7.3.7.1 Measurement principleThe residual voltage is measured continuously, and compared with the set values,U1> and U2>.To avoid oscillations of the output START signal, a hysteresis has been included.7.3.7.2 Time delay7.3.7.3 BlockingIt is possible to block two step residual overvoltage protection (ROV2PTOV) partiallyor completely, by binary input signals where:BLOCK: blocks all outputsBLKST1: blocks all startand trip outputs related to step 1BLKST2: blocks all start and trip inputs related to step 27.3.7.4 DesignThe voltage measuring elements continuously measure the residual voltage.Recursive Fourier filters filter the input voltage signal. The single input voltage iscompared to the set value, and is also used for the inverse time characteristicintegration. The design of Two step residual overvoltage protection (ROV2PTOV) isschematically described in Figure 75.1MRK 511 287-UEN A Section 7Voltage protection173Technical manual
