Electric Power Systems Synchronization

Megohmmeter

High DC voltage

Trends in resistance values

<p>To ensure accurate comparison of results</p> Signup and view all the answers

<p>Development of problems</p> Signup and view all the answers

<p>Maintenance scheduling</p> Signup and view all the answers

<p>Fully isolate and tag out the motor</p> Signup and view all the answers

<p>Vessel's safety procedures</p> Signup and view all the answers

<p>To identify warning signs</p> Signup and view all the answers

<ol> <li>Contamination by oil / dirt - possible tracking path from windings that requires a full clean</li> <li>Phase to earth (Conductor) - If conductor insulation has failed then it will need to be replaced</li> <li>Phase to casing - Check for loose connections in terminal box, possible stray strands of the cable where a ferrule has been connected</li> <li>Flooding with water - Remove, fresh water flush and drying process measuring insulation</li> <li>Failure of winding insulation to casing - This would almost certainly require a full rewind unless the failure is external to the winding and could be re-lacquered</li> </ol> Signup and view all the answers

<ol> <li>Contamination by oil / dirt - Requires a full clean</li> <li>Phase to earth (Conductor) - The conductor insulation will need to be replaced</li> <li>Phase to casing - Check for loose connections and remove any stray strands</li> <li>Flooding with water - Remove, flush with fresh water, and dry out the insulation</li> <li>Failure of winding insulation to casing - This would likely require a full rewind, unless the failure is external and can be re-lacquered</li> </ol> Signup and view all the answers

<p>The earth lamp connection diagram for a 3 phase, 3 wire distribution system would include:</p> <ul> <li>3 phase bus bars</li> <li>Push button</li> <li>Fuses</li> <li>Lamps</li> <li>Resistances</li> </ul> Signup and view all the answers

<p>An earth fault is indicated by a reduction in brightness of the earth lamp on the faulted phase. A small earth leak on the red phase would reduce the potential difference through the red phase earth lamp, causing it to appear dimmer compared to the other two lamps.</p> Signup and view all the answers

<p>In an insulated neutral distribution system, a single earth fault will result in the generator star point being insulated. This means the line (full) voltage potential to earth will remain, making the system dangerous. However, an essential electric motor will continue to run despite the earth fault.</p> Signup and view all the answers

<p>In an earthed neutral system, the result of a single earth fault is that the current flow has a path through the hull steel and earthed neutral back to the system. This means the fault current will flow, unlike in an insulated neutral system.</p> Signup and view all the answers

<p>Contamination by oil or dirt can create a possible tracking path from the windings to earth, leading to an earth fault. The contamination provides a conductive path for current to flow from the windings to ground.</p> Signup and view all the answers

<p>If the conductor insulation has failed, causing a phase to earth fault, the only remedy is to replace the failed conductor insulation.</p> Signup and view all the answers

<p>To remedy a phase to casing fault, you need to check for loose connections in the terminal box and remove any stray strands of cable where a ferrule has been connected.</p> Signup and view all the answers

<p>In an insulated earth system with a single earth fault, the generator star point is insulated so there is no fault current, allowing essential motors to continue running. However, the system becomes dangerous. In an earthed neutral system, motors will trip with a single fault.</p> Signup and view all the answers

<p>Preferential tripping involves non-essential load shedding to protect essential supplies when initiated by a generator overload or underfrequency condition. It has a lower setting than IDMT or instantaneous trips and uses a separate timing relay with 1, 2, or 3 stages.</p> Signup and view all the answers

<p>The three necessary checks are: 1) Voltage, 2) Frequency, and 3) Phase rotation.</p> Signup and view all the answers

<p>Connecting an incorrect shore supply voltage can cause overvoltage trips to activate and unprotected systems may be damaged. Transformers will be affected based on the voltage ratio, so both higher and lower voltages pose risks.</p> Signup and view all the answers

<p>Running a 50Hz motor at 60Hz frequency is not recommended as it can potentially cause the motor to overheat and become overloaded due to the 20% higher speed.</p> Signup and view all the answers

<p>An incorrect phase rotation when connecting a shore supply can cause motors, pumps, fans, and other rotating machinery to run in the reverse direction, which may damage equipment or disrupt processes.</p> Signup and view all the answers

<p>In an insulated earth system with a single earth fault, the line voltage is raised to the full potential to earth, making the entire system operate at line voltage to ground and creating a shock hazard.</p> Signup and view all the answers

<p>The timing relay stages (1, 2, or 3) in preferential tripping allow for sequential load shedding, where less essential loads are tripped first to protect critical systems if the overload persists.</p> Signup and view all the answers

<p>Verifying phase rotation is crucial because an incorrect rotation can cause motors and other rotating machinery to run in reverse, potentially damaging equipment and disrupting processes that rely on the correct direction of rotation.</p> Signup and view all the answers

<p>When generators are in synchronism, there is no potential difference between them, and therefore no current flows. Synchronism is determined using a synchroscope, where the needle at the 12 o'clock position indicates synchronism, or by using synchronizing lamps, where no voltage difference results in the lamps being extinguished.</p> Signup and view all the answers

