电力系统震荡与失步(POWER SWING AND OUT-OF-STEP CONSIDERATIONS )

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ＩＥＥＥ　电力系统震荡与失步(POWER SWING AND OUT-OF-STEP CONSIDERATIONS )

ER SWING AND OUT-OF-STEP CONSIDERATIONS )

DONGBEI

4.2 ADDITIONAL POWER SWING DETECTION METHODS
4.2.1 Continuous Impedance Calculation
0 w6 v1 \2 `; O  vThis method determines a power swing condition based on a continuous impedance calculation.
Continuous here means, for example, that for each 5 ms step an impedance calculation is
  f+ ^$ A$ O6 d/ g0 B, bperformed and compared with the impedance calculation of the previous 5 ms. As soon as there is
* F! }! H/ T8 f7 p9 F6 p0 Sa deviation, an out-of-step situation is assumed but not proven yet. The next impedance that
should be calculated 5 ms later is predicted based on the impedance difference of the previous
8 @+ X; `/ k4 U( V- G& V0 rmeasured impedances. If the prediction is correct, then it is proven that this is traveling impedance.
/ U8 H  D4 R$ u+ g9 }In this situation a power swing condition is detected. For security reasons additional predictive
4 X2 c1 W( A% C9 O0 G  F2 b! }calculations may be required.
A delta impedance setting is not required anymore, because the algorithm automatically considers
, P- _9 l! ^) Q7 p# ~2 Wany delta impedance that is measured between two consecutive calculations and sets the delta
* ~* S9 R& ~) ]( ^2 i% Pimpedance for the next calculation automatically in relation to the previous calculation. This leads
, J: {& O. y; {to a dynamic calculation of the delta impedance and an automatic adaptation to the change of the
power swing impedance. Also the delta time setting is not required anymore because it is
& x* b1 k3 l$ m. fdetermined by the calculation cycles of the algorithm.
2 D. }4 k( S" NR
/ V" |" U' x: e: p9 s2 v) T: J+ `X
* ?  h4 h/ Z, \# ?" p0 t5 k2 g1 p% zStable power swing
impedance trajectory
DZ1 DZ2 DZ3
% u' T4 Y. G7 i4 h" k6 w  wLoad
- l2 L  Q0 u# hFigure 7 Power swing detection with continuous impedance calculation
As long as the changing impedance vector is not approaching a tripping zone faster than the relay
- L9 c5 X- {: J" Q) Z5 C8 P1 Fcan confirm the out-of-step condition (at least 3 calculations 10 ms) the detection will be successful.
POWER SWING AND OUT-OF-STEP CONSIDERATIONS ON TRANSMISSION LINES
4 t6 p$ H5 t9 \0 w5 ?  Z/ ]IEEE PSRC WG D6
! D# h2 r. M$ y3 _. Q# H7 Y$ s' s$ Z17 / 59 2005-07-19
4.2.2 Swing-Center Voltage and its Rate of Change
Swing-center voltage (SCV) is defined as the voltage at the location of a two-source equivalent
# e: n5 }: V' m2 l9 [. Y. u3 o% lsystem where the voltage value is zero when the angles between the two sources are 180 degrees
7 z8 c0 c) S5 n8 u7 Sapart. When a two-source system loses stability and goes into an OOS situation after some
4 s$ L# w4 s8 ndisturbance, the angle difference of the two sources, d(t), will increase as a function of time. Figure
8 illustrates the voltage phasor diagram of a general two-source system, with the SCV shown as
9 A+ E* D  S- d/ {0 [" athe phasor from origin o to the point o'.
$ ~6 _; |- m2 q- ^# q# Wo'
0 }  N. z; o* l! s9 j3 Qo
o"
Z1S•I Z1L•I
VS
5 x# }8 a: r( _3 \* Y2 P6 bj ER
d
; e/ x+ z0 j5 E4 I, Z3 g% KSCV
" Q0 |% Y- i: U, @Z1R•I
( w) {9 R# ?& U$ n5 r4 N5 U- q  pq
I
/ \6 ^0 K: q4 j+ L" _) AES
VR
Figure 8 Voltage Phasor Diagram of a Two-Source System
1 B0 }4 Q, h  n1 A+ dAn approximation of the SCV can be obtained through the use of locally available quantities as
follows:
  B* P9 C. k9 H/ bSCV »| V | ×cosj S (6)
Where |VS| is the magnitude of locally measured voltage, and j is the angle difference between VS
and the local current as shown in Figure 9. In Figure 9, we can see that Vcosj is a projection of VS
! m' F4 {( y8 oonto the axis of the current, I. For a homogeneous system with the system impedance angle, q,
3 S2 _# s. X. {" ~" A% `! E' T& Y# U) x/ Wclose to 90 degrees, Vcosj approximates well the magnitude of the swing-center voltage. For the
8 B3 N- B3 t; epurpose of power-swing detection, it is the rate of change of the SCV that provides the main
information of system swings. Therefore, some differences in magnitude between the system SCV
6 E* r6 O' p6 Band its local estimate have little impact in detecting power swings. Ilar [6] first introduced the
0 m# p1 ^. ^( S$ nquantity of Vcosj for power swing detection.

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