Protector network for A-C equipment

The protector network disclosed in U.S. Pat. No. 4,675,772 is improved by omitting a specific inductor element from the filter means disclosed in that patent. The improved protector network is also used in a building having a main breaker panel or service entrance and subpanels.

TECHNICAL FIELD OF THE INVENTION 
The present invention relates to the general art of protective apparatus 
for a-c equipment, and to the particular field of protecting electronic 
apparatus from damaging power surges and transients. 
BACKGROUND OF THE INVENTION 
There are many applications where it is necessary to protect a-c load 
equipment from power surges and voltage transients which could 
deleteriously affect and possibly damage such equipment. This protection 
is particularly important for equipment comprising highly sensitive or 
complex multiple loads susceptible to electrical noise. For example, 
modern sophisticated data processing equipment includes highly sensitive 
electronic components which are particularly susceptible to damage or loss 
of stored data therein due to reactive voltage spikes occurring as a 
result of power surges in the feeder lines, switching transients, or as a 
consequence of external causes such as lightning or corona discharges or 
merely due to the internal circuitry itself. Some of these conditions can 
also occur with respect to, and thus damage, sophisticated 
telecommunication and telephone equipment installations. 
Numerous types of protective networks have been designed in an attempt to 
protect such equipment from these power surges and transients; but most of 
these existing protective networks have not been entirely satisfactory for 
all conditions of service. Specifically, it would be desirable that such 
protective networks be adapted for convenient installation with existing 
equipment, prevent the deleterious effects of such surges and transients 
occurring at the source, or as a consequence of the circuit breaker 
switching, as well as being effective to prevent reactive spike build-up 
or other spikes or noise at the load side of the network. This is 
especially true in many modern buildings where there are numerous 
electronic components, especially PC's, connected to one subpanel. In 
fact, it is not uncommon to have several thousand PC's in a single office 
building. Thus, the inventor has found that one source of noise and spikes 
can be a computer itself. The large number of PC's, printers, etc in many 
modern office buildings can make the building load generated noise a major 
problem. Furthermore, it would be desirable to provide such surge and 
transient protection in synergistic combination with power filtering, as 
well as to adapt such protective networks for convenient installation 
with, and therefore protection of, multiple type loads, i.e. 3-phase and 
single-phase loads. 
One protective network that has been effective is disclosed in U.S. Pat. 
No. 4,675,772, the disclosure of which is incorporated herein by 
reference. This network provides power surge and transient voltage 
protection for a-c load equipment, and is illustrated in FIG. 1. The 
network 10 illustrated in FIG. 1 includes an L-C filter portion 11 and a 
pair of voltage suppressors 12 and 13. The voltages suppressors 12 and 13 
are connected across lines 14 and 15 supplying a-c power to input 
terminals 1 and 2 of a load 16. As shown, the filter network 10 includes 
an inductor 11a and a capacitor 11b and is located PG,4 between the 
suppressors 12 and 13. 
While the network disclosed in the incorporated patent works extremely 
well, it does introduce some costs into an overall system. Thus, reducing 
the costs associated with the protector network disclosed in the 
incorporated patent would further improve that network. 
Accordingly, there is a need for a protector network for a-c equipment 
which has a minimum cost, yet is still as effective as the network 
disclosed in U.S. Pat. No. 4,675,772, and which can be incorporated in a 
building. 
OBJECTS OF THE INVENTION 
It is a main object of the present invention is to provide a protector 
network for a-c equipment which has a minimum cost. 
It is another object of the present invention to provide a protector 
network for a-c equipment which has a minimum cost, yet is still as 
effective as the network disclosed in U.S. Pat. No. 4,675,772. 
It is another object of the present invention to economically distribute 
building protection throughout a building. 
It is another object of the present invention to economically distribute 
building protection throughout a building and to provide filtering between 
various sensitive loads in the building or workspace. 
SUMMARY OF THE INVENTION 
These, and other, objects are achieved by a protector network for a-c 
equipment which improves the network disclosed in U.S. Pat. No. 4,675,772 
by removing the inductor element 11a from the network. 
Line inductance of the line conductor 14 is used in place of the actual 
inductor element 11a of the incorporated patent. The line 14 is of 
sufficient length to have a line inductance between the suppressors 12 and 
13 which is effectively equivalent to the inductance 11a existing in the 
filter network 10 of the incorporated patent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Comparing FIGS. 1 and 2, it can be seen that the present invention is 
embodied in the use of self-inductance of the line 14 in place of the 
inductor 11a shown in FIG. 1. The filter network 10' shown in FIG. 2 is 
identical to the filter network 10 shown in FIG. 1 with the exception of 
the deletion of inductor 11a. 
