變電所畢業(yè)設(shè)計(jì)外文翻譯-文庫(kù)吧資料
2025-07-02 11:35本頁(yè)面
【正文】 s that the two conditions stated earlier are fulfilled: (1) the power input increases to match the power output, and (2) the primary MMF increases to offset the tendency of the secondary MMF to reduce the flux.In general, it will be found that the transformer reacts almost instantaneously to keep the resultant core flux essentially constant. Moreover, the core flux φ0 drops very slightly between n o load and full load (about 1 to 3%), a necessary condition if Ep is to fall sufficiently to allow an increase in Ip.On the primary side, Ip’ is the current that flows in the primary to balance the demagnetizing effect of Is. Its MMF NpIp’ sets up a flux linking the primary only. Since the core flux φ0 remains constant. I0 must be the same current that energizes the transformer at no load. The primary current Ip is therefore the sum of the current Ip’ and I0.Because the noload current is relatively small, it is correct to assume that the primary ampereturns equal the secondary ampereturns, since it is under this condition that the core flux is essentially constant. Thus we will assume that I0 is negligible, as it is only a small ponent of the fullload current.When a current flows in the secondary winding, the resulting MMF (NsIs) creates a separate flux, apart from the flux φ0 produced by I0, which links the secondary winding only. This flux does no link with the primary winding and is therefore not a mutual flux.In addition, the load current that flows through the primary winding creates a flux that links with the primary winding only。 that is, it has no losses. ThusPm = PoutorVpIp primary PF = VsIs secondary PFwhere PF is the power factor. For the abovestated assumption it means that the power factor on primary and secondary sides are equal。 thus the induced quantities Ep and Es vary as a sine function. The average value of the induced voltage given byEavg = turnswhich is Faraday’s law applied to a finite time interval. It follows thatEavg = N = 4fNφmwhich N is the number of turns on the winding. Form ac circuit theory, the effective or rootmeansquare (rms) voltage for a sine wave is times the average voltage。, therefore, they are 180186。 in phase behind the primary voltage VP. It is this ponent that sets up the flux in the core。 and (2) it provides a ponent to account for the hysteresis and eddy current losses in the core. There bined losses are normally referred to as the core losses.The noload current Iθ is usually few percent of the rated fullload current of the transformer (about 2 to 5%). Since at noload the primary winding acts as a large reactance due to the iron core, the noload current will lag the primary voltage by nearly 90186。英文文獻(xiàn)附錄1：外文資料翻譯TRANSFORMER1. INTRODUCTIONThe highvoltage transmission was need for the case electrical power is to be provided at considerable distance from a generating station. At some po
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