GE 469 Instruction Manual page 39

CHAPTER 1: GETTING STARTED
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
• Starts/Hour
When available, set starts/Hour to the number of cold starts as per the data sheet.
• Time Between Starts
In some cases, the motor manufacturer will specify the time between motor starts.
This information is not given so this feature can be left disabled. If the information is
available, the time provided on the motor data sheets should be programmed.
• 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.
R
r2
K
= ------- -
R
r1
230 230
------------ -
=
2 2
6.31
(EQ 1.1)
≈ 6
(EQ 1.2)
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