RU2563331C1 - Method of determination of losses in transformer and device for its implementation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method consists in measurement of the transformer temperature and ambient temperature through time intervals which are two, three orders less than thermal time constant, calculation of the transformer temperature increment, determination of the difference between the transformer temperature and ambient temperature and in calculation of losses of the active electric power in the transformer. The loss counter includes the first analogue to digital converter, the first and the second univibrators, the first divider, the adder-accumulator, the square-pulse generator, the timer, the clock timer, the counter, the reprogrammable memory, the transceiver, the computer, the indicator and the second temperature sensor, the second analogue-digital converter, the first and second subtracters, the third univibrator, the memory register, the first, the second, the third and the fourth multipliers, the second divider, the adder, the parameter setter of the transformer.

EFFECT: improvement of accuracy and simplification of measurement.

2 cl, 1 dwg

Description

The invention relates to electrical apparatuses and can be used for integrated measurement of electrical energy losses in transformers of power plants and substations.

A known method of thermal monitoring of the characteristics of voltage transformers [RU No. 2291455 C2, publication date 10.27.2005, IPC G01R 35/02], based on measuring the intensity of the optical radiation of a voltage transformer having a total height H of the side surface and being energized for a time interval, exceeding the duration of transients, using a thermal imaging receiver and determining the surface temperature of a voltage transformer from a fixed optical radiation intensity, and in control essays determine total heat flow Q _1, extending from the side surface of the voltage transformer, at the start of its operation, this surface side of the voltage transformer conventionally divided into portions equal in height

ΔH _i = H / N,

where N is the total number of plots;

determine the temperature of these individual sections, then calculate the heat flux power ΔQ _i , while the total heat flux power is taken equal to the active power of the transformer dissipated in the core of the transformer, and the voltage error Δf _u and the angular error Δδ are determined by the formulas

Δf _u = -c ₁ · (P _a2 -P _a1 ),%;

Δδ = c ₂ · (P _a2 · P _a1 ), min,

where P _a2 , P _a1 are the values of active power calculated on the basis of thermal imaging measurements;

c ₁ , c ₂ are constants determined by the type of apparatus.

The disadvantage of this method is the lack of consideration of the influence of ambient temperature on the temperature of the transformer, which leads to a deterioration in the accuracy of the measurement. Using a thermal imaging receiver significantly increases the cost and complicates the monitoring equipment, and also does not allow continuous measurements, since this requires constant use of the thermal imager and its location on the object.

A known counter of electric energy losses [SU No. 1656466 A1, publication date 15.06.91, IPC G01R 11/60], comprising an ampere-square hour meter, a thermosensitive element, a current transformer, the primary winding of which is included in the power supply circuit of the measured object, the first secondary terminal the windings are connected to the first output of the ampere-square-hour meter, and the heat-sensitive element is made in the form of a resistor that is in thermal contact with the measured object, and an additional brake winding is introduced in the ampere-square-hour meter, the first A output of which is connected to a first terminal of current transformer, and the second through the resistor coupled to second terminals of the counter-ampere-squared hours and the secondary winding of the current transformer, the additional brake winding included in antiphase with the main run winding.

The disadvantage of this invention is the need to include a current transformer in the circuit of the measured object, which requires significant additional costs for the reconstruction of power circuits, leads to a rise in the cost of the meter, especially when used in high voltage networks, and generally complicates the measurement of electric energy losses.

The temperature of the measured object can vary from the cooling mode (ambient temperature), which will affect the heating of the thermosensitive element and introduce an additional error and, accordingly, worsen the accuracy of the measurement of electric energy losses by the meter.

The prototype of the method is a method for determining losses by temperature of the transformer windings [Petrov G.N. Electric cars. In 3 parts. Part 1. Introduction. Transformers Textbook for high schools. M., "Energy", 1974, pp. 191-194]. The essence of the method lies in the fact that the electrical energy lost in the transformer during the conversion of alternating current is released in the form of heat in the windings, core and other parts of the transformer.

