RU2687893C1 - Method of determining losses of active electrical energy in transformer and device for its implementation - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical apparatus and can be used for integral measurement of active electric energy losses in transformers of electric stations and substations. Summary: method of determining active electric energy losses in a transformer consists in that known values of thermal time constants are set separately for a magnetic system and windings of a transformer, losses of idling speed and short-circuit of transformer, as well as steady-state temperatures separately for magnetic system and windings of transformer. Then temperature of magnetic system and windings of transformer is separately measured. Temperature increments of magnetic system and transformer windings are calculated through time intervals of measurement by two or three orders less than thermal time constants. Difference between temperatures of magnetic system of transformer and environment, as well as windings of transformer and ambient medium is determined, and losses of active power in transformer are calculated. Device implementing method comprises five temperature sensors, unit for setting parameters of transformer, generator of rectangular pulses, microcontroller, a memory register, an indicator, a reprogrammable memory, a transceiver, a computer.

EFFECT: high accuracy of measuring losses of active electrical energy and simple design of the device.

2 cl, 1 dwg

Description

The invention relates to electrical apparatus and can be used for integral measurement of active electrical energy losses in transformers of power stations and substations.

There is a method of determining losses by the temperature of the transformer windings [Petrov GN. Electric cars. In 3 parts. 4.1. Introduction Transformers. Textbook for universities. M., "Energy", 1974, p. 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 as heat in the windings, core and other parts of the transformer.

Thermal energy ⋅dt released in the body for an elementary period of time dt will be partly spent on increasing body temperature per dv and partly discharged into the surrounding space. At any time, there will be a balance of heat energy expressed by a differential equation

where C is the total heat capacity of the body;

- разность температур между данным телом и окружающей средой;

- the temperature difference between the body and the environment;

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

Heating of the windings relative to the oil at steady state thermal conditions can be taken as proportional losses in the windings.

The disadvantage of this method is that the windings and the magnetic system, made of different materials, are replaced by a homogeneous body. This assumption reduces the accuracy of determining the loss of active electrical energy in the transformer.

The formula specified in the method is in no way related to the load of the transformer, which also reduces the accuracy of determining the loss of active electrical energy, since the load directly affects the losses in the transformer windings and, as a consequence, the amount of heat they emit.

Physical quantities, which are constructive 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.

Known electricity loss counter [RU # 2380715 C1 date of publication January 27, 2010, IPC G01R 19/02 G01R 11/00], containing the first one-shot, functional converter, division unit, square pulse generator, first and second counters, indicator, analog-digital the 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 it additionally introduces a reprogrammable memory device, a transceiver, computer, timer, timer-clock, second one-shot accumulator, current sensor whose output is connected to the information input of the analog-to-digital converter, information input of the accumulating adder 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 a reprogrammable storage device, the output of which through the transceiver is connected to the information input of the computer, output 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 start input of the analog-to-digital converter, the output of the end of the conversion cycle of which is connected to the control input of the accumulating adder, output timer-hours are connected to the combined clock input of the first counter and the inverse input of the first one-oscillator, the output of which is connected to the combined The control input of the record of the reprogrammable memory and the inverse input of the second one-shot, the output of which is connected to the combined inputs of the zero accumulation of the 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 this invention is that it determines only the energy loss 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, it is necessary to know the resistance of the object on which measurements are made, which varies depending on the heating temperature and the environment, and therefore the accuracy of measuring the loss of electrical energy is reduced.

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 a known device.

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

The prototype of the method is a method for determining losses in a transformer [RU # 2563331 C1 date of publication September 20, 2015, IPC G01R 35/02], which consists in measuring the temperature of the transformer and the ambient temperature, at intervals equal to two, three orders of magnitude less than the thermal time constant , calculating the temperature increment of the transformer, determining the difference between the temperature of the transformer and the environment, and calculating the loss of active electricity in the transformer using the formula:

where P _XX - loss of idling;

Rkc - loss of short circuit;

T is the thermal time constant;

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

dΘ is the temperature increment of the transformer;

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

dt is the measurement time interval.

