CN201846089U - Voltage-regulating type three-phase loading unbalance limiter - Google Patents

Abstract

The utility model relates to a method for safety, energy saving and power quality improvement of a low-voltage distribution network and a power distribution device, namely a three-phase load unbalance limiting method and a voltage-regulating three-phase load unbalance limiter, which are used in the low-voltage distribution network At important nodes of the load, a voltage-regulating three-phase load unbalance limiter slightly larger than the load capacity of the branch line is installed. The three-phase load unbalance limiter forms a new three-phase power supply system with the load at the node and generates a new ground neutral line N', thus limiting the zero-sequence current path below the node; voltage-regulating three-phase load unbalance limiter The device is composed of an auto-coupling three-phase load unbalancer, or an isolated three-phase load unbalancer and a voltage regulating switch; the utility model limits the zero-sequence current that causes the unbalanced low-voltage system to below the node of the installed line, making it The phase-to-phase load balance between the lines above the node and the distribution transformer eliminates the considerable loss of this part and various hazards caused by the three-phase imbalance, and improves the safety level of the low-voltage distribution network.

Description

Voltage regulating three-phase load unbalance limiter

technical field

The utility model relates to a method for safety, energy saving and power quality improvement of a low-voltage distribution network and power distribution equipment, namely a three-phase load unbalance limiting method and a voltage-regulating type three-phase load unbalance limiter. the

Background technique

As we all know, the three-phase imbalance of the low-voltage power grid has always been one of the main problems plaguing the power supply unit, and it is a "small problem in the world". The low-voltage distribution network is the network that provides the most direct and most power to users. Three-phase power consumption and single-phase power consumption are often mixed together, especially for some uncontrollable capacity increases. High-power single loads are connected to low-voltage distribution networks, plus various single loads Due to factors such as different nature and different timeliness of use, the unbalanced three-phase load of the low-voltage power grid is prominent and common. If the voltage is low, the electrical appliances cannot operate normally, and the voltage of some phases is too high or even very high, which will damage the electrical appliances. The unbalanced load will also significantly increase the loss on the three-phase live wire and transformer winding, and the zero line current will increase the loss of the low-voltage line. , especially for distribution transformers with large loads and long lines, the power loss is more significant; the three-phase load is unbalanced, and the load is concentrated on the first and second phases, which reduces the output of the distribution transformer and easily damages some phase windings of the transformer. Or the zero line current is overloaded, and the zero line is blown, further causing accidents and endangering safety. With the rapid development of social economy and the rapid increase of low-voltage power consumption, the distribution network is also rapidly expanding, and it has become more complex, and the problem of three-phase load imbalance has become more prominent. For this reason, many people have conducted research on this issue. At present, advanced electronic technology has been applied in foreign countries, and the unbalanced three-phase current undergoes a series of AC-DC-AC conversions, and then obtains AC power with stable voltage, frequency and phase, which is equivalent to a three-phase motor. Running a three-phase generator can eliminate the unbalanced current of the corresponding power grid, but it is expensive and expensive, and the harmonic pollution is relatively serious. At present, it is only suitable for some precision instruments and some electronic equipment in a small range. In China, there is a method of phase-separated compensation for single-phase capacitors. This method can sometimes make the three-phase currents approximately equal in size and magnitude. However, due to the different nature of the load and the different power factors of each phase, the vector sum of the three-phase currents is not equal. There is still a certain amount of current flowing through zero and neutral lines, and because the single-phase load changes randomly, the neutral point displacement is still prominent, and the three-phase voltage is asymmetrical, so the natural effect is not ideal. Although some improvement methods have appeared recently, they are still There are such and such problems. the

Utility model content

The purpose of this utility model is to provide a kind of equipment, which is used to limit the "unbalanced loss" and abnormal state or failure caused by the unbalanced three-phase power load, and improve the safety status and power quality, that is, the voltage-regulating three-phase Load imbalance limiter. the

The technical scheme of the utility model: the pressure-regulating three-phase load unbalance limiter is composed of an auto-coupling three-phase load unbalancer, or an isolated three-phase load unbalancer and a voltage regulating switch;

The self-coupling three-phase load unbalancer is a three-phase three-column coil. The three-phase three-column coil is divided into a common coil and a voltage regulating coil. Lead out the neutral line N', the first voltage regulating coil of phase A is connected to the common coil of phase B, the first voltage regulating coil of phase B is connected to the common coil of phase C, and the first voltage regulating coil of phase C is connected to the common coil of phase A;

