1. Field of the Invention
The present invention relates to a control system for automatically reconnecting power to customers in a distribution automation multi-feed power network on detection of a fault disconnecting customers in the power network.
2. Description of the Related Art
Most customers in an electrical power network are connected to the power source via a low-medium voltage distribution network. The distribution network consists of a web of distribution feeders that are fed from one or more power source via distribution substations. Each distribution feeder supplies power from at least one power source to one or more customers is connected to each distribution feeder. Each of these feeders are fed through further customer feeders via isolation switches which will normally have a number of switches which can be opened to isolate faults should a fault occur. Due to the large quantities of customers and their wide distribution from remote rural areas to densely populated urban areas, the distribution network is extensive and very dispersed. Some of the power network is fed over ground and some is fed underground.
Because the network is so extensive, it is frequently the subject of system generated faults or externally generated faults. System generated faults are caused by equipment failures due to problems with the actual equipment in the network. These faults are inherent in the network itself being caused due to malfunction of equipment or other failures of equipment or due to operating failures caused by the operators or the customers in the network. Externally generated faults are caused by environmental conditions the network for example, storms may knock trees onto power lines, lightening may strike power lines. Construction machinery may dig up or knock down power lines. Whatever the reason, the distribution network is prone to frequent faults.
A fault on a distribution feeder will generally lead to loss of supply for some or all of the customers connected to that distribution feeder. Once this happens, the main objective is to minimise the number of customers disconnected by the fault and isolate the fault.
Generally, there is a protection device or Autorecloser switch at the distribution substation that will trip under fault condition to disconnect the feeder and isolate the fault. This disconnects all the consumers connected to the feeder. In order to reduce the number of customers disconnected, there are generally more isolating devices along the feeder that can be opened to isolate the fault closer to the fault point. This minimises the number of customers disconnected.
This still leaves all the circuit, downstream of the fault switch, without power. To improve this situation, circuits can frequently be supplied from more than one source, generally known as dual feed or multi-feed power sources. Where multiple sources can supply a network, the sources must not be connected together via the circuits at any time. To avoid this, there is always an Open-point in the circuit, namely, a switch deliberately left in the open state to keep the sources disconnected to remove the danger of a short circuit. Taking the simplest example in a single power source supply the basic known schemes to restore power from a single power source supply include:                a) Using manual operation of the switches and breakers to isolate the fault and restore power to the maximum number of consumers. This operation of the switches and breakers can be done locally at the devices or remotely via some communications media. This is a slow and time consuming process as the operator must physically travel to each switch to operate it.        b) Using an Autorecloser in conjunction with the main substation circuit breaker to try to reclose the breaker and re-establish power following a fault. This is effective for instantaneous faults but does not help for permanent faults.        c) Using several Autoreclosers along the distribution line with each Autorecloser being configured with different re-closing times. By selecting the correct timings, the device closest to the fault will lock-open first and isolate the fault while the other devices can safely reclose with the fault isolated. These can only be programmed to isolate the fault from one supply and cannot be used to restore power from an alternative supply.        
There are various schemes used at present to isolate distribution faults and minimise the number of consumers disconnected in a multi-feed power network. Most of these schemes, however, concentrate on isolating the fault and restoring power from the original supply. Very few schemes focus on automatically reconnecting to another supply via the Open-point. The basic schemes to restore power from an alternative supply in a multi-feed system include:                d) Manual operation of the switches and breakers to isolate the fault section and close an Open-point to restore power from an alternative supply. This is a slow and time consuming process as the operator must physically travel to each switch to operate it.        e) Remote manual operation of the switches and breakers to isolate the fault section and close an Open-point to restore power from an alternative supply. This remote operation requires a communication system that allows data to be transferred between each device and the controlling station. It requires information from each device to be available to a control manager or a control operator and commands from the controlling stations to operate the appropriate device.        f) Remote automatic operation of the switches and breakers to isolate the fault section and close an Open-point to restore power from an alternative supply. This is similar to the previous scheme but instead of an operator controlling the devices remotely, the system will automatically analyse the information and try to restore power without manual intervention.        
Some schemes rely on remote operation of the Open-point and isolating switches from some central controlling station. This requires a communications means to each device and a comprehensive master controller that maintains information from all devices and allows either manual operator control or automatic decision making on how best to restore power. These are very costly capital investments, have substantial running costs and technical problems associated with them.
U.S. Pat. No. 5,701,226 discloses an apparatus and method for distributing electrical power from power substation circuits. The apparatus disclosed by this U.S. patent includes at least one fault isolating switch positioned in series with the feeder conductors of each substation circuit so as to define a line side and a load side. A current sensor connected to the isolation switch is provided to measure the current on the load side of the isolating switch. Each isolating switch is connected to a switch controller which controls the movement of the isolating switch, the switch controller determines if the measured current from the current sensor exceeds a predetermined value and selectively activates the isolating switch when the predetermined value is exceeded. The switch controller further has a distribution station controller located remotely from the isolating switch for sending and receiving data. The data transferred to the switch controller from the distribution station controller includes instructions for actuating the isolating switch. The fault condition is only determined by measuring the current at each switch. While this U.S. patent adequately proposes a solution to solve the problem of isolating faults within a power distribution system, the switching technology employed is quite cumbersome and expensive. Therefore, a problem arises for multi feed systems, when this U.S. patent isolates the fault, all the customers between the isolated fault and the open point which is necessary to incorporate dual feed systems, are disconnected. Further control and complex communications are necessary to move the open point which has resulted in that heretofore no effective solution has been proposed by any utility company to effectively solve the above-mentioned problems. The apparatus relies on a centralised distribution controller and a substation controller. The open-point or switch is only moved by the centralised distribution controller opening the isolation switch and determining what other power source can supply power. This implementation requires complex software and expensive distribution controller with communications to each switch.