Instrument transformer: classification and device of voltage and current converters

Measuring transformer - an electromagnetic device installed in a controlled electrical circuit and designed to measure and monitor voltage, current or phase readings. It is mainly used in cases where it is impossible to measure electrical indicators by direct connection of measuring instruments. Calculate them in such a way as to ensure the minimum effect on the measured circuit.

Electrical apparatus

The main purpose of measuring transformers is to lower the primary current to a value that allows the connection of electrical measuring devices, protective systems, etc.

In addition, they provide galvanic isolation between high and low voltage, allowing maintenance personnel to work safely. This device consists of the following components:

• primary winding with the calculated number of turns;
• secondary winding;
• core made of special steel.

The electrical wires of the primary winding are connected in series to the operated circuit in which the readings are checked. Measuring devices, a set of automatic devices to protect the circuit from damage, various automation systems, etc. are connected to the wires of the secondary winding.

To prevent short circuits between the windings and the turns in them, insulation is required. They also carry out mandatory grounding of the secondary winding in case of a short circuit between the coils.

Unit classification

All devices are divided into measuring current and voltage transformers. Moreover, there are two types of current devices: for direct and alternating current. According to the transformation method, they are divided into converters of current to current, current to voltage and current to a non-electrical function (for example, luminous flux).

In this case, transformers are divided into analog and discrete (depending on the method of obtaining information). All measuring devices classified according to the following characteristics:

• by the type of installation;
• by her way;
• by the number of transformation ratios;
• by the number of conversion steps;
• by the type of primary winding;
• by the nature of isolation;
• according to the principle of current transformation.

These units are designed for outdoor operation, in closed rooms. They are directly built into electrical equipment and special installations (on ships, in mines, electric locomotives, etc.).

They are directly installed in the openings of walls, ceilings or in special metal structures, if they are intended to be used as an input. Reference measuring transducers are mounted on a flat plane, and built-in transformers are installed directly in the plane of the electrical equipment.

There are varieties of devices with one transformation ratio, and with several, which are obtained by changing the number of turns of the primary or secondary winding.

They are also distinguished by the method of manufacturing insulation, which is solid, viscous and combined. All instrument transformers are divided into electromagnetic and optoelectronic, depending on the method of current conversion.

Voltage measuring transducers

Such devices are used to reduce the voltage in the primary circuit from 6 kV and above, to 100 V in the secondary winding. They are capable of converting these readings in the primary circuit into standard electrical current and provide overload protection for connected electrical appliances.

In addition, such units provide the maintenance personnel with a safe work. This technique interacts with alternating and direct current, and in its functioning it approaches the idle mode, since there is no power transfer. In terms of their functional actions, these devices practically do not differ from power transformers. There are several types of them.:

1. Grounded device is a converter with one live phase and one end of the primary circuit grounded. In three-phase units, the neutral conductor of the primary coil is grounded.
2. Non-earthed transformers - all parts of the primary coil, including the contacts, are isolated from the earth connection to the recommended level corresponding to the voltage class.
3. Capacitive devices - capacitors are included in the design, providing voltage reduction.
4. Cascade transformers - the primary circuit has several parts that are connected to the secondary circuit with tie and equalizing windings.

And there are also devices with one secondary circuit, and with two: the main and the additional.

Current transformers

These transmitters perform a number of special functions. They are connected to measuring devices capable of taking readings in various modes.

The main functions of the unit are:

1. Converting AC to 1 or 5 A.
2. In normal operation, it protects the secondary circuit from the high voltage primary winding.
3. The work is carried out in the protective mode of the secondary circuit against overloads.

In addition, such transformers have rectifiers in their design, and the secondary circuits are necessarily grounded at one point. The design features of this unit prohibit breaking the secondary circuit under voltage, since at this moment, a violation of the insulation occurs, the core heats up and a violation of the normal mode occurs work.

Before installing and starting up the transmitter, be sure to check it. Diagnose its operation in all modes and check the insulation condition. In conditions of long-term operation, the units are periodically serviced, which avoids unforeseen breakdowns.