RU118481U1 - DEVICE FOR DETERMINING THE ACCEPTABLE DURATION OF OVERLOADING AND MONITORING THE EFFICIENCY OF THE COOLING SYSTEM OF A POWER OIL TRANSFORMER - Google Patents

Abstract

A device for determining the permissible overload duration and monitoring the efficiency of the cooling system of a power oil-filled transformer, containing a transformer winding current sensor, an ambient temperature sensor, an upper oil layer temperature sensor, an oil moisture sensor, an oil temperature sensor in a moisture sensor, an analog-to-digital converter, to the corresponding the inputs of which are connected to the outputs of these sensors, and the computing unit, connected by the first digital interface to the output of the analog-to-digital converter and equipped with the second and third digital interfaces for communication with the operator's terminal and the transformer control and monitoring system, respectively, while the computing unit is configured to receive the third digital interface of information on the current and maximum available number of switched on coolers, calculation, taking into account the received information, of the current values of the efficiency coefficient of coolers, the predicted value of the cooling efficiency for the overload mode, the predicted value of the allowable overload duration and the transfer of the calculated values to the transformer control and monitoring system.

Description

Technical field

The utility model relates to the electric power industry and can find application in automated control systems and diagnostics of transformer equipment of electrical substations.

State of the art

Power transformers and autotransformers with oil-air or oil-water cooling are one of the most expensive types of electrical equipment of electrical substations. In such transformers, the active part (magnetic core and windings having pulp and paper insulation) is immersed in an insulating liquid - transformer oil. As a result of natural convection or forced circulation, the oil passes through the cooling channels in the windings and the magnetic circuit of the transformer, ensuring the removal of heat generated by losses in the windings and the magnetic circuit. For safe operation of the transformer, it is important that the temperature of the winding in the hottest place (the so-called "most heated point", NNT) does not exceed permissible values. Power transformers are designed in such a way that at an electric load not exceeding the rated power of the transformer, the temperature of the NNT is below the maximum permissible. At the same time, the operating conditions of power systems require in some cases to transmit power exceeding the nominal value through a transformer. The magnitude and duration of the permissible overload is determined by the current (initial) thermal state of the transformer, and the dependence of the permissible overload time on the overload coefficient of each winding, current oil temperature, and ambient temperature is quite complex and non-linear. At the same time, it is desirable that the power system dispatcher, when managing power flows in the system, especially in emergency situations, have information on how much and for how long each transformer can be overloaded without increasing the risk of damage or an unacceptable reduction in service life. The proposed device is intended for receiving and transmitting to the operator of the power system with predictive information about the transformer overload levels and the allowable overload time, acceptable at each moment of time, depending on its size. In case of violation of the conditions acceptable for the thermal state of the transformer, the device should issue a warning or alarm. Known technical solutions for a similar purpose, for example:

1. Patent RU 2242830, IPC H02H 7/04, H02H 6/00;

2. Patent EP 1085534 B1, IPC H01F 27/12;

3. Patent US 4148086, US C1. 361/37, IPC H01H 37/0, H02H 7/00;

4. Patent US 5225992, US C1. 364/483, IPC H02H 7/00;

5. Patent US 6424266, US C1. 340/588, IPC G08B 17/00;

6. Patent US 6727821 B2, US C1. 340/588, IPC G08B 17/00;

7. Patent US 6906630 B2, US C1. 340/646, IPC G08B 21/00;

8. Application RU 2010134228/28 (048622), IPC G01R 31/02 (2006/01), decision on the grant of a patent dated 05/30/2011, publication of 02/27/2012.

Closest to the alleged invention (its prototype) is a technical solution according to the application RU 2010134228/28 (048622), publication of 02.27.2012.

The prototype device comprises a transformer winding current sensor, an ambient temperature sensor, a top oil temperature sensor (BCM), an oil moisture sensor, an oil temperature sensor in a humidity sensor, an analog-to-digital converter, to the corresponding inputs of which the outputs of these sensors are connected, and a computational a device connected by the first interface to the output of the analog-to-digital converter and equipped with a second digital interface for communication with the operator terminal. The computing device calculates and transmits to the operator terminal the values of the permissible transformer overload time, depending on its current thermal regime, oil moisture level in the transformer tank and the predicted load level of all windings.

The disadvantage of the prototype is as follows.

