The power system is configured with equipment in series. In a long chain of equipment, system efficiency and reliability both suffer in the following way.
System efficiency = Multiplication of all individual equipment efficiencies
System reliability = Multiplication of all individual equipment reliabilities
For this reason, long chains of equipment in series should be avoided for good system design.
A water pumping line has a chain of equipment in series from the prime mover to the end pump that must deliver 1000 hp output.
Efficiency of ship water pump
The motor is powered via cable and a step-down transformer connected to a dedicated 3-phase generator.
Assume the following efficiencies:
- generator 97%
- transformer 98%
- cable 99%
- motor 96%
- pump 95%
The efficiencies of series equipment multiply; hence, the total efficiency of the power delivered from the prime mover to the end pump is
ηTotal = ηpump × ηmotor × ηcable × ηtrfr × ηgen = 0.95 × 0.96 × 0.99 × 0.98 × 0.97 = 0.8583
Ship prime mover output calculation
Prime mover output = 1000 hp motor output ÷ 0.8583 overall efficiency = 1165 hp