RU211492U1 - Device for monitoring the time of self-excitation, readiness to receive the load and amplitude modulation of the voltage of synchronous generators - Google Patents

Abstract

The utility model relates to the field of measuring technology, includes a power supply located in the instrument case, input circuits in the form of a step-down transformer, the secondary winding of which is connected to a voltage divider unit, which includes four voltage dividers with different division ratios, each of which is associated with a corresponding input multiplexer, the output of which is connected to the input of the driver of an analog-to-digital converter built on operational amplifiers, connected through a low-pass filter to the analog input of a 14-bit analog-to-digital converter to convert the analog signal into digital, the digitized data from which are transmitted via a serial interface to the microcontroller , the frequency with which discrete samples of the analog signal are carried out is set using the control signal supplied to the control input of the analog-to-digital converter from the output of the microcontroller associated with those located on the front panel device by the device operating mode switch, the generator nominal parameters switch and the display unit, which displays the measured parameters depending on the selected device operation mode and the nominal parameters of the synchronous generator. EFFECT: creation of a small-sized device with extended functionality.

Description

The device for monitoring the time of self-excitation, readiness to receive the load and amplitude modulation of the voltage belongs to the field of measuring technology and is designed to measure the self-excitation time of the generator, the time the generator is ready to receive the load, the amplitude modulation of the voltage, as well as the frequency and voltage of the synchronous generator.

Modern electric generating sets (electrical generating sets and power plants) in both military and civil engineering in a number of areas of application are subject to requirements for a controlled time to reach the nominal parameters. These requirements are important both for the operation of a backup power generating set, if a break in the consumer's power supply is unacceptable or acceptable in a very short period of time, and for military equipment with strict requirements for the generator to be ready to turn on the load. To meet these requirements, in the technical specifications, the generators are set with a self-excitation time (the time from the start-up of the electrical installation to reaching the minimum allowable voltage) and the time for readiness to receive the load, i.e. reaching the nominal voltage value with a permissible deviation from this value within the specified accuracy (deviation of the steady value of the generator voltage). Also, modern power generating sets are subject to high demands on the quality of electricity, in particular on the stability of the voltage at no load and under load. One of the power quality parameters is voltage amplitude modulation, the requirements for which are included in the standards and specifications for generators and power generating sets and, therefore, voltage amplitude modulation must be controlled during acceptance tests and during maintenance of power generating sets.

Also in modern electrical installations, protection systems are used that control the voltage in the control zone and in the case when the voltage of the electrical installation does not enter the control zone for a specified time from the moment it is started, they consider this situation an emergency and turn off the excitation of the generator of this electrical installation in order to exclude the inclusion of a load on incomplete tension.

Thus, the control of the parameters of the amplitude modulation of the generator voltage, the generator self-excitation time and the time the generator voltage enters the control zone is important and should be carried out both during acceptance tests of generators and power generating sets, and during maintenance of these products. It is inconvenient to control these parameters in the conditions of test stations and in the conditions of maintenance sites using universal measuring instruments, because voltage oscillography is required, followed by the calculation of these parameters from the received oscillograms.

The task to be solved by this utility model is to create a small-sized device with extended functionality that allows you to determine the time of generator self-excitation, the time the generator voltage enters the control zone, the amplitude modulation of the voltage and, additionally, the frequency of the alternating voltage of the generator and the rms value of the generator voltage without carrying out additional voltage oscillography with subsequent calculation of these parameters from the received oscillograms.

The claimed device can be used in measuring the above parameters for synchronous alternating voltage generators with a rated voltage of 230 V and 400 V and a rated frequency of 50 Hz and 400 Hz.

The technical task is to create a device that is compact with extended functionality, which allows measuring the self-excitation time, the time the generator voltage enters the control zone, the amplitude modulation of the voltage, as well as the RMS value of the generator voltage and the frequency of the generator voltage.