The thermal energy P · dt allocated in the body for an elementary period of time dt will be partially spent on increasing the body temperature by dυ and will be partially transferred to the surrounding space. At any moment in time, there will be a balance of thermal energy expressed by the differential equation

where C is the total heat capacity of the body;

υ is the temperature difference between this body and the environment;

K is the amount of heat removed by the cooling surface per unit time with a difference between the surface temperature and the ambient temperature of 1 ° C.

The heating of the windings relative to the oil under steady-state thermal conditions can be assumed proportional to the losses in the windings.

The disadvantage of this method is that the measurement of losses only by the temperature of the transformer using coefficients characterizing the design of the transformer without taking into account the ambient temperature, which significantly affects the temperature of the transformer, leads to an increase in the error in calculating the loss of electric energy according to the formula specified in the prototype.

The physical quantities that are the design parameters of the transformer (mass and surface area of the transformer) are not passport data and are difficult to determine in practice with high accuracy.

The closest in technical essence to the claimed one, taken as a prototype for the device, is an electricity loss counter [RU No. 2380715 C1, publication date 01/27/2010, IPC G01R 19/02 G01R 11/00] containing the first one-shot, functional converter, division unit , a rectangular pulse generator, the first and second counters, an indicator, an analog-to-digital converter, the output of which is connected to the input of the functional converter, the information output of the second counter is connected to the input of the divider of the division unit, characterized in that In addition, a programmable storage device, a transceiver, a computer, a timer, a clock-timer, a second one-shot accumulator, an accumulator, a current sensor, the output of which is connected to the information input of an analog-to-digital converter, the information input of the accumulator, is connected to the output of the functional converter, and the output is connected to the combined indicator input and the input of the divisible division unit, the output of which is connected to the information input of the reprogrammable storage device , the output of which through the transceiver is connected to the computer information input, the output of the square-wave generator is connected to the combined clock inputs of the analog-to-digital converter, timer-clock and timer, the overflow output of which is connected to the combined clock input of the second counter and the analog-to-digital converter start input, output the end of the conversion cycle of which is connected to the control input of the accumulating adder, the output of the timer-clock is connected to the combined clock input counter and the inverse input of the first one-shot, the output of which is connected to the combined input of the recording control of the reprogrammable memory device and the inverse input of the second one-shot, the output of which is connected to the combined inputs of the zero setting of the accumulating adder and the second counter, the information output of the first counter is connected to the address input of the reprogrammable memory .

The disadvantage of the prototype is that it determines the energy losses in the transformer windings, but the losses also include losses in the magnetic circuit, tank, as well as losses from asymmetry and non-sinusoidal current. To account for losses in the prototype, it is necessary to know the resistance of the object on which measurements are made, which varies depending on the temperature of the heating and the environment, and therefore the accuracy of measuring the loss of electric energy decreases.

To account for losses in a three-phase network, it is necessary to install three devices (one for each phase), which complicates and increases the cost of using the known device.

Current sensors (which are usually used current transformers) require a lot of space in the switchgear, so their placement in existing electrical installations is difficult and significantly complicates the device.

The objective of the invention is to improve the accuracy and simplify the measurement of losses of active electrical energy in a transformer.

The technical result of the invention is achieved by measuring and taking into account the ambient temperature, the refusal to use the design parameters of specific transformers, which are not passport data, when calculating electrical energy losses, and the use of two temperature sensors as measuring organs, one of which (transformer temperature sensor) is a full-time.

The essence of the invention in terms of the method lies in the fact that the temperature of the transformer and the environment are measured and at intervals of time equal to two, three orders of magnitude less than the thermal time constant, the increment of the temperature of the transformer is calculated, the difference between the temperature of the transformer and the environment is determined and the active losses are calculated electricity in the transformer according to the formula:

where P _XX - idle loss;

P _KZ - loss of short circuit;

T is the thermal time constant;

ΔΘ is the difference between the transformer temperature and the ambient temperature;

dΘ - increment of the transformer temperature;

Θ _∞ - steady-state temperature of the transformer;

dt is the measurement time interval.

