FIELD: engine devices and pumps.
SUBSTANCE: in static multi-level frequency converter for powering asynchronous and synchronous electric motors, a control unit is provided with an 'blocking" input, a protection unit is introduced against single-phase ground short-circuit and with an analog control input and an "emergency" discrete output which contains resistive voltage divider that is protection unit analog input, an integrator, a bipolar threshold element with direct and inverse inputs, an RS flip-flop, an actuator which is discrete output of the protection unit, a time delay element and a 2I logic element, the output of voltage divider is connected to the input of the integrator, whose output is connected to the input of the threshold element, the direct output of the threshold element is connected to the s-input of the RS flip-flop, and its output with input of actuator element and the time delay element, the 2I logic element is connected to inverse output of the threshold element and the time delay element, and via circuit connected to R-input of RS flip-flop. The resistive voltage divider is connected by one lead to common point of power modules connected in Y connection, and the by second one-to the circuit of the grounding contour, the output of the actuator element is connected to the "blocking" input of the control unit.
EFFECT: providing detection of the output voltage of the static multi-level converter at during the single-phase fault both at nominal values and low value of output voltage, and prevention of emergency situation consequences at initial stage the electric motor starting at low level of output voltage of the static multi-level frequency converter.
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