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df/dt Relay - Rate of Change of Frequency (ROCOF) Relay

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Rate of Change of Frequency (ROCOF or df/dt) relay is used for fast load shedding, to speed up operation time in over- and under-frequency situations and to detect loss of grid. For better understanding of role and operation of df/dt relay, let us first study the variation of frequency with load for a Grid. Graphical relationship between power and frequency of a Grid is shown in figure below. We can have two things to be noted from the above graph: a)     If the power available in the Grid increases i.e. in other words generation is more than the load, frequency will go up. b)     If the generation is less than load i.e. power deficient in the Grid then frequency will decreases. Large power grids (here large power grid means having large installed capacity in MW) are characterized by a very high stiffness constant which means that a large perturbation (load generation mismatch) is required to cause the grid frequency to change by 1...
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Single Line to Ground Fault Analysis

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In earlier posts we discussed, Concept of Symmetrical Components and  Calculation of Symmetrical Components . It is recommended to go through these topics before analyzing Single Line to Ground Fault. You must read,  Concept of Symmetrical Components  and  Calculation of Symmetrical Components Let us consider a three phase system with earthed neutral as shown below. Let us assume that a ground fault takes place in A phase (In many industries and numerical relays, normally the phases are said as A, B and C instead of R, Y and B, though they represent the same thing i.e. A phase means R phase, B means Y phase and C means B phase). E a , E b and E c are the Generator terminal voltage per phase. Bold letters here represent vector form.  Because of ground fault in A phase, the voltage at the point of fault will become zero and current through the other phases i.e. B and C phases will become zero. Therefore we can write as V a = 0 I b = 0 I c = 0 Therefore, from...
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STATCOM – Working Principle, Design and Application

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What is SATACOM? STATCOM or Static Synchronous Compensator is a power electronic device using force commutated devices like IGBT, GTO etc. to control the reactive power flow through a power network and thereby increasing the stability of power network. STATCOM is a shunt device i.e. it is connected in shunt with the line. A Static Synchronous Compensator (STATCOM) is also known as a Static Synchronous Condenser (STATCON). It is a member of the Flexible AC Transmission System (FACTS) family of devices. The terms Synchronous in STATCOM mean that it can either absorb or generate reactive power in synchronization with the demand to stabilize the voltage of the power network. Working Principle of STATCOM: To understand the working principle of STATCOM, we will first have a look at the reactive power transfer equation. Let us consider two sources V1 and V2 are connected through an impedance Z = Ra + jX as shown in figure below. In the above reactive power ...
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