Based on the law of conservation of energy, we can write the heat balance equation:

where c is the specific heat;

G is the mass of the transformer;

α is the heat transfer coefficient from the surface;

S is the surface area;

ΔР - active power loss in the transformer per dt.

The transformer heating time constant can be determined as follows:

When a steady-state temperature is reached, the first term in formula (2) becomes equal to zero, and the losses become equal to the losses in the nominal mode and are the sum of the short-circuit idling losses.

In accordance with formula (3), equation (2) at the steady-state temperature of the transformer will take the form:

where from

Using equations (3) and (4), we find α · S:

Given that G, s, S, α are constant values for a particular transformer, and using formulas (3) and (4), the energy conservation law (2) will take the form of formula (1).

The terms of formula (1) have the following physical meaning:

- количество аккумулированного тепла в трансформаторе;- $$\frac{(P_{XX}+P_{\mathrm{TO}3})\cdot T}{\Delta \Theta }d\Theta$$

- the amount of accumulated heat in the transformer;

- количество тепла, отдаваемого в окружающую среду.- $$\frac{(P_{XX}+P_{\mathrm{TO}3})\cdot T}{{\Theta }_{\infty }}dt$$

- the amount of heat released to the environment.

The essence of the invention in terms of the device is that in a device comprising a first analog-to-digital converter, a first and second one-shot, a first division unit, an accumulating adder, a rectangular pulse generator, a timer, a clock timer, a counter, a reprogrammable memory device, a transceiver, a computer , an indicator, and the square-wave generator is connected to the clock input of the timer, the digital output of the timer is connected to the input of the timer-clock, the output of the clock timer is connected to the input of the counter, the output of the counter is connected to the input address of the reprogrammable memory device, the output of the latter through the transceiver is connected to the information input of the computer, the first and second temperature sensors, the second analog-to-digital converter, the first and second subtractors, the third one-shot, the memory register, the first, second, third are additionally introduced and a fourth multiplier, a second division unit, an adder, a transformer parameter setting unit, the outputs of the first and second temperature sensors being connected respectively to a the analog inputs of the first and second analog-to-digital converters, the output of the first analog-to-digital converter is connected to the second input of the first subtractor, the first input of the second subtractor and the information input of the memory register, the output of the first analog-to-digital converter is connected to the input of the first three subtractors, the output of the second analog the digital converter is connected to the second input of the second subtractor, the output of the memory register is connected to the first input of the first subtractor, and its output is connected to the first input of Vågå multiplier, the output of the first multiplier is connected to the first input of the second division unit, an output of the second subtractor is connected to a second input of the second block division and the first input of the third multiplier, the first output «Θ _∞» parameter setting unit a transformer connected to the first input of the first divider, the outputs of the two "P _XX " and three "P _KZ " are connected respectively to the first and second input of the adder, the fourth output of "T" is connected to the second input of the second multiplier, the output of the adder is connected to the first input of the second multiplier and the second input the house of the first division block, the output of the division block is connected to the second input of the third multiplier, the output of the second multiplier is connected to the second input of the first multiplier, the output of the third multiplier is connected to the first input of the fourth multiplier, the digital output of the timer is connected to the second input of the fourth multiplier, and the timer overflow output is connected with the start inputs of the first and second analog-to-digital converters, the input of the first and second one-shots, the output of the first one-shot is connected to the input of the memory register record, output The od of the timer-clock is connected to the input of the third one-shot and the fifth input “Record of hourly measurement” of the accumulating adder, the output of the second one-vibrator is connected to the third input of “Recording the measurement dt” of the accumulating adder, the output of the third one-vibrator is connected to the fourth input of “Reset” of the accumulating adder, the output of the second the division unit is connected to the first input of the accumulating adder, the output of the fourth multiplier is connected to the second input of the accumulating adder, the output of the latter is connected to the indicator input and information input reprogrammable memory device.

