24th International Conference & Exhibition on Electricity Distribution (CIRED)

12-15 June 2017

Session 3: Operation, control and protection

Power management system

implementation on off-shore gas platforms
ISSN 2515-0855
doi: 10.1049/oap-cired.2017.1279
Ivan Goran Kulis ✉, Filip Vidovic, Mario Peric, Miljenko Boras www.ietdl.org

Control and Protection Business Unit, Koncar – Power Plant and Electric Traction Engineering
Inc., Zagreb, Croatia
✉ E-mail: ivangoran.kulis@koncar-ket.hr

Abstract: Electrical power production system of Ivana A&K platforms consists four three-phase generators driven by gas
motors. Besides, there are two emergency diesel generator sets for emergency power supply. Generators are feeding
power motor control centre board and essential user board on each platform. Due to the reliability, security, efficiency
and stability of this islanded industrial electric power system, it was decided to implement a comprehensive power
management system which should provide load-shedding solution and protect the plant against blackouts and power
source outages due to system disturbances. Selected system consists of a power management intelligent electronic
device with remote I/O and measuring devices deployed throughout the power system. System relies on IEC 61850
GOOSE communication for fast and accurate data exchange. In this study, the process of the system selection and
implementation has presented and described according to the conducted procedure.

1 Introduction 3 Analysis
Ivana A and Ivana K are a joint system of production and processing Upon reviewing of the technical documentation and visiting the
off-shore gas platforms. On Ivana K are facilities for receiving (from platforms the first analysis was conducted:
Ivana A and other production platforms), processing and
compression of gas into submarine pipeline to the coast. † Primary gas production and processing system has been analysed.
Electrical power production system of Ivana A&K platforms † Electric power system single line diagram has been updated.
consists four three phase generators driven by gas motors. Besides, † ECS functioning with normal operational states have been analysed.
there are two emergency diesel generator sets (EDG) for † Generator governors, automatic voltage regulators (AVR) and
emergency power supply. Generators are feeding power motor relay protection system have been analysed.
control centre (PMCC) board and essential user board (EUB).
Due to the reliability, security, efficiency and stability of this According to available data, it can be simply concluded that 2 of 4
islanded industrial electric power system, it was decided to generators are quite enough to satisfy the entire typical load
consider an implementation of a comprehensive power consumption in steady states. However, in this case, the problem is
management system (PMS). PMS should provide load-shedding outage of one of operational generators. Since large power
solution and protect the plant against blackouts and power source unbalance, system frequency will change rapidly causing protection
outages due to system disturbances. trip of the remaining generator. Such situation will lead to power
consumption collapse and therefore, to primary gas production and
processing system stopping. Upon primary process stopping it take
2 System description several hours to restore the process due to loss of pressure.
Also problem could represent switching of large loads (asynchronous
Electrical power production system of Ivana A&K platforms consists of motor driven pumps) due to governor and/or AVR malfunctions.
four three-phase generators G1 to G4 [406 kVA (325 kW) each] driven
by gas motors. Generators G1–G4 are feeding PMCC and EUB boards
on Ivana A&K platforms in normal operation condition. Besides, there 3.1 Load analysis
are two EDG sets – EDG 1 and 2 (330 and 250 kVA, respectively) – for
emergency power supply of EUBs (Figs. 1, 3). Loads have been enumerated and grouped by bays and
According to electricity control system (ECS) logs the typical corresponding switches. Then, have been categorised in three
daily load varies between 440 and 580 kW depending on the time groups corresponding to the priority. Third group has highest
of the year and loads that are not constantly running (Fig. 2). priority which mustn’t be switched off when gas processing and
Due to the reliability and stability reasons electrical power compression is running. When a failure on one generator occurs,
production system of Ivana A&K is always in operation with more remaining one has to power up following essential loads:
generators than it is needed in terms of load. In the case of one
generator failure, the rest of running generators should be able to † Sea water pump (SWP, one of four): 140 kW.
satisfy the load without electricity supply interruption. This is † Gas gen ventilation on Ivana A&K: 2 × 12 kW.
important because gas processing and compression process mast † MCC booster: 15 kW.
not be stopped to avoid pressure drop in pipe lines. † MCC solar (two of four): 2 × 25 kW.
Sometimes, in periods with low electric power consumption, there † TEG UCP: 15 kW.
is a need for using resistors for artificial load increase. † Total: 244 kW.
Inspired by cost reduction, it was decided to find solution for
reducing the number of generators in operation without reducing One SWP with motor control centre (MCC) set is enough to hold
power system reliability. the process for a few minutes. This gives enough time for starting of

CIRED, Open Access Proc. J., 2017, Vol. 2017, Iss. 1, pp. 1374–1378
1374 This is an open access article published by the IET under the Creative Commons
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 Second category loads are connected on EUB and supplied from
EDG within 1 min from power blackout. One minute is starting time
for EDG which are as well as spare gas generators in hot standby.
Starting time for gas generators is around 3–5 min.
First category can be switched off for a several minutes.

