RU55219U1 - MICROPROCESSOR TERMINAL OF DIFFERENTIAL-PHASE PROTECTION OF THE ELECTRIC TRANSMISSION LINE - Google Patents

Abstract

The utility model relates to the electric power industry and, in particular, to the protection of power lines (power lines) from short circuits (short circuit). The objective of the utility model is to provide noise immunity of the protection without reducing its performance during short circuit on the protected line. The microprocessor terminal of the differential-phase protection of the power line contains an analog-to-digital conversion unit for secondary currents and voltages connected to the system bus, an interface unit with external devices, equipped with an input designed to connect to the output of the RF signal receiver, the outputs of the protection and control signals of the RF transmitter, and a programmable digital processing unit, configured with the ability to start the protection to calculate the current integral of the function, taking in a pause and when the presence of the RF signal at the input of the receiver is constant, the ratio of which is negative and equal in magnitude to the first specified value, and when the current integral reaches the second specified value, limit its further growth and issue a command to generate a protection response signal to the interface unit with external devices. The utility model has a development according to which a programmable digital processing unit can be configured to reset it to a third predetermined value by decreasing it to a third predetermined value and issuing a command to remove the protection response signal to the interface unit with external devices. This allows you to reduce the protection return time and thereby increase the reliability of its operation. 1 C.p.F., 3 ill.

Description

Microprocessor-based terminal for differential phase protection of a power line

Technical field

The utility model relates to the electric power industry and, in particular, to the protection of power lines (power lines) from short circuits (short circuit).

State of the art

Known differential-phase protection of the power line [1].

The action of the differential-phase protection of power lines is based on a comparison of the phases of the currents, in a certain way formed by protection half-sets installed on opposite ends of the protected line. Information about the phase of the current is transferred to the opposite end of the line using a current-manipulated high-frequency (HF) signal. This signal is transmitted to the half-protection device installed on the opposite end of the line, and together (in total) with the RF signal manipulated by the current of the opposite half-set, it is transmitted through the RF receiver to the phase-comparison element of the differential-phase protection. The function of the phase comparison body is to evaluate the location of the short circuit (external or internal short circuit with respect to the protected line) by the angle, which in the period T of the industrial frequency takes a pause in the total manipulated signal at the output of the RF receiver.

The phase comparison body is triggered by the differential-phase protection starting element, which responds to the value of the generated inrush current in a certain way and allows the protection to turn off the power line with the corresponding phase comparison result.

In the absence of a short circuit or external short circuit with respect to the protected power line, the phases of the manipulation currents formed by the opposed protection sets are such that the pauses of the two manipulated high-frequency

The signals entering the phase comparison body do not overlap. In this case, a pause is not formed in the total RF signal, the duration of which exceeds the set angle of protection blocking.

In the case of a short circuit on the protected power line, the phases of the manipulation currents of the opposite sets are such that the pauses of the two manipulated high-frequency signals overlap one another, which leads to a pause in the total high-frequency signal, the duration of which exceeds the set protection blocking angle.

The disadvantage of the device [1] - low noise immunity to transients with external (relative to the protected line) short circuit.

Modern protection devices are based on microprocessor terminals programmed to implement the functions of the corresponding protection.

A known microprocessor-based terminal block for differential-phase protection of power lines, selected as a prototype, contains an analog-to-digital conversion unit for secondary currents and voltages connected to the system bus ("common bus"), a digital processing unit, and an interface unit with external devices equipped with an output of the RF transmitter control signal , the output of the protection actuation signal and the input intended for connecting to the output of the receiver an RF signal [2]. To implement the functions of the differential-phase protection of power lines, the digital processing unit in the terminal is programmed accordingly. At the same time, the terminal implements, in particular, the function of the phase comparison body: a signal to activate the protection (line shutdown) is issued as a result of comparing the angular duration of a pause in the total manipulated signal at the output of the RF signal receiver and a given blocking angle, with the pause being measured in each period whatever. Protection is triggered if the angular duration of the pause exceeds a predetermined blocking angle in one, two or more

consecutive periods (the number of periods is set according to operating conditions). Such protection is more resistant to interference with external short-circuit.

The disadvantage of the prototype is the stability of the protection against interference caused by transients during external short-circuit, is achieved by reducing its speed during short-circuit in the protection zone.

