Differential Protection Relay

Definition: The relay whose operation depends on the phase difference of 2 or more electrical quantities is caalled as the differential protection relay. It works on the principle of comparison between the phase angle & the magnitude of the same electrical quantities.

e.g: Consider the comparison of the input & output current of the transmission line. If the magnitude of the input current of the transmission line is more than that of output current that means the additional current flows through it because of the fault. The difference in the current can operate the differential protection relay.

The following are the essential condition needed for the working of the differential protection relay.

  • The network in which the relay use should have 2 or more similar electrical quantities.
  • The quantities have the phase displacement of approx. 180º.

The differential protection relay is used for the safety of the generator, transformer, feeder, large motor, bus-bars etc. The following are the classification of the differential protection relay.

  • Current Differential Relay
  • Voltage Differential Relay
  • Biased or Percentage Differential Relay
  • Voltage Balance Differential Relay

Current Differential Relay

A relay which senses & operates the phase difference between the current entering into the electrical system & the current leaving the electrical system is known as current differential relay. An arrangement of overcurrent relay connected to operate as a differential relay is shown in the figure below.

The arrangement of the overcurrent relay is shown in the figure below. The dotted line shows the section which is used to be protected. The current transformer is placed at both the ends of the protection zone. The secondary of the transformers is connected in series with the help of the pilot wire. Thereby, the current induces in the CTs flows in the same direction. The operating coil of the relay is connected on the secondary of the CTs.

In the normal operating condition, the magnitude of the current in the secondary of the CTs remains same. The zero current flows through the operating coil. On the occurrence of the fault, the magnitude of the current on the secondary of CTs becomes unequal because of which the relay starts operating.

Biased or Percentage Differential Coil

This is the most used form of the differential relay. Their arrangement is same as that of the current differential relay; the only difference is that this system consists an additional restraining coil connected in the pilot wires as shown in the figure below.

The operating coil connects in the centre of the restraining coil. The ratio of the current in the current transformer becomes unbalance because of the fault current. This problem is determined by the use of the restraining coil.

Induction Type Biased Differential Relay

This induction type relay consists of a disc which freely rotates between the electromagnets. The each of the electromagnet consists the copper shading ring. The ring can move in or out of the electromagnet. The disc experiences a force because of the restraining & the operating element.

The resultant torque on the shaded ring becomes 0 if the position of the ring is balanced for both the element. But if ring moves towards the iron core then the unequal torques acting on the ring because of the operating & restraining coil.

Voltage Balance Differential Relay

The current differential relay is not appropriate for the protection of the feeders. For the protection of the feeders, the voltage balance differential relays are utilized. The voltage differential relay uses 2 similar current transformer places across the protective zone with the help of the pilot wire.

The relays are connected in series with the secondary of the current transformer. The relays are connected in such a way that no current can flows through it in the normal operating condition. The voltage balance differential relay uses the air core CTs in which voltages induces regarding current.

When the fault occurs in the protection zone, the current in the CTs become unbalance because of which voltage in the secondary of the CTs disturbs. The current starts flowing through the operating coil. Thus, the relay starts operating & gives the command to the circuit breaker to operate.

Q – With respect to MARPOL Annex V:-

a) please explain the regulations stipulated for disposal of garbage under annexe V of marpol 73/78. NOV 2018 ( 8 Mark) .

b) please state the special area notified under annexe V of marpol 73/78 (4 mark). NOV 2018

C) also state what precautions you will take during disposal of waste from electrical workshop (4 mark). NOV 2018

Ans – Introduction- In accordance with regulation 9 of Annex V of the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 (MARPOL 73/78), a record is to be kept of each discharge operation. This includes discharges at the sea, to reception facilities, or to the other ships.

Garbage and garbage management

All ships of 100 gross tonnages(GT) & above, every ship certified to carry 15 persons or more, & every fixed or floating platform must carry a garbage management plan on board, which includes written procedures for minimizing, collecting, storing, processing & disposing of the garbage, including the use of the equipment on board (regulation 10.2). The garbage management plan must designate the person responsible for the plan & be written in the working language of the crew.

