Hi, fellas. I am Rose. Today I will introduce the transformer to you. The device that increases or decreases the voltage in an AC circuit is known as a transformer. The transformer is an AC voltage converter that works on the mutual inductance concept.

Ⅰ. What is a transformer?

1. The definition of transformer

The device that increases or decreases the voltage in an AC circuit is known as a transformer. The transformer is an AC voltage converter that works on the mutual inductance concept. It can transform any voltage value into the voltage value we need at the same frequency to meet requirements for electrical energy transmission, distribution, and use. Electricity from a power plant, for example, has a lower voltage level and must be boosted before being transmitted to a remote power consumption location. To supply power equipment and daily electricity, the power consumption region must be decreased to an appropriate voltage level. Equipment.

The primary coil, secondary coil, and iron core are the structural elements. An alternating magnetic flux is formed in the iron core when an alternating current travels through the primary coil, causing the secondary coil to induce a voltage. It is made up of a coil and an iron core. There are two or more windings on the coil. The primary winding is connected to the power source, whereas the secondary winding is made up of the remaining windings.

2. The main components of the transformer

(1). Iron core

One of the most basic components of a power transformer is the iron core. It's a twisting skeleton with a "magnetic" route. The transformer's primary and secondary windings are wound on the iron core. The iron core is the part of the iron core that is covered by the winding. An iron yoke is a column that is used to connect the core and column without winding windings to make a closed magnetic circuit. Hysteresis and eddy current loss will occur because the magnetic circuit in the transformer core is alternating. The transformer core is commonly formed of silicon steel sheet with a thickness of 0.3-0.5mm, covered with a 0.01-0.13mm thick insulating varnish on the surface, and laminated according to particular regulations after drying, in order to minimise these losses.

(2). High and low voltage winding

The transformer's winding is one of the most basic components. It is coupled with the iron core to form the power transformer's main body. It is the circuit part of the transformer that creates the magnetic field and transmits electrical energy, as well as the channel for the transformer's "electricity."

The high and low voltage windings can be classified into two types based on their various arrangement positions: concentric and overlapping.

1) Concentric winding

The main and secondary windings are coiled into varied diameter cylindrical coils and installed on the iron core column. Insulating materials are used to separate the high and low-voltage windings. The low voltage windings are usually put inside to make the extraction of the high voltage windings easier. Outside, the high-voltage winding is sleeved. The procedure of low-voltage winding leads is complicated for big-capacity power transformers with significant output currents, and the low-voltage windings are frequently positioned outside the high-voltage windings.

2) Overlap winding

High-voltage windings and low-voltage windings, also known as staggered windings, are alternately stacked on the same iron core column, with greater gaps, intricate insulation, and a lot of binding labor. The advantage is that the mechanical performance is better, the lead wire arrangement and welding are easier, and the leakage reactance is low. Low-voltage, high-current transformers commonly use this material (such as electric furnace transformers, welding transformers, etc.).

(3). Tap switch

The voltage regulating switch, also known as the tap changer, is a device that changes the tap position of the transformer's high-voltage winding. Changing the position of the tap changer can modify the voltage ratio and adjust the output voltage by increasing or decreasing the number of spins on the primary winding. There are two types of voltage regulation: on-load and no-load.

1) No-load voltage regulation

When both the primary and secondary windings of the transformer are removed from the network, this approach of altering the number of turns of the primary and secondary windings to perform step-by-step voltage control is known as non-excitation voltage regulation. Tap-changers for small-capacity transformers usually have three locations. The rated voltage is similar to position II. Set the tap-changer to position I when the system voltage is too high, and to position III when the system voltage is too low. "High to high key, low to low key," to put it another way.

2) On-load voltage regulation

Under the load current, the tap of the main or secondary winding is changed, the number of turns is altered, and the voltage is regulated in stages when the transformer is running with a load. During the process of changing taps on an on-load tap changer, reactance and resistance transition can be employed to control the circulating current.

