Balancer for three-phase networks with neutral wire

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.

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The invention relates to electrical engineering and can be used for self-balancing currents and voltages in three-phase networks with zero wire when connected to the unbalanced load.

It is known device [1] electromagnetic type, the windings of which are connected according to the scheme counter zigzag.

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

The closest technical solution, selected as a prototype, is filtersysteme device for three-phase networks with zero wire containing a three-phase electromagnetic device having a three phase output and one neutral, each phase output is intended for connection to the phase wires of the network, and the neutral - zero-wire [2].

The disadvantage of this device is the constancy of its parameters, which does not allow to regulate the power of the device when changing the unbalance currents in an electrical network.

The objective of the invention is to improve the quality of balancing the currents and voltages in three-phase networks with zero wire through self-regulation capacity of the device when changing the current in the ground wire.

The invention consists in the following. Winding each of the electromagnetic apparatus is of the ATA is connected according to the scheme counter zigzag and have three phase and one neutral conclusions. Each phase output is intended for connection to the phase wire network, and a neutral output to a zero wire. Each electromagnetic device forms one stage of power. Each stage power turns on when the circuit power contacts of the respective magnetic starter, the coil of which is driven by a scheme of automatic control, working in the function current bullet wire and includes a current transformer. established in bullet wire electrical network and two current relay and one time relays on each output step. The result is improved quality of balancing the currents and voltages in three-phase networks with zero wire.

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

Figure 1 shows the diagram of the device, figure 2 - scheme of automatic control of the balancing device.

In the proposed device has three levels of power.

Symmetrise device for three-phase networks with zero wire consists of three three-phase electromagnetic machines, windings are connected according to the scheme counter zigzag with three phase output and one neutral, each phase output is intended for connection to the phase wires of the network, and the neutral to the ground wire. Each three-phase electromagnetic apparatus forms one stage of power balancing device. At the first stage power connected first three-phase electromagnetic apparatus. With increasing unbalance of currents and voltages in the power of the device increases. This is achieved by connecting an additional one or two three-phase electromagnetic devices to the electrical network. The proposed device is completely disconnected from the network while achieving current in the ground wire is the minimum value corresponding allowable unbalance currents and voltages specified by GOST 13109-97.

For automatic control of the balancing device are encouraged to use the scheme, which regulates the function of the current bullet wire (figure 2). The circuit includes a current transformer TL, six current relay KA1-CA, three time relay KT1-CT and three magnetic contactor KM1-KM3. Elements SA1, CA, KT1 KM1 and are designed to control the first output step of balancing device; CA, CA, CT KM2 and to control the second stage of the power balancing device; CA, CA, CT and KM3 for the management of the third stage of the power balancing device.

The principle of operation of the device let us consider the following example of setting values of the current relay KA1 - 1A, CA - 2A, CA, CA - 4A, CA - 5A, CA - 6A.

With increasing current in the ground wire in the secondary circuit of the current transformer TA to 1F closes normally open contact relay KA1, with a further increase of the current up to 2A - work (closes) normally open contact relay CA will receive power relay coil time KT1, with time delay closes normally open contact relay KT1 is powered on and the coil of the magnetic contactor KM1. After that, a magnetic starter closes his power contacts KM1 (figure 1) and includes a first output step of balancing devices. Disconnect from the network the first step of capacity balancing will occur after the device of the current reduction to the value of 1A. Thus closing contact KA1 comes in its original position (opened) and the coil of the time relay KT1 loses power. contact KT1 opens with a time delay, the coil of the magnetic contactor KM1 loses power and power contacts of the contactor KM1 open (figure 1). When this occurs, disable the first stage symmetrised device from the network. By reducing the current to 2A shutdown will not occur, since the normally open contact relay KA blocks auxiliary contact of the magnetic contactor KM1.

Work (connecting and disconnecting to the network) the second and third stages of power balancing device is similar: connecting the second STU is Yeni power occurs when the current relay KA, equal to 4A, and off - by reducing the current to 3A, i.e. by reducing the current below setpoint current relay KA.

The third step of balancing device is connected with increasing current up to 6A, and the network disconnection occurs when the current is reduced to below the value of 5A.

The time delay when connecting or disconnecting the speed of the power balancing device is performed using the three time relay KT1, KT and KT to prevent actuation of the speed of the device at short-term load fluctuations.

A current transformer THAT is installed in the neutral wire of the electrical network 0,38 kV and is designed to connect current relay TA1-TA.

Thus, the capacity of the self-adjusting device as a function of current neutral conductor and the parameters of the proposed device rebuilt from the level of unbalance of the currents in the network 0,38 kV, taking place in a given time.

SOURCES of INFORMATION

1. As the USSR №1206881, 23.09.83.

2. As the USSR №1206881, 23.09.83 prototype.

Symmetrise device for three-phase networks with zero wire containing three-phase electromagnetic apparatus, characterized in that the winding of each of the electromagnetic devices are connected according to the scheme counter zigzag and have three phase and one neutral conclusions, each phase output is intended for connection to the phase wire network,and a neutral output - zero wire, each electromagnetic device forms one output step, each stage power turns on when the circuit power contacts of the respective magnetic starter, the coil of which is driven by a scheme of automatic control, working in the function current zero wire and includes a current transformer installed in the neutral wire of the electrical network and two current relay and one time relays on each output step.



 

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