Adaptive protection method for impedance of parallel capacitors

Abstract

An adaptive protection method for impedance of parallel capacitors comprises monitoring a terminal voltage and current of the capacitor; automatically calibrating the initial impedance of the capacitor when the capacitor is put into operation; calculating a real-time impedance of the capacitor during operation, dynamically updating the actual impedance of the capacitor periodically; comparing the real-time impedance of the capacitor with the actual impedance, updating the actual impedance if the relative value of the modulus of the real-time impedance change does not exceed the dynamic update limit threshold and the dynamic update reaches update period; generating an update failure alarm if the relative value of the modulus of the real-time impedance change exceeds the dynamic update limit threshold; generating a protection alarm if the relative value of the modulus of the real-time impedance change satisfies the protection alarm condition and the delay time is reached; and protecting the trip outlet if the relative value of the modulus of the real-time impedance change satisfies the protection trip condition and the delay time is reached. The protection method is applicable to various fault conditions of the capacitor and the capacitor bank, the set value is simple to calculate, the implementation is simple, and the sensitivity and reliability of the protection for capacitor are effectively improved.

Claims

1. An adaptive protection method for an impedance of parallel capacitors, characterized in that, the method comprising: monitoring a terminal voltage and current of the capacitors; automatically calibrating an initial impedance of the capacitors when the capacitors are put into operation; calculating a real-time impedance of the capacitors during operation, dynamically updating an actual impedance of the capacitors periodically; comparing the real-time impedance of the capacitors with the actual impedance, updating the actual impedance if a relative value of the modulus of the real-time impedance change does not exceed a dynamic update limit threshold and the dynamic update reaches an update period; generating an update failure alarm if the relative value of the modulus of the real-time impedance change exceeds the dynamic update limit threshold; generating a protection alarm if the relative value of the modulus of the real-time impedance change satisfies the protection alarm condition and a delay time is reached; and protecting a trip outlet if the relative value of the modulus of the real-time impedance change satisfies the protection trip condition and the delay time is reached.

2. The adaptive protection method for impedance of parallel capacitors according to claim 1, characterized in that, the terminal voltage and current of the capacitors are monitored; the terminal voltage of the capacitors is a vector difference between a bus voltage of each phase and a neutral point voltage of the capacitors, or is a terminal voltage of a discharge potential transformer; the current is a current of each phase of the capacitors, or is a vector sum of the currents of each phase branch of the capacitors.

3. The adaptive protection method for impedance of parallel capacitors according to claim 1, characterized in that, the protection trip condition of the impedance of the capacitors is calculated as follows:
.sub.dyn_(P)>.sub.set_trip wherein, (P) refers to the three phases A, B, and C, .sub.dyn_(P) is a relative value of the modulus of the real-time impedance change per phase when the capacitors fail, and .sub.set_trip is a value of the impedance protection trip.

4. The adaptive protection method for impedance of parallel capacitors according to claim 1, characterized in that, the protection alarm condition of the impedance of the capacitors is calculated as follows:
.sub.dyn_(P)>.sub.set_alm wherein, (P) refers to the three phases A, B, and C, .sub.dyn_(P) is a relative value of the modulus of the real-time impedance change per phase when the capacitors fail, and .sub.set_alm is a value of the impedance protection alarm.

5. The adaptive protection method for impedance of parallel capacitors according to claim 3, characterized in that, the relative value of the modulus of the real-time impedance change per phase of the capacitors is calculated as follows: ${\mathrm{.Math.}}_{\mathrm{dyn\_}\left(P\right)}=\frac{.Math.Z_{\mathrm{dyn\_}\left(P\right)}-Z_{\mathrm{real\_}\left(P\right)}.Math.}{.Math.Z_{\mathrm{real\_}\left(P\right)}.Math.}100\%$ wherein, Z.sub.dyn_(P) is a real-time impedance per phase of the capacitors, and Z.sub.real_(P) is an actual impedance per phase of the capacitors.

