DE3402126A1 - Device for the protection of multiphase electrical machines - Google Patents

Abstract

This device is provided for the protection of multiphase electrical machines having winding phases (LR, LY, LB) in a star circuit against fault currents. It has a first relay (R1) which responds to a fault of one of the winding phases in the region of the faulty winding phase (for example LR) remote from the star point, and a second relay (R3) which responds to a fault of one of the winding phases in the region of the faulty winding phase (LR) close to the star point. In the event of a fault, this arrangement is intended to detect, in a simple manner, both the winding phase (for example LR) having an earth short and the location of this earth short in this winding phase. This is achieved in that each phase (for example R) has allocated to it a first differential current transformer (for example WR) and each combination of two of the phases (for example R,Y) has allocated to it a second differential current transformer (for example WRY). In this case, the primary windings of the second differential current transformers (for example WRY) are formed by fault current measurement circuits (for example ZR, ZY) which are arranged in the opposite sense and in which the secondary windings of the first differential current transformers (for example WR, WY) of the associated phases (for example R,Y) are connected. <IMAGE>

Description

138/83

11/30/83
K a / eh

- JL -

Device for the protection of multiphase
electrical machines

The invention is based on a device for protecting multiphase electrical machines
the preamble of claim 1.

With this generic term, the invention takes on one
State of the art of devices for the protection of multi-phase electrical machines, as described in the article "Performance of third harmonic ground fault protection
schemes for generator stator windings "by RL Schlake
et al. in IEEE Transactions on Power Apparatus and Systems, Vol. PAS-IOO, No. July 1981, p. 3195 ff

is. With this device, the star point of the winding phases of a generator to be monitored for earth faults is on the primary side of an earthing transformer
connected. A burden is provided on the secondary side of the earthing transformer, to which two relays are each connected in parallel. One of the two relays is at the base frequency of the generator voltage
coordinated and is used to detect earth faults

in the area of the winding strands remote from the star point, whereas the other of the two relays to the third The harmonic of the generator voltage is matched and to Detection of earth faults in the area of the winding phases close to the star point is used. The value of the third harmonic however, the generator voltage is both by design of the generator as well as its operating status, i.e. its reactive and / or active power. In the case of large real powers, the value of the third The harmonic of the generator voltage is a multiple of that which occurs with a comparatively low active power Worth of this tension. There is therefore a difficulty in referring to "the third harmonic of the generator voltage Matched relays for detecting earth faults in the area of the winding phases close to the star point to adapt to the generator to be protected, that depends on the operating state of the generator significantly changing value of the third harmonic of the Generator voltage has no influence on the response of this relay and false tripping is certain be avoided.

The invention as characterized in the claims solves the problem of a device of the generic type Type to indicate which in a simple way both the winding phase affected by an earth fault determined as well as the location of this earth fault in this winding phase selected.

The task is performed in conjunction with the features of the Generic term according to the characterizing part of Patent-30, claim 1 solved. The invention is characterized by this from that the fault location of an earth fault in the winding of a polyphase electrical machine both with regard to the position of the faulty winding phase as well as with regard to the position of the fault location

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is possible on this winding phase. In addition, the inventive device even when a ground fault occurs in the neutral point a high responsiveness irrespective of the operating condition (load current) of the polyphase electric machine and in ^K ffers. There is also a need for the ability to effectively protect a multi-phase electrical machine from both short-circuit and earth-fault currents.

From the journal article "The Generator Earth Fault Protection" by H. Stalder in Brown Boveri Mitt., Dec. 1944,

P. 392 is a protective device for a three-phase generator known, in which the position of the winding phase, in which an earth fault occurs, by means of a three-pole wattmetric relay is detected. The localization the fault location within the faulty winding phase causing this ground fault is with this Protective device, however, not possible.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing.

The single figure shows a basic circuit diagram a residual current protective device according to the invention.