The disadvantage of this method, taken as a prototype, is that the transformer is considered as a homogeneous body, having a certain average thermal time constant, as well as measured and steady-state temperatures, which leads to an increase in the error in determining the active power losses in the transformer using the formula specified in the prototype, t .to. The transformer consists of two heated surfaces of the magnetic system and windings made of different materials, each of which has its own parameters indicated above.

The formula specified in the prototype is valid for the nominal operating mode of the transformer, with a uniform load graph, since loss of no-load and short-circuit transformer taken unchanged. In fact, under real loads, the load on the transformer changes, as a result of which the magnitude of losses changes and, consequently, the use of the method taken as a prototype will lead to an increase in the error in determining the loss of active electric power.

The closest in technical essence to the claimed device is the counter loss of active electricity in the transformer [RU # 2589498 C1 publication date 07/07/2016, IPC G01R 11/00], adopted for the prototype.

The counter of losses of the active electric power in the transformer, contains the first analog-digital converter, the first and second one-oscillators, the first division unit, the square-wave generator, the timer, the timer-hours, the counter, the indicator, the reprogrammable memory, the transceiver, the computer accumulating adder , the output of which is connected to the input of the indicator, and the generator of rectangular pulses is connected to the combined clock inputs of the timer and timer-hours, the output of which is connected to the clock input of the sc This output is connected to the control input of the recording of the reprogrammable memory, the output of which is connected via the transceiver to the information input of the computer, with the first and second temperature sensors, the second analog-to-digital converter, the first, second, third and fourth subtractors additionally introduced; units, third and fourth one-shot, first and second memory registers, first, second and third multipliers, second and third division units, adder, parameter setting unit mp an unformator (BZPT), a unit for raising to the negative degree the base of the natural logarithm, the output of which is connected to the second input of the first multiplier and the input of the subtraction unit from one, and the input is connected to the output of the first division unit, to the first input of which the digital output of the timer is connected, and the second input connected to the first output of the transformer parameter setting block, the second and third outputs of the transformer parameter setting block are connected respectively to the first and second input of the adder, and the fourth output of the reference block n The transformer is connected to the first input of the fourth subtractor, the output of which is connected to the second input of the third division unit, the output of which is connected to the second input of the second multiplier, and the first input to the third division unit is connected to the output of the adder, the outputs of the first and second temperature sensors are connected, respectively analog inputs of the first and second analog-digital converters, the output of the first analog-digital converter is connected to the first input of the second subtractor and the information input of the transducer pvogo memory register, and the start input of the first analog-to-digital converter is connected to the overflow output of the timer, which is connected to the start input of the second analog-to-digital converter and the inputs of the first, second and third single-oscillators, the output of the last is connected to the second input of the accumulating adder, the third input connected to the output of the fourth one-shot, the fourth input to the output of the timer-hours, and the first input to the output of the third multiplier, the first input of which is connected to the output of the second multiplier, and w The input is connected to the digital output of the timer, and the output of the second analog-digital converter is connected to the second inputs of the second and fourth subtractors, as well as to the information input of the second memory register, the output of which is connected to the second input of the first subtractor whose output is connected to the first input of the first multiplier The output of which is connected to the second input of the third subtractor, the output of which is connected to the first input of the second division unit, the output of which is connected to the first input of the second multiplier, the output signal The end of the conversion cycle of the second analog-to-digital converter is connected to the third input of the third subtractor, the first input of which is connected to the output of the second subtractor, the output of the first memory register is connected to the first input of the first subtractor, the output of the accumulating adder is connected to the information input of the reprogrammable memory device, the output of the block subtraction from the unit is connected to the second input of the second division unit, the outputs of the first and second one-shot are connected respectively to the inputs for ishi first and second memory registers timer-clock output connected to an input of the fourth monostable multivibrator.

The disadvantage of the prototype is that when using a single temperature sensor to measure the temperature of a transformer, the error in determining active electricity increases, due to the fact that the magnetic system and windings have different temperatures depending on various factors. The amount of heat emitted by the magnetic system depends on the losses in it, which in turn depend on the supply voltage of the transformer. The amount of heat released by the windings depends on the losses in them, which in turn depend on the amount of current flowing through them.

