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Homework 3: Ece Dept, Csu Fresno, Ece 152, K. Mcbee

This document contains homework problems from an electrical engineering course involving the use of current transformers (CTs) and relays. It provides details on the CT and system attributes for 5 problems, including CT ratios and ratings, maximum load currents, fault currents, and relay settings. It asks the student to determine if the CTs will saturate for different conditions, identify recommended relay pickup settings, and determine acceptable time dial settings for the relay to operate during a fault based on graphs of CT and relay performance characteristics.

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97 views4 pages

Homework 3: Ece Dept, Csu Fresno, Ece 152, K. Mcbee

This document contains homework problems from an electrical engineering course involving the use of current transformers (CTs) and relays. It provides details on the CT and system attributes for 5 problems, including CT ratios and ratings, maximum load currents, fault currents, and relay settings. It asks the student to determine if the CTs will saturate for different conditions, identify recommended relay pickup settings, and determine acceptable time dial settings for the relay to operate during a fault based on graphs of CT and relay performance characteristics.

Uploaded by

jjj
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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ECE Dept, CSU Fresno, ECE 152, K.

McBee

Homework 3
Utilize a SEL 351 Relay for problems P1 – P4. The relay possesses the following setting and burdens.

Burden:
5 Amp setting – 0.01  for all currents
1 Amp setting – 0.15  for all currents

Pickup Settings available:


0.25, 0.50, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0

P1- Determine if the CT will saturate utilizing the calculation method. Based upon your results, make a
recommendation for a pickup setting. (pickup should be at least 20% greater than maximum load)

CT ratio: 200:5
Type: single ratio
CT rating: C200
Lead Impedance: 1.10 

System Attributes
Imax load = 105 A
Imax 3 fault = 6000 A
Imin fault = 340 A

P2- Determine if the CT will saturate utilizing the calculation method. Based upon your results, make a
recommendation for a pickup current setting. (pickup should be at least 10% greater than maximum
load)

CT ratio: 200:5
Type: 600:5 multi-ratio
CT rating: C200
Lead Impedance: 1.10 

System Attributes
Imax load = 105 A
Imax 3 fault = 6000 A
Imin fault = 340 A
For problems P3 and P4 utilize Figure 1: Characteristic graph for a C100 multi-ratio CT to identify the
operation of the circuit.

P3- Identify pickup setting based upon CT ratio below. (pickup should be at least 10% greater than
maximum load). Determine if CT will saturate utilizing excitation curves.

CT ratio: 200:5
Lead Impedance: 1.10 

System Attributes
Imax load = 175 A
Imax 3 fault = 7000 A
Imin fault = 560 A

P4- Identify pickup setting based upon CT ratio below. (pickup should be at least 10% greater than
maximum load). Determine if CT will saturate utilizing excitation curves.

CT ratio: 400:5
Lead Impedance: 0.90 

System Attributes
Imax load = 250 A
Imax 3 fault = 6000 A
Imin fault = 670 A

P5- The relay for P4 needs to operate between 2 and 3 seconds for the maximum fault current. Based
exclusively on the exact settings listed in P4, what are the acceptable time dials settings for this CT
and relay combination. Utilize Figure 2.
Figure 1
Figure 2

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