Magneto Optics Current Transformer | Electrical Seminar Topic
Magneto Optics Current Transformer
An accurate electric current transducer is a key component
of any power system instrumentation. To measure currents, power stations and substations
conventionally employ inductive type current transformers with core and
windings. For high voltage applications, porcelain insulators and
oil-impregnated materials have to be used to produce insulation between the
primary bus and the secondary windings.
The insulation structure has to be designed carefully to
avoid electric field stresses, which could eventually cause insulation
breakdown. The electric current path of the primary bus has to be designed
properly to minimize the mechanical forces on the primary conductors for
through faults.
The reliability of conventional high-voltage current
transformers have been questioned because of their violent destructive failures
which caused fires and impact damage to adjacent apparatus in the switchyards,
electric damage to relays, and power service disruptions.
With short circuit capabilities of power systems getting
larger, and the voltage levels going higher the conventional current
transformers becomes more and more bulky and costly also the saturation of the
iron core under fault current and the low frequency response make it difficult
to obtain accurate current signals under power system transient conditions. In
addition to the concerns, with the computer control techniques and digital
protection devices being introduced
into power systems, the conventional current transformers
have caused further difficulties, as they are likely to introduce
electro-magnetic interference through the ground loop into the digital systems.
This has required the use of an auxiliary current transformer or optical
isolator to avoid such problems.
It appears that the newly emerged Magneto-optical current
transformer technology provides a solution for many of the above mentioned
problems. The MOCT measures the electric current by means of Faraday Effect,
which was first observed by Michael Faraday 150 years ago.
The Faraday Effect
is the phenomenon that the orientation of polarized light rotates under the
influence of the magnetic fields and the rotation angle is proportional to the
strength of the magnetic field component in the direction of optical path.
The MOCT measures the rotation angle caused by the magnetic
field and converts it into a signal of few volts proportional to the electric
currant. It consist of a sensor head located near the current carrying
conductor, an electronic signal processing unit and fiber optical cables
linking to these two parts.
The sensor head consist of only optical component
such as fiber optical cables, lenses, polarizers, glass prisms, mirrors etc.
the signal is brought down by fiber optical cables to the signal processing
unit and there is no need to use the metallic wires to transfer the signal.
Therefore the insulation structure of an MOCT is simpler
than that of a conventional current transformer, and there
is no risk of fire or explosion by the MOCT. In addition to the insulation
benefits, a MOCT is able to provide high immunity to electromagnetic
interferences, wider frequency response, large dynamic range and low outputs
which are compatible with the inputs of analog to digital converters. They are
ideal for the interference between power systems and computer systems. And
there is a growing interest in using MOCTs to measure the electric currents.
