Performance of synchronous motors loss-of-synchronism protection
Synchronous motors are rarely designed to operate asynchronously for extended periods of time. When a synchronous motor experiences a mechanical load exceeding its pull out torque, it enters asynchronous operation, under which the interaction between the stator and rotor magnetic fields causes damaging mechanical stress and vibrations. Also, induced currents in the rotor cause extra heating that quickly damages the rotor windings. Asynchronous operation must be detected and dealt with by allowing time for resynchronization or by tripping the motor to avoid thermal overload and damage. Two protection elements are often used to detect asynchronous motor operation: the power factor element and the out-of-step element. This paper compares the performance of the two elements to protect a 20 MW synchronous motor subjected to pull out conditions.
Out-of step and single phasing protection of synchronous chipper motors
Chipper motors in pulp and paper mill environment are of special design-the stability on impact loads is one important consideration. The power factor under normal operation will continuously swing due to varying loads. The paper describes guesswork free rigorous calculations of pull out (out-of-step) power factor based on the parameter of an actual installation. Single phasing is rather a rare occurrence; however, such an event has been experienced in an installation due to overheating and arcing at the fuse clips in a NEMA E2 starter of a chipper motor. Discussions on single phase protection of synchronous motors and recommended settings are provided.
The Gospel and the land;: Early Christianity and Jewish territorial doctrine,
Ostensibly Davies' patient study of the concepton of the "land" (Israel, Jerusalem) in early Christianity is an essay in Biblical theology, but he also wishes to raise serious questions about Christian understanding (or misunderstanding) of Judaism. "Christians have usually understood Judaism in too theological, and therefore, too intellectual terms. And they have also looked at their own foundation document, the New Testament, in the same way. In their proper concern to unravel theological developments and subtleties in primitive Christianity, they have neglfected to search for evidences of an encounter between it and the realia of Judaism and for any possible resolutions of such an tencounter. In particular, they have failed to inquire after the place of the land in the thought and lives of early Christians" (p. 161). Davies observes, for example, that bible dictionaries often have no references whatsoever to "land" and those that do allot it but a few pages. Even in Old Testament scholarship, where the land is of central significance in the documents themselves, it has been neglected. His work is an attempt to provide a context of Jewish thinking from early Israelite writings up to the Talmud in which to place the Christian materials. The bulk of the book is an account of the historical and theological process by which early Christianity gave a "spiritual" interpretation of traditional Jewish views of the land. Read against the Jewish background, the radical spiritualizing of the tradition is striking. Yet Davies also shows that Jewish attitudes were not monolithic in the first century, that notions of a preexistent, heavenly or eschatological Jerusalem were present, and that some Jews considered the viability of Judaism apart from the land. At some point however what could be entertained as an abstraction in Judaism, when it was made concrete in the life of the Christian movement, could not be tolerated. The conflict was heightened, of course, by the destruction of Jerusalem and the continued existence of Christianity as a movement increasingly receptive to non-Jews. Christianity, however, while rejecting the link between the land and religion, did create a new sense of "holy space" by hallowing the places where Christ had been, a development which would find fullest expression some several centuries later. As a result of the Holocaust and the establishment of the modern state of Israel Christians are faced with a whole new series of issues which have lain dormant since the destruction of Jerusalem in A.D. 70. Davies' work must be read against this backdrop to appreciate its significance. It is as much a book about modern Christian thinking as it is about the past, as many of his citations and his several appendices of speeches at Jewish-Christian conferences show. To some it may appear that he has sided too closely with certain strands of Judaism and allowed this to color his way of handling the pre-Christian and pre-Rabbinic material, but such criticism is carping. Much of the material here is gathered together in this fashion for the first time, and he has successfully shown that a major preoccupation of ancient Judaism is missing in contemporary biblical scholarship. Further, he has given us a moving yet scholarly statement of the pathos of the modern Christian who cares about Christ and Israel and who tries to understand Israel while loving Christ.