Siemens siprotec SJ62 User Manual page 144

Overvoltage Pro-
tection - Negative
Sequence System
V2
Dropout Threshold
of the Overvoltage
Protection
Undervoltage Pro-
tection - Positive
Sequence System
V1
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
The three-phase voltage transformer connection for the overvoltage protection can be
configured by means of parameter 614 OP. QUANTITY 59. Either the largest of the
phase-to-phase voltages (Vphph) or the negative system voltage (V2) are evaluated
as measured quantities. The negative system detects negative sequence reactance
and can be used for the stabilization of the time overcurrent protection. With backup
protection of transformers or generators, the fault currents lie, in some cases, only
slightly over the load currents. To obtain a pickup threshold of the definite time over-
current protection which should be as sensitive as possible, it is necessary to stabilize
the definite time overcurrent protection by the voltage protection.
Overvoltage protection includes two elements. Thus, with configuration of the negative
system, a longer time delay (address 5004, 59-1 DELAY) may be assigned to the
lower element (address 5015, 59-1 PICKUP V2) and a shorter time delay (address
5007, 59-2 DELAY) may be assigned to the upper element (address 5016, 59-2
PICKUP V2). There are no clear cut procedures on how to set the pickup values 59-
1 PICKUP V2 or 59-2 PICKUP V2, as they depend on the respective station con-
figuration. Since the negative sequence voltage V2 corresponds to a phase-ground
voltage, their threshold value must be set as such.
The parameter 5002 59-1 PICKUP and 5005 59-2 PICKUP or 5003 59-1 PICKUP
and 5006 59-2 PICKUP are deleted during configuration of the negative sequence
voltage and the setting values are activated under the addresses 5015 59-1 PICKUP
V2 or 5016 59-2 PICKUP V2. Be aware that the parameter device 614 OP.
QUANTITY 59 is ignored with single-pole voltage transformer connection and the ac-
tivation of the threshold value for the phase-to-phase voltages takes place. The time
delays of the overvoltage elements are entered at addresses 5004 59-1 DELAY and
5007 59-2 DELAY and should be selected to allow the brief voltage spikes that are
generated during switching operations and to enable clearance of stationary overvolt-
ages in time.
The dropout thresholds of the 59-1 element and the 59-2 element can be set via the
dropout ratio r = V
dropout
RATIO). In this, the following marginal condition always holds for r:
r · (configured pickup threshold ) ≤ 150 V with connection of phase-to-phase voltages
or
r · (configured pickup threshold ) ≤ 260 V with connection of phase-to-ground voltages.
The minimum hysteresis is 0.6 V.
The positive sequence component (V1) is evaluated for the undervoltage protection.
Especially in case of stability problems, their acquisition is advantageous because the
positive sequence system is relevant for the limit of the stable energy transmission.
Concerning the pickup values, there are not clear cut procedures on how to set them.
However, because the undervoltage protection function is primarily intended to protect
induction machines from voltage dips and to prevent stability problems, the pickup
values will usually be between 60% and 85% of the nominal voltage. Please note that
with frequency deviations of > 5 Hz of the calculated r. m. s value of the voltage will be
too small and the device will perform unwanted operations.
With a three-phase connection and a single-phase connection of a phase-to-phase
voltage the thresholds are set as phase-phase quantities. Since the positive sequence
component of the voltages corresponds to a phase-ground voltage, their threshold
value has to be multiplied with √3. With a single-phase phase-to-ground connection
the threshold is set as phase-ground voltage.
(5117 59–1 DOUT RATIO or 5118 59–2 DOUT
/V
pickup
2.6 Voltage Protection 27, 59
142