Alarm Level Operation - ABB RELION 670 Series Applications Manual

Section 6
Differential protection
Calculation:
>
UR
EQUATION1219 V1 EN-US
Select a setting of
The current transformer saturation voltage at 5% error can roughly be calculated from the
rated values.
E P 5
EQUATION1220 V1 EN-US
that is, greater than 2 ˣ
Check from the table of selected resistances the required series stabilizing resistor value to
use. Since this application requires high sensitivity, select
gives a current of 40 mA.
To calculate the sensitivity at operating voltage, refer to equation
gives around 10% minimum operating current.
300
IP =
5
EQUATION1221 V2 EN-US
The magnetizing current is taken from the magnetizing curve for the current transformer
cores which should be available. The current value at
dependent resistor current the peak value of voltage 40 ˣ √2 is used. Then the RMS current is
calculated by dividing obtained current value from the metrosil curve with√2. Use the
maximum value from the metrosil curve given in Figure 48.
6.2.4.7

Alarm level operation

The 1Ph High impedance differential protection HZPDIF function has a separate alarm level,
which can be used to give alarm for problems with an involved current transformer circuit. The
setting level is normally selected to be around 10% of the operating voltage
As seen in the setting examples above the sensitivity of HZPDIF function is normally high,
which means that the function will in many cases operate also for short circuits or open
current transformer secondary circuits. However the stabilizing resistor can be selected to
achieve sensitivity higher than normal load current and/or separate criteria can be added to
the operation, like a check zone. This can be either another IED, with the same HZPDIF
function, or be a check about the fault condition, which is performed by an earth overcurrent
function or neutral point voltage function.
For such cases where operation is not expected during normal service the alarm output should
be used to activate an external shorting of the differential circuit avoiding continuous high
voltage in the circuit. A time delay of a few seconds is used before the shorting and alarm are
activated. Auxiliary relays with contacts that can withstand high voltage shall be used, like
RXMVB types.
The metrosil operating characteristic is given in the following figure.
134
250
( )
× × + =
15 0.66 0.8
300
U>Trip =40 V.
( )
> + × =
10 0.66 20 213.2
U>Trip
(
× 40 0 ° + 5 0 ° + × 4 20 60
18.25 V
V
− 3
)
− ° × 10 ≤ approx 33
U>Trip is taken. For the voltage
(Equation 33)
(Equation 34)
SeriesResistor = 1000 ohm which
35 which is acceptable as it
A
U>Trip .
1MRK 504 152-UEN B
(Equation 35)
M16850-196 v6
Application manual