LV13922B - Method for determination of distance to fault place by phase-to-earth fault in distribution networks - Google Patents

Abstract

The invention object relates to electrical distribution networks the neutrals of which are not directly earthed, i.e. to networks with isolated, through arc suppressing coils or through resistors earthed neutrals, in the concrete - to single phase-to-earth faults in medium voltage power lines. The aim of invention is to determine the distance to single phase-to-earth fault using measurements at the monitoring point of the line. For this purpose, the real and imaginary component of apparent impedance ¦a by classical formula for single phase-to-earth fault are used. As a result, direct sequence reactance X1 to fault place is obtained. To enable it, not only specific reactance X1sp of protected line must be known but also several other specific quantities of the line: Xosp - specific zero sequence reactance, Rcsp - specific resistance of phase conductor, Rgsp - specific ground resistance; llin - length of the protected line grid. The faulty phase voltage , current ?ph ground current ?g must be measured. To diminish the influence of resistance Rcsp instability, the ground current should not be less than sufficient fraction of maximum load current. To raise the accuracy, also temperature Tc of faulty phase conductor should be measured using which the resistance Rcsp can be determined more accurately. To raise the accuracy still more, capacitive current phase-earth ?clin of the faulty line network and specific capacitive currents of the faulty line - current phase-to-earth ?csp and phase-to-phase ?cssp must be taken into account; in the classical formula, the voltage should be used, instead of faulty phase voltage , which is the difference between and the voltage , the last being calculated by iteration procedure using faulty line capacitive currents. The distance to fault place is calculated using obtained reactance X1 and the specific one X1sp.

Description

METHOD FOR DETERMINING DISTANCE TO SINGLE-PHASE LOWERING IN DISTRIBUTION NETWORKS

Description of the Invention

The invention relates to electrical distribution networks, the neutrals of which are not directly grounded, i.e., networks with isolated, compensated or resistive earth. Such networks can work with single-phase earthing (ZS) for extended periods of time, but if one of the weakest points in the network isolation, the ZS time isolation breaks, the network will produce double-sided, high-current currents. Therefore, the first earth leakage that has occurred must be found and unlocked faster.

There are several analogues to the method of measuring the distance to a single-phase earth leakage point in distribution networks:

1.The use of fault finding indicators, such as the Linetroll 3500 type [1], placed on overhead line supports for the indication of the earth leakage current in overhead lines in any neutral mode, with isolated, compensated or resistive earth. The sensors for these indicators are the horizontal coil (responsive to the change in the horizontal component of the line magnetic field induction corresponding to line zero current) and the electric field sensor (responsive to the line's electric field intensity change corresponding to the line zero voltage). The indicator determines the angle between zero-current and voltage and is triggered accordingly if the earth fault is behind the indicator on the power side but does not trip when it is before the indicator. The disadvantage of this method is the large number of required indicators, which are usually mounted on every other support, and the inaccuracy of the method makes it possible to determine not the distance to the fault, but only the direction of the earthing in relation to the indicator;

2.Using a zero-current relay protection against a single-phase earth fault, such as that provided in the 7SJ62 digital kit [2] or the ARCZEM-3F type earth leakage alarm relay [3] developed by ARCUS ELECTRONICS, which is installed on each output medium voltage line. The relay trip indicates that the fault is on this line. The disadvantage of this method is the need for zero-current and voltage sensors for each relay, the high cost of digital relays, and even greater inaccuracy than the first analogue.

.Using the increased content of high earthing currents on the line, for example, by means of the Zond apparatus [4], which responds to the 11th harmonic, and the "Tungiloc" earthquake detector [5], which responds to the 5th. These devices give maximum indication on the defective line until failure. The main disadvantage of this method is the need for the operational team to make measurements manually on all lines, but on the damaged line, moving to ground. The analogues described do not allow the distance to the site of damage to be determined.

