7-2
QChannel identification is performed by referencing the internal data table of the EPM device, by
specifying the Line Number and Point Number for a particular value. For example: to monitor 1
second VAN values, use Line 34, Point 0; 1 second VBN, use Line 34, Point 1; 1 second IA, use Line
36, Point 0; Thermal Average VAN, use Line 51, Point 0. To leave a Limit unassigned, use Line
65535, any point.
QComparison values are entered using percentages relative to the programmed full scales of the
system. For VAN, the phase-to-neutral Voltage Full Scale would be referenced. If it is programmed
to 120.0 V secondary with a phase voltage PT of 120:1, then a comparison of 13.2 kV primary
would be a limit of 108 V secondary or 90.00% of the Full Scale. A 90.00% comparison for IAwith
a phase Current Full Scale of 5.0 Asecondary and a phase current CT of 2000:5 would be a
comparison of 4.5 Asecondary or 1800 A primary. Negative percentages would be used where
appropriate (Watts, VAR, etc.). Special cases like PF and KF would depend on fixed internal Full
Scales. Human interfaces could represent this in terms of quadrature and angle, instead of the
internal percentage representation.
QEach comparison has a direction associated with it - Above or Below. A90.00% comparison could
be for above 90.00% or below 90.00%.
QFinally, each limit object is able to produce a third output which is a combination of the two
comparisons. This combination could be an AND, OR, NAND, NOR, XOR or Hysteresis. So, a user
can produce a band of between 40.00% and 80.00% by combining above 40.00% AND below
80.00%; over 110.00%/under 90.00% alarms by combining above 110.00% OR below 90.00%, on
after over 110.00%, off after below 90.00% by combining above 110.00% and below 90.00% with
Hysteresis.
The structure for a combination is :
2 byte Line Number
1 byte Point Number
1 byte Direction and Combination (SAB)
2 byte Comparison 1 Percentage (Value 1)
2 byte Comparison 2 Percentage (Value 2)
Total of 8 bytes per Limit Object, total of 256 bytes for 32 Limit Objects.
The structure for the Direction and Combination byte is:
Bits 7-5 Unused, set to 0
Bit 4 Negate combination (AND -> NAND, etc.)
Bits 3-2 00 = AND combination
01 = OR combination
10 = XOR combination
11 = Hysteresis combination
Bit 1 0 = Comparison 2 is below
1 = Comparison 2 is above
Bit 0 0 = Comparison 1 is below
1 = Comparison 1 is above