Grounding neutral

Figure 15.5(b) An RVT under ground fault on a 3-p four-wire grounded neutral system... 

Grounding conditions Whether an isolated neutral system, an effectively grounded system or a non-effectively grounded neutral system ... 

Where three CTs for unrestricted or four CTs for restricted ground fault or combined O/C and G/F protections are employed in the protective circuit, the VA burden of the relay is shared by all the CTs in parallel and a normal VA CT may generally suffice. Such is the case in most of the protective schemes discussed in Sections 21.6 and 15.6.6(1), except for those employing only one CT to detect a ground fault condition, such as for a generator protection with a solidly grounded neutral (Figure 21.12). 

When the system is grounded through its neutral, either solidly through a resistance or through an arc suppression coil (inductor), it becomes a grounded neutral system. This type of system grounding may be classified as follows ... 

The naturai zero phase sequence inductive reactance of the grounded neutral may be considered to be too small compared to this and ignored for ease of calculations. Thus the resistance Rq of the grounded neutral circuit may be considered as its impedance, i.e. 

The theory of operation of such a protection scheme is based on the prineiple that in a balanced cireuit the phasor sum of currents in the three healthy phases is zero, as illustrated in Figure 21.7, and the current through the grounded neutral is zero. In the event of a ground fault, i.e. when one of the phases becomes grounded, this balance is upset and the out-of-balance current flows through the grounded neutral. A healthy three-phase circuit, how ever. 

Current polarization through the grounded neutral of aW/t> power transformer... 

When there is a fault in the local generating area (Figure 22.10(a)) the return path will be through the grounded neutral of the generator. The switchyard s other remote power sources may also contribute to... 

It is common practice to leave the star-connected capacitor banks ungrounded when used in the system or use delta-connected banks to prevent the flow of third harmonic currents into the power system through the grounded neutral. 

Triple harmonic quantities are unbalanced ( uantities and can exist only on a system, which has a grounded neutral. The configuration of the windings of the source generating the harmonics, the system to which it is connected, and its grounding conditions, thus play a significant role in transmitting the harmonics to the whole system as discussed below ... 

Grounded neutral When the neutral is grounded, the third harmonic quantities will be able to find their w ay through it. This system can thus be considered to contain the third harmonic quantities and will affect operation of the equipment connected on it and communication networks if existina in the vicinitv (Figure 23.12(c)),... 

But when the neutral is grounded through an arc-suppression coil (reactor) the current through the grounded neutral may be of a limited amplitude, say, up to its continuous rating (Section 20.5) and it may exist for longer. 

Generators typically are Y-connected to provide three phases and a neutral for a 3-phase, 4-wire system. The neutral can be grounded or ungrounded, but a grounded neutral is usually preferred. 

The pulp is ground, neutralized with lime, and pressed. The press liquor is concentrated to make molasses for animal feed. The pressed pulp is dried and used as an animal feed. 

The usual legume inoculant now in use consists of finely-ground neutral sedge peat to which the bacteria have been added from liquid cultures. Years of research have shown that peat is an ideal medium in which to keep the bacteria in good viable condition for several months under commercial handling conditions. 

Surge arresters Floating neutral type Grounding neutral type Floating neutral type... 

Do not use the grounded neutral conductor of a circuit for the grounding of equipment. No neutral shall be grounded, unless electrically isolated from the plant power distribution system in or immediately adjacent to the equipment in question. This is to prevent current imbalances in the power distribution system which would affect ground fault detection. 

At a new site, it is often advisable to perform ground system tests before the power company ground/ neutral conductor is attached to the system. Conduct a before-and-after test with probes in the same position to determine the influence of the power company attachment [ 11 ]. It is also worthwhile to install permanent electrodes and marker monuments at the original P2 and C2 probe positions to ensure the repeatability of future tests. 

V. A three-phase, three-wire system, delta-connected, with 240 V between phase conductors and no ground or neutral conductor. Used for motor and three-phase power loads. This system is gradually being replaced by the more modern 120/208-V system with grounded neutral. 

For many years industrial plants relied on an ungrounded system, essentially a delta-connected system without a grounded neutral. In this system, a single Une-to-ground fault does not cause automatic circuit tripping. However, a second undetected ground on such a... 

Since this system is alternant, it must have tt-electron densities of unity in its ground neutral state. This would be necessary however, even if the molecule were not alternant, due to the fact that all carbons are equivalent by symmetry. Hence, they must all have the same electron density. Since it must sum to four electrons, the density of each atom must be unity. The same argument applies to the cyclopropenyl radical, a nonaltemant that, nevertheless, has all electron densities equal to unity (if the unpaired electron is divided between degenerate MOs). 

It is useful to consider this attractive electrostatic energy quantitatively, assuming one ion with a charge e- at a distance of 0.2 nm (dose to the ionic radius of Br) from a non-grounded neutral metal sphere with a radius of 3 nm The electrostatic energy of interaction is then -147 kj/mol. Note that an approaching electrically neutral molecule would not lead to this type of electrostatic interaction. However, weak interaction due to dipole or higher multipole moments is possible. 

The processes differ in that the transition probability in the former is determined by the ionization continuum, whereas it is governed by the transition to the excited neutral state, AB", in the latter. Of interest to the PEPICO experiment is the decay of these autoion-izing resonances and their effect on the ability to select electrons of a given energy. It has been found that, because of autoionization, ions can be prepared in Franck-Condon gap regions that are normally not accessible by direct photon excitation from either the ground neutral or the ground ionic state. 

---