How to calculate large DC motor efficiency?

AI Thread Summary
Two primary methods for calculating large DC motor efficiency are experimental and analytical approaches. The analytical method involves recording motor nameplate values, calculating the electrical power for the shunt field and armature, and dividing the mechanical output power by the total electrical power. An example calculation shows that a 400 HP motor yields an efficiency of 93.8%. The experimental method requires a dynamometer to measure output shaft power while recording armature and field voltage and current. Additionally, both Swinburne’s Test and Hopkinson’s Test can be utilized, with Hopkinson's Test providing greater accuracy due to its use of two identical machines.
Ana Mido
Messages
21
Reaction score
0
What are the two methods for calculating large DC motor efficiency ?
 
Engineering news on Phys.org
Experimentally and analytically.
 
  • Like
Likes Asymptotic and PhysicoRaj
billy_joule said:
Experimentally and analytically.
In detail, please.
 
For a reasonable estimate at full power rating:
  • Record motor nameplate values.
  • Calculate electrical power required by the shunt field, and armature power. Add them together.
  • Divide mechanical output (shaft) power into the electrical power required to generate it.
Example: 400 HP. 1750 RPM. 500V/633A armature. 300V/4.84A shunt field.
316.5 kW + 1452 watts = 317.952 kW
400 HP = 298.28 kW
298.28/317.95 = 93.8%

Experimentally, design and build a suitably sized dynamometer (or haul the motor to a rewind shop large enough to have the requisite equipment), and couple it to the motor. Measure output shaft power while simultaneously measuring and recording armature and field voltage and current. Do the math.
 
  • Like
Likes Ana Mido and billy_joule
Asymptotic said:
For a reasonable estimate at full power rating:
  • Record motor nameplate values.
  • Calculate electrical power required by the shunt field, and armature power. Add them together.
  • Divide mechanical output (shaft) power into the electrical power required to generate it.
Example: 400 HP. 1750 RPM. 500V/633A armature. 300V/4.84A shunt field.
316.5 kW + 1452 watts = 317.952 kW
400 HP = 298.28 kW
298.28/317.95 = 93.8%

Experimentally, design and build a suitably sized dynamometer (or haul the motor to a rewind shop large enough to have the requisite equipment), and couple it to the motor. Measure output shaft power while simultaneously measuring and recording armature and field voltage and current. Do the math.
What about Swinburne’s Test and Hopkinson’s Test ?. Can they be used for calculating large Machine efficiency?
 
Ana Mido said:
What about Swinburne’s Test and Hopkinson’s Test ?. Can they be used for calculating large Machine efficiency?

Sure.
To do a Hopkinson you need two identical DC machines, but it's more accurate than a Swinburne (which is run no-load, and doesn't account for several significant effects).
 
  • Like
Likes Ana Mido

Thread 'How might electronics be different if AC voltage was 72V at 45 Hz?'

Hey guys. I have a question related to electricity and alternating current. Say an alien fictional society developed electricity, and settled on a standard like 73V AC current at 46 Hz. How would appliances be designed, and what impact would the lower frequency and voltage have on transformers, wiring, TVs, computers, LEDs, motors, and heating, assuming the laws of physics and technology are the same as on Earth?
View full post »

Thread 'Why does the amperage go real high if there is a low voltage short?'

I used to be an HVAC technician. One time I had a service call in which there was no power to the thermostat. The thermostat did not have power because the fuse in the air handler was blown. The fuse in the air handler was blown because there was a low voltage short. The rubber coating on one of the thermostat wires was chewed off by a rodent. The exposed metal in the thermostat wire was touching the metal cabinet of the air handler. This was a low voltage short. This low voltage...
View full post »
Thread 'Electromagnet magnetic field issue'

Thread 'Electromagnet magnetic field issue'

Hi Guys We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns. What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design. Any help will be appreciated. Thanks. edit: even same wire diameter and coil was wounded by a...
View full post »

Similar threads

12V DC Motor in Light Fixture with Dimmer & 12V DC to 110V AC Inverter
Replies
21
Views
2K
Eliminating a differential of an e-rickshaw by using 2 motors.
Replies
3
Views
279
Modelling the voltage measured across a dc motor
Replies
19
Views
2K
I need help with a Baldor dc motor, 15kw 240 volt ,150 volt field
Replies
12
Views
3K
Can a DC motor work without either a commutator or a controller?
Replies
13
Views
4K
Electric motor - variable torque vs speed
Replies
13
Views
2K
DC Motor Overspeed: Cause & Effect
Replies
24
Views
5K
Sizing an Isolation Transformer for a DC Power Supply
Replies
8
Views
2K
What is the best DC motor for spinning a vortex impeller at 3000 rpm?
Replies
2
Views
2K
Cost Efficiency Study Comparation of PMSM and BLDC Motor
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top