Air gap Voltage

The torque Tf, developed in the rotor shaft can be expressed as a function of the air-gap voltage Vm.-... 

Where R2 and X2 are both functions of the slip as explained above. The air-gap voltage can be found from the supply voltage Vs by noting that a voltage divider circuit exists which consists of the series components of the stator and the parallel combination of the magnetising branch and the rotor circuit. Hence becomes -... 

A 250 kW three-phase, fonr-pole, 50 Hz, 415 V, indnction motor is fed from a voltage source inverter. The motor has the following parameters for its star-wonnd windings. Find the cnrrents and air-gap voltage in the circnit. 

Harmonic number Stator current Rotor current Magnetising current Air-gap voltage ... 

Figure 15.12 shows the synthesised currents and air-gap voltage using the first 61 harmonics. 

The same motor as used in the worked example of sub-section 15.4.3.1 is fed from a cnrrent source inverter. Find the currents and air-gap voltage in the circuit. 

When the equivalent circuit is suitable it can be treated as a passive circuit in that no differential equations need to be solved for the currents or voltages in the circuit. The only differential equation associated with the circuit is the torque necessary to accelerate the rotor and its coupled load. For this purpose the standard form of equations for the electrical torque are appropriate, in which the air-gap voltage V , should be used. 

Fig. 8-3 ac voltage, U, in a current-limiting choke as a function of the ac flowing through it, /, for different numbers of windings, w, with and without an air gap. 

PrImary-Voltage-Control-AC Motor Driver. Induction motor torque at any slip s is proportional to primary V. Rotor-power dissipation is equal to s times the air-gap power. These two relationships define the boundary of operation of an induction motor with primary voltage control of speed. As the speed is reduced (s increased) at constant torque, the air-gap power remains fixed, but the power divides between rotor circuit dissipation and mechanical shaft power. 

Just as for the primary-voltage control system, the air-gap power at slip s divides between mechanical power and rotor-circuit power in the wound-rotor drive. Except... 

Figure 2. Surface voltage decay as a function of time for corona poled PS (O) and PMMA ( ) films doped with 4 wt.% DANS. Films poled at -3000V (0.6 cm air gap) for 15 min at 25°C.

Whereas further effects are determined by the frequency converter, this effect is determined by the asymmetry of the motor itself. The voltage levels arising here typically range below 500 mVpeak which, under normal conditions, does not cause trouble. These bearing voltages cannot be entirely eliminated, but can be reduced by precise adjustment of the air gap. One... 

Figure 6. Low-resolution STM survey image of a partly oxidized graphite flake. The asymmetric V-shape of the deep trenches is a tip artefact. Conditions Burleigh AR1S 6000, air, W tip, constant current mode, gap voltage 200 mV.

Figure 16. STM images (Burleigh ARIS 6000. air, W tip. constant current mode, 200 mV gap voltage, graphite natural single crystals, oxidation in air at 900 K) of (a) pristine and (b) oxidized graphite surfaces.

The condition to obtain electromodulation (electro- and photo-reflectance) spectra is the existence of a built-in electric field in a structure under investigations. This condition is usually fulfilled in majority structures. Typical CER method utilizes a capacitor-like system with one top semitransparent electrode and one bottom copper-block electrode. The sample is glued to the bottom electrode by using a silver pasta. The front electrode is separated from the sample surface by a spacer (e.g. 0.1 mm). Thus there is nothing in direct contact with the sample. It means that the sample does not conduct any currents and the external electric field is able to change the carriers distribution inside it. Note that the voltage drop appears mainly in the air gap between the front electrode and the sample. The limit for the applied voltage is the electric breakdown in this air gap. It means that the maximal amplitude of EM in the CER technique usually is more limited than the EM amplitude in ER or PR techniques. 

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