CN114221299A - Electroslag furnace transformer excitation surge current suppression device and method - Google Patents

Abstract

An electroslag furnace transformer excitation surge current suppression device and a method belong to the field of excitation surge current suppression devices and methods, are provided aiming at the problems of misoperation of a transformer protection device caused by excitation surge current, induced operation overvoltage and damage of electrical equipment and insufficient system safety caused by lack of trip protection, and comprise an isolation transformer, a first photoelectric isolation module, a second photoelectric isolation module, a communication module, a man-machine interface module and a main control module; the isolation transformer, the first photoelectric isolation module and the second photoelectric isolation module are respectively connected with the main control module, the communication module and the human-computer interface module are respectively connected with the main control module, the main control module calculates a switching-on angle and sends a switching-on instruction, and the overvoltage can be prevented from damaging electrical equipment through judging the voltage on a load side and a constant value and judging and protecting the system of the current on a power supply side and an overcurrent protection constant value, and the safety of the system is guaranteed through a tripping protection function.

Description

Electroslag furnace transformer excitation surge current suppression device and method

Technical Field

The invention relates to the technical field of magnetizing inrush current suppression, in particular to a device and a method for suppressing magnetizing inrush current of an electroslag furnace transformer.

Background

The induction coil with ferromagnetic magnetic circuit features that when applied voltage rises suddenly, it will produce magnetic bias and stable alternating magnetic flux, which can offset original residual magnetism and increase original residual magnetism to make the magnetic circuit enter saturation, and if the magnetic circuit is saturated, the exciting reactance drops rapidly to produce large value exciting surge current. Therefore, the level of residual magnetism caused by sudden rise of the externally applied voltage is controlled, the saturation of a magnetic circuit is avoided, the suppression of the magnetizing inrush current can be realized theoretically, and the magnetizing inrush current magnetic flux formula is as follows:

φ＝φ_m cosα-φ_m cos(ωt+α) (1)

in the formula (1), phi is the magnetizing inrush current magnetic flux, phi m is the main magnetic flux peak value, alpha is the initial phase angle of the voltage at the moment of closing, omega is the angular frequency, t is the period,

the bias phi P generated by the air-drop transformer is as follows:

φ_P＝φ_m cosα (2)

it can be seen that different initial closing phase angles correspond to different biases, and it can be seen that the bias has a maximum value in the positive and negative directions when α is 0 and α is pi, and has a minimum value when α is 90 degrees and α is 270 degrees.

At the instant of circuit breaker opening and closing operations, the phase angle of the system voltage is typically random and indeterminate. When some primary equipment is switched, if magnetic circuit saturation occurs, magnetizing inrush current can be generated. Not only can damage operating equipment, but also can cause misoperation of a transformer protection device, induce overvoltage operation, damage electrical equipment and seriously threaten the safety, reliability and stability of system operation.

The magnetizing inrush current is generated due to magnetic saturation of the iron core, the magnetizing inrush current usually starts to be generated after 1/4 cycles of power on, the maximum amplitude value may exceed several times or even dozens of times of rated current of the transformer, the duration is long, and the magnetizing inrush current is different from dozens of power cycles to dozens of seconds.

When the switch-on phase angle of the transformer at the switch-on moment is just closed at the position of the maximum current, the voltage just crosses zero, the magnetic flux is maximum because the magnetic flux lags the voltage by 90 degrees, and the magnetic flux in the iron core cannot be suddenly changed, so that direct current magnetic flux which is opposite to the direction of the alternating current magnetic flux and attenuates along with the time is generated to offset the alternating current magnetic flux. After half a period, the alternating current flux is opposite in direction, and at the moment, the alternating current flux is superposed with the direct current flux, so that the synthetic flux is far larger than the normal working flux of the transformer, the flux in the iron core is saturated, the no-load current of the transformer is increased rapidly to reach 6-8 times of the rated working current of the transformer, and the no-load current is called magnetizing inrush current. When the direct current magnetic flux is attenuated, the magnetic flux in the iron core is normal working magnetic flux, and the no-load current is normal exciting current.

