RE: magneto optical current transformer
||Magneto Optical Current Transformer
Magneto Optical Current.DOC (Size: 507.5 KB / Downloads: 10)
MOCT.DOC (Size: 334.5 KB / Downloads: 8)
An accurate 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 short circuit capabilities of power system getting larger and the voltage level going higher the conventional current transducers becomes more bulky and costly.
It appears that newly emerged MOCT technology provides a solution for many of the problems by the conventional current transformers. MOCT measures the rotation angle of the plane polarized lights caused by the magnetic field and convert it into a signal of few volts proportional to the magnetic field.
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.
The Magneto-Optical current transformer is based on the Faradays effect. Michael Faraday discovered that the orientation of linearly polarized light was rotated under the influence of the magnetic field when the light propagated in a piece of glass, and the rotation angle was proportional to the intensity of the magnetic field. The concept of Faraday Effect could be understood from the Fig.1.
Almost all transparent material exhibits the magneto-optical effect or Faraday Effect, but the effect of some of the material is very temperature dependent, and they are not suitable for the sensing material. The optical glasses are good candidate for the sensing material, because the Verdet constants are not sensitive to the temperature changes, and they have good transparency properties. They are cheep and it is easy to get large pieces of them. Among the optical glasses SF-57 is the best choice, as it has larger Verdet constant than most of the other optical glasses. And MOCT made out of these materials can achieve higher sensitivity. In the MOCT
This paper presents a new kind of current transducer known as magneto optical current transducer. This magneto optical current transducer eliminates many of the drawbacks of the conventional current transformers. In an conventional current transformers, there is a chance of saturation of magnetic field under high current, complicated insulation and cooling structure, a chance of electro magnetic interference etc.
By applying Faraday’s principle this transducer provides an easier and more accurate way of current measurement. This MOCT is widely used in power systems and substations nowadays. And a new trend is being introduced, which known as OCP based on adaptive theory, which make use of accuracy in the steady state of the conventional current transformer and the MOCT with no saturation under fault current transients.