(4). Gas relay

It's also known as a Buchholz relay, and it's positioned in the middle of the connecting pipe between the oil tank and the oil pillow as a protection device for internal transformer defects. A gas protection device is created by connecting the gas relay to the control circuit. The light gas signal is connected to the upper contact of the gas relay, and the lower contact is connected to the external circuit to produce a heavy gas protection circuit. The circuit breaker trips as a result of the heavy gas action, and a heavy gas action signal is sent out.

All oil-immersed transformers with a capacity of 800KVA or more, as well as factory transformers with a capacity of 400KVA or more, must be supplied with gas relays, according to the laws.

(5). Explosion-proof tube

It is also known as a safety airway since it is a protection mechanism installed to prevent the transformer from deforming when a fault occurs inside the transformer. It is mounted on the transformer's big lid. The nozzle is built of thin film glass plate and communicates with the atmosphere through a horn-shaped tube. Or phenolic cardboard that has been sealed.

(6). Oil pillow

It is a mechanism for refilling and storing oil while the transformer is in operation. It is positioned obliquely above the oil tank and is connected to the tank via oil pipes. The oil tank can always be filled with insulating oil to limit the contact surface between the oil and the air and prevent the oil from being oxidized too quickly and becoming damp when the volume of the transformer oil expands and shrinks with the temperature of the oil. The oil cushion is typically one-tenth the size of the transformer tank. On one side of the oil pillow, an oil level indication (oil gauge tube) is attached to monitor the oil level change, and the upper half of the oil pillow has an oil injection hole and an air exit flap.

(7). Respirator

It's also referred to as a moisture absorber. The oil pillow communicates with the ambient through a respirator in order to prevent moisture from entering the oil pillow. The respirator contains silica gel, and the desiccant inside the silica gel absorbs moisture and pollutants in the air to keep the insulating oil in the transformer performing well. The respirator's silica gel is usually color-changing silica gel, which is light blue while dry and progressively turns light red when saturated with moisture. The silica gel can now be removed and dried at a high temperature of 120-160°C. When the dried turns blue, you can keep using it.

(8). Cooling device

A radiator and a cooler are part of an oil-immersed power transformer's cooling system. The one with weak oil circulation is referred to as a radiator, while the one with robust oil circulation is referred to as a cooler.

Radiator pipes or fins are fitted around the transformer tank to form the radiator. When the transformer is in operation, the temperature difference between the upper and lower layers of oil causes the oil to flow through the radiator, allowing the high-temperature oil around the transformer core to be cooled by the radiator before being returned to the transformer. It lowers the transformer's working temperature within the oil tank.

(9). Thermometer

It's a meter that keeps track of the transformer's operating temperature. In most cases, the temperature measurement point is on the oil's top layer. Mercury thermometers, barometer thermometers, and resistance thermometers are all commonly used.

Only mercury thermometers should be installed in oil-immersed transformers below 1000KVA; for oil-immersed transformers 1000KVA and above, a thermometer with alarm signal and two transformers with forced oil circulation cooling must be installed; and for oil-immersed transformers 8000KVA and above, a thermometer with alarm signal and two transformers with forced oil circulation cooling must be installed. Two temperature measurement components, namely resistance thermometers and transformers for forced oil circulation cooling, must be installed for distant temperature measurement.

(10). High and low voltage insulation casing

Porcelain insulating sleeves are the major insulation device outside the transformer box, and most transformers employ them. The dry-type transformer's insulating sleeve is made of resin. Through the high and low voltage insulating bushing, the transformer conducts its high and low voltage windings from the oil tank to the outside. The transformer winding is insulated from the earth (shell and iron core) by the high and low voltage insulation bushing, which also serves to secure the lead and external wiring. The essential elements.

3. The types of transformer

According to the number of power phases: single-phase transformer, three-phase transformer, multi-phase transformer.

According to the moisture-proof method, there are open transformers, potted transformers, and sealed transformers.

According to the purpose: power transformer, voltage regulating transformer, audio transformer, intermediate frequency transformer, pulse transformer, high frequency transformer.