The self-inductance of the line 14 is selected to be essentially similar 
to, or in many cases, better than, the inductance associated with inductor 
11a. The self-inductance of the line 14 is a function of the outer 
diameter of the line, the length of the line, the material of the line as 
well as the proximity of line 14 to other lines. For example, in a 
multi-line system, the flux linkage associated with line inductance can be 
determined by relationships such as: =[L]i, where is an nx1 vector 
containing .sub.1, .sub.2, . . . .sub.n ; i is an nx1 vector containing 
i.sub.1, i.sub.2, . . . i.sub.n, and [L] is an nxn matrix whose general 
entry is l.sub.ij =(/2)ln(1/D.sub.ij) henry/m, with i,j=1,2, . . . n, and 
D.sub.ij =r.sub.ij ', the geometric mean radius of a thin walled 
conductor. Tables of geometric mean radii or calculational techniques, 
such as disclosed in the Appendix of "Power System Analysis" by Charles A. 
Gross, and published by John Wiley and Sons in 1979 (which Appendix is 
incorporated herein by reference) can be used to determine the value of 
the inductance existing between suppressors 12 and 13. The line 14 is thus 
effective to provide the inductance necessary to achieve the results 
taught in the referenced patent so the overall network effectively 
suppresses power surges, voltage transients, spikes and the like from both 
the source and the load. 
The inventor has found that even sixty feet of number 2 wire (medium-big) 
appears to provide enough inductance to be of value. In most buildings, 
the distance from a main panel to a subpanel is greater than sixty feet, 
and hence the inventor has found that inductance provided by the 
self-inductance of a line complying with National Electric Code Standards 
is sufficient to carry out the objects of the present invention. 
Shown in FIGS. 3 and 4, is the network of the present invention in 
conjunction with a single phase load (FIG. 3) and in conjunction with a 
three phase load (FIG. 4). The various elements shown in FIGS. 3 and 4 are 
discussed in the incorporated patent, and attention is directed thereto 
for such discussion. 
Shown in FIGS. 5-8 are applications of the present invention for use in a 
building. With a plurality of protection units connected to the supply 
lines or bus bar risers, such as bar BR, at various locations in the 
building being shown in FIGS. 6-8. As discussed in the referenced U.S. 
Pat. No. 4,675,772, the protection units and devices located on the load 
side of the network will protect the protection units and elements on the 
line side of the network against voltage surges initiated at the load side 
of the network. A suppressor 12' can be located in the building main 
circuit breaker panel 50 which joins the building wiring 14 and 15 to a 
utility power source 52. Lines 54 and 56 represent building wiring that 
extends from the main breaker panel throughout the building and which 
connect the utility or source power to loads, such as load 16', which are 
located at various places throughout the building, such as on various 
floors of a multi-story building, or the like. 
Suppressor 13 and capacitor 11b are located in a subpanel 58 which can be 
located on the floor which contains the load 16', and the overall filter 
network 10' is comprised of the line 14, with its self-inductance 
replacing the inductor 11a, the subpanel 58 with its capacitor 11b and its 
suppressor 13, and the main breaker panel with its suppressor 12. 
Alternatively, the elements shown may be located at other strategic 
positions by being attached directly to wire elements 14 and 15 as needed. 
An alternative form of the FIG. 5 setup is shown in FIG. 6 where the main 
panel 50 at a power service entrance connects the building bus bar riser 
54 to various point-of-use panels, such as panels S-S.sub.n, which 
includes a subpanel power surge and transient protector unit, shown as 
subpanels 58.sub.1 through 58.sub.n, with each subpanel corresponding to 
the just-described subpanel 58. Some of the subpanels are connected to the 
point-of-use subpanels to protect all equipment associated with that 
point-of-use subpanel, and some of the subpanels, such as subpanel 
58.sub.2, can be spaced from the point-of-use subpanel to provide 
additional protection for special elements. 
While FIG. 6 shows a bus bar riser set up, FIGS. 7 and 8 show each of the 
point-of-use panels S being connected to the main panel 50 via line 
conductors, such as line conductor 59.sub.5. In such a set up, each 
point-of-use panel is fed by a separate line from the main breaker panel. 
As shown in FIG. 8, a second point-of-use panel S.sub.nn reiterates a 
point-of-use panel S.sub.n. Further point-of-use panels S.sub.nnx can be 
connected to the reiterative point-of-use panels as indicated in FIG. 8. 
