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This is DigSilent Technical Reference Documentation of the Ct block that simulates the behavior of a current transformer in the programm.
Descripción: DIgSILENT Technical Reference Documentation of the Distance Polygonal “RelDispoly” block that implements the typical polygonal and quadrilateral impedance distance protection.
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Prot rote ect ctio ion n Relay Relay Load Encroa Encro ach chment ment
DIg SIL ENT Paci Paciff i c Melbourne Office
Suite 310 · 370 St Kilda Road · Melbourne · Victoria · 3004 · Australia
Perth Office
Suite 11 · 189 St Georges Terrace · Perth · Western Australia · 6000 · Australia
Protection Relay Load Encroachment
Managing the risk of distance protection load encroachment during contingencies •
Traditional use of software tools by protection engineers • Modelling of relays considered time consuming/complex • Benefit of relay simulation not apparent • Unsure of accuracy/reliability of data • Hesitance to use DPL • Force of habit
•
Typical project example • Project specific confidential • Risk of load encroachment due to network configuration changes • Risk of incorrect directional EF relays due to contingencies • Altered source impedance impact on all OC and EF relays • Impact on breaker failure requirement • Formulation of approach • Network model: Transformer vector groups
Protection Relay Load Encroachment
Protection relay mix • Many older electro-mechanical distance relays • Some modern distance relays (SEL 311, SEL 321) • External starters • Mixture of OC and EF relays and elements in distance relays • No documentation was available for some older relays
Project was ideally suited for automation • Large number of contingencies to consider (>40) • Very complex interconnected 66 kV network • Different operating conditions (12 base cases) • Large number of relays (124 relays modelled) • Various load flow and fault conditions to evaluate (3) • 40 x 12 x 124 x 3 = 178,560! • Difficult enough to make sense of such a large number of tests
Protection Relay Load Encroachment
Far reaching starter elements for breaker failure backup T N E L I S g I D
d i r G l a n r e t x E
Line
. . l a n r e t x E
Line(1)
A
C
. . g n i d n i W 2
B
D
General Load
Protection Relay Load Encroachment T N E L I S g I D
188. [pri.Ohm] 175. 163. 150. 138. 125.
REL 15080 Zl A 139.897 pri.Ohm 10.73° Zl B 139.897 pri.Ohm 10.73° Zl C 139.897 pri.Ohm 10.73° Zl A 139.897 pri.Ohm 10.73° Zl B 139.897 pri.Ohm 10.73° Zl C 139.897 pri.Ohm 10.73° Z A 139.897 pri.Ohm 10.73° Z B 139.897 pri.Ohm 10.73° Z C 139.897 pri.Ohm 10.73° Fault Type: Tripping Time: 9999.999 s
Initial study • Simply measured load without system modification • Repeated study with system modification • Report load flow for each case and try to make a comparison • Percentage change meaningless for small loads • Absolute value meaningless for large loads • Report concluded that system change would not impact on load encroachment • Some doubt remained
Protection Relay Load Encroachment T N E L I S g I D
Import network model from PSS/E or other source Create relay models not available (made use of generic models) Model and set all relay elements Set up all load flow cases to be considered Prepare DPL script to export all RX plots Prepare DPL script for contingency events and reporting (relay identification an operating time; graphics and/or spreadsheet) • Prepare DPL script for sensitivity analysis and reporting • Analyse results (relay operation for load flow) and write report
Challenges • • • •
Non-standard relay models Lack of protection scheme understanding (no substation level SLD) Accurate settings database (StationWare!) Complex relay responses
