SU565258A1 - Device for measuring and fixing frequency change rate in power system - Google Patents

Description

one

The invention relates to the field of automation of power systems and can be used in system emergency control automation: automatic frequency unloading, emergency unloading of stations, with automatic pumping of reserve power units, etc., as well as for measuring the frequency of measuring frequency in power systems under operating conditions and emergency modes.

A device for measuring and fixing the rate of change of frequency in the power system is known, comprising a series-connected low-pass filter, a pulse shaper, a first And element, a first control unit, a decoder, a reference frequency generator and a second And element, a reversible counter, the second output of the first block control is connected to the second input of the second element I, and the outputs of the reversible counter are connected to the second inputs of the decoder, and the block of output relays 1.

A disadvantage of the known invention is the low measurement accuracy of the device.

In order to improve measurement accuracy, the proposed device for measuring and fixing the rate of change of frequency in the power system includes a serially connected restart unit, an initial setup unit, a prohibition unit, a serially connected shutdown unit, the first OR element, the second control unit, the second OR element, and the second input Which is connected to the output of the first element OR, a series connected sign detection unit and a display unit, the second inputs of which are connected to the outputs of the output relay unit, and that Also, a preparation unit connected between a remote control unit and an output relay unit and a third OR element connected between the second output of the second control unit and the inputs of the preparation unit, the second input of which is connected to the second output of the second control unit, the third output of the last connected to the second input of the first And, the third input of which is connected with the second output of the initial installation unit and with the second input of the second element And, and the fourth input of the first element And is connected to the second output of the shutdown unit and the third input of the second element And, the third output of the setup block is connected to the second input of the first element OR, the third input of the last is connected to the third output of the first control unit, the fourth output of the last is connected to the first input of the reversible counter, the second input of which is connected to the second input of the first control unit , the output of the prohibition block is connected with the third input of the decoder, the fourth input of which is connected to the second output of the counter counter, the third input of the latter is connected through the sign detection unit with the output of the second element enta I.

The drawing is a block diagram of the proposed device.

The device contains a reversible counter 1, which determines the difference in the number of impulses of the reference frequency in two time intervals, for this purpose it is provided for its switching from the subtraction mode to the addition mode; after both intervals, a number proportional to the rate of change of frequency is recorded in the meter; decoder 2, shutdown unit 3, setup unit 4, low-pass filter 5, pulse generator 6, exemplary frequency generator 7, output relay unit 8, indication unit 9, first control unit 10, second control unit 11, preparation unit 12, unit 13 restart, block 14 sign detection, the first element AND 15, the second element AND 16, the first element OR 17, the second element OR 18, the prohibition block 19, the third element OR 20.

In order to distinguish the reduction in frequency from the meter input circuit, a sign detection unit 14 is provided that switches the inputs of the meter.

Decoder 2 determines the number of pulses recorded in the counter and is a multi-terminal, each output of which corresponds to a specific combination of input signals.

Blocks 3 and 4 prohibit the operation of the device when the input voltage drops below 0.4 t / H, transfer it to its original state through elements 15 and 16, resetting all triggers to the state of bullets during feeding and switching 3 prices x supply voltage.

The device can operate in single and periodic modes.

When the device operates in a single mode, a return button 21 is provided for returning to the initial state. When operating in a periodic mode of monitoring the current speed, a device restart unit 13 is used, which specifies the monitoring intervals.

The low-pass filter 5 reduces the errors of the device from the presence of high harmonics in the controlled voltage, which distort the moments of voltage crossing through zero.

The pulse shaper 6 is designed to receive short pulses from a sinusoidal signal corresponding to the instant of a positive transition of the monitored zero voltage, and includes a full-wave rectifier and a limiter amplifier.

An exemplary frequency generator 7 is a multivibrator in which frequency stabilization is carried out using a quartz resonator.

Block 8 of the output relays serves to obtain the contact output of the device. When operating in the control mode of the current speed, the matching unit and the recorder or oscilloscope are connected to them.

The display unit 9 indicates the number of triggered queues or the current speed in the monitoring interval.

The control unit 10 switches the counter

1 from the subtraction mode to the addition mode, fixing for this the third pulses at the output of the imager; gives out to the decoder

2 permitting signal is read and simultaneously removes the signal from the element 15, thus stopping the flow of pulses from the generator 7 to the counter 1, for which the fifth pulses are recorded at the output of the driver; generates a reset signal of the reversible counter 1 and itself through the OR elements 17 and 18, as well as the reset of the control unit 11 through the OR element 17, for which the sixth pulse is ixified. The "read" signal from control unit 10 is removed with some delay, as a result, after disconnecting generator 7 from reversing counter 1, the transient process ends in the latter.

A similar delay is introduced to the " reset " pulse, which is done to eliminate the simultaneous feeding of the setting pulse and the " reset " pulse.

The control unit 11 together with the unit

Preparation 12 is intended for organizing the push-pull mode of the device and performs the following operations: resets the control unit 10 of the reversible counter 1 through the OR elements 18 and 20 to the initial position as soon as the signal appears at any output of the decoder 2 at 0.25 Hz / s; “apexes the work of the preparation unit and the supply of signals in the second one also from the decoder 2 to the unit 8; through element and 16 stops

the device thus carried out the operation "memory of the magnitude of the speed, at the time of arrival of the second pulse from the decoder or at a predetermined point in time.

