Generator Systems and Neutral Earthing Resistors

Vocabulary flashcards covering generator dependencies, high voltage values and transformers, cooling methods, and characteristics of Neutral Earthing Resistors.

Voltage Depends on what two things

Excitation and speed.

Polarization testing

Score over 2 is good

Test for one minute then 10 min

Induction testing

Time 10min

Divide by

Time 1min

Class makes you

Certified

Not

Qualified

HV Cable Insulation Generic Selection Criteria

The suitability of insulating material selected for HV transmission is determined by looking at each these properties:

Electric (dielectric) strength O Dielectric properties Thermal properties Mechanical properties Environmental suitability Processing possibilities Availability and costs

Neutral Earthed Resistor (NER)

A component connected to the neutral Wye that limits current flow to ground during a ground fault or phase loss. Key characteristics:

(1) only one is connected at a time across the whole ship to prevent voltage differential potential; (

2) monitored via a dedicated monitoring relay;

(3) prevents arcing during ground faults;

(4) sized to limit current flow from $1\,\text{A}$ to $500\,\text{A}$; and

(5) does NOT operate in a short circuit.

Frequency Depends on what 2 factors

Number of poles and speed.

A/C Synchronous Motor Operation

Operates at a precise speed with no slip on the motor side, runs at synchronous speed or not at all, and maintains speed independently of the load.

Engine Size is Determined by what factor

Alternator size.

High Voltage Transformer is what kind?

A step-up transformer.

Typical High Voltage Values

$4160\,\text{VAC}$ and $6,600\,\text{VAC}$.

Generator Cooling Methods

Air to air, air to water, and water to air.

HV Generator Special Features

Connected as a WYE wound generator and connection to ground

Neutral Earthing Resistor (NER)

A resistor that in a phase loss or ground will limit the current flow to the ground in a ground fault, used to prevent arcing during ground faults.

Neutral Earthing Resistor is connected how

Connecting only one resistor at a time (to the neutral Wye) to prevent voltage differential potential.

Neutral Earthing Resistor Sizing and Limitations

Can be sized to limit current flow from $1\,\text{A}$ to $500\,\text{A}$, is monitored via the NER Monitoring Relay, and does NOT work in a short circuit.

characteristics of a Neutral Earthing Resistor?

A) Is a resistor that in a phase loss or ground will limit the current flow to the ground in a ground fault

b) Only one is connected at a time (to the neutral Wye) to prevent voltage differential potential

C Monitored via the NER Monitoring Relay Used to prevent arcing during ground faults

D Can be sized to limit current flow from 1A to 500A

f Does NOT work in a short circuit

A/C Induction Motor Operation

Most common type_of A/C motor

because:

◦ Slip between rotor and supplied frequency is only 1 to 5 %.

◦ Power converters adjust for slip with_motors_ paired to_ another

Direction of rotation is changed in PWM or by changing any two leads in the power supply.

◦ Cooled by air- the rotor has an attached fan

A/C Synchronous Motor Power Factor Correction

Able to operate and provide power factor corrections depending on the excitation of the rotor.

A/C Synchronous Motor Holding Position Condition

Holds position when a DC current is applied to both the stator and the rotor windings.

A/C Synchronous Motor Speed Formula

$$\text{RPM} = 60 \times \left(\frac{\text{Hz}}{\text{number of pole pairs}}\right)$$

A/C Synchronous Motor Direction of Rotation

Changed by swapping two leads of the power supply in the power modulator.

A/C Synchronous Motor Cooling Method

Cooled by air through winding gaps.

Major advantage of pulse Width Modulator Variable Frequency Drive

can use standard induction motor

Major disadvantage of pulse width modulator variable frequency drive.

Will not allow power to be back fed into system for braking

Define Dielectric Constant

The ratio between the capacitance of the material to the capacitance of a vacuum is Dielectric constant

Define Dielectric Strength

The maximum electric field that the material can withstand under ideal conditions without undergoing electrical breakdown and becoming electrically conductive

Definition of... Breakdown or critical voltage.

The minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically conductive is the definition of.. Breakdown or critical voltage.

Define partial discharge.

A spark or arc that occurs in a defect in insulation the definition of... partial discharge.

definition of.. Breakdown strength

The minimum voltage for spark breakdown to occur across a material of given thickness held between electrodes producing a uniform electric field iS the definitior of.. Breakdown strength

Insulation

Electrically nonconductive material used in bulk to wrap electrical cables or other equipment.

Define insulating

Support and separate electrical conductor. that do not allow current to pass through them is the definition of. Insulators.

Dedicated Propulsion (DP) Plant

A shipboard system that exclusively powers vessel motion without supplying house electricity, typically using slow-speed or medium diesel engines.

Integrated Electrical Plant (IEP)

A centralized electrical network that provides power for hotel and auxiliary services in addition to vessel propulsion.

Four Marine Prime Movers

Pods, diesel-mechanical propulsion, and electrical propulsion.

Slow speed diesel engine

Medium Speed Diesel engine

Gas turbine

Steam engine

Four Marine Prime Movers

Slow-speed diesel engines, medium-speed diesel engines, gas turbines, and steam turbines.

Advantages of an Integrated Electrical Plant (IEP)

Potential for lower fuel costs, flexible layout allowing generator placement anywhere, lower weight, and reduced vibration and noise

Name 1 through ten in attached diagram

1 prime movers

2 generator

3 switch board

4 neutral earth resistor

5 transformer

6 transformer

7 harmonic filter

8 vfd

9 excitor

10 propulsion elect motor

Name 1 through ten in attached diagram

1 prime movers

2 generator

3 switch board

4 neutral earth resistor

5 transformer

6 transformer

7 harmonic filter

8 vfd

9 excitor

10 propulsion elect motor

Ac induction motor operation

Power conversation adjusts for slip with motors paired to one another

Third Harmonic creates what problem

Heat

Passive Harmonic Filter works how

Absorbs frequency by creating a path of low impedance tuned to one frequency 3rd,5th,7th,9th,11t

Low voltage vs high voltage enclosures

Low voltage is metal enclosure

High voltage is metal clad ie. Controls and circuit breaker etc all in their own enclosure

ACTIVE HARMONIC FILTER WORKS HOW?

"Active" works by injecting opposing waveforms to cancel out harmonics

Standoff insulators

Typically made of epoxy resin ◦ Resist high vibration and heat present in marine environment

Maintain electrical isolation of current conducting materials from other materials that could conduct current but are used as a support.

How does "Drive Dedicated/Broadband" harmonic filter work

"Drive Dedicated/Broadband" = Tuned to 2 to 3 frequency's 3rd and 5th etc., placed on an individual drive

IEP DISADVANTAGES

Higher cost initially

Higher training requirements

Higher chance if Higher voltage accidents

Need to compensate for regenerated power

Increased reliance on Automation

Special requirements for High Voltage (HV) systems

Grounded systems, power factor corrections, increased insulation size relative to conductor size, additional safety measures, decreased motor size with increased power availability, power switching capability, and physical equipment design.

Disadvantages of an Integrated Electrical Plant (IEP)

Higher initial equipment cost, higher crew training requirements, greater electrical hazard, and the need to handle regenerative power.

What Voltage separates HV from LV?

1000 VAC

Name two types of propulsion electric motor...

Fixed pods, azimuthing pods, traditional PEMs with a line shaft output

Name three specifications for a HV generator

Three-phase; Wye wound; Brushless; Synchronous; 60Hz; 4.16 kV, 6.6 kV, 11 kV, or 13 kV; increased insulation requirements

Name the two most common types of shipboard HV Voltage ratings

4160

6.6kv

What does every PEM produce that must be taken into account in both design and operation?