Such a possibility is provided by the classical distance protection method from single-phase short circuits [6 -8], which works according to the expression (1) where Ž _a - shows the total resistance to single-phase short circuit with earth; L /, - current of the damaged phase; l _g - ground current flowing through the earth from the fault location to the transformer neutral; K _N compensation factor which takes into account the difference between the zero-order resistance Zo and the direct-order resistance Zj up to the point of failure (or their specific value, the index 'sp'):

-7 & Kf - '

3Z (2) lsp

The distance l to the site of damage is calculated using the formula:

'= T' '0)

- \ sp where Xi _S p - line specific reactance impedance, X _a - apparent reactance Jjj = Im (Ž _a ). This method is thus inappropriate for determining the distance to single-phase earth circuits in distribution networks because the load current is high relative to the fault current, the phase voltage Ū _h is comparable to the drop in fault resistance and low relative to the line voltage. Under these conditions, the reactive impedance X _{a is} unacceptably different from the direct order impedance Z j to the fault site and the distance / according to formula (3) is not nearly as close to the required accuracy. This claim explanation will transform the expression (1) aligning the visible resistance 7 _a direct sequence impedance 7; to the point of failure, which can be done if the earth-fault is without fault resistance (metallic earth-fault):

ū _pb = ipp _h ⁺ W · (4)

If earth leakage occurs through a fault resistor Rf, then the voltage of the faulted phase will be: Ū _ph -7 _} {i _{ph +} K _{N g g} ) ₊ R _{f f f} , (5) where 7 / / and K boj fault resistance and fault current.

The impedance Ž _a (apparent impedance) calculated according to the classical method will be:

Žl G _P h +) + ^R fh _ _| Rf ¹ /

I ph + 1g I pli R-NIg I ph + g

It can be seen from (6) that the apparent resistance Ž _a was different from their direct sequence resistance Ž _} , so that the visible reactance X _a of the direct sequence also differed from the direct sequence resistance to the fault site Xl. This error is the greater the greater the fault resistance Rf. The situation is further worsened by the fact that the exact specific active resistance of the phase conductor at the time of R _csp failure is unknown, the capacitive current of the damaged line network is not taken into account, the voltage Ū _{ph in the} formula (1) power. If these drawbacks were overcome, the classic approach to distribution networks could be used.

The technique described on page 311 of the information source [6] in the form of an expression (11-38) is taken as a prototype of the invention.

Invention is to enable a classical algorithm apparent impedance using the distance to a single phase ground fault in the determination conditions when phase voltage W _ph is comparable to the voltage drop of the damage resistance and small in comparison with the line voltage phase runs precisely specific active resistance R _csp damage is not known . This is achieved by using the direct-order reactive resistance to the fault location Xj instead of the apparent resistance X _a in formula (3), which is determined by using the real resistances Ž _a real Ā _a = Re (Ž _a ) and the imaginary Χ _α = ΙΐΏ. component and a priori known line parameters: Xpl _sp ~ specific direct-order reactance, Xo _sp - specific zero-order reactance, R _csp - phase conductor specific active resistance, R _gsp - ground specific active resistance. To prevent the effect of the phase impedance variability, the neutral of the network is earthed so that the single-phase earth-fault current is not less than a sufficient portion (for example, half) of the peak load current. To determine the distance to the fault location, the temperature of the damaged phase conductor at the time of failure is measured and then the exact active resistivity of the damaged phase conductor is calculated to calculate the compensation factor K _N. For fault current is taken into the power ow _e, measured at the zero-sequence current transformers (such as the Ferranti transformers) or otherwise, the faulted line network i _c i _in the current amount. For further accuracy increase in (1) is used for voltage G _{ph ph} voltage G instead according to the relation W _p; W = _{ph ph} -Mj (7) and AU _p h are used to determine additional values a priori known - specific capacitance phase of current to ground Î _csp and the specific _phase-phase capacitance current _cssp - and Δί / γ- are determined by iterative calculation.