The isolated three-phase load unbalancer is a three-phase three-column coil, which is composed of a power-side coil and a load-side coil without electrical connection. The load-side coil is divided into a basic coil and a voltage regulating coil. The end of the three-phase basic coil Connected into a star shape, the neutral point leads to the neutral line N', and the load side coil is connected as follows: the second voltage regulating coil of phase A is connected with the basic coil of phase C, the second voltage regulating coil of phase B is connected with the basic coil of phase A, The second voltage regulating coil of phase C is connected with the basic coil of phase B;

The voltage regulating switch is composed of a selector switch and a transfer transition switch, wherein the transfer transition switch is a non-contact thyristor switch connected in series with a current limiting resistor, and the voltage regulating switch is also provided with a voltage regulation controller and a non-contact thyristor controller. the

Described voltage regulating controller is made up of sampling circuit, A/D conversion circuit, output locking circuit, drive circuit, timing permission circuit. the

The non-contact thyristor controller is composed of a light control element, a thyristor, a piezoresistor, a voltage protection circuit, a rectification circuit and a load driving circuit. the

Beneficial effect

1. Limit the zero-sequence current that causes the imbalance of the low-voltage system to below the node of the installed line, so that the load above the node and the phase-to-phase load of the distribution transformer are balanced, thereby eliminating the considerable loss of this part. At the same time, it eliminates various hazards caused by three-phase imbalance, which can greatly improve the safety level of low-voltage distribution network. the

2. A small-capacity load unbalance limiter is used to match the load of the branch line, which is flexible to use; when the load of the branch line increases, the load unbalance limiter can be used in parallel, which has wide application and good effect. the

3. After adjusting the voltage with the voltage regulating device, the advantages of ensuring the voltage quality of users, improving product quality and saving electricity are very obvious. the

4. It has a variety of comprehensive protection functions. In particular, it has the protection functions of phase loss, neutral line disconnection, phase line and neutral line misconnection, which greatly improves the safety level of electrical equipment and personnel. the

5. The three-phase load unbalance limiter is a solid structure, which is novel, reliable, long in life and affordable. the

Description of drawings

Fig. 1 is a schematic diagram of the electricity saving applied in the low-voltage power distribution system when the voltage regulating type unbalanced load limiter of the utility model includes an auto-coupling three-phase load unbalancer. the

Fig. 2 is a schematic diagram of power saving applied in a low-voltage power distribution system when the voltage-regulating unbalanced load limiter of the utility model includes an isolated three-phase load unbalancer. the

Figure 3 is a schematic diagram of the structure of the self-coupling three-phase load unbalance limiter. the

Figure 4 is a structural schematic diagram of an isolated three-phase load unbalance limiter. the

Fig. 5 is a schematic diagram of the electric connection between the changeover switch and the selector switch of the voltage regulating switch when the utility model includes the self-coupling three-phase load unbalancer. the

Fig. 6 is a schematic block diagram of a voltage regulating controller circuit of the voltage regulating switch of the present invention. the

Fig. 7 is a functional block diagram of the non-contact thyristor controller circuit of the voltage regulating switch of the present invention. the

Detailed ways

The implementation of the utility model eliminates the factors that cause unbalanced three-phase loads, that is, the influence of zero-sequence current, and cuts off the path of zero-sequence current flow through the analysis of the operation of the low-voltage distribution network and the study of the structural characteristics of the power distribution transformer. and limited to a minimum. This is our zero-sequence current limiter, also known as the three-phase load unbalance limiter. Measures are taken inside it to offset the zero-sequence magnetic flux generated by the zero-sequence current. Without the effect of zero-sequence current, there will be no The loss of zero-sequence current in the three-phase load unbalance limiter is eliminated. At the same time, the voltage regulating device can adjust the user voltage according to the line voltage change, so as to ensure the power quality and protect the safety of electrical equipment. That is to say, at the important nodes of the load of the low-voltage distribution network, the utility model that is slightly larger than the load capacity of the branch line is installed, that is, the voltage regulating type three-phase load unbalance limiter. The voltage regulating three-phase load unbalance limiter forms a new three-phase power supply system with the load at the node and generates a new neutral line N', thus limiting the zero-sequence current path below the node. At the same time, in addition to the general over-current and over-voltage protection, a safety voltage (36V) protector is installed on the N' line. When a high voltage appears on the N' line, the N' line is grounded or the power supply line is disconnected. , in order to prevent the zero line disconnection and phase failure, set up the corresponding protection and signaling devices. the

