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51N

Three phase CT

summated

Single CT

YN/D or YN/Y

transformer

Single phase-

to-ground fault

ANSI05000492_3_en.vsd

alt

ANSI05000492 V3 EN

Figure 196: Step 1 fault calculation 1

This calculation gives the current fed to the protection: 3I

0fault1

To assure that step 1, selectivity to other ground-fault protections in the network a

short delay is selected. Normally, a delay in the range 0.3 – 0.4 s is appropriate. To

assure selectivity to line faults, tripped after a delay (typically distance protection zone

2) of about 0.5 s the current setting must be set so high so that such faults does not

cause unwanted step 1 trip. Therefore, a fault calculation as shown in figure

197 is made.

1MRK504116-UUS C Section 3

IED application

433

Application manual

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General

Rated Frequency	50/60 Hz
Inputs	Analog and binary inputs
Application	Protection of power systems
Communication Protocols	IEC 61850, DNP3, Modbus
Operating Temperature Range	-25°C to +55°C
Mounting	Rack mounted
Number of Binary Inputs	Up to 48
Number of Binary Outputs	32
Protection Functions	Overcurrent Protection
Outputs	Binary outputs
Enclosure	IP 54
Type	Line Differential Protection
Number of Analog Inputs	24