Current Transformer - Design

Design

Like any other transformer, a current transformer has a primary winding, a magnetic core, and a secondary winding. The alternating current flowing in the primary produces a magnetic field in the core, which then induces a current in the secondary winding circuit. A primary objective of current transformer design is to ensure that the primary and secondary circuits are efficiently coupled, so that the secondary current bears an accurate relationship to the primary current.

The most common design of CT consists of a length of wire wrapped many times around a silicon steel ring passed over the circuit being measured. The CT's primary circuit therefore consists of a single 'turn' of conductor, with a secondary of many tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry current through the magnetic core. Window-type current transformers (aka zero sequence current transformers, or ZSCT) are also common, which can have circuit cables run through the middle of an opening in the core to provide a single-turn primary winding. When conductors passing through a CT are not centered in the circular (or oval) opening, slight inaccuracies may occur.

Shapes and sizes can vary depending on the end user or switchgear manufacturer. Typical examples of low voltage single ratio metering current transformers are either ring type or plastic moulded case. High-voltage current transformers are mounted on porcelain bushings to insulate them from ground. Some CT configurations slip around the bushing of a high-voltage transformer or circuit breaker, which automatically centers the conductor inside the CT window.

The primary circuit is largely unaffected by the insertion of the CT. The rated secondary current is commonly standardized at 1 or 5 amperes. For example, a 4000:5 CT would provide an output current of 5 amperes when the primary was passing 4000 amperes. The secondary winding can be single ratio or multi ratio, with five taps being common for multi ratio CTs. The load, or burden, of the CT should be of low resistance. If the voltage time integral area is higher than the core's design rating, the core goes into saturation towards the end of each cycle, distorting the waveform and affecting accuracy.

Read more about this topic:  Current Transformer

Other articles related to "design, designs":

Shea Stadium - Features - Design
... The design also allowed for Shea Stadium to be expandable to 90,000 seats (by completely enclosing the grandstand), or to be later enclosed by a dome if warranted ...
Terminology - Process Design
... "Process design" (in contrast to "design process" mentioned above) refers to the planning of routine steps of a process aside from the expected result ... Processes (in general) are treated as a product of design, not the method of design ... and executives have found the term useful to describe the design of business processes as well as manufacturing processes ...
56th Tony Awards - The Ceremony
... of a Play, Direction of a Musical, Book of a Musical, Original Score, Choreography, Costume Design, Lighting Design and Scenic Design ...
Boeing 747 - Design
... For more design details, see Boeing 747-400, 747-8, and 747SP ... The Boeing 747 is a large, wide-body (two-aisle) airliner with four wing-mounted engines ...
Very-large-scale Integration - Structured Design
... Structured VLSI design is a modular methodology originated by Carver Mead and Lynn Conway for saving microchip area by minimizing the interconnect fabrics area ... In complex designs this structuring may be achieved by hierarchical nesting ... Structured VLSI design had been popular in the early 1980s, but lost its popularity later because of the advent of placement and routing tools wasting a lot of area by routing, which is tolerated ...

Famous quotes containing the word design:

    If I commit suicide, it will not be to destroy myself but to put myself back together again. Suicide will be for me only one means of violently reconquering myself, of brutally invading my being, of anticipating the unpredictable approaches of God. By suicide, I reintroduce my design in nature, I shall for the first time give things the shape of my will.
    Antonin Artaud (1896–1948)

    Nowadays the host does not admit you to his hearth, but has got the mason to build one for yourself somewhere in his alley, and hospitality is the art of keeping you at the greatest distance. There is as much secrecy about the cooking as if he had a design to poison you.
    Henry David Thoreau (1817–1862)

    A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering.
    Freeman Dyson (b. 1923)