How to Choose Pad Mounted Transformer?
Table of Contents Selecting the right pad-mounted transformer requires careful consideration of several critical factors,
ELECTRIC, WITH AN EDGE
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ELECTRIC, WITH AN EDGE
The development and use of voltage regulation of transformers can significantly reduce the no-load losses of transformers. This article gives you a detailed overview of voltage regulation of transformers.
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Transformer operation consumes a large amount of electrical energy, its power consumption occupies most of the power system power consumption, at the same time in the operation of the power grid, different time periods and different areas of the power peak and valley load there are great changes, when the load is in the low valley, the transformer is close to the no-load operation state, at this time the transformer loss is most of the loss of no-load operation, and such no-load power loss occupies the power transformer Most of the power consumption. Therefore, how to reduce transformer losses, especially no-load losses, is a key element in the operation and management of power grids.
The voltage regulation of transformers has significant features, voltage transformers and regulators can be adjusted according to the actual situation of the load, to improve the reliability of the transformer, and to reduce the no-load losses. The development potential and application value of the voltage transformers and regulators is very high.
The voltage regulation of transformer is mainly used in the 10kV rated voltage and 630kVA capacity and below distribution stations, mainly with automatic capacity and voltage regulation, wireless four remote and distribution monitoring and other functions.
The automatic voltage regulation of transformers is mainly when the voltage fluctuates due to unstable load of users or lines, voltage transformers and regulators can automatically adjust the voltage level, improve the quality of power supply and extend the life of equipment, and solve the problem of low voltage qualification rate in the peak and valley phases of the distribution network.
The automatic regulation of capacity is mainly based on the size of the load, so that the voltage regulation of transformers can automatically run in the small capacity gear during the low load period, and the no-load loss is significantly reduced during light load. Therefore, it has obvious energy-saving effect.
In the distribution monitoring and wireless four remote functions, mainly through GPRS, WiFi and GSM and many other means of communication to achieve real-time monitoring and remote control of the operating status of the transformer, to view and modify the fixed value, etc., to achieve automatic control of the distribution network station area.
The principle of capacitance regulation: In a voltage regulation of transformer, the low-voltage winding consists mainly of a small number of line turn I sections and a large number of line turn II and III sections.
In large capacities, the three-phase high-voltage winding is connected in a triangle, in small capacities, the three-phase high-voltage winding is connected in a star.
In large capacity, sections II and III are connected in parallel and then in series with section I. In small capacity, sections I, II and III are connected in series; when adjusting from large capacity to small capacity, the number of turns of the low-voltage winding will increase, while the high-voltage winding will become a Y-connection situation.
The voltage transformers and regulators are controlled by a capacitance and voltage switch, mainly through the capacitance controller. The controller consists of a central processing unit, a communication unit and an acquisition unit to collect, analyse, judge, record and store data; the on-load capacitance and voltage switches are switched according to the instructions of the controller to achieve the purpose of voltage transformers & regulators.
In the study of capacitive voltage regulation of transformers, the realisation of their functions is mainly related to the capacitance and voltage switches, which directly determine the development of such voltage regulation of transformers.
The article focuses on the analysis of the development of such voltage transformers and regulators switches, which also directly reflects the current situation and direction of the development of such voltage regulator transforme.
This type of mechanical tap changer consists of a motorised mechanism, a diverter switch and a tap selector, which is changed by the transformer voltage regulation tap changer to achieve the effect of voltage regulation.
During voltage regulation, the tap selector first cuts to the target tap position in the uncharged state and then switches the dynamic contact of the switch so that its current static contact switches to the target static contact, which is supported by the power of the diverter switch and tap selector through the motor-drive unit.
This type of transfer switch uses a drive motor to convert the high voltage winding from a triangular connection to a star connection in accordance with the actual load situation, when the low voltage winding is converted from parallel to series, thus achieving the purpose of capacity regulation.
This type of switch is very simple in structure and has the advantages of high reliability and low losses.
At the same time it also has certain disadvantages, such as the diverter switch being in the separation of contacts, which can easily produce an arc.
it is difficult to achieve accurate control of the regulating moment and if continuous shifting leads to higher oil temperatures and accelerated gas production.
The tap-changer action is relatively slow, with a long response time; in the regulation is easy to slip gear situation, in the switching, the presence of ring current between the gears will lead to overvoltage phenomenon, and thus the impact on the grid; but also regular implementation of the tap-changer insulation oil filtration and replacement, or monitoring device to add.