3.2 Site testing’s

Due to possibility investigation of PMS implementation, operational

tests with transient recordings were conducted on the platforms.
Tests comprise various switching combinations of generators and
loads such are:

† analysis of generators behaviour in transient state with outage of

large load,
† analysis of generators behaviour in transient state with outage of
one generator,
† analysis of generators behaviour in transient state with start of
large load,
† analysis of generators behaviour in transient state caused by
Fig. 1 Single-line diagram of the platforms electric power system
disconnection of ventilation system (ECS should stop a generator
without ventilation),
† analysis of single generator behaviour in transient state caused by
start and disconnection of large motor loads.

For example, in Fig. 4 are shown diagrams from a test with

following workflow:

† G3 is running with base load of ∼75 kW.

† Start-up of SWP1 110 kW.
† Start G2.
† Start-up of SWP2 130 kW.
† Start-up of SWP3 110 kW.
† Start-up of gas heater 5 kW.
† Stop of SWP3 110 kW.

Fig. 4 shows diagrams of:

Fig. 2 Four-day ECS voltage, current, power and frequency records (23–
27 March 2016) (a) bus-bar phase voltages L1, L2 and L3;
(b) L1, L2 and L3 phase currents of G3;
(c) L1 phase current of G3 and L1 phase current of G2;
(d) phase L1 P and Q of G3 and of G2;
(e) frequency.

From diagrams and from EDC records, it is obvious that AVR’s on

generators work uncoordinated. There is large difference between
reactive powers (215 kvar on G2 and 110 kvar on G3).
Prime mover regulators (governors) are working coordinated with
certain frequency oscillations which are in some extent allowable for
gas engine governors.

Fig. 3 Ivana K platform photographed from Ivana A

one of other gas generators connected on PMCC, since the nominal

power of one gas generator is 325 kW. This is greater than total
power of category three loads with safety margin of 33%. It can
be concluded that one generator can feed category three loads.
This hypothesis justifies the detail analysis to be performed.
ECS and other control equipment as well as emergency lightning Fig. 4 Voltage, current, power (P and Q) and frequency diagrams from one
remain supplied from uninterruptible power supply system. of the tests

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3.2.1 Notes on tests: During the tests, a fault on an AVR has
been found.
The analysis shows that governors (prime movers) and AVRs
should be better set and coordinated. In a case of PMS application,
the best solution will be replacing them with new ones due to
deterioration caused by years of operation in wet and salt
conditions. Service reports also mention corrosion and deterioration.
When generators work synchronised, there is a difference in
individual reactive power (Q) production. Active power (P) is
better harmonised but there are different oscillations in frequency
in different generator and load combinations.
Also, when generators work individual their behaviour is
different. For example, G1 is unstable on lower demand while G2
is unstable on higher demands (loads).

3.3 Electricity system modelling

For further analysis, a model of Ivana A&K electricity system has

been made in power system analysis tool Neplan 360.
The aim of this modelling is to investigate the operative conditions
of Ivana A&K plants by means of load flow calculations and
transient stability analysis [1, 3].
The normal running configuration has been studied by means of load
flow calculations, to validate the correctness of the component sizing
and to verify that all the electrical quantities are within the limits.
The transient stability analysis highlighted the dynamic
performances of the electrical system when it is subjected to
electromechanical transients. The results should allow the correct
manage of the plant and the proper setting of the electrical
protections and the control systems. Also, transient analysis helped
in PMS implementation analysis.
System component data are taken during site visit and from data
sheets and are implemented in the model. Model correctness has been
validated by test results respectively voltage, current and power records.

3.3.1 Load flow analysis: According to the load flow results it

can be concluded that normal system operation configurations are
characterised by the correct operation of all the components and
that all the electrical quantities are within the limits:

† The load flow calculation demonstrates that all the components Fig. 5 Diagrams of voltage, current, rotor speed, frequency and power (P
are correctly sized. and Q) of single operational generator G1
† The bus bar voltages do not exceed the rated limits (±10%) in the
configuration.
† The currents flowing through the cables do not exceed the cable Upon model calibration and verification, transient analysis has
ampacity. been used in PMS implementation analysis. Fig. 6 shows diagrams
† The power production of the generators respects the limits of the of generator G1 line voltage, current, rotor speed, frequency and
machines. power and power of G3. Generators 1 and 3 have been operated
with base load which consisted of SWP 1–3, MCC Solar 1–3,
TEG UEP and HVAC system.

