ABB REL650 series, Technical Manual

Page: 157 / 856

value. Both voltages and currents are filtered out and evaluated. The condition for fault
type classification for the voltages and currents can be expressed as:
( , , )
( , , )
VA VB VC
FaultType
Max IA IB IC
å D D D
=
D D D
EQUATION1808-ANSI V1 EN
(Equation 33)
( , , )
( , , )
IA IB IC
FaultType
Max IA IB IC
å D D D
=
D D D
EQUATION1809-ANSI V1 EN
(Equation 34)
The value of FaultType for different shunt faults are as follows:
Under ideal conditions: (Patent pending)
Single phase-to-ground;
FaultType=1
Phase-to-phase fault FaultType=2
Three-phase fault; FaultType=3
The output signal is 1 for single phase-to-ground fault, 2 for phase-to-phase fault and 3 for
three-phase fault. At this point the filter does not know if ground was involved or not.
Typically there are induced harmonics in the non-faulted lines that will affect the result.
This method allows for a significant tolerance in the evaluation of FaultType over its
entire range.
When a single phase-to-ground fault has been detected, the logic determines the largest
quantity, and asserts that phase. If phase-to-phase fault is detected, the two largest phase
quantities will be detected and asserted as outputs.
The faults detected by the delta based phase selector are coordinated in a separate block.
Different phases of faults may be detected at slightly different times due to differences in
the angles of incidence of fault on the wave shape. Therefore the output is forced to wait
a certain time by means of a timer. If the timer expires, and a fault is detected in one phase
only, the fault is deemed as phase-to-ground. This way a premature single phase-to-
ground fault detection is not released for a phase-to-phase fault. If, however, ground
current is detected before the timer expires, the phase-to-ground fault is released sooner.
If another phase picks up during the time delay, the wait time is reduced by a certain
amount. Each detection of either ground-to-phase or additional phases further reduce the
initial time delay and allow the delta phase selector output to be faster. There is no time
delay, if for example, all three phases are faulty.
1MRK 506 335-UUS A
Section 6
Impedance protection
151
Technical manual