Ship monitoring relays

Ship monitoring relays are not intended to substitute fuses or motor protection switches.

Instead, they signal irregularities earlier before the corresponding protective devices are tripped.
Trips from a ship’s thermal relays are linked to:

• Ship power system current imbalance
• Abnormal temperature rise of the PTC (Positive Temperature Coefficient) thermistor probes
• cosfi measurement dropping too low
• Locked rotor and over-torque detection
• Underload
• Earth fault currents
• Phase rotation reversals
• Prolonged starting

Only a few of the trips listed in the control circuits are used onboard ships and are restricted to essential electrical equipment:

• Current monitoring relays
• Voltage monitoring relays
• Phase imbalance and phase sequence relays
• PTC relays

Some other terms commonly used for this subject are:
Starting override – Measured values outside the tolerated range are ignored during startup. This is when the starting override is active. The purpose is to tolerate brief fluctuations, such as motor inrush currents.
Response delay -Threshold value violations are accepted within the delay time. A signal is only generated if the threshold value violation continues beyond the delay time.
Threshold value – If the measured value passes the set minimum or maximum, the relay will trip.
Reset value -The value where the relay picks up again.
Hysteresis – The range between the threshold value and the reset value.

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To avoid mistakes it is suggested that the relay order form should include the following information:
• Relay manufacturer
• type of relay
• coil voltage
• number of contact blocks
• contact reference numbers or contact reference letters.
The relay order should be similar to this table.

* Ship Automation for marine engineers and ETOs

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A normally open momentary pushbutton (S1,S2) only remains closed while the button is pressed.

A normally closed momentary pushbutton only remains open while pressed.

A maintained pushbutton (S3,S4) will fasten and remain in the changed state when pressed.

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• Limit switches
• foot switches
• pressure switches
• level switches
• temperature-actuated switches
• flow switches
• selector switches

As with contacts, switches require a device or an operator’s action to change their state, eg pressing a light switch.

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They create a general overview of the entire plant.

Units within a plant, shown in blocks, are connected by cables with their corresponding ship cable numbers voltage and number of cores.

Block references consist of: unit reference number, for instance =A1.0 and relative manufacturer’s diagram number (9-A-0050-00).

Cable reference, as a part of ship diagrams, consists of: the cable’s cores, cable type and the number of Incorporated cords.

Any onboard modifications to electrical equipment should be red-lined on the ship’s drawing for future reference.

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In day-time engineers can execute planned maintenance and repairs or replacement of defective parts. Because engine-rooms are usually warm, damp and noisy, an un-manned engine-room is advantageous.

For ships with simple electrical installations it may be feasible to design a manned engine-room and delete the expensive and complicated automation for remote control, alarm and monitoring systems, fire-detection systems, fuel leakage detection, etc.

Automatic starting of a stand-by generator set, automatic closing of a dead bus bar after failure of the running set and automatic starting of all essential electric consumers is a SOLAS requirement for all ships, including those with a manned engine-room.

Unmanned (UMS) notation

On ships with notation UMS there is no need for a person permanent on watch in the engine-rom. These ships (UMS) are required to have additional warning systems such as:

Fire-detection system
- automatic safety systems and remote-control systems for machinery

Automatic control systems for air compressors alarm and monitoring system

Automatic starting of stand-by pumps for propulsion auxiliaries  on ship such as:

• seawater pumps
• freshwater pumps
• lubricating-oil pumps
• fuel-oil pumps
• propeller hydraulic pumps 
when not directly engine- driven

These systems have to be arranged in such a way that under normal operating conditions no manual intervention by engineers is required. Alarm and monitoring functions must be independent from safety systems.

Alarms that are not acknowledged in the space within a predetermined time must be automatically relayed to the engineer on duty via the engineer’s call system .

When the engineer on duty fails to act within a predetermined time the alarms will be relayed to other engineers.

When on patrol in the unmanned engine-room the duty engineer will activate the operator fitness system. This system consists of start/ stop panels at the entrances to the engine-room and timer-reset panels in the engine-room.

When the timer, normally set at 30 minutes, runs out and is not reset, an alarm will be given on the bridge and in the accommodation.

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An overvoltage on an incandescent lamp produces a brighter and whiter light because the filament temperature is increased.

Its operating life is, however, drastically reduced.

A 50% increase over its rated voltage will reduce the lamp life by 50%.

Conversely ,a supply voltage reduction will increase the operating life of a GLS lamp but it produces a duller, reddish light.

Lamps rated at 240V are often used in ship’s lightning system operating at 220V.

This under-running should more than double the lamp life.

Similar effects on light output and operating life apply to-discharge lamps but if the supply-voltage is drastically reduced (below 50%) the arc discharge ceases and will not re-strike until the voltage is raised to nearly its normal value.

A fluorescent tube will begin to flicker noticeably as the voltage is reduced below its rated-value.