In FIG. 1 is a functional diagram of the claimed device for implementing a method for determining losses in a transformer based on temperature measurement.

The energy loss counter in the transformer contains the first 1 and second 2 temperature sensors, the first 3 and second 4 analog-to-digital converters, the first 5 and second 6 subtractors, the first 7, second 8 and third 9 single-vibrators, memory register 10, first 11, second 12 , the third 13 and fourth 14 multipliers, the first 15 and second 16 division blocks, the accumulating adder 17, the adder 18, the parameter setting block of the transformer 19, the rectangular pulse generator 20, the timer 21, the timer-clock 22, the counter 23, the programmable memory 24, indicator 25, reception transmitter 26, computer 27, wherein the first temperature sensor 1 measures the temperature of the transformer (not shown in FIG. 1), the second temperature sensor 2 measures the ambient temperature, the first 3 and second 4 analog-to-digital converters convert signals from the first 1 of the second 2 temperature sensors in the digital code, the first subtractor 5 calculates the increment of the transformer temperature over the measurement interval, the second subtractor 6 calculates the difference between the transformer temperature and the environment, the first one-shot 7 is necessary for the recording signal is recorded in the memory register 10 on the trailing edge of the pulse coming from the timer 21, the second one-shot 8 is needed to generate a recording signal for the time interval into the accumulating adder 17 along the trailing edge of the pulse coming from the timer 21, the third one-shot 9 is needed to generate the reset signal in the accumulating adder 7, the memory register 10 is needed to record the temperature value of the transformer in the previous calculation step, the first multiplier 11 calculates the product of the temperature increment of the transformer RA calculated in the first subtractor 15 and the data obtained from the second multiplier 12, the second multiplier 12 calculates the product of the heating time constant of the transformer and the sum of losses in the transformer in nominal mode, the third multiplier 13 calculates the product of the difference between the temperature of the transformer and the environment and the quotient from dividing the sum of losses in the transformer in the nominal mode by the steady-state temperature of the nominal mode of the transformer, the fourth multiplier 14 calculates the product of the data obtained by the output of the third multiplier 13, and the time increment generated by the timer 21, the first division unit 15 performs a division operation in which the sum of losses in the transformer in the nominal mode is divisible, and the divider is a constant transmitted from the first output of the transformer 19 parameter setting block, the second block of division 16 performs a division operation in which the data calculated in the first multiplier 11 is divisible, and the divider is the difference between the temperature of the transformer and the environment, the accumulating adder 17 produces accumulation of losses of active electric energy during each hour for the time intervals specified by timer 21, adder 18 summarizes the values of no-load and short-circuit losses set in the parameter setting block in the nominal mode in the transformer, the parameter setting block of the transformer 19 ensures storage of constants after writing nominal parameters of the transformer, the rectangular pulse generator 20 is used to set the appropriate measurement interval, the timer 21 forms the measurement interval, counts by hours 22 it generates a signal every hour, the counter 23 generates the address of the memory cell in the reprogrammable memory 24, the reprogrammable memory 24 is used to record, and the indicator 25 is used to display the values of active electric energy losses per hour received from the output of the accumulating adder 17, the transceiver 26 serves to transfer data accumulated over a period of time from a reprogrammable memory 24 to a computer 27.

Consider the operation of the device on the example of a specific implementation of the method for determining losses in a transformer based on temperature measurement.