Lime digits | O the device, organizing time intervals to determine the speed and frequency change, realize the expression

d /

, g, - city

(one)

A / i-t-ACa

m

7, g.

Where

f 1 - T - Tt / 1 - g G

2I I - 2

D /,

a and 4/2 are the measurement times of the frequency fi and / 2 go, respectively.

From expression (1) it is obvious that determining the rate of change of frequency requires multiplication and division operations.

The operation of the proposed device is based on that the denominator in the expression (1)

replaced by a constant Coefficient pt where n is the number of periods of the measured frequency contained in the controlled intervals II & t: t2, and T is some predetermined value of the period. Such a change leads to some methodological error, which does not exceed 3% relative to the minimum setting or discreteness of the fixed values of the current rate of change of frequency. The value of n 7 is determined by a certain choice of time intervals, the frequency of filling the exemplary frequency generator and the design of the decoder. Replacing the denominator with a constant number reduces the measurement of the speed of the frequency to measuring only the difference of the periods in the defined time interval mine division operation.

When power is applied to the device, the unit 4 of the initial installation resets the counter 1 to the state "zero" and sets the blocks 10 and 11 to the initial position, while the element 15 is closed and the element 16 is opened, thereby signal is not output to the preparation unit 12. With the arrival of the first pulse at the control unit 10, the element 15 opens, the pulses from the generator 7 of the exemplary frequency begin to flow to the negative input of the reversible counter 1. During the time corresponding to two periods of the input frequency, the counter 1 operates on the subtraction. In the control unit 10, pulses are fed from the imager 6. These pulses are formed only: At the moment of a positive zero crossing, the pulse period is equal to the input signal period. With the arrival of the third pulse at the control unit 10, the counter 1 switches in the addition mode. Thus, two periods counter 1 ra: works for subtraction, and the next two periods for addition. With the arrival of the fifth pulse (four periods from the beginning of the measurement) on the control unit 10, the element 15 is closed and the enabling signal is output to the decoder 2.

If the rate of change of frequency / 0.25 Hz / s, then on one of the outputs of the decoder 2 a signal appears, which through the OR element 17 goes to control unit 11, the latter generates a reset signal of unit 10 and counter 1 to its original position. At the same time, unit 10 outputs a preparation signal to preparation unit 12, and a signal output circuit is prepared in proportion to the output relay unit 8 in the second cycle.

Starting from the sixth impulse of the former 6, the cycle of operation of the device is repeated. With the arrival of the tenth pulse from the generator 6, the control unit 10 outputs a signal to the decoder 2 and the signal from counter 1 arrives at the output relay unit 8. The signal from the decoder through the OR element 17 also goes to the AND block, which outputs the signal to the AND element 16 and closes . Since the elements of AND 16 and 15 are closed, the circuit remains in the state in which it arrived after the tenth of the pulse. The device switches to the mode of "memorizing the magnitude of the velocity in the power system." The circuit can be reset to its initial state manually by pressing the button 21, whether bo from the restart block 13, which determines the frequency of monitoring the current speed. If the speed is less than 0.25 Hz / s (the speed that it is advisable to fix), then the signal from the counter to the decoder does not flow, the control block 11 remains in the initial state, and the And 16 element will remain open after the fifth pulse control block 10 . In this case, the reset unit 10 and the counter

1 is produced by the sixth pulse from the driver 6. The same pulse is reset to the state of the pool block 11 in case in the first clock for any reason a signal from the element OR 17 arrives at its input. In case the input voltage drops below 0.4 FH unit 3 turns off the device and returns it to its original state.

Claims (1)

Invention Formula A device for measuring and fixing the rate of changing the frequency in the power system, comprising a series-connected low-pass filter, a pulse shaper, a first AND element, a first control unit and a decoder, a reference frequency generator and a second And element, as well as a reversible counter, the second output of the first control unit connected to the second input of the second element I, and the outputs of the reversible counter are connected with the second inputs of the decoder, as well as the block of output relays, characterized in that, in order to improve accuracy, sequentially connected restart block, the initial installation block, the block block, series-connected disconnecting unit, first OR element, second control unit, second OR element, the second input of which is connected to the output of the first P1LI element, series-connected sign detection unit and b indication block, the second inputs of which are connected to the outputs of the output relay unit, as well as the preparation unit connected between the decoder and the output relay unit and the third OR element connected between the second output of the second control unit and the inputs of the preparation unit whose second input is connected to the second the output of the second control unit, the third output of the latter is connected to the second input of the first element I, the third input of which is connected to the second output of the initial installation block and to the second input The second element is AND, and the fourth input of the first element PI is connected to the second output of the shutdown unit and the third input of the second element AND, the third output of the initial installation block is connected to the second input of the first element I. OR, the third input of the last connected to the third output of the first control unit; the fourth output of the last control unit is connected to the first input of the reversible counter, the second input of which is connected to the second input of the first control unit, and the output of the inhibit unit is connected to the third input of the decoder, the fourth input of which is connected to the second output of the reversible counter , the third input of the latter is connected through a block for detecting the sign with the output of the second element I. Sources of information taken into account in the examination 1. Ontario Hydro, Berry D. N., Broron R. D., Redmond I. I., Watson. W. H. Underfrequency proteetion of the Ontario hudro System. “CIQRE-Jut. Paris. 1970 № 30-14 (prototype).