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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Two position numbers adjacent to each contact terminal.

Modules can be from either side of the contactor on ship power system. This means that one of the two numbers is the right way up while the other is upside-down.

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Contacts, carrying such a load are called ‘Main Contacts’.

These are always NO (normally open) contacts and designated by single digits in pairs: 7-2, 3-4, 5-6 (for three pole contactors), and 7-8 (for four pole contactors). In addition to reference numbers, the following reference letter code is used: Li, L2, (.This is shown on the top of the contactor, representing three-phase power supply terminals and T1, T2, T3, from the bottom of the contactor, representing the load side terminals.

Ship electrical contactor arrangement

The main contacts marked with (1) are movable, but the main contacts marked with (2) are fixed.

The auxiliary contacts, (3) fixed and (4) movable, are only used in control circuitry for monitoring purposes.
If the contactor coil is designed to be energized with AC (alternating current), aluminum or copper (shading) rings are crimped to both ends of the magnetic core creating an out-of-phase current that increases the minimum pull on the armature during the AC cycle.

Maintenance of ship electrical contactors

Modern ship electrical contractors are extremely reliable but may have common faults. Worn main contacts due to the arc-effect is a known problem. The operating coil should be opened for internal inspection under recommended routine maintenance systems.
A high standard of maintenance on contactors is paramount to the efficient operation of a vessel. High standards of preventive maintenance will minimize ship inefficiency and related downtime.

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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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In addition to basic unit contacts, top-mounted auxiliary contact modules offer two or four contact extensions.

To prevent duplicating terminal markings when NO and NC contacts are combined, the modules will have different position digits.

Picture iustrates the difference between early make (EM) and late break (LB) contacts and make (NO) and break (NC) contacts that are met at top-mounted auxiliary contact modules.

The contacts layout for the module illustrated is, from left to right: 53-54 NO, 61-62 NC, 75-76 NC/
LB and 87-88 NO/EM.

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Relays are used to controlling and regulate circuits for the indirect control of electric motors, valves and clutches.
A modular system is formed around functional basic units, consisting of an AC or DC operated drive (coil with armature) and auxiliary contacts.

The control relay’s basic unit consists of four contact blocks (poles) marked with reference numbers:
• 13-14 (NO contact)
• 21-22 (NC contact)
• 33-34 (NO contact)
• 43-44 (NO contact).

Reference numbers are also shown as a table in most control diagrams, usually below the relay’s coil symbol.
The manufacturer’s stamp should be marked on the unit and reference letters marked adjacent to the terminals (53NO, 61A/C, 75NC, 87A/0).These manufacturer’s numbers are an important reference for reordering or cross-ordering with other manufacturers components.

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Magnetic latching relays on ship power system

This relay uses one pulse to move the contacts in one direction. A second pulse from a different input is required to return the contacts. Pulses that are repeated from a single input will not have any effect.

Mechanical latching relays on ship power system

This relay uses a locking mechanism to maintain contacts in the set position, a second coil is normally required to change the state. As the latch does not rely on a magnet it does not degrade with time or weaken during thermal cycling.

Impulse Sequencing relays on ship electrical system

Impulse sequencing relays, also known as impulse relays, move contacts with every pulse without redirecting the pulse or reversing the polarity.

Many impulse relays consist of a magnetic latch relay and a solid-state steering circuit. When power is applied, the steering circuit determines the position of the relay, and the opposite coil is energized, transferring and latching the contacts. When the coil is reenergized the contacts transfer once again.

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A current passes through the coil creating a magnetic field that attracts the armature, causing the contacts to move, either making or breaking a connection. The following contacts are known by how they can be thrown:

Ship Normally open contacts (NO)
When the relay is activated, NO contacts connect the circuit and will disconnect the circuit when it is inactive.
Ship Normally closed contacts (NC)
NC contacts disconnect the circuit when the relay is activated and connect when inactive.

