摘要:

The normal method used to measure the temperature of the windings of transformers, reactors and other heavy electrical plant is by change of resistance. By means of a simple d.c. test, resistances are measured before and after the heat run. The temperature at shutdown is calculated using the known temperature coefficients of resistance for copper.It is well recognised that inductance may cause errors in these measurements, especially in large transformers.A simple test procedure is presented which enables the presence of inductive errors to be detected. Should they be present, a numerical correction to the measured resistances is readily applied.The principle involved is to place a d.c. millivoltmeter across a winding other than the one under test and note its readings during the period of the cooling curve. By transformer action, the induced e.m.f. may be related to the winding under test and a quantitative correction in ohms derived.The method may be easily applied at any test bench, irrespective as to whether the volt-ammeter, Wheatstone bridge or Kelvin bridge circuits are employed. The only additional equipment required is a vacuum-tube millivoltmeter of common type.

DOI:10.1049/piee.1964.0240

出版商:IEE    

年代:1964

数据来源: IET

摘要:

Iron-loss measurements on grain-oriented silicon-iron transformer steel show that the anomalous loss under normal transformer core working conditions now amounts to about one half of the total iron loss. Experimental data have been obtained for five different directions in the sheet. The results show that the theory, as at present expounded, that anomalous losses arise from eddy currents at moving domain boundaries, is not adequate to account for the high magnitude of these losses. The origin of anomalous losses seems, therefore, to be still in doubt.

DOI:10.1049/piee.1964.0242

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The paper analyses the behaviour of induction motors under transient conditions of changing the supply frequency. This is necessary owing to the possibility of utilising induction motors in position-control servomechanisms in which the control signal determines the frequency of supply to the stator. The analysis achieves a torque differential equation and frequency-response loci. The analytical results are compared with experimental results obtained on an induction motor and from an analogue simulator. The effects of rotor inertia and rotor (electrical) time constant are studied using the simulator.

DOI:10.1049/piee.1964.0243

出版商:IEE    

年代:1964

数据来源: IET

摘要:

Optimal and suboptimal digital controllers are developed for the control of a linear, oil-fired boiler model specified by discrete state variables and transition functions.The model is based on design and steady-state test data and the resulting equations are transformed into a normal co-ordinate reference frame for isolating the time-dependent modes of the system. Analytical techniques are developed for reducing the system order, and the open-loop behaviour of the reduced system is shown to be similar to that of the original system.Controller design is based upon measurement and subsequent minimisation of a quadratic performance index related to the displacement of the discrete state variables.For suboptimal control, minimisation is considered at each successive forward sampling point with input amplitude constraints, and this is shown to produce an approximately time-optimal system. The concepts of dynamic programming are used for investigation of the optimal controller. This requires a complex iteration procedure, and the response of the controlled system does not appear to be superior to that of the simplified suboptimal system.The use of Lyapunov functions in the performance index are also investigated, and these are shown to produce local stability of the controlled system.

DOI:10.1049/piee.1964.0244

出版商:IEE    

年代:1964

数据来源: IET