DPT parallel excitation starting circuit in current function

Start of DC motor is performed by actuation of QF circuit breaker and pressing of SB1 "Start" button. At that the coil of KM1 contactor operates and closes its contacts. Starting current passes through the power circuit of the engine, under the action of which the maximum current relay KA1 operates. Its contact is opened and the coil of contactor KM2 is not powered. When the current decreases to the minimum value, the maximum current relay KA1 drops off and closes its contact. The coil of contactor KM2 operates and shunts the first section of starting resistor and relay KA1 with its main contact. When switching, the current increases to a value. When the current is again increased to a value, contactor KM1 is not turned on because its coil is shunted by contact KM2. Under the influence of current of the KA2 relay works and disconnects the contact. When the current again decreases to a value during acceleration, the relay KA2 drops off and the coil of the CMZ contactor turns on. When the current is increased to a value, contactor KM2 is not turned on because its coil is shunted by contact KM3. Under the action of current, the relay KA3 operates and opens its contact. When the current is again reduced to a value during acceleration, the relay KA3 drops off and the coil of the contactor KM4 is turned on. Start-up ends, the engine operates on a natural mechanical characteristic. It is necessary for the correct work of the scheme that the response time of the KA1, KA2 and KA3 relay was less than the response time of contactors. To stop the engine, press the SB2 "Stop" button and turn off the QF circuit breaker to de-energize the circuit.