Cargo Port

1. Lightning attack

Lightning disaster has been threatening the production safety of cargo port seriously. A large number of fixed and mobile handling equipment on the site are generally scattered in storage and freight yard areas of port. Such handling and transport equipment, generally of large volume, are easily struck by lightning.

Accident case

On the evening of November 22, 2011, 100,000-DWT oil tanks #31 and #32 in tank field of a Dalian group were stuck by lightning and on fire. Dalian Fire dispatched more than 700 firemen and 180 firefighting trucks quickly and extinguished the big fire basically after more than one hour of emergency fire-fighting.

From the analyses on historical lightning disasters data, according to the meteorological lightning-prevention experts, lightning disaster is a major meteorological one, which ranks only second to torrential rain and flood and meteorological geological disasters in Qingdao with respect to the hazard degree. Qingdao Port is located in the area with frequent lightning disasters. In each year, there are up to three months in frequent thunderstorm period, with average 21.8 days of thunderstorm annually.

2. Fault arc

The handling and transport in port mainly depend on handling and transport machinery (e.g. crane and charging crane), which generally are equipped with high-power motor. Due to the moist production environment and heavy dust in port and constant starting of motor, however, electrical equipment and line faults may occur easily, which may cause fault arc, electric spark and short circuit and then fire consequently.

Accident case

On March 4, 2015, fire occurred in a certain largest port of Canada, where dark smoke billowed. The main cause to fire, according to the official spokesman, was ignition of inflammable goods by the high temperature arc incurred by electrical equipment fault.

3. Harmonic and imbalance

Most electric equipment for cargo port purpose include silicon rectifying equipment and silicon controlled convertor equipment, as well as the discharge-type electric light source equipment generally used for the illumination of stack yard. The higher harmonics produced by such nonlinear loads can heat transformer and motor, as well as loop due to overload, which will cause frequent trip of breaker and even fire.

3.1 Cause

Transformer

Due to the saturation of transformer core, nonlinearity of magnetizing curve, and economy considered during design of transformer, the flux density for the operation of transformer is located at the nearly saturated segment of magnetizing curve, which makes magnetizing current in spire waveform, hence producing odd harmonics.

Electrical equipment applying power electronic converter equipment

There are more electromechanical devices in port such as portal crane and container shore bridge, which apply power electronic converting techniques such as rectification, inversion and frequency conversion, which will produce higher harmonics easily for the higher nonlinearity degree.

Electric light sources in gas discharge type

Most Chinese port enterprises basically adopt the electric light sources in gas discharge type for illumination. Through measurement and analysis of the whole voltage current characteristics of such sources, it is found that these light sources are of very serious nonlinearity and negative voltage current characteristic.

Computer and other office equipment

The power supplies of computer and other office equipment are switching ones and will generate harmonics.

3.2 Impacts

Impact electric transmission lines

Both harmonic current and unbalanced current will increase the loss of electric transmission lines. In the power supply system of port, cable power supply is almost adopted for all lines. Due to the large ground capacitance and low inductive reactance, besides, these cable lines will generate harmonics and resonances easily and break down the insulation.

Impact transformers

Both harmonic current and unbalanced current will cause transformer loss to different extents, hence causing heated transformer and even fire.

Impact the reliability of electric systems

Generally harmonics will cause protective relaying and malfunction or operation rejection of automatics to make the operation out of selectivity and reduce reliability, which will cause system fault easily and then heavily threaten the safety and reliable operation of power supply system in port.

Impact motors

Increase the additional loss of motor, reduce its efficiency, and even superheat the motor in severe case.

Interfere with the operation of measurement & control instruments and communication system

For the weak current equipment such as computer networks, communication devices, cable TV, alarms and building automation installations, the harmonics in power supply system can be coupled to such systems through electro-magnetic induction, electrostatic induction and conduction to interfere with them.