Information about the temperature of the transformer from the first 1 temperature sensor is fed to the analog input of the first 3 analog-to-digital converter (ADC), the output of which is a digital code corresponding to the measured temperature, which then goes to the input of the memory register 10, where it is written to the register memory moreover, the recording occurs on the trailing edge of the pulse coming from the timer 21, forming the measurement time intervals (dt) through the first 7 one-shot. Information about the ambient temperature from the second 2 temperature sensors is fed to the analog input of the second 4 ADCs, at the output of which a digital code is generated corresponding to the measured temperature. The start of the first 3 and second 4 ADCs is performed by the signal from the output of the timer 21 corresponding to the measurement interval specified by the square-wave generator 20.

At the input of the first 5 subtracters, a digital code is received from the output of the first 3 ADCs and memory register 10, at the output of which a digital code is generated corresponding to the increment of the transformer temperature (dΘ). The code recorded in the memory register 10 corresponds to the previous time interval for measuring the temperature of the transformer, and the temperature increment is calculated for the current measurement time, and subtraction is performed after the conversion in the first 3 ADCs.

The input from the second 6 subtractor receives a code from the first 3 and second 4 ADCs and at its output after the subtraction operation a digital code is obtained corresponding to the temperature difference between the transformer and the environment (ΔΘ).

In the unit for setting transformer parameters (BZPT) 19, codes corresponding to the parameters of the nominal mode of the transformer are recorded and stored: the steady-state heating temperature of the transformer in the nominal mode (Θ _∞ ); loss of idling (P _XX ) and short circuit (P _KZ ), constant thermal heating time (7).

The total losses of active power in the transformer in the nominal mode are calculated in the adder 18, the course of which from the output of the BZPT 19 receives the constant codes of the corresponding R _XX and R _KZ .

To calculate the expression (Р _ХХ + P _КЗ ) / Θ _∞ , the first 15 division block is used, the input of which receives the codes of the total active power losses in the transformer in the nominal mode (Р _ХХ + Р _КЗ ) and the steady-state temperature in the nominal mode (Θ _∞ ) .

The product of the total losses of the active power of the transformer in the nominal mode (Р _ХХ + Р _КЗ ) and constant thermal heating time (T) equal to (Р _ХХ + P _КЗ ) · Т is calculated in the second 12 multiplier, the input of which is from the adder 18 and БЗПТ 19 the codes of the corresponding constants are received.

The product of expression (P _XX + P _RS) / Θ _∞ of the transformer temperature difference and the environment (ΔΘ) is calculated in the third 13 multiplier, the output of which receive a code corresponding to the expression ((R _XX + P _RS) · ΔΘ / Θ _∞, and the product of the expression (P P + _{XX RS)} · T by the increment of temperature of the transformer (dΘ) calculated in the first multiplier 11, the output of which is formed by the code corresponding to the expression (P + P _{RS XX)} · T · dΘ.

The expression ((R _XX + P _SC) · T · dΘ) / ΔΘ is computed in the second 16, the division unit, the input of which receives the codes from the first 11 of the multiplier and a second 6 subtractor corresponding respectively (P _XX + P _SC) · T · dΘ and ΔΘ.

At the output of the fourth 14 multipliers generated code corresponding to the expression (((R _XX + P _{RS) · ΔΘ) / Θ ∞)} dt, the input of which receives the codes from the third 13 multiplier and a timer 21, corresponding to ((P _XX + P _SC) ΔΘ) / Θ _∞ and the measurement interval dt.

The sum of the losses of active electric energy in the transformer during each hour for the measurement intervals dt according to the formula:

carried out in the accumulating adder 17.

Recording for the measurement interval dt is carried out on the trailing edge of the pulse from the timer 21 through the second 8 single vibrator with inversion.

The code generation of the total active power losses per hour at the output of the accumulating adder 17 is carried out by the signal received from the input of the hour meter 22. The generated code is fed to the input of the reprogrammable memory device (PROM) 24 and is recorded in the memory cell with the address generated by the counter 23, on the counting the input of which pulses are received from the hour counter 22, which changes its input code, and therefore, every hour the cell address, as well as the indicator 25.