4. The function of the transformer

The lower the voltage, the greater the current, the larger the cross-section of the wire, and the higher the line laying cost when the power transformer is transmitting power over long distances, such as when the power is constant; if the voltage is increased by a step-up transformer, the line laying cost is reduced. If the current is reduced, the cost will be reduced as well. After the high voltage has been transferred to the user center, a step-down transformer is required to convert the high voltage to a number of different voltages that can be used by the users. As a result, the transformer is a critical piece of electrical equipment.

Ⅱ. What is a transformer used for?

Transformers are generally divided into two categories: power transformers and special transformers.

1. The use of power transformers

The transformer utilized in the primary circuit of the power system for transmission, distribution, and power supply is known as a power transformer.

1) Increase the voltage

Because the generator's output voltage is restricted by its insulation level, it is normally 6.3kV, 10.5kV, and the maximum does not exceed 20kV. Because the current is significant while employing such a low voltage for long-distance transmission, the electrical energy expended on the transmission line's resistance will be large. To reduce the transmission current and energy loss on the transmission line without increasing the cross section of the wire, a step-up transformer is used to increase the generator's terminal voltage to hundreds of thousands or millions of volts. This allows electrical energy to be transported remotely.

2) Reduce voltage

After the transmission line sends hundreds of thousands or millions of volts of high-voltage electrical energy to the load area, a step-down transformer must convert the high voltage to a low voltage appropriate for use by electrical equipment. A significant number of step-down transformers are required in the power supply system to convert the high voltage carried by the transmission line into various levels of voltage to satisfy the needs of varied loads.

3) Connect the transmission line

Transformers are required to connect several lines with unequal voltages to build a system when many power stations are integrated to make a power system, in addition to power transmission lines and other equipment.

2. The purpose of special transformers

Particular transformers are transformers that are used in special power supply, control systems, and telecommunication equipment and have a specific function, performance, and structure.

1) Rectifier transformers, electric furnace transformers, and intermediate frequency transformers used in industrial and mining enterprises.

2) Detect voltage transformers and current transformers used for high voltage and high current.

3) Test transformer and voltage regulating transformer used in the test.

4) Control transformers, pulse transformers, audio transformers, etc. used in automatic control systems and automatic devices.

Ⅲ. How does a transformer work?

Two wires make up a simple single-phase transformer. A fluctuating magnetic field is created when a particular quantity of current (such as alternating current or pulsed direct current) travels through one of the conductors. According to the theory of electromagnetic mutual inductance, the second conductor will generate a potential difference when the magnetic field changes. When the second conductor is connected to a closed circuit, the closed circuit generates a current. The electricity is then sent out. Because the magnetic field generated by a coil is substantially larger than that generated by a straight wire, the relevant conductor in ordinary transformers is a wire (usually copper) to form a coil. A transformer, in general, is a device that converts alternating voltage, alternating current, and impedance. An alternating magnetic flux is formed in the iron core (or magnetic core) when an alternating current is supplied through the primary coil, causing a voltage to be induced in the secondary coil ( Or current). The voltage VS, VP of the primary and secondary coils and the number of turns NS, NP of the two windings have a proportional relationship:

The current or voltage ratio between the two sides of a transformer is determined by the number of turns on both sides of the circuit coils. Higher voltage but the lower current is found in the one with more turns, and vice versa. When leakage is taken into account, the voltage ratio on both sides of the transformer equals the ratio of the coil turns on both sides, implying that the voltage is proportional to the number of turns.

As a result, the primary and secondary coils' turns ratios can be reduced or increased, resulting in an increase or decrease in voltage. The transformer is a crucial device for voltage conversion due to its nature. Furthermore, disregarding the effect of leakage, the transformer will not be an amplifier because it follows these two laws. The current flowing through the two sides of the transformer will be different if the voltage on the two sides of the transformer is different, and the difference between the two is inversely proportional. If one side of the transformer's current is lower than the other, the side with the lower current will have a higher voltage and vice versa. The power consumed by both sides of the transformer, however, should be equal (that is, the two values of voltage and current on one side should be multiplied).

Ⅳ. How to use a transformer?

Using methods：

1. Before using the transformer, read the transformer's instruction manual as well as the instruction handbook for the accompanying control box (set) thoroughly. The connecting cable should be connected as directed in the handbook, and the grounding wire should be securely grounded.