To account for the losses of a three-phase dry transformer, you will need to install four of these devices (3 pieces for each of the three windings and 1 piece for the magnetic system), since their temperature will be different, especially if one considers that the real load in the existing electrical networks is asymmetrical. The installation of additional known devices will lead to the complication of a system for measuring the loss of active electrical energy of a transformer, and, as a consequence, to a higher cost.

The objective of the invention is: improving the accuracy of measuring the loss of active electrical energy and reducing economic costs in the manufacture of devices implementing the method by simplifying the design.

The technical result of the invention consists in the separate measurement and accounting of the temperature of the magnetic system and the transformer windings, as well as the environment and used in the calculations of the known data of the transformer.

The technical result is achieved by determining the loss of active electricity in a transformer, which consists in measuring the temperature of the transformer and the environment, while setting the known values of thermal time constants separately for the magnetic system and the transformer windings, the loss of idling and short-circuit of the transformer, the steady-state temperatures of the magnetic system and windings transformer, separately measure the temperature of the magnetic system and the transformer windings, and at intervals Measurements equal to two, three orders of magnitude less than the thermal time constants are calculated magnetic system temperature increment and the transformer windings, the difference between the temperatures of the transformer of the magnetic system and the environment, as well as transformer windings and the environment, and calculating the losses of active power in the transformer according to the formula:

where ΔР is the active power loss in the transformer released as heat during the measurement time interval dt;

where ΔРхх - losses in the magnetic system of the transformer emitted in the form of heat for dt;

Θxx _{i + 1} is the temperature of the transformer’s magnetic system at the end of the measurement time interval dt;

Θcp _{i + 1} is the ambient temperature at the end of the measurement time interval dt;

Θxx _i is the temperature of the magnetic system of the transformer at the beginning of the measurement time interval dt;

Θcp _i is the ambient temperature at the beginning of the measurement time interval dt;

Txx is the time constant of heating the magnetic system of the transformer;

ΔPxx.n - passport idling of the transformer;

Θxx _∞ - the steady-state temperature of the magnetic system of the transformer;

ΔРкзL1 - losses in the windings of phase Ы of the transformer emitted in the form of heat for dt;

ΘкзL1 _{i + 1} - the temperature of the windings of the phase L1 of the transformer at the end of the measurement time interval dt;

ΘкзL1 _i - temperature of windings of phase Ы of the transformer at the beginning of the time interval of measurement dt;

ТкзL1 - time constant of heating the windings of the transformer phase L1;

ΔРкз.н - passport short circuit losses of the transformer;

ΘкзL1 _∞ - the steady-state temperature of the windings of the transformer phase L1;

ΔРкзL2 - losses in the windings of the L2 phase of the transformer released as heat in dt;

ΘкзL2 _{i + 1} - the temperature of the windings of the transformer phase L2 at the end of the measurement time interval dt;

ΘкзL2 _i - the temperature of the windings of the transformer phase L2 at the beginning of the measurement time interval dt;

ТкзL2 - time constant of heating the windings of the transformer phase L2;

ΘкзL2 _∞ - the steady-state temperature of the windings of the transformer phase L2;

ΔРкзL3 - losses in the windings of phase L3 of the transformer released as heat in dt;

ΘкзL3 _{i + 1} - the temperature of the windings of the transformer phase L3 at the end of the measurement time interval dt;

ΘкзL3 _i - temperature of the windings of the transformer phase L3 at the beginning of the time interval of measurement of dt;

ТкзL3 - time constant of heating the windings of the transformer phase L3;

ΘкзL3 _∞ - the steady-state temperature of the windings of the transformer phase L3.

