Phase Differential Protection Of A Transformer (87T And 87Hs) - Siemens 7UT51 Instruction Manual

2
Description of Relay
2.6 Phase Differential Protection of a Transformer
(87T and 87HS)
Settings
Operational status
Minimum differential current required for pickup (87T)
Maximum differential current allowed before pickup (87HS) 0.5 to 20.0 times I
Restraint based on total current level
-
Restraint for through fault causing CT saturation
Inrush restraint based on 2nd harmonic current
Restraint based on 3rd, 4th, or 5th harmonic current
Time delay before trip (separate settings for 87T and 87HS) 0.00 to 60.00 s (step 0.01 s), or ∞
Time delay before reset
Events that can control signal contacts or trip contacts
Inherent Operating Times
-
Pickup time with single ended infeed:
≥ 1.5 times 87T pickup threshold level (approx.)
I
DIFF
≥ 1.5 times 87HS pickup threshold level (approx.)
I
DIFF
≥ 5.0 times 87HS pickup threshold level (approx.)
I
DIFF
Dropout time (approximate)
Dropout Ratios
87T and 87HS dropout ratios
(dropout/pickup; approximate)
Operating Tolerances (with default settings)
Pickup characteristic
Inrush restraint
Set time delays
Effect of Environmental Influences on Times and Tolerances
Supply power voltage
Ambient temperature
System frequency

Phase Differential Protection of a Transformer (87T and 87HS)

Table 2.3
20
-
Active, inactive, or block contacts; can be temporarily changed
-
using binary signal inputs
0.15 to 2.00 times I (0.01 steps)
n
(0.01 steps)
n
Characteristic with two sloped segments (see Figure 4.9)
Through current 5.00 to 15.00 times I
restraint (2 to 250 cycles, or ∞); relay can detect an evolving
internal fault and release this restraint.
10% to 80% of fundamental current (step 1%); option to
crossblock other phases for a selectable duration (in cycles); is
released when the differential current exceeds 87HS.
10% to 80% of fundamental current (step 1%); option to
crossblock other phases for a selectable duration (in cycles); is
released when the differential current exceeds a set value (0.5
to 20.0 times I , step 0.1)or 87HS.
n
0.00 to 60.00 s (step 0.01 s)
Change in operational status; pickup events, start of time delay
before trip; start and end of restraint; trip events. All events are
logged, as are the differential and restraint current levels at the
time of a trip.
60 Hz
35 ms
25 ms
17 ms
25 ms
0.7
±5% of characteristic value (for I < 5× I
±5% of setting value (for I
2nd harmonic
±1% of setting value or 10 ms, whichever is greater
≤ 1% if between 80% and 115% of nominal voltage
≤ 0.5% / 10 K if between 0°C and 40°C (32°F and 104°F)
≤ 1% if between 95% and 105% of nominal frequency.
Note: 87T function is blocked when frequency is less than
about 85% of the nominal frequency, or more than about
120%; see Figure 4.12.
7UT51 v3
(step 0.01); duration of
n
-
50 Hz 16 2/3 Hz
35 ms 85 ms
25ms 55 ms
18 ms 25 ms
30 ms 90 ms
)
n
≥ 15% of I
fundamental
PRIM-2330C
)