SU1157609A1 - Device for differential protection with braking - Google Patents

Abstract

DEVICE FOR DIFFERENTIAL PROTECTION WITH BRAKING, containing current sensors installed on. the ends of the protected object, the outputs of which are connected to the inputs of the unit for forming the working signal and the braking signal forming unit, the outputs of which are connected to the comparator unit and the threshold organ connected in series with the purpose of twisting sensitivity and improving the selectivity, the braking unit The signal is made in the form of a serially connected analog smart sensor and an amplitude memory unit of the negative half-wave containing a differentiating element, a zero-body, a di the differential chain, the sample and storage element, the analog multiplier inputs being connected to the input terminals of the brake signal formation unit, the analog multiplier output connected to the differentiating element and sampling inputs (L and storage, the output of the differentiating element of the sampling and storage, the output of the differentiating element through the zero-or-, gan and differentiating chain is connected to the control input of the sample and storage element, the output of which is connected to the output terminal b loader ka formation of the brake signal. O) o with

Description

The invention relates to electrical engineering, in particular to devices for differential current protection against short circuits of such electrical installations as synchronous generators, compensators, motors, and non-spanning power lines. The purpose of the invention is to increase the sensitivity and improvement of selectivity. FIG. 1 shows a block diagram of the proposed device; in fig. 2 is a block diagram for storing the amplitudes of negative half waves; Fig. 3 shows an embodiment of the sampling and storage element. The device (Fig. 1) contains installed on both sides of the protected electrical installation 1, current sensor data 2 and 3, the secondary windings of which are connected to the operating signal generating unit 4 and the braking signal generating unit, consisting of an analog multiplier 5 and amplitude storage unit negative half wave. Outputs of blocks 4 and & connected to a comparative unit 7 connected to a threshold organ 8. The amplitude-storage unit 6 of negative half-waves (Fig. 2) consists of differentiating element 9, zero-organ 10 and differentiating chain t1 connected in series, element 12 of sampling and storage, To the gate input of which the output of the differentiating chain t1 is connected. In block 4, the formation of

signal is the formation of a working signal by law. .g. where1. „and1 secondary sensor currents i proportionality coefficient output voltage. In accordance with the algorithm of operation of the working signal shaping unit, it can be made in the form of series-connected cytMaTOpa on the operational amplifier and rectifier. The working signal (s) at the output, block 4 is equal to

To 1st mzh. Rneij ((cos C - po & ptai -.- ttf))

U

s en an. 6, "" "Wt t 1 ,, Sinfiot Cf JI; L-sinftot Sab Inoif if - angle between t Н1 ufcitiet iftme lift mot Т TCOS 4 1 ft max "" flow circuit short external 180) CHMYK 8. internal short circuit (H 0) working signal is equal to sir uit Р "in- (II i6m "" "so the analog multiplier 5 multiply the secondary currents of the sensor according to the law" h, 1, ", Sir fOt. 1 ,, sm (WJ. go - output voltage of the analog multiplier; proportionality factor. As an analog multiply, you can take commercially available Roschem After the transformation, the output can be represented in the following way: With an external short circuit (1 1 „„ „а, 1ё, h tSO.) To t (Itcos2o t) U nk“ м2 ftMxotij In case of internal short circuit ftp ,, „- (A-cos2Mt). Ho, 0Differentiating element 9 is intended for phase shift by 90 and the elimination of the constant component of the output signal of the analog multiplier. It can be performed on the operational amplifier and the RC-chain.

3

The null organ 10 is intended to enhance the instant the output signal of the differentiating device passes through zero. It can be made on the basis of the nullcomparator.

The differentiating chain 11 is designed to isolate a narrow pulse with a positive front of the output voltage of the null organ and is an RC-chain,

Selement 12 of sampling and storage is intended to record the voltage applied to it at the time of the appearance of the strobe pulse and store it until the next strobe pulse, followed by its use as a brake signal.

As an element of sampling and storage, an element can be used, the scheme of which is shown in FIG. 3

When the positive gate gates arrive at its control (gate) input, transistors 13 and 14 open, and the storage capacitor 15 is charged to the amplitude of the input signal. In the absence of strobe-pulse transistors 13 and 14 are closed and the circuit is in the mode of storing the amplitude of the signal. The transistor 14 and the resistor 16 serve to reduce the leakage currents of the transistor 13 in the signal storage mode.

The comparator unit 7 produces the summation of the working and braking signals, arriving with different signs from the units of forming the working signal 4 and storing the amplitudes of the negative half-waves 6.

As it can be used adder on the operational amplifier.

The threshold for triggering protection, due to the unbalance of the current sensors, is provided by the threshold body 8, which is triggered when the difference between the working and brake signals of the setpoint is exceeded.

 The device works as follows. 576094

In case of an external short circuit, a signal appears due to an imbalance of the current sensors, g having a positive sign, at the output of the operating signal shaping unit 4. At the output of the analog multiplier, a signal with a double network frequency appears, having only negative values. The amplitude of this signal memorizes to c in the block of storage of the amplitudes of negative signals and acts as a brake signal to the input of the comparator unit 7, thereby ensuring reliable failure of the threshold

5 organ 8. The magnitude of the amplitude of the brake signal is proportional to the square of the amplitude of the flowing through current, i.e. provides strong braking for large end-to-end

0 selectivity currents and low braking at low through currents.

In the event of a short circuit in the zone with one-sided powering of the protected object from either side, one of

5 of the secondary currents is zero, the brake signal, which is proportional to the product of the amplitudes of the secondary currents, is also zero, no protection deadening occurs. With a short

- short-circuit in the zone with a two-sided power supply of the protected object in the absence of a through-current, the voltage at the output of the analog multiplier is always greater than zero, the brake voltage, which is proportional to the negative amplitude of the output signal of the analog multiplier, is zero. The protection is triggered without braking, which contributes to its lack of sensitivity. In case of a short circuit in the zone in the presence of through current, a brake signal appears, depending on the shear angle. between the currents of the arms and the amplitudes of the secondary currents. It is always less than with an external short circuit, and due to the nonlinearity of the dependence of the brake signal on the secondary currents, is small enough to ensure the protection operation.

Claims (1)

DEVICE FOR DIFFERENTIAL PROTECTION WITH BRAKES, containing current sensors installed by. the ends of the protected object, the outputs of which are connected to the inputs of the working signal generating unit and the brake signal generating unit, the outputs of which are connected in series to the comparison unit and the threshold organ, characterized in that, in order to increase sensitivity and improve selectivity, the brake signal generating unit made in the form of an analog multiplier connected in series and a unit for storing the amplitude of negative half-waves, containing a differentiating element, zero-organ, different a chaining element, a sampling and storage element, and the inputs of the analog multiplier are connected to the input terminals of the brake signal generation unit, the output of the analog multiplier is connected to the inputs of the differentiating element and the sampling and storage element, 'the output of the differentiating sample and storage element, the output of the differentiating element through a series-connected zero-op. The gun and the differentiating chain are connected to the control input of the sampling and storage element, the output of which is connected to the output terminal of the brake signal generation unit. >