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The relay type STR is intended for the complete protection of high power motors, with medium voltage or low voltage supply. Several protection functions, incorporated in a single relay, assure the protection of the motor against all the different fault conditions: overheating caused by mechanical overload or by an abnormal supply, locked rotor, too long starting, interruption of one phase conductor, current unbalance, short circuit between phases, short circuit between turns, earth fault, underload running, too frequent startings.
The relay STR features the following principal characteristics:

• three input measuring circuits for the line currents;
• measuring circuit, provided with a band pass filter, for the residual current;
• protection functions and final relays completely programmable by the user;
• direct read-out of all the quantities by means of digital display on the front panel;
• counting of the number of operations performed for each function;
• storing the values of input quantities corresponding to the last operation;
• optional blocking circuit, to perform accelerated protection schemes;
• serial communication circuit with MODBUS© protocol;
• continuous monitoring of internal circuits.