When performing a predictive calculation of the temperature of the HSR, it is implicitly assumed that when overloading, all coolers in the transformer cooling system are turned on, and at the same time they have a nominal thermal conductivity from oil to ambient air. However, in practice, with old transformers, the heat transfer of coolers can be significantly reduced due to surface contamination, fluff and plant leaves getting into the cooling channels of radiators, lowering the supply voltage of electric motors, and the wear of their bearings. In addition, part of the electric motors of the oil pumps and blower fans may be malfunctioning and will not be turned on. In such a situation, the overall efficiency of the cooling system in the overload mode can be significantly lower than the calculated one, and the forecast will give overestimated values of the permissible level and time of the overload.

Utility model creature disclosure

The purpose and technical result of the utility model is to increase the operational reliability of transformer equipment due to a more reliable determination of the allowable size and duration of the overload of a power oil-filled transformer, taking into account the real effectiveness of its cooling system.

The subject of the utility model is a device for determining the permissible overload duration and monitoring the efficiency of the cooling system of a power oil-filled transformer, containing a transformer winding current sensor, an ambient temperature sensor, an oil temperature sensor, an oil humidity sensor, an oil temperature sensor in a humidity sensor, and an analog-digital a converter, to the corresponding inputs of which the outputs of the indicated sensors are connected, and a computing unit connected by the first digits interface to the output of the analog-to-digital converter and equipped with a second and third digital interfaces for communication with the operator terminal and with the transformer control and monitoring system, respectively, while the computing unit is configured to receive information on the current and maximum available number of coolers turned on on the third digital interface calculation taking into account the received information of the current values of the coefficient of efficiency of coolers, the predicted value of the coefficient of efficiency of coolers REPRESENTATIONS for overload mode, predictive values of the allowable duration of an overload and transmitting calculated values to the control and monitoring of a transformer.

The technical result is achieved by introducing into the device a third digital interface for communication with a transformer control and monitoring system and executing a computing unit with the possibility of receiving information on the current and maximum available number of turned-on coolers through the third digital interface, calculating, taking into account the received information, the current values of the cooler efficiency coefficient values of the coefficient of cooling efficiency for overload mode, the predicted value of the permissible length nosti overloading and transmit calculated values to the control and monitoring of a transformer.

Utility Model Implementation

Figure 1 shows a block diagram of the proposed device.

The figure shows an ambient temperature sensor 1a, an upper oil temperature sensor 1b, current sensors 2a, 2b in different windings of a controlled power transformer, an oil moisture sensor 3, a temperature sensor 4 for measuring oil temperature in a humidity sensor 3, an analog-to-digital converter 5 with inputs 6a ... 6e, to which the outputs of these sensors are connected, and a computing unit 7, to which an analog-to-digital converter 5 is connected via the first digital interface 8. The computing unit has discrete outputs 9 and 10 for issuing, respectively, warning and alarm signals about unacceptable overload of the controlled power transformer, a second digital interface 11 for communication via line 12 with the operator terminal 13, and a third digital interface 14 for communication with the transformer control and monitoring system 15.

The computing unit 7 is configured to receive information on the current and maximum available number of coolers turned on via interface 14, to calculate, taking into account the received information, the current values of the efficiency coefficient of the coolers, the predicted value of the coefficient of cooling efficiency for the overload mode, the predicted value of the allowable overload duration, and the transmission of the calculated values into the transformer control and monitoring system 15.

Information on the permissible transformer overload time, depending on its current thermal regime and humidity level, is transmitted to the operator terminal 13 through the interface 11

The proposed device operates as follows.

At predetermined time intervals Δt, the computing unit 7 takes from the unit 3 the readings of the sensors 1a, 1b, 2, 9, and 10.

The measured value θ _{o of the} temperature of the upper layers of oil is compared with the user-specified first and second limit levels θ _o1 and θ _o2 . If the value of θ _o exceeds the first limit level θ _o1 , a warning signal is issued to the digital output 9. If the value of θ _o exceeds the second limit level θ _o2 , an alarm is issued to the digital output 10.

Using the measured values of θ _o and load factors of the individual windings, the current values Θ _{H of the} temperature of the most heated points of all windings are calculated by the ratios

Where

Δθ _h - excess temperature of the warmest point of the winding over

the temperature of the upper layers of oil,

Δθ _hr is the value of Δθ _h at the rated load of the transformer,

K is the load factor of the winding, equal to the ratio of the current value of the load to its nominal value,

k ₂₁ , k ₂₂ - constant coefficients (transformer parameters),

τ ₀ - thermal time constant of the transformer in oil,

τ _w - thermal time constant of the transformer winding

y is an exponent for determining the dependence of the temperature rise of the most heated winding point over the temperature of the upper layers of oil with a change in the load factor K.

