RU2342754C2 - Method for carrying out selectivity of protection against one-phase earth connections in isolated-neutral systems - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: application: in electric engineering in particular in relay protection devices. Essence of invention: zero-sequence current integration is performed in unit (1) and difference of voltage signals in zero-sequence and at unit (1) output is formed in unit (2). Modulus of signal at unit (2) output is formed in unit (3). Sum of voltage signals of zero-sequence and unit (1) output is formed in unit (4). Modulus of signal at unit (4) output is formed in unit (5). Subtraction of signals from unit (3) and unit (5) is performed in unit (6). Signal from unit (6) output is applied to input of unit (7) which represents aperiodic link of the first order. Signal from unit (7) output is compared with set value and when it is exceeded cutoff signal is generated.

EFFECT: providing selectivity in case of one-phase earth connection in isolated-neutral systems.

1 dwg

Description

The invention relates to the field of electrical engineering, and in particular to devices for the relay protection of electrical networks with isolated neutral from single-phase earth faults. Known methods for implementing the selectivity of such protections are based on the implementation of the power direction relay of the zero sequence of the fundamental harmonic. At the same time, active or passive filters are included to highlight the fundamental harmonic at the input of such protections. Such protections make it possible to selectively disconnect earth faults through low resistance (metal faults). The proposed method of ensuring selectivity of protection is based on well-known mathematical expressions:

where A and B are any physical quantities.

In case of single-phase earth faults in a network with isolated neutral, a zero sequence voltage and a zero sequence current appear. Moreover, inverted by one hundred and eighty electrical degrees, the zero-sequence current vector at the damaged connection is ahead of the zero-sequence voltage vector by ninety electric degrees of the fundamental harmonic of the electric current; at the undamaged connection, it lags the same angle from the zero-sequence voltage vector.

The technical result consists in providing selectivity for single-phase earth faults in networks with isolated neutral.

The drawing shows a diagram of a device that implements a method for implementing the selectivity of protection against single-phase earth faults in networks with isolated neutral.

In block 1, the zero-sequence current is integrated, and in block 2, the difference of the zero-sequence voltage signals and the output of block 1 is formed. In block 3, the signal module from the output of block 2 is formed. In block 4, the sum of the zero-sequence voltage signals and the output of block 1 is formed. block 5 form the signal module from the output of block 4. In block 6, the signals from the output of block 3 and block 5 are subtracted. The signal from the output of block 6 is fed to the input of block 7, which is an aperiodic first-order link. The signal from the output of block 7 is compared with the setting, when exceeded, a trip signal is generated.

To implement the proposed method for the implementation of selectivity of protection against single-phase faults, at the first stage of the conversion of input signals, the signal is received, which is received from the zero-sequence current sensor and turned over one hundred eighty electrical degrees. In this case, there is a shift in the direction of advancing by ninety electrical degrees of all harmonic components present in the signal. In this case, the main component of the integrator's output signal vector will be out of phase with the main harmonic vector of the zero sequence voltage at the damaged connection and in phase at the undamaged connection.

Further, the signal conversion is performed in two parallel channels. In the first channel, a module of the sum of signals from the output of the zero-sequence voltage sensor and the output signal of the integrator is formed, in the second channel, the difference module of these signals is formed.

Next, the difference of the signals received at the outputs of the first and second channels is formed, and the received signal is fed to the input of the block with the transfer function of the aperiodic link of the first order.

Moreover, if the device operating according to the proposed method is installed on an intact connection, then, according to expression (1), a positive signal will be received at the input of the block with the transfer function of the first-order aperiodic link, and therefore, a positive signal will be at the output of this block (under the values A and B, the signal from the zero-sequence voltage sensor and shifted by one hundred eighty electrical degrees, integrated, the signal from the zero-sequence current sensor) should be understood.

If the device is installed on a damaged connection, then, according to expression (2), a negative signal is received at the input of the block with the transfer function of the first-order aperiodic link, an increasing negative signal appears at the output of this block, which is compared with the setting and is used to disconnect this connection.

Claims (1)

A method for selectively disconnecting a single-phase earth fault in a multiphase network with an isolated neutral, which consists in converting and comparing the signals received from the current and voltage sensors of the zero sequence, when the signal from the current sensor of the zero sequence is integrated and then, together with the signal from the voltage sensor of the zero sequence two parallel circuits, in one of which the module of their sum is formed, and in the other - the module of their difference, the difference of the signals from the outputs e their chains, which is input to the first-order delay element, the output of which is used to selectively disable the single-phase ground fault.