RU2629827C1 - Device for controlling cooling system of oil-filled power transformer - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises a digital processing unit (1) provided with an input interface (2) for connecting sensors of the transformer electrical state, for example one or more load current sensors (3), and an output interface (4) for outputting signals for controlling adjustable drives of oil and air coolers of the mentioned transformer. According to the indications of the sensors (3), the unit (1) determines the permissible thermohydraulic states of the power transformer and of the performance of the oil and air coolers, at which the set temperature value of the most heated point will not be exceeded. The unit (1) selects the thermohydraulic state and the combination of oil and air cooler capacities necessary for its maintenance from the obtained data, at which the total energy consumption for the power transformer cooling and the losses in it will be minimal. If the selected capacity is below the preset threshold, the unit (1) takes one of the coolers out of operation and recalculates the minimizing total cost of the combination of capacities for the coolers remaining in operation. In order to extend the functionality, additional interfaces can be added to the device.

EFFECT: total power consumption for cooling the power transformer and for the losses in it are reduced.

8 cl, 1 dwg

Description

Technical field

The invention relates to the field of electric power, namely, to control the cooling system of powerful oil-filled equipment of power plants and substations, and can be applied to control the cooling of oil-filled power transformer.

State of the art

Powerful oil-filled transformers are equipped with forced cooling systems, including several air coolers (fans) and one or more oil coolers (oil pumps). As a rule, the greater the load on the transformer, the greater the power consumption for cooling. The temperature of the transformer windings, their resistance and power loss in the windings decrease with more intensive (and, accordingly, energy-consuming) cooling. As a result, for each specific load mode of the transformer there is an optimal cooling mode, in which the total power consumption for cooling the transformer and for losses in its windings will be close to minimum.

A technical solution is known aimed at reducing the indicated total power costs due to the appropriate choice of the number of turned-on coolers, according to which the cooling control device of a powerful transformer periodically calculates the thermal state of the transformer and the corresponding total power costs at three values of the number of turned-on coolers - current, by one greater and one less and selects for the next time interval that of these three values for the number of coolers turned on, wherein the oil temperature and the windings does not exceed the predetermined limit values, and total power costs less [RU 2377682].

With this control, at least part of the coolers (fans and oil pumps) operate in intermittent mode (periodic on and off mode of electric motors), which is characterized by incomplete use of the heat exchange surface of the transformer and high energy consumption.

From this drawback, a freely selected transformer cooling system control device for a powerful transformer [RU 2432591]. The prototype contains a digital processing unit equipped with input and output interfaces. Sensors of the current electrical state of the transformer are connected to the input interface. The output interface generates control signals for the adjustable drives of oil and air coolers. Based on the readings of these sensors, the digital processing unit determines the thermo-hydraulic state of the transformer, which ensures the temperature, according to the selected setting, of the most heated point of the power transformer (hereinafter, the term “permissible thermo-hydraulic state of the transformer” is used for this state), as well as the performance of oil and air coolers necessary for maintaining this condition.

The prototype regulates the performance of coolers by changing the rotation speed of their drive electric motors, which is more economical than changing the number of coolers operating simultaneously.

However, despite the use of controlled electric drives in the prototype, the total energy costs for cooling the power transformer and losses in it are above the minimum that can be achieved with the optimal combination of the performance of oil and air coolers.

SUMMARY OF THE INVENTION

As the studies conducted by the authors showed, in a number of practical cases, the permissible temperature of the most heated point of a power transformer with its current electrical state can be provided not with one but with a certain set of permissible thermo-hydraulic modes of the transformer, and if there are two types of coolers (pumps pumping oil through transformer tank, and fans, cooling the pumped oil with air), as a rule, several elements correspond to one element of such a multitude of modes to allowable load for this oil and air coolers (i.e., combinations of capacities) characterized unequal total power cost for cooling the power transformer and the loss therein.

The prototype does not have the ability to choose the most economical option for loading coolers from several possible combinations of capacities (rotational speeds) of coolers capable of supporting this permissible thermo-hydraulic mode.

