CC BY
84
Section 11. Electrical engineering
Kutin Vasyl Mykhaylovych, Vinnytsia National Technical University, PhD, professor, Department of electromechanical systems of automation in industry and transport Shpachuk Oleksandr Oleksandrovych, Vinnytsia National Technical University, postgraduate student, Department of electromechanical systems of automation in industry and transport E-mail: shpachuk2@gmail.com
Protection against single phase ground fault of the stator winding synchronous generator
Abstract: The article presents a protection from single phase earth fault of the stator winding synchronous generator that works in the block with a transformer, whose work is based on the calculation of the current at the place of a single-phase ground fault, by using the combined principle of the imposition of direct current in the circuit that contain insulation windings stator to determine the active resistance of the stator winding insulation to earth, the energy level previously charged capacitor for determining the transition resistance at the site of ground fault, control of voltage of zero-sequence, and consideration of capacitance of stator winding insulation to earth. Keywords: synchronous generator, single-phase ground fault, relay protection.
Introduction. Currently, for the performance de- cause [1]. Protection does not react to symmetrical reduction of active resistance of insulation.
To realize the protection based on a second concept you need to create an artificial circle with an external source grounded, which includes a generator stator winding [2].
The main disadvantage of this protection is the presence of galvanic connection protective device circuits with primary circuits of generator. Because of this lack is difficult to guarantee the safety of service personnel in the event of breakage circuit of imposition on the part of the grounding and the emergence of high potential on protection device and significant exposure operation time [3].
The purpose and objectives of the study. Research purpose is to improve the speed and sensitivity of the protection device from single phase ground fault of the stator winding synchronous generator that works in the block with a transformer, by indirect definition of the current of single-phase ground fault. The object of the study is to develop a concept of protection device that implements the method of protection, based on the calculation of the current in the place of a single-phase ground fault, by using the combined principle of the im-
vices of relay protection from single-phase earth fault of the stator winding synchronous generator, which operates in the block with a transformer, using two basic concepts: the first is based on the use of first harmonic zero-sequence voltage and third harmonic voltage that arising during single phase ground fault; second — on use imposed of direct or alternating current to circuit that contain insulation resistance to ground. On these concepts based advanced protection devices companies such as Siemens (SPPA-T2000, SPPA-T3000, SPPA-D3000, SPPA-M3000), ABB (SPAG 332S, SPAG 333S, REM 543, REM 545), General Electric (G60 with modules GPM-S, G30), BpecAep (BpecAep mr 2114). Protection that are based on the above concepts are not deprived of fundamental flaws that lead to false positives of protection devices.
Protection devices that are based on the use of first concept have a significant minus — the zone of insensi-tivity near the neutral of the generator. Also protection provides time delay (time delay is usually set 1-1,5 seconds) for detuning device from from external short circuit to ground in networks with grounded neutral and appearance of ferroresonance voltage increases that they
position of direct current in the circuit that contains the insulation of the stator winding to determine the active insulation resistance of the stator winding relative to the ground, the energy level previously charged capacitor for determining the transition resistance at the site of ground fault, control of zero-sequence voltage and consideration the capacitance of stator winding insulation.
Materials and methods. Protection device based on the combined principle of imposition of direct current on the circuit that contain insulation of stator winding. Current, which is superimposed on circuit that contain the stator winding insulation resistance is inversely proportional to the stator winding insulation resistance to earth, and the maximum value of the discharge current pre-charged capacitor, at the time of single-phase ground fault is inversely proportional to the transition resistance in place of ground fault. Direct current is applied through the zero point of the high voltage winding of transformer voltage. By controlling the above two currents we get to control the insulation resistance of the stator winding of the generator to earth and transition resistance at the site of ground fault. Control of zero sequence voltage is carried out by voltage transformer that contain the winding with circuit connection "open delta".
