10 SIPROTEC 7SJ81/7SK81 V4.70, Product Information
E50417-K1150-C462-A2, Edition 02.2012
6 Functional Description
General
Unlike the 7SJ80/7SK80, the SIPROTEC device 7SJ81/7SK81 has 4 low-
power current transformers (LPCT) inputs and optionally 3 low-power
voltage transformers (LPVT) inputs. One low-power current transformer
(LPCT) is sufficient to cover a very large range of primary rated line
currents. Objects with rated currents in the range from 40 A to 5000 A can
be protected when using low-power current transformers. The following
low-power current transformer ratios are suitable for the following primary
current operating ranges:
• 100 A/225 mV for a primary operating current range of 40 A to 600 A
• 50 A/22.5 mV for a primary operating current range of 200 A to 3000 A
• 400 A/225 mV for a primary operating current range of 200 A to 2500 A
• 100 A/22.5 mV for a primary operating current range of 400 A to
5000 A
Resistive voltage dividers are provided as low-power voltage transformers
(LPVT). This product information describes device-specific modifications
compared to the 7SJ80 manual (order number E50417-G1140-C343) and
the 7SK80 manual (order number E50417-G1140-C344). The manuals
provide more detailed information.
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