FR2511204A1 - Phase difference protection for electric motor - compares series current converter phases to control motor disconnection block - Google Patents

Abstract

The protection is afforded by current converters connected in series and corresponding in number to the required degree of protection. The first and last current converter respectively have inputs and outputs coupled to opposite sides of the secondary windings of current transformers having primary windings formed by the current rails for the electric motor. The current converters are coupled to phase comparators controlling a motor disconnection block. The phase difference protection is designed to prevent false disconnection of the motor, while providing a continuous operating control.

Description

 The present invention relates to electrical engineering and more particularly to differential protection devices against short circuits between the phases of an electric motor.

 It can be successfully used to protect powerful electric motors against short circuits between phases.

 The permanent increase in the unit powers of electric motors requires a significant increase in the reliability of short-circuit protection devices, for example, differential protection devices against short-circuits between the phases of an electric motor. At the same time, there is a need to control these devices during operation.

 There is a differential short-circuit protection device between the phases of an electric motor (cf., for example, URUS author's certificate No. 599309, Cl. H02H, 7 (08) comprises current transformers, the primary of each being represented by a current conductor bar of the electric motor, a main current conversion block whose inputs are connected to terminals of the secondary of the current transformers, a main block for comparing the phases whose inputs are connected to the current conversion block, a power source electrically connected to the current conversion block and to the phase comparison block, as well as an electric motor stop block electrically connected to the block phase comparison and power source.

 However, this device has low reliability because breakdowns of the "breakdown" or "break" type, in any block, lead to device failure or faulty operation, which causes damage to the electric motor or its erroneous shutdown. and, therefore, the disruption of the technological process.

 Besides this, in order to locate the faults of the device, it must be switched off and this requires stopping the electric motor.

 The invention aims to provide a device for differential protection against short circuits between the phases of an electric motor, comprising auxiliary blocks which would make it possible to increase the reliability of the device and to carry out a permanent control of the operation of the latter.

 It therefore relates to a differential protection device against short circuits between the phases of an electric motor, which comprises current transformers, the primary of each of them being represented by a current conducting bar of the electric motor. , a main current conversion block whose inputs are connected to the terminals of the secondary transformers of the current transformers, a main phase comparison block whose inputs are connected to the current conversion block, an electrically connected power source the current conversion block and the phase comparison block and an electric motor stop block electrically connected to the phase comparison block and to the power source, said protection device being characterized in that it comprises: an even number of auxiliary current conversion blocks connected in series and connected to the power source, this number depending on the redundancy necessary of the device, the inputs of one of the auxiliary blocks being connected to the main current conversion block and the outputs of the latter being connected, respectively to the other terminal of the secondary of each current transformer, of the auxiliary comparison blocks phases whose number is a function of the number of auxiliary current conversion blocks, certain inputs of said comparison blocks being connected to the power source, other inputs being connected to the auxiliary current conversion blocks and their outputs being connected to the inputs of the electric motor stop block.

 It is useful that the differential protection device against short circuits between the phases of an electric motor further comprises blocks for counter operation of the device electrically connected to the power source, their number being equal to the total number. main and auxiliary current conversion blocks, the input of each of said blocks being connected to a corresponding phase comparison block, while the output of each of them is connected to the corresponding input of block d stopping the electric motor.

 It is also useful that the counter block for the operation of the device comprises a relay, a resistor and a signaling lamp connected in series.

 It is also advantageous for the relay of the control block for the operation of the device to have two windings, the first terminals of which are connected together and connected to the power source, two contacts placed in series, the connection point of which is connected to the resistance of the device operating control block, one of these contacts being connected to the other terminal of one of said windings, as well as two diodes whose anodes are connected to the other contact, the cathode of a diodes being connected to the other terminal of the service winding.

 If the differential protection device comprises two auxiliary current conversion blocks, it is advantageous to provide the electric motor stop block with three relays electrically connected together, with thyristors in a number equal to the number of relays, the anode of each being connected to a terminal of the respective relay, resistors in accordance with the number of relays, one terminal of each of which is connected to the co-electrode of the respective thyristor.