Protection Relay Load Encroachment
RAZOA Starter • Current measurement is always phase current • Voltage measurement is either phase to phase (2 or 3 phase faults) or phase to ground (in case of all faults to ground) • Applied setting measures correct for phase to ground fault with K0 = 1 (Zf = Uan/Ian) where K0 = (Z0 – Z1)/3Z1 • For a single phase fault with K0 = 1; Z0 = 4 x Z1 • Zf = (2 x Z1 + Z0)/3 = 2 x Z1 • For a 3-phase fault (similar to load encroachment) • Z’f = Ubc/Ib = √3 Z1|- 30°| • Hence Z’f = √3/2 x Zf |-30°| • The measurement of the “fault” impedance is therefore less than the setting and hence the relay can overreach the setting to compensate for undermeasurement • Similarly Zf = 2 x Z1 for a phase to phase fault
Relay B Zl A 2.429 sec.Ohm 85.08° Zl B 2.429 sec.Ohm 85.08° Zl C 2.429 sec.Ohm 85.08° Zl A 2.429 sec.Ohm 85.08° Zl B 2.429 sec.Ohm 85.08° Zl C 2.429 sec.Ohm 85.08° Z A 2.429 sec.Ohm 85.08° Z B 2.429 sec.Ohm 85.08° Z C 2.429 sec.Ohm 85.08° Fault Type: ABC Tripping Time: 9999.999 s Relay A Zl A 2.429 sec.Ohm 85.08° Zl B 2.429 sec.Ohm 85.08° Zl C 2.429 sec.Ohm 85.08° Zl A 2.429 sec.Ohm 85.08° Zl B 2.429 sec.Ohm 85.08° Zl C 2.429 sec.Ohm 85.08° Z A 2.429 sec.Ohm 85.08° Z B 2.429 sec.Ohm 85.08° Z C 2.429 sec.Ohm 85.08° Fault Type: ABC Tripping Time: 3.01 s
RAZOA Starter Implementation Options • Special polarising element • Relay logic • Self polarised with parameter characteristics
Protection Relay Load Encroachment
Large spreadsheets were prepared with fields: – Relay name – Base case tripping times – Contingencies – Contingencies tripping times Open columns clearly shows where load flows did not converge.
Protection Relay Operation
Direction OC and EF Test • • • • • •
Fault at both sides of each line/feeder Single phase to earth fault with 0 Ohm; 50 Ohm and 500 Ohm resistance Monitor both forward and reverse relay operation List for each relay all elements that operate as well as operating times Flag relays that operate for “reverse” faults – some would be non-directional Flag relays that do not operate for forward faults – could be according to element class • Repeat test for all operating conditions and contingencies • Analyse 178,560 relay operations times the number of relay elements
Challenges • • • •
Script took only two days to prepare Long run time 2 hour per base case Information overload Testing of non-standard relay types
Protection Relay Operation
Again large spreadsheets with columns: – Contingency – Line – Relay – Relay type – Relay polarity relative to fault (forward/reverse) – Busbar names – 0; 50 and 500 ohms fault resistance tripping times – Name of element picking up for each fault – Repeat the list for second/remote busbar.
Protection Relay Operation
Time – distance diagram • Easily interpreted as long as not too many relays are involved T N E L I S g I
Time – distance diagram • Ideal for grading evaluation between OC, EF and distance relays • Ideally a time – distance diagram consisting of two line lengths each • Repeated definition of paths and diagrams • Typically 4 relays per cubicle – long paths not sensible T N E L I S g I D
3.00
[s]
2.00
loc_name Ph-Ph 1
1.00
0.00 0.0000
1.6353
3.2705
4.9058
36502 MWTS/B.. 36502MWTS/B.. 8.1763
[pri.Ohm]
6.5410
4.9058
3.2705
0.00
1.00
loc_name Ph-Ph 4 2.00
[s]
3.00
6.5410
[pri.Ohm]
8.1763
36941 YPS/B1
36499 LV1/TE
36941 YPS/B1
36499 LV1/TE
1.6353
0.0000
Protection Relay Operation
Lessons learnt • Scope of exactly what tests and how to test needs to be clearly defined • Lack of client knowledge about what is possible • Client has no idea of what tasks are labour intensive and what not • Interpretation of vast amounts of data could be difficult • Understanding of PowerFactory relay elements • Access to good relay manuals not guaranteed