The normal sinusoidal a.c. voltage wave form causes discharge lamps to extinguish at the end of every half cycle  (every 10ms at 50Hz or every 6.7ms at 60Hz). Although this rapid light fluctuation is not detectable by the human eye, it can cause a stroboscopic effect where by rotating shafts in the vicinity of discharge lamps may appear stationary or rotating slowly could be a dangerous illusion to operators.

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Make sure that all core ventilating ducts are clean and clear.

If an internal fan is fitted it must be in good condition if it is to provide adequate cooling.

If cage-rotor induction motor has been flooded with seawater and its insulation resistance is down to zero MO.

Wee need to restore the insulation resistance of the stator winding to a high value. This is achieved in three stages:

Cleaning

Drying

Re-varnishing

Salt contamination can be removed by washing with clean, fresh water. Any grease or oil on the windings has to be removed using a degreasant liquid such as Armaclean.

Dry the stator windings with low power electric heaters or lamps with plenty of ventilation to allow the dampness to escape.

Alternatively, the windings can be heated by current injection from a welding set or from a special injection transformer. Be sure to keep the injected current level weII below the motor’s full load rating.

With the windings clean and dry, and if the IR test remains high over a few hours, apply a couple of coats of good quality air-drying insulating varnish.

The motor starter and other control equipment should be regularly inspected to check and maintain the following items:

Enclosure of ship rotor:

Check for accumulations of dirt and rust. Any corroded parts must be cleaned and repainted. Examine the starter fixing bolts and its earth bonding connection – particularly where high vibration is present, e.g. in the steering flat and the forecastle.

Maintain of contactors and relays on ship

Check for any signs of overheating and loose connections. Remove any dust and grease from insulating components to prevent voltage breakdown by surface tracking. Ensure that the magnet armature of contactors moves freely. Remove any dirt or rust from magnet faces which may prevent correct closing.

Maintain of contacts on ship motor

Examine for excessive pitting and roughness due to burning. Copper contacts may be smoothed using a fine file. Copper oxide, which acts as a high resistance, can be removed using glass-paper. Do not file silver alloy contacts or remove silver oxide as it acts as a good conductor. A thin smear of electrical contact lubrication helps to prolong the life of all contacts. When contacts have to be replaced, always replace both fixed and moving contacts in pairs.
Check contact spring pressure and compare adjacent contact sets for equal pressure. Examine power and control fuse contacts for signs of overheatig – lubricate the contact blades on fuse-holders.

Connections of ship motors

Examine all power and control connections for tightness and signs of overheating. Check flexible leads for fraying and brittleness.

Maintain Overcurrent relays on ship system

Check for proper settings (relate to motor FLC).

Inspect for dirt, grease and corrosion and for freedom of movement (not possible with an electronic type of OCR).

A thorough OCR performance test can only be carried out by calibrated current injection.

Control operation of ship el motors

Observe the sequence of operation during a normal start-up, control and shut-down of the motor. Particularly look for excessive contact sparking (only possible with open-type contactors). Remember to check the operation of emergency stop and auto-restart functions.

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• contact resistance low
• Keep insulation resistance high and
• Lubricate correctly and maintain a uniform air gap
• Ensure both the interior and exterior are always clean and dry

Provided these requirements are met, an induction motor should give trouble- free service during its long life.

The most common cause of induction motor failure is failure of stator insulation due to dampness is a major problem with marine motors.

Open ventilated motors are most at risk, particularly when they are not used for long periods.

Anti-condensation heaters should be regularly checked to see that they are actually working and keeping the motor dry.

For all motors, cleanliness is next to godliness.

A regular cleaning routine is required to remove harmful deposits of dust, dirt, grease and oil from both inside and outside the motor. The cleaning of the external surface is especially important for totally enclosed motors which run continuously.

The heat generated in these motors is removed through the external surface. A thick laver of dust will reduce the heat dissipation and result in very high temperatures. Internal dust and dirt in open ventilated motors must be regularly removed by blowing or extraction and ventilation screens and ducts cleared out.

If motors are to be blown out, the air used must be absolutely dry and the pressure should not be more than 1.75bar.

If the pressure is higher than this it forces the dust into the winding insulation rather than removing it.

When blowing out a motor remember to cover up other machines in the area to protect them from flying dust. Suction cleaning is better than blowing out.

How often should a marine motor be cleaned?

Basically this will be determined by the local conditions and the type of ventilation. Only the external surfaces of totally enclosed motors will require regular cleaning. But both the outside and inside of open ventilated motors will require routine attention.

The inside of a totally enclosed motor can be cleaned if the motor has been dismantled for bearing replacement.

Motors in areas where considerable amounts of air-borne dust are expected, hatch-cover motors are an example, will obviously require more frequent cleaning.

Contamination by oil and grease from motor bearings is often a cause of insulation failure.

The insulation should be cleaned by brushing or spraying with one of the many proprietary brands of cleaning fluid which are available. Badly contaminated motors may require total immersion of the stator windings in cleaning fluid.

Broken or missing bearing covers must be repaired or replaced to prevent grease escaping.

When a motor has been dismantled for cleaning and overhaul it should be thoroughly inspected. In this way, faults can be detected before they evolve into a major breakdown.

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