Increase of pickup value
2.25 Jump of Voltage Vector
General It is not uncommon that consumers with their own generating plant feed power directly into a network. The incoming feeder is usually the ownership boundary between the utility and these consumers/producers. A failure of the input line, e.g. because of a three-pole automatic reclosure, can cause a deviation of the voltage or frequency at the feeding generator which is a function of the overall output. When the incoming feeder line is switched on again after the dead time, it may meet with asynchronous conditions which cause damage to the generator or the gear train between generator and drive.
One criterion for identifying an interruption of the incoming feeder is the monitoring of the phase angle in the voltage. In case of a failure of the incoming feeder, the abrupt current interruption causes a phase angle jump in the voltage. This jump is detected by means of a delta process. As soon as a preset threshold is exceeded, an opening command for the generator or bustie coupler circuit-breaker is issued.
This means that the vector jump function is mainly used for network decoupling.
Figure 2-79 shows the evolution of the frequency when a load is disconnected from a generator. Opening of the generator circuit breaker causes a phase angle jump that can be observed in the frequency measurement as a frequency jump. The generator is accelerated in accordance with the power system conditions (see also Section 2.24 Rate-of-Frequency-Change Protection).
Figure 2-79 Evolution of the Frequency after Disconnection of a Load (Fault recording with 7UM6 - the figure shows the deviation from the rated frequency)
-1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 1
7
6
5
4
3
2
0
s t Hz
f-fn
Jump of Voltage Vector
2.25.1 Functional Description
Measuring Principle
The vector of the positive sequence system voltage is calculated from the phase-to-earth voltages, and the phase angle change of the voltage vector is determined over a delta interval of 2 cycles. The presence of a phase angle jump is an indicator for an abrupt change of the current flow. The basic principle is shown in Figure 2-80. The di-agram on the left shows a steady state, and the didi-agram on the right the vector change following a load shedding. The vector jump is clearly visible.
Figure 2-80 Voltage Vector Following a Load Shedding
The function features a number of additional measures to avoid spurious tripping, such as:
− Correction of steady-state deviations from rated frequency
− Frequency operating range limited to fN± 3 Hz
− Detection of internal sampling frequency changeover
− Minimum voltage for release
− Blocking on voltage connection or disconnection
Logic Figure 2-81 shows the logic diagram. The phase angle comparison determines the an-gle difference, and compares it with the set value. If this value is exceeded, the vector jump is stored in an RS flip-flop. Tripping can be delayed by the associated time delay.
The stored pickup can be reset via a binary input, or automatically by a timer (address 4604 T RESET).
~
ZGen
∆U
U I1
Z Z NET
I2
Network
Up
Generator
Network/Load
∆U
U
φ
~
Up
ZGen
∆U
U I1'
Z Network Z NET
Up
Generator
Network/Load
∆U
U
∆φ
U'
The vector jump function becomes ineffective on leaving the permissible frequency band. The same is true for the voltage, for which the limiting parameters areU MIN andU MAX.
On violation of the frequency or voltage band, the logic generates a logical “1”, and the reset input is continuously active. The result of the vector jump measurement is sup-pressed. If, for instance, the voltage is connected, and the frequency band is correct, the logical “1” changes to “0”. The timerT BLOCKwith reset delay keeps the reset in-put active for a certain time, and thus prevents a pickup caused by the vector jump function.
If a short-circuit causes the voltage to drop abruptly to a low value, the reset input is immediately activated to block the function. The vector jump function is thus prevented from causing a trip.
Figure 2-81 Logic Diagram of the Vector Jump Detection
2.25.2 Setting Hints
General The vector jump function is only effective and accessible if address0146 VECTOR JUMPhas been set toEnabledduring configuration.
Address4601 VECTOR JUMPis used to switch the function ON or OFF, or to block only the trip command (Block relay).
4602 DELTA PHI 4603 T DELTA PHI
4604 T RESET
f<(frated-3 Hz)
f>(frated+3 Hz)
U1<U MIN
Jump of Voltage Vector
Pickup Values The value to be set for the vector jump (address4602 DELTA PHI) depends on the feeding and load conditions. Abrupt load changes in the active power cause a jump of the voltage vector. The value to be set must be specifically determined for the power system considered. This can be done on the basis of the equivalent circuit diagram in Figure 2-80, or by means of a network calculation software.
If the setting is too sensitive, the protection function is likely to perform a network de-coupling every time loads are connected or disconnected. Therefore, the default set-ting is 10°.
The permissible voltage operating range can be set in the addresses4605AforU MIN and4606AforU MAX. The limit values of the setting range are to some extent a matter of the utility’s philosophy. The value forU MINshould be less than the permissible level of short voltage dips for which network decoupling is required. The default setting is 80 % of the rated voltage.U MAXshould be the maximum permissible voltage. This will be in most cases 130 % of the rated voltage.
Time Delays The time delayT DELTA PHI(address4603) should be left at zero, except if you wish to transmit the trip indication with a delay to a logic (CFC), or to leave enough time for an external blocking to take effect.
After expiry of the timerT RESET(address4604), the protection function is automat-ically reset. The reset time depends on the decoupling philosophy. It must have ex-pired before the circuit breaker is reclosed. Where the automatic reset function is not used, the timer is set to∞. The reset signal must come in that case from the binary input (circuit breaker auxiliary contact).
The timerT BLOCKwith reset delay (address4607A) helps to avoid overfunctioning when voltages are connected or disconnected. Normally, the default setting need not be changed. If changes are necessary, they can be performed with the DIGSI commu-nication software (advanced parameters). It must be kept in mind thatT BLOCKshould always be set to more than the measuring window for vector jump measurement (2 cycles).
2.25.2.1 Settings of the Vector Jump Detection
Addr. Setting Title Setting Options Default Setting Comments
4601 VECTOR JUMP OFF
ON
Block relay for trip com-mands
OFF Jump of Voltage Vector
4602 DELTA PHI 2..30° 10° Jump of Phasor DELTA PHI
4603 T DELTA PHI 0.00..60.00 sec;∞ 0.00 sec T DELTA PHI Time Delay
4604 T RESET 0.10..60.00 sec;∞ 5.00 sec Reset Time after Trip
4605A U MIN 10.0..125.0 V 80.0 V Minimal Operation Voltage U
MIN
4606A U MAX 10.0..170.0 V 130.0 V Maximal Operation Voltage U
MAX
4607A T BLOCK 0.00..60.00 sec;∞ 0.10 sec Time Delay of Blocking
2.25.2.2 Information for the Vector Jump Detection
F.No. Alarm Comments
05581 >VEC JUMP block >BLOCK Vector Jump
05582 VEC JUMP OFF Vector Jump is switched OFF
05583 VEC JMP BLOCKED Vector Jump is BLOCKED
05584 VEC JUMP ACTIVE Vector Jump is ACTIVE
05585 VEC JUMP Range Vector Jump not in measurement range
05586 VEC JUMP pickup Vector Jump picked up
05587 VEC JUMP TRIP Vector Jump TRIP
90–%–Stator Earth Fault Protection (ANSI 59N, 64G, 67G)