Ship current transformers CT which steps down the monitored current to a secondary (output) range of 0 to 5 amps (AC) to power the protective relay.
If the monitored current becomes excessive, the relay triggers a contact-switching auxiliary control circuitry to the breaker’s trip coil.

By using the selected time delay between 0.05 and 30s, short current peaks can be bridged.

Connecting the ship current transformer CT to the current monitoring relay terminals is depicted on the relay diagram’s symbol Terminals coded with the letter B represent connections to the current transformer.

Terminals B1 to B3 connect ship current transformer CTs with different step-down current ratios.

C shows another connection terminal, common for any CT ratio.

Example of a current monitoring relay and a related electrical diagram

The power is applied across A1/A2, and the current signal being monitored is applied across B1 and C. Depending on the measurement of the current ratio, the following connections are allowed:
B1/C: 3-30 mA, B2/C: 10-100 mA, B3/C: 0.1-1 A.
The relay operates with changeover contacts, the motor starter control circuits use NO (normally open) contacts in series with stop button contacts. The result Is that an occasional break in the power supply will stop the motor.

The relay can operate both contact groups, either with or without a time delay, depending on the rotary selector switch (Tv) position.
Whatever mode of operation is adjusted for the relay (either instant or delayed), only one relevant reference number will be used throughout a diagram.
Relay set for overcurrent detection (/>)
If the current Is greater than the set threshold, the output relay is energised, with or without a time delay. When the current returns to a value below the threshold, depending on the hysteresis setting, the relay Is Instantly de-energized.

How to set ship relay set for undercurrent detection

If the current is less than the setting threshold IS1, the output relay Is energized, with or without a time delay.

When the current returns to a value IS2 above the threshold, depending on the hysteresis setting, the relay is instantly de-energized.

The post Ship Current Monitoring Relay (over/ under current monitoring relay on ship electrical system) appeared first on Electro-technical Officer (ETO).

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.

The post How Ship Protection and Monitoring Relays Works appeared first on Electro-technical Officer (ETO).

The itemized overview of contactor accessories should help while sending routine ship technical inspections or ship spare orders and when ordering relays or contactors in an emergency.

Check basic ship contactor accessory

1. Basic unit
2. Side-mounted (lateral) auxiliary contact module
3. Pneumatic time module (On- and Off-delay), top-mounted
4. Two pole top-mounted auxiliary contact module
5. Four pole top-mounted auxiliary contact module
6. Mechanical latching module
7. Surge protector

The post Ship electrical contractors and contactor modules appeared first on Electro-technical Officer (ETO).

This addition provides the ordinary relay with time-delay actuation. Time-delay modules are constructed to delay armature motion on coil energisation, de-energisation or both.

A relay with such an accessory becomes a timer and is illustrated with a timer symbol.

The post Control relays and timer modules on ship’s electrical system appeared first on Electro-technical Officer (ETO).

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.

The post Ship electrical contactors, description and maintenance appeared first on Electro-technical Officer (ETO).

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.

The post Ship control relays, terminals and working principles appeared first on Electro-technical Officer (ETO).

Being a solid state there are no moving parts to wear out, no sparking on contact, and no contact corrosion and they can be switched on and off quicker than mechanical relays for massive ship electrical system sound great. However, they are expensive to build for very high current ratings where electromechanical contactors dominate.

Solid state relays will only open the AC circuit at a point of zero current as their inherent hysteresis (memory) maintains current continuity after the LED is de-energised, until It falls below the holding current’. Known as ‘zero-crossover switching’, this is the advantage of uninterrupted operation during the sine wave when using AC power and avoids large voltage spikes.
A problem associated with SCRs is that they are more likely to fail shorted (or closed) rather than open, as is the case of EM relays. As a ‘fail-open’ condition is deemed to be safer, EM relays are often preferred for certain applications.

The post Advantages and disadvantage Solid State Relays on ship power systems appeared first on Electro-technical Officer (ETO).

The reeds provide a magnetic operating gap and serve as a contact pair providing NO, NC and CO combinations.
Reed relays on ship electrical systems have the advantage of being hermetically sealed and as a result, are protected from atmospheric contaminants.
To make NC or CO contacts, reed switches will occasionally use permanent magnets for magnetic biasing. The current rating of the reed, normally up to one amp, depends on the size, type and amount of plating.

The post Reed Relays or Electromechanical Printed Circuit Board Relays on ship electrical system appeared first on Electro-technical Officer (ETO).

The sample illustrates cable DSE-55, shown by a heavy line, which connects two appliances (=A1.2 and =A5) into common circuitry. The cable conductors (cores 1 to 10) are shown as light lines.

Next sample illustrates the entire set of -4KA01 relay contacts. It is not possible to represent both multi-core cable ends on a single sheet. Therefore the cable Is split through subsequent diagram sheets as illustrated.

Any onboard modifications to ship electrical equipment should be red-lined on the ship’s drawing for future reference.
For example, cable DSE-75 has a continuation reference (2.2).The continuation of cable DSE-56 should be found on sheet 3, section 6.
To provide detailed information about the cable’s connective features, a table giving the cable’s designation will be provided.

The post Ship electrical cable system and diagrams appeared first on Electro-technical Officer (ETO).

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.

The post What is ship electrical block diagrams appeared first on Electro-technical Officer (ETO).