The method is implemented by a device for determining the loss of active electricity in a transformer containing a rectangular pulse generator, indicator, reprogrammable memory, transceiver, computer, first, second, third, fourth and fifth temperature sensors, microcontroller, memory register, transformer parameter setting unit, and the transceiver output connected to the information input of the computer, the outputs of the first to fifth temperature sensors are connected to a common bus connected to the digital input via A microcontroller that, the clock input of which is connected to the output of the generator of rectangular pulses, the outputs of ports B, C, D are respectively connected to the microcontroller: B - through the register memory input indicator, C - to the input of reprogrammable memory device, D - to the input of the transceiver.

FIG. A functional diagram of the claimed device is presented for implementing a method for determining active energy losses in a transformer.

A device that implements a method for determining the loss of active electricity in a transformer contains the first temperature sensor (DT) 1, the second DT 2, the third DT 3, the fourth DT 4 and the fifth DT 5, a transformer parameter setting unit (BZPT) 6, a rectangular pulse generator (STI) 7 , microcontroller (MK) 8, register 9, indicator 10, reprogrammable memory (PROM) 11, transceiver 12, computer 13, the outputs of the first 1, second 2, third 3, fourth 4 and fifth 5 DT are connected to the common bus connected to the digital input of port A MK 8, BZ T 6 is also connected to a digital input port A of the MC 8, a clock input connected to the output of the GUI 7, port outputs B, C and D are respectively connected to the MC 8: In -through register 9 to the input 10 of the indicator; C - with the entrance of the EPROM 11; D - with the input of the transceiver 12, the output of which is connected to the information input of the computer 13.

Consider an example implementation of the method for determining the loss of active electricity in a transformer using a device for its implementation.

The electrical energy lost in the transformer during the conversion of alternating current is released as heat in its active part (windings and magnetic system). In existing electrical networks, the loading of the transformer and the voltage of its power supply change all the time, as a result of which the magnitude of the loss of active electric power changes both in the windings and in the magnetic system. In this regard, when determining the loss of active electricity in a transformer, it is necessary to find the loss of active power in the windings and the magnetic system of the transformer at each i-th dt measurement time interval. The solution of the differential equation describing the law of energy conservation in a transformer in the general case is

ΔP⋅dt = c⋅G⋅dΘ + α⋅S⋅Δdt,

and for specified time intervals, measurements can be recorded in the following form:

where ΔР is the active power loss in the transformer, released as heat during the time interval of measurement of dt;

c is the specific heat;

G is the mass of the transformer;

dΘ is the temperature increment of the transformer;

α is the heat transfer coefficient from the surface;

S is the surface area;

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

Θ _{i + 1} - the temperature of the transformer at the end of the interval dt without taking into account the ambient temperature;

Θ _i - transformer temperature without taking into account the ambient temperature;

T is the time constant of transformer heating;

Θ _∞H - the steady-state temperature of the transformer without taking into account the ambient temperature.

From expression (7) you can determine Θ _∞H :

At the same time

from where

where ΔP _n is the active power loss in the transformer in nominal mode equal to the sum of the passport losses of idling (ΔPxx.n) and short circuit (ΔРкз.н).

The α⋅S value is constant for each element of the transformer design.

On the basis of the expression (9), taking into account (8) and (10), the power loss for the time dt is calculated in general:

Considering that the transformer is not a uniform body, and consists of heated surfaces of the windings and a magnetic system, which are made of different materials, each of which has its own temperatures at the beginning and end of the measurement interval, the heating time constants, the steady-state temperatures, the expression (11) for a magnetic system, it will become (3), for windings of phase L1 - (4), for windings of phase L2 - (5), for windings of phase L3 - (6).

The expression for calculating the total loss of active power in the transformer (windings and magnetic system) released as heat during the measurement time dt will be (2).

The expression for calculating the loss of active electric energy in the transformer for the measurement interval, the measurement time interval dt will be (1).

To account for losses in a three-phase dry transformer, you will need to install one specified device, which will simplify the measurement of active electrical energy losses in the transformer, and as a result, simplify the design and reduce the economic costs of its manufacture in comparison with the analogue and the prototype. At the same time, five temperature sensors will be used as measuring bodies, four of which (temperature sensors of the magnetic system and transformer windings) for dry transformers are standard, which will also lead to lower economic costs in the manufacture of the device.

