6.Optimum size of Components
The electric motors used in ESP service belong to the most common type of electricmotors and are three-phase, two-pole, squirrel cage inductionmotors. These work on the principle of the electromagnetic induction that states that n electric current is induced in any conductor moving in relation to a magneticfield. The magnetic field is generated in the stator, the standing part of the motor containing one coil for the each phase. This field rotates with the changes of direction of the AC current because the electromagnets change their magnetic poles twice for every cycle of the AC current.To select the proper motor size for a predetermined pump size, you must first determine the brake horsepower required by the pump. The horsepower per stage is obtained by again referring to the performance curve for the selected pump and reading the value of the right scale. The brake horsepower required to drive a give pump is easily calculated by the following formula:
BHP = Total Stages x BHP/Stage x Sp. Gr. Refer to catalog for motor specifications.
"Motor drives the Seal Section, Intake/Gas Separator and pump ESP Motor are two pole, three phase, AC, induction type motor, rated in Horse Power HP .The HP can be High Volts and Low Amps or High Amps and Low Volts Rotor speed approximately 3500 RPM at 60 Hertz Constructed of rotors and bearings stacked on the shaft with a wound stator Contains oil for lubrication, heat dissipation and insulation Relies on the fluid specific heat and flow rate past motors for cooling"
Motor operating temperature is determined by 5 factors
a.Wellbore Temperature BHT
b.% Load VS. Nameplate Rating
c.Fluid Velocity Past Motor (Motor OD against casing ID)
d.Cooling Properties of the Well Fluid (% gas, water cut, scaling,etc.)
e.Power Quality, 3 Phase Imbalance, waveform distortion
All of the above factors determine if, and when, a motor will overheat
Note: Insulaltion life is decreased in half for every 10 degree C rise in temp (e.g. Class N insulation rated for 200,000 hours at 200C. If temp rises to 210C, life expectancy drops to 100,000 hours. And vice versa
The largest diameter that will fit in the casing, will be a shorter motor for same HP (Deviated wells, greater fluid velocity) Its cheaper to build, shorter larger diameter motor less components for same HP, more HP per foot.
Rating Selection
a.Standard Option Low Operating temperatures
b.High Temperature High Rated Operating temperatures
c.XTI Motors - E Series Motors Extra High Temperature Very High Rated Operating temperatures TR 5 Series only at this time (other series under development) (program is used to confirm actual operating temperature)
Qd (desired production rate) used to calculate velocity of fluid past the motor (Engineering Data)
Qd = 1000BPD
400 Series Motor
5 ½ Casing
Fluid velocity greater than 1 ft/sec
Cooling properties due to well fluid velocity OK
If the fluid passing the motor is a mixture of oil, gas and water care must be taken to size the motor adequately to ensure correct cooling
Chart shows motor heat rise above ambient temperature vs fluid velocity passing the motor At 1ft/sec and higher, no additional cooling is occurring Oil has lower specific heat than water, allows motor temperature to rise nearly twice as much as water.
Gas is worse
Shaft Selection
Shaft Selection
400 Series TR 4 Motor
Fixed Speed Application 60Hz
STD Shaft = 490 HP
Loading (60/490)x100 = 12%
HS Shaft = 662 HP
Loading (60/669)x100 = 9%
High and low cost options are both
available for this application
Motor Loading
Motor Loading Comparison Loading 100%, 85% & 75% RPM, higher loads increase slip resulting in slower Motor & Pump speed, slight reduction in production From Graph Best Efficiency Above 70% and fairly constant 70% to 120% motor loading Motor Amps increase proportional to motor loading.
Low Amps, High Volt Options
Recommended wherever possible considering surface voltage limitations Lower Amps , reduced I2R losses, possible reduced cable conductor size Lower capital costs.
Low Volts, High Amps Option.
Local Power Utility might force the Low Voltage High Amp Option Cheaper topside equipment to suit local utility supply.
Seal Selection
Isolation
Isolates the well fluid from clean motor oil
Equalization
Equals the pressure between the annulus and inside motor housing
Absorption
Absorbs the thrust of the pump
Expansion
Provides space for motor oil expansion due to thermal cycling
Bag/Bladder
Isolates the clean motor oil from the well fluid; Expansion capacity due to thermal cycling of the motor
Labyrinth Chamber
Isolates the clean motor oil from the well fluid; Expansion due to the thermal
cycling of the motor oil in near vertical wells
Thrust Bearing
Protects motor from thrust loads from above
Mechanical Seals
Prevents fluid from migration down the shaft isolating the clean motor oil from the well fluid
“…the seal’s only purpose in life is to protect the motor while surviving the downhole conditions itself as well as the thrust from the pump.”
