Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-07-19
2002-10-01
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C700S292000, C700S293000, C700S294000, C361S064000, C361S066000, C361S068000, C340S661000
Reexamination Certificate
active
06459998
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the detection of downed electrical power lines used to distribute power in an electrical power system and, in particular, to the control of the voltage applied to, and the current flowing through, these power lines.
A problem which exists in detecting the nature of certain power line fault conditions will be explained with the aid of
FIGS. 1 and 2
.
FIG. 1
illustrates a scheme for distributing power to, and along, a street lighting system. Typically the street lighting system includes a “primary” power line
21
(carrying, for example, 7.9 KV phase to ground) coupled via a disconnect switch (SW
21
) to the primary of a power transformer PT
21
. The secondary of power transformer PT
21
is coupled via a contactor C
21
to a power line
23
which is shown to branch off into a power line
25
a
and a power line
25
a.
Each one of the power line branches (e.g.,
25
a,
25
b
) may extend, for example, from 100 feet to 3 (or more) miles. The contactor
21
is controlled by means of a photovoltaic sensor PC
21
which closes the contactor C
21
at night to energize the lighting system and which opens the contactor C
21
during the day to de-energize the lighting system. In addition, there are fuses (FZ
1
, FZ
2
) along lines
25
a
and
25
b,
in series with the contactor C
21
, which in response to an overload condition are caused to “open” or “blow” when conducting currents ranging from 10 amperes to more than 100 amperes.
Typically, the power lines
23
,
25
a,
25
b
are run above ground, supported by poles. In the event any of the poles are damaged (e.g., during a storm, as a result of an automobile accident, or mechanical failure of the supporting structure) and/or due to lightning striking the power lines and/or their supporting structure, a power line may be broken (“ruptured”) resulting in a short circuit condition or in an open circuit condition. If the break is such that there is a short circuit condition, an overload current may be drawn through the power line causing a fuse (e.g., FZ
1
, FZ
2
) to blow. However, if the break is such that the power line is either dangling in the air or contacting ground via a high impedance connection, little, if any, current is drawn. The disconnect switch SW
21
would not be opened and the fuses (e.g., FZ
1
, FZ
2
) along the line would not be blown. Yet, the broken (“dangling”) line presents a grave danger to human life. For, if a human, or an animal, makes contact with the “dangling” broken power line serious injury or death may occur at currents as low as 0.05 amperes. Therefore, it is necessary to positively sense any “ruptured” power line; particularly when the power line is “live” in order to remove the application of power to that line.
An open circuit along a power line may be sensed via monitors (e.g., M
1
, M
2
) located at the termination (end point) of each power line (e.g., ep
1
a,
ep
1
b,
ep
2
a,
ep
2
b
). If either (or both) of the monitors (M
1
and/or M
2
) senses that no current flows through the monitor or that there is no voltage across the lines, the monitor can indicate that there is an open circuit along the line (i.e., no power being distributed). However, the fact that there is an electric “open circuit” along a particular power line does not necessarily mean that there is a physical break (“rupture”) in the power line.
Referring to
FIG. 1
, note that there is a fuse FZ
1
along line
25
a
inserted into the line to protect the line and equipment (not shown) against an overload condition. This fuse (e.g., FZ
1
) can blow and the monitor (e.g., M
1
) will indicate that there is an open circuit along that line (e.g.,
25
a
). However the fact that there is an open circuit (due to the fuse being blown) does not mean that the line is physically broken (ruptured or downed). Consequently, if, on the basis of what the monitor senses, it is assumed that the line is broken and the disconnect switch is opened, then power will be removed from line
25
b
as well as line
25
a.
This is highly undesirable since the disconnect switch controls the distribution of power to other branches and power to these branches should not be interrupted unless there is a real question of harm to human life. On the other hand, if there is a broken line, it is imperative that power to the line be removed.
The problem of detecting a broken power line has been illustrated using a “secondary” distribution system (i.e., the relatively lower voltage for the street light line distribution scheme). A similar and perhaps more significant problem exists in detecting breaks in “primary” distribution systems (i.e., those distributing high voltages) as shown in FIG.
2
.
FIG. 2
shows a substation
10
which is used to control the switching and distribution of electrical power from a generating source (e.g.,
11
a,
11
b
) to various distribution points and loads within a power system. Substation
10
includes a plurality of circuit breakers (e.g., CB
1
-CB
9
) which are coupled to the incoming transmission lines (e.g., PL
1
, PL
2
) and which enable the application of power to the power transformers (e.g., PT
1
, PT
2
) and to the outgoing feeders (i.e., conductors or power lines such—f
1
-f
4
). The circuit breakers are used to disconnect (and hence protect) the respective power lines and/or pieces of equipment when a fault (e.g., an overload) condition is sensed. The switching (opening and closing) of the circuit breakers (e.g., CB
1
-CB
9
) within a substation is typically controlled by protective relays (e.g., REL
1
-REL
4
) which, by controlling the opening and closing of the circuit breakers protect the incoming transmission lines, the power transformers, the outgoing feeders as well as the circuit breakers contained within the substation.
The protective relays used in the system may be any of a number of relays, including electromechanical, non-programmable static, and programmable microprocessor based relays. Each protective relay is generally designed to sense and/or respond to a fault condition based on a plurality of settings maintained in, or applied to, each relay. When a relay senses a fault condition it causes its associated circuit breaker(s) to interrupt the power to, or out, of the device(s) being protected.
As noted above, if a relay senses loss of power along one line and interprets the loss as a broken or downed line, power may be removed from lines servicing users who may suffer significant economic damage due to the power interruption. If, in fact, the loss of power is due to a broken line which is “live”, then the potential harm to life warrants the interruption of power distribution. However, if the loss of power is due to a blown fuse, then the disruption of power distribution is not warranted, Thus, when an open circuit condition is sensed, a problem exists in detecting whether the sensed open circuit is due to the line being broken and requiring additional removal of power, or to another cause (e.g., an open relay or a blown fuse) requiring no additional action.
SUMMARY OF THE INVENTION
The distribution of power along a power line may be interrupted by among others, a physical break (rupture) of the power line, the blowing of a fuse along the power line or the opening of a disconnect switch. Interruption of power distribution results in the interruption of current flow and in the absence of a voltage beyond the point where the power line is broken or the fuse is blown or the disconnect switch is opened. Applicant's invention resides, in part, in the recognition that different conditions causing interruption in the power distribution provide different “signatures”. For example, the characteristics of the voltage, current and power signals and their transient responses generated on a power line resulting from a rupture of the power line are different than the voltage, current and power signal characteristics generated and sensed due to the blowing of a fuse or the opening of a disconnect switch or a circuit breaker. The different responses generated (and sen
Assouad Patrick
Schanzer, Esq. Henry I
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