The voltage transformer is a special transformer made according to the principle of electromagnetic induction. Its structure is not complicated. It is used to change the voltage on the line. The purpose of transforming the voltage of the transformer is to deliver electric energy. Therefore, the capacity is very large, generally The kilovolt-amperes or megavolt-amperes are the unit of calculation; the purpose of the voltage transformer to change the voltage is mainly to supply power to the measuring instrument and the relay protection device, to measure the voltage, power and electrical energy of the line, or to be used in the line. In the event of a fault, the valuable equipment, motors and transformers in the line are protected. Therefore, the capacity of the voltage transformer is very small, generally only a few volts, several tens of volts, and no more than one thousand volts.
The role and principle of voltage transformerThe structure of the voltage transformer is shown in Figure (a). Its function is to expand the range of the AC voltmeter and isolate the high voltage from the electrical workers. Its working principle is similar to that of ordinary transformers. In use, the high-voltage winding with a large number of turns should be connected to the power supply line whose voltage needs to be measured, and the low-voltage winding with a small number of turns connected to the voltmeter, as shown in the following figure (b).
Because U1/U2=K, U1=KU2, which shows that the voltage of the high-voltage line is equal to the product of the voltage measured by the secondary side and the transformation ratio (Review: transformer working principle, original secondary voltage calculation formula and transformer transformation) More than explanation). When the voltmeter is used in conjunction with a dedicated voltage transformer, the scale of the voltmeter can be marked according to the voltage on the high voltage side of the voltage transformer, so that the high voltage line can be read directly from the voltmeter without conversion. Voltage value.
Usually, the rated voltage of the secondary winding of the voltage transformer is designed to have the same standard value of 100 volts. Therefore, voltage transformers used in circuits of different voltage levels have different transformation ratios, such as 1000/100, 600/100, and the like.
In order to work safely, one end of the secondary winding of the iron-shell machine of the voltage transformer must be grounded to prevent the high-voltage coil measuring instrument from generating a high voltage on the ground when the insulation between the high-voltage and low-voltage coils is damaged, and the safety of the crisis workers.
Voltage transformer model meaningIt consists of the following parts, each part of the letter, the symbol indicates the content:
1st place: J-PT
2nd place: D—single phase; S—three phase; C—cascade; W—five iron core column
3rd place: G—dry type; J—oil immersion; C—porcelain insulation; Z—casting insulation; R—capacitor type; S—three phase
4th position: W—five iron core column; B—with compensation angle difference winding;
Behind the hyphen: GH—high altitude; TH—wet hot zone
Number: voltage level (KV)
For example: JDZF7-10GYW1
J Voltage Transformer Voltage transformer
D single phase Single phase
Z Casting CasTIng type
F with residual voltage winding With residual voltage winding
7 Design No. Design Number
10 voltage class (kV) Voltage class (kV)
GYW1 Plateau Pollution Plateau Dirty
Graphical symbol of voltage transformerThe voltage transformer is a transformer with a core, which is mainly used to proportionally change the voltage on the line. According to GB4728-6-84 "Generation and Conversion of Electrical Energy", the voltage transformer symbol is clearly defined in electrical engineering applications.
Voltage transformer: PotenTIal transformer referred to as PT, in the new national standard is also called Transformer voltage, also referred to as TV, and the old national standard "YH" (voltage transformer "pressure", "mutual" two words of the first letter of the combination of Chinese alphabet )Corresponding.
Single-phase voltage transformer symbol
In the left figure, two circles represent one primary winding and one secondary winding; in the right figure, three circles represent one primary winding and two secondary windings; in the other circle, the uppermost one is the primary winding, and the other is Secondary winding. Both legends in the figure above represent single-phase voltage transformers. The three-phase voltage transformer symbol is similar to the single-phase voltage transformer symbol, except that three lines representing three phases are added to the line end, as shown in the following figure:
Three-phase voltage transformer symbol
Selection of voltage transformersThe voltage transformer is an important component of the power distribution system. Whether the selection of the product is reasonable or not depends on the operation status of the entire power system. The selection of the voltage transformer is also a problem that our electric power practitioners must understand. The model of the voltage transformer The types are divided into many types, different models, and different types of voltage transformers. Their uses, installation methods, and structures are different. Let's take a closer look at the selection of voltage transformers.
First, when purchasing the transformer, first understand the main role of the voltage transformer. According to the purpose of classification, the voltage transformer can be divided into the protection voltage transformer and the voltage transformer for measurement, and the function of the protection voltage transformer. The high voltage is replaced by the secondary component of the power system (such as the microcomputer protection device and the intelligent control of the switch cabinet). The low voltage required for the device, instrumentation, etc., and the main function of the voltage transformer for measurement is to measure and measure the voltage state of the primary circuit high voltage and secondary circuit high voltage. Understand what the transformer used in the project is used for. If it is the former, choose the voltage transformer for protection. If it is the latter, select the voltage transformer for measurement.
