Figure 3.2.3 : Common subsea motor with pump assembly .
compact water pump ( usually a centrifugal pump ) has to be capable of operating up to 4000 RPM at its maximum performance thus a hydraulic motor that has the same or more RPM is needed to drive the pump .
Alternatively , a water pump can be directly driven by an electrical motor , but the motor will normally be in a 2-pole type . Only a 2-pole motor can provide more than 3500 RPM to run most of the suitable water pumps for the trenching system . Details of the trenching unit will be explained later .
3.3 Vehicle Electrical and Control System
The main source of power for a trenching ROV is normally provided by the ship ’ s power unit . However , a generator set is provided on the ROV as a contingency power supply . The main power source supplies power to the control cabin and the surface hydraulic power unit for the winch and A-frame control . There is a termination cabinet and power distribution unit ( PDU ) inside the control cabin where the power from the main supply is distributed according to the requirement for three phase ( 3000VAC ) or single phase ( 1200VAC ) equipment . A transformer is installed to step down the main supply where required .
Referring to Figure 3.3.3 , the 3000V supply is directed to the main HPU of the trencher while the 1200V is supplied to a subsea step-down transformer to supply all the auxiliary systems such as camera , lights , sensors , sonar , valve packs , etc .
The control cabin is the pilot control station where the overall trencher system is controlled and monitored . There are two methods of communicating with the subsea trencher , one is using fibre optic and the other using hard wire .
Figure 3.2.4 : A directly mounted water pump on to an electrical motor . ( Source : SilverCrest Submarine Pte Ltd ).
Figure 3.2.5 : Water pump unit using a hydraulic motor . ( Image from : Q1000 Reef Jet Trencher by SMD - Subsea Animation – YouTube )
Figure 3.2.6 : Another example of a hydraulic motor mounted water stage pump from WeSubsea UK Ltd .
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