Schweitzer Engineering Laboratories SEL-311C - View or Reset Demand Metering Information

8.26
SEL-311C Relay Instruction Manual Date Code 20060320
Breaker Monitor and Metering Functions
Demand Metering
51GP = 1.50 A secondary
If a ground fault occurs, the residual ground time-overcurrent element 51GT
operates with the sensitivity provided by pickup 51GP = 1.50 A secondary.
The thermal demand meter, even with setting DMTC = 5 minutes, does not
respond fast enough to the ground fault to make a change to the effective
residual ground time-overcurrent element pickup—it remains at 1.50 A
secondary. Demand meters respond to more “slow moving” general trends.
Residual Ground Demand Current Goes Above Pickup GDEMP
When unbalance current I
G
increases, unbalance demand current I
G(DEM)
follows, going above corresponding demand pickup GDEMP = 1.00 A
secondary, and Relay Word bit GDEM asserts to logical 1. This results in
SEL
OGIC control equation torque control setting 51GTC being in the state:
51GTC = !GDEM + GDEM * 50G2 = NOT(GDEM) + GDEM * 50G2 =
NOT(logical 1) + (logical 1) * 50G2 = logical 0 + 50G2 = 50G2
Thus, the residual ground time-overcurrent element 51GT operates with an
effective, less-sensitive pickup:
50G2P = 2.30 A secondary
The reduced sensitivity keeps the residual ground time-overcurrent element
51GT from tripping on higher unbalance current I
G
.
Residual Ground Demand Current Goes Below Pickup GDEMP Again
When unbalance current I
G
decreases again, unbalance demand current
I
G(DEM)
follows, going below corresponding demand pickup GDEMP =
1.00 A secondary, and Relay Word bit GDEM deasserts to logical 0. This
results in SEL
OGIC control equation torque control setting 51GTC being in the
state:
51GTC = !GDEM + GDEM * 50G2 = NOT(GDEM) + GDEM * 50G2 =
NOT(logical 0) + (logical 0) * 50G2 = logical 1
Thus, the residual ground time-overcurrent element 51GT operates on its
standard pickup again:
51GP = 1.50 A secondary
View or Reset
Demand Metering
Information
Via Serial Port
See MET D—Demand Metering on page 10.22. The MET D command
displays demand and peak demand metering for the following values:
Currents
I
A,B,C
Input currents (A primary)
I
G
Residual ground current (A primary; I
G
= 3I
0
= I
A
+ I
B
+ I
C
)
3I
2
Negative-sequence current (A primary)
Power
MW
A,B,C
Single-phase megawatts
MVAR
A,B,C
Single-phase megavars