SU1029310A1 - Device for earth (frame) fault protection of synchronous generator in single point of excitation circuit - Google Patents

Abstract

DEVICE FOR PROTECTION OF THE SYNCHRONOUS GENERATOR FROM THE CIRCUIT TO THE EARTH (HOUSING) AT ONE POINT OF THE EXCITATION CHAIN, containing a rectifier, the input of which is connected to the first output of the intermediate transformer, comparator and the actuator, the body, as a matter of purpose, the aim of the organization, the aim of the organization, the aim of the organization, the purpose, the aim, the purpose, the aim, the aim of the aim, the aim is to get the right; eliminating the dependence of sensitivity on the point of closure and the magnitude of the excitation circuit voltage, it additionally contains the first and second resistors, a square pulse generator, a step voltage generator and, a key, a delay unit, a control unit, a data processing unit, a setting unit and a decipheror, while the negative output of the rectifier is connected through the first resistor with the positive output of the generator excitation winding, the positive output of the rectifier is connected to the first input of the comparator and through the second resistor to the ground, the second input of the comparator is connected to the output of the step voltage generator, the main input of which is connected to the output of the square pulse generator, to which the input of the control unit is also connected The first input of the processing unit, the second input of which is connected to the second output of the intermediate transformer, the input to the stop of the processing unit and the input of the delay unit are connected to the output of the comparator, the control input of the key is connected to the first output of the control unit, the second output of which is connected to the starting input the data processing unit, the third and fourth to the outputs of the control unit are connected respectively to the inputs of the “Setting the zero voltage generator of the step voltage generator and the interconnected inputs of the Installation to the zero of the data processing unit and the setting unit, the output of the data processing unit is connected to the first input of the setting unit, the second input of which is connected to the fifth output of the control unit, the starting input of the setting unit is connected to the output of the delay unit, and the output of the setting unit is connected to the input of the actuator, the input of the intermediate transformer is connected via a switch to the power source.

Description

The invention relates to electrical engineering, in particular, to relay protection of electrical equipment, and can be used to monitor the state of isolation of operational DC circuits and to protect synchronous generators from grounding of the excitation circuit. Devices are known for protecting {1 synchronous generators from ground fault (housing) at one point of the excitation circuit, based on applying an alternating current voltage to the protected circuit from an auxiliary source (1 to 4. The sensitivity of protection devices based on this method depends on from the voltage and frequency fluctuations of the auxiliary source and from the magnitude of the capacitance of the excitation circuit, while the sensitivity of the devices 3 and 4 is insufficient, since it is necessary to detun in the rectifying voltage of the excitation circuit. The sensitivity of the device described in 4 and 5 depends on the voltage fluctuations of the auxiliary source. They have a minimum setting of 5 kΩ, although a two-step protection may require a setting less than 5 kΩ (see operating circular E no. 12/76 Also known are protection devices for synchronous generators against grounding (housing) at one point of the excitation circuit, based on imposing a dc voltage on the protected circuit, in which the current is compared with the specified voltage. Ichin, the largest current value is judged on the transition insulation resistance, and when the current in the circuit exceeds a predetermined value, the protection device is triggered. A constant voltage applied to the protected circuit is obtained either by straightening the harmonic components of the voltage of the excitation circuit 6 or from an auxiliary source 7. The protection device of the synchronous generator containing the excitation source of the synchronous generator, the excitation winding, is the closest to the invention. synchronous generator, trans; isolation resistance - capacitance to ground of the excitation circuit, rectifier, the negative pole of which through a comparator made on the current relay, One to the positive terminal of the winding cart-excited and positive - to ground loops. The comparator lead is connected to the actuator, the intermediate transformer is connected to the mains, and its lead is connected to the rectifier 7. However, this protection device has a sensitivity dependence on the magnitude of the excitation voltage and on the location of the circuit. This is related to those who desire it. The sensitivity of protection, characterized by the value of the transition resistance Gd, to which it reacts, is determined by the expression UMCT Uvoz g - where UJ, C.T is the voltage of the auxiliary source; - voltage at the site of damage, determined by the excitation voltage; 1sr - current relay operating current; Gr is the resistance of the winding of the current relay. The first of the terms of the numerator (the voltage of the auxiliary source) practically varies slightly (± 10–15%). The second term (voltage at the fault site) is variable and varies from zero to the nominal field voltage and cannot be directly measured. For high-power generators, the nominal field voltage exceeds the voltage of the auxiliary source by a factor of times (for example, when the auxiliary voltage of the UHCT source is 100 V). Without taking into account the resistance of the winding of the current relay, we have .ci ilH "iSince the protection is triggered at the same current value, the first term is constant and the second term is variable and can exceed the constant value once more. Consequently, the magnitude of the transition resistance at which the protection operates may differ from the true one by seven times. When shorted to earth anywhere in the field of excitation of an unexcited generator, the protection has minimal sensitivity to transient resistances. Thus, a disadvantage of the known device is the dependence of the sensitivity of the protection on the location of the circuit and the magnitude of the excitation circuit of synchronous generators, and therefore a decrease in reliability work. The purpose of the invention is to increase the reliability of the protection by eliminating the dependence of sensitivity on the place of squeezing and the magnitude of the excitation circuit of synchronous generators. The goal is achieved due to the fact that a known device containing a rectifier, whose input is connected to the first output of the intermediate transformer, comparator and actuator, additionally includes the first and second resistors, a square pulse generator, a step voltage generator, a key, blocks delays and control, data processing, settings and descrambler,

