GE N60 Instruction Manual page 180

5.2 PRODUCT SETUP
The configuration menu allows a maximum of four ASDUs containing measurands.
Measurands are sent as a response to Class 2 requests, which are cyclic requests coming from the master.
TYPE IDENTIFICATION (TYP)
ASDU. Each ASDU can take either 4 or 9 measurands maximum, depending on the type identification (3 respectively 9).
FUNCTION TYPE (FUN) AND INFORMATION NUMBER (INF)
as defined in IEC60870-103.
SCAN TIMEOUT (SCAN TOUT)
response. The measurand is sent as response to a Class 2 request when the corresponding timeout expires. The default
value 0 means 500 ms.
: This field contains the actual measurand to be sent in the response to the master. The measurands can be
ANALOG #
mapped using elements from a list of FlexAnalog operands. The measurands sent are voltage, current, power, power fac-
tor, and frequency. If any other FlexAnalog is chosen, the N60 sends 0 instead of its value. Note that the power is transmit-
ted in KW, not W. Measurands are transmitted as ASDU 3 or ASDU 9 (type identification value set to measurands I,
respectively measurands II).
Each IEC60870-5-103 measurands list ends at the first unconfigured ("Off") value. Any measurand assigned after the first
"Off" value is ignored.
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At least one measurand per ASDU must be configured in order to configure the following ASDU. For example, the user can
configure only one measurand for each ASDU, but the user is not allowed to skip ASDU2 and configure measurands in
ASDU3.
ANALOG # FACTOR AND OFFSET
factor and offset allow for scaling to be performed on measurands. The final measurement sent to the IEC60870-103 mas-
ter is then "a*x + b", where x is the measurand, a is the multiplying factor and b is the offset. The master has to perform the
reversed operation in order to retrieve the actual value if such scaling is done. By default a = 1 and b = 0, so no scaling is
done if these values are left at their defaults. Examples of when scaling is appropriate are as follows:
• If the measured value contains decimals and it is important to preserve the resolution. Since the format for transmitting
the measurand does not permit decimals, a factor a>1 can be applied before transmission. For example, a frequency
F=59.9Hz can be transmitted as Ft = 10 * F = 10 * 59.9 = 599. In this case a = 10, b = 0. The master receives 599 and
has to divide by 10 to retrieve the real value 59.9.
• If the measured value is larger than what fits in the format defined in IEC103. The format defined in the standard allows
for signed integers up to 4095. By offsetting, unsigned integers up to 4096 + 4095 = 8191 are supported. Scaling using
factors <1 can be required in such cases. The calculation is outlined in the IEC60870-5-103 appendix. Two examples
follow, where you decide factors a and b.
Example 1: Nominal power Pn = 100MW = 100000KW (power is transmitted in KW)
Since P can be both positive and negative:
Transmitted power Pt = (4095/(Pn*2.4)) * P = (4095/(100000 * 2.4) ) * P
= 0.017 * P
a = 0.017
b = 0
Pt = 0.017 * P
For a max power 100000KW * 2.4 = 240000KW, we transmit
Pt = 0.017 * 240000 = 4080
A value above 240 MW is indicated by overflow.
Example 2: Nominal voltage Vn = 500000V
Since RMS voltage V can be only positive:
Transmitted voltage Vt = (8191/(Vn*2.4)) * V - 4096 =
= (8191/(500000 * 2.4) ) * V - 4096 = 0.0068 * V - 4096
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: The configuration field TYP indicates how many measurands are present in the corresponding
: These two fields form the Information Object Identifier of the ASDU
: This is the cyclic period used by the N60 to decide when a measurand ASDU is included in a
: For each measurand included in the ASDU, a factor and offset can also be configured. The
N60 Network Stability and Synchrophasor Measurement System
5 SETTINGS
GE Multilin