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Name: Abdullah Al Ghamdi Company: GCCIA Position: Head of HVDC
The GCC Interconnection Project
Connects six countries with 400 and 220KV links
GCC NETWORK & Objectives
Ensure Power System stability
Reduce overall Spinning Reserve
Reduce Installed Capacity
Requirement for Reserves
Support during Blackout
Energy Trading
*
3 x 600 mw Al-fadhili btb hvdc converter
GCCIA HVDC Back-to-Back CONVERTER FACILITY
AC Voltages / Frequency: 400 kV (50 Hz) / 380 kV (60 Hz)
Rated Power : 3x616 MW @ 55C ambient temp.
Valves COOLING: De-Ionized Water Cooled
Thyristor Triggering: Electrically Triggered
Converter Transformers 50Hz: 380MVA
Converter Transformers 60Hz: 385 MVA
HVDC operational Setup
HVDC Back-to-Back station consists of three poles with 600 MW for each
HVDC has modes of operations
Dynamic Reserve Power Sharing (DRPS) mode
Economic Power Dispatch (EPD) mode
The DC links are initially in standby mode or transferring power (EPD)
Supply of reserve power is done automatically by the HVDC control system
HVDC can be remote controlled from ICC or locally
Valve Hall
HVDC Converter Transformers
Switchyard
HVDC BACK-TO-BACK CONVERTERS FACILITY
HVDC Functions
To interconnect the 50Hz and 60Hz systems
To provide reserve power sharing
To stabilize the interconnected systems following a critical loss
of generation
To permit up to 1200MW of economic active power transfer between the
member states
HVDC modes of operations
HVDC
modes
Hot Standby
Mode
The Poles are kept
energized from the AC
(50Hz and 60Hz) grid,
with no power transfer i.e. poles in the
blocked mode
Dynamic Reserve Power Sharing (DRPS)
Mode
Power transfer is activated
automatically when pre-defined criteria is met to
assist in achieving dynamic
stability in either the 50Hz
or 60Hz systems.
60 events since 2009
Economic Transfer (ET)
Mode
Frequency Control (FC)
Mode
Up to 1200MW of active power
transfers between 50 Hz
and 60Hz systems can be scheduled and implemented
The Triggering Criteria enables
operating reserve sharing between
both blocks following the N-1
loss of generation or demand within
either system. 21 events O/F 99 EVENTS U/F
Total FC events 120 SINCE 2015
When df/dt >0.1hZ /s
After 500ms the power
requirement is at least
240MW(0.39pu)
Now the soonest that
the pole will be de-
blocked is after 550ms
from an event.
Will Deblock to
between 240MW and
550MW
DRPS Triggering Criteria STAGE-1
10
fo
F
HVDC acts automatically when frequency drop below
frequency dead band ∆ F for specific time t
Power contributions for any
deviations is calculated based on two
different power/frequency slope
characteristics on either side
HVDC support
Frequency Control
11
FC
Operation & maintenance challenges
Because of the climatic and environmental conditions in the
Kingdom of Saudi Arabia where HVDC is located, the extreme
and daily seasonal variations in temperature and high level of
pollution from sand and dust has impact on the following:
Control and Protection
Valve Cooling System
Valve hall Component failure
Outdoor Switchyard equipment
Operation & maintenance challenges
Control & Protection
• Interlocks signals causing pole to become not ready for service
• dust contamination inside panels because there is no dust filter on the control panels and no bag filters on HVAC
• Maintenance procedure and intervals have been changed to clean racks dust filter monthly and replace them yearly
Operation & maintenance challenges
Control & Protection
• Other common control and protection challenge is the obsolescence of spare parts
• Processor cards became obsolete in 2013
0
1
2
2011 2012 2013 2014 2015 2016 2017 2018
Power supply module Sharc Processor Card Pentium Processor Card Change over unit Analogue card Media Converter
C&P Components Failure Statistics
Valve Cooling (VC) System challenges
Operation & maintenance challenges
Valve cooling system few Protection philosophies as following,
Inlet coolant temperature Protection
Valve coolant inlet temp low alarm : 15° C
Valve coolant inlet temp low Trip : 5° C
Coolant Condensation
Valve coolant inlet temp – valve hall dew point temp ≤ 5° C “Valve cooling condensation risk” minor alarm will be triggered.
Valve coolant inlet temp – valve hall dew point temp ≤ 2° C “Valve cooling condensation danger” major alarm and will initiate blocking of poles and tripping of converter transformer & filter CB’s.
Control measures for condensation
Operation & maintenance challenges
Temperature controlled shunt valves are installed to
prevent passage of coolant during low temperatures
Shunt valve & bypass valve operated using PID
controller for the inlet temperature of 30°C
15% Mono Ethylene glycol is added to avoid coolant
freezing in outdoor coolers.
Before (Without Shunt Valve) Current (With Shunt Valve) Detailed view of Shunt Valve
VC Emergency Backup support
440V, 150 Ah VRLA battery bank is integrated with the VC
system. Battery bank supports the main pump, by feeding VFD
DC bus, during the temporary auxiliary power supply
interruptions.
Back up system supports the pump for 45 sec by switching the
pump to Low speed. If interruption exceeds 45sec tripping
command will be initiated.
Short cycling of the battery bank, because of intermittent ATS,
bank resulted in under voltage protection operation in UMD
that feeds the cooler fan of main VFD.
