Table of Contents
What is EF relay?
Earth Fault Relay (EFR) It is a safety device used in electrical installations with high earth impedance. It detects small stray voltages on the metal enclosures of electrical equipment. The result is to interrupt the circuit if a dangerous voltage is detected.
What is MHO relay?
Mho relay is a voltage restrained directional relay. Important Points: Reactance relay is suitable for the protection of a short transmission line because its operation is independent of arc resistance. The relay which is selected for a long transmission line should be less affected due to power swings.
What does loop impedance mean?
Earth fault loop impedance is the path followed by fault current when a low impedance fault occurs between the phase conductor and earth, i.e. “earth fault loop”. So in short it is the impedance of the earth fault current loop starting and ending at the point of earth fault. This impedance is abbreviated to Zs.
What is induction Cup relay?
Induction Cup Relay. The relay which works on the principle of electromagnetic induction is known as the induction cup relay. The relay has two or more electromagnet which is energized by the relay coil. The static iron core is placed between the electromagnet as shown in the figure below.
What is function of Buchholz relay?
The Buchholz relay purpose is to give the protection to a transformer from the different faults happening in the transformer like the Short circuit, inter-turn, core, incipient, etc. This relay will sense these faults and shuts the alarm circuit.
What is R1 and R2?
R1 = resistance of phase conductor ie Live. R2 = resistance of cpc ie earth.
What are earth faults?
Faults are fractures in Earth’s crust where rocks on either side of the crack have slid past each other. Sometimes the cracks are tiny, as thin as hair, with barely noticeable movement between the rock layers.
Where is MHO relay used?
These relays are used in long transmission, medium, and short transmission lines. The working principle of Mho relay is, it used for long-distance transmission lines because these lines generally experience power swinging transients as well as load shedding problems.
What is the overshoot time of a cdg11 relay?
-Tfre type CDG31 relay is a triple pole version (with fhree overcurrent units or two overcurrent units and one earth fault unit in the centre) of type CDG11. On removal of a current equal to 20 times current setting the overshoot times of the ahove are 0.065 second and 0.04 second respectively.
What are the characteristics of a CDG relay?
number of units (ie CDG3x is a 3 element / unit CDG relay) characteristic (for CDG, 1= std inverse (3s), 2= long time delay, 3=very inverse (1.55s), 4=extremely inverse (0.6s), 6=Long Time Standard Earth Fault) case size (15 different cases, A=size 1 draw out, 10 terminal etc.)
How many earth fault units are in a cdg21 relay?
The type CDG21 relay is either a, double pole version (with two earth fault units or two ovEr-current units) of the type CDG11, oi type CDG11 with an instantaneous unit. -Tfre type CDG31 relay is a triple pole version (with fhree overcurrent units or two overcurrent units and one earth fault unit in the centre) of type CDG11.
How is the tripping time of a relay determined?
Relay characteristics are sometimes classified according to the tripping time at 10 times the setting current (i.e. [3s/10] – a standard inverse curve which will trip in 3 seconds at 10 times the current setting). Tripping times for the various relays are: