Alfred Papp

Magnetooptical current transformer. 1: Principles.

The principles of measuring currents in high-voltage lines by magnetooptical means are described. Particular attention is payed to using an optical fiber both as a transmission line and a measuring sensor. The influence of birefringence on the measuring signal is discussed.

Magnetooptical current transformer. 2: Components

In this second part, the most important components of a magnetooptical current transformer are described and their suitability is discussed. Today He-Ne gas lasers and laser diodes seem to meet best the requirements of the light source. Single-mode optical fibers are capable of transmitting polarized light without depolarization. A fiber coil wound on a special coil former is used as a measuring sensor. Two P-I-N photodiodes, together with an analog electronic circuit, transform the optical into an electrical measuring signal.

Magnetooptical current transformer. 3: Measurements

A laboratory setup of a magnetooptical current transformer was established. A ingle-mode fiber acts as both a measuring sensor and a transmission line. The overall measurement accuracy at room temperature within a primary current range 50-1200 A is better than 0.24%, the SNR at 1000 A is 85 dB. Current measurements of high accuracy were also performed in the -20-+ 45 degrees C temperature range.