the negative output of the rectifier through the first resistor is connected to the positive output of the generator excitation winding, the positive output of the rectifier is connected to the first input of the comparator and through the second resistor to the ground, the second input of the comparator is connected to the output of the step voltage generator, the main input of which is connected to the output of the square pulse generator, to which the input of the control unit and the first input of the processing unit are also connected, the second input of which is connected to the second output p transformer, the stop input of the data processing unit and the input of the delay unit are connected to the output of the comparator, the control input of the key is connected to the first output of the control unit, the second output of which is connected to the starting input of the data processing unit, the third and fourth outputs of the control unit are connected respectively to the inputs " Zero generator settings of the step voltage and the combined inputs. Zero unit settings of the data processing unit and the settings unit, output of the data processing unit, via a decoder connection n to a first input setting unit, the second input of which is connected to a fifth output of the control unit, the trigger input setting unit is connected to the output of the delay block, and an output setting unit connected to the input of the executive authority intermediate transformer input through the switch is connected to a power source.

FIG. 1 shows a block diagram of the device; in fig. 2 shows time diagrams of voltages at the outputs of the control unit.

The excitation source 1 is connected to the excitation winding 2 of the synchronous generator. The windings and the excitation source of the synchronous generator are relative to the earth (housing) transient insulation resistance 3 and the distributed capacitance presented in the block diagram by the adjacent capacitance 4. The negative output of the rectifier 5 is connected via the first resistor 6 to the positive output of the excitation winding of the synchronous generator 2 and source excitation 1, and the positive output connected to the first input of the comparator 7 and through the second resistor 8 - to ground. The input of the intermediate transformer 9 is connected via an electronic switch 10 to a power source. The output of the generator 11 of the step voltage is connected to the secondary input of the comparator 7. A comparison of the voltage falling on the second resistor 8 with the step voltage goes to the comparator. The output of the generator 12 rectangular pulses is connected to the inputs of the generator 11 of the step voltage, the control unit 13 and to the first input of the data processing unit 14. Generator, step voltage

serves to convert the rectangular and 5piles arriving at its input into a step voltage, with each input pulse corresponding to a well-defined output voltage level. The first output of the control unit 13 is connected to the control input of the electronic key 10, the second output of the unit 13 is connected to the starting input of the data processing unit 14, the third output is connected to the installation input, to the zero state of the generator 11 of the step voltage, the fourth output to the installation inputs to the zero state of the processing unit 14 and the unit