Utility Model Disclosure

The objective of the utility model is to provide noise immunity of the protection without reducing its performance during short circuit on the protected line.

The subject of a utility model is a microprocessor-based terminal for differential-phase protection of a power line, containing an analog-to-digital conversion unit for secondary currents and voltages connected to the system bus, an interface unit with external devices, equipped with an input designed to connect to the output of the RF signal receiver, and outputs of protection operation signals and control the RF transmitter, and a programmable digital processing unit, made with the ability to start protection to calculate the current integral l of the function b, receiving a pause and the presence of the RF signal at the input of the receiver constant values, the ratio of which is negative and equal to the modulus of the first predetermined value k, and when the current integral of the second predetermined value N _cp limit its further growth and provide a coupling unit with external devices, a command to generate a protection trip signal.

This allows you to increase the resistance of the protection to interference caused by transients during external short-circuit, without reducing its performance when short-circuit on the protected line.

The utility model has a development according to which the programmable digital processing unit is configured to reduce the calculated current integral to a third predetermined

values N _return to issue to the interface unit with external devices a command to remove the protection trip signal.

This allows you to reduce the protection return time and thereby increase the reliability of its operation.

Brief Description of the Drawings

The implementation of the utility model, taking into account its development, is illustrated in figures 1-4. Figure 1 presents the structural diagram of the microprocessor protection terminal, figure 2 is a block diagram illustrating the implementation of the terminal body phase comparison. (This function is performed by the terminal along with the other functions of the differential-phase protection of power lines). The graphs in figure 3 illustrate the implementation of the function of comparing the phases with the parameters specified in accordance with the description in the example. Figure 4 presents the algorithm confirming the ability to perform programmable digital processing of the functions disclosed in the claimed formula of the utility model.

Utility Model Implementation

The structural diagram of the device of figure 1 contains connected to the system bus ("common bus") 1:

- block 2 analog-to-digital conversion of secondary currents and

stresses;

- block 3 interface with external devices;

- block 4 digital processing (programmable).

In addition, the diagram of figure 1 shows the RF transmitter 5 and the RF receiver 6, not included in the terminal and delivered separately. The output of the receiver 6 is connected to one of the inputs of the unit 3. One of the outputs of the unit 3 gives a signal for the protection to be activated (“Operation of protection”), the other - a signal for controlling the transmitter 5 (“RF transmitter control”).

The block diagram of figure 2 contains the following functional blocks:

- block 7 start protection shutdown;

- block 8 phase comparison;

- block 9 issuing values of the integrand b;

- block 10 integrating the value of b (accumulating adder);

- the first block 11 comparison;

- second block 12 comparison.

Figure 2 also shows the RF transmitter 5, to the inputs of which a control signal is connected, and a receiver 6, the output of which is connected to the control inputs of block 9. The output of block 9 is connected to one of the inputs of block 10. The “Start protection” command is received at its other input ". The output RF signal of the transmitter 5 and the signal from the transmitter of the remote protection half-mix are mixed (summed) at the input of the receiver 6.

The functions of blocks 7 and 8, including the functions of blocks 9, 10, 11 and 12, are implemented by the corresponding execution of programmable block 4 (see figure 1).

The microprocessor terminal (see figure 1) operates as follows.

The inputs of block 2 receive the secondary phase currents i _W and secondary voltages u _{W of the} protected power transmission line. Block 2 converts the input analog values into digital values supplied through line 1 to block 4. Block 4, in accordance with the digital processing program incorporated in it, uses the digital values of secondary currents and voltages to implement the differential phase protection functions, including those described above. At the same time, it issues control commands to block 3 to highway 1, which generates a transmitter control signal 5 (“Transmitter Control”) corresponding to these commands and a “Protection Trip” signal, which is input to the actuating element (not shown in the drawing), which acts to trip lines.

The differential phase protection functions described above in the section "prior art", when operating the inventive device are as follows (see figure 2).

Block 7, analyzing the values of the secondary phase currents i _W and secondary voltages u _W , generates protection currents and controls the RF transmitter 5. The protection currents are compared with the specified threshold values, and the comparison results in the form of the “Start Protection” command and the “RF Transmitter Control” signal arrive at blocks 10 and 5, as shown in figure 2.

