Guidelines for using generators with submersible well pumps

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Home > Pumps & Wells > Well Pumps > Use of generators with submersible well pumps

Franklin Electric


Use of Engine Driven Generators - Single-Phase or Three-Phase

http://www.franklin-electric.com/aim-manual/page-5.aspx

Table 5 lists minimum generator sizes based on typical 80 °C rise continuous duty generators, with 35% maximum voltage dip during starting, for Franklin’s threewire motors, single or three-phase.

This is a general chart. The generator manufacturer should be consulted whenever possible, especially on larger sizes.

There are two types of generators available: externally and internally regulated. Most are externally regulated. They use an external voltage regulator that senses the output voltage. As the voltage dips at motor start-up, the regulator increases the output voltage of the generator.

Internally regulated (self-excited) generators have an extra winding in the generator stator. The extra winding senses the output current to automatically adjust the output voltage.

Generators must be sized to deliver at least 65% of the rated voltage during starting to ensure adequate starting torque. Besides sizing, generator frequency is important as the motor speed varies with the frequency (Hz). Due to pump affi nity laws, a pump running at 1 to 2 Hz below motor nameplate frequency design will not meet its performance curve. Conversely, a pump running at 1 to 2 Hz above may trip overloads.

Generator Operation

Always start the generator before the motor is started and always stop the motor before the generator is shut down. The motor thust bearing may be damaged if the generator is allowed to coast down with the motor running. This same condition occurs when the generator is allowed to run out of fuel.

Follow generator manufacturer’s recommendations for de-rating at higher elevations or using natural gas.

  Table 5  Engine Driven Generators
Motor Rating Minimum Rating of Generator

HP

KW
Externally Regulated Internally Regulated
KW KVA KW KVA
1/3 .25 1.5 1.9 1.2 1.5
1/2 .37 2 2.5 1.5 1.9
3/4 .55 3 3.8 2 2.5
1 .75 4 5.0 2.5 3.13
1 1/2 1.1 5 6.25 3 3.8
2 1.5 7.5 9.4 4 5
3 2.2 10 12.5 5 6.25
5 3.7 15 18.75 7.5 9.4
7 1/2 5.5 20 25.0 10 12.5
10 7.5 30 37.5 15 18.75
15 11 40 50 20 25
20 15 60 75 25 31
25 18.5 75 94 30 37.50
30 22 100 125 40 50
40 30 100 125 50 62.5
50 37 150 188 60 75
60 45 175 220 75 94
75 55 250 313 100 125
100 75 300 375 150 188
125 93 375 469 175 219
150 110 450 563 200 250
175 130 525 656 250 313
200 150 600 750 275 344
NOTE: This chart applies to 3-wire or 3-phase motors. For best starting of 2-wire motors, the minimum generator rating is 50% higher than shown.
WARNING: To prevent accidental electrocution, automatic or manual transfer switches must be used any time a generator is used as standby or back up on power lines. Contact power company for use and approval.

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