Components used for data transmission or communication 7625013-S

Components used for data transmission or communication 7625013-S

Components used for data transmission or communication 7625013-S

The minimum operating voltage has to be calculated (all loops) and the IED function is set higher than the highest achieved value (setting U>Trip). As the loop resistance is the value to the connection point from each CT, it is advisable to do all the CT core summations in the switchgear to have shortest possible loops.

This will give lower setting values and also a better balanced scheme. The connection in to the control room can then be from the most central bay. For an internal fault, all involved CTs will try to feed current through the measuring branch. Depending on the size of current transformer, relatively high voltages will be developed across the series resistor. Note that very high peak voltages can appear. To prevent the risk of flashover in the circuit, a voltage limiter must be included.

The voltage limiter is a voltage dependent resistor (Metrosil). The external unit with stabilizing resistor has a value of either 6800 ohms or 1800 ohms (depending on ordered alternative) with a sliding link to allow adjustment to the required value. Select a suitable value of the resistor based on the UR voltage calculated. A higher resistance value will give a higher sensitivity and a lower value a lower sensitivity of the relay. The function has a recommended operating current range 40 mA to 1.0A for 1 A inputs and 200 mA to 5A for 5A inputs.

This, together with the selected and set value, is used to calculate the required value of current at the set U>Trip and SeriesResitor values.