SU1656624A2 - Device for fault protection of network - Google Patents

Abstract

The invention relates to electrical engineering and can be used to protect electrical networks with adjustable electric drive. The aim of the invention is to improve the accuracy of protection against leakage of current to earth when the network capacity changes. When the power is turned on, the operational voltage generator 1 is connected to the cores of the monitored network via key 5 for the time determined by the driver. The parameters of the operating voltage of the integration unit 6, the memory unit 8 calculates the magnitude of the operational current, the multiplier 29, the setting unit 28 calculates the capacitive component of the leakage resistance, the division unit 24 calculates the complex leakage resistance, blocks of squares 31. 32. adder 26, the square-root extraction unit 33 calculates the active component of the leakage resistance If the operating current exceeds the setpoint value of the threshold element 20 corresponding to a short circuit or ysheni quantities of the active component setpoint threshold element 21, operates the actuating unit 38 as a result of source 37 is turned off and the display unit 15 indicates the cause of emergency shutdown yl with 1 / C

Description

The present invention relates to electrical engineering and can be used to protect electrical networks with insulated neutral from leakage currents and short circuits, including for mining machines with adjustable electric drive.

The aim of the invention is to improve the accuracy of protection against leakage of current to earth when the network capacity changes.

The drawing shows a block diagram of the proposed device.

The device contains a source of operational voltage of alternating current (generator) 1 with an isolation transformer at the output, sensors of operational

voltage 2 and operating current 3, first 4 and second 5 keys, first 6 and second 7 integrators, first 8 and second 9 elements of MEMORY, unit set to zero 10, trigger 11, pulse shaper 12, pulse divider 13, amplifying unit 14, display unit 15, attachment unit 16, load resistor 17, third and fourth integrators 18 and 19, first 20 and second 21 threshold elements, first 22, second 23 and third 24 voltage dividers, first 25 and 26 and 26 adders, first 27 and second 28 setting blocks multiplier 29, reference element 30, first 31 and second 32 quadrants, square-root extraction unit 33, element

ate

Os

0

Yu

four

to

And 34, the sensors of the mains voltage 35 and the load current 36, the power source - a controlled rectifier 37, an output control unit 38, a shunt resistor 39 and a diode 40.

The drawing also shows the designation of the following parameters and elements: RH is the insulation resistance of the cable cores to the earth, LL is the capacitance of the cable cores to the earth, RK, Cc is the insulation resistance and the capacitance between the power wires of the cable, Rc is the resistance of the network section D1 , 41 (D) is a DC motor, 42 (VD) is a semiconductor diode, a shunt motor D.

The source of operational voltage 1 has a transformer output. The first output winding of the isolation transformer (W2) through the second switch 5 is connected to the conductors of the power network. The output parameters of this source are measured by operational voltage 2 and current 3 sensors. The second switch 5 is controlled by the separation / amplifying unit 14.

The first integrator 6 serves to sum the load current of the operational voltage generator for a predetermined period of time ti created by a series-connected pulse generator 12 and a pulse divider 13 from its first output. The value of ti for increasing the reliability of measurements can be taken in the range from units to tens of periods of network or operating voltage. The first key A, when opened, connects the output of the first integrator 6 to the input of the first element MEMORY 8 to record information about the magnitude of the operational current in it. The second element MEMORY 9 serves to store the value of the output voltage of the operational generator 1. The second integrator 7 serves to sum the signal proportional to the total (active and capacitive component) leakage current generated by the power source 37 in the monitored network. The third integrator 18 serves to sum the load current of the power source 37. The fourth integrator 19 serves to sum the signal proportional to the output voltage of the power source 37. The summation is performed over a period of time t2 defined by a pulse divider 13 from its second output.

The setup block at zero 10 is used for initial resetting to the zero state of the integrators 6, 7, 18. 19, the elements of MEMORY 8 and 9, and the trigger 11. The trigger 11 determines the operating mode of the separation-amplifying block 14 and the element I34.

Pulse generator 12 and pulse divider 13 serve to form a time interval ti during which the operating voltage source is connected to the network, and a time interval t2 for which the network voltage and load and leakage currents in the power network are measured. The introduction of a diode 40 with a load resistor 39 into the input circuit of the pulse shaper 12 allows

5 receive a time delay ti. multiple to an integer number of periods of operational stress.

Isolation unit 14 serves to match the output circuit.

0 flip-flop 11c with the input circuits of the second key 5 and the galvanic isolation between the high-voltage circuits of this key and the low-voltage control circuits.

The display unit 15 provides service personnel with information on the activation of protection in the event of emergency conditions.

