Siemens SIPROTEC Manual page 40

Functions
2.1 General
Distance protection
Depending on the version ordered, the distance protection of the 7SD5, if configured as the main protection
function or in combination with differential protection, features a range of pickup modes, from which the type
best suited for the particular system conditions can be selected. If according to the ordering code the device is
equipped with impedance pickup only (7SD5***-*****-*E** and 7SD5***-*****-*H***), you can select the tripping
characteristic to be used by the distance protection. To do so, select address 115 for the phase-to-phase mea-
suring units Phase Distance and address 116 for the phase-to-earth measuring units Earth Distance.
You can select between the polygonal tripping characteristic Quadrilateral and the MHO characteristic
MHO. The sections 2.5.2 and 2.5.3 provide a detailed overview of the characteristics and measurement meth-
ods. The two adresses can be set seperately and differently. If the device is to be used only for phase-to-earth
loops or only for phase-to-phase loops, set the function that is not required to Disabled.
Other pickup procedures are available with the ordering variants 7SD5***-*****-*D**, 7SD5***-*****-*G**,
7SD5***-*****-*K**, and 7SD5***-*****-*M**. The properties of these procedures are described in detail in
Section 2.5.1.
If the fault current magnitude alone is a reliable criterion for distinction between a fault occurrence and load
operation (incl. tolerable overload), set Address 117 Dis. PICKUP = I> (overcurr.) (overcurrent pickup).
If the voltage drop is required as another pickup criterion, select the setting U/I (voltage-dependent current
pickup). For heavily loaded high-voltage lines and extra-high-voltage lines, the setting U/I/ϕ (voltage and
phase-angle dependent current pickup) may be required. With the setting Z< (quadrilat.) (... pickup) the
distance zones which are set highest establish the pickup criteria. If you set address 117 Dis. PICKUP to
Disabled, the distance protection function and all associated functions will not be available.
If a pickup of zone Z1 of the distance protection shall be possible only after exceeding an additional current-
threshold value, set the parameter 119 Iph>(Z1) to Enabled. Select the setting Disabled if the additional
threshold value is not required.
Please note that the power swing supplement (see also Section 2.6) only works together with the Z<
(quadrilat.) pickup. In all other cases it is ineffective, even though you have set address 120 Power
Swing = Enabled.
To complement the distance protection function by teleprotection schemes, you can select the desired scheme
at address 121 Teleprot. Dist.. You can select the permissive underreach transfer trip with pickup PUTT
(Pickup) and with overreach zone PUTT (Z1B), the teleprotection scheme POTT, directional comparison
pickup Dir.Comp.Pickup, unblocking with Z1B UNBLOCKING, blocking scheme BLOCKING, and the
schemes with pilot wire comparison Pilot wire comp and Rev. Interlock (reverse interlocking). If you
do not want to use teleprotection in conjunction with distance protection set Disabled.
The Direct Local Trip (address 122 DTT Direct Trip) is a command that is initiated from an external device
for tripping the local circuit breaker.
With address 125 Weak Infeed you can select a supplement to the teleprotection schemes. Set Enabled to
apply the classical scheme for echo and weak infeed tripping. The setting Logic no. 2 switches this function
to the French specification. This setting is available in the device variants for the region France (only version
7SD5***-**D** or 10th digit of order number = D).
At address 126 Back-Up O/C you can set the characteristic group which the time overcurrent protection uses
for operation. In addition to the definite time overcurrent protection, an inverse time overcurrent protection can
be configured depending on the version ordered that operates either according to an IEC characteristic (TOC
IEC) or according to an ANSI characteristic (TOC ANSI). The different characteristics are depicted in the Tech-
nical Data. You can also disable the time overcurrent protection (Disabled).
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SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011