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BETA Monitoring
Monitoring of Electrical Values
5
TT3 voltage relays
13/10
Siemens ET B1 · 10/2008
13
■
More information
General voltage monitoring
For general device and plant protection, voltage relays with
switching thresholds of 0.7 × U
c
,
i.e.161 V are used. If they have
fixed, unchangeable switching thresholds, they switch back to
normal operation at 0.85 × U
c
, 195
V or at 0.9 × U
c
, 207
V, depend-
ing on the version. If they have adjustable threshold values, they
switch back to normal operation with 4 % hysteresis, 9 V.
1, 2
or 3 phases against N or 3 phases against N
All voltage relays require an N-conductor. Devices for single, two
or three phases against N can be used for 1, 2, or 3-phase operation.
Devices for 3 phases against N require all three phases,
whereby the sequence in which they are connected is irrelevant.
Asymmetry detection
If different voltages occur in a three-phase network, this is called
phase asymmetry. Some voltage relays detect an asymmetry of
approx. 6 to 8 % of the phase-to-neutral voltage, i.e. approx.
14
to 16 V and switch off. This type of operation is used to
protect motors against a "skew" (for example).
N-conductor monitoring
An N-conductor break causes a "skew", depending on the phase
load. In extreme cases, this could cause 400 V to be applied to
a phase, which would destroy any connected devices. Each
voltage relay with asymmetry detection is tripped by an
N-conductor break, if the phase displacement is at least 14 to 18 V.
The 5TT3 410 N-conductor monitor detects a phase displacement
of 5 %, which is roughly 12 V. This provides earlier protection
against overvoltage for connected devices. The N-conductor
monitor does not react if the voltage drops or rises in all phases
simultaneously; or if a phase is swapped with the N-conductor.
Reverse voltage detection
If a phase fails, the motors feed a reverse voltage to the missing
phase. However, voltage relays with reverse voltage detection
will disconnect in this case because they are monitoring the
phase angle.
Phase failure detection
If a phase fails completely, the voltage relays disconnect with a
delay as specified in the technical specifications.
Short-time failure detection
Short-time failures upwards of 20 ms cannot be detected with
conventional voltage relays. However, they can occur in the case
of system transfers or lightning strikes and can lead to uncertainty
for sensitive process sequences or measuring procedures. The
5
TT3 407 short-time voltage relay has a reset function that allows
a procedure to be permanently interrupted after a fault.
Back-up fuse
The voltage relays do not require a back-up fuse as device
protection. However, they are often installed in junctions, i.e. in
main supply systems with high fusing. In this case, the supply
lead to the voltage relay must be short-circuit resistant. The
back-up fuse only serves as line protection.
5
TT3 411 and 5TT3 412 voltage relays
For control elements of the 5TT3 411 and 5TT3 412 voltage
relays,
see "Monitoring of medical premises" on page 13/40.
5
TT3
194
5
TT3
195
5
TT3
400
5
TT3
401
5
TT3
402
5
TT3
403
5
TT3
404
5
TT3
405
5
TT3
406
5
TT3
407
5
TT3
408
5
TT3
410
Overvoltage
✓ ✓
--
--
--
--
--
--
--
--
✓
--
Undervoltage
--
--
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
--
Monitoring of safety light devices
--
--
--
✓
--
--
--
✓
--
--
--
--
Monitoring of medical premises
--
--
--
--
--
--
--
--
✓
--
--
--
Monitoring of N-conductor
--
--
--
--
--
--
--
--
--
--
--
✓
Monitoring of short-time interruptions
--
--
--
--
--
--
--
--
--
✓
--
--
1, 2, 3
phases against N
✓
--
✓ ✓ ✓ ✓
--
--
--
✓
--
--
3
phases against N
--
✓
--
--
--
--
✓ ✓ ✓
--
✓
--
Asymmetry detection
--
✓
--
--
--
--
✓ ✓ ✓
--
✓ ✓
N-conductor monitoring
--
--
--
--
--
--
✓ ✓ ✓ ✓ ✓ ✓
Reverse voltage detection
--
✓
--
--
--
--
✓ ✓ ✓
--
✓
--
Short-time failure detection
--
--
--
--
--
--
--
--
--
✓
--
--
Phase failure detection
--
--
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
--
Switching thresholds:
--
--
--
--
--
--
--
--
--
--
--
--
0.7/0.9
× U
c
,
not adjustable
--
--
✓
--
✓
--
✓
--
--
--
--
--
0.8/0, 85
× U
c
,
not adjustable
--
--
--
--
--
--
--
--
--
✓
--
--
0.85/0.95
× U
c
,
not adjustable
--
--
--
✓
--
✓
--
✓
--
--
--
--
0.7 ... 0.95
× U
c
, 5 %
hysteresis, adjustable
--
--
--
--
--
--
--
--
✓
--
--
--
0.7 ... 1.1
× U
c
, 4 %
hysteresis, adjustable
--
--
--
--
--
--
--
--
--
--
✓
--
0.9 ... 1.3
× U
c
, 4 %
hysteresis, adjustable
✓ ✓
--
--
--
--
--
--
--
--
✓
--
Adjustable time delay
--
--
--
--
--
--
--
--
--
--
✓
--
Contact: 1 CO contact
--
--
✓ ✓
--
--
--
--
--
--
--
--
Contact: 2 CO contacts
✓ ✓
--
--
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
© Siemens AG 2008