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Power System Analysis and Design

Mulukutla S Sarma, J D Glover, Thomas Overbye

Computer Science

6th Edition · 925 pages

ISBN: 9781305632134

Chapter 10: Q1CSQ (page 667)

What is the normal lifetime of a numeric relay? What is the basis of numeric relay lifetime?

Short Answer

Expert verified

The age of the relay is between 15 to 20 years.

Step by step solution

01

Define the numeric relay

The numerical relays are the important protection devices in the power system that are provided with the software-based electrical fault detection method. The numerical relay are configure for the different input and the output to detect the fault at various levels which give them the other name of microprocessor relay.

02

Determine the answer

The numerical relay has various advantages such as:

The age of these relay is long
The relay employs solid state devices making them more reliable
The relay has easy maintenance

Due to these advantage the life of the numeric relay ranges between 15 to 20 years.

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Most popular questions from this chapter

A three-phase 34.5 kV feeder supplying a 3.5 MVA load is protected by 80E power fuses in each phase, in series with a recloser. The time-current characteristic of the 80E fuse is shown in Figure 10.43. Analysis yields maximum and minimum fault currents of 1000 and 500 A, respectively, (a) To have the recloser clear the fault, find the maximum clearing time necessary for recloser operation. (b) To have the fuses clear the fault, find the minimum recloser clearing time. Assume that the recloser operating time is independent of fault current magnitude.

(a) Draw the protective zones for the power system shown in Figure 10.45. Which circuit breakers should open for a fault at (a) $P_{1}$ , (b) $P_{2}$ , and (c) $P_{3}$ ?

Question:A three-phase, 500 MVA ,345 KV $∆$ /500 KV transformer is protected by differential relays with taps. Select CT ratios, CT connections, and relay tap settings. Determine the currents in the transformer and in the CTs at rated conditions. Also determine the percentage mismatch for the selected relay tap settings. Available relay tap settings are given in Problem 10.26.

Given the open-delta VT connection shown in Figure 10.38, both VTs having a voltage rating of 240 kV : 120 V, the voltages are specified as $V_{A B} = 230 ∠ 0^{\circ}, V_{B C} = 230 ∠ - 120^{\circ} a n d V_{B C} = 230 ∠ 120^{\circ}$ . Determine V_ab, V_bc and V_ca for the following cases: (a) The dots are shown in Figure 10.38. (b) The dot near c is moved to b in Figure 10.38.

A CT with an excitation curve given in Figure 10.39 has a rated current ratio of $500 : 5 A$ and a secondary leakage impedance of $\emptyset 1 + j 0.5$ . Calculate the CT secondary output current and the CT error for the following cases: (a) The impedance of the terminating device is $\emptyset 9 + j 0.5$ and the primary CT load current is $400 A$ . (b) The impedance of the terminating device is $\emptyset 9 + j 0.5$ and the primary CT fault current is $1200 A$ . (c) The impedance of the terminating device is $\emptyset 4.9 + j 1.5$ and the primary CT load current is $400 A$ . (d) The impedance of the terminating device is role="math" localid="1655725625321" $\emptyset 4.9 + j 1.5$ and the primary CT fault current is $1200 A$

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