2. The AC 220V and 380V power supplies of the dry-type transformer control box (set) are output to the low-voltage side input end of the transformer via a voltage regulator. After the variable ratio, the output is continually adjustable to the rated voltage.

3. To avoid damaging equipment or test products, consider the safety of dry-type test transformers and the rigor of high-voltage testing.

4. When doing a DC withstand voltage or leakage current test, start by spinning the high-voltage silicon stack and micro-ammeter on the high-voltage output end of the high-voltage test transformer, then progressively increase the voltage to perform the DC test.

Precautions for the use of transformers：

There are three types of sounds that occur during the withstand voltage test as a result of the electrical distance: The sound of air ionization is "cracking crackling." The sound of air stream is "zi, zi." "Slap": The sound of insulation (or air) being broken down is loud and crisp, with sparks accompanying it. Air discharge is usually separated into three parts. Ionization is the initial stage. The electric field will enter the streamer stage when it is large enough, and the air will be broken down at the huge point. In theory, it meets the national criteria if it sounds exactly like the "cracking" sound of cooked beans and can last for one minute without breaking down. If there is a "zi zi" sound but it does not break down for one minute, it complies with the national norm, but the risk of long-term transformer operation with streaming is higher. The main cause of the high-pressure noise is the main air passage's insufficient air distance (high-voltage coil and low-voltage coil). When D is small, E is large, and the air withstands a field strength of 0.7KV/mm under standard air pressure and humidity, E=U/D E electric field, U voltage, the distance between D electrodes. The molecules are easily ionized when the electric field is bigger than this value. However, air will not conduct electricity if it is not broken down. By the way, while estimating the insulation of the transformer's main airway, don't only look at the air; the high and low voltage coils have inner and outer layers of insulation as well, so composite insulation should be taken into account.

Ⅴ. The main parameters of the Transformer

1. Rated capacity SN

When the tap changer is positioned in the main tap, the rated capacity of the transformer refers to the apparent power of the transformer under the rated working state (rated voltage, rated frequency, and rated use circumstances) specified on the nameplate. The unit is KVA.

Single phase transformer SN=UN2*IN2

Three-phase transformer SN=√3UN2*IN2

2. Rated voltage UN1 and UN2

The primary rated voltage UN1 is the grid rated voltage, while the secondary rated voltage UN2 is the no-load voltage value recorded on the secondary side when the primary side plus the rated voltage is applied.

The line voltage is represented by the primary and secondary rated voltages of a three-phase transformer.

Under no-load conditions, the rated voltage ratio is the ratio of the rated voltage on the primary side to the rated voltage on the secondary side.

3. Rated current IN1 and IN2

The line current that the primary and secondary windings are allowed to pass for a long period under the specified voltage and rated ambient temperature is referred to as the transformer primary and secondary rated current.

Single-phase transformer      IN1=SN1/UN1

                                              IN2=SN2/UN2

Three-phase transformer      IN1=SN1/√3UN1

                                              IN2=SN2/√3UN2

4. Impedance voltage

Short-circuit voltage is another name for impedance voltage. That is, the transformer's secondary winding is short-circuited, and the primary winding's voltage is gradually increased. The voltage applied on the primary side is equal to the rated current when the short-circuit current is equal to the rated current.

One of the criteria for parallel operation of two transformers is same impedance voltage. Calculating the short-circuit current and determining the relay protection features are both based on the magnitude of the short-circuit voltage value.

5. No-load current I0

The no-load current flows through the primary winding when the secondary side of the transformer is open and the rated voltage is provided to the primary side. The magnitude of the no-load current is determined by the transformer's capacity, the magnetic circuit's structure, and the silicon steel sheet's quality. A distribution transformer's no-load current is typically 3 percent to 8% of the primary rated current.

6. No-load loss P0

When the transformer is opened for the second time and the rated voltage is applied once, it refers to the power lost by the transformer. Excitation and eddy current losses are included. The transformer's size is determined by the manufacturing process and the applied voltage, and has nothing to do with the load's magnitude.

