Using A Generator; Special Applications - Pentair Pentek Series Electronic Manual

SECTION 4: Electrical Power
4.7

Using a Generator

Selecting a generator
Select a generator that can supply at least 65% of rated
voltage upon start-up of the motor.
The chart shows ratings of generators, both externally
and internally regulated. This chart is somewhat
conservative. Consult the generator manufacturer if you
are uncertain.
Table 4-3: Ratings of Generators
Motor Externally Regulated
HP kW KVA
1/2 2.0 2.5
3/4 3.0 3.8
1 4.0 5.0
1-1/2 5.0 6.3
2 7.5 9.4
3 10.0 12.5
5 15.0 18.8
7-1/2 20.0 25.0
10 30.0 37.5
15 40.0 50.0
20 60.0 75.0
25 75.0 94.0
30 100.0 125.0
40 100.0 125.0
50 150.0 188.0
60 175.0 220.0
Frequency
It is highly important that the generator maintain
constant frequency (Hz), since the motor's speed depends
upon frequency.
A drop of just 1 to 2 Hz can noticeably lower pump
performance. An increase of 1 to 2 Hz can cause
overload conditions.
Voltage Regulation
There is a significant difference in the performance of
internally and externally regulated generators.
An external regulator senses output voltage dips
and triggers an increase in the voltage output of the
generator.
An internal regulator, senses current and responds to
increased current by supplying more voltage.
Generator Operation
Start the generator before starting the pump motor.
The pump motor must be stopped before turning off
the generator.
If the generator runs out of fuel, and the pump is still
connected, it will put excess strain on the thrust bearings
as the generator slows.
switches when the generator is used as a backup to the
power grid. Contact your power company or generator
manufacturer for proper use of standby or backup
Internally Regulated
generators.
kW KVA
1.5 1.9
4.8
2.0 2.5
2.5 3.1
Using Phase Converters
3.0 3.8
Phase converters allow three-phase motors to operate
4.0 5.0
from one-phase supply. Various styles of phase
5.0 6.25
converters are available. Many converters do not supply
a properly balanced voltage, and using these will void the
7.5 9.4
motor's warranty unless approval is obtained first.
10.0 12.5
15.0 18.8
Guidelines For Phase Converters:
20.0 25.0
• Current unbalance must be less than 5%.
25.0 31.0
• Converter to be sized to service factor capacity
30.0 37.5
• Maintain motor cooling with a cooling flow of at least
40.0 50.0
50.0 62.5
• Fuses and circuit breakers must be time-delay type.
60.0 75.0
Motor Starting with Reduced Voltage
75.0 94.0
Starting a motor with full voltage will bring it to full speed
in less than 1/2 second. This can:
• Spike the load current, causing brief voltage dips in
• Over-stress pump and piping components because of
• Cause water hammer.
Motor Starters (3-Phase Only)
Various types of motor starters are available.
Autotransformers are recommended because of reduced
current draw.
When motor starters are used, they should supply
a minimum of 55% of rated voltage for adequate
starting torque.
Risk of electrocution. Use transfer

Special Applications

3' per second.
other equipment.
high torque.
11