The technical result of the invention in relation to the prototype using an adjustable electric drive for oil and air coolers is a further decrease in the total cost of electricity for cooling the power transformer and for losses in it.

The subject of the invention is a control device for a cooling system of an oil-filled power transformer, comprising a digital processing unit equipped with an input interface for connecting sensors of the current electrical state of the transformer and an output interface for generating control signals for adjustable drives of oil and air coolers, and configured to determine the permissible thermohydraulic state of the power transformer and produce of oil and air coolers necessary to maintain the specified acceptable state, characterized in that the digital processing unit is configured to determine a plurality of combinations of the indicated capacities, generate control signals corresponding to the combination of capacities, minimizing the total energy costs for cooling the power transformer and losses in it, decommissioning of one of the coolers if, in accordance with the generated control signal, its performance below a predetermined threshold, and redefining a minimizing combination of capacities for coolers remaining in operation.

This allows you to get the specified technical result.

In addition, the claimed invention allows to simplify the device and increase its reliability due to the ability to control the cooling of the transformer without the use of a temperature sensor or oil viscosity, which is necessary when implementing the prototype.

The development of the invention related to particular cases of its implementation, is that the digital processing unit is equipped with:

- an interface for entering the temperature setpoint of the most heated winding point of the cooled power transformer;

- an interface for connecting moisture and gas oil sensors and is configured to take their readings into account when determining the permissible thermo-hydraulic state of a power transformer;

- an interface for connecting an ambient temperature sensor and is configured to take into account its readings when determining the performance of air coolers;

- an interface for connecting sensors of pressure and humidity of the ambient air and is configured to take into account their readings when determining the performance of air coolers;

- an interface for connecting a temperature sensor of the upper layers of oil and is configured to determine the specified temperature as one of the parameters of the permissible thermo-hydraulic state of the transformer and to issue a signal to the operator about its inconsistency with the readings of the specified sensor;

- an interface for connecting a temperature sensor of the upper layers of oil and is configured to determine the specified temperature as one of the parameters of the permissible thermo-hydraulic state of the transformer, calculate the deviation of this temperature from the readings of the specified sensor and regulate the performance of the coolers, aimed at reducing the specified deviation.

Another development of the invention is that the input interface for connecting sensors of the electrical state of the transformer is configured to connect an indicator of the position of the voltage regulator under load, which is equipped with a power transformer, and the digital processing unit is configured to take into account the readings of this indicator when determining the permissible thermo-hydraulic state of the power transformer.

The implementation of the invention in view of its development

The drawing shows the inventive control device.

It contains a digital processing unit 1, equipped with an input interface 2 for connecting sensors of the electrical state of the transformer, for example, one or more sensors 3 of the load current, and an output interface 4 for issuing control signals for adjustable drives of oil and air coolers of the specified transformer.

In special cases, block 1 can be equipped with:

- an interface 5 for entering the setpoint _{Tnt extra} for temperature _{Tnt the} most heated winding point of the cooled power transformer;

- interface 6 for connecting sensors 7 and 8 of moisture and gas oil content, respectively;

- interface 9 for connecting the sensor 10 temperature T _OS environment;

- an interface 11 for connecting sensors 12 and 13 of pressure and humidity, respectively;

- an interface 14 for connecting a temperature sensor 15 T of the upper oil layers and is _configured to determine the specified temperature as one of the parameters of the permissible thermo-hydraulic state of the transformer and to issue a signal to the operator about its inconsistency with the readings of the sensor 15;

- an interface 14 for connecting a temperature sensor 15 T of the upper oil layers and is _configured to determine the specified temperature as one of the parameters of the permissible thermo-hydraulic state of the transformer, calculate the deviation of this temperature from the readings of the sensor 15 and control the performance of the coolers, aimed at reducing the specified deviation.

In addition, the input interface 2 of block 1 can be configured to connect an indicator 16 of the position of the voltage regulator under load, which is equipped with a cooled power transformer.

All interfaces of unit 1, designed to connect analog sensors, are equipped with analog-to-digital converters, or for this purpose, in block 1, one multichannel converter can be used.

Block 1 is based on a digital controller programmed to implement the functionality that is described in detail below.

