Fault Locating PRESENTED BY ERIK SCHELLENBERG IDAHO POWER

Transcription

1 Fault Locating PRESENTED BY ERIK SCHELLENBERG IDAHO POWER

2 Topics Impedance Based Reactance Method Takagi Method Modifications to Takagi Method TWS & Double Ended Negative Sequence

3 One Line Equivalent Thevenin Sources Bus Line Relay with CT & CCVT

4 Radial Line Apply a fault m distance down a radial line m is a percentage of the line. For example if the fault is 25% from Bus S then (1 m) yields 75%, for a total line impedance, Z L,of 100%

5 V/I = mz L (sometimes) Using ohms law the fault locator at S can calculate the impedance, (mz L ), that the voltage V is being dropped across for three phase bolted faults.

6 V/I Calculation The equivalent circuit with respect to Bus S clearly shows that the measured voltage V is being dropped across the portion of the transmission line to the fault point. (m)z L = V/I (Ohms) (V/I) m = (%) Z L Fault Location = m (Line Length) (miles)

7 V/I & Fault Resistance Assume the fault has some resistance, R and the transmission line is purely inductive.

8 Simplified V/I with some R V LINE V s = V LINE + V F Let I s = 10 0 A, X L = 10Ω, & R F = 5Ω V LINE = 10 0 (10 90 ) = V X L Distance V F = 10 0 (5 0 ) = 50 0 V V s = V LINE + V F = V Distance = V S /I S = Ω R F I s V F mzl Distance

9 V/I Limitations Using ohms law directly as fault locator is impractical for a variety of reasons. Some of these include: Only works on three phase faults Only works on radial lines Only works on bolted faults Impacted by Load

10 Simple Reactance Method Transmissions line impedance, Z, is typically dominated by the reactive component, X. Fault impedance is typically dominated by the resistive component, R.

11 Fault Resistance & Reactance Method Lets look at the radial example with fault resistance again. The forward voltage drop measured by the fault locator is V s = mz L (I s ) + I s (R F )

12 Minimize the Effect of R F using Reactance Divide by the measured current I s Retain only the imaginary component of each quantity

13 Reactance Method with Remote Source No longer is the system radial The current flowing through R F is now the sum of the local source, I s, and the remote source, I R

14 Same Reactance Technique: Now with I R Write the forward voltage drop equation, Divide by I s to calculate a measured Impedance, Take the imaginary component of each term to mitigate fault resistance,

15 Homogenous System & Reactance If you have a homogenous system then both I S and I R will have the same angle and the imaginary part of (I f /I s )R f is zero. I R I f = I S +I R I s Ө Ө

16 Non Homogenous System & Reactance I S and I R will not have the same angle and the imaginary part of (I f /I s )R f will show up in the fault location calculation as an error term. l f l S l R α δ β

17 Simple Reactance Summary The simple reactance method was an improvement over the straight Ohms Law calculation but it still has some drawbacks: Impacted by Load Non homogenous systems introduce error in fault resistance term

18 Takagi Method In 1979 Toshio Takagi and Yukinari Yamakoshi filed for a U.S. Patent for a new single ended fault locating method. In 1982 Takagi, et al. deliver their paper. T. Takagi, Y. Yamakoshi, M. Yamaura, R. Kondow, T. Matsushima, Development of a New Type Fault Locator Using the One Terminal Voltage and Current Data, IEEE Transactions on Power Apparatus and Systems, Vol. PAS 101, No. 8, August 1982.

