Consider the system below. The purpose of this problem is to conduct an analytical study in order to determine the minimum and maximum fault currents that may occur in order to design the protection system. The system nominal phase to phase voltage is 120 V. Three phase fault are considered as maximum fault currents. Phase to phase fault currents are considered as minimum fault currents. Note that only positive sequence impedances are given. Suppose the load is neglected and that all pickup taps are available. The relay characteristic is given at the last page of this booklet. 120 V R1 j6 R3 R2 R4 із R5 j2 VF VF Three phase fault: IF = Phase to Phase fault: Ip = 2+Z₁ Z₁ 1. Find the three phase fault currents in breakers 1, 2 and 5. 2. Find the phase to phase fault currents in breakers 1, 2 and 5. 3. For each of the three breakers, set and select the instantaneous relays. 4. For each of the three breakers, set and select the time delay OC relays.

Electric Motor Control
10th Edition
ISBN:9781133702818
Author:Herman
Publisher:Herman
Chapter14: Phase Failure Relays
Section: Chapter Questions
Problem 2SQ: What are the hazards of phase failure and phase reversal?
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Consider the system below. The purpose of this problem is to conduct an analytical study in order
to determine the minimum and maximum fault currents that may occur in order to design the
protection system. The system nominal phase to phase voltage is 120 V. Three phase fault are
considered as maximum fault currents. Phase to phase fault currents are considered as minimum
fault currents. Note that only positive sequence impedances are given. Suppose the load is
neglected and that all pickup taps are available. The relay characteristic is given at the last page of
this booklet.
120 V
R1
j6
R3
R2
R4
із
R5
j2
VF
VF
Three phase fault: IF =
Phase to Phase fault: Ip
=
2+Z₁
Z₁
1. Find the three phase fault currents in breakers 1, 2 and 5.
2. Find the phase to phase fault currents in breakers 1, 2 and 5.
3. For each of the three breakers, set and select the instantaneous relays.
4. For each of the three breakers, set and select the time delay OC relays.
Transcribed Image Text:Consider the system below. The purpose of this problem is to conduct an analytical study in order to determine the minimum and maximum fault currents that may occur in order to design the protection system. The system nominal phase to phase voltage is 120 V. Three phase fault are considered as maximum fault currents. Phase to phase fault currents are considered as minimum fault currents. Note that only positive sequence impedances are given. Suppose the load is neglected and that all pickup taps are available. The relay characteristic is given at the last page of this booklet. 120 V R1 j6 R3 R2 R4 із R5 j2 VF VF Three phase fault: IF = Phase to Phase fault: Ip = 2+Z₁ Z₁ 1. Find the three phase fault currents in breakers 1, 2 and 5. 2. Find the phase to phase fault currents in breakers 1, 2 and 5. 3. For each of the three breakers, set and select the instantaneous relays. 4. For each of the three breakers, set and select the time delay OC relays.
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