EUS 260

Cap & Case StudyIn EURST

  1. Course purpose:

This course is designed to combine and show case many of the skills that have been learned by the students during the EUS program. The course will consist of only one final grade based on the successful completion of the project.

  1. Course description:

The student will be given specific electrical information associated with a T-D or T-T transformer. Each student will be given a unique set of values. The student will then develop a program for a SEL 351S.The program shall be designed to operate a circuit breaker for the down steam protection of feeder.Students may work in teams to develop the basic program but all enhancements must be individual work and unique.

  1. During demonstration of the project each student should be able to describe in detail the purpose of each action of the relay, what it accomplishes and how the circuit breaker simulator relay will respond. The student must also demonstrate their ability to operate the Doble 6150 relay test set and Protest software.
  1. Instructor requirements:
  2. Lecture on the capabilities of the SEL 351S relay.
  1. Demonstrate the operation of the relay front panel controls.
  1. Demonstrate the SEL acSELerator quick set software.
  1. Lecture on the SEL programing language.
  1. Demonstrate how to create a new setting file and down load to the relay.
  1. Describe the circuit breaker simulator.
  1. Demonstrate the operation of the Doble 6150 relay test set to test the relay program.
  1. Develop programing values for each student.
  1. Provide support as the students began to develop their relay programs.
  1. Approve any program enhancements the students wish to create for their program.
  1. Observe that the student’s program functions correctly for all conditions.

Settings:

Project Values
Transformer Voltage HS: / Transformer Voltage LS: / Transformer MVA:
Transformer Impedance: / Relay CTR: / Relay PTR:
51 Ø Trip Primary Amps: / 51 Ø Relay Time Curve / 51 Ø Time Dial Setting:
51G Trip Primary Amps: / 51G Relay Time Curve / 51 G Time Dial Setting:
50 Ø Trip Primary Amps: / 50G Trip Primary Amps:
UF Trip: / UF Time Delay: / Reclose Times:


Student Calculations:

  1. Transformer full load current.
  2. Transformer turns ratio.
  3. Chose the appropriate CT on the primary and secondary of the transformer.
  4. What is the full load current in the secondary of each CT?
  5. Maximum short-circuit current on the transformer HS and LS?
  6. What is the maximum current in the CT secondary during a fault?
  7. Determine the needed interrupting capacity of the breaker in low side.
  8. If a breaker is installed in the high side what is the needed interrupting capacity of the breaker?
  9. Choose the proper fuse size if you wish to install a fuse in the high side.
  10. What class of CT is needed in the low side assuming a burden of 4 ohms?

C800 ~ 200 VA, C400 ~ 100 VA, C200 ~ 50 VA, C100 ~ 25 VA

  1. Explain why the CT selected was chosen.
  2. Calculate the primary Ø minimum pickup current assuming
  3. Calculate the CT secondary minimum pickup current for the primary current above.
  4. What relay tap setting should be chosen if an electromechanical relay is used?

Assume testing the 51Ø and 51G relay elements in the SEL 351 S relay with multiples of tap value = 4 and TD=1 and answer the following:

  1. Choose the U4 time over current relay curve and calculate the trip time for the relay. (Refer to page 9-3 of the SEL351S relay manual)
  2. Calculate the trip time using the U1 time curve.
  3. What is the difference between the two curves; U4 and U1?
  4. What is the trip time of the 51 Ø relay at the maximum short circuit current using the U3 time curve?
  5. Set the 50Ø element for 1.2 times maximum short circuit current.
  6. Choose the appropriate PT ratio for the low voltage line.
  7. What is the PT secondary voltage?
  8. Set the under and over voltage for 80% and 120% of nominal.
  9. Set 51 G relay equal to 25% of 51Ø set point.
  10. Set 50 G relay equal to 25% of 50Ø set point.