Results. To fulfill the problem posed in the article proposed principal scheme of protection device against single phase ground fault of the stator winding synchronous generator that works in the block with a transformer. The scheme realizes the method of protection, based on a calculation of the current of single-phase ground fault and performs parallel processing of signals controlled parameters (fig.1).
Let us consider operation of the device with parallel processing of signals controlled parameters. Source of a direct current imposed to the winding of the stator consists of a step-down transformer T2, diode bridge VD9-VD12 and capacitor C3. After straightening voltage and charging capacitor C4 constant current through limiting resistors R1 and R3 and shunts R2 and R4 fed to the neutral point of the high voltage winding of voltage transformer type HTMH and from there to the stator winding of synchronous generator.
To power the output circuits in a device offers separate power supply consisting of a transformer T4, a diode bridge VD1-VD4 and capacitor for reducing pulsation C1. Rectified voltage is applied to the input voltage stabilizer U10 through the diode VD13. This circuit also includes capacitors C6-C8 that used in typical circuit connection of voltage stabilizer. Output circuits also includes a resistor R13, which forms the output current and the
transistor VD16 that serves as an electronic key.
Information processing unit receives power from the step-down transformer T3 through the diode bridge VD5-VD8, capacitor C2 and voltage stabilizer U11. Typical connection diagram U11 includes diode VD 14 and capacitors C9-C11. The typical scheme of the accession of the central and peripheral microcontroller (MC) containing capacitors included between power terminals and grounding terminals of MC. For the central MC (CMC) U1 — capacitors C12 and C13; for U2 — C14 and C15; for U3 — C16 and C17; for U4 — C18 and C19.
U1 realizes the a logical part operation of the protection device, controls peripheral MC (PMC) U2-U4 and output circles of device. MC begins fulfill their programs after powering. CMC establishes communication with the PMC and after the time delay that required for charging the capacitor C4, starts the procedure of primary measurement. To this goal signal of the beginning of the conversion send to PMC. Communication between CMC and PMC realized through a standard serial data interface. The external clock generator U12 receives power from U11 and is used for synchronization of the central and peripheral MC. PMC U2-U4 manage external analog-digital converter (ADC) U5-U7 and perform the primary processing of information. Typical circuit connection ADC composed of two resistors and a capacitor, for U5 — R20, R21 and C20; for U6 — R18, R19 and C21; U7 — R16, R17 and C22. PMC feed signals to the relevant ADC for start of conversion. Then PMC begin to question the definition inputs for the purpose supply the signals of completing the conversion from the ADC. Upon receipt of the signal happens read information from the ADC and its primary processing in the PMC, that convert digital signals into values controlled parameters. Communication between PMC and the respective AD C is designed so that each category of data using a separate channel. ADC U5 converts the signal voltage of zero sequence. The signal comes from the secondary winding "open delta"of voltage transformer type HTMH through R-C filter (filter includes capacitors C22 and resistor R22) and intermediate transformer T1. After converting the signal digitally transferred to PMC U2 for further processing according to the ratio
U0 = UskT, (1)
U0 — voltage of zero sequence; US — signal of voltage of zero sequence coming from T1 to U4; kj, — resulting coefficient of transformation, taking into account the coefficient of transformation of the voltage transformer and intermediate transformer [4].