3.3.2 Transient stability analysis: According with available 1. event is outage of G3 in 10th second of simulation.
data, AVRs and governors are modelled by the most similar 2. event is disconnection of SWP 2 and 3 and MCC 2 and 3 by PMS
software models. load shedding.
For AVR is used simplified excitation system and for engine
governor is used model prepared for diesel/gas governors.
The models of the controllers have been parametrised and 4 PMS implementation analysis
validated comparing the simulation results with the test report
diagrams. The comparison shows that the modelled regulators are 4.1 System requirements
close to the actually implemented ones.
Fig. 5 shows diagrams of generator line voltage, current, rotor Due to the reliability, security, efficiency and stability of Ivan A&K
speed, frequency and power of single generator in operation. islanded industrial electric power system a fast load shedding (FLS)
Generator has operated with base load which consisted of SWP 1, system should be implemented. PMS should provide FLS solution
MCC Solar 1, MCC Solar 2 and heating, ventilation and air and protect the plant against blackouts and power source outages
conditioning (HVAC) system. due to system disturbances [2].
Selected FLS System should consist of one power management
1. event is disconnection of SWP 1 in 1st second of simulation. intelligent electronic device (IED) with remote I/O and measuring
2. event is connection of SWP 1 in 10th second of simulation. devices deployed throughout the power system. PMS should rely
3. event is disconnection of MCC Solar 2 in 20th second of simulation. on optical IEC 61850 GOOSE communication for fast and
4. event is connection of MCC Solar 2 in 30th second of simulation. accurate data exchange.

CIRED, Open Access Proc. J., 2017, Vol. 2017, Iss. 1, pp. 1374–1378
1376 This is an open access article published by the IET under the Creative Commons
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 4.3 Proposed system description

PMS provides a safe, efficient and reliable operation of Ivana A&K

power system. The PMS functionality includes load shedding,
generator supervision, PMCC and EUB power exchange and
synchronisation. PMS protects and optimises the stability of power
systems against disturbances [4].
Load shedding should operate when the electrical load demand
exceeds the capacity of available generators subsequent to the loss
of one of them. The load-shedding system has to ensure the
availability of electrical power to critical loads (category three) on
the platforms. This is achieved by switching off the noncritical
loads in case of a lack of power in the electrical system caused by
loss of generation capacity.
Based on the shortfall of available power in the power system, the
load-shedding action initiated by PMS ensures that only identified
loads are shed, system remains stable after load shedding and
impact on the process is minimal. The system allows flexibility to
select or deselect the loads to be shed at any point in time during
operation.
Furthermore, the load-shedding function should not operate if the
situation in the power system does not necessitate such an action.
Thus, it has to be accurate and selective.
PMS provides system level protection from the system
disturbances. Central IED supports different modes of
load-shedding functions:

† fast load shedding,

† slow (overload or maximum demand violation based) load
shedding,
† manual load shedding,
† under-frequency load shedding as a backup to fast and slow load
shedding.

A network power deficit occurs when one of operational

generators trips.
The fast load-shedding function protects the power system during
a power deficit. The fast load-shedding function takes corrective
action before the system frequency drop and provides fast and
accurate load-shedding action based on the power balance
calculations and defined priorities. Thus, the function also
contributes towards faster improvement of the frequency profile of
the system.
The slow load-shedding function prevents the tripping of a
generator during overload conditions. The slow (overload)
load-shedding function triggers the load-shedding and resets the
overload condition by acting faster than the dedicated overload
protection function for the generators. The overload situation can
arise due to the overcurrent detection in a generator for a specified
period of time. Based on the amount of the overload, the slow
load-shedding function determines the required load to be shed
and uses the power balance calculations for arriving at the
load-shedding priority and to initiate the load-shedding action.
The under-frequency-based load-shedding function detects
frequency decay and activates the shedding mechanism described
for fast load-shedding functions.
Fig. 6 Diagrams of voltage, current, rotor speed, frequency and power (P
and Q) of G1 and power (P and Q) of G3
4.4 PMS architecture

Central IED performs load-shedding actions based on the binary and

4.2 Existing control and protection scheme measurement data it receives from the peripheral units associated
requirements with generator, motor, load and bus coupler bays.
Using dedicated peripheral units based on IEC 61850 all
Existing ECS control and relay protection scheme and characteristic bays can be adapted for the load-shedding
settings should not be changed. PMS is parallel and superior to functionality. All the binary IO signals and the transducer inputs
existing control and protection scheme and does not affect usual can be connected to peripheral units without influencing the
operation. existing wiring scheme.
To ensure proper functioning of system in any way, it is necessary After making a decision to take load-shedding action, central IED
to ensure proper functioning of primary control devices, sends shedding commands to motor or load bays through their
respectively, AVR and gas engine governors by means of tuning respective peripheral units. Auxiliary relays are needed to extend
and replacing where is necessary. the shed commands from the binary output modules.

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5 Conclusion network. Also, it can be applied for island operation detection of
distributed generation.
Electric power system of Ivana A&K platforms is an industrial power
system operating only in islanded mode. Considering that the power
system supplies important, expensive and vulnerable process the 6 References
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CIRED, Open Access Proc. J., 2017, Vol. 2017, Iss. 1, pp. 1374–1378
1378 This is an open access article published by the IET under the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/3.0/)