5 LOGIC SYMBOLS AND TERMS
Symbol Description Units
&
Logical "AND": Used in logic diagrams to show an AND-gate function.
S
"Sigma": Used to indicate a summation, such as cumulative current interrupted.
t
"Tau": Used to indicate a time constant, often associated with thermal characteristics.
d
Angular displacement rad
q
Angular displacement rad
F
Flux rad
f
Phase shift rad
w
System angular frequency rad
<
Less than: Used to indicate an "under" threshold, such as undercurrent (current dropout).
>
Greater than: Used to indicate an "over" threshold, such as overcurrent (current overload)
1
Logical "OR": Used in logic diagrams to show an OR-gate function.
ABC
Anti-clockwise phase rotation.
ACB
Clock-wise phase rotation.
C
Capacitance A
df/dt
Rate of Change of Frequency protection Hz/s
df/dt>1
First stage of df/dt protection Hz/s
F<1
First stage of underfrequency protection: Could be labeled 81-U in ANSI terminology. Hz
F>1
First stage of overfrequency protection: Could be labeled 81-O in ANSI terminology. Hz
fmax
Minimum required operating frequency Hz
fmin
Minimum required operating frequency Hz
fn
Nominal operating frequency Hz
I
Current A
IÙ
Current raised to a power: Such as when breaker statistics monitor the square of ruptured current squared (Ù power =
2).
An
I’f
Maximum internal secondary fault current (may also be expressed as a multiple of In) A
I<
An undercurrent element: Responds to current dropout. A
I>>
Current setting of short circuit element In
I>1
First stage of phase overcurrent protection: Could be labeled 51-1 in ANSI terminology. A
I>2
Second stage of phase overcurrent protection: Could be labeled 51-2 in ANSI terminology. A
I>3
Third stage of phase overcurrent protection: Could be labeled 51-3 in ANSI terminology. A
I>4
Fourth stage of phase overcurrent protection: Could be labeled 51-4 in ANSI terminology. A
I0
Earth fault current setting
Zero sequence current: Equals one third of the measured neutral/residual current.
A
I1
Positive sequence current. A
I2
Negative sequence current. A
I2>
Negative sequence overcurrent protection (NPS element). A
I2pol
Negative sequence polarizing current. A
IA
Phase A current: Might be phase L1, red phase.. or other, in customer terminology. A
IB
Phase B current: Might be phase L2, yellow phase.. or other, in customer terminology. A
IC
Phase C current: Might be phase L3, blue phase.. or other, in customer terminology. A
Idiff
Current setting of biased differential element A
Appendix A - Symbols and Glossary MiCOM P747
416 P747-TM-EN-1
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