Page 5-12
FPU-32 Feeder Protection Unit
Rev.
2-A-103014
Protective Functions
5.4 D
EFINITE-
T
IME
O
VERCURRENT
Menu:
Setup
|
Protection
|
Ph Def Time
The definite-time overcurrent function has both trip and
alarm settings. With the DFT measurement method it
may be possible to set the overcurrent protection closer to
the desired value as compared to the RMS measurement
method.
The asymmetrical-current multipliers for RMS and
DFT measuring methods are shown in Fig. 5.10. Typical
X/R values are 6.6 for a low-voltage system, 15 for a
medium-voltage system, and can be as high as 25 for a
high-voltage system. The DFT filters the dc component
so that the overcurrent setting can be set closer to the
symmetrical fault value.
A
S
YMMETRICAL MUL
TIPL
YING F
A
CT
OR
0
4
X/R
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
2
6
8
10
12
14
16
18
20
DFT
RMS
FIGURE 5.10 Asymmetrical-Current Multipliers.
Trip Level ................................. 0.10 to 15.00 x CT-
Primary Rating (I
p
)
Trip Delay (D) .......................... 0.00 to 10.00 s
(see
Table
5.2)
Alarm Level ............................. 0.10 to 15.00 x I
p
Alarm Delay (D) ....................... 0.00 to 10.00 s
(see Table 5.2)
Protection ................................. Enable/Disable Trip1, 2, 3
Enable/Disable
Alarm1, 2, 3
Measurement Method ............... DFT c/w CT-saturation
compensation
Set-Point Groups ...................... Group 1 and Group 2
TABLE 5.2 F
AULT
D
URATION
R
EQUIRED
FOR
T
RIP
(1)(2)
F
AULT
L
EVEL
(multiples of trip-
F
AULT
D
URATION (FD)
(ms)
level setting)
D
30 ms
(3)
D > 30 ms
(3)
2
5
10
FD = 10 ms
FD = 5 ms
FD = 2 ms
FD = (D – 20) ms
FD = (D – 25) ms
FD = (D – 28) ms
(1)
For overcurrent less than 15 x CT-Primary Rating.
For earth faults less than 1 x EF-CT-Primary Rating.
Fixed frequency, 60 Hz.
(2)
Minimum relay operating time: 25 to 45 ms.
(3)
D is the trip-time setting.
5.5 I
NVERSE-
T
IME
3I
0
E
ARTH
F
AULT
Menu:
Setup
Protection
3I
0
Inverse
This protection function is based on the zero-sequence
current calculated from the three phase currents.
The
Curve
menu is used to select one of the curve
shapes listed in Table 5.1.
Pickup
is in per unit of phase
CT rating and specifies the location of the curve’s vertical
asymptote (I
M
= I
DFT
/I
pickup
= 1).
Time
Multiplier
selects
the specific curve within the curve type.
The FPU-32 uses the same time multiplier range of
0.05 to 1.0 for both IEC and IEEE curves.
The
Metering
Inverse Status
menu indicates whether
current is above or below
Pickup
and the UPI face-plate
LED can be programmed to indicate that current is above
Pickup
. See Section 4.1.1.
Curve ........................................ Table 5.1
Pickup ...................................... 0.10 to 10.00 x CT-
Primary Rating (I
p
)
Pickup Curve Threshold ........... 1.1 x Pickup setting
Reset Curve Threshold ............. 0.9 x Pickup setting
Time Multiplier ........................ 0.05 to 1.00
Protection ................................. Enable/Disable Trip1, 2, 3
Measurement Method .............. DFT - Derived 3I
0
Set-Point Groups ...................... Group 1 and Group 2
N
OTE:
For IEEE curves, a multiplier of 1 corresponds to
a IAC/CO “time-dial” setting of 15.
N
OTE:
CT saturation is not detected. Enable overcurrent
protection when fault levels can exceed 15 times the
phase-CT-primary rating.
5.6
D
EFINITE-
T
IME
3I
0
E
ARTH
F
AULT
Menu:
Setup
|
Protection
|
3I
0
Def Time
This protection is based on the zero-sequence current
calculated from the phase currents.
Trip Level............................. 0.10 to 15.00 x CT-Primary
Rating
(I
p
)
Trip Delay (D) ...................... 0.00 to 10.00 s
(see
Table
5.2)
Alarm Level ......................... 0.10 to 15.00 x I
p
Alarm Delay (D) .................. 0.00 to 10.00 s
(See
Table
5.2)
Protection ............................ Enable/Disable Trip1, 2, 3
Enable/Disable Alarm1, 2, 3
Measurement Method .......... DFT - Derived 3I
0
Set-Point Groups .................. Group 1 and Group 2
N
OTE:
For IEEE curves, a multiplier of 1 corresponds to
a IAC/CO “time-dial” setting of 15.
