A. Sampling unit — it will be the physical quantity (parameter) in the operation of the protected power system through electrical isolation and conversion into the signal acceptable by the comparison identification unit in the relay protection device. It is composed of one or several sensors such as current and voltage transformers.
B. Comparison identification unit — including the given unit, the signal from the sampling unit is compared with the given signal, so as to determine what signal the next level processing unit sends out. (normal state, abnormal state or fault state) comparison identification unit can be composed of four current relays, two for quick-break protection, the other two for over-current protection. The setting value of the current relay is the given unit, and the current coil of the current relay receives the current signal from the sampling unit (current transformer). When the current signal reaches the current setting value, the current relay operates and sends out the signal to make the circuit breaker finally fall through its contact to the next level processing unit. If the current signal is less than the setting value, the current relay does not operate, and the signal transmitted to the subordinate unit does not operate. Identify and compare signal “fast break”, “overcurrent” information is transferred to the next unit for processing.
C, processing unit — to accept the signal of the comparison identification unit, according to the requirements of the comparison identification unit for processing, according to the size of the output of the comparison link, the nature of the combination of ways appear in order to determine whether the protection device should act; It is composed of time relay and intermediate relay. Current protection: quick break — intermediate relay action, over current – time relay action. (delay process)
D. Execution unit — Fault handling is implemented through the execution unit. The execution unit is generally divided into two categories: one is acoustic and optical signal relay; (such as electric whistle, electric bell, flashing light, etc.) The other type is the circuit breaker operating mechanism of the switching coil, so that the circuit breaker switching.
E, control and operation power supply — the relay protection device requires its own independent AC or DC power supply, and the power supply is also increased or decreased by the number of the control equipment; Ac voltage is generally 220 volts, power above 1KVA.

ABB 0745745Q 0745648E Circuit board, Sensor-CPU