This type of switch is gradually developed from a mechanical switch, is the switch mechanical structure into power electronic components to achieve, such switches in the industry are more common thyristor and relay composite switch type, etc. 3.2.1 power electronic regulator switch thyristor device on-load arcless regulator switch as shown in Figure 1, all switches are thyristor.
Suppose auto transformer voltage regulation operation initial position is W1, then A0, K21 and K22 are in the state of conduction, at this time to switch the connector W1 to W2, the switching process is: first to A0 disconnect, resistance R received in the circuit; to K21 disconnect, and to K31 on, and tap W1 and W2 The switching process is completed by disconnecting K22 and closing K32 and A0. At this point, the current from tap W2 passes through the series branch of K32 and A0 and the K31 thyristor, and the switching process is arc-free.
Within this circuit topology, the K32 and K31 thyristors can be redundant with each other, and the current in the on-state of each device is 1/2 the winding current, which reduces the losses in the on-state of the devices and improves the reliability of the circuit, while the number of thyristors increases significantly.
The principle of the thyristor type capacitance switch is shown in Figure 2, all switches are thyristors. When adjusting the capacitance, the six anti-parallel thyristors are used to convert the high-voltage side of the winding into a star-shaped triangle; the nine anti-parallel thyristors are used to convert the low-voltage side of the winding into a series-parallel connection.
If SA1, SB1 and SC1 are in conduction, the windings are connected in a triangular way; if SA2, SB2 and SC2 are in conduction, the windings are connected in a star way.
In the low-voltage side of the winding, if Sa11, Sa12, Sb11, Sb12, Sc11 and Sc12 are in conduction, then the winding is II and III sections in parallel and then in series with I section; if Sa2, Sb2 and Sc2 are in conduction, then the winding is all in series.
Through the above control, can make auto transformer voltage regulation in the size of the capacity between the realization of no arc has the effect of load regulation.
This type of on-load tap-changer presents the advantages of fast switching, a voltage regulation process without arc and a controllable on-off time. However, it also has certain disadvantages, mainly the number of power electronic devices is relatively large, the requirements for equal current and voltage technology is relatively high, the topology is more complex.
At the same time the through-state losses of the devices are relatively high, and often the cooling system needs to be put into use for a long time.
and the performance of the system is also influenced by the characteristics of the power electronics, which vary from device to device.
The transistor IGBT has a low effect on the reverse voltage blocking, and cannot be used in a two-way blocking situation; in addition, the thyristor GTO has a high peak value for the current of the forward and reverse pulse of the shutdown gate, and its trigger circuit is more complex.
The thyristor type hybrid regulator switch is shown in Figure 3. In this figure 4 and 5 are the main contacts of the switch, while 1, 2 and 3 are the auxiliary contacts. When the diverter switch is required to close, the establishment of voltage, current and direct conduction processes need to be implemented.
In the voltage build-up, the main contact 4 slides from the right to the left, it first makes contact with the auxiliary contact 3, and the thyristor connected to 3 is in a disconnected state, and when 3 is connected to the main contact 4, the voltage is built up between thyristor 6 and 7.
In the current build-up, the main contact 4 continues to run to the left, while the auxiliary contacts 2 and 3 are connected to the main contact 4, at which time the voltage exists on the primary winding of T11 of the transformer voltage regulation, so that the voltage also exists on the secondary windings of T21 and T22, at which time the thyristors 6 and 7 are triggered on, and the current passes between the main contacts 4 and 5, which The voltage drop is the voltage drop of a single number of diodes.
In the direct conduction establishment, its main contact continues to move to the left, when the main contact 4 and the auxiliary contact 1 are connected, because there is only the voltage drop of the diode, so there is no arc occurring when 4 and 1 are connected, at this time the winding T11 is short-circuited, and the circuit of the thyristor is invalid, the current of the load flows directly to 5 via the main contact 4, achieving the effect of arc-free conduction.
There are significant advantages to this type of switch, as the switching of the mechanical contacts is assisted by the power electronics. This switching process is arc-free and does not lead to the deterioration of the transformer’s insulating oil, thus extending the service life of the switch; after the switching is completed, the power electronics will exit the current-carrying circuit and carry the current through the mechanical contacts, reducing the losses generated by the conduction of the power electronics. However, the switching speed of such switches is relatively slow and the structure is relatively complex.
In the continuous research and development of many types of voltage regulation of transformers, voltage transformers and regulators have different advantages and disadvantages, in order to give full play to the role and value of transformer voltage regulation. In order to give full play to the role and value of transformer voltage regulation, the technology of auto transformer voltage regulation needs to be continuously researched so as to better serve the operation and construction of power grids.
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