The obtained values of the NNT temperatures of all windings are compared with the user-specified first and second limit levels Θ _H1 and Θ _H2 . If the value Θ _H exceeds the first limit level Θ _H1 , an alarm signal is output to digital output 9. If the value Θ _H exceeds the second limit level Θ _H2 , an alarm is issued to digital output 10.

From the measured values of w _{and the} relative humidity of the oil and the temperature Θ _and oil in the moisture meter, the absolute moisture of the oil in the transformer tank, the relative humidity of the oil in the NNT zone for all controlled windings, the limit value W _{rel∞ of the} relative humidity of the solid insulation and the critical temperature Θ _Nmax NNT are _determined by the relations (5) ... (9):

Absolute oil moisture in the transformer tank:

where C _a (Θ) is the ultimate solubility of moisture in the oil used at a temperature of Θ.

Relative oil humidity in the NNT zone for all controlled windings

limit value of relative humidity of solid insulation for each of the windings W _rel∞ :

,

where

and the coefficients a, b, c, d, f, g, h depend on the type of insulation used.

The current value of the relative humidity of the insulation is determined taking into account the inertia of the process, with a time constant

Based on the calculated values of the relative humidity of the solid insulation of the windings, the critical temperatures Θ _Nmax NNT are _calculated according to the condition of the formation of bubbles. With a humidity of solid insulation in the NNT zone equal to 0.5% or less, Θ _Hmax is 160 ° C, with a moisture content of 7% or more - 80 ° C. Between these two points, the dependence of Θ _Hmax on humidity is piecewise linear.

The calculated temperatures Θ _H NNT of all windings and the critical temperatures Θ _Hmax obtained for them are _compared . If the temperature of the NNT of any of the windings exceeds a critical value of Θ _Hmax , a warning signal is issued to digital output 9 and the countdown of the first time delay T1 begins.

If the temperature of the NNT of any of the windings exceeds a value (Θ _Hmax + 10 ° C), the second delay time T2 begins.

If the NNT temperature of any of the windings exceeds a value (Θ _Hmax + 30 ° C) or the time T1 reaches a preset level T1 _max , for example 30 minutes, or the time T2 reaches a preset level T2 _max , for example 10 minutes, an alarm signal is output to a digital output 10.

Using the values of the current number n of included coolers and their maximum available amount n _max obtained via the interface 14, the coefficient of cooling efficiency decrease is determined by the relation (10)

where α is the coefficient of change in the resistivity of copper with temperature (α = 0.00425 1 / ° C), υ _h , υ _hr is the excess of the winding temperature over the oil temperature and its value in the nominal mode,

υ _h = K ^y · υ _hr ,

R is the ratio of load losses in the transformer windings at rated load P _kr to idle losses P _x ,

b is the heat transfer coefficient of the transformer tank, referred to the nominal heat transfer of one cooler,

and by expression (11) - the value of p _r - for the predictive calculation :

The value of p _r via interface 14 is transmitted to the transformer control and monitoring system 15.

For each ith value from a series of values of the overload coefficient K _i , the integration of equation (12) for the HSR temperature is carried out

where θ _a is the ambient temperature,

Δθ _or - the excess of the temperature of the upper layers of the oil over the ambient temperature at the rated load of the transformer,

k ₁₁ - constant coefficient (transformer parameter),

x is an exponent for determining the excess of the temperature of the upper layers of the oil over the ambient temperature with a change in the load coefficient K,

and equations (1) ... (4) for the hottest winding (predictive modeling of thermal conditions).

The rest of the predictive calculation and the formation of the results are carried out similarly to the prototype device.

Thus, the description shows that in the proposed device, the predicted values of the temperature of the upper layers of oil and the temperature of the most heated points of the windings are developed taking into account the real efficiency of the transformer cooling system and, therefore, are more reliable.

Claims (1)

A device for determining the permissible duration of the overload and monitoring the effectiveness of the cooling system of a power oil-filled transformer, comprising a transformer winding current sensor, an ambient temperature sensor, an upper oil temperature sensor, an oil humidity sensor, an oil temperature sensor in a humidity sensor, an analog-to-digital converter, to the corresponding the inputs of which are connected the outputs of these sensors, and a computing unit connected by the first digital interface to the output of analog a frame converter and equipped with a second and third digital interfaces for communication with an operator terminal and a transformer control and monitoring system, respectively, while the computing unit is configured to receive information on the current and maximum available number of coolers turned on via the third digital interface, taking into account the received information of the current values of the coefficient of efficiency of coolers, the predicted value of the coefficient of efficiency of cooling for the overload mode, forecast Nogo values permissible overload duration and transmitting calculated values to the control and monitoring of a transformer.