1 2 3 4 A - SIPROTEC

SIPROTEC, 7UT6x, Manual
C53000-G1176-C230-2, Release date 06.2012
Functions
2.2 Differential Protection
The current sum definition is extended for more than 2 measurement locations, e.g. for 4 measuring locations
(figure 2-18 or 2-19), therefore:
I diff = |I 1 + I 2 + I 3 + I 4|
I stab = |I 1| + |I 2| + |I 3| + |I 4|
I diff is derived from the fundamental frequency current and produces the tripping effect quantity, I stab counteracts
this effect.
To clarify the situation, three important operating conditions with ideal and matched measurement quantities
are considered.
Figure 2-20 Definition of current direction
1. Through-flowing current under undisturbed conditions or external fault:
I 1 flows into the protected zone, I 2 leaves the protected zone, i.e. is negative according tot he definition of
signs, therefore I 2 = –I 1 ;
moreover |I 2 |=|I 1 |
I diff =|I 1 + I 2 |=|I 1 – I 1 |=0
I stab =|I 1 |+|I 2 |=|I 1 |+|I 1 |=2·|I 1 |
No tripping effect (I diff = 0); the stabilisation (I stab ) corresponds to double the through-flowing current.
2. Internal short-circuit, e.g. fed with equal currents each side:
The following appliesI 2 = I 1 ; moreover |I 2 |=|I 1 |
I diff =|I 1 + I 2 |=|I 1 + I 1 |=2·|I 1 |
I stab =|I 1 |+|I 2 |=|I 1 |+|I 1 |=2·|I 1 |
Tripping effect (I diff ) and restraint value (I stab ) are equal and correspond to the total fault.
3. Internal short-circuit, fed from one side only:
The following applies I 2 = 0
I diff =|I 1 + I 2 |= |I 1 +0|=|I 1 |
I stab =|I 1 |+|I 2 |=|I 1 |+0=|I 1 |
Tripping quantity (I diff ) and stabilising quantity (I stab ) are equal and correspond to the single-sided fault
current.
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