SU1262625A1 - Method of automatic frequency off-loading - Google Patents

Abstract

The invention relates to an emergency control automation and is used for automatic frequency unloading (AChR). The purpose of the invention is to provide the possibility of restoring the frequency according to a given law. With an emergency frequency in the power system, the rate of change of the frequency greater than the setpoint, and the rate of recovery of the frequency less than the setpoint, the time delay of all the frequency response lines begins. The first phase of the AChR is instantaneous. When the power system frequency is restored, the time delay countdown is suspended. With a subsequent decrease in the rate of rise of the frequency, the time delay countdown will continue. In the case of an increase in the frequency above the trigger setpoint frequency, the time count is terminated. When restoring the nominal frequency, C /) resets the time delay and the system returns to its original state. In this method, the law of frequency recovery can be chosen not only exponentially, but also others, for example, approximated by separate time-frequency linear sections. 2 Il.

Description

The invention relates to emergency control of power systems and can be used, for example, to realize automatic frequency unloading, disconnect part of the power system consumers during a frequency accident and restore the frequency after its emergency reduction.

The purpose of the invention is to provide the possibility of restoring the frequency according to a given law, which ensures a fast recovery of the frequency without unnecessary disconnection of consumers.

In order to improve the performance of the frequency gain system, frequency recovery should occur according to a given law, for example, exponential,

fi f, +. (Eist-e -O (1st),

where f is the frequency at the start

about

frequency recovery ;, mtb value to which the frequency is restored in the process of eliminating the power shortage (as a rule, this is the nominal frequency value);

fj is the time constant from which the frequency is restored.

The frequency recovery rate df./dt at any value of frequency f can be expressed as

  . (f p dt g ms, b -

If the process of frequency restoration in the power system proceeds according to a given law, then the rate of change of frequency in the system is equal to the speed df / dt. If iai6paTb is the frequency recovery time constant t: the system frequency (Cj T), which is obviously larger than the maximum value of the time constant, which generally changes depending on the mode in the power system, the condition df / dt - dfj / dt says - that recovery is not in accordance with the prescribed law - and it is required to make an additional disconnection of consumers.

In Fig. 1, a diagram of a device realizing the proposed method on 4ig.2 — the time-frequency diagram of the operation of the device is arrived.

The device contains a unit of measurement 1 frequency, relay. 2 boosts frequency, speed measurement unit 3 changes frequency, frequency converter 4, speed converter 5 from / frequency, adder 6, amplifier 7, comparator 8, logic element AND 9, time delay unit 10 and responsive organ II.

The device works as follows.

The voltage of the measured frequency is applied to the inputs of blocks 1 and 3 of frequency measurement and frequency measurement speed change, frequency increase relay 2, frequency converter 4 and frequency change speed converter 5.

At the rated frequency, there is a signal in the power system at the output of frequency increase relay 2, there is no signal at the output of frequency measurement unit 1, and at the outputs of frequency converter 4 and frequency converter 5 there is a voltage proportional to the frequency deviation from the nominal (or other) frequency. given value and rate of change of frequency. The signal from the output of the relay 2 block 10 time delay is set to zero. When the frequency decreases in the system, below the triggering setpoint level of АЧР-П f д, the frequency measurement unit 1 fails and from its output a signal is fed to one input of logic element 9. The setting of unit 3 is selected so that the output signal takes place

5 condition df / dt A, where A is a very small negative value or zero.

The signal f from the output of frequency converter 4 is applied to one input of the adder 6, to the second input of which the setpoint signal f is applied. . The adder 6 subtracts these signals and at its output there is a signal f ,, g -f. This difference is multiplied in amplifier 7 by 1/7,. So obfi. .

At the same time, in the comparator S, the values df / dt (from the output of the converter 5) and df, / dt (f, -f) / tj are compared (from the output of the amplifier 7). If three conditions are met - the frequency in

the system is abnormal (frequency measurement block 1 is triggered), the frequency reduction is stopped (block 3 is triggered), and the frequency recovery rate is less than the specified df / dt df./dt

5 (comparator 8 is triggered) - there are signals on all three inputs of the logical element 9. In this case, the signal is fed to the control input of the time delay unit 10 and starts from the time delay count of all the ACR-P queues. The first queue of АЧР-П is triggered instantly at time t (point а- in Fig. 1). Suppose that turning off this queue is enough for that to speed up the process of frequency recovery (df / dt (curve B in Fig.L). The signal from the output of the comparator 8 disappears and, therefore, the signal from the output of the logical element AND 9 disappears. The timing of the time delay stops. The frequency in the system rises to the level fc, f f ,, (figure 1). At the point in time corresponding to point b in FIG. 1, the rate of the frequency rise again becomes less than the target, all three signals appear and the input of the logic element AND 9 continues counting the time delay of all the queues of АЧР-П. At the moment of time t (point C) the second turn of АЧР-П is triggered, the speed of raising the frequency increases, but, for example, still remains less than the value of df . / dt. The frequency tends to a new value f.,, fsev.6 Cheat at the time of the cut, the time interval tj is triggered by the next AFR-P (point d in figure 1). Figure 1 shows the case when turning off the three queues was enough to restore often according to a law close to the given one. 35

When the frequency rises above the f level, the signal from the output of the frequency measurement block I disappears, this stops the reading of the AFR-P time delay, and when the frequency rises above the f level, ...

a signal is given to the time delay reset input of the time delay unit 10 and the circuit returns to its original position.

In the case of a cascade alarm, when the frequency is reversed, as the speed df / dt A, the time count of the time elements is suspended. The unloading is performed by the AFR-1 category and the subsequent frequency recovery is performed using the remaining AFR-P queues in the already known order

The law of frequency recovery can be chosen not only exponentially ss

Other technologies, for example, are approximated by individual frequency variations of the frequency greater than the setpoint, which is different from the fact that, in order to restore the frequency according to a given law, the rate of change of the frequency in the power system is additionally compared to

J d-sf

where f,

value to which

ws-t.e ,. restore the frequency in the power system; f - current frequency value 1j - specified value of constant time,

Claims (1)

moreover, the time delay countdown of the queues of the frequency unloading is triggered in the case when it is skewy and less than the second speed setpoint. temporary linear sections. In this case, the technical implementation of the method remains unchanged. In the proposed method, the accuracy of the frequency restoration according to a given law is the higher, the smaller the time interval between the individual ACP-R lines. Therefore, the time interval can be reduced to a level of 0.50, 7 s. As elements of the device, standard elements of emergency control systems of power systems can be used, as well as standard electronic elements. The use of the proposed method and the construction of a device with the specified switching on of elements allow for the restoration of the frequency in the power system during a frequency failure according to a given law, reduce unnecessary disconnection of consumers and avoid overshooting the frequency in the system. The invention method of automatic frequency unloading by measuring the frequency in the power system, comparing it with the starting set point, measuring the rate of change of frequency and disconnecting customers in certain intervals between them when the frequency drops below the set point of start and the rate of change of frequency is greater than