6. The adaptive protection method for impedance of parallel capacitors according to claim 5, characterized in that, the actual impedance per phase of the capacitors is calculated as follows: $Z_{\mathrm{dyn\_}\left(P\right)}=\frac{{\stackrel{.}{U}}_{\mathrm{dyn\_}\left(P\right)}}{{\stackrel{.}{I}}_{\mathrm{dyn\_}\left(P\right)}}$ wherein, {dot over (U)}.sub.dyn_(p) is a fundamental vector of the real-time terminal voltage per phase of the capacitors when put into operation, and .sub.dyn_(P) is a fundamental vector of the real-time current per phase of the capacitors when put into operation.

7. The adaptive protection method for impedance of parallel capacitors according to claim 5, characterized in that, the actual impedance Z.sub.dyn_(P) of the capacitors is updated periodically with the real-time impedance Z.sub.real_(P) which satisfies requirements.

8. The adaptive protection method for impedance of parallel capacitors according to claim 7, characterized in that, the real-time impedance update period is set by the value of dynamic update period of the actual impedance.

9. The adaptive protection method for impedance of parallel capacitors according to claim 7, characterized in that, the dynamic period update of the actual impedance Z.sub.real_(P) of the capacitors satisfies the condition as follows:
.sub.dyn_(P)<.sub.set_alm_dyn
max(|.sub.dyn_A.sub.dyn_B|,|.sub.dyn_B.sub.dyn_C|,|.sub.dyn_C.sub.dyn_A|)<.sub.set_ub_dyn wherein, .sub.set_alm_dyn is a limit value of the relative value of the modulus of the dynamic update impedance change, and .sub.set_ub_dyn is a limit value of the inconsistency relative value of the modulus of the change of the three-phase dynamic update; if the condition is satisfied, update the actual impedance; otherwise, the actual impedance is not updated and the dynamic update fails.

10. The adaptive protection method for impedance of parallel capacitors according to claim 5, characterized in that, the initial value of dynamic period update of the actual impedance Z.sub.real_(P) of the capacitors is an actual impedance after automatic calibration when put into operation; if the automatic calibration is accomplished, the actual impedance Z.sub.real_(P) is an initial impedance Z.sub.init_(p) of each phase after calibration of the capacitors when put into operation, otherwise the actual impedance Z.sub.real_(P) is a single-phase theoretical rated impedance $Z_{\mathrm{ideal}}=\frac{{\stackrel{.}{U}}_n}{{\stackrel{.}{S}}_n}$ of the capacitors; {dot over (U)}.sub.n is a rated line voltage, and {dot over (S)}.sub.n is a rated capacity.

11. The adaptive protection method for impedance of parallel capacitors according to claim 10, characterized in that, the initial impedance of the capacitors is automatically calibrated when put into operation, wherein the calibration equation for the initial impedance is described as follows: $Z_{\mathrm{init\_}\left(P\right)}=\frac{{\stackrel{.}{U}}_{\mathrm{init\_}\left(P\right)}}{{\stackrel{.}{I}}_{\mathrm{init\_}\left(P\right)}}$ wherein, {dot over (U)}.sub.init_(P) is a fundamental vector of initial voltage per phase of the capacitors when put into operation, and .sub.init_(P) is a fundamental vector of initial current per phase of the capacitors when put into operation.

12. The adaptive protection method for impedance of parallel capacitors according to claim 10, characterized in that, the initial impedance of the capacitors is automatically calibrated when put into operation, wherein the accomplishment of the automatic calibration is determined by the following:
.sub.inh_(P)<.sub.set_alm_inh wherein, .sub.inh_(P) is a relative value of the modulus of inherent deviation of the initial actual impedance when put into operation, and .sub.set_alm_inh is a limit value of the relative value of the modulus of inherent deviation.

