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Electrical System Protection Coordination

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Pre Test

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1. It is the graphial representation of electrical equipment and protective devices current and time characteristics.
Single line diagram Time Current characteristic curve Damage curve Schematic diagram
2. What is the minimum time coordinating interval between static relays?
0.4s 0.3s 0.2s 0.1s
3. How long can a transformer inrush current exists?
1s 0.1s 0.01s 10s
4. What is the typical value of locked rotor current with respect to motor full load current?
7x 6x 4x 8x
5. The current pickup setting must always be:
Above the fault current magnitude Below the fault current magnitude The same with fault current magnitude None of the above
6. Evaluate the per-unit impedance of conductor using the given set of parameters:
0.0538 p.u 0.0267 p.u 0.0385 p.u 0.0835 p.u
7. Evaluate the new per-unit impedance at of transformer using the given set of parameters:
0.75 p.u 0.70 pu 0.65 pu 0.85 pu
8. Evaluate the actual fault current using the given set of parameters:
1798.23 A 1875.93 A 1912.13 A 1865.93 A
9. Evaluate the Phase quantities Ia from the sequence components:
0 1 -1 1.5
10. Evaluate the Positive, Negative and Zero sequence components for the unbalanced phase vectors:
Vao = 0.434 ∟-54.896, Va1 = 0.966∟15, Va2=0.211∟150 Vao = 0.344 ∟-45.689, Va1 = 0.989∟13, Va2=0.231∟160 Vao = 0531 ∟-54.896, Va1 = 0.966∟23, Va2=0.231∟180 Vao = 0443 ∟-58.496, Va1 = 0.923∟15, Va2=0.251∟165