The transmitter 5 gives the RF signal to the line and to the input of the receiver 6, where this signal is mixed (summed) with the manipulated RF signal coming from the opposite protection half-set. The receiver 6 gives in block 8 a binary signal with a period T corresponding to the envelope of the total RF signal at the input of the receiver 6. One level of the binary signal at the output of the receiver 6 corresponds to a pause, and the other to the presence of an RF signal at the input of the receiver 6.

Block 8, which performs the function of the phase comparison body, upon receipt of the “Start Protection” command, enables the protection action to turn off the power line with the corresponding result of the phase comparison.

In more detail, the operation of differential-phase protection in the part that coincides with the functioning of known devices is described in [1].

The function of comparing the phases in the proposed device illustrates the functional structure of block 8 in figure 2. The phase comparison is as follows.

In the initial state (in the absence of a short circuit and the “Start Protection” command), the zero value of the current integral calculated in block 10 of the function b is maintained. Upon receipt of the “Start Protection” command, block 10 starts the integration of function b over time. The value of function b, issued by block 9, is determined by the binary signal coming from the output of receiver 6.

The signal at the output of the receiver 6 takes a state during a pause of the RF signal, which ensures that the block 9 gives a positive _pause value b to the block 10. In the presence of an RF signal at the input of the receiver 6, it gives

a signal providing the input from block 9 to block 10 of the negative value of b _RF , whose module is k times less than the value of p _pause . The current state M of the integral, calculated in block 10, is compared by blocks 11 and 12 with the given numbers N _cp , and N _return, and for M> N _cp a command is issued to give a signal “Protection _tripping ”, and when M <N _return - a command to remove this signal.

This execution of the phase comparison function in programmable unit 4 allows you to set (for example, in degrees):

- angular duration δ ₁ pauses (blocking angle), to which the protection does not work at any time the signal from the receiver 6;

- the angular duration δ ₂ pauses, after which the protection is guaranteed to operate within one period of the industrial frequency after a signal from the receiver 6.

With intermediate values of the angular duration δ ₁ <δ <δ ₂ pauses, the time (number of periods) of the protection operation decreases with increasing pause duration.

In practice, first, the desired values of the angular durations δ ₁ and δ ₂ are selected based on the specific conditions and characteristics of the protected power transmission line, and then the values k and N _cp corresponding to the selected δ ₁ and δ ₂ are set by the following formulas:

Example.

Let, for example, p _pauses = 10 ⁵ and the selected values of δ ₁ and δ ₂ be 120 ° and 180 °, respectively. Then k = 2 and at T = 20 ms N _cp = 1000.

The operation of the device with the parameters of this example is illustrated in Fig. 3 (a, b, c).

According to the condition of continuity of the signal “Protection tripping” it is necessary that

N _return -N _cp. = δ _{1 MAX} · T _MAX · b _HF / 360 °, where b _HF = -b _pauses / k.

Shown in figure 4, the algorithm for performing the above functions in the form of a sequence of operations confirms the possibility of implementing a utility model based on a programmable microprocessor device.

Information sources

1. A.I. Leviush, N. A. Doni and others. High-frequency directional and differential-phase protection PDE 2003 for 500-750 kV overhead lines. Scientific and Educational Center ENAS, M., 1996

2. Terminal MICOM 547. Manual guide. Areva, Stufford, GB, 2002.

Claims (2)

1. Microprocessor-based terminal for differential-phase protection of a power line, comprising a unit for analog-to-digital conversion of secondary currents and voltages connected to the system bus, an interface unit with external devices, equipped with an input designed to connect to the output of a high-frequency signal receiver, outputs of protection and control actuation signals high-frequency transmitter, and a programmable digital processing unit, made with the ability to start the protection to calculate the current integral from function, taking in a pause and in the presence of a high-frequency signal at the input of the receiver, constant values, the ratio of which is negative and equal in absolute value to the first specified value, and when the current integral reaches the second specified value, limit its further growth and issue a command to the unit for interfacing with external devices protection trip signal. 2. The device according to claim 1, in which the programmable digital processing unit is configured to reset the calculated current integral to a third predetermined value to zero and issue a command to remove the protection response signal to the interface unit with external devices.