Transcript Reactive Power Control

WELCOME
HVDC Challenges
in Grid Operation
By
V.G.Rao
Chief Manager
HVDC Kolar
TALCHER KOLAR SCHEMATIC
TALCHER
Electrode
Station
Electrode
Station
KOLAR
+/- 500 KV DC line
1370 KM
400kv System
B’lore
Hoody
Cudappah
220kv system
Hosur
Salem
Udumalpet
Kolar
Madras
Chintamani
Points related to operation of HVDC
• RPC control
– Filter switching seq.
– Limitations by RPC
• Stability Controls
–
–
–
–
•
•
•
•
•
Power Limitations
Frequency limit controller
Run-backs / Run-ups
Power Swing damping control
GRM operation & electrode limitation
Overload of HVDC
SPS scheme
Power / current limits due to protection
Power reversal
Reactive power control / RPC : 2 modes
– Q- mode – Reactive Power control mode –
• The switching limit for the filter can be adjusted by
entering the maximum set value of Reactive power (Q) by
the operator.
• Possibility to select between Q-basic or Q-extended mode
• Max limit for Q-basic: Talcher - +100MVAr, Kolar +500MVAr
• Max limit for Q-extended: Talcher - +500MVAr, Kolar +500MVAr
Reactive power control / RPC : 2 modes
• U-mode – Voltage control mode
– The switching limit for the filter can be adjusted by a
maximum and minimum set values of AC bus
Voltage.
– is maintained.
– If the voltage of the bus reaches the minimum limit,
filter will be switched into service.
– If the voltage of the bus reaches the maximum limit,
filter will be switched out of service
– Upper limit : Talcher / Kolar 440kV
– Lower limit : Talcher / Kolar 360kV
– Bandwidth of 20KV
Reactive Power Control
• Reactive Power Control is mainly achieved by switching
individual reactive power sub banks
• Provided Reactive Power Sub Banks - Kolar
Double tuned 12/24 harmonic (type A) – 8 no’s- 120MVAr each
Double tuned 3/36 harmonic (type B) – 4 no’s- 97MVAr each
Shunt capacitor sub-bank (type C) – 5 no’s – 138MVAr each
• Provided Reactive Power Sub Banks - Talcher
Double tuned 12/24 harmonic (type A) – 7 no’s- 120MVAr each
Double tuned 3/36 harmonic (type B) – 4 no’s- 97MVAr each
Shunt reactors (type L) – 2 no’s – 80MVAr each
Shunt capacitor sub-bank (type C) -1 no. -66MVAr
Reactive Power Control
• Switching ON criteria of individual sub banks and their
hierarchy:
– sub bank switching according to Harmonic Performance –
given higher priority and depends on actual DC power flow
– AC bus bar voltage within operator reference values – if
RPC is in U-mode – next priority
– total station reactive power within operator reference values
– if RPC is in Q-mode – next priority
• Switching OFF criteria of individual sub banks and their
hierarchy:
– Sub banks switches out based on the AC bar voltage only
Filter Switching settings for Kolar
Bipolar operation -100% DC voltage
Load / Idc
No. of filters
Bipolar operation -80% DC voltage
>10%
1A+1B
>25%
2A+1B
Load / Idc
>40%
3A+1B
>12.5%
1A+1B
>55%
4A+1B
>25%
2A+1B
>70%
4A+2B
>40%
3A+1B
>85%
5A+2B
>55%
>95%
6A+2B
>70%
>100%
7A+2B
>85%
>105%
7A+3B
>100%
>110%
8A+3B
OR
7A+4B
>120%
>125%
>130%
8A+4B
No. of filters
4A+2B
Filter Switching settings for Kolar
Monopolar operation -100% DC
voltage
Load / Idc
No. of filters
Monopolar operation -80% DC
voltage
>10%
1A+0B
>25%
1A+1B
Load / Idc
>40%
2A+1B
>12.5%
1A+0B
>55%
>25%
1A+1B
>70%
>40%
2A+1B
>85%
3A+1B
>55%
>100%
4A+2B
>70%
>110%
5A+2B
>85%
>120%
6A+2B
>100%
>125%
>130%
No. of filters
3A+1B
Reactive Power Control
• Manual control of sub banks is possible by the operator
• AC voltage limitation is permanently active irrespective of manual / automatic
switching of filters
• CONNECT INHIBIT level – filters/shunt-c cannot be connected in manaul /auto
– AC bus voltage is above 431kV ( reset at 424kV) or
– Reactive power export to the grid is high compared to active power (refer table)
• ISOLATE level - filter sub banks/ shunt C are switched OFF in 0.5 seconds interval
automatically at 440kV
• ISOLATE INHIBIT - Switching off of sub-banks is blocked if the AC voltage drops
below 380kV
• CONNECT limit - additional banks will be switched on (in 1 second interval)
automatically if the AC voltage reaches 360kV
RPC sub bank connect inhibit levels
Bipole Power
at Kolar
Maximum no. of
filters / shunt C
500
6
550
7
600
8
650
9
700
10
800
11
1000
12
1200
13
1400
14
1600
15
1800
16
2000
17
At Connect Inhibit
level – Control system
prevents switching
ON of filters / shunt C
in auto or manual
irrespective of AC
voltage to prevent
export of excessive
reactive power
STABILITY FUNCTIONS
– Power Limitations
•
•
•
•
•
Always enabled in the control system
Becomes active once the AC switchyard configuration
for NTPC at Talcher or 400kV S/y at Kolar changesrefer tables
Introduced to improve stability in the regions, self
excitation of generators, failure of control systems etc.