7. Short-circuit loss Pk

When the secondary side of the transformer is short-circuited and the main winding passes the rated current, this is the power absorbed by the transformer. It can show the advantages and disadvantages of the transformer's financial performance.

8. Temperature rise

The temperature rise of the upper oil surface of the transformer must not exceed 55°C, according to the state. The temperature of the upper oil surface of the transformer should not exceed 85°C in order to prevent rapid aging and damage of the transformer oil.

9. Connection group

The connection group of the transformer is the mark that indicates the connection method of the transformer's windings on both sides and the phase relationship of the corresponding line voltage.

1) The name of the connection group

There are two pieces to the connection group label: letters and numbers.

(1) From left to right, the preceding letters represent the primary and secondary windings' connection modes, with uppercase letters indicating the primary winding and lowercase letters indicating the secondary winding's connection method. D or d is a delta connection, while Y or y is a star connection. There is no sign indicating that there is no neutral line, and the letter n is put after the letter Y with neutral line since there are two types of Y connections with neutral line and without neutral line.

(2) The phase displacement of the secondary winding line voltage to the primary winding line voltage is represented by the following value, which might be an integer between 0 and 11. The secondary winding line is obtained by multiplying this value by 30°. The number of angles by which the voltage lags behind the primary winding line voltage's phase change. 0 indicates that the primary and secondary windings' line voltages are in phase. The line voltage phasor of the primary winding is used as the minute hand, which is placed at the 12 o'clock position of the clock, and the line voltage phasor of the secondary winding is used as the hour hand, which is fixed at the 6 o'clock position of the clock. The number indicates how many transformer winding groups there are.

2) Standard connection group

The national standard specifies that single-phase dual-winding power transformers have only one connection group; three-phase dual-winding power transformers have only Y, yn0, Y, d11, YN, d11, YN, y0 and Y, y0 five standard connection groups to minimize confusion in manufacture and use. The connection group number is 0 when both the high and low voltage windings are star-connected; 11 when the high voltage winding is star-connected but the low voltage winding is delta-connected.

Ⅵ. Transformer fault type

The defect of the transformer is separated into two categories based on the location of the fault point: the fault in the fuel tank and the fault outside the fuel tank.

① Malfunction inside the fuel tank

The phase-to-phase short-circuit on each side, the single-phase grounding short-circuit on the high-current system side, and the inter-gate short-circuit between the windings of the same phase are the most common internal problems of the transformer oil tank.

② Failure outside the fuel tank

The failure of the insulating bushing and the short lead wire of the transformer group's lead-out end. Ground faults on the high-current side and ground faults on the low-voltage side, as well as two-phase and three-phase short-circuit faults.

Ⅶ. What kinds of tests should be done during the operation of the transformer?

(1) Temperature test.

The temperature of the transformer is critical, regardless of whether it is performing regularly or not. The highest oil temperature must not exceed 85 degrees Celsius, according to the standards (that is, the temperature rise is 55C). Transformers are typically equipped with temperature measurement equipment.

(2) Load measurement.

It is vital to evaluate the power supply capacity that the transformer can truly bear in order to optimize the transformer's utilization rate and reduce electric energy loss during operation. The measurement is often done during the peak period of electricity usage during each season, and it is done with a clamp ammeter. The current value should be 70-80 percent of the transformer's rated current. If it surpasses, it signifies the system is overloaded, and it needs to be corrected right away.

(3) Voltage measurement.

The voltage variation range must be within 5% of the rated voltage, according to the standards. If the voltage exceeds this range, a tap should be used to bring it back within the prescribed range. A voltmeter is typically used to measure the secondary coil's terminal voltage and the terminal voltage of the terminal user.

(4) Measurement of insulation resistance.

The insulation resistance must be assessed to prevent insulation aging and accidents and to keep the transformer in normal functioning at all times. When taking measurements, try to turn off the transformer. Measure the transformer's insulating resistance with a shaker. The measured resistance must be at least 70% of the prior measurement. The low-voltage coil can be 500 volts when the shaker is selected.