In BZPT 6, codes of known transformer data are recorded and stored that correspond to the parameters of the magnetic system and transformer windings: passport losses of the transformer idling (ΔPxx.n); passport loss of transformer short circuit (ΔРкз.н); time constant heating the magnetic system of the transformer (Txx); time constant for heating the windings of the transformer phase L1 (TкзL1); time constant for heating the windings of the transformer phase L2 (TкзL2); time constant for heating the windings of the transformer phase L3 (TкзL3); steady state magnetic system of the transformer (хх _∞ ); steady-state temperature of the transformer phase L1 windings (ΘкзL1 _∞ ); steady-state temperature of the windings of the transformer phase L2 (ΘкзL2 _∞ ); steady-state temperature of the transformer phase L3 windings (ΘкзL3 _∞ ).

The transformer temperature is measured separately for the magnetic system of the transformer (Θxx _i ) by the first DT 1, for windings, respectively: for the winding of phase L1 (ΘкзL1 _i ) by the second DT 2, for the winding of phase L2 (фазыкзД2 _i ) by the third DT 3, for the winding of phase L3 ( ΘкзL3 _i ) the fourth DT 4; and for ambient temperature (Θcp _i ) fifth DT 5.

At time intervals of measurement (dt) equal to two, three orders of magnitude less thermal time constants, formed taking into account the clock frequency specified by GUI 7, MK 8 polls and receives data on the temperature of the magnetic system of the transformer (Θxx _i ) from the first DT 1, on the temperature of the windings phase L1 (ΘкзL1 _i ) from the second DT 2, about the temperature of the windings of phase L2 (ΘкзL2 _i ) from the third DT 3, about the temperature of the windings of the phase L3 (ΘкзL3 _i ) from the fourth DT 4, about the ambient temperature (Θcp _i ) from the fifth DT 5. The specified DT 1-5 are connected by a common data bus connected to a digital input. port A MK 8. The data obtained are formed as an array and recorded in the RAM MK 8 within an hour.

After one hour, the MK 8 calculates the value of active power loss in magnetic field based on the array of measured data of the magnetic system temperature and transformer windings stored as an array in RAM, as well as codes corresponding to the constant parameters of the magnetic system and transformer windings recorded in BZPT 6 transformer system, released in the form of heat for each time interval of measurement of dt in accordance with the expression:

and the values of active power losses in the windings of the transformer L1, L2, L3 phase, released as heat during each measurement time interval dt in accordance with the expressions:

The resulting values of the loss of the magnetic system and the transformer windings (ΔPxx, ΔРкзL1, ΔРкзL2, ΔРкзL3) are formed as an array and recorded in RAM MK 8, after which the total losses of active power in the transformer allocated in the form of heat for the measurement time interval dt are calculated in accordance with the expression:

The loss of active electricity in a transformer for a measurement interval of 1 hour is calculated as the sum of the products of the total active power loss calculated in this period by the value of the measurement time intervals dt in accordance with the expression:

Calculated MK 8 value of active energy losses in the transformer for the measurement interval equal to 1 hour by pulses from the output of port C of the MK 8 is written to the memory cell of the PROM 11 and from the exit of the port of B MK 8 to register 9. After that, all arrays recorded in the RAM of the MK 8 and the process of measuring the temperature and calculating the loss of active electric power in the transformer repeats for the next hour, at the end of which 11 new pulses are written to register 9 and the next PROM memory cell 11 pulses, respectively, from ports B and C of the MK 8 The values of the active power losses.

The indicator 10 displays the calculated value of the active energy losses in the transformer recorded in the register 9 for an hour, after which the new value recorded in the register 9 is displayed.

The contents of the EPROM 11 for the time interval (hour, day, month, year, several years) is transmitted to the computer 13 by the transceiver 12, when receiving from him the appropriate command to transmit data about the loss of active electricity in the transformer.

