Startup; Startup With Three-Phase Motors - Grundfos SP Series Installation And Operating Instructions Manual

4. Startup

After the pump has been set into the well and the
wiring connections have been made, the
following procedures should be performed:
1. Attach a temporary horizontal length of pipe
with installed gate valve to the riser pipe.
2. Adjust the gate valve one-third of the way
open.
3. On three-phase units, check direction of
rotation and current unbalance according to
the instructions below. For single-phase units
proceed directly to 4.1.3 Developing the well
on p. 11.
4. Under no circumstances should the pump be
operated for any prolonged period of time with
the discharge valve closed. This can result in
motor and pump damage due to overheating.
A properly sized relief valve should be
installed at the well head to prevent the pump
from running against a closed valve.

4.1 Startup with three-phase motors

4.1.1 Check the direction of rotation
Three-phase motors can run in either direction
depending on how they are connected to the
power supply. When the three cable leads are
first connected to the power supply, there is a
50 % chance that the motor will run in the proper
direction. To make sure the motor is running in
the proper direction, carefully follow these
procedures:
1. Start the pump and check the water quantity
and pressure developed.
2. Stop the pump and interchange any two leads.
3. Start the pump and again check the water
quantity and pressure.
4. Compare the results observed. The wire
connection which gave the highest pressure
and largest water quantity is the correct
connection.
4.1.2 Check for current unbalance
Current unbalance causes the motor to have
reduced starting torque, overload tripping,
excessive vibration and poor performance which
can result in early motor failure. It is very
important that current unbalance be checked in
all three-phase systems. Current unbalance
between the legs should not exceed 5 %
under normal operating conditions.
The supply power service should be verified to
see if it is a two or three transformer system. If
two transformers are present, the system is an
"open" delta or wye. If three transformers are
present, the system is true three-phase.
Make sure the transformer ratings in kilovolt
amps (KVA) is sufficient for the motor load;
see section 7.3 Transformer capacity required
for three-phase submersible pump motors on
p. 20.
The percentage of current unbalance can be
calculated by using the following formulas and
procedures:
Total of current values
Average
=
current
Greatest amp
difference from
% Current the average
=
unbalance
average current
To determine the percentage of current
unbalance:
1. Measure and record current readings in amps
for each leg (Hookup 1). Disconnect power.
2. Shift or roll the motor leads from left to right so
the drop cable lead that was on terminal 1 is
now on 2, lead on 2 is now on 3, and lead on 3
is now on 1 (Hookup 2). Rolling the motor
leads in this manner will not reverse the motor
rotation. Start the pump, measure and record
current reading on each leg. Disconnect
power.
3. Again shift drop cable leads from left to right
so the lead on terminal 1 goes to 2, 2 to 3 and
3 to 1 (Hookup 3). Start pump, measure and
record current reading on each leg.
Disconnect power.
4. Add the values for each hookup.
5. Divide the total by 3 to obtain the average.
6. Compare each single leg reading from the
average to obtain the greatest amp difference
from the average.
7. Divide this difference by the average to obtain
the percentage of unbalance.
Use the wiring hookup which provides the lowest
percentage of unbalance. See section
7.6.4 Correcting for three-phase power
imbalance on p. 25 for a specific example of
correcting for three-phase power unbalance.
4.1.3 Developing the well
After proper rotation and current unbalance have
been checked, start the pump and let it operate
until the water runs clear of sand, silt and other
impurities.
Slowly open the valve in small increments as the
water clears until the desired flow rate is reached.
Do not operate the pump beyond its maximum
flow rating. The pump should not be stopped
until the water runs clear.
If the water is clean and clear when the pump is
first started, the valve should still be slowly
opened until the desired flow rate is reached.
As the valve is being opened, the drawdown
should be checked to ensure the pump is always
submerged. The dynamic water level should
always be more than 3 feet (0.9 m)above the
inlet strainer of the pump.
Disconnect the temporary piping arrangements
and complete the final piping connections.
measured
on each leg
3
X 100
11