Garbage includes all kinds of food, domestic & operational waste excluding fresh fish & parts thereof, generated during the normal operation of vessel & liable to be disposed of continuously or periodically except those substances which are defined or listed in other annexes to the MARPOL 73/78 (such as oil, sewage or noxious liquid substances).

The Guidelines for the Implementation of Annex V of MARPOL 73/78 should also be referred to for relevant information.

Description of the garbage

The garbage is to be grouped into categories for the purposes of this record book as follows:

1. Plastics

2. Floating dunnage (loose wood, matting, or similar material), lining, or packing material

3. Ground-down paper products, rags, glass, metal, bottles, crockery, etc.

4. Cargo residues, paper products, rags, glass, metal, bottles, crockery, etc.

5. Food waste

6. Incinerator ash.

4) Entries in the Garbage Record Book- Entries in the Garbage Record Book shall be made on each of the following occasions:

(a) When garbage is discharged into the sea:

(i) Date and time of discharge

(ii) Position of the ship (latitude and longitude). Note: for cargo residue discharges, include discharge start & stop positions.

(iii) Category of garbage discharged

(iv) Estimated amount discharged for each category in cubic meters

(v) Signature of the officer in charge of the operation.

(b) When garbage is discharged to reception facilities ashore or to other ships:

(i) Date & time of discharge

(ii) Port or facility, or name of ship

(iii) Category of garbage discharged

(iv) Estimated amount discharged for each category in cubic meters

(v) Signature of officer in charge of the operation.

(c) When garbage is incinerated:

(i) Date & time of start and stop of incineration

(ii) Position of the ship (latitude & longitude)

(iii) Estimated amount incinerated in cubic meters

(iv) Signature of the officer in charge of the operation.

(d) Accidental or other exceptional discharges of garbage

(i) Time of occurrence

(ii) Port or position of the ship at time of occurrence

(iii) Estimated amount and category of garbage

(iv) Circumstances of disposal, escape or loss, the reason therefore and general remarks.


The master should obtain from the operator of port reception facilities, or from the master of the ship receiving the garbage, a receipt specifying the estimated amount of garbage transferred. The receipts must be kept on board the ship with the Garbage Record Book for 2 years.

Amount of garbage

The amount of garbage on board should be calculated in cubic meters, if possible separately according to category. The Garbage Record Book contains many references to estimated amount of the garbage. It is recognized that the accuracy of estimating amounts of garbage is left to interpretation. Volume estimates will differ before & after processing. Some processing methods may not allow for a usable estimate of the volume, e.g. the continuous processing of food waste. Such factors should be taken into consideration when making & interpreting entries made in a record.

Garbage categories:

1 Plastic.

2 Floating dunnage, lining, or packing materials.

3 Ground paper products, rags, glass, metal, bottles, crockery, etc.

4 Cargo residues, paper products, rags, glass, metal, bottles, crockery, etc.

5 Food waste.

6 Incinerator ash except from plastic products which may contain toxic or heavy metal residues.

Note: The discharge of any garbage other than food waste is prohibited in special areas. Only garbage discharged into the sea must be categorized. Garbage other than category 1 discharged to reception facilities need only be listed as a total estimated amount. Discharges of cargo residues require start and stop positions to be recorded.

* Refer to the Guidelines for the Implementation of Annex V of MARPOL 73/78, as amended by resolutions MEPC.59(33) and MEPC.92(45).

Special areas

The special areas established under Annex V are:

  • the Mediterranean Sea area
  • the Baltic Sea area
  • the Black Sea area
  • the Red Sea area
  • the Gulfs area
  • the North Sea area
  • the Wider Caribbean Region and
  • the Antarctic area.

These are sea areas where for the recognized technical reasons relating to their oceanographic & ecological condition & the particular character of traffic, such as heavy maritime traffic, low water exchange, extreme ice states, endangered marine species, etc., the adoption of the special mandatory methods for the prevention of marine pollution by garbage is required.

Polar Regions

Chapter 3 of MARPOL Annex V makes use of the environment-related provisions of the Polar Code mandatory, &  requires that ships trading the Polar Regions must comply with strict environmental provisions specific to the harsh conditions in Polar waters – the Arctic waters & the Antarctic area.


