Transformer cognition and detection

The Transformer is a device that changes the AC voltage using the principle of electromagnetic induction. The main components are a primary coil, a secondary coil, and a core (magnetic core). The main functions : voltage conversion, current conversion, impedance conversion, isolation, voltage regulator (magnetic saturation transformer) and so on. According to the use, it can be divided into: power transformers and special transformers (electrical furnaces, rectifiers, power frequency test transformers, voltage regulators, mining transformers, audio transformers, intermediate frequency transformers, high frequency transformers, impact transformers, instrument transformers, electronic transformers , reactors, transformers, etc.). Circuit symbols commonly used as the beginning of a number.

Transformer status

There are about 1,500 transformer manufacturers in China. There are nearly 30 manufacturers of transformers with more than 500kV, about 50 companies with 220kV and above, and about 130 manufacturers with 110kV and below in the statistical scope. In the past three years, the annual demand for transformers in China has been around 1.5 billion kVA. The industry insight research “Transformer Market Analysis Report” shows that the capacity of the transformer industry in China is about 3 billion kVA, and the production capacity of Shen, Xi and Baosan Group is about 500 million kVA. In the past few years, China’s power construction has been developing rapidly, and the demand for transformers has increased rapidly. As a result, a considerable number of domestic transformer enterprises have rapidly expanded their production capacity, and even the production capacity of individual enterprises has doubled. Since 2009, the national power construction has slowed down, and the demand for domestic transformers has decreased. In particular, State Grid Corporation and South China Net Company purchased transformers through centralized tendering, which resulted in unprecedented fierce competition among enterprises. In addition, due to the fierce competition in the domestic market, the bid price is lower than the cost price, leading some companies to start overseas routes, export products, and build factories abroad. In addition, many companies have begun to develop new, energy-saving, environmentally friendly, intelligent products. However, the general economic benefits of domestic transformer companies have been significantly reduced, and many companies are at the edge of losses or losses. A large number of distribution transformer companies have even witnessed a situation of malicious competition at the expense of product quality. In addition, the quality of transformer products has decreased and the accident rate has increased. The qualified rate of distribution transformers in the country is only 70%. The transformer accident rate on the Internet is on the rise, resulting in more than five-year-old transformers in the event of an accident, and the security of the power grid is threatened.

working principle

A transformer is a device that converts alternating voltage, alternating current, and impedance. When alternating current flows in the primary coil, an alternating magnetic flux is generated in the core (or core), causing a voltage (or current) to be induced in the secondary coil. . The transformer consists of a core (or core) and a coil, and the coil has two or more windings, wherein the winding of the power supply is called the primary coil and the rest of the winding is called the secondary coil.

The main parameters

The main technical data is generally marked on the nameplate of the transformer.

Mainly include: rated capacity, rated voltage and its tap, rated frequency, winding connection group and rated performance data (impedance voltage, no-load current, no-load loss and total load loss.

A. Rated capacity (kVA): rated voltage. The capacity that can be delivered when continuously operating at rated current.

B. Rated voltage (kV): The working voltage that the transformer can withstand when it is operated for a long time. In order to meet the needs of the grid voltage change, taps are tapped on the high voltage side of the transformer, and the output voltage of the low voltage side is adjusted by adjusting the number of turns of the high voltage winding.

C, rated current (A): transformer under rated capacity, allowing long-term current.

D. No-load loss (kW): When the rated voltage is applied to the terminals of one winding, the remaining windings draw active power when they are open. With iron core silicon performance and manufacturing process, and the application of voltage.

E, no-load current (%): When the transformer under the rated voltage secondary side no-load, the current through the primary winding is generally expressed as a percentage of the rated current.

F, load loss (kW): Short-circuit the secondary winding of the transformer, pass the rated current at the rated tapping position of the primary winding, and the power consumed by the transformer at this time.

G, Impedance voltage (%): Short-circuit the secondary winding of the transformer, gradually increase the voltage in the primary winding, when the short-circuit current of the secondary winding is equal to the rated value, the voltage applied by the primary side is generally rated voltage. The percentage is expressed.

H, phase number and frequency: The three-phase head is denoted by S, and the single-phase head is denoted by D. China’s national standard frequency f is 50Hz. There are 60Hz countries abroad (such as the United States).

I. Temperature rise and cooling: The difference between the transformer winding or upper oil temperature and the ambient temperature of the transformer is called the temperature rise of the winding or the upper oil level. The temperature rise limit of the oil-immersed transformer winding is 65K, and the oil surface temperature rises to 55K. There are also a variety of cooling methods: oil-immersed self-cooling, forced air-cooling, water-cooled, tube-type, and sheet-type.

J, insulation level: There is insulation grade standard. Examples of the insulation level are as follows: The high-voltage rated voltage is 35kV and the low-voltage rated voltage is 10kV. The insulation level of the transformer is represented by LI200AC85/LI75AC35, where LI200 indicates that the transformer high-voltage lightning impulse withstand voltage is 200kV, and the power frequency withstand voltage For 85kV, low voltage lightning impulse withstand voltage is 75kV, and power frequency withstand voltage is 35kV.

Common malfunctions

Common faults When the transformer is powered off or tested after power off, it is often found that the voltage is abnormal, such as two phases high and one phase low or indicating zero; some of the new three-phase transformers put into operation are high voltage, so that some use Electrical equipment is burned due to excessive voltage;

(2) The high voltage fuse blows and does not power up;

(3) The transformer will not be powered on after the thunderstorm;

(4) The sound of the transformer is abnormal, such as the sound of ”吱吱” or ‘霹啪’; in the course of the operation, sounds such as frogs, ‘wow, wow, wow’ are issued;

(5) Burnout of the high-voltage terminal, severe damage to the high-voltage bushing;

(6) Under normal cooling conditions, the temperature of the transformer is abnormal and keeps rising;

(7) The oil color changes too much and carbon appears in the oil;

(8) The transformer emits squeaks, sprays oil from the safety airway and the oil conservator, deforms the oil tank and the heat pipe, leaks oil, and leaks oil. Measurement methods

Today we talk about the transformer measurement method:

1. The measurement dimensions are secondary. Primary. The longer the primary distance of the transformer is, the shorter the primary distance is the primary.

The following is the measurement transformer body

2. Measure the primary and secondary resistances

3. Measurement of initial voltage and current

Each transformer will clearly indicate the rated parameters. According to the voltage debugging frequency power supply voltage value. Link the primary test, pay attention to the use of electricity to complete an action in a timely manner to turn off the variable frequency power supply to prevent leakage or accidental short circuit

4. Withstand pressure test

Short-circuit the primary 2 pins. Stage 2 short-circuits. High-voltage test according to the transformer specification

5. Temperature aging

According to the transformer rated voltage debugging frequency conversion power supply +20% voltage test 4-8H temperature aging test record °C / H

6 Aging Voltage. Current Test Steps Same as Step 3 above

7. No load. Load voltage. Current test

Need to intervene in adjustable resistors link the secondary. The primary or the variable-frequency power supply is connected to the multimeter’s secondary voltage and current values.

The above is a 115V-230V transformer measurement method if there is any omission please pay attention to timely follow-up

leave a message

Ztelec Group