What is current voltage transformer?

Answer 1

A transformer is a device that steps up, or steps down voltage. During this process current is also stepped up or down:however, voltage and current are inversely proportional ( meaning an increase in voltage results in a decrease in current and vice versa ) As an example: A step up transformer of 10:1 ratio with 12 volts and 10 amper of current applied to the primary will have ten times the voltage ( 120 volts ) and ten times less current ( 1 amrere ) at the secondary...and a step down transformer with the same turns ratio with 120 volts and 1 ampere applied to the primary will have 12 volts and ten ampere available at the secondary. The electricity supplied into homes and business uses wires carrying very high voltage and low current over long distances, then uses step down Transformers to step down the voltage and step up the current.

However, in power engineering and protective relaying applications, there are what are called "instrument transformers" which have the specific purpose of providing information to devices (such as relays or meters) about the voltages or currents in the power system. Therefore, there are some differences in construction and connectivity between a Current Transformer (CT) and a Voltage (or Potential) Transformer (PT).

A CT will typically have a toroidal core and evenly distributed secondary windings so as to minimize leakage reactance. The primary is typically the main power line conductor, which passes directly through the toroidal core. This type of transformer is specifically for the purpose of measuring current values, and the secondary windings cannot be left open-circuited, or a large voltage will be produce, resulting in dielectric failure (and often an explosion). If a device is not connected to the CT, its secondary must be short-circuited.

A PT is connected between the main conductor and ground and can be either wound in the normal way, or the voltage can be taken from a subsection of a string of capacitors (this is called a Capacitive Voltage Tansformer or CVT, and is usually cheaper than the wound type, but is typically not as accurate). This type of transformer measures voltage values, and the secondary winding cannot be short-circuited, as this will produce excessively high currents, resulting in the failure of the PT or the wires it is connected to. A PT can be left open-circuited.

Answer 2

A current transformer is a donut (toroidal) shaped transformer. You use it to measure current (expressed in amperes). You run your wire to be measured through the transformer and it produces a variable output based on the current.

A potential transformer is basically a high ratio transformer that is used to measure voltage on high-voltage lines. For example: They will use a 10:1 ratio potential transformer to convert 4160v to 416v. Then they can measure this lower voltage with a meter. The meter then applies a user programmed multiplier (10) to this number to calculate the voltage.

Answer 3

A current transformer is a transformer that takes a ratio of primary current, and delivers this ratio to the secondary. The voltage across the primary will be insignificant, and the voltage across the secondary is dependent upon the resistive burden put across it (since the current is a constant ratio of the primary current).

A voltage transformer is a transformer that takes a ratio of primary voltage and steps this down to a specific secondary voltage. Primary current is typically very small and secondary voltage is typically very small.

A power transformer is a voltage transformer that is designed for "large" primary and secondary currents.

Answer 4

There are various type of transformer, named according to the purpose for which they are intended. Most are 'mutual transformers', consisting of primary and secondary windings that are electrically-isolated from each other; others are 'autotransformers' which have a single winding, part of which is common to the primary and secondary circuits. A voltage transformer (UK terminology) -also known as a 'potential transformer' (North American terminology)- together with a current transformer, fall into a category called 'instrument transformers. These transformers are used to measure or to monitor the voltage (voltage transformer) or current (transformer) in, usually, high-voltage systems, while electrically-isolating the measuring instruments (or protection relays) from the high-voltage primary circuits.