7SR11 & 7SR12 Description Of Operation
©2017 Siemens Protection Devices Limited Chapter 1 Page 25 of 88
Figure 2-9 LED Indication Label
2.6 Current Inputs
Either one or four current inputs are provided on the Analogue Input module. Terminals are available for both 1A
and 5A inputs.
Two types of current input are incorporated within the relay, one type is used for phase fault and earth fault
protection, while the other is used for sensitive earth fault (SEF) and restricted earth fault (REF).
Relays with one current input, can be ordered with an earth fault input or a sensitive earth fault input (SEF).
Relays with four current inputs, can be ordered as an earth fault input or a sensitive earth fault input (SEF).
Current is sampled at 1600Hz for both 50Hz and 60Hz system frequencies. Protection and monitoring functions of
the relay use either the Fundamental Frequency RMS or the True RMS value of current appropriate to the
individual function.
The waveform recorder samples and displays current input waveforms at 1600Hz.
The primary CT ratio used for the relay instruments can be set in the CT/VT configuration menu.
2.7 Voltage Inputs
Three voltage inputs are provided on the Analogue Input module on the 7SR12 relay.
Voltage is sampled at 1600Hz for both 50Hz and 60Hz system frequencies. Protection and monitoring functions of
the relay use fundamental frequency voltage measurement.
The waveform recorder samples and displays voltage input waveforms at 1600Hz.
The primary VT ratio used for the relay instruments can be set in the CT/VT configuration menu.
2.8 Binary Inputs
The binary inputs are opto-couplers operated from a suitably rated power supply.
Relays are fitted with 3, 4 or 6 binary inputs (BI) depending on the variant. The user can assign any binary input to
any of the available functions (INPUT CONFIG > INPUT MATRIX).
Pick-up (PU) and drop-off (DO) time delays are associated with each binary input. Where no pick-up time delay
has been applied the input may pick up due to induced ac voltage on the wiring connections (e.g. cross site
wiring). The default pick-up time of 20ms provides ac immunity. Each input can be programmed independently.
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