2-18 M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUALSIGNAL PROCESSING CHAPTER 2: PRODUCT DESCRIPTION22.4 Signal processing2.4.1 UR signal processingThe UR series relays are microprocessor-based protective relays that are designed to measure power system conditionsdirectly via CT and PT inputs and via other sources of information, such as analog inputs, communications inputs andcontact inputs. The following figure shows the overall signal processing in URs.An analog low pass anti-aliasing filter with a 3 dB corner frequency is set at 2.4 kHz and is used for current and voltageanalog filtering as well as signal conditioning. The same filtering is applied for phase, ground currents, phase-to-phase(when applicable), and auxiliary voltages. The 2.4 kHz cut-off frequency applies to both 50 Hz and 60 Hz applications andfixed in the hardware, and thus is not dependent on the system nominal frequency setting.Figure 2-3: UR signal processingThe UR samples its AC signals at 64 samples per cycle, that is, at 3840 Hz in 60 Hz systems, and 3200 Hz in 50 Hz systems.The sampling rate is dynamically adjusted to the actual system frequency by an accurate and fast frequency trackingsystem.The A/D converter has the following ranges of AC signals:
