Power Dissipation - Magtrol HD-106 User Manual

Chapter 4 – Testing
Note:
4.1.3 P D
ower iSSiPaTion
All Magtrol Dynamometers are power absorption instruments. As a dynamometer loads a test
motor, it is absorbs horsepower from the motor into the hysteresis brake. The brake then converts
this mechanical energy into heat.
There are finite limits to the amount of energy and resulting temperature rise that any absorption
brake can withstand. Rapidly rising operating temperatures from excessive power input can cause
severe mechanical distortion of the rotor assembly. This, in turn, may cause the rotating assembly
to contact the stationary members that surround it. Once this happens, metal transfer and ultimately
seizing of the brake assembly may occur.
Excessive power over extended periods of time may result in more obscure damage including
breakdown of bearing lubricants and degradation of magnetic coil insulation. Also, exposure to
temperatures over 690 °C (1275 °F) will alter the rotor's magnetic properties.
Note:
Note:
4.1.3.1 Power Absorption Curves
The following graphs (Figures 4–1 through 4–15) represent the maximum power (heat) that the
dynamometer can dissipate over time. The specifications shown are conditional upon the following:
None of the above take into account the long-term drift effects
on digital readout instrumentation. This is covered for each
instrument by their individual specifications. Also, many
of the above factors are dependent upon motor horsepower,
fixturing and other circumstances beyond the control of Magtrol.
If reasonable care is exercised, and calibration and maintenance
are performed on a regular basis,, motor test data accuracy better
than 0.25% of torque-speed value can be expected.
Do not instantaneously apply maximum power (torque-speed) to a
cold dynamometer. High temperature gradients cause differential
expansions resulting in misalignment of the running air gaps
between the rotor and stator assembly on the load brake. Allow
all dynamometers to warm up before heavy loading. This is
accomplished by gradually increasing the load to the motor. If
a motor must be tested cold, warm up the dynamometer with a
different motor first.
Operating at the continuous power rating for periods of up to 4 hours
is acceptable. However, operating for extended periods at high
temperatures will result in premature component and bearing failure.
Limiting the length of the cycle and the component temperatures
will guard against premature failure. Where continuous duty is
desired for longer time intervals, component temperatures should
be maintained less than 100°C; monitoring the outside brake surface
temperature is a sufficient reference.
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Magtrol Hysteresis Dynamometers