AN OVERVIEW OF TECHOP ODP 09 (D) (A METHOD FOR … · A METHOD FOR PROVING THE FAULT RIDE-THROUGH...

AN OVERVIEW

TECHOP_ODP_09_(D)

(A METHOD FOR PROVING THE FAULT RIDE-THROUGH CAPABILITY

OF DP VESSELS WITH HV POWER PLANT)

OCTOBER 2014

A METHOD FOR PROVING THE FAULT RIDE-THROUGH OF DP VESSELS WITH HV POWER PLANT

Acknowledgements

• The MTS DP Committee thanks ABS, DNV and the

following companies for their contribution to the

preparation of this Techop:

– ABB

– GE

– Siemens

– AKA

CASE FOR ACTION

• There is a need to improve efficiency and reduce

emissions from DP power plants – Operating power

plants with closed busties is a means of achieving this.

• Industries experience of loss of position incidents on

DP vessels operating with closed busties suggests a

lack of sufficient fault ride through capability – Loss of

all thrusters or blackout.

• 18 examples of such incidents are given in the Techop.

• Increasingly difficult to get stakeholder concurrence for

operation with closed busties.

PURPOSE OF TECHOP

• Build confidence in common power systems by

testing fault ride-through capability using an

established method.

• Contribute to proof of equivalent station keeping

integrity for DP class 3 vessels IMO MSC 645

Section 3.2.4.

• Communicate experience of doing it successfully.

• Enhance the knowledge of stakeholders.

• NOTE: If there is no intention to carry out DP

operations with closed busties then you don’t need

to prove fault ride through capability.

CONTENT OF TECHOP

• Information on one method of proving fault ride-

through that has been carried out safely and

effectively.

• Practical details on how to carry out the testing.

• Details of the power system attributes to be proven.

• Guidance on computer simulation and preparatory

• To provide focus on risk assessment, typical roles

and responsibilities for stakeholders.

FAULT RIDE-THROUGH TESTING IS NOT NEW

VOLT RISEVOLT DROP

GENERATOR

TERMINAL

VOLTAGE FALLS

FAULT CURRENT

BUS VOLTAGE

MAINTAINED

VOLT RISEVOLT DROP

• Fault Ride-Through

Testing on LV DP

DSVs in the 1980s.

• Built to be tested.

• Tested by

application of

bolted short circuit

to 660V feeder.

• Requirements for fault ride-though capability have

always existed based on single failure criteria.

• What has changed is that more focus is now placed

on proving this capability by testing.

• Traditional methods inadequate to meet stakeholder

expectations:

– History of too great a reliance on limited analysis only e.g.

short circuit calculations.

– FMEA testing did not create realistic conditions for fault

ride through proof.

FAULT RIDE THROUGH CAPABILITY –

A LOOK BACK

SEVEN PILLARS

tiatio

ult to

ult re

sistan

ult rid

Predictability

Incident Free DP Operations

These pillars

require more

focus when

cross-connections

are introduced.

• Expertise - Already available from several

well known sources.

• Qualification and approval – Early

engagement with class.

• Roles and responsibilities – Agree in

advance.

• Action in the event of unsuccessful tests –

Agree in advance.

PRE-REQUISITES FOR CARRYING OUT FAULT RIDE -

THROUGH TESTING

INDUSTRY READINESS FOR TESTING

• Recent experiences of successful testing.

• More than 10 tests carried out - plus

experience of real short circuits on DP

vessels.

• Initial apprehension overcome: – Crew safety.

– Test personnel safety.

– Risk assessment.

– Equipment damage – leaving hidden failures (weakness) –

actually helps reveal them.

EFFECT ON CIRCUIT BREAKER LIFE

BREAKING CURRENT (r.m.s. value)

2000030000

10 20 50kA31.5

BUSTIES

TEST FEEDER

You need to check what your circuit breakers are rated for.

Build to test

EFFECT ON BUSBARS

• Forces on bus bars are proportional to the

square of the current.

• As peak test current in the example in the

Techop is around 1/3rd of rating.

• Forces are around 1/10th of rating.

EFFECT ON GENERATORS

• Generators rated for a defined number of

short circuits – for example 3.

• Generator sees ‘almost’ a full short – there

is some impedance – more could be added

but considered unnecessary on HV systems

by manufacturers – no reports of damage.

PRACTICAL CONSIDERATIONS FOR

CARRYING OUT TESTING

1. Advance modelling.

2. Building confidence for the fault ride-

through test – commissioning.

3. Fault ride-through test.

4. Earth fault test.

TEST CONDITIONS

• Vessel at sea trials location.

• DP system in full auto DP.

• Two generators online (on different busses).

supplying DP & Hotel.

• All transformers connected.