15 sets, the fifth output - with the second input of the setting unit 15. The output of the comparator 7 is connected to the stop input of the data processing unit 14 and through the delay block 16 - to the starting input of the setting unit 15. Block

The 16 delays count the pulses arriving at its input from the comparator and after the arrival of the second pulse with a small delay, send a signal to the starting one, the block of settings. The output of the data processing unit 14 through the decoder 17 is connected to the first input of the setting unit 15. In the setting block, a comparison is made of the value of the transient-insulation resistance with the setting of the protection device. The output of the block of settings is connected to the input of the executive body 18, which stores the pulse coming from the output of the block of settings. The second input of the data processing unit 14 is connected to the output of the intermediate transformer 9. The data processing unit converts the number of pulses into a binary code; divides the voltage supplied to the second input by the difference in currents 2 and Ij flowing at different times through a constant resistor 10, and from the result, subtracts the value corresponding to the total internal resistance of the block 5 and resistors 6 and 8.

The operation of the device is considered in the following two cases:

insulation resistance is greater than setpoint resistance;

insulation resistance is less than set point resistance;

Isolation resistance is greater than setpoint resistance.

The operation of the protection device is controlled by the control unit 13. Let at some moment of time the voltage at the third output of the control unit is equal to logical "1, and on the remaining outputs - logical" O (Fig. 2). The signal from the third output of the control unit enters the input to the zero state of the generator 11 of the step voltage, while the voltage at the generator output is zero until the end of the input signal. At the time when the signal at the third output of block 13 is equal to logical "O, the voltage of the generator 11 begins to increase stepwise and simultaneously the second output of the control unit of the voltage becomes equal to logical" 1, the data processing unit 14 records the number of pulses arriving at its first input from the square-wave generator 12. When the step voltage at the second input of the comparator 14 becomes equal to or greater than the voltage at its first input, a signal appears at its output, and in the data processing unit isyvaets number nmpulsov received on. its first input over the time interval between the occurrence of a logical voltage, “1 to the appearance of a signal at the comparator output. At the next point in time, when the voltages on the first and third outputs of block 13 are logical "1, and on the second, fourth and fifth outputs, logical" O, the voltage at the output of the generator 11 becomes equal to zero, the electronic switch 10 closes and The output of the rectifier 5 appears voltage. In this case, the duration of the voltage pulses at the third output of the block 13 is selected such that during this time the capacitance 4 of the excitation circuit is fully charged. When the voltage at the second output of the block 13 becomes equal to logical "1, and at the third output - logical" O, the voltage at the output of the generator 11 of the step voltage will become a step. then increase in proportion to the number of pulses that came to its input. In data processing unit 14, the number of pulses arriving at its input is recorded. When the voltages are equal at the first and second inputs of the comparator 7, a signal appears at its output, in the data processing unit the recording of the number of incoming pulses stops. In data processing unit 14, the difference in the number of pulses recorded in the first and second times is selected; the ratio of the values corresponding to the voltage at the second input of the data processing unit (from the second output of the intermediate transformer) to the difference indicated above is taken. The value corresponding to the total resistance of the element 5 and resistors 6 and 8 is subtracted from the result. The output value of the data processing unit through the decoder 17 enters the first input of the setting unit 15. A signal that appears with a short delay at the output of the delay unit 16 after two triggers of the comparator 7, does not pass to the output of the setting block 15, since the value of the transient resistance of the insulation is greater than the value of the resistance of the set point, and there will be no signal at the output of the actuator 18 stroystvo protection does not work. The appearance of the signal at the fourth output of the control unit 13 sets the data processing unit 14 and the setting block 15 to the zero state. After the fourth output of the block 13 is set to zero

The potential cycle of operation of the device is repeated first.

Isolation resistance is smaller, setpoint resistance.

