The Principle of Operation of Electrical Circuit Breakers - Coursework Example

Digital Signal Processing in Electrical Circuit Breakers: Literature Review

Introduction

Circuit breakers are electromechanical devices applied in electrical systems to connect and disconnect the flow of power. They are critical devices in the application of power systems because of their ability to interrupt power when there is a fault. In this connection, circuit breakers must be extremely reliable and accurate to ensure that their primary objective of disconnecting power when there is a fault is achieved. These devices can be manually operated to interrupt the current during normal conditions and automatically performed when there is a fault to disconnect the faulty part from a healthy portion.

They are usually situated at the generator, sub-station, or load station. More specifically, the circuit breakers will often carry currents under normal conditions. They will not take excess flow under short circuit or overload conditions, and instead, when the current through the circuit breaker exceeds its rating, it will automatically break the circuit. Circuit breakers consist of mechanical or electrical parts; thus can be mechanically or electrically operated. The contacts are responsible for making/breaking or opening/closing mechanism as well as controlling the circuit breaker. Circuit breakers can be in operation for over 40 years before they develop any problems (1999 Index IEEE Transactions on Power Systems Vol. 14, 1999). However, sometimes their lifetime can be interrupted due to mechanical issues and deterioration because of the current they carry. The fact that they give currents during normal and faulty conditions, they are prone to degradation because of the heating effect.

Basic Operation principle of Circuit Breakers

Mostly, circuit breakers remain closed and only work as electrical conductors, while still perform their intended function of protecting the system. The circuit breakers can incorporate relays in their capacity for the efficiency of operation. The relays can detect faults in the power system and then identify the circuit breaker, which is appropriate to open the circuit to remove the defect. In the occurrence of a fault, for example, a short circuit current, it is necessary to make the protective device to operate and interrupt the current and isolate the right part from an unhealthy one. This interruption of current usually occurs during transient conditions currents are very high (Bibliography on the Application of Discrete Supplementary Controls to Improve Power System Stability IEEE Working Group on Special Stability Controls, Power System Engineering Committee, 1987). The interruption initiates another transient that is meant to superimpose on the instantaneous condition of the current. Therefore, it is evident that such devices must bear the load produced by the transients; these transients include current and voltage transients, in turn, this creates a hostile condition for the circuit breakers. Therefore, these devices must be ruggedly constructed and in the right terms to enable them to interrupt the current and also to offer adequate protection to the power system.

Additionally, circuit breakers can be operated manually as well. For instance, sometimes the circuit breaker may not open or close as required, giving room for the device to carry the fault current for a more extended time while operating normally. Poor operation ability of the invention can cause damage to the circuit breakers as well as generating power shortages in power lines.

Digital Signal Processing in Electrical Circuit Breakers

Circuit breaker operation can be monitored in a real-time situation by the use of Remote Terminal Units (RTUs) of Supervisory Control and Data Acquisition (SCADA) (Kezunovic et al., 2005). Depending on the voltage levels detected from the CB contacts, RTUs can provide information on the status of the circuit breaker such as 'OPEN or CLOSE' (Kezunovic et al., 2005). The changes in time of control signals, for example, Trip or close, will result in X and Y coil currents as well as control and voltages. This makes it challenging to monitor the operation of circuit breakers using RTUs and SCADA systems. A solution to this problem has been developed by Texas A&M University (Kezunovic et al., 2005). According to the University, the problem can be solved by incorporating software and hardware components into a single real-time monitoring and a system for analysis. Real-time monitoring system for circuit breakers is an extension of a device that has been used for testing circuit breakers.

The devices that are used traditionally for testing are connected to the circuit breaker control circuit on temporary conditions to record analogue and digital signals. To perform the test, the operator should open and close the CB every time the analysis is being performed and subsequently, the data is also recorded. However, this traditional monitoring is manually done, making it very hard to get real-time data and thus difficulty in making a judgement on the behaviour of an electrical system or that system under monitoring and control.

In today's world, it is vital to ensure that electric utilities and devices are made in such a manner that they can reduce the overall operation and maintenance cost of the power system. At the same time, maintenance has a remarkable effect on the performance of the power system, including the reliability of the system (Vingerhoeds, 1997). Therefore, to ensure that the system operation is in order, not only the maintenance of the line is essential, but also the condition of the circuit breakers. It can be applied in controlling the sequence at which the circuit breaker operates and the alterations in system behaviour. Further, it can be used to improve the accuracy of the controls for smooth operation.