The residual current protective device shown in the figure has three identical differential current transformers W _R , Wq and W _T with toroidal cores, which each have one of three star-connected winding phases in opposite directions from the supply lines acting as primary windings

L _D , L_ and L _{x of} an electrical machine penetrated K b I

are. This machine can be, for example, an electric motor that can be connected to a three-phase network with phases R, S, T ^{via a switch S 1, but also a transformer or a generator.} The secondary windings of the differential _{current transformers W n} , W_ and W _T are each in

K b I

a fault current measuring circuit Z _n , Z _c and Z _T arranged.

K b I

Each of these measuring circuits penetrates one toroidal core of one of three identical inductive current transformers M _R , M_ and M _T as well as two toroidal cores of three identical further differential current transformers

W _RS , W _R , and Wp .. Here, the fault current measuring circuits Z _R , Z- and Ij are guided in such a way that two measuring circuits each use the ring core of one of the differential _{current transformers W DC} , W _DT

Kb class

and W_ _T - as indicated by arrows in the figure penetrate in opposite directions. The opposite of any currents flowing in the fault current measuring circuits is generated by staring _{the secondary windings of the differential current transformers W D} , W_ and W _T

K b i

are. The toroidal cores of the residual current transformers W _DC , W _DT

Kb Kl and W_ _T are successively traversed in opposite directions by the measuring circuit pairs I ₀ -Z-, Z _D -Z _T and Z _C -Z _T. KbKIbI

The secondary windings of the current transformers M _R , M ,, and M _T are connected one after the other to excitation organs (not shown) of identical differential relays D _R , 0 _ς and D _T , whereas the secondary windings of the differential _{current transformers W DC} , W _DT and W_ _{T are connected one after the other} with

Kb Kl bI

identical facilities E _D _, E _OT and E _CT for protection

Kb Kl bI

connected by earth faults. These devices E _R _, E _R , and Ε-., Each have low-F, and high-pass filters F, and relays R, and R on. The connections of the secondary windings of the residual current transformer W _DC ,

K b

W _DT and W _CT are each on the one hand via one of the low Kl b I

pass filter F, to one of the relays R, and on the other hand via one of the high pass filters F .. to one of the relays R-z connected.

This residual current protective device now works as follows:

In the error-free state, the difference in disappears

to each of the three winding strands L _R , 1_ _ς and l_ _T flow-

138/83

the and the current flowing back from this winding phase, so that the magnetic fields of these currents in each of the three differential current transformers W _D , W _c and W _x

K b I

cancel and the _{residual current transformers W D} , W- and W _x

K b I are not excited. The natural earth currents flowing through the natural earth capacities of the respective winding phases, however, flow through the differential current transformers W _n , W_ and W _T and cause K b I in theirs

Secondary windings currents, which via the fault current measuring circuits Z _n , Z_ and Z _x the measuring transformers M _n , M _c and

KbI Kb

M ₁ . as well as the _{residual current transformers W nc} , W nx and W ,. _x i KbKIbI

Flood through on the primary side. Since the winding _{phases L R} , L_ and L _{x have} approximately the same natural earth capacities

O I

the natural earth currents of the windings are also the same. Due to the suitable routing of the residual current measuring circuits Z _R , Z and Z- flooding two earth current proportional currents and, if the winding of the machine is free from damage, currents of the same size for each of _{the residual current transformers W-_, W RT} and W, - ,. in opposite directions, so that their magnetic effects cancel each other out and the differential current transformers

W _n -, W _nT and W- _T with a damage-free machine no Se- Kb Kl bI

generate secondary electricity.

However, at least one of the differential _{current transformers W R} , W- and W _x responds if in at least one of the windings L _D , L _c and L ₁ . a fault current is flowing. Such a K b I

Residual current can be caused by a short circuit, for example. If the short circuit exists - as shown in the figure - between the winding phases L- and L _T , the uncompensated short-circuit current flowing through the differential current transformers W- and w causes currents in its secondary windings, which flow in the fault current measuring circuits Z_ and Z _x and signals cause which are above 0.1 or 0.2 times the rated current of the machine to be protected, for example.

^ 5 the threshold value tripping of the differential relay

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De and D_ cause. The differential relays D _q and D _T emit trigger signals A and A, as well as locking signals V and V _T. The trigger signals A ~ and A, cause the opening of the switch S ¹ and thus the interruption of the power supply to the electrical machine. In contrast, the locking signals cause V_ and V-. a blocking of the earth fault protection devices E _{R (;} , E _RT and Ε _ςτ .

