Introduction
1.2 Application Scope
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
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Protection functions
Generally speaking, two basic functions are available in the 7SD5 line protection relay, namely differential and
distance protection. One of the protection functions can be configured at a time as the main protection function
(Main1). As an alternative, differential protection can be selected as the main protection function, and distance
protection as backup protection (Main2).
Recognition of short-circuits in the protection zone is the basic function of the differential protection. Also high-
resistance faults with small currents can be recognized. Even complex multiphase faults are precisely detected,
as the measured values are evaluated separately for each phase. The protection system is restrained against
inrush currents of power transformers. When switching onto a fault at any point of a line, an undelayed trip
signal can be emitted.
The basic function of the distance protection is the recognition of the fault distance by distance measurement.
In particular for complex multiphase faults, the distance measurement is of a multi-circuit design. Different
pickup schemes enable a good adaptation to system conditions and user philosophy. The system starpoint can
be isolated, compensated or earthed (with or without earth current limiting). Application is possible on long,
high-loaded lines with or without serial compensation. The distance protection may be supplemented by tele-
protection using various signal transmission schemes (for fast tripping on 100 % of the line length). In addition,
an earth fault protection (for high-resistance earth faults, order variant) is available, which may be directional,
non-directional and additionally with signal transmission. On lines with weak or no infeed at one line end, it is
possible to achieve fast tripping at both line ends by means of the signal transmission schemes. When switch-
ing onto a fault at any point of a line, an undelayed trip signal can be emitted.
The integrated time overcurrent protection can be configured as a permanent backup protection at all line ends,
or as a protection for emergency operation. Emergency operation is a state in which the differential protection
cannot operate, for example because of a communication failure, and in which no parallel distance protection
is available (e.g. because of a measuring voltage failure). The time overcurrent protection has three definite
time overcurrent stages and one inverse time stage; a number of characteristics according to various standards
is available for the inverse time stage.
Depending on the order variant, the short-circuit protection functions can also trip single-pole. They may co-
operate with an integrated automatic reclosure function (optionally) with which single-pole, three-pole or single-
and three-pole automatic reclosure as well as multi-shot automatic reclosure are possible on overhead lines.
Before reclosure after three-pole tripping, the validity of the reclosure can be checked by voltage and/or syn-
chronism check by the device (can be ordered optionally). It is possible to connect an external automatic reclo-
sure function and/or synchronism check as well as double protection with one or two automatic reclosure func-
tions.
In addition to the short-circuit protection functions mentioned, other protection functions are possible. A thermal
overload protection has been integrated which protects in particular cables and power transformers from undue
overheating due to overload. Other possible functions are multi-stage overvoltage, undervoltage and frequency
protection, circuit breaker failure protection and protection against the effects of power swings (simultaneously
active as power swing blocking for the distance protection) and earth fault differential protection (ordering op-
tion). To rapidly locate the damage to the line after a short-circuit, a multi-end fault locator is integrated which
also may compensate the influence of parallel lines, and of the fault resistance when power is flowing in the line.
Control Functions
The device is equipped with control functions which operate, close and open, switchgear devices via control
keys, the system interface, binary inputs and a PC with DIGSI software. The status of the primary equipment
can be transmitted to the device via auxiliary contacts connected to binary inputs. The present status (or posi-
tion) of the primary equipment can be displayed on the device, and used for interlocking or plausibility monitor-
ing. The number of the devices to be switched is limited by the binary inputs and outputs available in the device
or the binary inputs and outputs allocated for the switch position feedbacks. Depending on the mode of opera-
tion, one binary input (single point indication) or two binary inputs (double point indication) can be used. The
capability of switching primary equipment can be restricted by appropriate settings for the switching authority
(remote or local), and by the operating mode (interlocked/non-interlocked, with or without password validation).