 I1 is also desirable that the electrical connection between the relays be made as the electrical connection between the contacts of all three relays.

 It is also preferable to connect the contact of the first relay to a contact of the second relay, a second contact of which is connected to a contact of the third relay, and to provide the electric motor stop block with an auxiliary diode, the anode is connected to the common point of the contacts of the first and second relays and whose cathode is connected to the common point of the contacts of the second and third relays.

 The invention makes it possible to preserve the operating capacity of the device in the event of damage to one of the blocks, which excludes the failure or false functioning of the device, that is to say increases the reliability of the device and ensures, a uninterrupted service of the electric motor.

 In addition to this, the invention provides continuous monitoring of the operation of the device and signaling of faults which makes it possible to eliminate them during operation. This also improves the reliability of the device and ensures uninterrupted operation of the electric motor.

Other characteristics of the invention will appear during the description which follows, made with reference to the appended drawings given solely by way of example and on which
- Fig. I represents the block diagram of a differential protection device against short circuits between the phases, according to the invention
- Fig. 2 shows the block diagram of a differential protection device against short circuits between the phases, in accordance with FIG. I, provided with blocks for controlling the operation of the device, according to the invention; ;
- Figs. 3 and 3 ′ together show the basic electrical diagram of the current conversion blocks and of the phase comparison blocks according to the invention
- Fig. 4 is the functional diagram of the control block for the operation of the device according to the invention
- Fig. 5 shows the electrical circuit diagram of a relay of the counter block for the operation of the device according to the invention
- Fig. 6 shows the block diagram of an electric motor stop block according to the invention
- Fig. 7 shows the electrical diagram of the connection principle of the relay of the stop block of the electric motor, according to the invention.

 As an example, we examine a differential protection device against short circuits between the phases of an electric motor, designed for the case where it is necessary to have two auxiliary current conversion blocks in order to obtain the necessary redundancy of the device.

 The differential short-circuit protection device between the phases of an electric motor includes current transformers 1, 2, 3, 4, 5, 6 (Fig.l), the primaries of which are in the form of bars current conductors 7 of the electric motor 8. On the first terminals of the secondary 9, 10, 11, 12, 13, 14 of the transformers 1, 2; 3, 4, 5, 6, respectively, are connected respectively to inputs 15, 16, 17, 18, 19, 20 of a main current conversion block 21, while on the other terminals of the secondary 9, 10, 11 , 12, 13, 14, are connected outputs 22, 23, 24, 25, 26, 27 of an auxiliary current conversion block 28. On block 21 is connected an auxiliary current conversion block 29 by its inputs 30, 31, 32, 33, 34, 35. On block 29 is connected block 28 by its inputs 36, 37, 38, 39, 40, 41. On blocks 21, 29, 28 are, respectively, connected entries 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, entries 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65 and inputs 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77 of the phase comparison blocks 78,79,80. On blocks 78, 79, 80, a stop block 81 of the electric motor is connected by its inputs 82, 83, 84, respectively. On the inputs 85, 86, 87, respectively, of the blocks 21, 29, 28, is connected the positive pole of a power source 88. On the inputs 89, 90, 91, respectively, of the blocks 78, 79, 80 is connected the negative blade of a source 88. Inputs 92, 93 of block 81 are respectively connected to the positive and negative blades of source 88. Block 81 is connected to an input 94 of a switch 95 connected to the bars 7 serving primary for transformers 4, 5, 6.

 According to another alternative embodiment, the differential protection device against short-circuits between the phases of the electric motor comprises control blocks of the operation 96, 97, 98 (Fig. 2) of the device. Inputs 99, 100, 101 of these blocks are respectively connected to blocks 78, 79, 80. Inputs 102, 103, 104, respectively, of blocks 96, 97, 98 are connected to the negative pole of source 88. The inputs 82, 83, 84 of block 81 are respectively connected to blocks 96, 97, 98.

