RU2136099C1 - Device for checking and protecting transformer windings against deformation under short-circuit conditions - Google Patents

Abstract

FIELD: on-line checking of heavy-power transformer windings for condition. SUBSTANCE: device has three-phase power supply, three-phase circuit breaker, three-phase transformer under check, current transformers, potential transformers, resistive load, frequency meter, primary-to-secondary voltage reducing unit, voltage difference calculating unit, mean voltage calculating unit, current derivative determining unit, unit calculating voltage drop across resistor, resistance setting unit, inductance calculating unit, unit for reducing inductance to rated frequency, cycle mean inductance calculating unit, deviation determining unit, inductance setting unit, inductance deviation checking unit, and protective unit. EFFECT: provision for on-line monitoring and protecting transformer windings against deformation and other kinds of damage. 1 dwg

Description

 The invention relates to electrical engineering and can be used for operational monitoring of the state of the windings of powerful power transformers during operation without disconnecting them from the network.

 As an analogue of the invention can be considered a device that monitors the internal windings of power transformers during operation under operating voltage. In this similar device, primary, secondary voltage, secondary current and frequency are measured. The main parameter in [1], which determines the state of the windings, is the value of short circuit resistance (SC), calculated as the product of the ratio of the difference between the winding voltage vectors and the magnitude of currents and the measured frequency to the reference. The disadvantages of the analogue [1] are, firstly, a very complex system for measuring primary and secondary voltage using four intermediate transformers and, secondly, the fact that the resistance value is a very inaccurate parameter, which includes the active component of the resistance, changing depending on the temperature.

 Another analogue closer to the proposed invention is a device [2] (prototype). The prototype [2] is designed to control and protect the transformer windings during electrodynamic tests. The prototype measures primary and secondary voltage, secondary current. The main parameters by which the state of the protected object is controlled are the transformer inductance value, defined as the ratio of the average voltage to the derivative of the current; the average value of the inductance over the period and the deviation of the inductance from the reference value.

 The purpose of the invention is the provision of continuous monitoring of the windings of the power transformer during operation without disconnecting from the network and the inclusion of protection in the event of the onset of deformation of the transformer windings or their damage.

 The technical result that can be achieved by using the invention is to prevent emergency failures of transformer equipment or to reduce the extent of possible damage.

 The drawing shows a schematic diagram of a device for monitoring and protecting transformer windings from deformation during short circuits.

 The device comprises a three-phase power supply 1, a three-phase protective switch 2, a primary winding 3 of a controlled power transformer, a three-phase controlled power transformer 4, a secondary winding 5 of a controlled power transformer, a three-phase primary voltage transformer 6, the first, second and third current transformers 7, first, second and the third transformers 8 of the secondary voltage, a three-phase active load 9, a frequency meter 10, a block 11 of bringing the primary voltage to the secondary, block 12 computing voltage difference calculating unit, average voltage value calculating unit 13, current derivative unit 14, active resistance calculating unit 15, active resistance setting unit 16, inductance calculating unit 17, inductance value adjusting unit 18, average value calculating unit 19 inductance for the period, the deviation calculation unit 20, the inductance setting unit 21, the inductance deviation control unit 22, the protection unit 23 of the monitored power transformer.

 Each phase of the power supply 1 through a three-phase protective switch 2 is connected to the corresponding first terminal of the primary winding 3 of the three-phase controlled transformer 4, the second terminals of the primary windings of the three-phase controlled transformer are connected to a common terminal, the corresponding first conclusions of the secondary winding 5 of the three-phase controlled transformer 4 are interconnected according to the scheme "star", connected to the second terminals of the corresponding secondary winding 5 through the corresponding current meters 7, In the form of current transformers, the corresponding first terminals of the secondary voltage transformers 8 and the three-phase active load 9, which is connected according to the star circuit with a common ground point. The input terminals of the three-phase transformer 6 of the primary voltage are connected to the corresponding phases of the three-phase power supply 1, and the output terminals of the transformer 6 are connected respectively to the first, second and third inputs of the block 11 for bringing the primary voltage to the secondary. The first, second and third outputs of unit 11 are connected to the first, second and third inputs of the inductance deviation control unit 22 through series-connected units 12, 13, 17, 18, 19 and 20. The first, second and third inputs of the voltage difference calculation unit 12 are connected to the corresponding secondary terminals of voltage transformers 8.

