Maintenance and Repairing of Electrical System Equipment Switchboard

Maintenance and Repairing of Electrical System Equipment, Switchboard ds, Electric Motors, Generators and DC Electrical System and Equipment: Part 2

Pre Lecturing 04 Quiz Describe the principle of major and periodic overhaul, periodic and daily maintenance, survey after damage with the use of technical documentation! n Explain the principle of organization of maintenance, repairs, and describes how to document maintenance, repairs and trials. n Describe how to manage maintenance intervals repairs and spare part in the computer system (e. g. AMOS) n

Pre Lecturing 05 Quiz n Explain principles of maintenance and repair to equipment installed in main switchboards, emergency switchboards and distribution panels

Main Switchboard The Main switch board is an intermediate installation in the ship’s power distribution circuit connecting the power generators and power consumers. The power generators on ships are auxiliary engines with alternators and the consumers are different engine room machineries such as motors, blowers etc. n It is very important to isolate any type of fault in an electrical system supplied from the main switchboard (MSB) or else it will affect all the other system connected to the same. If such isolation is not provided then even a short circuit in a small system can cause blackout of the whole ship. n Therefore, different safety devices are used on board ship and installed on the main switchboard (MSB) and electrical distribution panels. n

KONGSBERG K-POWER SWITCHBOARD

Ship Distribution System n n n The main elements of a marine distribution system are the main and emergency switchboards, power panels/ boards, motor controllers, lighting and small power panels/ boards. The system is generally designed such that under all normal conditions of operation, power is distributed from the main switchboard. The distribution system is designed to keep cable costs to a minimum by distributing supply to power panels located close to the user services. The main switchboard is generally located near the centre of the distribution system and this is normally the main engine room or machinery control room. These locations are normally below the ship’s waterline or below the uppermost continuous deck of the ship i. e. the bulkhead or main deck. Consequently, in the event of a fire or flooding it is likely that the main generators and switchboard would be disabled.

Protective system for main Switchboard shipboard installations specific protective systems are required to shut down all ventilation systems and all fuel oil systems in the event of a fire. n When motor auxiliaries are grouped together and supplied from a Motor Control Centre (MCC) or a grouped distribution panel, this can best be achieved by providing the MCC supply feeder’s circuit breaker with an undervoltage tripping device and connecting this to the ventilation or fuel system’s: trip unit. n When grouped MCCs or grouped distribution panels are not used, separate cables must be installed for each motor controller; this leads to increased cable costs and increases the system’s susceptibility to failure. n

Main Switchboard’s Important Safety Devices n Circuit Breakers n Fuses n Over Current Relay n Dead from Panel

Circuit breakers n. A circuit breaker is an auto shut down device which activates during an abnormality in the electrical circuit. Especially during overloading or short circuit, the circuit breaker opens the supplied circuit from MSB and thus protects the same. Different circuit breakers are strategically installed at various locations.

n The main function of air circuit breaker is to: – Open and close a 3 phase circuit, manually or automatically. – Open the circuit automatically when a fault occurs. Faults can be of various types – under or over voltage, under or over frequency, short circuit, reverse power, earth fault etc. – The main feature of ACB is that it dampens or quenches the arcing during overloading.

Air Circuit Breaker (ACB) Construction & Working Source : https: //www. marineinsight. com/marine-electrical/electrical-safety-device-air-circuit-breaker-acb/

ACB has two sets of contacts i. e. main and auxiliary contacts. Each set of contact consists of a fixed contact and a moving contact. The main contact normally carries most of the load current. All the contacts are made of cadmium-silver alloy which has very good resistance to damage by arcing. n When the ACB is closed, the powerful spring is energized and the ACB is than latched shut against spring pressure. The auxiliary contact makes first & breaks last i. e. when ACB is closed, the auxiliary contact closes first then the main contact follows. n When the ACB is open, the main contact open firsts and then auxiliary contact opens. Thus the auxiliary contacts are subjected to arcing during the opening of ACB and can easily be replaced. n The main contact closing pressure is kept high so that the temperature rise in the contacts while carrying current remains within limit. Closing coil operating on D. C voltage from a rectifier is provided to close the circuit breaker by operating a push button. n

Ship air Circuit Breaker remote release fail n Most air circuit breakers used for generator and power switching systems are provided with an automatic release mechanism. Those that do not have an ‘under voltage‘ or ‘no-volt‘ automatic release (or where one is fitted but is not working) may accidentally remain closed even when a ‘trip‘ condition exists. In such a case, there is a serious fire hazard due to intense heating and/or arcing.

Fault on ship air circuit breaker It is usual for shipboard generators also to be fitted with remote interlocks that open the main breakers under ‘no-volt’ or ‘under voltage’ conditions. The first indication of a defective ‘no-volt’ or ‘under voltage’ release is often that the remote release system of the breaker does not operate, requiring manual tripping of the release to keep the breaker open. This condition should be recognized as potentially dangerous, in that other breakers will probably be inoperative as well, and arrangements must be made for immediate checking, overhaul or renewal, as appropriate. n Such an accident happened recently on board n

How returning ship breaker? n After withdrawing any breaker, make sure that the switching contacts are open before returning it to the operating position. Do not rely on built-in trips or mechanical stops. While the breaker is withdrawn, check that the indicator is showing true by sighting the switching contacts, or by using an ohmmeter. Check the indicator is showing open again before returning the breaker to the operating position.

