SU445094A1 - Equipment for transformer neutral grounding - Google Patents

Description

one

The invention relates to the field of electrical engineering and relates to the grounding of transformer neutrals in three-phase electrical networks with a voltage higher than 1000 volts.

A device for earthing a neutral transformer in networks with a voltage higher than 1000 V is known, containing a parallel-connected discharge circuit, a capacitor, AND a reactor with added resistance, incorporated into the neutral of the transformer.

The aim of the invention is to reduce the losses from zero-sequence currents in the normal mode of the network, the level of the ground current and the protection of the insulation from pulsed AND switching overvoltages.

This goal is achieved as a result of the fact that the reactor is supplied with a saturable magnetic conductor and has an inductive resistance in an unsaturated state, equal to it: the bone resistance of the capacitor, at the frequency of the network.

FIG. 1 is a schematic diagram of the device; in fig. 2 - volt-ampere characteristic of saturable throttle.

The device is a parallel k.ntu; p directly connected to the transformer's neutral; p, consisting of a series-connected saturating throttle .2 and active resistance 3, a capacitor 4, tuned in resonance with the inductor 2, and the surgeon 5, pro. looking for a neutral transformer I from overvoltages.

In normal mode, the displacement voltage of the neutral from the natural asymmetry of the network is below the saturation threshold of throttle 2. The inductive resistance of throttle 2 to saturation mode is constant. The capacitive impedance of the -capacitor 4 is equal to the inductive suppression of the choke 2 at the mains frequency. The resistance of the grounding device in this mode is large.

To ensure the operation of the device is selected. In this case, the neutral grounding is close to the insulated neutral mode. At frequencies significantly higher than the frequency of the network, and with impulse currents, the ontur has a very low resistance, and the neutral mode is close to the mode

spontaneous grounding. Increasing the voltage on the neutral to the level of the onset of the saturation of the throttle 2, the inductive resistance of the latter decreases sharply and the resonance in the circuit turns out to be disturbed.

The resulting loop resistance decreases and becomes unambiguously inductively active. The magnitude of the capacitor 4 and the characteristics of the droplets 2 are chosen so that the neutral voltage

with asymmetrical shorts x

the ground in the network did not exceed the maximum permissible value according to the operating conditions of the isolation of transformer 1 and the network, and the short-circuit currents were limited, based on the permissible voltages on the neutrals and on the operating conditions of the relay protection. Active resistance 3; in the circuit, acts as a damping element and increases the sozf. 3., and also reduces Ku due to an increase in

X

relationship -. g

At frequencies that are relatively low, but already significantly different from the resonant, the circuit can have significant conductivity. If overvoltages occur at these frequencies, the protective means is the voltage of 5, and the resonant 1n. Linear circuit limits the voltage of the fundamental frequency appearing on the neutral, thus providing a significant reduction of the associated currents of the fundamental frequency that flow through the 5 from switching overvoltages caused by asymmetrical earth faults in the electrical network.

Thus, the use of the proposed device provides a variable mode of operation of the neutral depending on the bias voltage of the neutral.

Subject invention

A device for earthing a neutral transformer in networks with a voltage higher than 1000 V, containing a parallel-connected discharge capacitor and a reactor, with additional resistance, included in the transformer neutral, characterized in that, in order to reduce losses from such a zero-sequence in normal mode the network, the coordination of the level of short-circuit currents on the ground and the protection of the insulation against impulse and switching overvoltages, the reactor is equipped with a saturable magitoprovod and has an impedance resistance of the lean state, an equal capacitive reactance of the capacitor at the mains frequency.