The connection unit 16 performs the functions of separation of power and measuring

0 chains. The load resistor 17 is a measuring element of the leakage current of the power source 37 to earth.

The first threshold element 20 serves to set the trigger threshold corresponding to the magnitude of the operational current during a short circuit in a de-energized power network. The setting of the second threshold element 21 corresponds to the level of protection of the current leakage to earth.

0 The first voltage divider 22 is used to calculate the resistance value of the load circuit of the operational generator 1.

5With the help of the second voltage divider 23, the set point of the short-circuit protection in the power network is calculated, corresponding to the minimum value of the short-circuit current at the actual voltage at the output of the power source 37. The third voltage divider 24 is used to calculate the complex leakage resistance to ground elements of the power network. In the first adder 25, the resistance of the cores of the power cable is calculated taking into account the resistances of the second switch 5 and the semiconductor peak diode VD in a conducting state, the values of which are determined in advance and entered into the first block of settings 27.

The multiplier 29 with the second block of settings 28 is used to calculate the capacitive component of the leakage resistance of the power network elements to ground. In the block of settings 28, the characteristic of the power cable X km / R km is entered, which corresponds to the ratio of capacitive Xc and active Ra, the components of the kilometric resistance of the power cable cores.

Using the comparison element 30, the current value of the load current is compared with the set value calculated in the second divider 23.

The first square 31 serves to square a voltage proportional to the capacitive component of the resistance of the power network Xc. The second quad 32 serves to square a voltage proportional to the leakage resistance Ry.

In the second adder 26, the difference of the squares of the leakage resistances Ry and the capacitance component Xc is calculated. Using the square root extraction unit 33, the active leakage resistance component Ra is calculated.

Element I34 serves to block, preventing the supply of control signals to the output execution unit 38 for the duration of the connection to the mains of the operating voltage source 1. The output execution unit 38 provides for the control of the power source 37 according to a predetermined law.

The device works as follows.

When applied to the input of the network voltage device, the source of the operating voltage 1 begins to work.

Keys 4 and 5 are in the closed state. The setting block at zero 10 sets the integrators 6, 7, 18, and 19 to zero, the elements of MEMORY 8 and 9, and turns on trigger 11. As a result, trigger 11 is turned on by a signal from its first output through a divider block 14 and turns on the second switch 5 and operational voltage generator 1 is connected to the conductors of the monitored power network. At the second output of the trigger 11, a logical zero signal is generated and the supply of control signals for the electric drive by blocking the element I34 is prohibited.

With the help of pulse generator 12 and pulse splitter 13, the time delay tt of connection of the operating voltage generator 1 to the monitored network is measured.

The voltage value of the source 1 from the operational voltage sensor 2 is fed to the second element of the MEMORY 9 and is stored in it.

The current in the circuit of the operating voltage source is created by the distributed leakage resistance Ru, RK of the network capacity Cc of the motor winding resistance and current through the diode VD. This current contains a constant and variable components. The variable component is determined by the complex impedances of the leakage and the electric motor core circuit. The constant component 1P is determined by the series-connected resistance of the cores of the cable RCI, the resistance of the elements of the second key 5 R 2, and the resistance RVD of the diode VD in the conducting state and is equal to

 --TG

where Don is the magnitude of the output voltage of the operational generator 1,

Ry Rr + R K2 + RVD.

In the first integrator 6, the signal is proportional to the current of the operational generator 1. The output voltage of the first integrator 6 for the period of the operational voltage is proportional to the constant component of the current In. Summation of the current value over a period of time n ensures its average value.

After the time delay ti has expired by a certain driver 12 and pulse divider 13, a pulse is formed at the first output of the pulse divider, which switches the trigger 11 to the second state. The voltage at the output of the first integrator during this time reaches the level

Ui Kitifonln, (2)

where KI is the proportionality coefficient;

fon is the frequency of the operational generator voltage,

and through the first key 4 will be written into the first element MEMORY 8.

The trigger 11, having switched its first output, turns off the separation-amplifying unit 14, and forms the logical unit at the first input of the I34 element by the second output. As a result, the second key 5 is turned off, stopping the supply of operational voltage to the monitored network and the lock is removed, prohibiting the passage of a control command to the output execution unit 38.

The signal from the output of the first element MEMORY 8 is supplied to the first threshold element 20. When a short circuit in the power network is constant, the output voltage Ui of the first integrator 6 is less than the specified value AI of the first threshold element 20, i.e. Ui Ai. When this condition is fulfilled, a command is issued at the output of the first threshold element 20 to prevent the output executive unit 38 from turning on, and information is given to the display unit 15 about the presence of an emergency mode. Power source 37 is not included.

