is 60ms, which is obviously larger than the DC component (dc%) 20% and the attenuation time constant 45ms of the main circuit breaker in the general-purpose steel raw material spot market on June 8; At the same time, the rated short-circuit making current is also different. Due to the large DC component, the rated short-circuit making current (peak value) of the generator circuit breaker is 2.74 times of the rated short-circuit current, while that of the general-purpose circuit breaker is only 2.5 times; In terms of expression, in addition to the rated short-circuit current value, the nameplate of the generator type circuit breaker also indicates the DC component (DC%) value, while the general-purpose circuit breaker is only marked with the rated short-circuit current value

through comparison, it can be seen that the breaking and closing conditions of generator type circuit breaker are stricter than those of general-purpose circuit breaker, and the assessment of type test is also much stricter

2 main type test and assessment contents of generator type circuit breakers

according to the current international ANSI/ieeec standard for AC high voltage generator circuit breakers based on symmetrical current, the type test and assessment contents of generator type circuit breakers are mainly: system source short-circuit breaking

breaking and closing, generator source short-circuit breaking and out of step breaking and closing. The contents of other type tests and assessments are basically the same as those of general-purpose circuit breakers

(1) breaking and making test of system source short circuit. The generator type circuit breaker is operated in the sequence of non auto reclosing operation. DC component can be divided into two conditions: DC% < 20% and DC% > 20%; The transient recovery voltage (peak value) is 1.7 times the maximum working voltage of the generator; The rise rate of transient recovery voltage is 3, which has good flame retardancy 5kV/ s; The closing test is conducted according to 2.74 times of the rated short-circuit current (peak value). When Westinghouse and Siemens abroad carry out this test, the DC component (dc%) is assessed according to 75% of the rated short-circuit current

general purpose circuit breakers are generally operated in the sequence of automatic reclosing. DC component (dc%) < 20%; The transient recovery voltage (peak value) is 1.71 times the rated working voltage; The rise rate of transient recovery voltage is 0.34kv/S; The making test is conducted according to the combination of 2.5 times of rated short-circuit current (peak value) and symmetrical breaking test. When the opening time of the circuit breaker is 60ms, it is not necessary to conduct asymmetric breaking test

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