19 Superposition The key to the Takagi method is the idea of superposition Composite Fault Network + Load Pure Fault Network

20 Takagi Local & Remote Current Composite Fault Network Pure Fault Network Voltage equation for the left hand side Voltage equation for the right hand side Both equations equal VF. Set the Left side equal to the right side

21 No Fault Current in Load Circuit I f = I f because there is no fault branch current in the pure load state Composite Fault Network + Load Pure Fault Network

22 Takagi Fault Current Plug into I F equation From the previous slide we calculated I R in terms of I S

23 Forward Voltage Drop & Takagi From the previous fault location algorithms we developed the forward voltage drop equation with respect to fault locator: = + Plug in our new equation for the fault branch current, I f :

24 Pause for Error If there is load flow on the system γ will be non zero but if the magnitude of fault duty is much greater than load, the angle γ will approach zero. β will be zero if the numerator and denominator have the same phase angle, (homogeneous system)

25 Takagi Distance If we: Multiply by the complex conjugate of I s, Take the imaginary part of the equation to eliminate fault resistance, Assume the system is totally homogeneous, and finally Solve for m We will get the following equation:

26 Zero & Negative Sequence Takagi The Takagi can use the zero sequence term for ground faults, eliminating the need for pre fault data The negative sequence can also be used

27 Mutual Coupling There is magnetic coupling between phases on a current carrying transmission line, Z m.

28 Mutual Coupling Apply a bolted fault some length m down the line. A voltage is induced in each phase through the mutual coupling. Here Z m is written explicitly as Z ab and Z ac.

29 Voltage Equation The forward voltage drop equation for the faulted phase is Adding & Subtracting the same quantity 0 Gathering terms

30 Voltage Equation Cont d Recognize that Ia+Ib+Ic is the residual or zero sequence current Zm is a difficult quantity to handle directly. Through the use of Symmetrical Component theory it can be shown that: Solving for Z s in the Z L0 equation and plugging this into the Z L1 equation yields a Z m that is equal to:

31 V a and the mysterious k V a is now expressed in terms of positive and zero sequence line parameters which can be loaded into a relay as settings Factor out mz L1, (the distance to the fault) Define k to make the equation prettier

32 Modified Takagi Once again take the imaginary component of both sides and solve for mz L1

33 Two Terminal Methods More accurate than single ended methods Minimizes/Eliminates effects of Fault Resistance Loading Line Charging Current More overhead. Data must be gathered or shared from multiple locations

34 Traveling Wave A fault will cause a transient to propagate along the line as a wave The wave is a composite of frequencies with a fast rising front and slower decaying tail The waves travel at near the speed of light and eventually decay By time tagging the wave fronts as they cross both terminals a very precise fault location can be calculated

35 Wave Propagation The waves leave the disturbed area traveling at the velocity of propagation which is a little less than the speed of light

36 Negative Sequence Quadratic In 1999 Demetrios A. Tziouvaras, Jeff Roberts, and Gabriel Benmouyal of SEL introduced a new double ended technique that uses the negative sequence quantities from both terminals to fault locate. D.A. Tziouvaras, J.B. Roberts, G. Benmouyal, New Multi Ended Fault Location Design For Two or Three Terminal Lines, presented at CIGRE Conference, 1999,

37 Double Ended Negative Sequence By using the negative sequence methodology proposed by SEL the following sources of error are mitigated: Prefault load Zero sequence mutual coupling Zero sequence infeed from line taps Fault Resistance

38 References T. Takagi, Y. Yamakoshi, M. Yamaura, R. Kondow, and T. Matsushima, Development of a New Type Fault Locator Using the One Terminal Voltage and Current Data, IEEE Transactions on Power Apparatus and Systems, Vol. PAS 101, No. 8, August W. A. Elmore, Zero Sequence Mutual Effects on Ground Distance Relays and Fault Locators, Proceedings of the 19th Annual Western Protective Relay Conference, Spokane, WA, October E. O. Schweitzer III, Evaluation and Development of Transmission Line Fault Locating Techniques Which Use Sinusoidal Steady State Information, Proceedings of the 9th Annual Western Protective Relay Conference, Spokane, WA, October K. Zimmerman, and D. Costello, Impedance Based Fault Location Experience, Proceedings of the 31st Western Protective Relay Conference, Spokane, WA, October J. Glover, M Sarma, and T. Overbye, Power System Analysis and Design, Global Engineering, W. Stevenson, and J. Grainger, Power System Analysis, McGraw Hill Series in Electrical and Computer Engineering, 1994 Hewlett Packard, Traveling Wave Fault Location in Power Transmission Systems, Application Note 1285