Voltage Transformer (VT), also called Potential transformers (PT). It is used in power supply systems to reduce system voltage at a safe cost, supplied to meters and relays with low ratings. Voltage transformers are parallel connected device transformers.
Voltage transformers are a type of instrument transformer, and these transformers are used to measure voltage in power lines or any electrical circuit. It is used to bring down high voltage.
Commercially available relays and counters are used for protection and measurement designed for low voltage. This is the simplest form of the definition of a voltage transformer.
A voltage transformer is a high-accuracy electrical device used to isolate or change the voltage levels. Although most often, voltage transformers are used to operate instruments or measurements from high voltage or high current circuits, reliably separating secondary control circuits from high voltage or current.
The transformer’s primary is connected to a high voltage or high current circuit, and the meter or relay is connected to a secondary circuit.
Uses Or Applications
Using a voltage or potential transformer is used to move the voltage to lower values and provide isolation between the high voltage power grid and the relay and other devices connected to the secondary direction.
We cannot measure high voltage (KV, MV) directly, but we can measure high voltage by subtracting it from a low voltage transformer, and we can easily measure this low PT voltage with a voltmeter.
While they have many turns on the primary winding and fewer turns on the secondary winding. The reason is clear ( i. E is proportional to the secondary voltage reduction and the number of voltage turns). And here, the primary system is connected by a high voltage power supply.
The relay needs to know the voltage’s amplitude – either for measurement or to enforce safety duties. The (VT) provides information about this value. It lowers the nominal system voltage (high voltage or KV) to 50 or 110 V (132.5 kV) and lowers the voltage below the transformer to 110 V, then fed to the relay. Installed on every part of the bus.
By definition, you can see that voltage transformers are not like a regular transformer, but a special transformer used to measure high voltage applications.
Types of Voltage Transformer
There are many different types of voltage or potential transformers. Commercial devices are well suited for extremely low current control applications, which describe below;
Inductive Voltage Transformers
An inductive voltage transformer is a conventional transformer. The measuring line is connected to the main aspect and, with the required ratio of turns, provides a secondary low voltage to measure. The transformer works by mutual inductance. The primary winding produces a voltage in the secondary through the magnetic effect.
Inductive voltage transformers drive high voltage to specific values and thus provide the standard, which is usable voltage levels in various types of power systems, monitoring, and measurement applications during high systems. Measurement and safety equipment are isolated from the voltage.
Used for voltage measurement and protection in high voltage networks. They convert high voltage to low voltage (suitable for processing in secondary equipment and safety equipment such as relays and recorders).
Capacitance Voltage Transformer
Capacitive voltage transformers (CVTs) are used at high voltage levels of 66 kV and above. A capacitive voltage transformer is a step-down transformer that converts extra-high-voltage to low-voltage. First, the voltage in the voltage divider circuit decreases, after which the step down is supplied to the main winding of the transformer. Therefore CVT is used in high voltage ranges.
It is used in a power system to drop an EHV signal and provide a low voltage signal to measure or control a safety relay. It converts transmission class voltage to standard low, and easily measurable values used to measure, protect, and control a high voltage system.
Capacitor voltage transformers are used to measure EHV transmission line voltage. It also provides electrical isolation like a voltage transformer. It is also useful in communication systems. Together with wave traps, CVT is used to filter high-frequency communication signals from electrical frequencies.
It forms the operator’s communication network in the transmission network for communication between substations. The variable is installed at a location after the electrical current is captured and before the wave mesh. High-frequency information (in MHz) is transmitted from one network to another on transmission lines; this is called power line communication.
Working of Capacitive voltage transformer
A capacitive transformer operates on a principle of a potential divider. Which consists of two capacitors forming a potential divider, a line square, and a step-down transformer. Here, the line square is used to compensate for the phase shift of the capacitor. The inductance value is adjusted.
The inductance compensates for the voltage droplets caused by the lack of current from the potential distribution found in the transformer. However, in practice, compensation is not possible due to the damages received. The voltage divider is connected in series with the inclusion of capacitance, compensation reactor. And wound transformer (inside the EMU), forming a resonant circuit.
There is a potential divider of capacity in combination with auxiliary transformer and incendiary elements. The potential part of a potential divider reduces the EHV signal to a low voltage signal. The capacitive potential through the auxiliary transformer further reduces the output voltage of the transformer.