13. The adaptive protection method for impedance of parallel capacitors according to claim 12, characterized in that, the relative value of the modulus of inherent deviation of the initial actual impedance when put into operation is calculated by the following equation: ${\mathrm{.Math.}}_{\mathrm{inh\_}\left(P\right)}=\frac{.Math.Z_{\mathrm{init\_}\left(P\right)}-Z_{\mathrm{ideal}}.Math.}{.Math.Z_{\mathrm{ideal}}.Math.}100\%$

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of an application scenario of the present invention;

(2) FIG. 2 is a schematic diagram of impedance circle for the impedance protection of parallel capacitors;

(3) FIG. 3 is a flowchart of a protection embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

(4) The invention will now be further described with reference to the accompanying drawings.

(5) Take a parallel capacitor bank of 35 kV voltage level as an example, the capacitor bank model is TBB35-12000/200AKW, the capacitor unit model BFM 11-200-1 W, the capacitor bank of each phase has 10 capacitors in parallel and 2 capacitors in series, the rated capacity of capacitor unit is 200 Kvar, the rated voltage is 11 kV and the capacitor unit is an external fuse capacitor.

(6) As shown in FIG. 3, an adaptive protection method for the impedance of parallel capacitor is implemented as follows:

(7) (1) According to the set capacitor rated capacity, rated voltage and other parameters, pre-calculate the theoretical set impedance of capacitor:

(8) $Z_{\mathrm{ideal}}=\frac{U_n^2}{S_n}=\frac{{11000}^2}{\frac{j200005}{2}}=j242$

(9) wherein, Z.sub.real is a single-phase theoretical rated impedance of the capacitor, U.sub.n is a rated line voltage, and S.sub.n is a rated capacity.

(10) (2) Set relevant equipment parameters and the protection set value;

(11) The relationship between the number of external fuse units of the capacitor unit that are blown and the overvoltage multiple of the sound phase unit and the total impedance of each phase is calculated according to the number of capacitors connected in parallel and in series, as follows:

(12) TABLE-US-00001 The number Overvoltage The modulus The relative of the fuse multiple of the phase value of the components of the sound impedance modulus of that are blown phase unit () the phase 0 100 242 0 1 105.34 255.44 5.55 2 111.11 272.25 12.62 3 117.62 293.857 21.43

(13) When 1 fuse of the capacitor is blown, the overvoltage multiple of the healthy component is 105.34%, which does not exceed 110%. Therefore, the capacitor is allowed to continue to work, and a fault warning is issued. When 2 fuses of the capacitor are blown, the overvoltage multiple of the component is 111.11%, the capacitor shall be tripped. Considering 1.5 times sensitivity to set the parameters as follows:
.sub.set_alm=5.55/1.5=3.7
.sub.set_trip=(12.625.55)/1.5+5.55=10.26

(14) The protection alarm set value and the trip set value are set as follows:

(15) TABLE-US-00002 Number Set Parameter Set Value Unit 1 Alarm Set Value .sub.set_alm 3.7 % 2 Trip Set Value .sub.set_trip 10.26 %

(16) According to the relevant provisions of GB/T 11024.1-2010 parallel capacitors with nominal voltage more than 11.000V used for AC power system, Part 1: General, the set values are as follows:

(17) TABLE-US-00003 Number Set Parameter Set Value Unit 1 Limit value of inherent 6 % deviation .sub.set_alm_inh 2 Limit value of dynamic update 1 % .sub.set_alm_dyn 3 Limit value of Three-phase 1 % inconsistency .sub.set_ub_dyn 4 Update period t.sub.dyn_set 1 h

(18) (3) Monitor the terminal voltage and current of the capacitor; the voltage at the capacitor terminal can be the voltage difference between the bus voltage of each phase and the neutral point voltage of the capacitor, or is the terminal voltage of the discharge PT; the current is the current of each phase of the capacitor, or is the vector sum of the currents of each phase branch of the capacitor. The real-time impedance of the capacitor is calculated based on the monitored current and voltage of the capacitor.