Reset (zeroing) of the accumulating adder is carried out on the trailing edge of the pulse coming from the output of the hours counter 22 through the third 9 single-vibrator with inversion.

The contents of the ROM 24 for a long time (hour, day, month, year, several years) are transmitted to the computer 27 by the transceiver 26. The data obtained in the ROM 24 is used to account for the loss of electricity in the transformers.

Thus, the use of the proposed method for determining losses in a transformer, based on temperature measurement, and a device that implements it, allows us to solve the problem, solved by using two temperature sensors that measure the temperature of the transformer and the environment and the parameters of the transformer obtained in the nominal mode of operation required to calculate the loss of active electricity in the transformer generated in the form of heat.

Claims (2)

1. The method of determining losses in the transformer, which consists in measuring the temperature of the transformer, characterized in that they additionally measure the ambient temperature, at intervals of two, three orders of magnitude less than the thermal time constant, calculate the increment in the temperature of the transformer, determine the difference between the temperature of the transformer and environment and calculate the loss of active electricity in the transformer according to the formula:

where P _XX - idle loss;
R _KZ - short circuit loss;
E is the thermal time constant;
ΔΘ is the difference between the transformer temperature and the ambient temperature;
dΘ - increment of the transformer temperature;
Θ _∞ - steady-state temperature of the transformer;
dt is the measurement time interval. 2. The counter of electricity losses in the transformer, which includes the first analog-to-digital converter, the first and second single vibrators, the first division unit, the accumulating adder, the rectangular pulse generator, the timer, the timer-clock, counter, the programmable memory, the transceiver, the computer, the indicator moreover, the square-wave generator is connected to the clock input of the timer, the digital output of the timer is connected to the input of the clock timer, the output of the clock timer is connected to the input of the counter, the output of the counter is connected connected to the address of the reprogrammable storage device, the output of the latter through the transceiver is connected to the computer information input, characterized in that the first and second temperature sensors, the second analog-to-digital converter, the first and second subtractors, the third one-shot, the memory register, the first, second are additionally introduced , the third and fourth multipliers, the second division unit, the adder, the unit for setting the parameters of the transformer, and the outputs of the first and second temperature sensors are connected respectively to to the tax inputs of the first and second analog-to-digital converters, the output of the first analog-to-digital converter is connected to the second input of the first subtractor, the first input of the second subtractor and the information input of the memory register, the output of the first analog-to-digital converter is connected to the third input of the first subtractor, the output of the second analog the digital converter is connected to the second input of the second subtractor, the output of the memory register is connected to the first input of the first subtractor, and its output is connected to the first the first multiplier, the output of the first multiplier is connected to the first input of the second division unit, the output of the second subtractor is connected to the second input of the second division unit and the first input of the third multiplier, the first output of the transformer parameter setting unit “Θ _∞ ” is connected to the first input of the first division unit, the outputs two "R _XX" and three "P _RS 'are respectively connected to first and second input of the adder, the fourth output of the" T "connected to the second input of the second multiplier, the adder output being coupled to the first input of the second multiplier and by the second input of the first division block, the output of the division block is connected to the second input of the third multiplier, the output of the second multiplier is connected to the second input of the first multiplier, the output of the third multiplier is connected to the first input of the fourth multiplier, the digital output of the timer is connected to the second input of the fourth multiplier, and the timer overflow output connected to the start inputs of the first and second analog-to-digital converters, the input of the first and second one-shots, the output of the first one-shot is connected to the input of the register register mint, the output of the timer-clock is connected to the input of the third one-shot and the fifth input “Record hourly measurement” of the accumulating adder, the output of the second one-vibrator is connected to the third input “Recording measurement dt” of the accumulating adder, the output of the third one-shot is connected to the fourth input “Reset” of the accumulating adder, the output of the second division unit is connected to the first input of the accumulating adder, the output of the fourth multiplier is connected to the second input of the accumulating adder, the output of the last is connected to the indicator input and information Discount input reprogrammable memory device.