The technical problem is solved due to the fact that the device for monitoring the time of self-excitation, readiness to receive the load and amplitude modulation of the voltage of synchronous generators includes a power supply located in the body of the device, input circuits in the form of a step-down transformer, the secondary winding of which is connected to a voltage divider unit (BDN), which includes four voltage dividers with different division ratios, each of which is connected to the corresponding input of the multiplexer (MUX), the output of which is connected to the input of the analog-to-digital converter driver (DADC), built on operational amplifiers, connected through a low-pass filter (LPF) to the analog input of a 14-bit analog-to-digital converter (ADC) for converting an analog signal into digital, digitized (discrete) data are transmitted via a serial interface to a microcontroller (MC), the frequency at which discrete analog signal samples are taken is set using the control signal input to the control input of the analog-to-digital converter (ADC) from the output of the microcontroller (MC), on the front panel of the device there are the device operation mode switch (PRR), the generator nominal parameters switch (PNP), and the display unit associated with the microcontroller (MC) (BI), which displays the measured parameters depending on the selected operating mode of the device and the nominal parameters of the synchronous generator.

The utility model is illustrated by the following graphics:

in fig. 1 shows a schematic diagram of the device;

in fig. 2 shows the front panel of the device;

in fig. 3 is a plot of a modulated voltage explaining an operation mode in determining the amplitude modulation factor;

in fig. 4 shows a graph of the input discrete signal, explaining the algorithm for determining the frequency;

in fig. 5 is a graph of the frequency and voltage curves when starting the generator.

The diagram (Fig. 1) shows: a step-down transformer 1, a voltage divider block 2, a multiplexer 3, an analog-to-digital converter driver 4, a low-pass filter 5, an analog-to-digital converter 6, a microcontroller 7, a device operation mode switch 8, a nominal value switch generator parameters 9, indication block 10, power supply 11.

As shown in FIG. 1 device for monitoring the self-excitation time, readiness to receive the load and amplitude modulation of the voltage of synchronous generators includes a power supply 11 located in the device case, input circuits in the form of a step-down transformer 1, the secondary winding of which is connected to a voltage divider unit 2, which includes four voltage dividers with various division ratios, each of which is connected to the corresponding input of the multiplexer 3, the output of which is connected to the input of the driver of the analog-to-digital converter 4, built on operational amplifiers, connected through the low-pass filter 5 to the analog input of the 14-bit analog-to-digital converter 6 for conversion of an analog signal into digital, digitized (discrete) data are transmitted via a serial interface to the microcontroller 7, the frequency with which discrete samples of the analog signal are carried out is set using a control signal supplied to the analog-to-digital control input transducer 6 from the output of the microcontroller 7. On the front panel of the device, there is a device operation mode switch 8 connected to the microcontroller 7, a switch for the nominal parameters of the generator 9 and a display unit 10. The display unit 10 displays the measured parameters depending on the selected operating mode of the device and nominal parameters synchronous generator.

The device for monitoring the time of self-excitation, readiness to receive the load and amplitude modulation of the voltage of synchronous generators works as follows: the device is connected to the output voltage of a synchronous alternating voltage generator. The output voltage of the generator is fed to the input of the step-down transformer 1 (see Fig. 1). The secondary voltage from the step-down transformer 1 is supplied to the block of resistive voltage dividers 2. The block of resistive voltage dividers 2 contains four voltage dividers with different division ratios. The output voltage from each resistive voltage divider is fed to the corresponding input of the multiplexer 3, the task of which is to connect to its output the output voltage from one of the four resistive dividers. The choice of a resistive divider, the output voltage from which must be connected to the output of the multiplexer 3, depends on the operating mode of the device and the nominal parameters of the synchronous generator (nominal voltage and frequency), to which the device is connected and controlled by means of control signals coming from the microcontroller 7 to the control inputs of the multiplexer 3 The output voltage from the multiplexer 3 is fed to the input of the analog-to-digital converter driver 4, built on operational amplifiers and used to match the output impedance of the input stage of the device with the input impedance of the analog-to-digital converter 6. The output voltage from the ADC driver is fed to the input of the low-pass filter 5 After passing through a low-pass filter, the voltage is fed to the analog input of a 14-bit ADC 6. The sampling frequency of the ADC, i.e. the frequency with which discrete samples of the analog signal are carried out is set using the control signal supplied to the control input of the ADC from the output of microcontroller 7. Digitized (discrete) data are transmitted via a serial interface to microcontroller 7. Microcontroller 7, depending on the selected operating mode of the device and nominal synchronous generator voltage parameters calculates the following parameters:

1. amplitude modulation of the generator voltage;

2. generator voltage frequency;

3. self-excitation time and generator voltage entry time into the regulation zone;

4. RMS value of generator voltage.

The choice of the operating mode of the device is carried out from the control panel using switch 8, which is connected to the microcontroller 7. 4 operating modes are available:

1. AM - calculation of the amplitude modulation of the generator voltage;

2. F - calculation of the generator voltage frequency;

3. U - calculation of the rms voltage of the generator;

4. t _in - calculation of the self-excitation time and the time the generator voltage enters the control zone.

