Metering Principles & Configurations

Transcription

1 Metering Principles & Cnfiguratins CT PT Startc Western Energy Cmpany DCS

2 Presenters Western Energy Cmpany Mnte Wilke Electrical Superintendent Curt Brckel Electrical Supervisr Brady Clbert Electrical Engineering Intern Andrew Schfield Electrical Engineering Intern Littelfuse Startc Jeff Glenney P.E. Sales Engineering Manager Drives & Cntrls Services Rb Marnell Sr. Field Engineer

3 Vectr frm B t C C Z BC = B

4 Vectr Negatin Change the angle by 180 t negate the Vectr Z AB -Z AB = Z BA -Z AB. A B Z AB -Z AB = Z BA

5 3-Wattmeter Methd 3 Single Phase Wattmeters P A = V A I A Nte Element Plarities A B Current Element P A W P B W A Vltage Element B P B = V B I B C P C W C P C = V C I C Frm 3φ Surce T 3φ Lad

6 Meter Cnnectins Line t Neutral Vltage Element f Wattmeter is Wye Cnnected A P A W A Line t Neutral Cnnectin (Phase Vltage) B C ` P B W P C W B C P Ttal = P A + P B + P C

7 Vltage Elements Cnnected Line t Line Line t Line Cnnectin B Phase Chsen as Cmmn A B C P A W P B W P C W A B C Vltage Element Cnnected n Same Wire P Ttal = P A + P B + P C

8 2-Wattmeter Methd Three-phase pwer can be measured by means f nly tw single-phase wattmeters having a cmmn ptential junctin n any f the three lines in which there is n current cil.

9 2-Wattmeter Methd Wye Lad A P 1 W Frm 3φ Surce B Z B N 3φ Lad C P 2 W P Ttal = P 1 + P 2

10 2-Wattmeter Methd Delta Lad A P 1 W Frm 3φ Surce B C P 2 W Z CA 3φ Lad P Ttal = P 1 + P 2

11 Angle Derivatin Vltage Vltage L-L = V AB V CN V NB V AB V AN + V NB = V AB V AN V BN V AB Is the Vltage at A Relative t B

12 A Phase V L-N vs. V L-L I A Lags V AN by φ I A Lags V AB by φ + 30 V CN 30 V AB V AN Line-t-Line vltage is displaced frm Line-t- Neutral vltage by 30 V BN I A Φ

13 C Phase V L-N vs. V L-L V CB I C Lags V CN by φ 30 V AB I C Leads V CB by 30 - φ V CN Φ I C 30 P 1 = V AB I A cs (30 + φ) I A V AN Φ P 2 = V CB I C cs (30 - φ) V BN V BC

14 2-Wattmeter Methd P Ttal = P 1 + P 2 A P 1 W P 1 = V L-L I L cs (30 + φ) P 2 = V L-L I L cs (30 - φ) B C P 2 W

15 2-Wattmeter Methd P Ttal = P 1 + P 2 P 1 = V L-L I L cs (30 + φ) P V L-L I L cs (30 2 = - φ) +

16 2-Wattmeter Methd P 1 + P 2 = V L-L I L cs (30 + φ) + V L-L I L cs (30 - φ) P Ttal = P 1 + P 2 = V L-L I L cs (30 + φ) + V L-L I L cs (30 - φ)

17 2-Wattmeter Methd P 1 + P 2 = V L-L I L cs (30 + φ) + V L-L I L cs (30 - φ) P 1 + P 2 = V L-L I L [cs (30 + φ) + cs (30 - φ)] Trig expansin cs (A+B) & cs (A-B)

18 2-Wattmeter Methd P 1 + P 2 = V L-L I L cs (30 + φ) + V L-L I L cs (30 - φ) P 1 + P 2 = V L-L I L [cs (30 + φ) + cs (30 - φ)] Trig expansin cs (A+B) & cs (A-B)

19 2-Wattmeter Methd P 1 + P 2 = V L-L I L [cs (30 + φ) + cs (30 - φ)] Substitute Identity Int Equatin cs (A+B) = cs(a)cs(b) sin(a)sin(b) cs (A-B) = cs(a)cs(b) + sin(a)sin(b) A = 30, B = φ

20 Simplify Equatin A = 30 B = φ = V L-L I L (cs 30 cs φ - sin 30 sinφ + cs 30 cs φ + sin 30 sinφ ) = V L-L I L (cs 30 cs φ + cs 30 cs φ) = V L-L I L 2 cs 30 cs φ

21 2-Wattmeter Methd P 1 + P 2 = V L-L I L 2 cs 30 cs φ cs 30 = cs 30 = = 3 P ttal = P 1 + P 2 = 3 V L-L I L cs φ Each Wattmeter Reads Half f the Ttal Pwer

22 2-Wattmeter Methd P Ttal = 3 P 1 + V L-L P 2 I L cs φ A P 1 W P 1 = V L-L I L cs (30 + φ) B P 2 = V L-L I L cs (30 - φ) C P 2 W

23 Manufacturer s Recmmendatin When installing pwer measurement systems, always fllw the manufacturer s schematics fr PT and CT plarities.

24 Schematic prvided by: Pwer Measurement LTD.

25 CT PT

26 Current Transfrmer (CT) Plarity Test

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30 Drives & Cntrls Services Rb Marnell Sr. Field Engineer

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43 Littelfuse Startc Jeff Glenney P.E. Sales Engineering Manager

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48 If readings appear t be Vab=Vbc=120 and Vac = 209 yu have a prblem

49 MPS Current Unbalance Readings The unbalance display may help t determine a CT cnnectin prblem. The fllwing table lists sme cmmn cnnectin issues and crrespnding unbalance readings. A 100 A lad is assumed. Cunter-clckwise rtatin is A- B-C rtatin.

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51 Nte that simultaneus errr cnditins can mask as a single errr. As shwn in the table, CT Open will result in the same reading as Ph Rev & CT Reversed. The scenaris generated in the table were btained using the Symmetrical Cmpnents Calculatr available frm startc.ca.

52 Current Threshld The MPS threshld level is 1.5% f the CT rating. In terms f FLA, this value changes based n the rati f FLA t CT rating accrding t the fllwing frmula: % FLA Threshld = 1.5 * CT Primary Rating / Full Lad Current Fr example if FLA is 50 but CT rating is 100, then the threshld is 3% FLA. Lightly laded equipment draglines can shw as ging frm run t start mde due t current drpping belw the threshld.

53 Why are CT s and PT s mislabeled

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