Each point-of-use panel includes its own protective network 58, as is 
indicated for network 58.sub.n2. As can be seen in FIG. 8, each 
point-of-use panel is filter protected and each has the neutral bus NB 
thereof connected to the adjacent panel neutral buses, and the phase bus 
PB thereof connected to the phase buses of adjacent panels. 
The arrangement of multiple filter elements such as shown in FIGS. 6 and 8 
is also effective to provide noise filtering and suppression between 
various loads, such as those on different panels. A capacitor C.sub.50 can 
be included at the main panel 50. This further enhances filtering between 
loads on various ones of the panels, and especially if sensitive loads are 
also connected the main panel 50 which could be upset by the summation of 
noise generated by the loads at various subpanels. Capacitors similar to 
C.sub.50 can be included in each of the reiterative point-of-use panels as 
suitable. 
Shown in FIG. 9 is a cascade network 70 in which a plurality of filter 
networks 72, 72.sub.2 are connected in tandem between a load line LL and a 
neutral line NL with the self-inductance SNL and SLL serving as the 
inductance element disclosed in the incorporated patent as discussed 
above. Other filter networks 72.sub.n can be connected to the lines LL and 
NL with self-inductance SLL.sub.n and SNL.sub.n being included. As is 
shown in FIG. 9, various other protective elements can also be included in 
the overall system, such as MOV 73, or the like. This permits various 
protective networks to be combined. This is especially important if the 
overall protective network is used in a building where several different 
modes of protection are, or can be, used. 
The cascade concept is shown in FIGS. 10 and 11 as networks 70' and 70" as 
including a transformer T in each network. The transformer has a 
transformer ratio 1:Z, and each of the networks 70' and 70" has suppressor 
elements, such as suppressor element M.sub.1 on one side of the 
transformer and suppressor element M.sub.2 on the other side of the 
transformer. The suppressor elements on each side of the transformer are 
related to each other by the transformer ratio. That is, all of the 
M.sub.2 side suppressors are related to all of the M.sub.1 side 
suppressors by the relationship M.sub.2 &gt;ZM.sub.1. This feature permits 
the transformer-containing networks, such as networks 70' and 70", to 
carry out the aforediscussed load side and supply side protection. This 
relationship also permits this feature to be retained while accounting for 
voltage suppressor manufacturing tolerances. The voltage suppressor 
elements M can be, for example, MOV's. Using this relationship having the 
line side suppression level lower than the load side suppression level for 
the values of the voltage suppressors on each side of the transformer 
results in the line side suppressor or suppressors turning on before the 
load side suppressors. 
The transformer-containing network 70" includes a reiterative panel setup 
similar to the setups discussed above in relation to FIG. 8. Thus, the 
network 70" includes a point-of-use panel S.sub.x connected to a filter 
panel 58.sub.x having a suppressor M.sub.2 connected between the phase and 
neutral buses thereof. Further point-of-use panels S.sub.nnx can be 
connected to each other and to the panel S.sub.x as above discussed. 
As will occur to those skilled in the art based on the teaching of the 
above disclosure, the present invention can be used in conjunction with 
single phase power, multi-phase power, as well as between phase-to-phase, 
phase-to-neutral, phase-to-ground, as well as phase-to-ground situations. 
The various forms of protective networks can be combined in any suitable 
and desirable combination to provide a maximum protection to electrical 
equipment located in a building. Various combinations of voltage 
suppressors, filter means, and capacitors can thus be formed to provide an 
overall system that includes a portion thereof already built into a 
building. Thus, a building can be initially designed to provide overall 
protection, and the various tenants in the building can modify or 
complement that in situ building protection as desirable and suitable for 
their own needs. On the other hand, a building tenant may not desire to 
add any further protection, and will be protected by the in situ network 
already in place in the building. For example, the assignee of the present 
invention manufactures several different types of power protection 
equipment, and any or all of these various types of power protection 
equipment could be used in conjunction with a building in situ protection 
system using the teaching of the present invention to modify and customize 
the building protection to suit the needs of each individual tenant, or 
the individual work stations of such tenant. 
A specific application of the present invention will include a unit at the 
service entrance, a unit at a panel and a plug-in unit such as shown in 
FIG. 12. 
Furthermore, it is observed that one skilled in the art will recognize that 
various capacitor values, or various values of the other elements in the 
system, may be selected based on an anticipated noise frequency range and 
impedences anticipated at each point. Thus, one skilled in the art will 
recognize that such elements may be scaled by the various transformer 
ratios described herein, and that active filter or connection elements may 
be used. Therefore, the present disclosure is not intended to be limiting, 
but an example only. 
It is understood that while certain forms of the present invention have 
been illustrated and described herein, it is not to be limited to the 
specific forms or arrangements of parts described and shown.