ABB RELION 670 Series Applications Manual page 125

1MRK 504 152-UEN B
For an internal fault, all involved CTs will try to feed current through the measuring branch.
Depending on the size of current transformer, relatively high voltages will be developed across
the series resistor. Note that very high peak voltages can appear. To prevent the risk of
flashover in the circuit, a voltage limiter must be included. The voltage limiter is a voltage
dependent resistor (Metrosil).
The external unit with stabilizing resistor has a value of either 6800 ohms or 1800 ohms
(depending on ordered alternative) with a sliding link to allow adjustment to the required
value. Select a suitable value of the resistor based on the UR voltage calculated. A higher
resistance value will give a higher sensitivity and a lower value a lower sensitivity of the relay.
The function has a recommended operating current range 40 mA to 1.0A for 1 A inputs and 200
mA to 5A for 5A inputs. This, together with the selected and set value, is used to calculate the
required value of current at the set
The tables 20,
voltages and selected resistances. Adjust as required based on tables 20,
between as required for the application.
Normally the voltage can be increased to higher values than the calculated minimum
with a minor change of total operating values as long as this is done by adjusting the resistor
to a higher value. Check the sensitivity calculation below for reference.
Table 20: 1 A channels: input with minimum operating down to 40 mA
Operating
voltage
U>Trip
20 V
40 V
60 V
80 V
100 V
150 V
200 V
Table 21:
Operating
voltage
U>Trip
20 V
40 V
60 V
80 V
Table continues on next page
Application manual
The CT inputs used for 1Ph High impedance differential protection HZPDIF
function, shall be set to have ratio 1:1. So the parameters
the relevant channel x of TRM and/or AIM shall be set equal to 1 A by PST in
PCM600; The parameter
21 below show, the operating currents for different settings of operating
Minimum ohms can be difficult to adjust due to the small value compared to
the total value.
Stabilizing Operating
resistor R current level
ohms 1 A
500 0.040 A
1000 0.040 A
1500 0.040 A
2000 0.040 A
2500 0.040 A
3750 0.040 A
5000 0.040 A
5 A channels: input with minimum operating down to 100 mA
Stabilizing Operating
resistor R1 current level
ohms 5 A
200 0.100 A
400 0.100 A
600 0.100 A
800 0.100 A
U>Trip and SeriesResitor values.
CTStarPointx may be set to ToObject .
Stabilizing Operating
resistor R current level
ohms 1 A
-- --
-- --
600 0.100 A
800 0.100 A
1000 0.100 A
1500 0.100 A
2000 0.100 A
Stabilizing Operating
resistor R1 current level
ohms 5 A
100 0.200 A
200 0.200 A
300 0.200 A
400 0.200 A
Differential protection
CT and CT
secx
21 or to values in
Stabilizing Operating
resistor R1 current level
ohms 5 A
-- --
100 0.400
150 0.400 A
200 0.400 A
Section 6
of
primx
U>Trip
119