USEFUL INFORMATIONS

GENERATOR SIZING

Power Factor Correction

Statutory regulations make it necessary to increase the power factor of a submersible motor. The table lists the capacitive KVAR required to increase the power factor of Deccan three phase submersible motors to the approximate values shown. Capacitors must be connected on the line side of the overload protection will be lost.

Splicing Submersible Cables

When the drop cable must be spliced or connected to the motor leads, it is necessary that the splice be watertight. This splice can be made with commercially available potting , heat shrink kits , or by careful tape splicing.

Tape splicing should use the following procedure.

1. Strip individual conductor of insulation only as far as necessary to provide room for a stake type connector outside diameter (OD ) is not as large as cable insulation , build up this area with rubber electrical tape.

2. Tape individual joints with rubber electrical tape , using two layers , with the first layer extended two inches beyond each end of the conductor insulating end , and the second layer extending two inches beyond the ends of the first layer. Wrap tightly, eliminating air spaces as much as possible.

3. Tape over the rubber electrical tape with electrical tape, using two layer, overlap the end of the preceding layer by at least two inches.

In case of a cable with three conductors encased in a single outer sheath , tape individual conductors as described , staggering joints. Total thickness of tape should be no less than thickness of the conductor insulation.

Shaft height and free end play

CURRENT UNBALANCE

Checking and correction rotation and current unbalance

1. Established correct motor rotation by running in both directions. Change rotation by exchanging any two of the three motor leads. The rotation that gives the most water flow is always the correction rotation.

2. After correct rotation has been established, check the current in each of the three motor leads and calculate the current unbalanced as explained below. If the current unbalance is 5% or less, leave the leads as connected.

3. To calculated percent of current unbalanced:

   1. Add the three line amps values together.

   2. Divide the sum by three , yielding average current.

   3. Pick the amp value which is furthest from the average current ( either high or low ).

   4. Determine the difference between this amp value current ( furthest from average ) and the average.

   5. Divide the difference by the average. Multiply the result by 100 to determine percent of unbalance.

4. Current unbalance should not exceed 5% at full load. If the unbalance cannot be corrected by rolling leads, the source of the unbalance must be located and corrected. If, on the three possible hookups, the leg farthest from the average stays on the same power leads , most of the unbalance is coming from the power source. However, if the reading farthest from the average moves with the same motor leads , the primary source of unbalance is on the “motor side” of the starter . in this instance, consider a damage cable , leaking splice , poor connection , or faulty motor winding.
   

EXAMPLES:

DISCHARGE CHART

TYPE OF STARTERS

Direct On Line (DOL) Motor Starter

Different starting methods are employed for starting induction motors because Induction Motor draws more starting current during starting. To prevent damage to the windings due to the high starting current flow, we employ different types of starters.

The simplest form of motor starter for the induction motor is the Direct On Line starter. The Direct On Line Motor Starter (DOL) consist of a Contactor and an overload relay for protection.

Typically, the contactor will be controlled by separate start and stop buttons, and an auxiliary contact on the contactor is used, across the start button, as a hold in contact. I.e. the contactor is electrically latched closed while the motor is operating.

Star Delta Starter

In star delta starter then motor is started initially from star and later during running from delta. This is a starting method that reduces the starting current and starting torque.The Motor must be delta connected during a normal run, in order to be able to use this starting method.

The received starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start. The Star/Delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. The currents through the winding are 1√3 = 0.58 (58%) of the current in the line. this connection amounts to approximately 30% of the delta values. The starting current is reduced to one third of the direct starting current.

Auto Transformer starters

To start the motor the switches are closed. This supplies the motor a lower voltage from the autotransformer. The lower voltage limits the input current to the initially stationary motor, which accelerates. The torque of the motor is also lowered.

The motor continues to increase its speed until the motor torque and the load torque balance each other and a steady speed is achieved. At this stage one switch is opened and momentarily the motor is supplied by even lower voltage, because the windings of the autotransformer act as inductors connected in series with motor. This time is short - just enough to disconnect this and engage other switch, which connects the full voltage to the motor. Further increase in speed begins and motor reaches its full rated speed.

At this point the "soft start" is ended and motor can work under full load. The autotransformer is no longer required and is de-energized by opening first switch. The motor is supplied directly from the three-phase network. To stop the motor, one more switch is opened.

Flex Compensated Magnetic Amplifiers (FCMA)

These Soft Starters work on “Flux Compensated Magnetic Amplifier basis, (FCMA). This is innovative technology for incremental motor voltage & torque at constant reduced current. The technology has received wide global acceptance & many FCMA Soft Starters are operating satisfactorily in India & Abroad. FCMA Soft Starters are step less reduced voltage starters, which provide a constant low starting current with incremental voltage & torque characteristics to accelerate the motor & pump from stand still to full speed smoothly without any jerks.

The FCMA is connected in series with the motor either on the line or neutral side, so that the starting current is limited to a low value. The motor starts smoothly with the reduced current & the reduced torque. As the motor speed increases the impedance of FCMA reduces steplessly to keep the current constant and increase the motor torque so that the load is accelerated.

The FCMA works on the principle of superimposition of sinusoidal fluxes on a common magnetic core where the net flux is the vector sum of the two components. As the net flux is sinusoidal the FCMA does not generate any harmonics. The motor current is kept constant due to the balancing effect of Cemf feedback. If the motor current tends to increase the main winding flux will increase thus increasing the total flux & increasing the FCMA impedance & reducing the current to the original value. The FCMA is thus primarily a constant current controller & naturally provides current limiting action during the acceleration.

Soft Starters

A soft starter continuously controls the three-phase motor’s voltage supply during the start-up phase. This way, the motor is adjusted to the machine’s load behavior. Mechanical operating equipment is accelerated smoothly. Service life, operating behavior and work flows are positively influenced. Electrical soft starters can use solid state devices to control the current flow and therefore the voltage applied to the motor. They can be connected in series with the line voltage applied to the motor, or can be connected inside the delta (Δ) loop of a delta-connected motor, controlling the voltage applied to each winding. Solid state soft starters can control one or more phases of the voltage applied to the induction motor with the best results achieved by three-phase control. Typically, the voltage is controlled by reverse-parallel-connected silicon-controlled rectifiers (thyristors), but in some circumstances with three-phase control, the control elements can be a reverse-parallel-connected SCR and diode.

Variable Frequency Drives, VFD

A variable frequency drive is used for adjusting a flow or pressure to the actual demand. It controls the frequency of the electrical power supplied to a pump or a fan. Significant power savings can be achieved when using a VFD.

A variable-frequency drive is a system for controlling the rotational speed of an alternating current electric motor. It controls the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, or inverter drives.

Reasons for employing automatic frequency control can both be related to the functionality of the application and for saving energy. For example, automatic frequency control is used in pump applications where the flow is matched either to volume or pressure. The pump adjusts its revolutions to a given set point via a regulating loop. Adjusting the flow or pressure to the actual demand reduces power consumption.

Water Flow around Motor

Deccan submersible motors are designed to operate up to full load horsepower in water Upto 30⁰ C. A flow of 7.62 cm/sec for 4” motors and 15.24 cm/sec for 6 and 8 inch motors is required for proper cooling. Table shows minimum flow rates, in Ipm, for various well diameters and motor sizes.

If the motor is operated in water over 30⁰ C, water flow past the motor must be increased to maintain safe motor operating temperatures.