page_title: High voltage interface relays
section_title: Opto-electronic interface relays
hierarchical_section_title: High voltage interface relays / Opto-electronic interface relays
caption_attribution_description: English: Opto-electronic interface relay. The HV insulator provides decoupling of circuits under different potentials.
context_page_description: High voltage interface relays, a.k.a., interface relays: or coupling relays or insulating interfaces is a special class of electrical relays designed to provide informational and electrical compatibility between functional components isolated from each other and not allowing for a direct connection due to a high difference of potentials. A common design principle of these devices is a special galvanic isolation module between the input and the output circuits of the relay. Interface relays are widely used in control and protection systems of high voltage electronic and electrophysical equipment and in high power installations.
context_section_description: The developmental trends of interface relay technology suggest the use of opto-isolator as the prevailing design principle of interface relays. An opto-isolator can be implemented in terms of an LED and a phototransistor (or photothyristor or a photodiode) or a lamp and a photoresistor. An example of an opto-electronic interface relay is shown in the figure. The transparent high voltage insulating barrier provides galvanic isolation of the circuits under the difference of potentials up to 5-7 kV.  For higher voltages, they use an optical fiber, the length of which (depending on the voltage level) can take from dozens of centimeters to several meters.
  Criticism
  It is agreed that the most important characteristic of opto-electronic systems is their noise robustness and insensitivity to electromagnetic fields. What is not considered, however, is that, in addition to the fiber optic line and the output actuator, such a system includes the source of light pulses on the transmitting side and the amplifier on the receiving side that are generally based on micro-circuitry. It is precisely these elements, with low trigger levels, that get damaged by pulse noise (interference, voltage spikes and discharges) of the high voltage power equipment, which negates the main advantage of opto-electronic systems. Moreover, the optical fibers themselves are subject to a severe negative effect of ionizing radiation and external mechanical impacts (which is critically important in military applications). The arrangement of input and output circuits of such systems needs to be widely spaced (requiring a lengthy optical fiber), which drives up the overall dimensions of interface unit. As such, the preferred use of an opto-electronic galvanic decoupling module in interface relays is not always warranted, and is merely the consequence of a stereotypical thinking of design engineers
caption: Opto-electronic interface relay. The HV insulator provides decoupling of circuits under different potentials.
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