The function of miniature transformer and its correct use

Miniature transformers play an important function and role in the power supply system. Because the number of turns of the primary winding of the current transformer is small, it is connected in series in the line to be tested. For the through-core current transformer, the line to be tested is connected in series. Through the transformer, P1 enters and P2 exits. The larger the current to be measured, the fewer turns it passes through.

Based on the structural characteristics of the miniature transformer, it is worth noting that the secondary side of the current transformer in the normal working state must never be open, because once the secondary side is open, the impedance of the secondary loop becomes infinite, and the secondary current is equal to zero , Then the primary current completely becomes the excitation current, and extremely high voltage is generated in the secondary winding, which directly endangers the safety of people and equipment on the secondary side. Therefore, it is not allowed to install a fuse on the secondary side of the current transformer, lest the fuse is blown, and the secondary side becomes an open circuit.　

When using a miniature transformer, you must first ensure that its range meets the requirements for use. Once the current to be measured exceeds the range of the ammeter, you need to replace a higher range AC ammeter and a matching current transformer. In addition, in practical applications, it is also necessary to ensure that the iron core and secondary side of the miniature transformer must be reliably grounded to prevent accidental charging of the iron core. Once the primary insulation is broken down, the secondary side will enter high voltage. It directly threatens the personal safety of the secondary side and causes equipment damage.

It should be noted that the miniature current transformer cannot be used as a voltage transformer, because the essential difference between a current transformer and a voltage transformer is that the primary winding of the current transformer has very few turns, often only one turn. When the secondary is connected to the rated When the load is applied, the impedance is very small when viewed at one time. As a voltage measurement, it is connected in parallel at both ends of the circuit under test and requires a large input impedance. This is the first obstacle to the use of current transformers as voltage transformers.

In addition, when the current transformer is running at rated load, the voltage drop of the primary winding is very small, which means that when the voltage transformer is used at both ends of the circuit under test, it can only measure very weak voltage. This is the second obstacle to the use of current transformers as voltage transformers. The principle of current transformer is based on the principle of electromagnetic induction. When working, its secondary circuit is always closed, so the impedance of the series coil of the measuring instrument and the protection circuit is very small, and the working state of the current transformer is close to short circuit. The current transformer converts the large current on the primary side into the small current on the secondary side for measurement, and the secondary side cannot be opened.