Before starting work, a work program is loaded into the controller’s memory that corresponds to this particular construct of the cooled transformer and this particular construct of its cooling system. The work program can be obtained, for example, on the basis of the mathematical modeling technique described in the article "Methodological approaches to cfd-modeling of thermal conditions of power oil transformers" published in the journal "Industrial Heat Engineering", 2008, v. 30, No. 6, p. 57-66.

The _setpoint T _{nnt extra} can be taken into account in the loadable work program or entered via interface 5. If there are sensors 7 and 8 of moisture and gas content of oil connected to interface 6, the set T _{nnt extra} by temperature T _nnt can be automatically determined by block 1 taking into account the readings these sensors.

The device operates as follows.

For each specific current electrical state detected by sensors 3 and indicator 16 connected to interface 2, block 1 determines (i.e., calculates and / or retrieves from its stored data array obtained by preliminary calculation) many sets of parameters, each of which characterizes one of the permissible thermohydraulic states of the power transformer (i.e., states that ensure the temperature _Tnt , not exceeding the setpoint _Tnt , taken into account in the loadable work program, data via interface 5 or calculated taking into account the readings of sensors 7 and 8) in combination with possible combinations of air and oil cooler capacities ensuring the maintenance of this acceptable state.

In addition, for each of these sets of parameters characterizing the possible state of the cooled transformer, block 1 determines the power of active losses in the transformer (taking into account the temperature dependence of the resistances of its windings) and the electric power spent on cooling the transformer for every possible combination of air and oil cooler capacities .

Then block 1 calculates the sums of the indicated capacities (characterizing the total energy costs), finds the combination of air and oil cooler capacities corresponding to the minimum sum, and generates corresponding control signals through the output interface 3.

The data processing algorithm in block 1, which allows to implement the described functionality of the claimed invention, is illustrated by interconnected elements of digital processing, represented by dashed lines in the drawing.

Element 17 denotes the first digital model - the model of a transformer having this construct. The first model allows you to determine the set of i-sets of parameters (including temperature T _nt ) that characterize the thermohydraulic state of the transformer, permissible for its current electrical state, determined by the readings of sensors 3 and 16. The admissibility of each ith thermohydraulic state is checked by comparing the values of T _nt i-th set of parameters with the selected or calculated according to the readings of sensors 7 and 8 _setting T _{nt extra} , which should not be exceeded. In the case of a finite number of _preset settings T _{nnt extra} for temperature T _{nnt, the} selection of permissible thermo-hydraulic states can be performed previously and taken into account in the downloaded program. This processing option (with pre-performed selection of states permissible at a temperature of T _nt ) is _shown in the drawing.

The parameters determined by the first digital model, designated as element 17, and characterizing the ith thermohydraulic state of the transformer, include the flow rate Q _{m of} oil, the difference ΔN _{m of} oil pressure at the inlet and outlet of the transformer tank, the temperature T _{m in} oil input transformer tank, as well as temperature T _{vsm. calculation of the} upper layers of oil.

In addition, for each i-th thermohydraulic state, the element 17 determines the amount of losses in the transformer windings [P _sweat ] _i .

The parameters [Q _m , ΔN _m , T _m.in. ] _i obtained as a result of the operation of the element 17 are further processed using the second digital model, designated as element 18, which reflects the operation of the cooling system having this construct.

For each i-th set of parameters obtained in the transformer model (element 17), the second digital model (element 18), determines the i-th pair of values of the rotational velocity of oil and air coolers and coolers corresponding to this velocity output [P _{OHL] i.} In this case, the second digital model (element 18) can take into account the readings T _{os of the} sensor 10 coming through the interface 9, and the readings of the sensors 12 and 13 coming through the interface 11, or use predicted, for example, averaged values of the corresponding parameters.

Next, the total power calculated [P _{Σ] i} = [P _{pot.tr] i} + [P _{OHL] i.} By sequentially comparing [P _∑ ] _{i with} each other, element 19 finds the number i _min for the minimum total power P _{∑ min} and transfers it to element 20. Element 20 captures the pair of rotation speeds of the coolers [n _m , n _air ] _immin corresponding to i _min . Based on these speed values, corresponding control signals for controlled cooler electric drives can be generated and output via interface 4.

