FIELD: electrical measuring equipment.
SUBSTANCE: invention relates to electrical measuring equipment and relay protection and is intended to improve safety in electrical networks of alternating, direct and double kind of current with the isolated neutral. Essence: the method is based on measuring the leakage current from an auxiliary source of test voltage in the form of a periodic sequence of pulses of the form
where U1, U2 are constant voltages, U1> U2; τ - time interval, T - repetition period of test voltage pulses, 
. The period of the voltage of the monitored network Tn is measured. The repetition period of the test voltage pulses is set equal to an even number of measured voltage periods of the monitored network Т=kТn, where k = 2, 4, …. The test voltage is connected through the star of the resistors to the phases of the monitored network, the leakage current is measured by measuring the voltage drop across the measuring resistance connected in series with the test voltage source, a delayed signal is formed with respect to the voltage drop across the measuring resistance for the interval 
the delayed signal is subtracted from the voltage drop across the measuring resistance, the resulting signal ui(t) is converted in accordance with the equation
where ε is a small time interval, ΔT ≤ ε < τ; ΔT is the maximum value of the increment of the test voltage period, the moving average value 
of the uk(t) signal is calculated in the period equal to the period Tn of the voltage of the monitored network, the insulation resistance is calculated by the formula 
where rt is internal resistance of the source, r0 is measuring resistor resistance. The obtained value is compared with the R0 setting and when rins ≤ R0, the electrical equipment is disconnected.
EFFECT: invention is aimed at improving accuracy of monitoring electrical resistance of the insulation and reliability of the protection of the electrical network from the isolated neutral when the frequency of the controlled network changes.
1 cl, 2 dwg
