Auxiliary Protection Functions; Potential Transformer Fuse Failure (Ptff) - GE LPS-D Instruction Manual

1 PRODUCT DESCRIPTION

1.4 AUXILIARY PROTECTION FUNCTIONS

Because a distance or directional function may operate for a full or partial loss of AC potential caused by one
or more blown fuses, PTFF is provided to block distance and directional function tripping when a fuse failure is
detected. If the backup overcurrent functions 50, 50G, and 51G are not directionally controlled, they are
allowed to trip during a potential fuse failure condition. If any of the backup, overcurrent functions, 50, 50G or
51G, is directionally supervised, then that function is not allowed to trip. Rather, a second overcurrent function,
50_FF, 50G_FF, or 51G_FF is placed in service during the fuse failure condition. The pickup level setting of
these functions is independent from the normal pickup setting. The PTFF functional logic is shown below.
If AC potential is lost on one or more phases, the Any Phase Under Voltage signal produces a logic 1 output,
and the upper input is present at AND1. The phase undervoltage pickup setting is fixed at 75% of nominal and
the pickup-to-dropout ratio is virtually 100%. The lower input to AND1 is dependent upon whether the fault
detector FD has operated or whether one or more phases of the protected line are de-energized (open). When
one or more phases of protected line are open, PTFF is disabled.
P H A S E
V A
V O L T A G E
D E T E C T O R
C U R R E N T
IB-A
D E T E C T O R
FAULT
F D
D E T E C T O R
P H A S E
V B
V O L T A G E
D E T E C T O R
C U R R E N T
IB-B
D E T E C T O R
P H A S E
V C
V O L T A G E
D E T E C T O R
C U R R E N T
IB-C
D E T E C T O R
V O L T A G E
D E T E C T O R
C U R R E N T
D E T E C T O R
FAULT
D E T E C T O R
A N Y P H A S E
O P E N
Figure 1–3: POTENTIAL FUSE FAILURE LOGIC DIAGRAMS
If AC potential is lost for any reason, including a blown fuse or fuses, and there is no disturbance on the power
system that operates the fault detector, the AND1 output causes timer TL1 to time out and produce a PTFF
output via OR2. The output of OR2 is routed to AND2 to seal-in the PTFF output, based on the Any Phase
Under Voltage signal, so that PTFF output is maintained as long as the potential is below normal. Setting 714:
FUSEFAIL determines whether PTFF operation blocks distance/directional tripping (FUSEFAIL = YES) or
merely issues an event (FUSEFAIL = NO). When the potential returns to normal, the Any Phase Under Voltage
signal resets to remove the seal-in, allowing the PTFF output to reset.
GE Power Management

1.4.1 POTENTIAL TRANSFORMER FUSE FAILURE (PTFF)

1A
1 A
1B
2
1 B
1C
1 C
V 1
1
IB 1
F D
1
LPS-D Line Protection System
1.4 AUXILIARY PROTECTION FUNCTIONS
SINGLE PHASE TRIPPING MODELS:
2
TL1
3 ~
3
2
0
THREE PHASE TRIPPING MODELS:
2
TL1
3 ~ 2
0
PTFF3.VSD
1
PTFF
PTFF
1-
13