 Each current conversion block 21, 29, 28 includes transformers 105, 106, 107, 108, 109, 110 (Fig. 3) with primaries 111, 112, 113, 114, 115, 116, respectively. Between the terminals of each secondary 117, 118, 119, 120, 121, 122 of the transformers 105, 106, 107, 108, 109, 110, on a connection point 123, are connected resistors 124 and 125, 126 and 127, 128 and 129, 130 and 131, 132 and 133, 134 and 135. Between resistors 124 and 127, 128 and 131, 132 and 135 are respectively connected resistors 136, 137, 138. Between resistors 125 and 126, 129 and 130, 133 and 134 are respectively connected to resistors 139, 140, 141. Each block 78, 79, 80 comprises diodes 142, 143, 144, 145, 146, 147 whose cathodes are joined at a point 148 , while on the anodes are connected first terminals respectively of resistors 149, 150, 151, 152, 153, 154 at respective connection points 155, 156, 157, 158, 159, 160. The other terminals of resistors 149 , 150, 151, 152, 153, 154 are joined at a common point 161. On the points 155, 156, 157, 158, 159, 160, the diode anodes 162 are respectively connected. and 163, 164 and 165, 166 and 167, 168 and 169, 170 and 171, 172 and 173.

 Each counter block 96, 97, 98 of the operation of the device comprises a relay 174 (Fig. 4) a resistor 175 and a signal lamp 176 connected in series.

 The relay 174 has windings 177 and 178 (Fig. 5), the first terminals of which are joined together and are connected to the negative blade of the source 88. On the other terminal of the winding 178 is connected a contact 179 connected in series with a contact 180 at a common point 181. On the other terminal of the winding 177 is connected the cathode of a diode 182 at a connection point 183. On the anode of the diode 182, at a connection point 184, the anode of a diode 185 and the contact 180 are connected.

 The block 81 for stopping the electric motor comprises, electrically connected to each other, at a connection point 186 (FIG. 6), relays 187, 188, 189 to which the anodes of thyristors 190, the cathodes of which are respectively connected are joined together at a common point 191 and are connected to the negative pole of the power source 88.

On the control electrode of each thyristor 190 is connected a resistor 192. At point 186 is connected a contact 193.

 Each relay 187, 188, 189 has> respectively, windings 194, 195, 196 (Fig. 7), the first terminals of which are joined at common point 186. The relay 187 comprises a contact 197, the relay 188 comprises contacts 198, 199 and the relay 189 includes a contact 200.

 The contacts 197 and 198 are joined at a common point 201. At the point 201 is connected the anode of a diode 202 whose cathode is connected to the contacts 199 and 200 at a common point 203.

 The differential short circuit protection device between the phases of the electric motor operates as follows.

 Current transformers 1, 2, 3, 4, 5, 6 (Fig. 1) supply signals to inputs 15, 16, 17, 18, 19, 20 of current conversion block 21. From the outputs of said blocks these signals arrive, respectively, on inputs 30, 31, 32, 33, 34, 35 of the current conversion block 29, and from this latter, on inputs 36, 37, 8, 39, 40, 41, of the current conversion block 28. The blocks 21, 29, 28 convert the signals and deliver them, respectively, to the comparison blocks of the phases 78, 79, 80 which process them. Power source 88 sends signals to inputs 85, 86, 87, 89, 90, 91 and 92, 93 of blocks 21, 29, 28, 78, 79, 80 and block 81 of stopping the electric motor, respectively .

 Each block 78, 79, 80 sends a signal to block 81 at the time of the appearance of a short circuit at 1 t inside the electric motor 8 or between its busbars 7, as well as in the event of faults of the "breakdown" type. or "breaks in the elements of blocks 21, 78, 29, 79, 28, 80, respectively. The opening signal of the switch 95 is sent from block 81 when two inputs, for example its inputs 82, 83, or well all three inputs 82, 83, 84, are attacked by signals.

 In order to control the operation of the device in the cases where short circuits and faults of the aforementioned type appear, the blocks 78, 79, 80 deliver signals, respectively, to the blocks 96, 97, 98 (Fig. 2) of control of the operation of the device which, in turn, provide signals to the inputs 82, 83, 84 of the block 81. Then, the device operates as described above.

