Ship Motor Starting Current, Voltage Dip & Generator Capacity Tool

Starting Current • Bus Voltage Dip • Locked-Rotor kVA • Generator Transient Strength • Start Sequencing • N-1 Capacity

Ship Motor Starting Current, Voltage Dip & Generator Capacity Tool

Screen shipboard motor starts against the actual generator bank instead of comparing motor kW with generator kW. Simple mode estimates starting current, locked-rotor kVA, initial bus-voltage dip and generator requirement. Advanced models multiple motors, start overlap, multiple generator sets, equivalent subtransient source strength, N-1 operation, voltage-squared torque retention and start-sequence risk.

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Eight inputs, focused on the start that stresses the bus.The allowable voltage dip is deliberately user-entered. Class, OEM, starter, contactor and vessel-specific requirements remain controlling.

MotorStarting amps & kVA

BusInitial voltage dip

GenerationCapacity & reserve

Motor Start

Motor rated currentA at rated voltage.

Ship bus voltageV line-to-line, 3-phase.

Starting current multipleLocked-rotor / limited-start current ÷ rated current.

Starting power factorUse motor/starter data where available.

Generator Bank

Online generator capacityTotal online generator kVA.

Equivalent generator Xdʺ% on the online-bank base. Use OEM transient/subtransient data.

Pre-start generator load% of online kVA, modeled at 0.85 PF.

Maximum allowable voltage dip% user-entered project/class/OEM criterion.

System Limits & Starting Study

Bus voltage

Frequency

Maximum allowable voltage dip% user-entered.

Target generator kVA reserve after start% of online bank kVA.

N-1 voltage-dip target% user-entered contingency screen.

Existing-load PF

Generator Register

Equivalent source strength is calculated from each online generator's kVA and entered Xdʺ. Pre-start load is shared in proportion to online kVA.

Use	Available?	Name	Rated kVA	Xdʺ %	Pre-start load %

Motor Starting Sequence

Start time and acceleration duration allow overlapping starts. Enter the effective starting-current multiple produced by the actual starter. The method label is descriptive; the entered current multiple controls the calculation.

Use	Motor / load	kW	Rated A	Run PF	Method	Start × FLA	Start PF	Start at s	Accel s	Min bus V %	Essential?

Study / Protection Checks

Generator OEM transient data checkedEntered Xdʺ/source data are suitable for the intended starting study. Starter current limit / method verifiedEffective start-current multipliers reflect DOL, star-delta, soft starter, VFD or other actual arrangements. Contactor / control undervoltage checkedControls are not assumed to ride through a deeper sag than their actual settings permit. Motor acceleration / load torque checkedVoltage-squared torque reduction is reviewed against the driven load. PMS start permissives reviewedRequired generator combinations and load-shedding logic are represented operationally. Largest idle essential motor reviewedStarting remains possible with the intended reserve / standby generator philosophy. Running-load power factor checkedPre-start generator kW/kVAr loading is credible for the operating mode. Sea-trial / measured dip comparison plannedCalculated results will be checked against actual vessel performance where applicable.

Engineering boundary: the transient-voltage model is a planning/screening calculation using generator subtransient source impedance and starting loads represented as voltage-dependent impedance. It does not replace OEM dynamic generator/AVR simulation, class approval, short-circuit studies, protection coordination or a measured vessel starting test.

Technical basis: IEC 60092-201:2019 covers system design for ship electrical installations; IEC 60092-301:2025 covers shipboard generators and motors. ABS marine rules require generator selection to consider motor starting current and, with reserve philosophy applied, sufficient capacity to start the largest idle essential motor without causing running motors to stall or control equipment to drop out. The acceptable transient voltage dip is therefore entered by the user rather than treated as a universal value.

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