Rated impulse voltage

Table 6.14 Rated impulse voltage for equipment energized directly from the low voltage mains (according to IEC 60664-1)...

Voltage line to neutral V AC or DC Rated impulse voltage kV Overvoltage category1 ... 

Impulse voltage withstand test of the insulation system for rated voltages 2.4 kV and above for machines wound with formed coils 11/261... 

Note What were traditionally called X and Y capacitors are now more accurately called X2 and Y2 capacitors respectively. From the viewpoint of safety regulations (like impulse voltage rating etc.), the XI and Y1 are considered virtually equivalent to two X2 and Y2 capacitors in series, respectively. For example Y1 caps are impulse tested to 8 kV. Also, the original terms X-caps and Y-caps have recently started getting defaulted to refer to the more uncommonly used (higher voltage) XI and Y1 capacitors instead. 

No ni ial syste n voltage kV r.m.s.) Rated maximum system voltage V, kV(r.tn.s.) Standard one-minute power frequency withstand voltage KV (r.m.s.) Standard lightning impulse (1.2/50 ps) withstand voltage phase to ground kV (peak) ... 

Nominal system Rated maximum One-minute power frequency Standard lightning impulse One-minute d.c. voltage ... 

Nominal system voltage Rated max. system voltage One-minute power frequency voltage withstand at a frequency between 45 and 65 Hz for LT and 25 and 100 Hz for HT systems Standard lightning impulse, 1.2/50 fis voltage withstand (phase to ground)... 

High voltage (kV) Rated short-duration power frequency withstand voltage (kV) Rated lighting impulse withstand voltage ... 

Choice of rated lighting impulse withstand voltage depends on exact site conditions and duties. 

Ulbricht W (1972b) Rate of veratridine action on the nodal membrane. II. Fast and slow phase determined with periodic impulses in the voltage clamp. Pflugers Arch 336 201-212... 

Initiation of postjunctional activity. If an EPSP exceeds a certain threshold value, it initiates an action potential in the postsynaptic membrane by activating voltage-sensitive channels in the immediate vicinity. In certain smooth muscle types in which propagated impulses are minimal, an EPSP may increase the rate of spontaneous depolarization, cause Ca + release, and enhance muscle tone in gland ceds, the EPSP initiates secretion through Ca + mobdization. An IPSP, which occurs in neurons and smooth muscle but not in skeletal muscle, wdl tend to oppose excitatory potentials simultaneously initiated by other neuronal sources. The ultimate response depends on the summation of ad the potentials. 

Neural Excitation of Muscle. Voluntary contraction of human muscle initiates in the frontal motor cortex of the brain, where impulses from large pyramidal cells travel downward through corticospinal tracts that lead out to peripheral muscles. These impulses from the motor cortex are called action potentials, and each impulse is associated with a single motor neuron. The principle structure of a motor neuron is shown in Fig. 6.IS. The action potential initiates in the cell body, or soma, and travels down a long efferent trunk, called the axon, at a rate of about 80 to 120 m/s. The action potential waveform is the result of a voltage depolarization-repolarization phenomenon across the neuron cell membrane. The membrane ionic potential at rest is distuibed by a surrounding stimulus, and Na ions are allowed to momentarily rush inside. An active transport mechanism, called the Na —K+ pump, quickly returns the transmembrane potential to rest This sequence of events, which lasts about 1 ms, stimulates a succession of nerve impulses or waves that eventually reach muscle... 

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