From current transformers to hybrid sensors, in HV

Introduction

Proper operation and safety of electrical power distribution networks, from the electrical power station right through to the point of use, is ensured by protection and control/monitoring equipment.

This equipment requires permanent knowledge of the two fundamental electrical values, namely current l and voltage U. The knowledge of these values has many angles:

• type of current (AC or DC);
• voltage level (low voltage – LV, high voltage – HVA and HVB-);
• transient evolutions of these values linked to status changes occurring naturally or accidentally in operation of electrical networks.

A number of physical phenomena can be used to measure AC currents. These methods result in levels of performance which have a varying degree of compatibility with those required by the various protection, operation and safety levels sought. Evaluation of sensor performance is vital to ensure their best possible specification for installation on a network. This requires knowledge of how the different types of sensors work.

Sensor functions

Sensors have three main functions:

• providing a correct image, as accurate as possible, of the electrical value to be measured;
• isolating the power networks from the measuring, protection and control/monitoring networks;
• ensuring either interchangeability between the measuring, protection and control/monitoring units or performing one specific function of these units.

Providing a correct and accurate image

Based on the two characteristic values of all electrical networks, i.e. current and voltage, the measuring, protection and control/monitoring equipment defines a certain number of parameters such as: cos j, threshold overshooting, instantaneous power,…

AUTHOR: Schneider Electric expert | Christian TEYSSANDIER