Using switch 9 on the control panel of the device (see Fig. 2), the nominal parameters (voltage and frequency) of the synchronous generator to which the device is connected are selected. The following generator ratings are available:

1. 230V/50Hz;

2. 230V/400Hz;

3. 400V/50Hz;

4. 400V/400HZ.

The result of the program algorithm of the microcontroller 7 (i.e., the calculation of any of the parameters) is displayed on the display unit 10.

The device is powered from the built-in power supply unit 11, which is connected to the AC voltage network 220 V/50 Hz.

To calculate the amplitude modulation of the voltage applied to the input of the device from the output of the synchronous alternating voltage generator, the following algorithm is implemented in the microcontroller 7:

Discrete data coming from the ADC output to the microcontroller input via a serial data interface are accumulated in the internal buffer of the microcontroller. When the buffer is full, its contents enter the queue for further processing, the buffer is cleared, and the process of accumulating data coming from the ADC resumes. The microcontroller retrieves data from the queue for processing in order to calculate the amplitude modulation factor.

The time interval t for calculating the amplitude modulation coefficient K _mod with subsequent display of the calculated data on a digital display is 500 ms. During this time, the amplitude value of the voltage supplied to the input of the device is calculated for each period and the simultaneous search for the largest U _max and the smallest U _min among them (see Fig. 2). After the period t, the average value between U _max and U _min is calculated using the formula:

, (1)

, (one)

where U _nom is the nominal amplitude value of the voltage in the time interval t;

U _min - the minimum amplitude value of the voltage in the time interval t;

U _max - the maximum amplitude value of the voltage in the time interval t.

This value is taken as the nominal peak voltage supplied to the instrument input from the output of the synchronous alternating voltage generator.

The resulting calculation of the voltage amplitude modulation coefficient is performed using the following formula:

, (2)

, (2)

where K _mod is the coefficient of amplitude modulation;

U _max - the maximum amplitude value of the voltage in the time interval t;

U _min - the minimum amplitude value of the voltage in the time interval t;

U _nom - nominal amplitude value of the voltage in the time interval.

The value K _mod is transmitted to the display unit for display and is updated every 500 ms.

To calculate the frequency of the voltage supplied to the input of the device from the output of the synchronous alternating voltage generator, the following algorithm is implemented in the microcontroller.

Discrete data coming from the ADC output to the microcontroller input via a serial data interface are accumulated in the internal buffer of the microcontroller. When the buffer is full, its contents enter the queue for further processing, the buffer is cleared, and the process of accumulating data coming from the ADC resumes. The microcontroller retrieves data from the queue for processing in order to calculate the frequency of the input voltage.

To determine the frequency of the alternating voltage supplied to the device input from the output of the synchronous alternating voltage generator, using the discrete data stream from the ADC output, it is necessary to determine the ADC discrete readings in this stream, corresponding to the beginning of the period a ₁ and the end of the period a _n for the alternating voltage (see Fig. 4) and calculate the period of the signal using the formula:

T=t _adc n, (3)

where T is the period of the signal;

n is the number of discrete samples between the beginning of the period a ₁ and the end of the period a _n ;

t _adc - time interval in seconds between adjacent discrete samples coming from the ADC output.

Knowing the sampling frequency of the ADC ƒ _adc , which is a constant value and is 50 kHz, the time interval t _adc is calculated:

(4)

(four)

where t _adc - time interval between adjacent samples of the ADC;

ƒ adc - _ADC sampling rate.

The signal frequency is calculated using the formula:

(5)

(5)

where ƒ is the value of the signal frequency;

T is the period of the signal.

The calculated frequency value ƒ is stored in the line array and the same calculation is performed for the next period of the input signal.

After the time interval t, equal to 500 ms, the frequency of the input AC voltage is calculated as the average of the frequencies accumulated in the array. This value is transmitted to the display unit of the device. The frequency calculation is performed cyclically while the instrument is in the input voltage frequency measurement mode.

