Megger Instruments Ltd.

Kings Hill, United Kingdom

Megger Instruments Ltd.

Kings Hill, United Kingdom
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Zurek S.,Megger Instruments Ltd.
IEEE Sensors Journal | Year: 2017

Power loss in magnetically soft magnetic materials can be measured by detecting magnetic field strength H and flux density B. H can be detected with the so-called H-coil sensor, which is an induction coil wound on a thin flat non-magnetic former. The accuracy of H measurement directly affects the measurement of power loss. For alternating (uni-directional) magnetization, H is applied mainly along the symmetry axis of the sample under test and the normal component is small due to magnetically closed circuit. So any off-axis H components usually have small amplitude and do not cause significant errors. However, under 2-D or rotational magnetization, the H-coils are exposed to strong H in all directions. It is shown in this paper that such off-axis H components can introduce significant amplitude and phase errors, which contribute to the differences in the calculated clockwise and anticlockwise power loss values. Theoretical analysis of order of magnitude of such off-axis sensitivity is given in this paper for three typical configurations of H-coils (with the return wire positioned along one side, diagonally and through the center). Experimental verification is also presented for the side wire configuration. © 2001-2012 IEEE.


This paper presents experimental data measured up to 2T under rotational circular flux density. The results show that at lower excitations there is significant anisotropy of permeability. However at 2T the anisotropy collapses so that the permeability varies only ±14% from the average value. On a qualitative level the results are very similar to the directional curves for single-crystal samples for the three significant crystallographic directions [100], [110] and [111] shown previously in the literature. © 2017, Wydawnictwo SIGMA - N O T Sp. z o.o. All rights reserved.


Practical implementation of digital feedback (DF) for waveshape control is described in the paper. It is shown that if the system has intrinsically sufficient phase margin then operation of DF can be controlled by changing just the DF gain even though the system gain can vary more than 2 orders of magnitude. Practical tips as well as typical difficulties are also discussed. The provided description should be sufficient to implement DF in any programming language and hardware configuration. © 2017, Wydawnictwo SIGMA - N O T Sp. z o.o. All rights reserved.


Kozlowski A.,Magneto Ltd. | Rygal R.,Magneto Ltd. | Zurek S.,Megger Instruments Ltd.
IEEE Transactions on Magnetics | Year: 2014

A large dc electromagnet with a 200 mm long air gap was designed, constructed, and tested. Analytical calculations provided the first approximation of required parameters. The design was refined with the aid of finite element modeling. Thermomagnetic processing required nominal flux density level to be 0.35 T. It was validated on a prototype that the average flux density in the air gap exceeded this value. The magnetizing coils were designed to be cooled by natural air convection. Despite a large size (∼1900 kg), the electromagnet was designed to consume less than 2.5 kW and could be energized from a single-phase mains socket. © 2014 IEEE.


Zurek S.,Megger Instruments Ltd
International Journal of Applied Electromagnetics and Mechanics | Year: 2015

Measurements of magnetic properties of toroidal samples of magnetically soft materials are defined by the group of international standards IEC 60404. These standards do not specify the actual value of the shunt resistor, but for instance just the fact that it should be "non-inductive". This study provides more information on the topic of selection of shunt resistance, which is crucial for many studies of magnetic measurements. It was found that the resistance value of a shunt resistor has no direct effect on the measurement results of magnetic properties. The quality of calibration of the value does have a direct effect, but not the value itself and it could have any value from 0.1 Ω to 10.0 Ω (as investigated). Care must be taken so that additional device-specific effects are not induced in the measurement equipment (e.g. reduced accuracy at the lowest or highest input ranges). The value of the shunt resistor should be such that the voltage drop across it would coincide with the most accurate input range of the voltmeter or data acquisition device. © IOS Press and the authors. All rights reserved.


Zurek S.,Megger Instruments Ltd
IEEE Transactions on Magnetics | Year: 2012

The paper describes results of two-dimensional finite element modeling of cut (gapped) magnetic cores. The influence of an irregular air gap on the apparent permeability of the core is calculated. Two magnetically soft materials are used: electrical steel M-27 and supermalloy (80% Ni). The results indicate that decreasing the minimum air gap between parts of the core can increase the initial effective permeability of the core, by a factor of 2 or 3 × despite the total volume of the gap remaining unchanged. © 2006 IEEE.


Zurek S.,Megger Instruments Ltd
IEEE Transactions on Magnetics | Year: 2012

The paper presents a practical view on industrially used magnetic cores wound from Ni-Fe tape. The discrepancies between various international suppliers are quite wide, which can have a significant impact on production and in effect on magnetic performance of the final devices. © 2006 IEEE.


Patent
Megger Instruments Ltd | Date: 2011-11-23

A test vessel assembly (10) comprises a central test vessel 12 defining a chamber 18 in which a sample to be tested may be stored. A pair of side adjustable electrodes 30, 30a is received in the chamber and immersed in the sample under test. A gap between the electrodes can be adjusted by respective electrode adjusting assemblies, each comprising a shaft 32 connected to a respective electrode, the shaft being moved in and out of the test vessel 12 by rotation of an associated adjusting wheel 60. In use, each electrode 30, 30a is electrically connected to a contact in an insulated horn of a test assembly via the respective shafts, for the supply of a steadily increasing voltage to determine the breakdown voltage of the sample. To prevent the breakdown in air rather than in the sample, care is taken to ensure sufficiently large creepage and clearance distances between the connections to the electrodes and from the connections to the electrodes to a wall of the test chamber. To this end, horn covers 46, 46a are placed over the horns. In addition, for the same purpose, the adjusting wheels 60 include convolutions 63, 65 that mesh with corresponding convolutions 70, 72 in the test vessel 12 and the horn covers 46, 46a.


Patent
MEGGER INSTRUMENTS Ltd | Date: 2010-09-24

A test vessel assembly (10) comprises a central test vessel 12 defining a chamber 18 in which a sample to be tested may be stored. A pair of side adjustable electrodes 30, 30a is received in the chamber and immersed in the sample under test. A gap between the electrodes can be adjusted by respective electrode adjusting assemblies, each comprising a shaft 32 connected to a respective electrode, the shaft being moved in and out of the test vessel 12 by rotation of an associated adjusting wheel 60. In use, each electrode 30, 30a is electrically connected to a contact in an insulated horn of a test assembly via the respective shafts, for the supply of a steadily increasing voltage to determine the breakdown voltage of the sample. To prevent the breakdown in air rather than in the sample, care is taken to ensure sufficiently large creepage and clearance distances between the connections to the electrodes and from the connections to the electrodes to a wall of the test chamber. To this end, horn covers 46, 46a are placed over the horns. In addition, for the same purpose, the adjusting wheels 60 include convolutions 63, 65 that mesh with corresponding convolutions 70, 72 in the test vessel 12 and the horn covers 46, 46a.


Patent
Megger Instruments Ltd | Date: 2016-08-09

A clamp for establishing an electrical connection with a conductor is provided. The clamp comprises a first body and a second body. The second body is pivotally coupled to the first body. The first and second bodies define a receiving region therebetween for receiving a conductor. The first and second bodies are biased towards each other at the receiving region to clamp a conductor. The clamp also comprises a shutter, movably coupled to one of the first body and the second body. The shutter is biased into a restricting position in which entry into the receiving region is restricted.

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