RU2490768C2 - Balancer for three-phase networks with neutral wire - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: balancer is purposed to improve quality of current and voltage balancing in three-phase networks with neutral wire due to self-adjustment of power in case of current change in the neutral wire. The device contains additionally two power stages and automatic control circuit operating as current function of the neutral wire.

EFFECT: improving quality of adjustment due to detuning parameters of the suggested device from current unbalance in the network of 0,38 kV present at the moment.

2 dwg

Description

The invention relates to electrical engineering and can be used for self-regulating balancing of currents and voltages in three-phase networks with zero wire when an asymmetric load is connected to them.

A device [1] of an electromagnetic type is known, the windings of which are connected in an oncoming zigzag pattern.

The disadvantage of this device is the use of complex circuits to control the device.

The closest technical solution, selected as a prototype, is a filter-balancing device for three-phase networks with a zero wire, containing a three-phase electromagnetic device having three phase terminals and one neutral, and each phase terminal is designed to connect to the phase wires of the network, and the neutral to zero the wire [2].

The disadvantage of this device is the immutability of its parameters, which does not allow to regulate the power of the device when changing the asymmetry of currents in the electric network.

The objective of the invention is to improve the quality of balancing currents and voltages in three-phase networks with a zero wire due to self-regulation of the power of the proposed device when the current in the neutral wire changes.

The invention consists in the following. The windings of each of the electromagnetic devices are connected in an oncoming zigzag circuit and have three phase and one neutral terminals. Each phase terminal is designed to be connected to the phase wires of the network, and the neutral terminal is to the neutral wire. Each electromagnetic device forms one power stage. Each power stage is switched on when the power contacts of the corresponding magnetic starter are closed, the coil of which is controlled by an automatic control circuit operating as a current function of the bullet wire and including a current transformer. installed in the bullet wire of the electric network and two current relays and one time relay for each power level. The result is an improvement in the quality of balancing currents and voltages in three-phase networks with a zero wire.

Figures 1 and 2 show a balancing device for three-phase networks with a zero wire.

Figure 1 presents a diagram of the proposed device, figure 2 is a diagram of the automatic control of a balancing device.

The proposed device has three power levels.

The balancing device for three-phase networks with a zero wire consists of three three-phase electromagnetic devices, the windings of which are connected in an oncoming zigzag circuit, having three phase terminals and one neutral, each phase terminal is designed to connect to the phase wires of the network, and the neutral one to the neutral wire. Each three-phase electromagnetic apparatus forms one power stage of the balancing device. At the first power stage, the first three-phase electromagnetic device is connected. With increasing asymmetry of currents and voltages, the power of the device increases. This is achieved by connecting additional one or two three-phase electromagnetic devices to the electrical network. The proposed device is completely disconnected from the network when the current in the neutral wire reaches the minimum value corresponding to the permissible value of the asymmetry of currents and voltages established by GOST 13109-97.

To automatically control the balancing device, it is proposed to use a circuit that controls the function of the current of the bullet wire (figure 2). The circuit includes a current transformer TL, six current relays KA1-KA6, three time relays KT1-KT3 and three magnetic starters KM1-KM3. Elements KA1, KA2, KT1 and KM1 are designed to control the first power stage of the balancing device; KA3, KA4, KT2 and KM2 - to control the second power stage of the balancing device; KA5, KA6, KT3 and KM3 - to control the third power stage of the balancing device.

The principle of operation of the device is illustrated by the example of the following settings of the current relays KA1 - 1A, KA2 - 2A, KA3 - 3A, KA4 - 4A, KA5 - 5A, KA6 - 6A.

With increasing current in the neutral wire and in the secondary circuit of the TA current transformer to 1F, the closing contact of relay KA1 closes, with a further increase of current to 2A, the closing contact of relay KA2 will operate (close), the coil of the timer relay KT1 will be powered, and the closing contact will be closed with a time delay relay КТ1 and the coil of the magnetic starter КМ1 receives power. After that, the magnetic starter closes its power contacts KM1 (figure 1) and the first power stage of the balancing device is turned on. Disconnection from the network of the first power stage of the balancing device will occur after the current decreases to 1A. In this case, the make contact KA1 comes to its original position (opens) and the coil of the KT1 time relay loses power. contact KT1 opens with a time delay, the coil of the magnetic starter KM1 loses power and the power contacts of the starter KM1 open (Fig. 1). In this case, the first stage of the balancing device is disconnected from the network. When the current decreases to 2A, shutdown will not occur, because the closing contact of relay KA2 is blocked by the auxiliary contact of the magnetic starter KM1.

The operation (connecting and disconnecting to the network) of the second and third power levels of the balancing device occurs similarly: the second power stage is connected when the response current of relay KA4 reaches 4A, and the shutdown occurs when the current decreases to 3A, i.e. when the current drops below the setting of the current relay KA3.

The third stage of the balancing device is connected when the current increases to 6A, and disconnection from the network occurs when the current decreases below 5A.

The time delay when connecting and disconnecting the power stages of the balancing device is carried out using three time relays KT1, KT2 and KT3 to prevent the operation of the device steps during short-term load fluctuations.

The TA current transformer is installed in the neutral wire of the 0.38 kV electric network and is designed to connect the TA1-TA6 current relays.

Thus, the power of the device is self-regulating as a function of the zero-wire current and the parameters of the proposed device are detuned from the current asymmetry level in the 0.38 kV network that is taking place at a given time.

INFORMATION SOURCES

1. A.S. USSR No. 1206881, 09/23/83.

2. A.S. USSR No. 1206881, 09/23/83 - prototype.

Claims (1)

A balancing device for three-phase networks with a zero wire, containing three three-phase electromagnetic devices, characterized in that the windings of each of the electromagnetic devices are connected in an oncoming zigzag circuit and have three phase and one neutral terminals, each phase terminal is designed to connect to the phase wires of the network, and neutral output - to the neutral wire, each electromagnetic device forms one power stage, each power stage is included in the work when the power contacts are closed, the corresponding its magnetic starter, the coil of which is controlled by an automatic control circuit operating as a function of the neutral wire current and including a current transformer installed in the neutral wire of the electric network and two current relays and one time relay for each power stage.

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