As shown in Figure 1, at a node of the low-voltage power distribution system, a balanced branch line of the three-phase balanced load 2 is connected, and the neutral line of the balanced load 2 is connected to the neutral line N of the low-voltage power distribution system 1, and the first end of the neutral line N is one point grounded. The branch line 4 of the three-phase unbalanced load 3 is also connected at the node, and the end of the branch line 4 at the node is installed with a voltage-regulating three-phase load unbalance limiter composed of an auto-coupling three-phase load unbalancer and a voltage regulating switch. A low-voltage switch 6 with overcurrent and overvoltage protection is installed on the upper side of the limiter 5, and the neutral line 7 of the three-phase unbalanced load 3 is connected with the neutral line N' of the limiter 5 to form a new system. Neutral, neutral not grounded. In order to prevent certain factors from causing dangerous overvoltage on the N' line, a 36V safety voltage protector 8 is installed on the N' line. the

As shown in Figure 2, a voltage-regulating three-phase load unbalance limiter 5 composed of an isolated three-phase unbalanced load limiter and a voltage regulating switch is installed at the node 4 of the branch line of the three-phase unbalanced load 3. The neutral point lead 7 of the load 3 and the neutral line N' of the limiter 5 are connected to form the neutral line N' of the new circuit system. Because of the electrical isolation from the original distribution network, for safety needs, the N' line can be connected to the load The unbalancer and the 5 installation point are directly grounded. In addition, an overvoltage protector 9 is installed at the 3 ends of the three-phase unbalanced load. the

From the above, it can be seen that the pressure regulating three-phase load unbalance limiter 5 at the node cuts off the connection between the zero line N of the original distribution network and the load, and the pressure regulating three-phase load unbalance limiter 5 and the unbalanced load 3 constitute a new In the three-phase four-wire system, the zero-sequence current no longer flows through the neutral line of the original distribution network and returns to the distribution transformer, but flows through a new very short neutral line N', which is compatible with the voltage-regulating three-phase load unbalance limiter 5 Self-contained loop, the zero-sequence magnetic flux is canceled by the zero-sequence magnetic flux coil of the limiter 5 after the zero-sequence current returns to the limiter, and the loss of the limiter itself caused by the zero-sequence current is also eliminated. the

As shown in Figure 3, the self-coupling three-phase load unbalancer is a three-phase three-column coil, which is composed of a common coil and a voltage regulating coil. The ends of the three-phase three common coils are connected in a star shape, and the neutral point leads out to the neutral line. N', the first voltage regulating coil 11a of phase A is connected to the common coil 10b of phase B, the first voltage regulating coil 11b of phase B is connected to the common coil 10c of phase C, and the first voltage regulating coil 11c of phase C is connected to the common coil 10a of phase A ; After the voltage regulating coil is connected to another common coil, the magnetic flux generated by the zero-sequence current must cancel each other, thereby reducing the loss and influence of the zero-sequence current to the limiter. The coil connected by this connection method can be called Zero-flux coils. A, B, and C are the input terminals of the self-coupling three-phase load unbalancer, which are connected to the low-voltage distribution network, and a, b, c, and N' are the output terminals, which are connected to the three-phase unbalanced load. the

As shown in Figure 4, the isolated three-phase load unbalance limiter is also a three-phase three-column coil, which is composed of a power-side coil 12 and a load-side coil. The load-side coil is divided into a basic coil and a voltage-regulating coil; the power-side coil 12 is the same rated voltage as the coil on the load side, but there is no electrical connection. The neutral point of the coil on the power supply side is not drawn out. The coil on the load side is divided into a basic coil and a voltage regulating coil. The point leads to the neutral line N'. The connection mode of the load side coil is: the second voltage regulating coil 14a of phase A is connected with the basic coil 13c of phase C, the second voltage regulating coil 14b of phase B is connected with the basic coil 13a of phase A, the second voltage regulating coil 14c of phase C is connected with the basic coil 13c of phase C The B-phase basic coil 13b is connected. The two coil connections must also cancel out the zero-sequence flux. A, B, C are the input terminals of the isolated three-phase load unbalancer, connected to the low-voltage distribution network, a, b, c, N' are the output terminals, connected to the three-phase unbalanced load. the

The implementation of the utility model is equipped with windings for eliminating zero-sequence magnetic flux, thereby offsetting the influence of zero-sequence current in the limiter; when the three-phase load unbalance limiter is in a situation such as a large load increase, the three-phase load unbalance limit can be used in parallel. the