To calculate the rms value of the AC voltage supplied to the device input from the output of the synchronous AC voltage generator, the following algorithm is implemented in the microcontroller:

Discrete data coming from the ADC output to the microcontroller input via a serial data interface are accumulated in the internal buffer of the microcontroller. When the buffer is full, its contents enter the queue for further processing, the buffer is cleared, and the process of accumulating data coming from the ADC resumes. The microcontroller retrieves data from the queue for processing in order to calculate the RMS value of the input voltage.

RMS voltage is calculated using the following formula:

(6)

(6)

where U is the rms value of the voltage;

u(t) - instantaneous voltage value;

T is the measurement period.

The rms voltage value is calculated cyclically at the time interval t=500 ms for each period in the discrete data stream coming from the ADC. To do this, indexes of discrete samples in the data stream are determined, corresponding to the beginning of the period - a ₁ and the end of the period - a _n . Having determined the beginning and end of one period, the number of discrete readings n included in this period is counted. After the beginning and end of the period and the number of discrete samples included in it are determined, the period T in seconds is calculated using formulas (4) and (3). Then the integral is calculated using the formula:

(7)

(7)

where a ₁ is the index of a discrete sample taken as the beginning of the period;

and _n is the index of the discrete sample taken as the end of the period;

t - time interval between adjacent discrete readings of the ADC;

u - instantaneous voltage at the input of the device.

When calculating the integral, discrete readings from the ADC output are converted into instantaneous voltages at the input of the device, taking into account the transfer coefficients of the step-down transformer 1 and the block of resistive voltage dividers 2.

Having calculated the integral and the period T, the calculation of the root-mean-square value of the voltage for this period is performed using the formula (6). The result obtained is stored in a linear array, and the above algorithm is repeated for the next period in the input data stream coming from the ADC.

After the expiration of the time interval t=500 ms, the average value is calculated among the values accumulated in the linear array. This value is transmitted to the display unit of the device.

The rms voltage calculation algorithm is executed cyclically as long as the instrument is in the rms voltage measurement mode.

To calculate the self-excitation time of a synchronous generator and the time the generator voltage enters the control zone, the following algorithm is implemented in the microcontroller:

Discrete data coming from the ADC output to the microcontroller input via a serial data interface are accumulated in the internal buffer of the microcontroller. When the buffer is full, its contents enter the queue for further processing, the buffer is cleared, and the process of accumulating data coming from the ADC resumes. The microcontroller extracts data from the queue for processing in order to calculate the excitation time and the time the generator voltage enters the regulation zone.

The self-excitation time of the generator t _in (see Fig. 5) is the time interval from the moment t ₀ when the frequency of the generator output voltage reaches 90% of the nominal and until the moment t ₁ when the generator output voltage reaches 90% of the nominal.

The time the generator voltage enters the control zone t _H (see Fig. 6) is the time interval from the moment t ₀ when the frequency of the generator output voltage reaches 90% of the nominal and until the moment t ₂ when the generator output voltage stabilizes at the level of the rated voltage with allowable deviation.

To calculate the self-excitation time t of the synchronous generator _{, the} microcontroller calculates the frequency of the input alternating voltage for each period from the input stream of discrete data from the ADC. The algorithm for calculating the frequency of each period is similar to the algorithm by which the frequency is calculated when the instrument is in the frequency measurement mode. Having calculated the frequency ƒ of the corresponding period, the microcontroller checks the following condition:

ƒ≥0.9ƒ _nom , (8)

where ƒ is the input voltage frequency;

ƒ _nom - nominal voltage frequency of the synchronous generator. If this condition is met, i.e. if the period frequency is greater than or equal to 90% of the rated frequency of the generator output voltage, the microcontroller enters the state of counting the self-excitation time t _in .

In this state, the microcontroller continues to calculate the frequency for each subsequent period in the data stream from the ADC and calculate the number of discrete samples n included in this period, and also starts calculating the rms voltage U for each period. The calculation of the rms voltage U is performed according to an algorithm similar to the algorithm when the digital meter operates in the rms voltage measurement mode. The number of discrete samples n from the ADC is accumulated in the SUM variable:

SUM=SUM+n

They will be used in the future when calculating the resulting excitation time of the generator t _in .