If one of the winding phases L _R , L ₁ . and I_ _{T show} an insulation fault, the earth current flowing in the case of a damage-free winding phase as a result of the natural earth capacitance of the winding phase increases considerably, depending on the location of the insulation fault. Since this earth current flows uncondensed through the residual current transformer monitoring the defective winding phase, this residual current transformer responds. If this is, for example, the differential _{current transformer W R} , which is currently detecting a ground fault in the phase winding L _R shown in the figure, then a secondary voltage occurs in the fault current measuring circuit Z _D

current, which the transducer M _n and the differential

current transformer W _RT and W _{R <} ~ flooded. Since a fault current based on a ground fault is orders of magnitude smaller than a fault current based on a short circuit, the differential _{relay D D} remains passive and can use the ground fault protective devices E _DC , E _DT and E _CT

Kj Kl ο I no longer by emitting a locking signal

Block V _n . The Sekun-K caused by the earth current

the residual current transformers W _DC and W _DT

Kb class

the filters F, and F, the earth fault protection devices E _oc and E _DT fed. Is the point of failure

Kb class

at a relatively large distance from the star point of the winding phases L _D , L_ and L _1. , so there is

K b I

the influence of the fundamental wave voltage of phases R, S and T before and the secondary currents are passed through the low-pass filter F. step through and the relay R, energize. Because now. the

138/83

If the relays R located in the two earth fault protective devices E _R _ and E _RT are excited, it is indicated that the fault is located in the winding phase L _R at a relatively large distance from the star point. If, on the other hand, the fault is in the area of the phase winding L _R near the star point or in the star point itself, the fault current is essentially driven by the third harmonic present in phases R, S and T and the secondary currents now occur through the frequency of the third harmonic Matched high-pass filter F_ of the earth fault protection devices E _oc and E _OT and excite the relay R. Since the E _DC . and E _DT located relay R, are excited, it is indicated that the fault in the winding phase L _D im

Area of the star point or in the star point itself.

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Claims (4)

Claims Device for the protection of multiphase electrical machines with winding phases (L _n , L_, L _T ^N in star connection against fault currents with a first relay (R,), which responds to a fault in one of the winding phases in the area of the faulty winding phase remote from the star point (e.g. 1_ _R ), and with a second relay (e.g. R,), which responds to a fault in one of the winding phases in the area of the faulty winding phase close to the star point (e.g. | _ _R ) responds, characterized in that each phase (e.g. R) is assigned a first differential current transformer (e.g. Wp) which is independent of the remaining phases (e.g. S, T) and whose primary winding is separated from the power connections of the phase connected to this phase (e.g. R) connected winding phase (eg L _n ) is formed, and its secondary winding in a fault current measuring circuit (e.g. Z _D ) is connected, and that every combination κ of every two of the phases (e.g. R, S) a second differential _{current transformer (e.g. W RC} -), independent of the remaining phases (e.g. T), with a primary winding is assigned, which is controlled by the fault current measuring circuits arranged in opposite directions (e.g. Z _n , Z _c ) of the assigned phases (e.g. R, S) K b is formed. 2. Device according to claim 1, characterized in that the fault current star are switched that the residual current measuring circuits (Z _R , Z ₅ , Z ,.) as 3. Device according to one of claims 1 or 2, characterized in that the secondary windings of the second differential current transformer (eg W _o _) each to the input Kb an earth fault protection device (e.g. E _RS ) are, and that parallel to the input of the earth fault protection device (eg E _RC .) in each case a series circuit of a low-pass filter (F,) with the first relay (R.) and a high-pass fi
Relay (R,) is arranged. (R.) and a high-pass filter (F-,) with the second 4. Device according to one of claims 1 to 3, characterized in that each fault current measuring circuit (eg Z _D ) has the primary winding of an inductive κ Measuring transducer (eg M _R ) forms the secondary winding of which activates a _{differential relay (eg D D} ) provided for short-circuit protection above a predetermined threshold value of the measured fault current.