SU299908A1 - METHOD OF DIRECTED PROTECTION AGAINST SINGLE-PHASE OUTLINES ON EARTH - Google Patents

Description

The invention relates to methods of directional protection against single-phase earth faults in compensated networks, based on the use of the sum of the higher harmonics of currents and zero-sequence voltages.

To increase the sensitivity and selectivity of the proposed method, they differentiate the voltage of the zero sequence, suppress the component of the primary frequency in the differential voltage and in the current of the zero sequence of the protected connection. The values obtained at the same time are fed to two inputs of a phase-sensitive organ that triggers or blocks protection, depending on the sign of the constant component of the signal at the output of the phase-sensitive organ.

The drawing shows a block diagram illustrating the proposed method.

The circuit contains a zero-voltage time differentiation unit 1, a main component of the differentiated zero-sequence voltage component 2, a main component in the zero-sequence circuit, phase-sensitive organ 4, and an organ 5 that performs triggering or blocking depending on from the sign of the constant component at its input.

With a single-phase short circuit outside the protected junction, the shape of the zero sequence voltage curve (after differentiation by block / and suppression by main component 2) and the polarity are completely identical to the shape and polarity of the electrical quantity proportional to the zero sequence of the protected junction after suppression block 3. These two electrical quantities applied to block 4 cause a certain sign of the constant component at the output of this block a (if both values are given for block 4 according to, then the plus sign, if opposite, minus). The block 5, with the adopted polarity of the switch-on unit 4, blocks the protection.

In the case of a single-phase closure at the protected connection, the shapes of the electrical quantities at the outputs of blocks 2 and 3 are identical, and their polarities are opposite. Under these conditions, the constant component at the output of block 4 is opposite with respect to the case of a closure outside the protected connection (with a consistent connection of block 4, the sign is "minus, with a counter" plus "). Under these conditions, block 5 triggers the protection.

x 6-35 sq. in the case of stationary, scheduling devices, and, when executing hand-held instruments, until the search for a place of one-to-one, the charging of air in the compensated air d JSjjjfjG-35 sq.

The independence of the operation of shields on the ratios of capacitive currents of the connections and on oscillations in a wide range of higher harmonic levels of the network allows a significant increase in the sensitivity of protection.

The zero sequence current of direct connection, i.e., its phase capacitance relative to earth Ci, is equal to

3i, i - for - or 3i, i for -,

where and is the phase voltage of the damaged phase with the opposite sign equal to the zero-sequence voltage {() The zero-sequence current of the damaged connection:

h (s,

3L

ai lyj

where LK is the resultant inductance

compensating coils network. For higher current harmonics / oi, the second term can be neglected in the above expression. Then for the higher harmonics of the currents gog and / 01 there will be relations:

 Q

s / l

dUon

- 3 (C5; - C.) dt

where n is the harmonic order.

Thus, the harmonic composition of the zero sequence of the connections is identical to the harmonic composition of the time derivative of the zero sequence voltage, with the main component removed from them, i.e., the shape of the curves of these quantities is the same. At the same time, the phase relations (polarity) of the curve of the aggregate of the higher harmonics of the zero sequence of the damaged connection and the curve of the maximum

opposite harmonics

and phase relations (polarity) of the curves of the set of higher harmonics of intact connections and the aggregate / o curve

higher harmonics function

match

give.

The application of the proposed method allows for the selective protection of all connections of any compensated networks, i.e., to expand the scope of the selective protection operation.

Subject invention

A method of directional protection against single-phase earth faults in compensated networks based on the use of the sum of high harmonics of currents and zero sequence voltage, characterized in that, in order to increase sensitivity and selectivity, they differentiate the zero sequence voltage, suppress the fundamental frequency component at

differential voltage and current of the zero sequence of the protected connection and the resulting values are fed to the two inputs of the phase-sensitive organ, which triggers or blocks the protection, depending on the sign of the constant component of the signal at the output of the phase-sensitive organ.