2-16 T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
SIGNAL PROCESSING CHAPTER 2: PRODUCT DESCRIPTION
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2.4 Signal processing
2.4.1 UR signal processing
The UR series relays are microprocessor-based protective relays that are designed to measure power system conditions
directly via CT and PT inputs and via other sources of information, such as analog inputs, communications inputs and
contact 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 voltage
analog 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 and
fixed in the hardware, and thus is not dependent on the system nominal frequency setting.
Figure 2-3: UR signal processing
The 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 tracking
system.
The A/D converter has the following ranges of AC signals:
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