METHOD OF PROTECTION AGAINST SINGLE-PHASE EARTH FAULTS IN NETWORKS WITH ISOLATED NEUTRAL AND DEVICE FOR ITS IMPLEMENTATION Russian patent published in 2017 - IPC H02H3/16 

FIELD: electricity.

SUBSTANCE: method is based on measuring the residual current 3I₀ of the connection to be protected, separating from it the component of the main frequency of 50 Hz I₅₀ as an affecting quantity, comparing the value of the main frequency component I₅₀ with the operating set current value I_set and forming the output signal while exceeding the component of the main quantity I₅₀ of the set current value I_set. Wherein from the current 3I₀ higher harmonic components I_HH are separated, the quantities of I₅₀ and I_HH are compared, and in case I₅₀>I_HH the set protection operating current value I_set is automatically reduced. The device of current protection against SPEF comprises a residual current filter, a filter separating the component of the main frequency of 50 Hz I₅₀, connected to the output of the residual current filter, a current measuring element, the first input of which is connected to the output of the filter separating the component of the main frequency 50 Hz I₅₀, the filter of higher harmonic components I_HH, a circuit for comparing the absolute values of the quantities I₅₀ and I_HH, the signal at the output of which appears if I₅₀>I_HH, the switch of set operating current values I_set. The input of the higher harmonic component filter is connected to the output of the residual current filter, the output - to the second input of the circuit for comparing the absolute values of the quantities I₅₀ and I_HH, the first input of which is connected to the output of the filter of the main component of 50 Hz, the output of the circuit for comparing the absolute values of the quantities I₅₀ and I_HH is connected to the control input of the switch of set operating current values I_set, the signal at the output of which I_set in the absence of the signal at the control input is equal to the first set value I_set1, set on the first information input of the switch of set operating current values I_set, and in the presence of the signal at the control input, the second set value I_set2, set on the second information input, the output of the switch of set current values I_set is connected to the second input of the current measuring element, the output signal of which appears at I₅₀>I_set.

EFFECT: increasing the sensitivity of the residual current protection against single-phase earth faults of medium-voltage electrical networks operating with isolated neutral.

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