Техническое чтение для энергетиков. Бухарова Г.П. - 65 стр.

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67
the core and the secondary winding surrounding another. In actual practice the two
windings would not be separated in this manner as the primary would be
superimposed on the secondary, but they are shown thus for the sake of** clarity in
the diagram. The primary terminals are indicated by the letters M and L, and the
secondary terminals by the same letters enclosed in a circle.
The cores of current transformers are usually built up with laminations of
silicon-steel but where a high degree of accuracy is desired a high-permeability
nickel-steel such as Mumetal or Permalloy may be used. Three types of magnetic
circuit are in common use, namely, "ring-type", "core-type" and "shell-type" and are
illustrated in Fig. 15.
* it is not convenient to provide a primary integral with the transformer нелегко сделать так,
чтобы первичная цепь составляла одно целое с трансформатором; to be integral with
составлять одно целое с ч. л., бить неотъемлемым от ч. л.
** for the sake of (составной предлог) ради
VOLTAGE TRANSFORMERS
Why Voltage Transformers are Used.–When an instrument or meter having a
voltage winding is connected to a high-voltage alternating-current circuit, the use of a
voltage transformer (sometimes called a potential transformer) is necessary. It is not
practicable to wind the voltage coil of a meter for direct connection to, say, an
11,000-volt supply, because the space available on the voltage electromagnet is not
sufficient to accommodate the number of turns of wire which would be necessary.
Moreover it would be quite impossible to insulate adequately the winding and the
terminals in such a manner as to render the meter safe to handle when the circuit to
which it was connected was alive. Accordingly, a voltage transformer is always used
when a meter is installed for use on a high-voltage system. In this connection
potentials in excess of 660 volts are regarded as high voltage.
A voltage transformer may be defined as an instrument transformer for the
transformation of voltage from one value to another, usually a lower one. The
primary winding of a voltage transformer is the winding to which is applied the
voltage to be measured or controlled, as the case may be. The secondary winding is
the winding the terminals of which are connected to the meter or instrument. The
standard voltage at the terminals of the secondary winding is 110 volts.
Construction of Voltage Transformers.– Voltage transformers are frequently fitted
in switchgear cubicles, and owing to the restricted space available the dimensions of
Fig. 15. Types of magnetic circuit for a current transformer

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