Ship Changeover contacts (CO)
The contacts have a common terminal and control two circuits. One is a NO contact and the other is an NC contact. It is also known as a ‘double throw'(DT),

Single Pole Single-Throw contacts on ship (SPST)
These have two terminals that can be connected or disconnected (11-12 or 13-14) and two terminals for the coil. The terminology ‘SPNO’ and ‘SPNC’is sometimes used to indicate the contacts’ de-energized state (Figure b).
Double Pole Single-Throw contacts on ship (DPST)
The relay has four terminals that can be connected or disconnected. This is equivalent to two SPST switches actuated by a single coil and has two terminals for the coil (Figure c).
Single Pole Double-Throw contacts on ship (SPDT)
With a total of five terminals, two for the coll, a further terminal connects to two others as a CO contact (Figure d).
Double Pole Double-Throw

Single Pole Single-Throw contacts on ship (SPST)
These have two terminals that can be connected or disconnected (11-12 or 13-14) and two terminals for the coil. The terminology ‘SPNO’ and ‘SPNC’is sometimes used to indicate the contacts’ de-energized state (Figure b).
Double Pole Single-Throw contacts on ship (DPST)
The relay has four terminals that can be connected or disconnected. This is equivalent to two SPST switches actuated by a single coil and has two terminals for the coil (Figure c).
Single Pole Double-Throw contacts on ship (SPDT)
With a total of five terminals, two for the coll, a further terminal connects to two others as a CO contact (Figure d).
Double Pole Double-Throw contacts on ship (DPDT)
This has eight terminals with two rows of CO contacts. It is equivalent to two SPDT relays actuated by a single coil (Figure e).

Ship miniature relays are also subdivided by their operation:

Non-Latching (stable type)
A relay that is activated when the coil Is energized and turns off when de-energized. Non-latching relays are used In control applications when the switch must return to a neutral state if power is lost.
Latching type relays on ship system
Latching relays are used when power consumption and dissipation are limited. For example, after the Initial actuation of the relay no further power is needed to maintain the state.

1 One Coil Latching Type
This relay uses a pulse input to a single coil and a latching mechanism to maintain the contact as either on or off. By applying signals of opposite polarities the relay is set and reset.

2 Two Coil Latching Type
This relay uses a latching construction and two coils, one to set and another to reset. Setting and resetting is achieved by applying pulse signals of the same polarity.

Miniature relays are designed so that the casing does not become detached under normal use, as performance could be reduced. Consequently, the DIN rail mounting system allows simple replacement of malfunctioned relays. A PCB (Printed Circuit Board) miniature relay, socket-mounted ‘ice cube miniature relays and their terminal designation.

Miniature relays are assembled into control cabinets with their sockets, which can in general be subdivided into two basic types:

• Screw terminals sockets miniature relays
• Screwless terminals sockets (for fast wiring).

All sockets are either panel- or 35 mm rail-mounted (EN 60715). Socket’s terminals as well as relays’ contacts pins are assigned with reference numbers, which should be used when troubleshooting to verify the condition of the contact in an energized and de-energized state.

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The markings make it possible to determine the terminals that are associated with the ship component, ie functions they are assigned to and standardize the markings for different manufacturers on ship electrical system.

Terminal markings adjacent to main contacts have a single digit reference.Three-phase contactor main contact pairs are designated with: 1-2; 3-4; 5-6.
Terminal markings adjacent to auxiliary contacts have a double digit reference numbers so that:
• The first digit is the contact’s position (the position digit) which indicates where the contact is physically situated on the block, ie 1,2,3,…, 8
• the second digit defines a contact’s function and is called the function digit.
Function digits have been given the following DIN standardized designations

Standardized designations for contactors

Break contacts (NC) have function digit 1 and 2
Late break contacts (LB) have function digits 5 and 6 also known as ‘Normally close Late’ (NCL)

Make contacts (NO) have function digits 3 and 4

Early make contacts (EM) have function digits 7 and 8 also known as’Normally open Early’ (NOE)

Change over contacts (CO) have function digits 1-2-4

Each auxiliary contact that is utilised by relays and contactors is clearly designated, the reference numbers are stamped on both sides of the contact terminals.

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