The protection device operates as in the previous case, however, if in the case of three successive cycles of operation of the device, the value of the insulation resistance remains less than the setpoint, then a signal appears at the output unit of the settings, which generates a pulse at the output of the actuator 18. This is necessary in order to build up a transient excitation system. If during the three cycles of operation of the protection device the value of the transition 5 isolation resistance will be greater than the resistance of the setpoint, then the output of the block of settings of the signal will not be. During the fourth cycle of operation of the device, the signal from the fifth output of the control unit 13 erases the information stored earlier in the setting block during the device operation cycles in which the value of the transient insulation resistance was less than the protection device setting.

The measured value of the insulation resistance nz depends on the magnitude of the excitation voltage and the location of the circuit.

The magnitude of the current I ,, flowing through the resistor 8 at a voltage at the output of the rectifier is zero.

 Eo.y

I,

Гп-t-Г

The magnitude of the current 1 flowing through the resistor 8 when the voltage at the output of the rectifier is equal to and

one . Гп + гв

where is the voltage in the place of damage, determined by the stress of the stress, stress;

TT, is the magnitude of the insulation resistance;

r - internal total resistance of the rectifier and two resistors 6 and 8

UBoji ii (ni); (Rm, + r) -and

four

Equating these expressions

Ii (- „+ g) Iz (r. + Rj- and.

hence r equals

and:

 i, -r,

2-il

55 Since in the last expression there is no V then Gy does not depend on. that is, the sensitivity of the protection does not depend on the location of the closure and the value of the excitation voltage. In the last expression for Gp, we replace the currents I, and 12 through the voltage drop across the resistor 8. t, Y - U2-U, where K. is the magnitude of the resistance of torus 8; - ni iT whereDi is the voltage of one step of the generator 11 of the step voltage; PI, T12I n - the number of pulses, and the magnitude of the transition resistance is equal to r - R - - L So. Thus, this device for protection of synchronous generators from ground fault (housing) at one point of the excitation circuit does not depend on the location of the circuit and the voltage value of the excitation circuit, which achieves the purpose of the invention - increasing the reliability of protection compared to the device -prototype Compared with the base object (protection of generators of the type KZR-3), the proposed device allows to measure transient resistances with high accuracy in the range up to 200 kΩ or more, while the protection of KZR-3 only up to 10 kΩ. This advantage of the proposed device makes it possible to detect damage at an early stage and to take appropriate measures to preserve the generator in operation. In this case, the control of the isolation circuit state of the excitation circuit is carried out continuously and automatically, since the device can be equipped with a display unit and easily connected with control microprocessors. Laboratory tests of the device layout show its reliable operation.

./

FIG. 2

Claims (1)

DEVICE FOR PROTECTING THE SYNCHRONOUS GENERATOR FROM CIRCUIT TO THE EARTH (HOUSING) IN ONE POINT OF THE EXCITATION Circuit, containing a rectifier, the input of which is connected to the first output of the intermediate transformer, a comparator and an actuator, characterized in that, in order to increase the reliability of protection by eliminating the dependence of sensitivity on the location of the circuit and the magnitude of the voltage of the excitation circuit, it additionally contains the first and second resistors, a rectangular pulse generator, a step voltage generator, a key , delay unit, control unit, data processing unit, setpoint unit and decoder, while the negative terminal of the rectifier through the first resistor is connected to the positive terminal of the excitation coil of the generator, the positive terminal of the rectifier is connected to the first input of the comparator and through the second resistor to ground, the second input the comparator is connected to the output of the step voltage generator, the main input of which is connected to the output of the rectangular pulse generator, to which the input of the control unit and the input of the data processing unit, the second input of which is connected to the second output of the intermediate transformer, the stop input of the data processing unit and the input of the delay unit are connected to the output of the comparator, the control input of the key is connected to the first output of the control unit, the second output of which is connected to the starting input of the data processing unit, the third and fourth · outputs of the control unit are connected respectively to the inputs of the "Zero" of the step voltage generator and the combined inputs of the "Zero" of the processing unit data and the settings block) the output of the data processing unit via a decoder is connected to the first input of the settings block, the second input of which is connected to the fifth output of the control unit, the starting input of the settings block is connected to the output of the delay unit, and the output of the settings block is connected to the input of the executive body, input an intermediate transformer through a key connected to a power source.