Having calculated the rms value of the voltage U for the period, the microcontroller checks its value for compliance with the condition:

U≥0.9U _nom , (9)

where U is the rms value of the voltage of one period;

U _nom - rated voltage of the generator.

When the microcontroller detects a period that satisfies the given condition, i.e. the rms value of the voltage of this period is greater than or equal to 90% of the rated voltage of the generator, the excitation time t _in is calculated. At this point in time, the SUM variable contains the total number of discrete samples received from the ADC output from the moment when the initial reference point of the excitation time t ₀ was determined (see Fig. 5) and until the moment when the end point of the reference time of excitation was determined ( see Fig. 5). The following formula is used to calculate the excitation time t _in :

t _in =SUM t _adc , (10)

where t _is the excitation time of the generator;

t _adc - time interval between adjacent discrete samples of the ADC. Calculated by formula (4).

The calculated time tv _is stored in the internal memory of the microcontroller, after which it enters the state of determining the time the generator voltage enters the regulation zone.

To determine the time when the generator voltage enters the control zone, it is necessary to find a period whose root mean square value of the voltage satisfies the following condition:

U=U _nom ±1%, (11)

where U is the rms value of the period voltage;

U _nom - rated voltage of the generator.

In this case, the root-mean-square values of the periods following it within 1 second must also satisfy this condition. To do this, the microcontroller:

1. Calculates the RMS value of the voltage U of the next period from the input data from the ADC.

2. Determines the number of discrete samples of the ADC n in this period.

3. Accumulates the total number of ADC samples in the SUM variable;

4. The fulfillment of condition (11) is checked. If the condition is met, the microcontroller operation algorithm continues from point 5 in order to determine the stabilization of the output voltage at the level of the nominal value. If the condition is not met, the work algorithm is repeated from point 1.

5. The value of the SUMTmp variable is reset:

SUMTmp=0

6. The value of the Time variable is reset:

Time=0

7. The rms value of the voltage U of the next period is calculated from the input data from the ADC.

8. The number of discrete readings and included in this period is determined.

9. The total number of discrete ADC samples is accumulated in the SUMTmp variable:

SUMTmp=SUMTmp+n

10. The period T is calculated according to the formula (3).

11. In the Time variable, the total time is calculated from the moment of detection of the first period that satisfies the condition (11):

Time=Time+T

12. The fulfillment of condition (11) is checked. If the condition is met, then the algorithm continues from point 13. Otherwise, the number of discrete ADC samples accumulated in the SUMTmp variable is added to the SUM variable and the algorithm continues from point 1.

13. The following condition is checked:

Time≥1s. (12)

If the condition is not met, the work algorithm resumes from step 7.

If condition (12) is met, the generator voltage is considered stabilized, and the number of discrete samples accumulated in the SUM variable is the total number of ADC samples from time t ₀ to time t ₂ (see Fig. 4). Calculation of the time when the generator voltage enters the regulation zone is carried out according to the formula:

t _H =SUM t _adc , (13)

where t _H is the time when the generator voltage enters the control zone;

t _adc - time interval between adjacent samples of the ADC (see Fig. 4);

SUM is the total number of ADC samples from time t ₀ to time t ₂ (see Fig. 4).

This design allows you to create a small-sized device with extended functionality, which allows you to determine the time of generator self-excitation, the time the generator voltage enters the control zone, the amplitude modulation of the voltage and, additionally, the frequency of the alternating voltage of the generator and the RMS value of the generator voltage.

Claims (1)

A device for monitoring the time of self-excitation, readiness to receive the load and amplitude modulation of the voltage of synchronous generators, including a power supply located in the body of the device, input circuits in the form of a step-down transformer, the secondary winding of which is connected to a voltage divider unit, which includes four voltage dividers with different division ratios , each of which is connected to the corresponding input of the multiplexer, the output of which is connected to the driver input of an analog-to-digital converter built on operational amplifiers, connected through a low-pass filter to the analog input of a 14-bit analog-to-digital converter for converting an analog signal to digital, digitized data from which are transmitted to the microcontroller via a serial interface, the frequency with which discrete samples of the analog signal are carried out is set using the control signal supplied to the control input of the analog-to-digital converter from the output of the microcontroller connected to the device operating mode switch located on the front panel of the device, the generator nominal parameters switch and the display unit, which displays the measured parameters depending on the selected device operation mode and the nominal parameters of the synchronous generator.

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