3
Description of
operation
The combined overvoltage and undervoltage
module SPCU 3C14 is a three-phase relay mod-
ule, which can be programmed for single-phase
operation by means of switch SG1/1 on the
front panel. The module contains an overvoltage
stage and an undervoltage stage. The overvoltage
stage can be given either definite time or inverse
time characteristic, whereas the operation of the
undervoltage stage is based on definite time
characteristic only.
If one of the voltages measured by the module
exceeds the set start value of the U> stage, the
module delivers a start signal SS1 after the set
start time has expired. The start time of the U>
stage is selected by means of switch SG1/2, and
two alternative values are available. After the
preset operate time t>, or at inverse time charac-
teristic, after a time depending on the level of the
overvoltage, the overvoltage stage operates de-
livering a trip signal TS1.
The operation characteristic of the U> stage, i.e.
definite time or inverse time characteristic, is
selected with switch SG1/3. At definite time
characteristic the setting range of the operating
time is programmed with switches SG1/4 and 5.
At inverse time characteristic two different sets
of voltage/time curves, called A and B, can be
selected by means of switch SG1/4. At inverse
time characteristic switch SG1/5 has no func-
tion.
If one of the voltages measured by the module
falls below the set start value of the U< stage, the
module delivers a start signal SS2 after the set
operate time has expired. The start time of the
U< stage is selected by means of switch SG1/7,
and two alternative values are available.
After the preset operate time t<, a trip signal TS2
is delivered by the undervoltage stage. The set-
ting range of the operate time is selected with
switch SG1/8.
To avoid unwanted operations, for instance
during an auto-reclose sequence, starting and
tripping of the undervoltage stage can be blocked
by turning switch SG1/6 into the position 1.
The blocking function is activated if the meas-
ured signal falls to a value below 0.2 x U
n
. This
function is illustrated in Fig. 1.
Fig. 1. Operation of the combined overvoltage and undervoltage relay module SPCU 3C14 when
the function of the undervoltage stage is internally blocked (SG1/6 = 1).
Tripping (TS2) of the U< stage alone, may be
blocked by applying a blocking signal BTS2 on
the stage. The blockings are programmed indi-
vidually for the various relay assemblies by means
of the switchgroup SGB on the relay module.
Programming instructions for the SGB switch-
group are given in the user's manual of the
concerned protection relay unit. Also see the
signal diagram of the concerned protection relay
unit.
