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Similar to TESCO Tuesday: Traditional Ratio, Burden, Admittance and Demag Testing – Part II
Similar to TESCO Tuesday: Traditional Ratio, Burden, Admittance and Demag Testing – Part II (20)
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TESCO Tuesday: Traditional Ratio, Burden, Admittance and Demag Testing – Part II
- 1. 1 Today’s session will begin shortly @tescometering @TESCO_Metering TESCO -The Eastern Specialty Company TESCO -The Eastern Specialty Company
- 2. 2 10/02/2012 Slide 2 CT Testing - Ratio, Burden, Admittance Part 2 Prepared by Rob Reese, TESCO The Eastern Specialty Company For TESCO Tuesday Tuesday, March 16, 2021
- 3. 3 Agenda • A Quick Review • Detail of Additional Considerations • Questions
- 4. 4 Review – Ratio, Burden, Admittance Three Test Methods 1. Ratio 2. Burden 3. Admittance
- 8. 8 Ratio Testing Ratio of Primary Current to Secondary Current 5A PHASE A SOURCE LOAD 400A 400A 400A 5A 5A Calculate Ratio
- 9. 9 Burden Testing Functionality with Burden Present on the Secondary Loop Example Burden Spec: 0.3% @ B0.1, B0.2, B0.5 or There should be less than the 0.3% change in secondary current from initial (“0” burden) reading, when up to 0.5Ohms of burden is applied
- 10. 10 Burden Testing Functionality with Burden Present on the Secondary Loop ANSI Burden Values 0.1 Ohms 0.2 Ohms 0.5 Ohms 1 Ohms 2 Ohms 4 Ohms 8 Ohms
- 11. 11 Burden Testing Functionality with Burden Present on the Secondary Loop PHASE A .1 Ohm
- 12. 12 Burden Testing 0.0000 1.0000 2.0000 3.0000 4.0000 5.0000 6.0000 0 2 4 6 8 Burden Reading 0 5.0000 0.1 4.9999 0.2 4.9950 0.5 4.9900 1 4.9800 2 4.9500 4 4.0000 8 0.8000 0.3% @ B0.1, B0.2, B0.5 Initial Reading = 5Amps 0.3% x 5A = 0.015A 5A – 0.015 = 4.985A
- 13. 13 Burden Testing 0.0000 1.0000 2.0000 3.0000 4.0000 5.0000 6.0000 0 2 4 6 8 Burden Reading 0 5.0000 0.1 4.9999 0.2 4.9950 0.5 4.9900 1 4.9800 2 4.9500 4 4.0000 8 0.8000 0.3% @ B0.1, B0.2, B0.5 Initial Reading = 5Amps 0.3% x 5A = 0.015A 5A – 0.015 = 4.985A
- 14. 14 Admittance Testing • What is Admittance? • Admittance testing measures the overall “health” of the secondary loop of the CT. • Measured in units of MiliSiemens (mS) • Admittance is the inverse of impedance. • Impedance is the opposition to current. • Therefore, admittance testing measures the overall “health” of the secondary loop of the CT.
- 15. 15 Admittance Testing • Admittance testing devices inject an audio sine wave signal into the secondary loop of the CT. • The resulting current is measured. • The voltage of the initial signal is known. • From these two parameters, the impedance, and thus the admittance can be calculated. Cat 6330 – Meter Site Analyzer
- 16. 16 Additional Considerations • Importance • Multipliers • Parallelograms • Accuracy Graphs • Shop vs. Field Testing • Standards • Pole Top CT’s • No Test Switches • Demag Function
- 17. 17 Additional Considerations Not many utilities around me test their CT’s – Is it really necessary?
- 18. 18 Additional Considerations • Yes! • The meter is only one small part of the whole system. • CT errors can be much bigger than meter accuracy errors SOURCE LOAD
- 19. 19 Additional Considerations Scenario 1: Meter Error If the customer’s bill should be $10,000, and the meter registers 98%, you are still getting $9,800 SOURCE LOAD 98%
- 20. 20 Additional Considerations Scenario 2: One CT is reversed If the customer’s bill should be $10,000, and on of the CT’s are reversed, you are losing 2/3rds of your revenue, or $3,300 left. SOURCE LOAD
- 22. 22 Additional Considerations What are meter multipliers?
- 23. 23 Additional Considerations • CT’s -> 400:5 • CT Multiplier = 80 • PT’s -> 480:120 • PT Multiplier = 4 • Total Multiplier = 320 SOURCE LOAD
- 24. 24 Additional Considerations My CT test equipment provides a parallelogram report - What does this show me?
- 25. 25 Additional Considerations Parallelogram – a quick reference showing if a given CT is in specification at a given test point
- 26. 26 Additional Considerations Parallelogram – a quick reference showing if a given CT is in specification at a given test point
- 27. 27 Additional Considerations Parallelogram – a quick reference showing if a given CT is in specification at a given test point
- 28. 28 Additional Considerations Are my CT’s as accurate at low current as they are at rated current?
- 30. 30 Additional Considerations Should I test CT’s in my shop and/or in the field?
- 31. 31 Additional Considerations Field Testing • Equipment relatively low cost • Tests the whole service • Limited to testing at customer’s current load Shop Testing • Sizeable Investment • Will test at high currents – 8000amps – through a CT’s complete operating range • Only tests the CT, not the entire service
- 32. 32 Additional Considerations Are there any ANSI or other governing standards that specify the length and thickness of the secondary wiring?
- 33. 33 Additional Considerations Governing Standards for CT’s • ANSI C12.11 • IEEE C57.13 standard requirements for instrument transformers • IEEE C57.13.6 standard for high-accuracy instrument transformers • IEC 60044-1 current transformers • IEC 60044-6 requirements for protective current transformers for transient performance • IEC 61869-2 additional requirements for current transformers
- 34. 34 Additional Considerations Secondary cable length and gauge is largely governed by a Utility’s internal specifications. 10AWG 12AWG 0.3% @ B0.1, B0.2, B0.5
- 35. 35 Additional Considerations What is the best way to test my CT’s if they are mounted at the top of the pole?
- 37. 37 Additional Considerations My transformer-rated meter installations do not utilize safety test switches – Can I still test my CT’s?
- 40. 40 Additional Considerations What is the benefit of the demag function on my test equipment?
- 41. 41 De-magnetization CT’s can become magnetized, due to a number of reasons, including leaving the shorting clip open, near lightning strikes, and harmonic content. CT’s can be demagnetized by slowly and smoothly increasing the secondary resistance until saturation occurs, and then slowly and smoothly decreasing the secondary resistance.
- 43. 43 Metering Configurations Presentation Date Realizing Your Investment in Technology Through Analytics 3/23 Shop Testing 3/30 Preparing for AMI Deployment 4/6 Communication Equipment 4/13 Sign up: tescometering.com/tesco-tuesdays
Editor's Notes
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