GE 469 Instruction Manual page 30

469
Motor Management Relay
1–22
• Stator RTDs
Set the RTD trip level at or below the maximum temperature rating of the
insulation. The data available shows class F insulation (temperature rating of
155°C), therefore the Stator RTD Trip level should be set to between 140°C to
155°C, with 155°C being maximum. The RTD alarm level should be set to
provide a warning that the motor temperature is rising. For this example, 135°C
would be appropriate since this motor is designed for class B rise, 130°C is it's
normal hot operating temperature.
• Bearing RTDs
The Bearing RTD alarm and trip settings will be determined by evaluating the
temperature specification from the bearing manufacturer.
• Unbalance bias of thermal capacity
Enable the Unbalance Bias of Thermal Capacity so that the heating effect of
unbalance currents is added to the Thermal Capacity Used.
• Unbalance bias K factor
The K value is used to calculate the contribution of the negative-sequence
current flowing in the rotor due to unbalance. It is defined as:
where: R = rotor negative-sequence resistance
r2
R = rotor positive-sequence resistance.
r1
A formula based on empirical data states that K is equal to 230 divided by the
per-unit locked rotor current squared.
From the data sheet, the locked rotor amps = 631% FLA or 6.31 × FLA.
Therefore,
K
= ---------------------------------------------------------------------------------------- -
(per-unit locked rotor amps)
• Hot/cold curve ratio
The hot/cold curve ratio is calculated by simply dividing the hot safe stall time
by the cold safe stall time or use the motor thermal limits curve. For this
example, both are available. Using the data sheets the, safe stall time H/C or
hot/cold curve ratio is given as 16/18 = 0.89
• Enable RTD Biasing
This will enable the temperature from the Stator RTD sensors, to be included in
the calculations of thermal capacity. This model determines the thermal
capacity used based on the temperature of the Stator and is separate from the
overload model for calculating thermal capacity used.
RTD biasing is a back up protection element, which accounts for such things as
loss of cooling or unusually high ambient temperature. This measured
temperature is used to bias or modify the thermal capacity value stored in the
relay.
: Set to 40°C, which is the ambient temperature, obtained
RTD BIAS MINIMUM
from the data sheets.
: The center point temperature is set to the motor's hot
RTD BIAS MID POINT
running temperature and is calculated as follows:
Temperature Rise of Stator + Ambient Temperature
The temperature rise of the stator is 80°C (class F rise by resistance) + 10%
hot spot allowance, obtained from the data sheets. Therefore, the RTD Center
point temperature is set to 90°C + 40°C or 130°C.
: This setpoint is set to the rating of the insulation or slightly
RTD BIAS MAXIMUM
less. A class F insulation is used in this motor which is rated at 155°C, so the
setting should be "155".
http://www.GEindustrial.com/multilin
R
r2
K
= -------- -
R
r1
230
230
≈
= ------------ -
6.31
2
Application Example
(EQ 1.1)
6
(EQ 1.2)
GE Multilin