C20-T 2 3 4 5
R21 R20 _7 8 9 10 11 _12. 13
Vdd Status
DB11(MSB)
CS DB10 DB9
R/C ADS574 DB8 CE DB7
NC* U5 DB6
2,5 V Ref Out Analog Commo DB5 n DB4
2.5 Ref In DB3
Vee DB2
Bipolar Offset DB1
10V Range DBO(LSB) tal Common
20V Range Dig
R22
to winding terminals "open delta" of = voltage transformer type HTMH
t
02^ 2 3 4 5
R19 R18 _7 8 9 10 11 _12 13
CE NC*
2,5 V Ref
C3?T 2 3 4 5
R17 R6 _7 8 9 10 11 _12 13
Ü
CE NC* 2,5V Re
ADS574
U7
FV3^ FV2=r°
to the neutral point of the high voltage winding of voltage transformer type HTMH
I
VD18
1(XCK)FB0 PA0;ADC0)40 2(T1)PB 1 PA 1(ADC1)39 3(INT2/AIN0)FB2 PA2;ADC2)38
5(SS)PB4 PA4(ADC4)36 6(MOSI)PB5 PA5(ADC5)35 7(MISO)PB6 PA6(ADC6)34 8(SCK)FB7 PA7(ADC7)33 9RESET AREF 32 10 VCC GND 31 11 GND ATmega16 AVCC 30 12 XTAL2 U2 PC7(TOSC2)29 13 XTAL1 PC6(TOSC1)28 14(RXD)FD0 PC5(TDI)27 15(TXD)PD1 PC4(TDO)26 16(INT0)PD2 PC3(TMS)25 17(INT1)PD3 PC2(TCK)24 18(OC1B)FD4 PC1(SDA)23 19(OC1A)FD5 FC0(SCL)22 20(ICF 1)FD6 FD7(OC2)21
28 27 26 25 24
C15 " ~zrz— I:
23
21
19 111111
17
15
□
1(XCK)FB FA0(ADC0)40
2(T1)FB 1 FA1(ADC1)39
3(INT2/AIN0)FB2 FA2(ADC2)38
4(OC0/AIN0)FB3 FA3(ADC3)37
5(SS)FB4 FA4(ADC4)36
6(MOSI)FB5 FA5(ADC5)35
7(MISO)FB6 FA6(ADC6)34
8(SCK)FB7 FA7(ADC7)33
9RESET AREF 32
10 VCC GND 31
11 GND ATmega 6 AVCC 30
12 XTAL2 U3 FC7(TOSC2)29
13 XTAL1 FC6(TOSC1)28
14(RXD)FD0 FC5(TDI)27
15(TXD)FD1 FC4(TDO)26
16(INT0)FD2 FC3(TMS)25
17(INT1)FD3 FC2(TCK)24
18(OC1B)FD4 FC1(SDA)23
19(OC1A)FD5 FC0(SCL)22
20(ICF1)FD6 FD7(OC2)21
signal for disconnection the generator from the network
1(XCK)FB 0 FA0(ADC0)40
2(T1)FB1 FA1(ADC1)39
3(INT2/AIN0)FB2 FA2(ADC2)38
4(OC0/AIN0)FB3 FA3(ADC3)37
5(SS)FB4 FA4(ADC4)36
6(MOSI)FB5 FA5(ADC5)35
7(MISO)FB6 FA6(ADC6)34
8(SCK)FB7 FA7(ADC7)33
9RESET AREF 32
10 VCC GND 31
11 GND ATmega 16 AVCC 30
12 XTAL2 U1 FC7(TOSC2)29
13 XTAL1 FC6(TOSC1)28
14(RXD)FD0 FC5(TDI)27
15(TXD)FD1 FC4(TDO)26
16(INT0)FD2 FC3(TMS)25
17(INT1)FD3 FC2(TCK)24
18(OC1B)FD4 FC1(SDA)23
19(OC1A)FD5 FC0(SCL)22
20(ICF1)FD6 FD7(OC2)21
signal to the service personnel of reducing UR13 of isolation
1(XCK)FB FA0(ADC0)40
2(T1)FB1 FA1(ADC1)39
3(INT2/AIN0)FB2 FA2(ADC2)38
4(OC0/AIN0)FB3 FA3(ADC3)37
5(SS)FB4 FA4(ADC4)36
6(MOSI)FB5 FA5(ADC5)35
7(MISO)FB6 FA6(ADC6)34
8(SCK)FB7 FA7(ADC7)33
9RESET AREF 32
10 VCC GND 31
11 GND ATmega 6 AVCC 30
12 XTAL2 U4 FC7(TOSC2)29
13 XTAL1 FCÉ(TOSC1)28
14(RXD)FD0 FC5(TDI)27
15(TXD)FD1 FC4(TDO)26
16(INT0)FD2 FC3(TMS)25
17(INT1)FD3 FC2(TCK)24
18(OC1B)FD4 FC1(SDA)23
19(OC1A)FD5 FC0(SCL)22
20(ICF1)FD6 FD7(OC2)21
j-v-Y-Y"j T2 |"Y"Y"V"| T4
power supply of device from the network of own needs of power station
Vdd
2.5 Ref
Vdd
2.5 Ref
Fig.1. Principle scheme of protection device from single-phase earth fault of the stator winding synchronous generator that works in the block with a transformer
The signal of current that applied to the stator winding is measured by using a shunt R2 and an operational amplifier (OA) U8. Typical elements connection OA U8 includes resistors R7-R9. After amplification signal of current comes to ADC U7 where it is converted into digital form and transfer for further processing in MC U4 on ratio
(2)
rz(li ) - ~t ~ ri - r3 - rt >
1
