DC Drive Motor Protection via Current Detection and Dynamic Resistor Control
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Solution Overview
Problem
Direct current electrical networks in underwater and surface vehicles face significant dynamic and thermal loads due to high short-circuit currents, which can lead to critical damage, such as 'commutator fire', during propulsion mode changes.
Innovation Solution
Incorporating a current measuring device to detect current increases at the direct current source and a controller to influence the motor phase, with a starting resistor connected upstream of the DC drive motor, and a circuit breaker for dynamic switching to reduce starting currents and prevent commutator fires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC motor operates in propulsion mode without protection, then the motor can function normally, but short-circuit currents cause dynamic and thermal loads leading to commutator fire and major damage
Solution Approach 1:
The current measuring device continuously monitors current at the DC source before a short circuit can cause damage. The controller is pre-programmed with protection logic that automatically activates when threshold values are exceeded, enabling preventive action before commutator fire occurs
Solution Approach 2:
The controller acts as an intermediary between the current measuring device and the DC motor, receiving current measurements and translating them into protective actions by controlling power semiconductor switches to limit or interrupt fault currents
2Ease of operation
If the starting resistor is permanently connected to reduce starting current, then the motor starts smoothly, but the resistor causes unnecessary energy loss during normal operation
Solution Approach 1:
The circuit breaker dynamically switches the starting resistor in and out of the circuit based on operating conditions. During motor startup, the breaker closes to include the resistor for current limitation. During normal operation, the breaker opens to exclude the resistor, eliminating energy loss while maintaining motor performance
Solution Approach 2:
The starting resistor is periodically connected only during the startup phase when needed, then disconnected for the remainder of operation. This periodic activation based on operational stage requirements optimizes both starting performance and energy efficiency
3Reliability
If the circuit breaker switches on the starting resistor during a short circuit, then the short-circuit current is limited, but the switching response time must be sufficiently fast to prevent damage
Solution Approach 1:
The current measuring device provides continuous real-time feedback on current magnitude and rate of change to the controller. This feedback enables the controller to detect short-circuit conditions immediately and trigger the circuit breaker without delay, achieving fast response times necessary for protection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables early detection and mitigation of short-circuit currents, reducing the dynamic and thermal load on the network, preventing commutator fires, and ensuring reliable protection of the direct current system by limiting or switching off the direct current.
Implementation Method 1
at least one starting resistor for reducing a starting current being connected upstream of the respective DC drive motor
Implementation Method 2
at least one current measuring device for detecting a current and/or current increase at the at least one direct current source
Data Source
Figure 1
Figure 2
AI summary
The invention relates to an electrical DC power supply system for underwater and above-water vessels and for offshore installations with at least one DC source (12, 13) arranged in a respective source phase and at least one DC drive motor (2) arranged in a respective motor phase. Furthermore, the invention relates to a method for influencing a direct current flowing in a DC power supply system. In order to ensure improved protection in the event of a short circuit in an electrical DC power supply system, it is proposed to provide in each case at least one current-measuring device (14, 15) for detecting a current and/or current rise at the at least one DC source (12, 13) and at least one controller (4) for influencing a direct current flowing in the respective motor phase of the DC power supply system if the current and/or current rise detected by the at least one current-measuring device (14, 15) is greater than a predeterminable current and/or current rise.