Frequencies core loss

For a lower range of motors, say up to a frame size of 355, the silicon steel normally used for stator and rotor core laminations is universally 0.5-0.65 mm thick and possesses a high content of silicon for achieving better electromagnetic properties. The average content of silicon in such sheets is of the order of 1.3-0.8% and a core loss of roughly 2.3-3.6 W/kg, determined al a flux density of I W[ym and a frequency of 50 Hz. For medium-sized motors, in frames 400-710, silicon steel with a still better content of silicon, of the order of 1.3-1.8% having lower losses of the order of 2.3-1.8 W/kg is prefeired, with a thickness of lamination of 0.5-0.35 mm. 

I will be using an E-E core since it has the largest wire area of all the core styles. The large wire area will be needed for all the additional insulating layers required for the VDE certification. No air-gap is needed for bipolar forwardmode converters. The core material is going to be 3C8 (Ferroxcube) or F (Magnetics, Inc.) material. This material will yield reasonable core losses at this frequency. 

I will be using an E-E eore with the neeessary Mylar tape insulating layers to meet the isolation requirements of the safety approval ageneies. At these operating frequeneies, a high-frequency core material will have to be used to minimize the core losses at 1 MHz. The material should be the K material from Magnetics, Inc, 3C85 material from Phillips, or N67 material from Siemans. 

Figure D-4 Curves showing volumetric core loss vs. frequency and B, shown). (Courtesy of Philips Components.)...

Core losses decrease with increasing silicon content and increase with increasing frequency. Oxide materials are very useful at high frequency because power losses decrease with increasing electrical resistance. 

It is possible to quantify some of the important transformer parameters through testing. Two simple tests, the open-circuit and short-circuit tests, allow the user to identify the leakage inductance, the coil resistance, the core loss, and mutual inductance of the transformer. Since the characteristics of the transformer change with frequency, the tests should be done at the frequency (or frequencies) of interest. 

The open-circuit test is done by leaving the terminals on one side of the transformer open, and applying the rated voltage to the coil on the other side. Figure 10.9 shows the equivalent circuit for this test, assuming the test is done at a midband frequency. Since the leakage inductance and core resistance are small compared to the mutual inductance and core loss resistance, they can be neglected for the open-circuit test. 

Based on the observed diesel generator failure rate and common cause failures and also on the frequency of loss of off-site power, the probability of a station blackout, exceeding a duration corresponding to the start of core damage, will be evaluated within the framework of a PSA. 

A standard wattmeter method was used to measure the total core loss. In this method, an important experimental difficulty may arise immediately if an ordinary variable-frequency power supply is used for measurement near or above saturation, distortion of both voltage and current wave forms will result, and the measured loss may depend as much on the impedance of the supply as on the magnetic core. In fact, if both waves are considered expanded in Fourier series, the measured power will contain components at a number of frequencies, so that it will be impossible to state the power loss as existing at one frequency nor obtain a reasonable value of hysteresis loss by extrapolation to zero frequency. 

By this arrangement, the core loss depends on a single frequency regardless of the H wave form. If the loss is... 

Figure 1. Total core loss as a function of frequency... 

Spinel ferrites, isostmctural with the mineral spinel [1302-67-6] MgAl204, combine interesting soft magnetic properties with a relatively high electrical resistivity. The latter permits low eddy current losses in a-c appHcations, and based on this feature spinel ferrites have largely replaced the iron-based core materials in the r-f range. The main representatives are MnZn-ferrites (frequencies up to about 1 MH2) and NiZn-ferrites (frequencies 1 MHz). 

Excessive healing of magnetic cores, as a result of harmonic frequencies due to hysteresis and eddy current losses (equations (1.I2) and (1.13)). 

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