Page 1 of 5 HW08 EE6560 Power System Protection 1For HW08 1) Set transformer differential relay. Complete the ABB HU differential relay table below for this transformer carrying...



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. Set transformer differential (using lecture notes) as attached and bus differential relays per

PVD setting procedure PJN910408.pdf

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Page 1 of 5 HW08 EE6560 Power System Protection 1 For HW08 1) Set transformer differential relay. Complete the ABB HU differential relay table below for this transformer carrying 30MVA. HS CT ratios available are 600, 400, 200/5. LS CT ratios available are 2000, 1500, 1000/5. HU Differential Relay Table 138kV side (HS) 13.8kV side (LS) CT connection (delta or wye) CT ratio CT secondary current Current to HU relay Relay current ratio ____________________________ HU relay taps selected Relay tap ratio ____________________________ Mismatch, using the ratios above ____________________________ Page 2 of 5 1b) Bonus: Determine SEL-587-0 TRCON, CTCON, CTR1, CRT2, TAP1, and TAP2 for this transformer. Other settings are already shown in the template below. Page 3 of 5 2) Use the PJN910408 PVD procedure (do 1-4, then parts A & C) to set Device 87BH-3 PVD21 bus differential voltage unit "87L" for 138kV substation bus 3. Please number your steps as shown in PJN910408. 1. Assume all the CTs are SN 41507… as given below. 2. 138/34.5kV xfmr 3 is furthest from these PVD relays and the weakest source. CT to relay is 800 ft of #10Cu one-way. 3. Calculate the maximum bus 3-phase and SLG faults using: 2b) (Bonus) PVD application variations. After you set 87BH-3 above, the field calls with this finding (do each one separately, not cumulative). Is the 'as-built' OK? If so, do you need to reset 87BH, and if so to what? Does anything else need to be changed? a. Contractor used #14Cu wire instead of #10; or, b. PVD relays in panel are Single Thyrite stack instead of double stack; or, c. Xfmr #3 CTs are the Meramec Products CT shown further below. AC connection Page 4 of 5 Application variation information below: Single Thyrite stack PVD Page 5 of 5 Different CT on Xfrm 3 from Meramec Products Paul Nauert 3/21/2023 Per Unit System 11a Transformer Differential EE6560 Power System Protection 1 Paul J. Nauert, PE Adjunct Professor / Lecturer Learning Objectives / Overview • Differential Principle / Scheme • Transformer considerations • Connections • EM HU example on WARR 161/34.5kV • Schematics • Reference Blackburn Chapter 9 2 Differential Scheme • Kirchoff’s Current law 3 Considerations in Transformer Application • When KCL ≠ 0 but there’s not a fault – Magnetizing inrush – Overexcitation – CT saturation • Different voltage levels • Different CT ratios • Phase shift ∆-Y • Transformer taps changing 4 5 Transformer Enerigization 6 Magnetizing inrush current Energizing a 138/230kV Autotransformer and 230kV Line 7 Transformer Inrush • Why do we care? • Magnitude • Depends on _______ • Harmonic content • What about over-excitation? 8 9 Transformer Differential – Blackburn Fig 9.5 Connecting the Transformer Differential • Start with the xfmr nameplate • CT location and polarity • Usually easier to start on the Y side 10 UE Bulk Tr Connections 11 34.5kV X1 c X3 a X2 b 161kV H1 φ1 H3 φ3 H2 φ2 1500/5 RF=1.5 56 MVA Conn 400/5 Xfmr Diff Connections 12 34.5kV X1 c X3 a X2 b 161kV H1 φ1 H3 φ3 H2 φ2 1500/5 RF=1.5 56 MVA Conn 400/5 Application & Connection • Use a restraint for each fault source • Avoid paralleling radial (no fault) and fault source CTs • Parallel feeder CTs carefully • Phasing adjustment • Ratio adjustment • Mismatch M=[(IH / IL ) – (TH / TL)] / S • Where S is smaller of these ratios 13 Transformer Differential example 14 15 HU 16 Transformer Differential example 17 18 19 Differential relay • CT saturation can cause incorrect operation • Per cent differential • EM / SS/ digital • Operate and restrain coils • Harmonic restraint 20 A B B H U D iffe re n tia l re la y 21 HU AC to DC Polar unit 22 HU Trip circuit 23 24 Sensitivity 25 26 What to trip for WARR Device 63 & 87T 27 MTGY 161kV Big Ck m 21 m m ∆ Y www www m 87 T www www m 63 m 97773 WARR 1L M&R 28 Device 63 & 87T on 161/34.5kV Tr 29 Transformer 86T Trip DC 30 52753 Tr 1 AC Schematic 31 Per Unit System 11b Bus Differential EE6560 Power System Protection 1 Paul J. Nauert, PE Adjunct Professor / Lecturer Learning Objectives / Overview • Primary protection for – Sub-transmission bus • Fault levels • CT performance • High Z differential principle • GE PVD example at Warrenton 34.5kV • KAB • Read Ameren Standard 15G rev 5 Section 5.0 for present SEL-587Z application 2 34.5kV Bus Primary Protection • Primary protection for phase and ground faults is 87B high impedance differential – Similar to 138 or 345kV bus protection, – Single CT circuit, single DC circuit, single 86BL lockout – Faults unlikely but fault levels tend to be high and must be cleared very fast – Backed-up by Bus splitting scheme from Lesson 06 3 WARR Device 87B on Low Side 4 MTGY 161kV Big Ck m 21 m m ∆ Y www www m 51 www www m 87B m m m 51 87B m m 51 mm m 51 HV Bus protection Practicum • Differential commonly used, Device 87B • Consequences of false trip are significant • External close-in fault can cause CT saturation – Time delay solution – Linear couplers – High impedance – Low impedance with very good CTs • Trip hand-reset lockout, Device 86B • Bus arrester considerations ASPEN Equivalent Z1 & Z0 6 WARR 1-Line 7 Z+ eq = .386+j3.08% at 161kV Each Transformer: Ztr = 1.14+j29.2% And 2.38Ω neutral grd reactor Calculate maximum fault external to 34.5kV 87B Zone CT Performance • So important for differential, cover again quickly 8 From GE (left); (right) CT Model: C class 9 WARR 34kV Breaker CTs 10 Asymmetrical Fault Current 11 Source: ABB Effect of dc component of primary fault current on flux demands of a CT core. For fully offset need VCT = (1 + X/R ) Vsym to avoid saturation. CT Performance on the DC Component, cont’d 12 Distortion in CT secondary current resulting from dc saturation Typical exciting current of CT during transient asymmetric input current Distortion in CT secondary current resulting from ac saturation High impedance differential 1. Elegant solution 2. Forces CT saturation for internal fault 3. Determine highest voltage for external fault 4. Set between Item 3 voltage and lowest Vex of CTs connected 5. Matched CTs on full ratio the best 6. Keep lead burden low 7. Always have 86 short the AC to protect varistor or thyrite 8. GE PVD, SBD; ABB KAB; Basler BE1-87B; SEL587Z 14 High Impedance Differential External Fault 15 High Impedance Differential Internal Fault GE PVD21 AC Connection 16 87L Burden: GE PVD21 87L Pickup Calc 17 See PVD Setting Procedure PJN910408 Warrenton 34.5kV 18 Control House WARR 34kV Bus Diff AC 19 Leads from CT to 87B relay 20 87BL PVD21C • Both busses set same 21 22 WARR 34kV Bus Diff DC 23 GE PVD21B & D Internal Schematic 24 MRSL 138 Bus 3 PVD21D example 25 MRSL 138 Bus 3 PVD21D example 26 ABB / Wgh KAB Method CTs connected to 87B ABB CT knee Voltage, Vk K A B A C c o n n e c tio n Margin Factor for V-unit Setting SEL-587Z • Present Ameren Standard 87B • SEL AN2008-01 recommends – One cycle trip delay for calculated Vs <200 v – 200 v minimum setting with no delay • sel ag2007-07 recommends – 1.25 cycle trip delay if arrester is within sel-587z zone 30 v="" –="" 200="" v="" minimum="" setting="" with="" no="" delay="" •="" sel="" ag2007-07="" recommends="" –="" 1.25="" cycle="" trip="" delay="" if="" arrester="" is="" within="" sel-587z="" zone="">
Mar 24, 2023

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