The magnitude of the excitation inrush current is related to the switching-on instant voltage phase (the inrush current is the largest when the voltage is zero and the inrush current is the smallest when the voltage is the largest), the residual magnetism direction in the iron core and the rated working magnetic flux.

In actual production operation, the excitation inrush current of an electroslag furnace transformer is large and limited by a superior power grid, a relay protection fixed value cannot be set and cannot be adjusted and amplified, and thus, the step-by-step tripping is caused, and the step-by-step tripping is also an electric cabinet. The phenomena seriously affect the power supply safety of a superior power grid and the smelting quality of an electroslag furnace, so that the problem of excitation inrush current is urgently needed to be solved.

The starting point for solving the technical problems is as follows: 1. purchasing a transformer with small excitation inrush current; 2. adding a current-limiting reactor; 3. magnetizing inrush current limiting devices and equipment are developed.

Through technical and economic comparison, the excitation inrush current limiting device and the equipment are developed to have the technical and economic force far less than other two starting points, and the excitation inrush current limiting device is researched for solving the technical problems.

Disclosure of Invention

The invention provides a device and a method for inhibiting the magnetizing inrush current of an electroslag furnace transformer, aiming at limiting the magnetizing inrush current of the transformer within a certain range and preventing the fault-free tripping of a system caused by large magnetizing inrush current of the transformer, and can solve the problems of fault-free tripping of a power supply system caused by large magnetizing inrush current of the transformer, influence on normal production and smelting of the electroslag furnace, abnormal quality of finished products and large economic loss.

The first technical scheme adopted by the invention is as follows:

the excitation surge current suppression device of the electroslag furnace transformer comprises an isolation transformer, a first photoelectric isolation module, a second photoelectric isolation module, a communication module, a human-computer interface module and a main control module;

the isolation transformer, the first photoelectric isolation module and the second photoelectric isolation module are respectively connected with the main control module, and the communication module and the human-computer interface module are respectively connected with the main control module;

the isolation transformer is used for anti-interference processing;

the first photoelectric isolation module is used for converting signals into weak current signals;

the second photoelectric isolation module is used for boosting and outputting a signal;

the main control module is used for receiving the signals, carrying out corresponding processing and then outputting a control instruction;

the communication module is used for carrying out information communication with external equipment;

the man-machine interface module is used for inputting the closing time of the circuit breaker, the opening time of the circuit breaker, the closing target angle of the circuit breaker, the opening target angle of the circuit breaker and an overcurrent protection fixed value.

Furthermore, the communication module comprises a fourth photoelectric isolation module and a communication interface, and the communication interface is connected with the main control module through the fourth photoelectric isolation module;

the fourth photoelectric isolation module is used for filtering and resisting interference;

and the communication interface is used for connecting external equipment for communication.

Furthermore, the human-computer interface module comprises a keyboard and display module and a third photoelectric isolation module, and the keyboard and display module are connected with the main control module through the third photoelectric isolation module;

the keyboard and display module is used for inputting parameters and displaying information;

and the third photoelectric isolation module is used for filtering and resisting interference.

The second technical scheme adopted by the invention is as follows:

the method for inhibiting the magnetizing inrush current of the transformer of the electroslag furnace comprises the following steps:

step S1, the main control module calculates the closing angle and sends a closing instruction;

collecting and calculating power supply side voltage, power supply side current, load side voltage and load side current, calculating a pre-issued switching outlet instruction angle range by a main control module according to set breaker switching-off time and switching-on time, calculating a switching-on angle by the main control module and issuing a switching-on instruction;

step S2, based on the judgment of the load side voltage and the voltage fixed value and the judgment of the power supply side current and the overcurrent protection fixed value, the protection of the system is implemented;

and after the switch-on, the main control module judges whether the voltage of the load side is greater than a preset value, if not, the switch-on fails, the relevant information of the current switch-on failure is recorded, if yes, the main control module continuously judges whether the current of the power supply side is greater than an overcurrent protection fixed value, if yes, the device sends a protection tripping instruction, and if not, the switch-on succeeds and the relevant information of the current switch-on is recorded.