I1 — signal of direct current that coming from the OA U8 to U2; R^ R3 — resistance of the resistors R1 and
R3; RT — resistance of high voltage winding of voltage transformer [5].
Similarly happens the transformation of maximum value of the current of discharge capacitor C4 by using OA U9, ADC U6 and PMC U4 by ratio
5 + fl 2
Rp (2 ) =
(3)
1 + gI 2 + hi 2
I2 — direct current signal coming from OA U9 to the ADC U3 and MC U1; s, f, g, h — coefficients that specifies the parameters limiting resistors and active and in-
ductive reactance of the primary winding of the voltage transformer [5].
After completion of the intermediate transformations values of R, Rp and U0 transferred to CMC U1 by using serial interface data. Upon completion procedure ofprimary measurement starts the main loop of the program. The main loop of the program starts with a signal to for PMC to start conversion signals of controlled parameters. After receiving the values R^, Rp and U0 happens the fulfillment logical part of protection. In case of reduction of insulation resistance below the established level happens filing of a light signal to service personnel from U1 through R14 and light-emitting diode VD15. In another case, happen the determination of the existence of emergency regime and the calculation of the current single-phase ground fault according to the expression [5]:
l = 3 U0RP+UR+U0RpG)2ClR+U0vCX ; (4) V2 (C R + R + 2RpRz+ R)
R =
RaRbRc
RaRB + rbrc + RARC
(5)
Q= CA + CB + Cc ; (6)
CC — the capacity of the stator winding phases A, B and C, respectively; RA, Rg RC — insulation resistance of stator winding phases A, B and C, respectively R — total resistance of the stator winding insulation C£ — the total capacity of the stator winding insulation
Rp — transition resistance in the place of ground fault; U0 — maximum of zero sequence voltage.
In case the calculated value of current exceeds setpoint operation, occurs a signal from U1 through R15 to key VD16 to disconnect generator from the network and enabling automatic oppression of field. Otherwise CMC gives the command to PMC to start the conversion of new sample of signals.
Conclusions. The paper presents a principal scheme of protection device from single phase earth fault of the stator winding of synchronous generator that works in a block with a transformer. Principal scheme developed a new method of protection based on the use of the combination of the principle of the imposition of direct current in the circuit that contains the insulation of the stator winding to determine the insulation resistance of the stator winding to earth, use of the energy of discharge previously charged capacitor for determining the transition resistance at the site of ground fault, zero sequence voltage control and the consideration of capacitance of stator winding insulation to earth and calculation of the current of single-phase ground fault of the stator winding in emergency mode. In the proposed scheme signals of controlled parameters are processed simultaneously through the use of separate microcontroller for processing of each signal. This reduces the operation time of protection device.
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