GE Industrial Solutions Record Plus FG600 SMR2 Modbus - Manual (Page 12)

SMR2 Modbus User Manual
Interpretation of SOS values
The Sum Of Squares values (SOS) of a phase is a
measure of the RMS value of current flowing through
that Phase.SMR2 calculates this values in every half
cycle and use this value as a measure of current to
perform the protection algorithm. The no. of current
samples used for SOS calculation depends on the
frequency.
When a current equal to sensor rating (I
CT
) value is
flowing through the breaker, a SOS value of 830304 will
be displayed if supply frequency is 50 Hz. For 60 Hz,
This value will be 691920.
I
CT
_SOS_Value for 50 Hz = 830304
I
CT
_SOS_Value for 60 Hz = 691920
Using this value we can calculate SOS value for any
current or current for any given SOS value.
For given current , SOS value can be calculated
using the following equation:
SOS value
9
= (input current/sensor rating) 2 x I
CT
_SOS_Value
For given SOS value ,Current amplitude can be
calculated using the following equation:
Input current
= (SOS Value / I
CT
_SOS_Value ) 0.5 x Sensor Rating
Example: Current to SOS conversion
sensor rating = 400A
Input current=500A
Frequency =50Hz
select I
CT
_SOS_Value based on frequency
SOS value = (input current/sensor
rating) 2 x I
CT
_SOS_Value
= (500/400) 2 x 830304
= 1297350
For 500A, 50Hz input current SOS value will be
equal to 1297350.
Example: SOS to current conversion
Sensor rating = 400A
SOS Value= 7472736
Frequency =50Hz
Select I
CT
_SOS_Value based on frequency
Input current = (SOS Value / I
CT
_SOS_Value ) 0.5 x Sensor Rating
= (7472736/830304) 0.5 x 400
= 1200 A
If SOS Value= 7472736 for 50 Hz , then
corresponding current is 1200A
Note:
UL/IEC bit (Bit 0) in Control Byte (Modbus Address
3012) is monitored and ETUs operating frequency is
determined based on this bit.
Setpoint Registers
Setpoint registers start at 3000, read by Function Code 03
Reg. Contents
Range Type R/W Format
Normal
mode - RO
3000 Hour 0 - 23
Test mode
RW
Unsigned int
(Unused)
Normal
mode - RO
3001 Minute 0 - 59
Test mode
RW
Unsigned int
(Unused)
UL/IEC bit (Bit
0) in Control
byte
Line
Frequency
0 - UL 60 Hz
1 - IEC 50 Hz