In cases where additional regulation of cooling is used using temperature feedback T _cfm , measured by a sensor 15 connected to interface 14, the value of i _min also goes to element 21. Element 21 captures the temperature value of the upper layers of oil from a number of values [ T _vsm ] _i issued by element 17, which corresponds to i _min . In the drawing, the temperature recorded by element 21 is indicated by T _{vsm calc} .

The difference ΔT _vsm = T _{vsm calculation} -T _{vsm ism} can be used by processing element 22 to further control the performance of coolers, which can be performed, for example, using proportional, integral and differential units (PID control).

Formed by the element 22 as a result of the above digital processing, the values of the control signals of the rotational speeds of the coolers are compared in block 1 with the set thresholds. In cases where one or both rotational speeds are below the threshold, one of the coolers (oil pump or fan) is taken out of operation, and block 1 re-determines the combination of capacities (rotational speeds) for the coolers that remain in operation.

As can be seen from the above, the claimed device can be implemented with the achievement of the specified technical result on the basis of a programmable digital processing unit equipped with the necessary interfaces.

Comparative calculations showed that the use of the invention instead of a prototype for controlling the cooling of one transformer AODTsTN 417000/750/500/10 using the cooling system DC 180 (designation according to GOST 11677-85 "Power transformers. General technical conditions") will reduce the total cost of electricity by cooling of the power transformer and losses in it by 10-12%, which will give annual energy savings of 25.0-30.0 thousand kW × hour.

Claims (8)

1. The control device of the cooling system of an oil-filled power transformer, containing a digital processing unit, equipped with an input interface for connecting sensors of the current electrical state of the transformer and an output interface for generating control signals for the adjustable drives of oil and air coolers, and configured to determine the permissible thermo-hydraulic by the readings of these sensors conditions of power transformer and oil and air performance x coolers necessary to maintain the specified acceptable state, characterized in that the digital processing unit is configured to determine a plurality of combinations of the indicated capacities, generate control signals corresponding to the combination of capacities, minimizing the total energy consumption for cooling the power transformer and losses in it, decommissioning one of the coolers, if, in accordance with the generated control signal, its performance is lower than the specified horn, and re-determining a minimizing combination productivities for coolers, remaining in operation. 2. The device according to claim 1, characterized in that the digital processing unit is equipped with an interface for entering the setpoint for the temperature of the most heated winding point of the cooled power transformer. 3. The device according to claim 1, characterized in that the digital processing unit is equipped with an interface for connecting moisture and gas oil sensors and is configured to take their readings into account when determining the permissible thermo-hydraulic state of a power transformer. 4. The device according to claim 1, characterized in that the digital processing unit is equipped with an interface for connecting an ambient temperature sensor and is configured to take into account its readings when determining the performance of air coolers. 5. The device according to claim 1, characterized in that the digital processing unit is equipped with an interface for connecting pressure sensors and humidity of the ambient air and is configured to take their readings into account when determining the performance of air coolers. 6. The device according to claim 1, characterized in that the input interface for connecting sensors of the current electrical state of the transformer is configured to connect an indicator of the position of the voltage regulator under load, which is equipped with a power transformer, and the digital processing unit is configured to take into account the readings of this indicator when determining permissible thermo-hydraulic state of the power transformer. 7. The device according to claim 1, characterized in that the digital processing unit is equipped with an interface for connecting a temperature sensor of the upper layers of oil and is configured to determine the specified temperature as one of the parameters of the permissible thermo-hydraulic state of the transformer and to issue an operator with a signal about its inconsistency with the readings of the specified sensor. 8. The device according to claim 1, characterized in that the digital processing unit is equipped with an interface for connecting a temperature sensor of the upper oil layers and is configured to determine the specified temperature as one of the parameters of the permissible thermo-hydraulic state of the transformer, calculate the deviation of this temperature from the readings of the specified sensor and control cooler performance aimed at reducing this deviation.

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