Siemens 7UT51 User Manual

7UT51 v3
Time Overcurrent Protection (50HS and 50/51)
8
PRIM-2330C 99
8 Time Overcurrent Protection (50HS and 50/51)
As a backup to the differential protection, the relay
provides time overcurrent protection that includes a
high-set element (50HS) and a choice of either a
definite-time element (50) or an inverse-time element
(51). These elements monitor one winding (or side) of
the protected object. A 7UT513 protecting a two-sided
object can use its third set of phase-current inputs to
protect an additional (virtual) object.
The overcurrent elements are for protection in the
event of a short circuit. Overload conditions are
handled by the thermal overload protection elements
(see Chapter 8.19).
By using a binary input, the relay can change the
behavior of the overcurrent protection during a manual
close of a circuit breaker.
8.1 Method of Operation
The 50 and 50HS elements each operate in the same
way. If the current of any phase of the monitored
winding (or side) reaches a specified threshold level,
the element picks up. If the current level of any phase
remains above the threshold for a specified time
period, the element trips.
The 51 (inverse time) element also picks up if a phase
current reaches a specified threshold level. After
pickup, the time delay before trip is determined by an
inverse-time characteristic that emulates an
electromechanical overcurrent relay (the element
provides a choice of three characteristic curve types:
Moderately Inverse, Very Inverse, and Extremely
Inverse, and a range of time dial settings). If the level
of the measured currents change after pickup, the
remaining time before trip will also change. See Figure
8.1 on page 103, Figure 8.2 on page 104 and Figure
8.3 on page 105.
Each pickup threshold is specified as a multiple of the
nominal rated current (I
N
) of the monitored winding (or
side) of the protected object. If the protected object is
a transformer, motor, or generator; the rated nominal
current is computed from the specified voltage and
power ratings for the winding. If the protected object is
a bus or virtual object, the rated nominal current is
specified directly in a setting.
A binary input can be used to signal the relay that a
manual close is occurring; therefore, the behavior of
the overcurrent element can be changed to use either
the 50HS or 50/51 pickup threshold without a time
delay before a trip (see Section 8.6 on page 102).
8.2 Normal Operational
Status
Like the other protection elements, the time
overcurrent elements (50HS and 50/51) can be either
Non
-
Existent/DISABLED
or a choice is made as to
which Reference side (or winding) is to be monitored.
The choice is made in Configuration Address 7821.
Once made existent, the 50HS and 50/51 elements
can be configured. Their normal operational status is
set in Address 2101.
7821 BACKUP O/C
Existence and choice of monitored winding of the time
overcurrent protection elements (50HS and 50/51).
Option Description
Non Existent/
DISABLED
50HS and 50/51 elements do not exist
(default).
REFERENCE
SIDE 1
50HS and 50/51 elements exist and
monitor Winding 1 (or Side 1) of the
protected object.
REFERENCE
SIDE 2
50HS and 50/51 elements exist and
monitor winding 2 (or Side 2) of the
protected object.
REFERENCE
SIDE 3
50HS and 50/51 elements exist and
monitor winding 3 (or Side 3) of the
protected object (7UT513 only).
VIRTUAL
OBJECT
50HS and 50/51 elements exist and
monitor a separate, “virtual” object (only
available for a 7UT513 protecting a
two
-
sided object).
2101 BACKUP O/C
Normal operational status of backup overcurrent
protection (50HS and 50/51).
Option Description
OFF 50HS and 50/51 elements are inactive
(default).
ON 50HS and 50/51 elements are active.
BLOCK
TRIPPING
50HS an3d 50/51 elements are active except
that trip contacts and signal contacts will not
respond to 50HS and 50/51 trip events.

Siemens 7UT51 Specifications

General

Brand	Siemens
Model	7UT51
Category	Relays
Language	English