 The fourth, fifth and sixth inputs of the inductance calculation unit 17 are connected respectively to the first, second and third outputs of the current derivative unit 14, the first, second, third, fourth, fifth and sixth inputs of which are connected respectively to the corresponding terminals of the first, second and third current transformers 7 . The first, second, third, fourth, fifth and sixth inputs of the resistance drop calculation unit 15 of the active resistance, the seventh, eighth and ninth inputs are also connected to the corresponding terminals of the current transformers 7 which are connected to the corresponding outputs of the block 16 of the active resistance setting. The first, second and third outputs of the resistive voltage drop calculating unit 15 are connected to the seventh, eighth and ninth inputs of the inductance calculating unit 17, respectively.

 The fourth and fifth inputs of the block 18 to bring the inductance value to the nominal frequency are connected respectively to the first and second terminals of the frequency meter 10, which is connected between the first terminals of the second and third current transformers. The first, second and third outputs of the inductance setting unit 21 are connected respectively to the corresponding fourth, fifth and sixth inputs of the deviation calculation unit 20.

 The first output of the inductance deviation control unit 22 is connected to the input of the protection unit 23 of the monitored power transformer 4. The second and third outputs of unit 22 are connected respectively to the fourth input of the average voltage value calculation unit 13 and the seventh input of the current derivative calculation unit 14. The control output of block 23 is connected to the control input of a three-phase protective switch 2.

 The device operates as follows. Continuous monitoring of the state of the windings of the monitored power transformer 4 is provided by constantly determining the value of the deviation of the inductance in block 20 from the basic value of the inductance, which is taken from the block 21 of the inductance setting.

During operation of a three-phase controlled power transformer 4 for a three-phase active load 9, the primary voltage U _{1 is} measured using the primary voltage transformer 6. The signal from the transformer 6 is fed to the input of the block 11 bringing the primary voltage to the secondary. In block 11, the reduced to the secondary value of the primary voltage U ₁ ^* = U ₁ / K _t , where K _t is the known specified value of the transformation coefficient of the power transformer 4, is calculated.

The input of block 12 receives signals from transformers 8 of the secondary voltage and signals from the output of block 11. In block 12 of the calculation of the difference of the voltages reduced to the secondary side, ΔU ^* = U $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ -U ₂ , where U ₂ is the value of the secondary voltage measured by transformers 8.

где Δu^*j - значения разности приведенных напряжений на трансформаторе 4;
t₁ и t₂ - временные границы интервала разбиения.In block 13, the calculation of the average voltage value is calculated at a given time interval

where Δu ^* j are the values of the difference of the reduced voltages on the transformer 4;
t ₁ and t ₂ are the time boundaries of the partition interval.

где ij - значение тока во вторичной обмотке 5 контролируемого трансформатора 4, измеренное трансформаторами тока 7.In block 14 for calculating the derivative of the current, the increment in current is calculated for a given time interval

where ij is the current value in the secondary winding 5 of the controlled transformer 4, measured by current transformers 7.

В блоке 18 приведения значения индуктивности к номинальной частоте вычисляется мгновенное значение индуктивности, приведенное к номинальной частоте

где f_изм - измеренное частотомером 10 значение частоты,
f_ном - номинальное значение частоты (f_ном = 50 Гц).In block 15, the voltage drop across the active resistance of the transformer is calculated as the product ij • R, where ij is the current value in the secondary winding 5 of the controlled transformer 4, R is the set value of the active resistance of the transformer, which is taken from block 16 and is determined by calculations and the results of a preliminary experiment . In block 17 calculating the inductance determines the instantaneous value of the inductance at a given time interval

In block 18 of bringing the inductance value to the nominal frequency, the instantaneous inductance value reduced to the nominal frequency is calculated

where f _ISM - measured by the frequency counter 10 frequency value,
f _nom - nominal frequency value (f _nom = 50 Hz).

где N - число интервалов разбиения.In block 19, the average value of the inductance for each period is calculated

where N is the number of partition intervals.

где L_ср - среднее значение нидуктивности за период:
L_oj - значение уставки индуктивности трансформатора, определяемое расчетами и по результатам предварительного эксперимента.In block 20 calculating the deviation is a comparison of the values of L _cf. for the period with the setting value L _oj from block 21 and their difference is calculated

where L _cf - the average value of the inductance for the period:
L _oj is the value of the transformer inductance setpoint, determined by calculations and by the results of a preliminary experiment.

