Manual MRG3
SEG Electronics GmbH
DOK-TD-MRG3, Rev. D
45
The recommended setting of the vector surge angle
in an efficient mains is 4 - 6 degrees. This
setting is sufficient in most cases, because low impedance mains never have a vector surge great-
er than this value. In case of an auto reclosing, this value is considerably exceeded.
In high impedance mains the setting should be 10° to 12° to avoid false tripping when switching on
or switching off big consumer loads.
The vector surge function of this device can be checked as follows:
a)
Generator in isolated operation: Switching off and on of loads (approx. 20% of the
nominal generator capacity) must trip the relay. Later in normal isolated operation the trip
ping of the relay is inhibited.
b)
In mains parallel operation switching on and switching off of user-defined consumer loads
and adjustment of the prime mover’s governor must not lead to tripping of the relay.
If possible the test described under a) and b) should be double checked by a real auto reclosing.
Threshold for the vector surge supervision
When the pickup value of the vector surge supervision is set, a value in angular degree is indicated
at the display. The pickup value requested can be adjusted by pushbuttons <+> and <-> in the
range of 2° to 22°. LED
_df lights up green during this setting. After adjustment of the sensitivity
for 1Pha or 3 Pha, LED 1/3_dt will be flashing in red.
Parameter setting of frequency gradient speed
The pickup value of frequency gradient (parameter df) can be set between 0.2 to 10 Hz/s. The
number of measuring repetitions (parameter dt) can be set between 2 - 64 cycles. This parameter
defines the number of consecutive df/dt measurements, which have to exceed the set value, before
tripping.
Setting information:
The power difference after mains failure causes a change in frequency, which can approximately
be calculated as follows:
𝑑𝑓
𝑑𝑡
= −
𝑓
𝑁
𝑇
𝐴
∙
P
with:
f
N
= rated frequency in Hz
T
A
= starting time at rated torque
P
= per unit power deficit with reference to the rated active power of the generator
If the inertia time constant is known and a power difference given, the frequency gradient can be
estimated by the a.m. equation. At a supposed power deficit of 20% and an inertia time constant of
10 s, the frequency gradient is 1 Hz/s.
To prevent false trippings at loading, deloading or failure signals, we would recommend a setting
value for dt of minimum 4 cycles.