Further, in step S1, the main control module calculates a closing angle, and the specific process of sending the closing instruction is as follows:

the main control module receives power supply side voltage, power supply side current, load side voltage and load side current, and calculates amplitude values and phase angles of the power supply side voltage, the current, the load side voltage and the current in real time;

the main control module calculates the angle range of the pre-issued switching-on outlet instruction according to the set switching-off time and switching-on time of the circuit breaker,

the method comprises the steps that a main control module calculates a closing angle after receiving a closing starting signal and sends a closing instruction, the main control module judges whether the closing starting signal is an effective closing starting signal or not in real time, when the main control module judges that the effective closing signal exists, the main control module starts to detect the closing outlet angle, and when the closing outlet angle meets the angle range of a pre-issued closing outlet instruction, the main control module immediately sends the closing outlet instruction, wherein the effective closing starting signal means that the closing angle is 70-110 degrees, if the closing angle is not 70-110 degrees, the closing angle is recalculated, and if the closing angle is 70-110 degrees, the device sends the closing instruction.

Further, the closing angle is 90 degrees.

The invention has the beneficial effects that:

1. the problem of misoperation of a transformer protection device is solved by controlling switching-on, and the problem that normal production and smelting of an electroslag furnace are influenced due to fault-free tripping of a power supply system caused by large excitation inrush current of a transformer can be solved.

2. By utilizing the characteristic that the synchronous device can automatically capture the system side voltage when the power grids are parallel, and carry out synchronous switching-on, the programming design and the transformation are carried out, and the switching-on is carried out when the system voltage phase angle is 70-110 degrees, so that the amplitude of the magnetizing inrush current switching-on current can be controlled to be minimum.

3. The method captures the closing phase angle waveform and the magnetizing inrush current waveform of the transformer, controls the magnetizing inrush current within an expected range, achieves an expected effect, and avoids the override trip phenomenon of high-voltage equipment.

Drawings

FIG. 1 is a block diagram of an excitation inrush current suppression device for an electroslag furnace transformer according to the present application;

FIG. 2 is a flow chart of the method for suppressing magnetizing inrush current of an electroslag furnace transformer according to the present application;

FIG. 3 is a diagram showing the effect of the closing angle of the excitation inrush current suppression device of the electroslag furnace transformer when the device is not in operation;

FIG. 4 is a diagram showing the effect of the maximum current value in the first cycle when the excitation inrush current suppression device of the electroslag furnace transformer is not in operation;

FIG. 5 is a diagram showing the effect of the switching-on angle of the excitation inrush current suppression device of the electroslag furnace transformer during operation;

fig. 6 is an effect diagram of the maximum current value in the first cycle when the excitation inrush current suppression device of the electroslag furnace transformer works.

Detailed Description

When the synchronous devices are utilized to be parallel to a power grid, the current and voltage can be automatically captured, the system voltage phase angle is 70-110 degrees during switching-on, the magnetizing inrush current amplitude of the transformer is minimum, program design and transformation are carried out, a magnetizing inrush current suppression device is developed, and the switching-on phase angle is fixed between 70-110 degrees, so that the purpose of the invention is achieved. The switching-on moment is designed by considering the inherent action time of the switching-on of the circuit breaker. Description of the contemporaneous devices: in the operation process of the power system, a connecting line or a connecting transformer of the system is often required to be parallel to the power system, and the operation of combining the small system into the system through a switch device such as a breaker and the like becomes synchronous operation. The synchronization means that voltages on two sides of the switch equipment are equal in magnitude, frequency and phase, and the synchronization device is a special device for judging whether two sides of the circuit breaker reach synchronization conditions or not so as to determine whether switching-on and grid connection can be executed or not. The initial phase angle of the transformer at the moment of switching on the high-voltage switch is changed by utilizing the characteristic of the synchronous device, so that the purpose of reducing the magnetizing inrush current of the transformer is achieved.