Control measures
Battery banks were replaced in year 2016
LVAC ATS scheme is revised
Operation & maintenance challenges
Operation & maintenance challenges
Valve Hall Components Failure statistics
Valve hall comprises 50 & 60 HZ converters in quadrilateral arrangement. Fundamental building block of converter is called Thyristor Clamped Assembly (TCA). TCA is equipped with di/dt reactor, Thyristor & it’s associated Gate drive units (Gate, divider card). Following figures depicts various element failure for 9 years,
Avg. annual failure rate for Thyristor = 0.1 %
Avg. annual failure rate for Gate card = 0.11%
Avg. annual failure rate for Divider card = 0.05%
Valve Hall Annual Preventive maintenance is covering two quadrivalves in one converter station, one on the 50Hz & another one on 60Hz side in a calendar year.
0
5
10
15
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
3 1 2 2
10
1 1 3 3 2 3
1 1 3
1 2
15
Co
un
t
Year
Thyristor & Card Failures
Gate card
Divider Card
Thyristor
0
1
2
3
4
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
1 1
2
1
2
3
4
1
2
Co
un
t
Year
Coolant Leak &di/dt reactor
di/dt reactor
Coolant leaks
GRP strap Failure
Coolant leaks & Detector
Two numbers of coolant leak detector is mounted at the bottom
of corona stress shield per Quadrivalve. Coolant leak in any
levels will be guided to bottom tray & collected in coolant leak
detector bucket. Bucket tips when filled with coolant (Approx.
100 Cm3).Fibre Optic senses bucket movement & relaying
bucket status to Valve Based Electronics (VBE).
Protection logic in Fadhili HVDC as follows,
Minor coolant leak Alarm- Bucket decants & returns to normal
position in less than 3 Seconds
Major coolant leak Trip- Bucket in decant position
continuously for more than 3 Sec (or) decants two times within
3 minutes.
Bottom Tray
Coolant Bucket
Operation & maintenance challenges
Coolant leak variants
di/dt Reactor connection
Drain Olive bloc
Isolation valve
Thyristor heat sink connection
Operation & maintenance challenges
Coolant leak Failure modes
Cracks on the fittings
Damaged ‘O’ rings
No other known failure modes.
Operational experience suggest that Low
temperatures coolant & thermal
expansions when the pole are DE blocked.
Operation & maintenance challenges
Leak Detector issues
Coolant leak detector bucket stuck-up during the
operation.
Rotating shaft support block clearance getting
affected by moisture absorption.
Operation & maintenance challenges
Operation & maintenance challenges
Switchyard component failure
0
2
4
6
8
10
2011 2012 2013 2014 2015 2016
3
9
4 3
0
4
Year
Harmonic Filter Capacitor Failure
Pole-1
Pole-2
Pole-3
Total
22, 54%
19, 46%
Capacitor Failure Mode
Capacitancedeviation
Oil leak
Capacitor oil leak attributed
to climate factor
Annual Average Harmonic filter capacitor failure is 0.06 %
0
2
4
6
0
4
0
6
3
5
Year
PLC Filter Capacitor Failure
50Hz PLC
60Hz PLC
PLC total
Annual Average PLC filter capacitor failure is 0.83 %
Operation & maintenance challenges
Switchyard component failure
Capacitor failure on 18.05.2019 nine capacitors were damaged and replaced
Recommendation:
Improve the design with fused type
capacitors.
Check the feasibility study for filter
switching improvement by Point-on-
Wave relay wherein the Circuit Breaker
of each phase of the harmonic filter
should close at an instant near the
voltage zero crossing.
Check the possibility of improving
temperature detection/protection system
Operation & maintenance challenges
Switchyard component failure
Burned PLC reactor due to bird’s nest
Mitigating measure: Bird’s spikes were
installed on top of the reactor
Cat’s intrusion to
energized equipment
caused short circuit
Mitigating measure:
barbed wire were
installed on the fence
and sealed the gap b/w
the ground and the fence
Operation & maintenance challenges
Adverse weather condition: Sandstorm
Regular cleaning/sand removal being done
380kV Cable joint & SVL failures
Random SVL failures occurred for 380kV & 400kV Cable
circuits. Failures statistics shown in below table,
- No apparent fault conditions reported within HVDC
- No Switching/Lighting surges recorded by Surge arrester
counter in the cable sealing ends.
In Nov 2017 380kV cable joint failure occurred
Root cause analysis is being conducted for SVL failures and
proposal to implement PD monitoring for cable circuits.
Operation & maintenance challenges
Period Pole-1 Pole-2 Pole-3
Nov 2015 –
May 2019
Nil 50Hz- Nil
60 Hz- 3 Nos
50Hz- 1
60 Hz- 3 Nos
Operation & maintenance challenges
Availability and Reliability
0
20
40
60
80
100 87.3
9
62.0
0 88.4
3
75.1
6
77.6
9
95.0
4
97.6
8
98.1
6
95.3
0
Energy Availability %
0
5
10
15
20
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
FOFI
Energy Availability of Al Fadhili HVDC Force Outage Frequency Index (FOFI)
Factors affecting the Reliability and Availability
-Oman HVDC Link
-Iraq HVDC link
-Upgrade of HVDC Control System
-Enhancement of power transfer from 1320 MW to 1980 MW
Future Plans
Conclusion
Most of the challenges on Al Fadhili HVDC project are related
to the unique design and operation on the facility being on
hot standby mode.
Despite of the challenges faced during the 10 years of
operations of HVDC it can still attain a high level of Energy
Availability and Reliability
Thank You
Abdullah Al Ghamdi- Head of HVDC
Email : aghamdi@gccia.com.sa
GCCIA www.gccia.com.sa
Saudi Arabia- Dammam
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