 The blocks 96, 97, 98 deliver a light signal to the operators characterizing the state of the device.

 The operation of the current conversion blocks 21, 28, 29 and of the phase comparison blocks 78, 79, 80 is then examined on the example of a joint operation of the blocks 21 and 78.

 Under load conditions of the electric motor 8, as well as under no-load conditions, the secondary 9 and 12, 10 and 13, 11 and 14 respectively the transformers 1 and 4, 2 and 5, 3 and 6, send respectively by inputs 15 and 16, 17 and 18, 19 and 20 of block 21, in transformers 105 and 106, 107 and 108, 109 and 110 (Fig, 3), signals which are in phase in each half-period of the industrial frequency because the currents flowing through the bars 7 (Fig. 1,2) which are at the same time the primaries of transformers 1 and 4, 2 and 5, 3 and 6, are also in phase. of this current and at the arrival of the signals on the primaries 111, 112, 113, 114, 115, 116 (Fig. 3), respectively, of the transformers 105, 106, 107, 108, 109, 110, their secondary 117, 118, 119, 120, 121, 122 deliver on the inputs 42, 44, 46, 48, 50, 52 of block 78, negative signals.

Consequently, the diodes 170, 173, 166, 169, 162, 165 of block 78 become conductive and there is no signal at input 99 of block 96 because the current from source 88 passes through the resistors 149, 150 151, 152, 153, 154, the diodes 170, 173, 166, 169, 162, 165, the resistors 124, 126, 128, 130, 132, 134 and the connection point 123.

 In the event of faults in the device, for example, in the event of breakdown of any of the diodes 170, 172, 173, 171, 166, 168, 169, 167, 162, 164, 163, 165 of block 78, the latter delivers a signal to input 99 of block 96. This is due to the fact that, for example, damage to diodes 170 or 171, winding 117 connects to diode 146.

 During the breakdown of one of the diodes 142, 143, 144, 145, 146, 147, of block 78, the input 99 of block 96 is also attacked by a signal.

 In the event of failure due to a ttrupturet, of one of the resistors 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, for example, of the resistance 124, during of the positive alternation of the industrial frequency, when the diode 171 becomes conductive, a signal arrives, via the resistor 153 and the diode 146, in block 78 which returns it to 11 input 99 of block 96.

 When one of the secondaries 117, 118, 119, 120, 121, 122, for example of the winding 117, breaks, in starting mode of the electric motor 8 (FIG. 1,2), the block 78 delivers at input 99 of block 96 a signal because diode 170 (Fig. 3) becomes conductive simultaneously with diode 171 as a result of the arrival of the signal supplied by lten- rolling 118 through resistors 139, 125, 124 .

 The counter blocks of operation 96, 97, 98 (Fig. 1, 2) of the device operate in the following manner.

 When a positive signal arrives, for example, at input 99 of block 96, winding 177 (Fig. 4, 5) of relay 174 lets current flow, its contact 180 closes and at through the diode 185, the signal arrives in the block 81, while through the diode 182 the signal arrives at the winding 177 of the relay 174.

 When the negative signal arrives, the contact 179 closes and the signal arrives at the winding 177 of the relay 174.

 The blocks 97, 98 work in the same way.

 The block 81 (Fig. 1, 2) for stopping the electric motor operates as follows.

 When the signals appear at the inputs 82, 83, 84 of block 81, the thyristors 190 (Fig. 6) become conductive and a signal attacks the windings 194, 195, 196 (Fig. 7), respectively, of the relays 187, 188, 189.

 In relay 187, contact 197 is closed, in relay 188, contacts 198 and 199 are closed, and in relay 189, contact 200 is closed.

 In the case of a short circuit inside the electric motor 8 (Fig. 1, 2) or between its conductive bars 7, for example, bars 7 which form the primaries of the transformers 4 and 5, the currents in the bars 7 which form the primaries of transformers 1 and 4 are in phase opposition. This is why these signals attack the inputs 15 and 16, 30 and 31, 36 and 37, respectively, of the blocks 21, 29, 28 also in phase opposition and at the same time there is blocking of the diodes 170 and 171 or 172 and 173 (Fig. 3) of blocks 78, 79, 80. Consequently, through the resistors 153, the diode 146, the resistor 154 and the diode 147 the signals reach the inputs 99, 100 and 101, respectively, blocks 96, 97, 98. Next, the device operates as described.