Heat generation

Advantages of podded propulsion

Extremely maneuverable;

Can be push or pull;

can be forward facing ,

aft facing,

fixed in position,

or azimuthing 360 degrees;

No rudder required; Can use speed or pitch control or a combination of both

Potential Electrical Energy Hazards in HV Systems

Shock (exposure to electrical current flow), arc (discharge of electrical current through the air), arc flash, and arc blast.

Three Methods of Describing Arc Faults

1. Level of energy released: In terms of system voltage and current.

2. Type of occurrence: Prime power outage, propulsion disruption, or service interruption.

3. Damage: Due to the cumulative, destructive effect of the energy released.

Five Types of Arcs

• Open air arc: Exposed arc from conductors in a non-confined space.

• Arc in a box: Directed via an enclosure that focuses it outwards, multiplying energy $2$ to $12$ times.

• Ejected arc: Arc plasma that hits the worker.

• Tracking arc: Arc plasma conducting on skin or through clothing.

• Running arc: Arc traveling along a conductor.

Open Air Arc

An exposed electrical arc originating from conductors in an unconfined space.

Arc in a Box

An electrical arc directed via an enclosure that focuses it outwards, multiplying the energy $2$ to $12$ times.

Ejected Arc

An arc condition where arc plasma directly hits or strikes the worker.

Tracking Arc

An electrical arc where plasma conducts along the skin or through clothing.

Running Arc

An electrical arc that travels along the length of a conductor.

Factors Affecting Electrical Shock Severity

1. Voltage

2. 2. Amount of current conducted through the body

3. 3. Path of the current through the body

List 5 types of Arcs

Open air arc: exposed arc from cond uctors in non confined space;

arc in a box: directed via the box focuses it outwards multiplies energy two to twelve times;

ejected arc: when arc plasma hits the worker;

tracking arc: arc plasma conducts on skin or through clothing;

running arc: along a conductor.

Effects of Contact with Live Conductors

Burns, nervous system damage, dismemberment, and death.

Describe arc flash and arc blast hazards

Exposure can result in a variety of serious injuries and may even be fatal, equipment can suffer permanent damage and nearby inflammable materials may be ignited resulting in secondary fires.

How the human element can contribute to accidents.

Human factors such as distraction, lack of situational awareness, fatigue, stress, you name it,

it can adversely affect your ability to realize the potentially deadly exposure you have allowed yourself to get into. Be wary

How does ppe mitigate risk when you wear it

. PPE is the lowest level method of risk mitigation but, it MAY save your life

List methods of establishing safe working conditions

LOTO

GROUNDING

TOOLBOX TALK

JSA

Qualified assistant

Permit to work

Ppe

Primary arc protection is ONLY

Gloves

After this course you are

Certified

2. How is a Restricted Approach Boundary determined?

Boundary is determined by system voltage and component

State the difference between Danger and Warning headers on equipment markings.

Metal Clad for HV and Metal Enclosure for Lv

Metal clad enclosure

HV uses metal clad. All components including the bus, instrumentation, and main circuit breaker are enclosed in separate metal compartments to provide

: ◦ An additional level of safety.

o Ruggedness. Ease of maintenance

Metal enclosed

Metal Enclosed for LV

◦ All components including the bus, instrumentation and main circuit breaker are mounted in common compartments.

Certified vs Qualified

Certified # Qualified, The higher risk present in HV systems implies that personnel should have proven skill before being assigned HV tasks. Qualified personnel are as defined by OSHA, are "..capable, as determined by their electrical knowledge and skills, of working safely on energized circuits." This capability includes familiarity with the proper use of special precautionary techniques, personal protective equipment, insulating and shielding materials and insulated tools. This is very important concept.

Warning vs Danger what is voltage

What color is warning

Warning=under 600 V typically (Orange in color)

Danger=Over 600 V typically (red in color).

Describe the value of a trapped key system when limited personnel access is required. controls access

Keys are locked in a position that can control power or access to system or area.

Boundaries

3 types

Limited Approach, Restricted Approach, Arc Flash

1. How do you disconnect grounding cables

. Disconnect all 3 phase cables then disconnect ground. (Opposite procedure of connecting) first.