The invention is explained by a drawing. The distribution network consists of a transformer 1 with a grounded earth through a complex resistor 2 in a neutral manner, buses 3, intact lines 4 represented by a single line, a defective line network comprising a defective line 5 with outgoing lines 6 at its terminating point. which implements the method, the switch 8 and the Ferranti current transformer 9 are located at the beginning of the line. Generally, single-phase earth leakage occurs through a fault resistance 10.

When one of the phases connects to the ground point F ⁽¹ \ of the land begins to flow a fault current ij. The current Ij of earth current I _g, the size Ferranti CT 9 and the faulted line capacitive current I _c an i _in. The current in L consisting of intact network 4 capacitive current oF _CSG and the current I _er through the grounding resistance 2, which may be inducible from the Petersen coil, also contain active components or pure active. dissipated faze-ground capacitive current I _c between the line end to the fault added to the diffuse capacitive current i _c an bf and form a faulted line network capacitive current i _c an n ". dissipated current i _c bf it occurs on the faulted line disparate capacities between fault location to the right and the attached line 6 distributed capacities. dissipated power Î _{c [in} the previously known. Defective phase current Î _p h is measured by the phase current transformer. Damaged the phase voltage inverter measures the phase voltage. _ph .

Thus, the specific direct and zero reactive resistances Xi _{sp and} X _Osp , the specific phase conductor active resistance R _CS p ⁰⁾ and the specific active earth resistance Rgsp are recorded in the device memory before the calculation begins. During the fault, the fault current current, ground current L, fault phase voltage Uph, and fault phase temperature Tc are measured. Safety device using resistance Rcsp ⁰⁾ and the measured temperature, calculate the real faulty phase Direct current resistance Rcsp ^(c) · The compensation coefficient K _N determination by the formula (2) are calculated values:

(8)

Further to the formula (1) is the visible impedance Z. and _a real-R _a and imaginary component X _a:

A _fl = Re (Ž _o ); V _o = Im (ŽJ.

(9)

Based on these values, the direct-order reactive resistance to the fault site Xg {f '+ f' _S 9 _f ) x _a - {ftg9 _f -nR _a f '(\ - returns <p _f ) + f''(tg) is calculated. <p _f + a)

The other values of formula (10) are calculated from a set of formulas:

(10)

Z, p Rcsp + jX \ sp '^ Osp X'Sp ^ Rgsp L j-JfjSp 5 η _ n (c), n. y _ \ sp ⁺ ^ Oip. ^ ssp ^Λ αρ T ^a gsp ' ^Λ ssp'

R ^(c) R csp, .S'OT

-; o - - ·

Isp

X.

\ sp cssp

Isp k = λx- U = Re (A); U '= Im (Z); k _dR J ^{csp + kRgsp} - k _dR '= ^ (k _dr y, * ph & ssp (3-k') X _{] sp} + kX _Osp

3X

^. '= Re (^); ^ = Im (^); (11) ssp

I j- <. "Ks if ^{= I} Fe ^{+ I} ciin * ^k f = y— ^k f = Re (k _f ); k _f = \ m (k _f ) ', tg <p _f = - * ph kyf - abk _dR ' -ack _dx '' + bk ^ '+ ck ^'; / = abk _dR λ-ack ^ '-bk _dR Xck _dx .

If more accurate results are required, the effect of dissipated capacitive currents in the interval to the point of failure must be considered. In order to comply with scattered capacitive current faze-ground ī _c and capacitive current faze faze _I-cs (symmetrical capacitive current), must use previously aware of the current value of the specific I _csp and I _CSSP respectively. The first iteration of the damaged line capacitance current ç _c to the fault site, symmetric capacitive current l _cs to the fault site, currents ri / is calculated. _c / and J / o _c yar zeroto the assumed distance l ⁽⁰⁾ to the point of fault, such as half the length of the line, to obtain the first iteration of the auxiliary _voltage to be calculated (Δύ _ρΙ , ^υ) :

u u) 3 i _c ^{(1) 2} = j J J ^m ; U ^I} - jicsspi ^m ; Δ /,

- - (- / ^v '+0 5 / ^σ) ) · Λ / ^V) = —— /' csp '' CS J -'- cssp * 'V Λ' c '' ^ Oc / '- * C' ž , ⁽⁷⁾ = l l ^{(n o (/)} = OsOs; „„ ^(/) = '} sp ^l »^ 0 ^ ^r jsp ^l 5 ph