In the absence of a short circuit in the power network, the condition Ui Ai is fulfilled and there is no signal at the output of the first threshold element 20. This completes the process of measuring the resistance of the power network and monitoring the presence of a short circuit in the de-energized state of the network and the operation of the electric drive can be carried out.

In the operating mode, the first voltage divider 22 performs the operation of dividing the voltage Una from the output of the second element MEMORY 9, corresponding to the average value of the operational voltage and voltage Uni from the output of the first element MEMORY 8. As a result, the Ugi signal is generated at its output proportional to the total resistance Rs of the power network, key 5 and diode D to the operational current, i.e. Un2 Um

 (3)

The value of UH is taken from the mains voltage sensor 35 and averaged over time t2 using the fourth integrator 19. The value of UH is fed to the inputs of the second and

the third voltage divider from the output of the fourth integrator 19.

Comparison element 30 compares the pickup setting Uamin calculated in the second voltage divider 23 with the load current n, the value of which is generated at the output of the third integrator 18. In the absence of a short circuit in the monitored power network IH IK a.min and at the output element

Comparison 30 is absent. If a short circuit occurs in the network, the condition

1n, 1k.e.t1p (6)

and at the output of the comparison element 30, a command is formed to shut down the output execution unit 38 and the signal to the display unit 15.

As a result, the power source 37 is de-energized.

Also, in operation, the capacitance component of the leakage current of the power network Xc is calculated using the multiplier 29 and the second block of settings 28 in accordance with the formula

R

Msm

km

(7)

(K2 - proportionality coefficient).

Using the first adder 25, the total resistances R k2 of the key 5 in the open state and the diode R UD in the conducting state, the values of which are set in the first block of the setting of settings 27, are subtracted from the total resistance Rt.

The signal at the output of the first adder 25 U d is proportional to the resistance of the cores

power cable rc i.e.

U ci - MV R к2 - RUD) KsRc (4) (Кз adder transfer coefficient).

Using the second voltage divider 23, the pickup setpoint of the protection device against short-circuit currents i.e. min, corresponding to the effective voltage in the power network in the UH operating mode and short circuit at the most specific point of the network, i.e., is calculated.

(five)

1k.z.gl1p - K $

RC

23).

(K / - divider transfer coefficient

where Hkm and RKM are the kilometric values of the capacitive and ohmic resistance of the cores of the power cable, the values of which are for

A specific type of cable is known and entered into the second block of the task settings 28.

Using the third voltage divider 24, the impedance of leakage in the power network Ry in

according to the formula

"W (8)

at

where 1U is the leakage current, the value of which is fed to the second input of the divider 24 from the output of the second integrator 7.

In squares 31 and 32, the squares of Xc and Ry are calculated. In the second adder 26, the square of the active component of the leakage resistance Ra2 is calculated in accordance with the formula

Ra2 Ry2 - XC2. (9)

Using a square root extraction unit 33, the active component of the leakage resistance Ra in the power network is calculated as

Ra Ry2-Xc2. (10)

With the help of the second threshold element 21, the magnitude of the active component of the leakage resistance Ra is compared with the leakage protection setting Ryo, the value of which is equal to the response threshold of the second block of settings 28, when the condition

Ra

Rycr

At the output of the threshold element 21, a command is generated to shut down the output execution unit 38 and a signal to the display unit 15.

As a result, the power source 37 is turned off and the cause of the emergency shutdown is recorded in the display unit.

In the absence of emergency situations, the output executive unit 38 provides for control of the power source 37 and, accordingly, the engine operation mode in accordance with specified laws.

Thus, this technical solution allows controlling the occurrence of emergency conditions in the electrical network of mining machines with adjustable drive - short circuits and leakages to the ground.

Improving the accuracy of protection against leakage of current when the network capacity changes is provided by introducing an algorithm

calculation of the active component of the leakage resistance in the power network in accordance with formula (10). This calculation algorithm automatically compensates for the capacitive component of the leakage current, regardless of the network capacity. This property of the proposed technical solution allows to expand the scope of application of adjustable DC electric drives.

Claims (1)

Claims of Invention A device for protection of an electrical network against damages according to the author. No. 1573497, characterized in that. In order to improve the accuracy of protection against leakage of current to the ground when the network capacity changes, two quadrs and a square root extraction unit are added, the multiplier output connected via a first quad, a second adder and a square root extraction unit to the input of the second threshold element, and The third voltage divider is connected via the second quad to the second input of the second adder.