4、An ordinary silicon rectifier diode consists of a p-n junction of which the p-layer is the anode .The thyristor, as shown in Fig.4.1, is a four-layer arrangement of p-n-p-n silicon. The end p-layer forms the anode, and the end n-layer is the cathode, while the p-layer adjacent to the cathode forms the gate or trigger electrode. The reverse characteristic is similar to that of the silicon diode, as it draws only a small leakage current when negative anode-to-cathode voltage is applied. If the critical reverse breakdown voltage is exceeded, a destructive breakdown occurs.
一个普通的硅整流二极管是由p-n结组成，这个结的p层是阳极。如图4.1所示，晶闸管是一个p-n-p-n硅片的四层结构。端头的p层形成阳极，端头的n层是阴极，而与阴极相邻的p层形成门极（即触发极）。其反向特性类似于硅二极管，这是因为当施加负的阳极对阴极电压时，晶闸管只引导微小的漏泄电流。如果超过临界反向击穿电压，就会发生破坏性的击穿。
5、Synchronous machines do not easily fall out of step under normal conditions. If a machine tends to speed up or slow down, synchronizing forces tend to keep it in step. Conditions do arise, however, in which operation is such that the synchronizing forces for one or more machines may not be adequate, and small impacts in the system may cause these machines to lose synchronism. A major shock to the system may also lead to a loss of synchronism for one or more machines.
在正常情况下，同步电机不易失去同步。如果一台电机有加速或减速趋势，则整步力趋向于使它保持同步。然而，一些情况的确会发生，其中有这样的运行情况，致使一台或多台电机的整步力可能不够，而系统的小冲击可能引起这些电机失去同步。对系统的大冲击同样也可能导致一台或多台电机失去同步。
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