GE SPM Series, Instruction Manual

Page: 63 / 126

GE Power Management SPM Synchronous Motor Protection & Control 5-
7
5 SETPOINTS 5.2 SETPOINTS MENU
5
5.2.14 FIELD OVERTEMPERATURE (HIGH FIELD OHMS) PROTECTION
FUNCTION:
The calculation of field (exciter) voltage divided by field (exciter) current yields field ohms. Tripping action is ini-
tiated if the calculated resistance exceeds the
HIGH FIELD
(
HI EXC FLD
) setpoint, indicating a field overtempera-
ture condition. A separate accessory package (PG2SPM or PG4SPM) is required to utilize this feature.
MOTOR TYPE:
Collector-Ring or Brushless
APPLICATION:
This function emulates a resistance temperature detector (RTD) on the field windings. The resistance of an
RTD is temperature dependent – it increases as the temperature increases. In this case, the RTD behavior is
emulated by examining the field voltage and current. As the ratio of field voltage to field current increases, the
field resistance increases, indicating an increase in temperature of the field windings.
The motor nameplate contains the motor's maximum temperature rise and field resistance. This information is
used with the multiplier from the table below to determine the maximum field ohms, and therefore the maxi-
mum field winding temperature, at which the motor should be allowed to operate.
EXAMPLE:
A motor with a nameplate field resistance of 2
Ω
at 25°C with insulated copper windings has a maximum tem-
perature rise of 80°C. This corresponds to a field resistance of 1.31 times the resistance at 25°C. So, the
FIELD
OHMS
setpoint is set to 1.31
×
2
Ω =
2.62
Ω
.
FL AMPS: 25
ENTER to modify
Range: 2 to 2000 A
Step 1
FL AMPS: 25
ENTER to modify
Range: 2 to 2000 A
Step 1
Table 5–2: FIELD OVERTEMPERATURE RANGE / STEP VALUES
DC CT PRIM
SETPOINT
HIGH FIELD
/
HIGH EXC FLD
FIELD OHMS
VALUE
STEP
MINIMUM MAXIMUM
5 to 19 A 10
Ω
450
Ω
< 1
Ω
0.01
Ω
20 to 200 A 1
Ω
40
Ω
< 10
Ω
0.1
Ω
201 to 1000 A 0.20
Ω
5
Ω
< 450
Ω
1
Ω
Table 5–3: FIELD OHMS MULTIPLIER
RISE °C MULTIPLIER RISE °C MULTIPLIER RISE °C MULTIPLIER
0 1.0 40 1.15 110 1.42
5 1.02 50 1.19 120 1.46
10 1.04 60 1.23 130 1.50
15 1.06 70 1.27 140 1.54
20 1.08 80 1.31 150 1.57
25 1.10 90 1.35 160 1.60
30 1.12 100 1.39 170 1.64