Overall Operation
The digital SIPROTEC 7SJ80 overcurrent protection is equipped with a powerful microprocessor. It allows all
tasks to be processed digitally, from the acquisition of measured quantities to sending commands to circuit
breakers. Figure 1-1 shows the basic structure of the 7SJ80.
Analog Inputs
The measuring inputs (MI) convert the currents and voltages coming from the measuring transformers and
adapt them to the level appropriate for the internal processing of the device. The device provides 4 current
transformers and - depending on the model - additionally 3 voltage transformers. Three current inputs serve
for the input of the phase currents, another current input (Ι
N
) may be used for measuring the ground fault
current Ι
N
(current transformer neutral point) or for a separate ground current transformer (for sensitive
ground fault detection Ι
Ns
and directional determination of ground faults ) - depending on the model.
[hw-struktur-7sj80-060606, 1, en_US]
Figure 1-1
Hardware structure of the digital multi-functional protective relay 7SJ80
The optional voltage transformers can either be used to input 3 phase-to-ground voltages or 2 phase-to-phase
voltages and the displacement voltage (open delta voltage) or any other voltages. It is also possible to connect
two phase-to-phase voltages in open delta connection.
The analog input quantities are passed on to the input amplifiers (IA). The input amplifier IA element provides
a high-resistance termination for the input quantities. It consists of filters that are optimized for measured-
value processing with regard to bandwidth and processing speed.
The analog-to-digital (AD) transformer group consists of an analog-to-digital converter and memory compo-
nents for the transmission of data to the microcomputer.
1.1
Introduction
1.1 Overall Operation
20 SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
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