ESP Motor consists of a stator housing, head and base and rotor-shaft subassembly. Three-phase power is fed through the cable pothead into the motor head, to the stator windings causing the rotor-shaft subassembly to rotate, delivering torque to the pump.
The stator takes electrical energy (KVA) from the surface and converts this to magnetic energy in the stator laminations.
The magnetic field of the stator induces current (electrical energy) flow in the rotor.
This electrical energy in the rotor induces a secondary magnetic field in the rotor laminations.
The magnetic poles of the rotor will be attracted to (and repelled by) the magnetic poles in the stator.
As the stator magnetic field moves, the rotor will move to try to follow it.
The Downhole Electric Motor :
- 3 phase
- Squirrel cage : Because the structure resembles the cage used to exercise squirrels, rotors of this type are called “Squirrel-Cage” rotors.
- 2 pole
- Induction Motor.
Motor Construction :
1-Stator :
Because of the way the stator is wound, the three phase power establishes a two pole magnetic field within the stator.
The stator is the core or electrical field of the motor.
The stator is composed of the housing material for a desired diameter, the stator core, and the stator windings .
The stator core is composed of laminations stacked under pressure to insure a permanently tight core.
Laminations are thin sheets of die-punched steel or bronze material.
The stator is hand wound by experienced craftsmen. Each stator is wound in three phases with the determined amperage and voltage for each order placement.
The windings are made from either Polyimid or PEEK material, for primary magnetizing winding wound through the die-punched slots in the stator core.
The rotor is a device that rotates inside of the stator core.
The rotor is made up of rotor laminations that are smaller in diameter from the stator laminations and these creates the iron core. Inside each slot are copper bars with supporting copper end rings.
The bars are shorted together at each end by a rotor “end ring”. Depending on the motor, the end ring is either braided or brazed to the rotor bars.
3- Rotor Bearings :
The Bearing Material is Babbitt-lined steel and machined after processing. There are fluid holes to insure oil circulation and wide angle oil grooves on the OD to distribute lubrication evenly over the entire length of the bearing surface.
The bearing sleeve is a bronze material for the sleeve construction of the bearing. This part is keyed to the shaft and the hole on the sleeve is aligned with the hole on the shaft to insure proper cooling and lubrication.
Its main purpose is to provide the axial and radial thrust capabilities.
4- Thrust Bearing :
The motor thrust bearing is installed at the top of the rotor string. It is designed to hold the weight of the entire rotor assembly.
The thrust bearing limits on the system will indicate the type of load required for the selected bearing material.
5- Pothead :
There is tape-in potheads and plug-in type for motor lead connection to the pothead.
Historically tie in potheads have been more reliable than plug in ones.
The disadvantage is the time taken for connections.
Tandem Motor Configuration :
Motors may be combined in tandem to provide the total power required by larger pumps
The motors should preferably be identical, with the same power ratings, and nameplate voltages and currents.
With two motors we double the HP (add the two HP’s together). We also double the voltage but the amperage remains the same.
Always take care when adding motors together so that the total voltage does not exceed the system limits. For example do not try to put 3400 volts on a 3 kV cable.
The top tandem motor is always a UT, the middle section(s) is a CT, and the bottom most is either an LT or a CT depending on whether a sensor will be installed or not. Depending on the type of motor, an adapter is required.
1- Single Section (S) - The motor head is designed to accept the power cable connection on top. The base has an integral "Y" connection at the bottom connecting the windings together and cannot be connected in tandem with any other motor.
2- Center Tandem (CT) - The motor head is designed to connect to the bottom of an upper tandem or center tandem motor and a base designed to connect to another center tandem motor, a lower tandem or a universal base. All flange connections are designed so that windings from one motor will connect to the corresponding windings
of the adjacent motors.
3- Upper Tandem (UT) - The motor head is designed to accept the power cable connection on top and either a center tandem motor, lower tandem motor, or universal base on the bottom.
4- Lower Tandem (LT) - The motor head is designed to connect to the bottom of an upper tandem or center tandem motor and an integral "Y" connection at the bottom connecting the windings together.
UMB is a Universal Motor Base. Use a UMB to provide a filter base on a UT or CT motor where no integral gauge is used.
UMH is a Universal Motor Head. Use a UMH to convert a CT or LT motor to connect to the protector and flat cable, but generally this should be a last-resort for emergencies.
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