Second, when selecting a voltage transformer, first understand whether the transformer is used indoors or outdoors. If it is used indoors, you must select the user's internal voltage transformer. Outdoors, you must choose an outdoor voltage transformer.
Third, when purchasing, the voltage level of the power distribution system of the project should be clarified. The general voltage transformers can be divided into four grades according to the voltage grade. One is a low-voltage transformer, and the low-voltage transformer is mainly at 1000V or below. Voltage level. The medium voltage transformer is mainly suitable for the power distribution system with rated voltage between 3KV and 110KV. The high voltage transformer is generally used for the voltage level of 220-500KV. For the above 500KV, the ultra high power transformer type must be selected. When selecting the product, our electric power practitioners must understand in which area the voltage level of our power distribution project is, and select the voltage transformer that meets the requirements according to the regulations.
Fourth, we must understand that the type of insulation and the type of insulation are the places we must pay attention to. If the choice is not correct, it will bring serious consequences to our power distribution system. Therefore, it must be clear that the voltage transformers are classified according to the insulation. Generally for two types, one is fully enclosed and the other is semi-closed. Although this is relatively simple, it must also be taken seriously.
Fifth, we must understand the type of insulating medium of the product. Voltage transformers can be divided into dry voltage transformers, cast voltage transformers, oil-immersed voltage transformers, gas-insulated voltage transformers according to the insulating medium, so the selection is made. Be sure to find out which of the electric transformers used in the project is which one. Don't make a mistake.
Sixth, we must understand the transformation principle of voltage transformers. Voltage transformers can be divided into two types: capacitive and electromagnetic. The electromagnetic voltage transformers convert high-voltage electricity into our secondary equipment. Low-voltage, and capacitive transformers are mainly to extract voltage from the capacitor, the two principles are not necessarily, before choosing the purchase, you must understand which one is more reliable for the entire power distribution system to purchase.
As long as we purchase the voltage transformer according to the above-mentioned principle, it will definitely give you a lot less things, and it will ensure the reliable and stable operation of the entire power system. At the same time, we hope that the industry colleagues will actively put forward their opinions and opinions. We will actively listen to and absorb the opinions of the majority of users, and make our own contribution to the power distribution industry.
Voltage transformer wiring and schematicThe voltage transformer has a primary winding, a secondary winding, a core terminal and an insulating support, and the working principle is as shown in the figure. The primary winding of the voltage transformer has more turns N1 and is connected to both ends of the circuit under test, and the insulation level corresponds to the voltage of the actual system. The secondary winding has a small number of turns N2, which can be connected to the voltage coil of the measuring instrument or the electric energy meter, and the secondary rated voltage is usually 100V.
When the voltage transformer works normally, it can be regarded as a step-down transformer running at no load. When the primary winding is connected to the power supply voltage 
When a no-load current flows through the primary winding 
, generating magnetic flux in the iron core 
Inducing an induced voltage in the secondary winding.
U1--voltage transformer primary voltage, V;
U2--voltage transformer secondary voltage, V;
N1--voltage transformer once, åŒ;
N2--voltage transformer secondary turns, åŒ;
K--voltage transformer ratio.
In the electric energy metering device, after the voltage transformer is used, the reading on the electric energy meter is multiplied by the ratio of the voltage transformer, which is the actual power consumption. The model of the voltage transformer consists of alphabetic symbols and numbers, which have the following meanings:
Double winding voltage transformer working principle diagram
Wiring method of voltage transformer
(a) One single transformer connection: (b), VV wiring; (c) YY. Wiring; (d) three-phase five-column voltage transformer wiring; (e) three single-phase three-winding voltage transformer wiring
Figure (a) shows the wiring of a single-phase voltage transformer, which can measure the line voltage of a system of 35kV and below, or the relative ground voltage of a direct grounding system of a neutral point above 110kV.
Figure (b) shows two single-phase voltage transformers connected to a VV-shaped wiring that measures the line voltage but does not measure the phase voltage. This type of wiring is widely used in neutral point indirect grounding systems.
Figure (c) shows the YY of a three-phase three-column voltage transformer. Wiring: It can only measure the line voltage and cannot be used to measure the relative ground voltage. The neutral point of the star connection of the secondary winding cannot be grounded because single phase grounding occurs in the neutral point indirectly grounded system. When the grounding voltage is zero relative to ground, the ungrounded voltage is increased by a factor of two.
Figure (d) is the Y of a three-phase five-column voltage transformer. -Y. /â–³ wiring, the primary side winding and the basic secondary winding are connected in a star shape, and the neutral point is grounded, and the auxiliary secondary winding is connected into an open triangle. Therefore, the three mutual-sensing voltage transformer can measure the voltage and the relative ground voltage, and can also be used as the insulation monitoring for the ground in the neutral point indirect grounding system and the single-phase grounding relay protection. This wiring is widely used in 6 ~10kV indoor distribution equipment.
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