Voltage Ū is also calculated. * first iteration:

¹ \ cf 1 '0e / 0 (12)

Ph ^ = ū _ph (B) and so on, Z _a is calculated; i _c r, _n ', 1 /; kg; ; k _dR -, k, f-, f ”·, tgq>j-; Xg lj. For the second iteration, we have to accept Z ^ = lj and so on. Practical calculations have shown that the iteration process moves quickly.

References:

1. Intelligent directional fault-current indicator LINETROLL 3500. User guide / Nortroll. 2000

2. SIPROTEC Numerical Protection Relays. SIEMENS / Catalog SIP. 2002.

3. ARCZEM-3F. Low-voltage alarm relay for 6 ... 35 kV power supply with isolated or compensated neutral. Technical description. ARCUS ELECTRONICS, Riga. 2000

4. Riga experimental plant “Energy automation”. Ustroistvo ZOND, Riga. 1980.

5. Earth leakage detector “TUNGILOC”, Seba dynatronic. 1998

6. ΚερΗοβροΒΟΒ H.B. PeeieīiHaa saipuTa. M., "OHeprua," §11-9, c. 311-1971.

7. d> a6pm <aHT B.JI. / ji-icTaHUHOHHaa 3amHTa. M., "Bticmaa niKOJia," §3-1, c. 68. 1978.

8. Protective relays. Application guide. GEC ALSTOM T&D, Printed London & Peterborough, §11.22, p. 198. 1995.

Claims (4)

1. Distance Measurement Method to Single-Phase Grounding in Distribution Networks Using Classical Distance Protection Formula to Determine ^Apparent Full Resistance Ž _a to Ground Damage, where the damaged phase voltages Ū _ph and currents _p h and ground currents _g are measured during the fault with a zero-current current transducer or otherwise, and the compensation coefficient K _N is calculated from the a priori known transmission line parameters the specific zero-order resistances Zho _sp and the specific direct-order resistances Ž] _Sp - according to Ž -Ž r> ^ Osp ^ \ sp and based on these, the distance 1 to the fault site is calculated according to the expression ^ _SP 'where X _a and Xi _sp - the apparent reactance of the direct sequence to the fault site and the specific direct sequence resistance of this line, characterized in that in order to accurately determine the distance to the fault MV line, direct-sequence reactance Xi up to a fault, which is substituted X _a is used in the apparent resistance Ž _a real R _a = Re (ZA _a) component and imaginary X _a = Im (Ž _a ) component and a priori known line parameters: X] _Sp - specific direct-order reactance, Xo _sp - specific zero-order reactive resistance, Rc _Sp - specific _{conductance of the} phase conductor, R _gsp - ground specific active resistance. Method according to claim 1, characterized in that, in order to reduce the variation of the specific active resistance of the damaged phase conductor to a lesser effect on the accuracy of the target function, the network neutrality is grounded through a resistive earthing current of not less than a sufficient part of the . Method according to claim 1, characterized in that, in order to increase the accuracy of the target function, the temperature of the damaged phase conductor during the fault is measured and based on that, the corrected specific active resistance Rc _Sp of the phase conductor is calculated, when calculating the compensation coefficient K _N. 4. The method of claim 1 .pretenziju, characterized in that to increase the accuracy of the objective function must take account of the faulted line network capacitive phase of current to ground l _{c n} ii 5. The method according to claim 1, characterized in that that in order to increase the accuracy of the target function, voltage is used instead of the voltage Ū _{ph to} calculate the apparent full impedance Ž _a . · # U _ph according to the relation _P u, W = -m _{ph) ph} and AUph are used to determine a priori known additional specific capacitive current fazezeme i _csp, specific capacitive phase of current-phase I _CS of _P; The value of Δί / χ is determined by an iterative calculation.