Well Deviation
• Labyrinth or Bag type seals can be used in near vertical wells
• Bag type seals must be used in deviated wells
Well Conditions
• Higher temp wells need larger volumetric expansion & premium rate elastomers
• Chemical treatment can damage bag material
Customer Economics
• Tandem seals can provide longer run life
• Use in high cost workovers
Customer inventory issues
Motor Size
Match the Seal to Motor and Pump Series Must be smaller diameter than Motor.
Labyrinth has advantages over bag and should be considered the seal
of choice or upper seal in tandem configuration.
Bag must be used when:
• Well Deviation >45°
• Well bore fluid & Motor Oil SG too close
To calculate Expansion Compensation
• Add oil volume of motor & accessories
• Add oil volume of seal section
• Calculate motor temperature rise
• Calculate volume of oil expansion
• Check expansion capacity of seal upper chamber
• Calculate loss of oil volume due to deviation
Motor Oil Volume
If model of motor not listed use next biggest Add accessory volumes Add volume of all motors in tandem motor string (table available in Sizing Manual)
Table 1: Oil Capacities of Motor & Accessories
60HP Motor = 3573ml
Bolt on Base = 125ml (CT motor only) Total = 3698 ml
Seal Oil Volume
Using Table 11 find the oil volume for the model of seal to be used Add to Motor & Accessories Volume
Motor Oil Volume + Seal Oil Volume = Total Oil Capacity
Table 2: Oil Capacity of Seal Section TR4 Seal Standard Oil Volume STD
STD = 5375ml
Total Oil Volume
Motor + Base = 3698 ml
STD = 5375 ml x 2
Motor, Base & Seal = 14448 ml
Expansion determined by temperature rise in oil from BHT to operating temperature
Must know fluid velocity & oil cut to use equation & graph
Where:
MT = Motor Temperature Rise
OR = Temperature Rise in 100% Oil
WR = Temperature Rise in 100% Water
MT = (OR-WR)*Oil% + WC
MT = Motor Temp Rise Δt
OR = Temp rise in 100% Oil
WR =Temp rise in 100% Water
Fluid Velocity = 2.84 ft/sec
Δt Due to Water SGw = + 45°F
Δt Due to Oil SGo = + 88°F
MT = (OR-WR)*Oil% + WR
OR = 88°F WR =45°F
20% Oil = 0.2
MT =(88-45)* 0.2 + 45
MT= 53.6 °F
BHT = 155°F
Operating Temp 208.6°F
Temp Rise = OT – BHT
= 208.6 – 155°F
= 53.6°F
Thrust Loading
Thrust capability based on:
• Oil used in system
• Operating temperature of oil
• Operating speed of system
Also consider operating temperature of bearing
(HL bearing for applications >180F BHT, Babbit melts at 230°F)
1. Force Acting on top of Pump Shaft
2. Weight of Pump Shaft
3. Weight of Seal Shaft
Compression pumps have additional loads:
1. Weight of the impellers and the
2. Hydraulic loading on the impellers
Motor is not designed to support this downward force, the thrust bearing supports and absorbs this thrust
Thrust loading for a floater pump:
TL = (LPS x Number of stages x MG) x Shaft Area
Load (lb) = Pressure x Area
π΄= ππ₯(ππ’ππ πβπππ‘ π·ππ) π↑2β/4β
= (π x 0.8752)/4 =0.60 inch2
Thrust loading for floater pump:
ππΏ=(πΏππ π₯ ππ’ππππ π π‘ππππ π₯ ππΊ)π₯πβπππ‘ π΄πππ
ππΏ=(30.3 π₯ 124π₯ 0.428)π₯0.60=ππππππ
Note: Shaft Area
Load (lb.) =Pressure (PSI) x Area (in2)
Load Due to TDH = 965Ib
Load Pump Shaft = 20Ib (est)
Load Seal Shaft = 15lb (est)
Thrust Bearing Load = 1000lb
Percentage Load at 60Hz
(1000/4400)x100 = 23% loading
