BENEFITS OF VARIABLE
SPEED DRIVES FOR
SUBSEA PRODUCTION AND
WELLHEAD HYDRAULIC
POWER UNITS
METHODS OF SUBSEA HYDRAULIC SUPPLY PRESSURE CONTROL
Options for pressure control of subsea hydraulic systems:
1. Gap Control – On‐Off Control of Electric Motor Driven pumps
2. Pressure Regulation – pressure reducing valves
3. Gap control with variable speed electric motor driven pumps
TYPICAL SUBSEA LAYOUT
SUBSEA HYDRAULIC SYSTEM
SUBSEA HYD SYSTEM SCHEMATIC SUBSEA HYD SYSTEM – PHPU SCHEMATIC
SUBSEA HYD SYSTEM – SCM SCHEMATIC
SUBSEA HYD SYSTEM – PHPU, GAP CONTROL
SUBSEA HYD SYSTEM – PHPU, GAP CONTROL
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Simplest, lowest cost
Minimal internal leakage
Higher accumulation
More frequent pump starts
SUBSEA HYD SYSTEM – PRESSURE REGULATION
PRESSURE REGULATION
Sectioned Pressure Regulator
‐ Control Spring
‐ Sensor (piston)
‐ Vent Seat
‐ Main Valve Seat
Variable outlet pressure
Minimum = Set point
Maximum = Internal relief setting
Outlet pressure within the min/max is dependent on relative internal leakage of regulator and downstream components.
PRESSURE REGULATION
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Highest internal Leakage
Higher maintenance
Higher variation in pressure
Allows independent pressure control
SUBSEA HYD SYSTEM – GAP CONTROL WITH VSD
GAP CONTROL WITH VSD –
SPEED/FLOW v PRESSURE
GAP CONTROL WITH VSD •
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•
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Lowest pressure variation
Least pressure cycling system fatigue
Lowest maintenance
Lower accumulation
ACTUAL PRESSURE TRENDS DATA – 3 OPTIONS
BENEFITS OF VSD DRIVEN PUMPS FOR PHPU’S
Pump Starting
Criteria
Single Speed Electric Motor Driven Pump (Gap control with or without pressure regulation)
Variable Speed Electric Motor Driven Pump
Pump starting
Motor starts abruptly at maximum speed
Soft-start capability.
Pressure spikes on start up
High
Low
Frequency of Pump Starts
High
Low
Flow rate
Constant at the maximum flow irrespective of demand.
Variable to match demand
Accumulator Capacity Required
High
Low
BENEFITS OF VSD DRIVEN PUMPS FOR PHPU’S
Pressure Variation
Criteria
Single Speed Electric Motor Driven Pump (Gap control with or without pressure regulation)
Variable Speed Electric Motor Driven Pump
Output Pressure Fluctuation
High.
Low.
(without pressure regulation)
1.0 ~ 2.0 MPa
0.2 ~ 0.5MPa
Output Pressure Fluctuation
High.
Low.
(with pressure regulation)
1.0 ~ 2.0 MPa
0.2 ~ 0.5MPa
BENEFITS OF VSD DRIVEN PUMPS FOR PHPU’S
Internal Leakage, Maintenance, Space envelope, Life Cycle Cost
Criteria
Internal Leakage
Single Speed Electric Motor Driven Pump (Gap control with or without pressure regulation)
Variable Speed Electric Motor Driven Pump
High
Low
Very High
Low
Component Fatigue
High
Low
Maintenance
High
Low
Space envelope
High
Low
Life cycle cost
High
Low
(without pressure regulation)
Internal Leakage
(with pressure regulation)
VSD SYSTEM DESIGN CONSIDERATIONS
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Motor cooling at slow speed.
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Consider oversizing motor so there is adequate cooling for motor running continuously at slowest speed for worst case ambient conditions.
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Electric motor supplier can provide motor simulation data
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Adequate motor overload and thermal protection – thermistors
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Filters to remove harmonic distortion •
Shielded power supply cables with 3 symmetrical grounding wires from VSD to electric motors to minimise Radio Frequency/Electro Magnetic Interference EMI/RFI
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Parameter set points on VSD will need adjustment for optimum performance and monitoring Thankyou for your interest.
Questions welcome.