The first implementation mode comprises the following steps:

as shown in fig. 1, the application provides an electroslag furnace transformer excitation surge suppression device, including isolation transformer, first optoelectronic isolation module, second optoelectronic isolation module, communication module, man-machine interface module and host system, isolation transformer and first optoelectronic isolation module are connected with host system respectively, man-machine interface module includes keyboard and display module and third optoelectronic isolation module, keyboard and display module pass through the third optoelectronic isolation module and are connected with host system, communication module includes communication interface and fourth optoelectronic isolation module, communication interface passes through the fourth optoelectronic isolation module and is connected with host system, the second optoelectronic isolation module is connected with host system. The communication module comprises a network port and a serial port communication loop.

The voltage, the current, the load side voltage and the current on the power supply side output signals to the main control module through the isolation transformer in the form of analog signals, and after the isolation transformer carries out anti-interference processing, the main control module calculates the amplitude and the phase angle of the voltage, the current, the load side voltage and the current on the power supply side in real time.

The circuit breaker closing time, the circuit breaker opening time, the circuit breaker closing target angle, the circuit breaker opening target angle and the overcurrent protection constant value are sequentially input to the main control module through the keyboard and the display module in the man-machine interface module and the third photoelectric isolation module, and the third photoelectric isolation module is used for filtering and resisting interference. The main control module calculates a pre-issued switching-on outlet instruction angle range and a pre-issued switching-off outlet instruction angle range according to the set switching-off time, switching-on time and angle parameters of the circuit breaker.

Strong current switching value input signals of a closing starting signal and an opening starting signal are converted into weak current signals through the first photoelectric isolation module, the weak current signals are transmitted to the main control module, and the main control module judges whether the signals are effective closing starting signals and opening starting signals in real time. When the effective closing signal is judged to exist, the main control module starts to detect the closing outlet angle, when the closing outlet angle meets the angle range of the pre-issued closing outlet instruction, the main control module immediately sends a closing outlet instruction, and the second photoelectric isolation module boosts and outputs the signal to drive a closing coil of the breaker to perform breaker closing operation. When the effective brake-separating signal exists, the main control module starts to detect the angle of the brake-separating outlet, when the angle of the brake-separating outlet meets the angle range of the pre-issued brake-separating outlet instruction, the main control module immediately sends out the brake-separating outlet instruction, and the second photoelectric isolation module boosts and outputs the signal to drive the brake-separating coil of the breaker to perform breaker-separating operation.

The device is characterized in that a closing event record, a switching-off event record, an overcurrent protection event and a waveform are sequentially transmitted to external hardware equipment through a fourth photoelectric isolation module and a communication interface in a communication module, wherein the fourth photoelectric isolation module is used for filtering and resisting interference, communication stability is improved, and functions of data storage, switching-off data, switching-on data and parameter analysis and the like are finally achieved.

And finally, the excitation inrush current amplitude of the transformer is controlled within 1-1.5 times of the rated current of the transformer, and override tripping is avoided.

The second embodiment:

as shown in fig. 2, the application provides a method for suppressing magnetizing inrush current of an electroslag furnace transformer, which comprises the following steps:

step S1, the main control module calculates a closing angle and sends a closing instruction, which includes the following specific contents:

the main control module receives power supply side voltage, power supply side current, load side voltage and load side current, and calculates amplitude values and phase angles of the power supply side voltage, the current, the load side voltage and the current in real time.

And the main control module calculates the angle range of the pre-issued closing outlet instruction according to the set opening time and closing time of the circuit breaker.

