Advanced Power System Protection Pdf Download
Power-system protection is a branch of electrical that deals with the protection of electrical power systems from through the disconnection of faulted parts from the rest of the. The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, whilst leaving as much of the network as possible still in operation. Thus, protection schemes must apply a very and pessimistic approach to clearing system faults.
The devices that are used to protect the power systems from faults are called protection devices. A digital (numeric) multifunction protective relay for distribution networks. A single such device can replace many single-function electromechanical relays, and provides self-testing and communication functions. Types of protection High-voltage transmission network Protection on the transmission and distribution system serves two functions: protection of plant and protection of the public (including employees). At a basic level, protection disconnects equipment which experiences an overload or a short to earth. Some items in substations such as transformers might require additional protection based on temperature or gas pressure, among others.Generator sets In a power plant, the protective relays are intended to prevent damage to or to the in case of abnormal conditions of operation, due to internal failures, as well as insulating failures or regulation malfunctions.
Such failures are unusual, so the protective relays have to operate very rarely. If a protective relay fails to detect a fault, the resulting damage to the alternator or to the transformer might require costly equipment repairs or replacement, as well as income loss from the inability to produce and sell energy.Overload and back-up for distance (overcurrent) Overload protection requires a current transformer which simply measures the current in a circuit.
There are two types of overload protection: instantaneous overcurrent (IOC) and time overcurrent (TOC). Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate.
Time overcurrent protection operates based on a current vs time curve. Based on this curve, if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate. The function of both types is explained in on.Earth fault/ground fault Earth fault protection also requires current transformers and senses an imbalance in a three-phase circuit. Normally the three phase currents are in balance, i.e. Roughly equal in magnitude. If one or two phases become connected to earth via a low impedance path, their magnitudes will increase dramatically, as will current imbalance.
If this imbalance exceeds a pre-determined value, a circuit breaker should operate. Restricted earth fault protection is a type of earth fault protection which looks for earth fault between two sets of current transformers (hence restricted to that zone).Distance (impedance relay) Distance protection detects both voltage and current. A fault on a circuit will generally create a sag in the voltage level.
If the ratio of voltage to current measured at the relay terminals, which equates to an impedance, lands within a predetermined level the circuit breaker will operate. This is useful for reasonably long lines, lines longer than 10 miles, because their operating characteristics are based on the line characteristics. This means that when a fault appears on the line the impedance setting in the relay is compared to the apparent impedance of the line from the relay terminals to the fault. If the relay setting is determined to be below the apparent impedance it is determined that the fault is within the zone of protection.
When the transmission line length is too short, less than 10 miles, distance protection becomes more difficult to coordinate. In these instances the best choice of protection is current differential protection. Back-up The objective of protection is to remove only the affected portion of plant and nothing else.
A circuit breaker or protection relay may fail to operate. In important systems, a failure of primary protection will usually result in the operation of back-up protection.
Remote back-up protection will generally remove both the affected and unaffected items of plant to clear the fault. Local back-up protection will remove the affected items of the plant to clear the fault.Low-voltage networks The generally relies upon fuses or low-voltage circuit breakers to remove both overload and earth faults.Cybersecurity The bulk system which is a large interconnected electrical system including transmission and control system is experiencing new cybersecurity threats every day. (“Electric Grid Cybersecurity,” 2019). Most of these attacks are aiming the control systems in the grids. These control systems are connected to the internet and makes it easier for hackers to attack them. These attacks can cause damage to equipment and limit the utility professionals ability to control the system.Coordination Protective device coordination is the process of determining the 'best fit' timing of current interruption when abnormal electrical conditions occur. The goal is to minimize an outage to the greatest extent possible.
Historically, protective device coordination was done on translucent log–log paper. Modern methods normally include detailed computer based analysis and reporting.Protection coordination is also handled through dividing the power system into protective zones. If a fault were to occur in a given zone, necessary actions will be executed to isolate that zone from the entire system. Zone definitions account for, buses,. Additionally, zones possess the following features: zones overlap, overlap regions denote circuit breakers, and all circuit breakers in a given zone with a fault will open in order to isolate the fault. Overlapped regions are created by two sets of instrument transformers and relays for each circuit breaker. They are designed for redundancy to eliminate unprotected areas; however, overlapped regions are devised to remain as small as possible such that when a fault occurs in an overlap region and the two zones which encompass the fault are isolated, the sector of the power system which is lost from service is still small despite two zones being isolated.
Disturbance-monitoring equipment Disturbance-monitoring equipment (DME) monitors and records system data pertaining to a. Alexandra Von Meier (2013). Electrical Engineer 137A: Electric Power Systems. Lecture 14:Introduction to Protection Systems, Slide 3. Retrieved 2 July 2013. Glover J.
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Power Protection And Control Pdf
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protection and monitoring of the electrical energy transmission network.