Basic insulation levels

BIL is the basic insulation level of equipment. When the system TOV or voltage surges exceed this level, the equipment may yield. In the latest international and national standards it is defined as follows ... 

Surge arresters Electrical characteristics of a ZnO surge arrester Basic insulation level (BIL) ... 

But consider the case of a high-voltage mosfet (switch) mounted on the (earthed) metal enclosure (for better heatsinking). Clearly, we can t provide any level of protection through physical separation. So in this case, we need to place one layer of approved insulator between the mosfet and the enclosure. Note that in this position, the insulator serves as basic insulation. ... 

What if we have an exposed conductor that is not connected to earth (such as for equipment with a two-wire ac cord), or if earthing is itself not an acceptable level of protection for that particular type of equipment as per safety regulations Then, besides the layer of basic insulation, we need another insulating layer (with identical dielectric withstand capability). This is called supplementary insulation. Together these two layers (basic + supplementary) are said to constitute double insulation. We could also use a single layer of insulation, with dielectric withstand properties equivalent to double insulation (i.e. 3000 V ac or 4242 V dc). That would then be called reinforced insulation. So for example, if the equipment is by design, meant only for a two-wire ac cord, we would need two layers of approved insulators (or... 

The European safety standards stress an important principle called the singlefault concept that is at the core of safety philosophy. This principle states that even under a single fault (a wire coming loose, component failure, short/open circuit, insulation failure, etc.) at least one level of protection (basic insulation) must be... 

Basic insulation. Insulation to provide basic protection (one level) against electrical shock. 

Supplementary insulation. An independent insulation applied in addition to basic to ensure protection against electric shock in the event of a failure of the basic insulation (equals two levels). 

Surge arresters. The use of modern surge arresters allows a reduction in the basic impulse-insulation levels of much transmission system equipment. The primary function of early arresters was to protect the system insulation from the effects of lightning. Modern arresters not only dissipate lightning-caused transients, but may also control many other system transients caused by switching or faults. 

The basic impulse level rating for a transformer winding identifies the transient overvoltage withstand capabihty of its insulation. 

The shape and splitting of the XPS Au5d band in the 55 atom cluster material, with its insulating jacket of ligands, reproduces nicely the basic shape of the 5d band of bulk gold, including a clearly visible density of states at the Fermi level. 

Device motivation for interface studies, and Optical absorption and emission in conjugated oligomers and polymers. The principles of device physics of metal insulator field-effect transistors (MISFETs) and light emitting diodes (LEDs) are oudined mainly as motivation for the contents of the chapters which follow, but also to point out certain features relevant to developing an understanding of the nature of the polymer-metal interface (chapters 5 and 6). The basic principles of electro-luminescence are reviewed here, at the level consistent with the aims of this work. 

There are some difficulties we should be aware of just the same. The maximum that is supposed to appear at co = 0 shows up in the INM calculations as a full-blown divergence (43,44). Indeed this infinity is just one instance of the fundamental problems with INMs at zero frequency. It probably should not be a surprise that a theory that pretends that basic liquid structure does not change with time is going to be ill-suited to studying behavior at the lowest frequencies. The same level of theory predicts liquid diffusion constants to be identically zero, for example. Fortunately, realistic molecular vibrational frequencies tend to be well outside this low-frequency regime, so the effects on predicted Tis are likely to be minimal. Still, as we shall note in Section VI, not every aspect of vibrational spectroscopy will be quite so insulated from this basic issue. 

The basic piping insulation units in Table 19.20 and the equipment insulation units in Table 19.23 were provided by an Eastern Shore contractor and have been escalated to late 2000 level. 

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