(19) (4) The initial impedance of the capacitor is automatically calibrated when put into operation, wherein the calibration equation for the initial impedance is described as follows:

(20) $Z_{\mathrm{init\_}\left(P\right)}=\frac{{\stackrel{.}{U}}_{\mathrm{init\_}\left(P\right)}}{{\stackrel{.}{I}}_{\mathrm{init\_}\left(P\right)}}$ wherein, P refers to the three phases A, B, and C, Z.sub.init_(P) is the initial impedance of each phase of the capacitor when put into operation, {dot over (U)}.sub.init_(P) is a fundamental vector of initial voltage per phase of the capacitor when put into operation, .sub.init_(P) is a fundamental vector of initial current per phase of the capacitor when put into operation.

(21) The calibrated initial impedance of capacitor must meet the following requirements:

(22) ${\mathrm{.Math.}}_{\mathrm{inh\_}\left(P\right)}=\frac{.Math.Z_{\mathrm{init\_}\left(P\right)}-Z_{\mathrm{ideal}}.Math.}{.Math.Z_{\mathrm{ideal}}.Math.}100\%$${\mathrm{.Math.}}_{\mathrm{inh\_}\left(P\right)}<{\mathrm{.Math.}}_{\mathrm{set\_alm}\mathrm{\_inh}}$

(23) wherein, .sub.inh_(P) is a relative value of the modulus of inherent deviation of the initial actual impedance when put into operation, and .sub.set_alm_inh is a limit value of the relative value of the modulus of inherent deviation, i.e., the radius of the auto-calibration alarm impedance circle in FIG. 2.

(24) If the capacitor wiring works normally, and the sensor accuracy meets the requirements, the capacitor is automatically calibrated successfully.

(25) (6) Then put into operation, in normal operation, calculate the real-time impedance of each phase of the capacitor and the relative change of the real-time impedance. The calculation equation is as follows:

(26) $Z_{\mathrm{dyn\_}\left(P\right)}=\frac{{\stackrel{.}{U}}_{\mathrm{dyn\_}\left(P\right)}}{{\stackrel{.}{I}}_{\mathrm{dyn\_}\left(P\right)}}$${\mathrm{.Math.}}_{\mathrm{dyn\_}\left(P\right)}=\frac{.Math.Z_{\mathrm{dyn\_}\left(P\right)}-Z_{\mathrm{real\_}\left(P\right)}.Math.}{.Math.Z_{\mathrm{real\_}\left(P\right)}.Math.}100\%$

(27) wherein, Z.sub.dyn_(P) is a real-time impedance per phase of the capacitor, and Z.sub.real_(P) is an actual impedance per phase of the capacitor, {dot over (U)}.sub.dyn_(P) is a fundamental vector of the real-time terminal voltage per phase of the capacitor when put into operation, and .sub.dyn_(P) is a fundamental vector of the real-time current per phase of the capacitor when put into operation, .sub.dyn_(P) is a relative value of the modulus of the real-time impedance change per phase of the capacitor.

(28) (7) Determine whether the capacitor is faulty. When the real-time impedance of the capacitor meets the fault condition, if the delay time of capacitor is reached at this time, the capacitor is considered to be faulty and protect the trip. The protection condition is:
.sub.dyn_(P)<.sub.set_alm_dyn
max(|.sub.dyn_A.sub.dyn_B|,|.sub.dyn_B.sub.dyn_C|,|.sub.dyn_C.sub.dyn_A|).sub.set_ub_dyn

(29) wherein, .sub.set_alm_dyn is a limit value of the relative value of the modulus of the dynamic update impedance change, i.e., the radius of the auto-calibration alarm impedance circle in FIG. 2; .sub.set_ub_dyn is a limit value of the inconsistency relative value of the modulus of the change of the three-phase dynamic update.

(30) If the update condition is satisfied, the impedance change calculation result is considered as normal, and the actual impedance Z.sub.real is updated, otherwise the update is not updated and the update fails.

(31) Under the non-fault condition, i.e., normal operation, the dynamic change of the capacitor is small in a short time, and the dynamic update period T can be set according to the actual situation, namely:
T=t.sub.dyn_set

(32) The above embodiments are merely illustrative of the technical idea of the present invention, and the scope of protection of the present invention cannot be limited thereto, any technical changes made in accordance with the present invention or based on the technical solutions should fall within the scope of protection of the present invention.