Measuring transformers are used in relay protection and automation circuits to analyze the magnitude of current and voltage. This is necessary so that the relay protection can operate in time according to the settings set by the engineers when setting up the electrical equipment. As a rule, current and voltage measuring transformers are used in relay protection and automation circuits. Consider each of the species separately.
Voltage transformers are used to orient the protection, this is a kind of support, relative to which the phase displacement angles are counted, and earth fault protection is also organized using windings connected according to the open triangle scheme.
Measuring voltage transformers are made with several cores: one is connected according to the "star" scheme, the second - according to the "open triangle" scheme. Today, manufacturers produce transformers with a third core, which is used for metering.
Three single-phase voltage transformers are installed for RU-35-110 kV. Separate automata are mounted for each connection group. For RU-6-10 kV, a three-phase VT in one housing is most often used.
Measuring current transformers are used in all switchgears and are installed phase by phase. These transformers are made of a monolithic bus, which is the primary. Secondary windings are fixed on the bus, there may be several of them, and each winding (hereinafter referred to as the core) is designed for a certain accuracy class and a specific power.
Cores are displayed for protection, accounting and measurement circuits. It is important that short cores are never left on the current transformers, otherwise the winding will burn out and the operating personnel are in danger of being electrocuted.
During installation, measuring current transformers must be installed according to the voltage input-output circuit (L1 - input, L2 - output). The direction of the current vectors of each phase depends on this. According to the physical meaning, between the current vectors, the windings of which are connected according to the "Star" scheme, there should be 120 degrees. If for some reason the vectors are located differently, it is necessary to change the connection of the TT cores by swapping the beginning with the end.
Current transformers are used for protection against short circuits and for organizing differential protection. Measuring current transformers are an important attribute of modern electrification, this is a kind of sensor that determines the magnitude of the current and its direction.
In electrical installations, a zero-sequence transformer is used. This element is relevant for RU-0, 4-6-10 kV,since the task of a transformer (in everyday life a donut) is to protect high voltage circuits from ground faults. His primary is the feeder itself, which is passed through a bagel. A value is taken from the secondary, which changes according to the change in the magnetic field of the feeder.
Thus, transformers for measuring current and voltage are the basis of protection. Thanks to them, modern microprocessors can independently calculate the power, the resistance of the circuit section, the angles between current and voltage. The results obtained do not need to be verified, as modern equipment is made using the latest technologies.
Today, devices that are a complex solution and include a switch, a disconnector, as well as built-in CTs and VTs are quite popular today - this is convenient and quite profitable.