 In the event of initial deformations, as well as in the case of an internal winding circuit in the transformer windings, a developing increase or decrease in ΔL from period to period occurs, which accompanies irreversible destruction of the windings of the controlled power transformer 4. At the same time, the signal from the inductance deviation control unit 22 23 protection, where a signal is formed to trip the protective switch 2. This stops the process of destruction of the windings of the transformer 4. Accounting for the value of active s disobedience transformer unit 15, and then in calculating the inductance at block 17 allows to increase the accuracy of measurement of the inductance of the transformer and to improve reliability of the device as a whole.

During operation, the clock signals from the inductance deviation control unit 22 synchronize the measurement of the di / dt and u _cp values with the corresponding sampling step.

 The proposed device allows you to continuously monitor the status of the windings of power transformers without disconnecting them from the network, as well as to protect them in the event of deformation of the windings or their damage. This increases the uninterrupted power supply of consumers of electric energy.

List of sources for consideration during the examination
1. Konov Yu.S., Tsurpal S.V. The method of controlling the internal windings of power transformers. A.S. USSR N 1221620, class G 01 R 31/02, 1986

 2. Schlegel O. A., Khrennikov A.Yu., Zhnjakin O. V. Device for testing transformers with short circuit currents. Auth. testimonial. USSR N 1821759, class G 01 R 31/02, 1993, Bull. N 22 (prototype).

Claims (1)

 A device for monitoring and protecting transformer windings from winding deformations during short circuits, containing a three-phase power supply, each phase of which is connected to the first terminals of a three-phase protective switch, the second terminals of the primary winding of a three-phase controlled transformer are connected to a common terminal, the outputs of current-measuring elements included in the circuit of each phase secondary windings connected to the inputs of the derivative current calculation unit, the outputs of which are connected to the corresponding inputs of the unit calculating the inductance, the first, second and third inputs of which are connected to the corresponding outputs of the average voltage value calculation unit, the outputs of the average inductance calculation unit for the period are connected to the corresponding inputs of the deviation calculation unit, the other inputs of which are connected to the outputs of the inductance set point, the outputs of which are connected to inputs of the inductance deviation control unit, the first and second outputs of which are connected respectively to the seventh input of the derivative calculation unit current and the fourth input of the average voltage value calculation unit, and the third with the input of the protection unit, the output of which is connected to the control input of the three-phase protective switch, the input terminals of the three-phase primary voltage transformer are connected to the corresponding phases of the three-phase power supply, characterized in that they are additionally introduced into it frequency meter, unit for bringing primary voltage to secondary, unit for calculating the voltage difference, reduced to the side of the secondary voltage, unit is calculated I drop the voltage at the active resistance of the transformer, the unit for setting the active resistance of the transformer, the unit for bringing the inductance to the nominal frequency and the active load, the current measuring element is made in the form of a current transformer, the first, second and third inputs of the unit for bringing the inductance to the nominal frequency are connected to the corresponding outputs inductance calculation unit, the fourth and fifth inputs of the inductance value reduction unit to the nominal frequency are connected respectively with the first and second outputs of the frequency meter, which is connected between the first outputs of the second and third current transformers, the first, second and third outputs of the unit for bringing the inductance value to the nominal frequency are connected to the corresponding inputs of the unit for calculating the average value of the inductance for the period, the first, second and third inputs of the block bringing the primary voltage to the secondary are connected respectively to the output terminals of the three-phase transformer of the primary voltage, the first, second and third inputs of the calculation unit the voltage differences are connected respectively to the outputs of the primary voltage reduction unit to the secondary, and the fourth, fifth and sixth inputs of the voltage difference calculation unit are connected respectively to the outputs of the first, second and third secondary voltage transformers, the first, second and third outputs of the voltage difference calculation unit the inputs of the unit for calculating the average voltage value, the first, second, third, fourth, fifth are connected to the corresponding terminals of the current transformers the sixth inputs of the unit for calculating the voltage drop across the active resistance of the transformer, the seventh, eighth and ninth inputs of which are connected to the corresponding outputs of the unit for setting the resistance of the transformer, the first, second and third outputs of the unit for calculating the voltage drop across the active resistance of the transformer are connected respectively to the additional seventh, eighth and the ninth inputs of the inductance calculation unit, the first conclusions of the secondary winding of a three-phase controlled transformer are connected between I mean, according to the “star” scheme, the second terminals of the corresponding secondary winding are connected through the corresponding current transformers to the first terminals of the secondary voltage transformers and connected to the active load, and the first terminals of the primary winding of the three-phase controlled transformer are connected to the second terminals of the three-phase protective switch.