Ge-industrial-solutions Record Plus FG600 SMR2 Modbus User Manual download pdf (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

) 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.

_SOS_Value for 50 Hz =

830304

_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

= (input current/sensor rating)

_SOS_Value

For given SOS value ,Current amplitude can be

calculated using the following equation:

Input current

= (SOS Value /

_SOS_Value

)

0.5

x Sensor Rating

Example: Current to SOS conversion

sensor rating = 400A

Input current=500A

Frequency =50Hz

select

_SOS_Value

based on frequency

SOS value = (input current/sensor

rating)

_SOS_Value

= (500/400)

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

_SOS_Value based on frequency

Input current = (SOS Value /

_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

Unsigned int

(Unused)

Normal

mode - RO

3001 Minute 0 - 59

Test mode

Unsigned int

(Unused)

UL/IEC bit (Bit

0) in Control

byte

Line

Frequency

0 - UL 60 Hz

1 - IEC 50 Hz

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 20 21

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Ge-industrial-solutions Record Plus FG600 SMR2 Modbus User Manual Page 12

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