Examples of the electronic waste include, but not limited to:

  • TVs, computer monitors, printers, scanners, keyboards, mice, cables, circuit boards, lamps, clocks, flashlight, calculators, phones, answering machines, digital/video cameras, radios, VCRs, DVD players, MP3 and CD players
  • Kitchen equipment(toasters, coffee makers, microwave ovens)
  • Laboratory equipment(hot plates, microscopes, calorimeters)
  • Broken computer monitors, television tubes (CRTs)

Electronic waste from equipment of all sizes covers dangerous chemicals like lead, cadmium, beryllium, mercury, & brominated flame retardants. When we dispose of gadgets & devices improperly, these hazardous materials have a high risk of polluting the air, contaminating soil, & leaching into water sources.

When e-waste sits in a typical landfill, for example, water flows through the landfill & picks up trace elements from these dangerous minerals. Eventually the contaminated landfill water, called “leachate,” gets through layers of the natural & manufactured landfill liner & other protection. When it reaches natural groundwater, it introduces lethal toxicity. Health risks range from kidney disease & brain damage to the genetic mutations. Even with the best intentions in mind, recycling e-waste often leads to illegal overseas shipping & dumping. Devices get left in the huge pit or burned.

Q – How will you fight a fire in a galley? How will you at least restrict the fire if you are the first person to sight the fire in the galley? (8 Marks) JUNE 2018

Ans- Fire in galley

1. Raise alarm and inform bridge.

2. If the fire is small- I will restrict the fire by the following procedure on seeing the fire as first person.

a. Immediately switch off the fan and galley oven supply. Cut off supply from distribution panel/ or by pressing emergency stop.

b. If fire in cooking range, I will use fire blanket to extinguish the fire.

c. If fire in electric connection, I will use portable CO2 fire extinguisher to extinguish the fire.

d. If fire in galley duct, I will operate the release button of CO2 cabinet by opening the valve. When the door will be opened the galley duct damper will automatically close. If not, then I will close it manually by pulling the chain at both end of duct.

e. If fire in deep fat fryer, I will operate foam type extinguisher or DCP extinguisher provided to release on deep fat fryer or by portable foam type or DCP extinguisher.

3. In case of big fire – Immediate actions by bridge team.

a. Sound fire alarm followed by Announcement by PA

b. Inform E/R and Reduce speed

4. Muster all crew as per emergency team. As per the muster card all the crew members to carry out their duties.

5. Carry out head count and brief the fire team

6. Check if any casualty/ missing personnel

7. Establish communication between emergency teams and bridge.

8. Command team will:

i. Check vessel’s position

ii. Check weather condition, wind direction, force

iii. Suit vessel’s course appropriate for minimum wind effect if traffic condition permits.

iv. Alter course

v. Reduce speed

vi. Record all the events and steps taken

vii. Send urgency or distress message depending on the extent of fire.

9. In-charge of emergency team to ensure

i. Any casualty

ii. Prepare firefighting team for fighting fire

iii. Investigate location and nature of fire, inform to bridge.

iv. Send two men donning firemen’s outfit to fight the fire with one fire hose with dry powder and another to produce protective curtain.

v. Rig fire hoses for boundary cooling and start boundary cooling by back up team

10. Roving team

i. to check adjacent compartments if there is sign of spreading fire. Continuously monitor temperature of affected area & its surroundings.

ii. Close all ventilators, flaps, blowers, fire doors

iii. Cut off electrical supply to galley

iv. Maintain fire watch when fire is extinguished

11. Back up team will ensure fire men’s outfit; SCBA sets & spare bottles are readily available. Two persons start donning the SCBA and stand by for emergency team.

12. Engine Room team will ensure:

i. Start emergency fire pump

ii. Start emergency generator

iii. Maintain fire pump pressure

iv. Consider loss of stability while using water to fight fire.

v. Refer to damage stability booklet for loss of stability.

13. Support team will prepare life boats for lowering

14. Medical team will remove the casualty and take care of casualty.