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Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
138
The spread angle of the load trapezoid characteristicis calculated based on the minimum power factor in the
same manner as for single line (Calculation Example 1).
Overcurrent, U/
I
and U/
I
/
ϕ
pickup
If the distance protection in the 7SD5 is configured as the main or backup protection function, the distance pro-
tection features a range of fault detection modes depending on the ordered version. It is possible to select the
appropriate mode for the particular system (7SD5***-*****-*
D
**, 7SD5***-*****-*
G
**, 7SD5***-*****-*
K
**, and
7SD5***-*****-*
M
**).
If the device does not feature an explicit pickup function or if during configuration of the protection functions
(Section 2.1.1.3) you have selected as pickup type
Dis. PICKUP = Z< (quadrilat.) (address 117 ), the
mentioned settings are not relevant and cannot be accessed.
Available pickup modes are described in Section 2.5.1 in detail. If the device has several alternative pickup
modes, one option has been selected when configuring in address
117 . Below, parameters are given and dis-
cussed for all pickup modes. With the following settings, only those parameters will appear that apply for the
selected pickup mode.
With the U/
I
(/
ϕ
) pickup mode you can determine the voltage measurement and, if applicable, the phase-angle
measurement for phase-to-earth measuring units, and for phase-to-phase measuring loops separately.
Address
1901 PROGAM U/I indicates which loop voltages apply to phase-to-earth and which to phase-to-
phase:
In networks with
earthed
starpoint, a selection using U
Ph-E
with earth faults and U
Ph-Ph
with non-earthed faults
is often preferred (address 1901 PROGAM U/I = LE:Uphe/LL:Uphp ). This mode has a maximum sensitivity
for all fault types; however, it requires the unambiguous detection of earth faults via the earth-fault detection
function (also see Section 2.5.1). Otherwise, a mode using U
Ph-E
for all fault types may be useful (address 1901
PROGAM U/I = LE:Uphe/LL:Uphe ), accepting lesser sensitivity for earth-free faults, since the overcurrent
stage
I
ph>> usually picks up there.
In networks with
low–resistance earthed
starpoint, the U/
I
/
ϕ
pickup should only come into effect on earth
faults as phase-to-phase faults are detected by the overcurrent pickup. In this case it is reasonable to set
address
1901 PROGAM U/I = LE:Uphe/LL:I>> .
In
isolated
or
resonant-earthed
power systems it is possible to control the U/
I
/
ϕ
pickup using phase-to-phase
voltages only (address 1901 PROGAM U/I = LE:Uphp/LL:Uphp ). Naturally, this excludes pickup by single
earth faults, nor does it allow a correct double earth fault detection. It is therefore suitable for small isolated
cable networks.
Two further general settings refer to the final times, i.e. the tripping times in a worst case scenario for faults
outside all distance zones. They should be set above the delay times for distance zones providing a final back-
up option (see also configuration of the function settings for the distance zones in Section 2.5.2.2).
The directional final time DELAY FORW. PU (address 1902 ) only works with short-circuits in forward (line) di-
rection if there is no impedance within a distance zone after pickup.
The non-directional final time DEL. NON-DIR PU (address 1903 ) works for all faults if there is no impedance
within a distance zone after pickup.
Overcurrent Pickup
The maximum operational load current that can occur is crucial for the setting of
overcurrent pick-up
. Pickup
due to overload must be ruled out! Therefore the pickup value Iph>> (address 1910 ) must be set above the
maximum (over-)load current that is expected (approx. 1.2 times). In this case, it must be ensured that the
minimum fault current is above this value. If this is not the case, U/
I
pickup is required.