Thus, the use of the proposed method of determining the loss of active electricity in a transformer and a device that implements it, based on separate measurement of the temperature of the magnetic system and the transformer windings, taking into account all the losses of active electricity in the transformer, released in the form of heat, and measuring the ambient temperature, allows you to solve the task to improve the measurement accuracy of the loss of active electric energy and reduce economic costs in the manufacture of the device p Aliso said process by simplifying the construction.

Claims (33)

1. The method of determining the loss of active electricity in the transformer, which consists in measuring the temperature of the transformer and the environment, characterized in that it additionally sets the known values of thermal time constants separately for the magnetic system and windings of the transformer, the loss of idling and short-circuit of the transformer, as well as steady-state temperatures separately for the magnetic system and the transformer windings, then separately measure the temperature of the magnetic system and the transformer windings, after h it is two or three orders of magnitude less than thermal time constants at intervals of time to calculate the temperature increment of the magnetic system and transformer windings, determine the difference between the temperatures of the magnetic system of the transformer and the environment, as well as the windings of the transformer and the environment, and calculate the loss of active electricity in the transformer using the formula :

where ΔР is the active power loss in the transformer, released as heat during the time interval of measurement of dt;

where ΔРхх - losses in the magnetic system of the transformer, released in the form of heat for dt;

Θхх _{i + 1} is the temperature of the transformer’s magnetic system at the end of the measurement time interval dt; Θcp _{i + 1} is the ambient temperature at the end of the measurement time interval dt; Θхх _i is the temperature of the magnetic system of the transformer at the beginning of the measurement time interval dt; Θср _i - ambient temperature at the beginning of the time interval for measuring dt; Tхх is the time constant for heating the magnetic system of the transformer; ΔPxx.n - passport idling of the transformer; Θхx _∞ - the steady-state temperature of the transformer magnetic system; ΔРкзL1 - losses in the windings of phase L1 of the transformer, released as heat in dt;

ΘкзL1 _{i + 1} - the temperature of the windings of the phase L1 of the transformer at the end of the measurement time interval dt; ΘкзL1 _i - temperature of windings of phase L1 of the transformer at the beginning of the time interval of measurement dt; ТкзL1 - time constant of heating the windings of the transformer phase L1; ΔРкз.н - passport short circuit losses of the transformer; ΘкзL1 _∞ - the steady-state temperature of the windings of the transformer phase L1; ΔРкзL2 - losses in the windings of the L2 phase of the transformer, released as heat in dt;

ΘкзL2 _{i + 1} - the temperature of the windings of the transformer phase L2 at the end of the measurement time interval dt; ΘкзL2 _i - the temperature of the windings of the transformer phase L2 at the beginning of the measurement time interval dt; ТкзL2 - time constant of heating the windings of the transformer phase L2; ΘкзL2 _∞ - the steady-state temperature of the windings of the transformer phase L2; ΔРкзL3 - losses in the windings of the transformer L3 phase, released as heat in dt;

ΘкзL3 _{i + 1} - the temperature of the windings of the transformer phase L3 at the end of the measurement time interval dt; ΘкзL3 _i - temperature of the windings of the transformer phase L3 at the beginning of the time interval of measurement of dt; ТкзL3 - time constant of heating the windings of the transformer phase L3; ΘкзL3 _∞ - the steady-state temperature of the windings of the transformer phase L3. 2. A device for determining the loss of active electricity in a transformer, containing a rectangular pulse generator, indicator, reprogrammable memory, transceiver, computer, first and second temperature sensors, memory register, transformer parameter setting unit, the transceiver output connected to an information input of a computer that the third, fourth and fifth temperature sensors, a microcontroller, are additionally introduced, with the outputs of the first, second, third, fourth and the fifth temperature sensors are connected to the common bus connected to the microcontroller port A digital input, the transformer parameter setting unit is also connected to the microcontroller port A digital input, the clock input of which is connected to the rectangular pulse generator output, the microcontroller port B output is connected to the indicator input via the memory register , the output of port C of the microcontroller is connected to the input of the reprogrammable memory device, the output of the port D of the microcontroller is connected to the input of the transceiver.

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