• All busties closed.

• Instrumentation and logging facilities

operating.

• Carry out test.

FAULT RIDE-THROUGH TEST

CLOSED

RUNNING

DRILLING

RUNNING

DRILLING

RUNNING

CLOSED

CLOSED CLOSED

EARTHINGTRANSFORMER

RUNNING

DRILLING

RUNNING

THIS CABLE MUST BE RATED FOR FULL S/C CAPACITY

THIS CIRCUIT BREAKER IS CLOSED REMOTELY TO APPLY THE TEST FAULT

CLOSED

X3 X3 X3

• Test fault applied.

• Busties open to isolate switchboard with

fault.

• All thrusters stay online and selected to DP.

• All DP essential systems continue to

operate without malfunction.

• Feeder removes test fault.

• Both generators remain on line.

• All buses healthy.

EXPECTED RESULT

TEST DATA AQUISITION

Signal sources that can be instrumented

(Build to Test) or used to collect data include:

• Generator VTs and protection & measuring CTs.

• Bus VTs and protection & measuring CTs.

• Feeder protection and measuring CTs.

• Serial links from protection relays.

• Serial links from governors and AVRs.

• Serial links from thruster drives.

Vessel management systems, history stations, data

loggers can be used to record any changes in plant

status.

POWER SYSTEM ATTRIBUTES TO BE VERIFIED

• This section of the Techop deals with

various functions and features to be verified

as part of the analysis and testing process:

– Fault cleared by busties.

– Voltage dip ride-through.

– No protection operation on plant recovery current.

– No protection operation on plant recovery over

voltage.

– Model mal-synchronisation and inadvertent gen CB

closure.

– Decrement curve and model validated.

FAULT CURRENT RECORDINGS

Peak test current 30% of rated

MAIN BUS VOLTAGE RECOVERY & OVERSHOOT

Overshoot

Recovery

PLANT RECOVERY

Plant recovery current

Fault applied

removed

Voltage dip

Fault Current

• Time Domain Modelling – e.g.

MatlabTM SimulinkTM or equivalent.

• Real Time Digital Simulation or similar.

– Protection relays.

– Enhanced generator protection.

– Drive controllers.

• Use test data to validate model

predictions.

COMPUTER SIMULATION

EARTH FAULT TEST

RUNNING

DRILLING

RUNNING

DRILLING

RUNNING

CLOSED

EARTHINGTRANSFORMER

RUNNING

DRILLING

RUNNING

THIS CIRCUIT BREAKER IS CLOSED REMOTELY TO

APPLY THE FAULT

CLOSED

X3 X3 X3

CLOSED CLOSEDCLOSED

EFFECT ON LINE TO EARTH VOLTAGE

Increase in line to earth voltage

This phase earthed

EARTH FAULT CURRENT

Fault isolated by busties

Fault isolated by test feeder

TEST REPORT

INTRODUCTION • Vessel, DP system and power systems description.

• Redundancy design intent and worst case failure design intent.

• Power plant configurations and fault types to be modelled and tested.

APPLICABLE RULES, STANDARDS AND CLASS NOTATION.

TEST METHODOLOGY

• Description of test method with supporting sketches.

DISCUSSION OF SIMULATION METHODOLOGY

• Simulation package, TDS, RTDS, HIL etc. Discussion of any

assumptions made in modelling of configurations which were

not tested. Means by which the worst case conditions were

identified.

TEST REPORT - CONT

RESULTS

• Comparison of measured and modelled waveforms.

• Comparison with the results of static studies such as short circuit

calculations.

• Results of RTDS or HIL demonstrating that actual protection and

control systems respond correctly.

• Presentation of worst case conditions and confirmation that the

severity of the failure effect does not exceed the DP system’s worst

case failure design intent.

CONCLUSIONS

• Compliance with the applicable rules & requirements.

INSPECTION AFTER TEST

• Removal of test equipment.

• A general inspection of the generators used for

testing could include visual inspection of:

– End winding.

– Auxiliary components, AVRs, CTs etc.

– Cable terminations.

CHALLENGES

• Build to Test – Thruster drives may need braking resistors.

• Special cases – HV power plant with limitations which make it more difficult

to test.

– Older power plants – Uncertainty in relation equipment spec.

– LV power plant.

• Complementary methods for periodic testing

where required.

CONCLUSIONS

• There is a case for action.

• It is possible to carry out fault ride

through testing with acceptably low risk

when properly executed.

• A combination of design requirements,

computer simulation and testing,

produces common power systems with

comparable integrity to independent

power systems.

AN OVERVIEW OF TECHOP ODP 09 (D) (A METHOD FOR … · A METHOD FOR PROVING THE FAULT RIDE-THROUGH...

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