<p>If the No. 1 generator fails, a blackout would initially occur. The no-volt relay would activate, disconnecting the emergency switchboard from the main switchboard. The start sequence for the emergency generator would initiate, and it should start and be on load within 45 seconds, as per SOLAS regulations, to restore power to essential circuits like navigation, communications, safety machinery, and blackout recovery.</p> Signup and view all the answers

<p>An insulated neutral is preferred over an earthed neutral to keep machinery operational where possible. In an earthed neutral system, a ground fault would trip the entire system, causing a complete shutdown. With an insulated neutral, the system can continue operating even with a ground fault, allowing for repairs without a complete shutdown.</p> Signup and view all the answers

<p>In the event of a main bus-bar overload, essential circuits are protected by being separated from the main bus-bar and supplied power from an emergency generator or other backup source. This ensures that critical systems like navigation, communications, and safety machinery remain operational.</p> Signup and view all the answers

<p>Using Ohm's law, $V = IR$, where $V$ is the potential difference, $I$ is the current, and $R$ is the resistance. Given $R = 5\Omega$ and $V = 24\text{V}$, we can solve for $I$: $I = V/R = 24\text{V}/5\Omega = 4.8\text{A}$. Therefore, the potential difference across the $5\Omega$ load is $24\text{V}$.</p> Signup and view all the answers

<p>A no-volt relay is used to disconnect the emergency switchboard from the main switchboard in the event of a main generator failure or other power loss. When the voltage drops below a certain threshold, the no-volt relay activates, opening the connection between the main and emergency switchboards. This allows the emergency generator to start and supply power to essential circuits without interference from the failed main system.</p> Signup and view all the answers

<p>To synchronize two generators before paralleling them, their voltage, frequency, and phase sequence must be matched. This is typically done using a synchroscope or synchronizing lamps. The generators are brought to the same voltage and frequency, and the phase is adjusted until the synchroscope needle is at the 12 o'clock position or the synchronizing lamps are extinguished, indicating synchronism. Once synchronized, the generators can be safely paralleled.</p> Signup and view all the answers

<p>The purpose of an emergency generator in a ship's electrical system is to provide backup power to essential circuits in the event of a main generator failure or blackout. According to SOLAS regulations, the emergency generator must be capable of starting and being on load within 45 seconds to supply power to critical systems like navigation, communications, safety machinery, and blackout recovery.</p> Signup and view all the answers

<p>A blackout is a complete loss of electrical power, while a brownout is a temporary reduction in voltage below the normal operating level. In a blackout, all electrical equipment would shut down until power is restored. In a brownout, some equipment may continue operating, but sensitive electronics or motors could be damaged or experience performance issues due to the low voltage.</p> Signup and view all the answers

<p>The '150 Ah at 15 hours' rating indicates that the battery can provide a current of 10 amps (150 Ah / 15 hours) for a duration of 15 hours before becoming fully discharged.</p> Signup and view all the answers

<p>The test switch is used to manually check the system, the power sensing circuit detects power failures, the spring solenoid automatically connects the batteries to the emergency load upon power failure, the transformer and AC supply provide charging power, the bridge rectifier converts AC to DC for charging, and the trickle charge maintains the batteries in a fully charged state.</p> Signup and view all the answers

<p>A boost charge is a high-rate charge over a short period, a slow charge is a low-rate charge to fully charge the battery without overheating or gassing, a trickle charge is a low-rate charge to compensate for self-discharge losses, and a float charge is a continuous charge to maintain the battery in a fully charged state without interrupting the supply to the load.</p> Signup and view all the answers

<p>Clear warning signs are required in a battery locker to alert personnel about the potential hazards associated with lead-acid batteries, such as the presence of corrosive acid, flammable hydrogen gas, and electrical shock risks.</p> Signup and view all the answers

<p>Ventilation is necessary in a battery locker to expel hydrogen gas generated during charging, which can create an explosive atmosphere if allowed to accumulate. The ventilation requirements may change depending on the charging rate, as higher charging rates produce more hydrogen gas and require increased ventilation.</p> Signup and view all the answers

<p>Two additional safety features could be: 1) Acid-resistant construction materials to contain and protect against corrosive battery acid spills, and 2) Emergency eye wash and shower stations to immediately flush any acid splashes or exposure from the body.</p> Signup and view all the answers

<p>Failing to maintain proper ventilation in a battery locker during charging can lead to the accumulation of hydrogen gas, which is highly flammable and can create an explosive atmosphere if ignited by a spark or flame. This poses a significant risk of fire or explosion, endangering personnel and property.</p> Signup and view all the answers

<p>The power sensing circuit continuously monitors the mains power supply and detects any interruptions or failures. Upon detecting a power failure, it triggers the spring solenoid to automatically switch the emergency load from the mains supply to the backup battery supply, ensuring an uninterrupted power source.</p> Signup and view all the answers

<p>A trickle charge is a low-rate charge used to compensate for self-discharge losses in batteries that are not in active use, while a float charge is a continuous low-rate charge applied to batteries that are actively supplying a load, to maintain them in a fully charged state. A trickle charge would be appropriate for backup batteries in standby mode, while a float charge is suitable for batteries in uninterruptible power supply (UPS) systems that must continuously supply critical loads.</p> Signup and view all the answers