The new development brings onboard a unique solution whereby the monitoring device is permanently connected to the sub-station circuit breakers. The circuit breaker monitor (CBM) receives all detailed information about the circuit breaker within a short time whether the circuit breaker is manually or automatically operated. The data is then stored in a COMTRADE file format (COMTRADE: a new standard for a common format for transient data exchange, 1992). After all, the information about the circuit breaker has been recorded and transmitted by a wireless link to the concentrator PC, the software responsible for carrying out the analysis begins to do so (1999 Index IEEE Transactions on Power Systems Vol. 14, 1999). The main advantage of the Circuit Breaker Monitor system is that it provides a better understanding of the way circuit breakers can be used to monitor and analyze the analogue and digital signals exhibited in the circuit breaker circuitry.

Circuit Breaker condition monitoring is a modern technology that has been realized perhaps mainly because of the new developments in electrical and electronics such as electronic sensors, data acquisition gadgets, and communication systems. These developments have not only made this idea feasible but also cost-effective in terms of installation and maintenance. CBM can be applied to develop and improve some of the following functions: determination of the condition of the individual circuit breaker, assessing the state of circuit breaker and other controls associated with it, optimization of maintenance, and facilitation of CB utilization among other benefits (Jung et al., 2012). In the meantime, there are several applications of circuit breakers, both commercial and experimental, that can be used to help understand the operation. The information collected by the circuit breaker condition monitor should not be used only for monitoring the performance of the circuit breaker but also to improve the performance of the power system. It is also possible that this data from the circuit breaker can also be used to enhance power system topologies, alarm processor function, and other application of system analysis. The most important thing to ensure circuit breaker monitoring is to make data acquisition. The data which is in the form of digital signals must be acquired and stored to make it possible to extract any information.

The Basic Structure of Circuit Breaker Monitoring System

The Circuit Breaker Monitoring System is made up of server/client architecture with the client part situated in the sub-station. The client consists of Circuit Breaker Management Devices connected to the circuit breakers and software installed in a computer known as concentrator PC. These are all installed permanently in the substation.

Fig. 1

The figure above can be used to illustrate the architecture of the Circuit Breaker Management System. When the circuit breaker is operated, the recorded data is wirelessly transferred to the concentrator PC. The client software immediately analyzes the recorded data signals that have been derived from the circuit breaker control circuit. The processing of the message which is the responsibility of the analysis module is achieved by extracting various parameters from the samples of the recorded signal and compares them with the standard stored parameters (Vingerhoeds, 1997). After the comparison, the resulting report is displayed. If there is any problem, the notification is sent to the server located at the central office for further action to be taken. The information can be used to help identify which circuit breaker is having abnormally and this call for maintenance of the system.

Similarly, the recorded information that is in the form of digital data can also be downloaded to the computer server through the Ethernet network. Therefore, using a server system makes it easy for other users to download the information from a remote location. For instance, the central office users can quickly identify the problems with the power system and make necessary arrangements for maintenance.

The Circuit Breaker Management system consists of monitors situated on every circuit breaker in the switchgear section and a personal computer whose work is to gather information. The signals from the circuit breaker are produced either tripping or closing of the contacts. Therefore, the most vital signs are the Trip initiate and Close initiate of the circuit breaker. These signals may also be initiated by other devices like relays or the user. They can result in the generation of other messages through the tripping or closing of the contacts of the circuit breaker (Upadhyay, 2016). The signals are in the form of voltage and current. However, those signals that are in the way of currents must be converted to appropriate voltage signals.

The block diagram below shows a Circuit Breaker Monitor (CBM) which is used to monitor the status of the circuit breaker:

Fig 2

In the diagram, the circuit breaker is connected to signal conditioning boards; analogue/digital converter; microprocessor; and wireless transmitter. The analogue/digital converter does the major work of converting analogue to digital signals which are the signals used in communication. Therefore, with the above arrangement, we can make the circuit breaker monitor the status of the power system or any other system that can be protected by the circuit breaker.

Conclusion

The Circuit Breaker Monitoring and Analyser (CBMA) system is a new technique of using a circuit breaker to achieve digital signal processing. It is one of the latest developments in technology to offer real-time monitoring and assessment of circuit breaker operations applied in power system analysis and performance improvement. In essence, if the circuit breakers can be permanently monitored by analyzing the data from the circuit breaker, the real-time monitoring of the performance and the conditions of power topology can be made easier and quicker. The system enhances the process of analysis by producing timely results that self-explanatory and reliable for the operator to understand. These are possible because of the speed by which they are received and the application of advanced signal processing and expert system techniques. At the same time, this new development allows easy retrieval of data from the database and the webserver, enhancing access speed and dissemination of information. Finally, other features of this system include high speed, vast network, ease of diagnosis and troubleshooting, low cost and low maintenance.