 In other cases of short circuit between the phases, the signals arrive at the inputs 99, 100, 101, respectively, of the blocks 96, 97, 98 through the resistors 149 150, 151, 152 and the diodes 142, 143, 144, 145.

 The present invention allows the replacement of defective blocks of the device without stopping either the device itself or the electric motor.

 The present invention also makes it possible to reduce the requirements as regards the qualification of the personnel and to reduce the number of operators.

Claims (7)

 1 - Differential protection device against short-circuits between the phases of an electric motor which comprises current transformers, the primary of each of which is represented by a conductor bar of the electric motor, a main current conversion block (21 ) whose inputs (15 to 20) are connected to the first terminals of the secondary (9 to 14) of the current transformers, a main phase comparison block (78) whose inputs are connected to the current conversion block ( 21), a power source (88) electrically connected to the current conversion block (21) and to the phase comparison block (78) and an electric motor stop block (81) electrically connected to the comparison block phases (78) and at the power source (88), said protection device being characterized in that it comprises: an even number of auxiliary current conversion blocks (28, 29) placed in series and connected to the power source entation (88), this number depending on the redundancy necessary for the device, and the Itun inputs (29) of these auxiliary blocks being connected to the main current conversion block (21), the inputs of another auxiliary block of current conversion (28) being connected to the other terminals of the secondary (9 to 14) of the current transformers, auxiliary phase comparison blocks (79, 80) in a number equal to the number of auxiliary current conversion blocks (28, 29), certain inputs of the first being connected to the power source (88) of other inputs, being connected to the auxiliary current conversion blocks (28, 29) and their outputs being connected to the stop block (81) of the electric motor (8).  2 - Device according to claim 1, characterized in that it is provided with blocks (96, 97, 98) for controlling the operation of the device electrically connected to the power source (88) their number being equal to the total number of main (21) and auxiliary (28, 29) current conversion blocks, 11 input of each counter block (96, 97, 98) being connected to the respective block (78, 79, 80) of phase comparison and the output of each control block being connected to the respective input of the block (81) for stopping the electric motor (8).  3 - Device according to claim 2, characterized in that each block (96, 97, 98) for controlling the operation of the device comprises a relay (174) a resistor (175) and a signal lamp (176) connected in series.  4 - Device according to claim 3, characterized in that the relay 174 of each block for controlling the operation of the device comprises two windings (177, 178) whose first terminals are joined and connected to the power source (88), two contacts (179, 180) placed in series, the common point (181) of which is connected to the resistor (175) of the device operating control block, one of these contacts (179) being connected to another terminal of one of the windings (178) and two diodes (182, 185) whose anodes are connected to the other contact (180) while the cathode of one of the diodes (182) is connected to the other terminal from the other winding (177).  5 - Device according to any one of claims 1 to 4, characterized in that in the case where the differential protection device against short circuits between the phases of the electric motor comprises two auxiliary current conversion blocks the block (81) stopping the electric motor comprises three relays connected (187, 188, 189) electrically, thyristors (190) in a number equal to the number of relays, the anode of each thyristor being connected to the output of a corresponding relay, resistors (192) in number equal to the number of relays, one of the terminals of each resistor being connected to the control electrode of a corresponding thyristor (190).  6 - Device according to claim 5, characterized in that the electrical connection between the relays (187, 188, 189) is carried out using an electrical connection between the contacts of all three relays.  7 - Device according to claim 6, characterized in that the contact (197) of the first relay (187) is connected to a contact (198) of the second relay (188) including a second contact (199) is connected to a contact ( 200) of the third relay (189) and in that the block (81) for stopping the electric motor comprises (8) an auxiliary diode (202) whose anode is connected to the common point (201) of the contacts of the first and second relay and the cathode of which is connected to the common point (203) of the contacts of the second and third relays.