Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Reexamination Certificate
1999-07-06
2001-08-14
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
C361S064000, C361S066000, C361S115000
Reexamination Certificate
active
06275366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power distribution systems. More particularly, the present invention relates to an automated power distribution system which incorporates a switching network responsive to control signals to fault isolate overcurrent events and minimize power outages.
2. Description of the Related Art
Electrical power distribution systems generally comprise substations having multiple circuits which have the capability to distribute three-phase electrical power to residential and/or industrial locations. Approximately 1500 customers are typically connected to each circuit. Each phase of each circuit is protected from an overcurrent event by a circuit breaker which is typically located at the substation. Examples of an overcurrent event include lightning striking the electrical conductors creating a current surge on one or more feeder conductors of the circuit, animals on the feeder conductors which create a short circuit, and actual short circuits. When an overcurrent is detected by the substation circuit breaker, the breaker initially actuates an “instantaneous trip and close” of the circuit breaker switch.
As shown in the voltage waveform of
FIG. 1
, the instantaneous trip of the circuit breaker switch (i.e., the switch opens) occurs at time t
1
, when the overcurrent (or fault) is detected. At time t
2
, the circuit breaker switch closes in an attempt to correct the cause of the overcurrent. For example, if an animal is on the conductors causing a short circuit, the animal may be dislodged from the conductors when the breaker trips and is closed to turn power back on. In the event the overcurrent was instantaneous, e.g., caused by lightning, then power will be restored to the circuit when the breaker closes. Typically, the circuit breaker switch closes within about four and six cycles of detection of the overcurrent, i.e., time t
2
occurs between about 66 ms and about 100 ms after time t
1
.
If the cause of the overcurrent is still present at the time the circuit breaker switch is closed, the circuit breaker switch again trips at time t
3
. At this time the circuit breaker enters a “first time delay” mode wherein the circuit breaker switch trips for approximately 30 seconds. At time t
4
the breaker switch is again closed. If the cause of the overcurrent is still present, the circuit breaker switch again trips at time t
5
and the circuit breaker enters a “lockout” mode, wherein the cause of the overcurrent must be ascertained before the circuit breaker switch can be closed. In the above configuration, when the circuit breaker is in the lockout mode, every customer connected to the circuit is without electrical power. As a result, it is desirable to isolate the fault and restore power to as many customers as possible connected to the circuit in a relatively short period of time.
One attempt to restore power to customers on a circuit has been to install automatic circuit reclosure (ACR) switches on the utility poles which support the feeder conductors. The ACR switches operate in a similar fashion as the circuit breaker, i.e., the switch opens when an overcurrent is detected. However, the ACR switches have similar operating characteristics as the circuit breaker, thus operating characteristic mismatches often occur between the operation of the ACR switches and the circuit breakers. To illustrate, if an ACR switch and the circuit breaker are designed to trip at a current of 200 amps, and the sensitivity of the circuit breaker is greater than the sensitivity of the ACR switch, then an overcurrent on the conductors would cause the circuit breaker to trip before the ACR switch, thus, circumventing the intended purpose of installing ACR switches. Moreover, since ACR switches trip when current is flowing through the switch, they must be constructed to withstand the arcing and high temperatures which occur between the switch contacts when opening and closing. This construction increases the cost of each ACR switch, rendering them highly uneconomical for usage in large quantities as required to protect each phase of each substation circuit.
Another attempt to fault isolate the cause of the overcurrent is to install multiple normally closed switches in series in each circuit on the utility poles. When an overcurrent is detected by the circuit breaker, each switch is opened and the circuit breaker is then closed. If no overcurrent is detected then each of the switches is sequentially closed until the circuit breaker trips, thereby causing the entire circuit to lose power again and causing damage to the line conductors and associated electrical equipment by closing the breaker into faults.
Therefore, a need exists for a power distribution system which utilizes a switching network that operates when the circuit breaker opens to avoid the arcing and high temperature problems associated with the opening and closing of switches when current flows therethrough and which quickly isolates overcurrent faults and restores power to at least a portion of the customers connected to the circuit.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus for distributing electrical power from power substation circuits. Typically, each substation circuit includes feeder conductors and a circuit breaker assembly located at the substation. The circuit breaker assembly is configured to trip when current flowing through the conductors exceeds a predetermined value, such as 725 amps.
The apparatus of the present invention includes at least one fault isolating switch member positionable in series with the feeder conductors of each substation circuit so as to define a line side and a load side. Current sensing means is operatively associated with the isolating switch member and is provided to measure the current on the load side of the isolating switch member. Isolating switch actuating means determines if the measured current value exceeds a predetermined value and selectively actuates the at least one isolating switch member when the predetermined value is exceeded. Preferably, the isolating switch actuating means has a predetermined time delay which corresponds with the tripping of the substation circuit breaker assembly before actuating the isolating switch member, thus, reducing the requirement of having a switch assembly which can withstand the arcing and high temperatures caused by the current flow. Each isolating switch member is preferably a normally closed switch member having a pair of electrical contacts connectable in series with the substation feeder conductors.
In the preferred embodiment, the isolating switch actuating means comprises a switch controller operatively connected to the isolating switch member and to the current and voltage sensing means so as to selectively move the isolating switch member between closed and open positions. The switch controller includes a microprocessor, memory and stored programs which receives the measured current and voltage values from the current and voltage sensing means and determines whether an overcurrent has occurred, a loss of voltage has occurred, and which controls the movement of the isolating switch member.
The isolating switch actuating means may further comprise a distribution station controller located remotely from the at least one isolating switch member. The distribution station controller is operatively connected to the switch controller and is configured to receive data from and transfer data to the switch controller. Preferably, the data transferred to the switch controller from the distribution station controller includes instructions for actuating the isolating switch member.
In an alternative embodiment, the apparatus of the present invention further comprises at least one restoration switch member connected between each of the substation circuits, and means for selectively actuating the at least one restoration switch member. The restoration switch actuating means actuates the restoration switch member when the substation circuit breaker is tripped
Andreas Philip B.
Gelbien Lawrence J.
Schweiger Werner J.
Dilworth & Barrese LLP
Jackson Stephen W.
KeySpan Technologies, Inc.
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