Terminals of the "MIR 100 SCD" series are microprocessor devices designed to implement the functions of automatic synchronous switching, relay protection, measurement, registration, oscillography, signaling and control for connections with inductive or capacitive loads in networks with a rated voltage of 6-110 kV. The devices are used in secondary switching circuits of power stations, substations and switchgears with alternating and direct operating current. Regardless of the type of protected element (inductive or capacitive) of the electrical system, common software is written to the terminal, which ensures the performance of the necessary functions.

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Synchronous commutation device (SCD)

Preferred turn-on or turn-off timesalways refers to the passage of voltage or current through zero. Depending on the case of switching (inductive or capacitive load), SCD transmits a start commandcircuit breaker devices with appropriate time delay and phase shift. Commands are given to all 3 phases (poles) of the circuit breaker independently of each other.

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RiWith. 1.Optimal moswitches on.

T – network period;

u - Voltage at the pole of the switch;

1 - Optimal tswitching point dfor inductive load;

2 - Optimum switching point for a capacitive load.

Capacitive load

When a discharged capacitor (capacitive load), which is a low resistance, is switched on, intense transients and current surges would occur near the voltage maximum. Therefore, when connecting, it is required to ensure the smallest potential difference, which is ensured by switching on at the moment the voltage passes near zero.

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Inductive load

When turned onand inductive load, which is a high resistance, large current differences at switch-on would require a strong current build-up and thus lead to high overvoltages. Therefore, it is most favorable to turn on at the moment the current passes through zero, that is, at the moment when the voltage is near the maximum.

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Grounded neutral

When choosing the optimal moment for switching on grounded devices for each phase, the determining factor is the value of current or voltage at a particular pole of the circuit breaker. The connection of each phase in itself leads to the passage of current through the ground. Thus, the target moment of the voltage passing through zero in each phase is different and all three phases are switched on with an offset by the phase shift of their zero crossings.

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Isolated neutral

When connecting a non-grounded device, the inclusion of the first phase does not yet lead to the passage of current. This would result in a difference between the two voltages for the second phase. To select the optimal switching moment in this case, it is necessary to consider the voltages between the phases. To prevent large voltage differences between the two phases, the first two phases are connected at the same time when the voltage difference between the two phases is zero. The third phase is connected at the moment when its voltage passes through zero relative to other phases.

The terminals are freely configurable. The use of programmable logic allows you to modify typical functional logic circuits, taking into account the specifics of the protected object.