It can be seen from Fig. 3, Fig. 4 and Fig. 5 that the output end of the voltage-regulating three-phase load unbalance limiter is provided with multiple voltage-regulating taps for the automatic voltage-regulating switch to adjust the output voltage. The voltage regulating switch is composed of a selector switch 15 and a transfer transition switch, wherein the transfer transition switch is composed of a non-contact thyristor switch 16 connected in series with a current-limiting resistor 17, and no arc is generated during the transfer process; the selector switch adopts a buffer compression spring Bridge-type moving contact, contact silver-plated switch; the operating mechanism is a DC bidirectional direct-acting electromagnetic mechanism, the brake uses a permanent magnet, and the entire voltage regulation process is arc-free voltage regulation. the

As shown in Figure 5, the changeover switch of the voltage regulating type three-phase load unbalance limiter voltage regulating switch of the utility model is used in parallel with the selector switch 15 to complete the voltage regulation. Wherein the transfer switch is composed of a thyristor switch 16 connected in series with a current limiting resistor 17 . Every time the voltage regulation is performed, the transfer switch is first connected, and when the voltage regulation process is completed, the transfer switch is immediately disconnected, thereby realizing no arc, and the voltage regulation switch is also provided with a voltage regulation controller and a non-contact thyristor controller. the

As shown in FIG. 6 , the voltage regulating controller is composed of a sampling circuit 18 , an A/D conversion 19 , an output locking circuit 20 , a driving circuit 21 , and a timing permission circuit 22 . Timing permission circuit 22 is a timing circuit that can be adjusted again after 5 minutes (or 10 minutes) of each voltage regulating switch action specially set in order to reduce some frequent actions of the voltage regulating switch; 23 is an overvoltage and overcurrent protection circuit; The voltage controller controls the opening of the voltage regulating switch, that is, the changeover switch and the selector switch 15, that is, the opening of the control non-contact thyristor controller. the

As shown in Figure 7, the non-contact thyristor controller of the selection switch of the pressure regulating type three-phase load unbalance limiter voltage regulating switch consists of a light control element 24, a thyristor 25, a piezoresistor 28, a resistor 29, a capacitor 30, a rectifier circuit 26 and load drive circuit 27. The varistor 28 is the voltage protection of the thyristor 25 and the light control element 24, and the absorption circuit composed of the resistance 29 and the capacitor 30 is the voltage protection circuit of the rectifier circuit 26 and the load 27, and the load driving circuit 27 is the wire package of the selector switch 15. , the non-contact thyristor controller realizes the voltage regulation each time, the transfer switch (thyristor) is first connected, and then the wire package of the selection switch 15 is connected. After the voltage regulation process is completed, the transfer switch is immediately disconnected, and the selection switch 15 remains connected On state, thereby realizing arc-free operation. the

Claims (4)

1. voltage-regulation type three-phase load unbalanced limiter, it is characterized in that: its by or the uneven weighing apparatus of autocoupling type three-phase load, or uneven weighing apparatus of isolated three-phase load and tap changer formation, the uneven weighing apparatus of described autocoupling type three-phase load is the three-phase three-limb coil, three-phase three-limb coil branch is made of shared coil and voltage regulation coil, three shared coil ends of three-phase are connected into star-like, neutral point is drawn zero line N ', A first voltage regulation coil (11a) mutually connects with the mutually shared coil of B (10b), B first voltage regulation coil (11b) mutually connects with the mutually shared coil of C (10c), C first voltage regulation coil (11c) mutually connects with the mutually shared coil of A (10a), the uneven weighing apparatus of described isolated three-phase load is the three-phase three-limb coil, constitute by mains side coil (12) that does not have electrical communication and load side coil, the load side coil is divided into basic coil and voltage regulation coil, the basic coil end of three-phase is linked to be star-like, mid point is drawn zero line N ', load side coil connected mode is: A second voltage regulation coil (14a) mutually is connected with the basic mutually coil (13c) of C, B second voltage regulation coil (14b) mutually is connected with the basic mutually coil (13a) of A, and C second voltage regulation coil (14c) mutually is connected with the basic mutually coil (13b) of B.

2. voltage-regulation type three-phase load unbalanced limiter according to claim 1, it is characterized in that: described tap changer is made of selector switch (15) and switch transition switch, wherein the switch transition switch is the contactless thyristor switch (16) of serial connection current-limiting resistance (17), and tap changer also is provided with voltage regulator controllers and contactless triac controller.

3. voltage-regulation type three-phase load unbalanced limiter according to claim 2, it is characterized in that: described voltage regulator controllers is by sample circuit (18), A/D change-over circuit (19), output lock-in circuit (20), and drive circuit (21), timing allow circuit (22) to form.

4. voltage-regulation type three-phase load unbalanced limiter according to claim 2 is characterized in that: described contactless triac controller is made up of light-dependent control element (24), thyristor (25), piezo-resistance (28), voltage protection circuit, rectification circuit (26) and load driving circuits (27).

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