And the main control module calculates a closing angle after receiving the closing starting signal and sends a closing instruction. The main control module judges whether the current signal is an effective closing starting signal or not in real time, when the current signal is judged to be the effective closing signal, the main control module starts to detect the angle of a closing outlet, and when the angle of the closing outlet meets the angle range of a pre-issued closing outlet instruction, a closing outlet instruction is immediately sent out. The effective closing starting signal refers to that the closing angle is 70-110 degrees (90-degree closing inrush current is minimum, a certain margin is reserved by considering the errors of the device outlet and the breaker opening and closing time), if the closing angle is not 70-110 degrees, the closing angle is recalculated, and if the closing angle is 70-110 degrees, the device sends a closing instruction.

The excitation inrush current suppression device is used for programming adjustment, a field closing phase angle is captured, and the closing phase angle is controlled within 70-110 degrees no matter the phase angle is positioned at any angle when closing is started, so that the minimum closing inrush current is ensured. The device has the functions of general protection, voltage and current sampling and overcurrent quick-break tripping at the same time. The realization principle is as follows: when the closing phase angle is between 70 and 110 degrees, the excitation inrush current amplitude is minimum, and the relay protection action value can be avoided. In the case of an alternating-current circuit,

always lagging the voltage by a phase angle of 90 degrees. If the voltage just reaches the maximum value at the moment of closing, the instant value of the magnetic flux is just equal toZero, i.e. a steady state flux is initially established in the core. In this case, the transformer does not generate a magnetizing inrush current. Between 70 and 110 degrees, and is just the current value between the magnetizing inrush current of the transformer and the rated current of the transformer from 0.

Step S2, protecting the system based on the judgment of the load side voltage and the voltage constant value and the judgment of the power side current and the overcurrent protection constant value, which includes the following specific contents:

after the switch-on, the main control module judges whether the voltage of the load side is greater than a voltage fixed value, if not, the switch-on is failed, relevant information of the current switch-on failure, such as event information and waveforms, is recorded, if so, the main control module continuously judges whether the current of the power supply side is greater than an overcurrent protection fixed value, if so, the current is considered to be overlarge, the device sends a protection tripping instruction, a circuit breaker is disconnected, the electrical cabinet which is subjected to the overload tripping is prevented, and if not, the switch-on is successful and the relevant information of the current switch-on is recorded.

As shown in fig. 3 and 4, in the inrush current waveform generated when the inrush current suppression device is not operated and switched on, the switching-on phase angle is 130 degrees, the maximum peak value of the inrush current of the first cycle after switching on is 24A, and the inrush current generated by switching on is large.

As shown in fig. 5 and 6, the inrush current suppression device has an inrush current waveform that appears when the inrush current suppression device is switched on after operation, the switching-on phase angle is 86.5 degrees, the maximum peak value 0.01813a of the first cycle inrush current after switching-on avoids the relay protection operation value, and the inrush current suppression effect of the inrush current suppression device is relatively ideal.

The auxiliary value of the magnetizing inrush current is maximum when the first cycle is carried out, the magnetizing inrush current gradually attenuates along with the time, and the attenuation is finished after 0.5 second. Because the time is needed for the device outlet and the breaker to be switched on, the software calculates the angle of a pre-issued outlet instruction during 90-degree switching on according to the set switching on time of the breaker, detects whether the system voltage angle during switching on is within a preset range (considering the time error of the device outlet and the breaker and reserving a certain margin) after receiving a switching on starting signal, directly switches on when the system voltage angle is within the preset range, and continuously detects for 0.5 millisecond if the system voltage angle is not within the preset range until the outlet requirement is met when the system voltage angle is 0.5 millisecond.

When the closing phase angle is between 70 and 110 degrees, the excitation inrush current amplitude is minimum, and the relay protection action value can be avoided.

It should be noted that, in the above embodiments, as long as the technical solutions can be aligned and combined without contradiction, those skilled in the art can exhaust all possibilities according to the mathematical knowledge of the alignment and combination, and therefore, the present invention does not describe the technical solutions after alignment and combination one by one, but it should be understood that the technical solutions after alignment and combination have been disclosed by the present invention.

This embodiment is only illustrative of the patent and does not limit the scope of protection thereof, and those skilled in the art can make modifications to its part without departing from the spirit of the patent.

