(英文,图示详细、实用)去除地环干扰的方法.doc

A? 30, 2008 Electrical noise and mitigation - Part 3: Shielding and grounding (cont.), and filtering harmonics This excerpt from the book Practical Grounding, Bonding, Shielding and Surge Protection concludes with a look at the shielded isolation transformer, zero signal reference grounds and signal transport ground planes, and the generation of harmonics in electrical systems and how they can be filtered. By G Vijayaraghavan, Mark Brown, Malcolm Barnes Receive a 15% discount on Practical Grounding, Bonding, Shielding and Surge Protection by ordering from and using offer code 92839. [Part 1 begins by defining electrical noise, examining the reasons for its generation and looking at ways to evaluate its effects. Part 2 looks at earth loop as a cause of noise, the ways in which noise can enter a signal cable and its control, and shielding.] 8.10 Shielded isolation transformerA shielded transformer is a two-winding transformer, usually deltastar connected and serves the following purposes: Voltage transformation from the distribution voltage to the equipments utilization voltage. Converting a 3-wire input power to a 4-wire output thereby deriving a separate stable neutral for the power supply wiring going to sensitive equipment. Keeping third and its multiple harmonics away from sensitive equipment by allowing their free circulation in the delta winding. Softening of high-frequency noise from the input side by the natural inductance of the transformer, particularly true for higher frequency of noise for which the reactance becomes more as the frequency increases. Providing an electrostatic shield between the primary and the secondary windings thus avoiding transfer of surge/impulse voltages passing through inter-winding capacitance. Figure 8.27 shows the principle involved in a shielded transformer. The construction of the transformer is such that the magnetic core forms the innermost layer, followed by the secondary winding, the electrostatic shield m