A new delayed action electrical protection device, depending on an adjusted magnitude.

摘要

This invention provides a delayed action electrical protection device which may be used for example to protect electrical lines and equipment against disturbances such as overload conditions and minimum voltage conditions. An analogue signal denoting the particular condition for which protection is to be provided is converted into a digital signal which is applied to a micro-processor. In the micro-processor this digital is compared with a prescribed value or values fed into the processor. The processor contains information relating to characteristic curves which define the time delay between the detection of a particular condition and the production of a tripping signal which may, for example, be used to interrupt the electrical circuit and/or provide an alarm. The time delay varies inversely with the magnitude of any disturbance and may, for example, be defined by the expression:- @@@@ where K is a constant i equals I/I@ where I is the measured current and In is the prescribed value.