Siemens SIPROTEC 7UT635*-* N series User Manual

2.14 Undervoltage Protection
255
7UT613/63x Manual
C53000-G1176-C160-2
2.14 Undervoltage Protection
Undervoltage protection detects voltage dips in electrical machines and avoids inad-
missible operating states and possible loss of stability in electrical devices. The stabil-
ity and permissible torque thresholds of an induction machine is affected by undervolt-
age. In network coupling this can be used as a criteria for the network decoupling.
The undervoltage protection can only be used for three-phase protective objects. This
implies that the device is connected to a voltage transformer. This is therefore only
possible for 7UT613 and 7UT633. As the undervoltage protection only gets its mea-
suring information from the connected voltage measurement, it leaves the assignment
of currents to one side or a measuring location for the function without coating. Setting
causes the same differences as in other protection functions. If the undervoltage pro-
tection is assigned to one side of the main protective object or the three-phase busbar,
the voltage limits in related values (U/UN) have to be set. The values are set to sec-
ondary in volts when assigned to a measuring location.
2.14.1 Function Description
The undervoltage protection in 7UT613/63x uses the positive sequence system from
the fundamental harmonic of the connected phase-to-earth voltages. Compared to
three single-phase measuring systems, the detection of the positive phase-sequence
system is not influenced by 2-pole faults or earth faults.
Overvoltage protection includes two stages. A pickup is signalled as soon as select-
able voltage thresholds are undershot. A trip signal is transmitted if a voltage pickup
exists for a selectable time.
If a fuse failure (failure of the measuring voltage) is detected, or a voltage transformer
protection breaker trip (via a correspondingly marshalled binary input) is indicated
(refer also to Subsection 2.19.1), both stages are internally blocked, in order to avoid
malfunction of the protection in the event of secondary voltage failure. Each stage can
be blocked individually and/or for both stages can be blocked, via binary inputs.
Particular attention must be paid to the status of the interrupted system during under-
voltage protection. As protective objects have no primary or measurement voltage, the
pickup conditions are therefore always fulfilled. The same can apply after a tripping of
the undervoltage protection or another protection function. The undervoltage protec-
tion should therefore (according to suitable criteria) be completely blocked externally
- e.g. dependent on circuit breaker - via an appropriate binary input.

Siemens SIPROTEC 7UT635*-* N series Specifications

General

Brand	Siemens
Model	SIPROTEC 7UT635*-* N series
Category	Protection Device
Language	English