Claims (6)

1. The excitation surge current suppression device of the electroslag furnace transformer is characterized by comprising an isolation transformer, a first photoelectric isolation module, a second photoelectric isolation module, a communication module, a human-computer interface module and a main control module;

the isolation transformer, the first photoelectric isolation module and the second photoelectric isolation module are respectively connected with the main control module, and the communication module and the human-computer interface module are respectively connected with the main control module;

the isolation transformer is used for anti-interference processing;

the first photoelectric isolation module is used for converting signals into weak current signals;

the second photoelectric isolation module is used for boosting and outputting a signal;

the main control module is used for receiving the signals, carrying out corresponding processing and then outputting a control instruction;

the communication module is used for carrying out information communication with external equipment;

the man-machine interface module is used for inputting the closing time of the circuit breaker, the opening time of the circuit breaker, the closing target angle of the circuit breaker, the opening target angle of the circuit breaker and an overcurrent protection fixed value.

2. The electroslag furnace transformer excitation inrush current suppression device according to claim 1, wherein the communication module comprises a fourth photoelectric isolation module and a communication interface, and the communication interface is connected with the main control module through the fourth photoelectric isolation module;

the fourth photoelectric isolation module is used for filtering and resisting interference;

and the communication interface is used for connecting external equipment for communication.

3. The electroslag furnace transformer excitation inrush current suppression device according to claim 2, wherein the human-computer interface module comprises a keyboard and display module and a third photoelectric isolation module, and the keyboard and display module is connected with the main control module through the third photoelectric isolation module;

the keyboard and display module is used for inputting parameters and displaying information;

and the third photoelectric isolation module is used for filtering and resisting interference.

4. An electroslag furnace transformer magnetizing inrush current suppression method depending on the electroslag furnace transformer magnetizing inrush current suppression device according to any one of claims 1 to 3, characterized by comprising the steps of:

step S1, the main control module calculates the closing angle and sends a closing instruction;

collecting and calculating power supply side voltage, power supply side current, load side voltage and load side current, calculating a pre-issued switching outlet instruction angle range by a main control module according to set breaker switching-off time and switching-on time, calculating a switching-on angle by the main control module and issuing a switching-on instruction;

step S2, based on the judgment of the load side voltage and the voltage fixed value and the judgment of the power supply side current and the overcurrent protection fixed value, the protection of the system is implemented;

and after the switch-on, the main control module judges whether the voltage of the load side is greater than a preset value, if not, the switch-on fails, the relevant information of the current switch-on failure is recorded, if yes, the main control module continuously judges whether the current of the power supply side is greater than an overcurrent protection fixed value, if yes, the device sends a protection tripping instruction, and if not, the switch-on succeeds and the relevant information of the current switch-on is recorded.

5. The electroslag furnace transformer magnetizing inrush current suppression method according to claim 4, wherein in step S1, the main control module calculates a closing angle, and the specific process of issuing a closing instruction is as follows:

the main control module receives power supply side voltage, power supply side current, load side voltage and load side current, and calculates amplitude values and phase angles of the power supply side voltage, the current, the load side voltage and the current in real time;

the main control module calculates the angle range of the pre-issued switching-on outlet instruction according to the set switching-off time and switching-on time of the circuit breaker,

the method comprises the steps that a main control module calculates a closing angle after receiving a closing starting signal and sends a closing instruction, the main control module judges whether the closing starting signal is an effective closing starting signal or not in real time, when the main control module judges that the effective closing signal exists, the main control module starts to detect the closing outlet angle, and when the closing outlet angle meets the angle range of a pre-issued closing outlet instruction, the main control module immediately sends the closing outlet instruction, wherein the effective closing starting signal means that the closing angle is 70-110 degrees, if the closing angle is not 70-110 degrees, the closing angle is recalculated, and if the closing angle is 70-110 degrees, the device sends the closing instruction.

6. The electroslag furnace transformer magnetizing inrush current suppression method according to claim 5, wherein the closing angle is 90 degrees.

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