Flowserve Pump Division - 17
Insulation Testing
Flowserve Pump Division recommends that the motor winding insulation be checked once the unit is in
place and prior to applying power to the unit. If the insulation resistance of the motor winding and power
supply cable is to be tested, use an instrument designed for this purpose (500 VDC). To measure the
insulation resistance, use to following procedure:
1. Disconnect all leads of the power supply cable and clean them carefully.
2. Measure the insulation resistance between one cable core and ground. All other cable
leads are kept away from ground during this procedure.
3. The insulation resistance of the new motor measured at the factory exceeds 500 mega-
ohms (connected to frame). If the test results in an insulation value less than 6 mega-
ohms, contact Flowserve Pump Division.
WARNING: WINDINGS AND POWER SUPPLY CABLES WILL, DURING INSULATION TESTING,
BE CAPACITIVELY CHARGED TO THE TEST VOLTAGE.
THE BARE CABLE ENDS MUST NOT BE TOUCHED DURING THE TEST AND
BEFORE THE WINDINGS AND CABLE BARE CONDUCTORS HAVE BEEN
DISCHARGED.
AFTER COMPLETION OF THE TEST, DISCHARGE THE CABLES BY APPLYING
THE CABLE BARE CONDUCTORS TO THE PROTECTIVE GROUND CONNECTION.
Current and Voltage Imbalance
Upon installation, the amount of current imbalance should be calculated. The pump should be operated
while submerged to simulate normal operating conditions and the current imbalance should be calculated
as described below. Current imbalance between phases should not exceed 4%. The current imbalance
is defined as follows:
Imbalance = (max current - average current of the three phases) / average current of the three phases
The current imbalance will further increase any imbalance in the line voltage. It is advisable to find the
"most even" balance by changing the phase connections of the motor in a clockwise order until the
smallest difference is obtained.
An imbalanced voltage of more than one percent will result in an even larger imbalanced current and
excessive heat generation. The motor should be derated according to NEMA MG-1, 14.35 in order that
the winding temperature not affect the life of the motor.
Motor Overload Protection
A motor overload relay with an approved heater element is to be used. Overload protection and
grounding should be in accordance with the National Electric Code and also be consistent with sound
local practices.
Protection Against Inadmissible Starting Frequency
Flowserve Pump Division recommends protecting the motor from frequent restarting via a time delay
relay. The frequency of restarts should not exceed recommendations by NEMA MG-10, Table 7.
If additional starts are required, it is recommended that none be made until all conditions affecting
operation have been thoroughly investigated and the motor is checked for excessive heating. The
number of starts should be minimized in order to maintain the life of the motor.
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