Fuses n Fuses are overcurrent protection devices that used for three primary purposes: – To prevent damage to electronic and electrical equipment. – To provide safety for equipment users and personnel. – To isolate subsystems from the main system after an over current occurs. Fuses are designed to allow electric currents to safely flow during normal operation but will quickly open when an over-current situation develops. (http: //electrotechnical-officer. com/all-about-fuses-on-ship-system/) n mainly used for short circuit protection and comes in various ratings. If the current passing through the circuit exceeds the safe value, the fuse material melts and isolates the MSB from the default system. Normally fuses are used with 1. 5 times of full load current.

Type of fuses on ship There are typically two types of overcurrents; short circuits and overloads. Overcurrents exist when the normal load for a circuit is exceeded. n An overload is any current flowing within the normal circuit path that is higher than the circuit normal full load current. n A short circuit is an overcurrent which greatly exceeds the normal full load current of the circuit. Also, as the name infers, a short circuit leaves the normal current carrying path of the circuit and takes a “short-cut” around the load and back to the power source. n Components and equipment can be severely damaged by both types of overcurrents. Fuses are used not to prevent overcurrents but rather to protect components, equipment and people when overcurrents do occur. n

Fuse Characteristics n Fuses are classified by the different fuse characteristics. These defining characteristics include: – Physical size – Interrupting Ratings – Construction – Opening Speed – Electrical Ratings – Safety Agency Approvals

Physical Size n Electronic fuses are available in a variety of sizes and shapes as predetermined by the user’s applications. The more popular fuse sizes include 1/4″ x 1 1/4″ (6. 3 x 32. 1 mm), 5 x 20 mm, 5 x 15 mm, 13/32″ x 1 1/2″ (10. 3 x 38 mm) as well as special use fuses such as surface mount, telecom indicating, and automotive type fuses.

Styles and Sizes of Fuses. Sources: https: //www. westmarine. com/West. Advisor/Circuit-Protection-and-Power-Distribution

Over current relay n is used mainly on the local panel and MSB for protection from high current. They are installed where a low power signal is a controller. Normally relays are set equivalent to full load current with time delay.

Overcurrent relay types on ship n Magnetic n Thermal n Electronic

n n n All relay types have an inverse current- time characteristic called OCIT (over- current inverse time), i. e. the bigger the current the faster it will operate. A magnetic relay, directly converts the current into an electromagnetic force to operate a trip switch. An electronic overcurrent relay usually converts the measured current into a proportional voltage. This is then compared with a set voltage level within the unit which may be digital or analogue. In analogue unit the time delay is obtained by the time taken to charge up a capacitor. This type of relay has separate adjustments for overcurrent and time settings together with an instantaneous trip. Both the magnetic and electronic relays can be designed to give an almost instantaneous trip (typically less than 0. 05 seconds or 50 ms) to clear a short- circuit fault. Thermal relays are commonly fitted in moulded case circuit breakers (MCCBs) and in miniature circuit-breakers (MCBs) to give a “long time” thermal overcurrent trip in addition to a magnetic action for an instantaneous trip with a short-circuit fault.

Overcurrent Protection of ship electrical system The general term “overcurrent” applies to a relatively small increase over the full load current (FLC) rating (e. g. due to mechanical overloading of a motor) rather than the massive current increase caused by a short-circuit fault. n Generally, an overcurrent, supplied from a CT, is detected by a relay with an appropriate time-delay to match the protected circuit. Short-circuit faults in LV distribution circuits are mainly detected and cleared almost instantaneously bf fuses, MCCBs or MCBs. n Main supply feeders are usually protected against shortcircuits by circuit breakers with instantaneous magnetic trip action. n

Dead front panel It is another safety device provided on the Main switch board individual panels wherein you cannot open the panel until the power of that panel is switched off. n Concept of dead front electrical panel is to ensure the safety of user or operator from accidental touching of bare electrical energized parts. This bare electrically energized parts are as examplethe bus bars in panel, connection point of circuit breakers and all applicable connection to various electrical appliances in the panel. n

Switchboard Equipments n n n n n Tripping Devices Contractors Relays Thermal Relays Busbars Terminal Strips Measuring Instruments PLC Controllers and Monitoring panels Heating and Ventilation circuits

Tugas 1. n Buat lah Deskripsi dari setiap switchboard equipments pada halaman sebelumnya.

Example of Marine Electrical System

Tugas 2. n Buatlah satu contoh kasus fault dari sistem kelistrikan kapal pada halaman sebelumnya dan berikan tahapan maintenance dan repair yang harus dilakukan!