Power capability depends upon the no. of generators /
lines connected to HVDC
Automatic limitation of power takes place
POWER LIMITATIONS-TALCHER
Signal (Bit code)
DC Power Limit in MW
No. of Generators &
pair of AC lines
0 000
loss of comm. between AC SC &PC
1 001
controlled shutdown or ESOF
0
1 010
500 MW
1
0 011
1000 MW
2
1 100
1500 MW
3
0 101
no limit
4
0 110
no limit
5
1 111
no limit
6
•Two lines / one pair of lines equivalent to 500MW
•If all the generators at Talcher trips / only lines are considered for
power limitation
POWER LIMITATIONS-KOLAR
Signal (Bit code)
DC Power Limit in MW
Number of pair of lines
0 000
loss of comm. between AC SC &PC
1 001
controlled shutdown or ESOF
0
1 010
controlled shutdown
1
0 011
500 MW
2
1 100
1000 MW
3
0 101
1500 MW
4
0 110
2000 MW
5
1 111
no limit
6
Ramp Rates
Talcher
Kolar
With telecontrol
1300 A / sec
66 A / sec
Without telecontrol
10A/sec
Nil
STABILITY FUNCTIONS
– Frequency limit controller
• Stability functions needs to be enabled by the operator
• FLC comes into action if the frequency limits are set
within a band of current frequency
• Enabled automatically during islanding or split bus
mode at Talcher
• Enabled automatically during split bus mode at Kolar
• Can be enabled individually at Talcher or Kolar
• If telecom is faulty – FLC of Kolar is disabled
auotmatically
STABILITY FUNCTIONS
– Run-backs / Run-ups
• If stability functions are enabled, these functions are automatically
enabled
• At present this functions are not programmed
• Automatic ramping up of power is possible with certain conditions
• 5 conditions can be programmed / hardware inputs
• Automatic ramping down of power is possible with certain
conditions
• 5 conditions can be programmed / hardware inputs
• Individual run ups/run backs can be enabled or disabled for
Talcher/Kolar station
STABILITY FUNCTIONS
– Power Swing damping control
• Stability functions are to be enabled & power swing damping
function to be enabled
• Power Swing Damping function provides positive damping to the
power flow in the parallel AC system
• This function becomes active automatically during emergency
conditions or major disturbance of the AC system
• Additional DC power is calculated based on the frequency variation
/ swing of the connected AC system
• This function is provided for each pole at each station
Modes of Operation
Bipolar
Smoothing Reactor
Thyristor
Valves
DC OH Line
Smoothing Reactor
Thyristor
Valves
Current
Converter
Transformer
Converter
Transformer
Current
400 kV
AC Bus
AC Filters,
Reactors
400 kV
AC Bus
AC Filters, shunt
capacitors
Modes of Operation
Monopolar Ground Return
Smoothing Reactor
DC OH Line
Thyristor
Valves
Thyristor
Valves
Converter
Transformer
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Current
Converter
Transformer
400 kV
AC Bus
AC Filters
Modes of Operation
Monopolar Metallic Return
Smoothing Reactor
DC OH Line
Thyristor
Valves
Thyristor
Valves
Converter
Transformer
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Current
Converter
Transformer
400 kV
AC Bus
AC Filters
Automatic MR-GR changeover
• Normal operation – Balanced Bipolar operation
• When one pole trips, healthy pole goes to Ground
Return mode
• Limitation in Kolar electrode
• Healthy pole goes to Metallic Return mode
automatically – power flow restricted to 1000MW
• Operator can increase the power manually to the
overload capability of the healthy Pole after one Pole
trips
Automatic MR-GR changeover
• If line fault / failure of Metallic return changeover healthy Pole
remains in GR mode
• Changeover from GR mode to MR mode takes around
75secs
• Failure of changeover may be due to problems in the DC
switches or tele-control failure
• If all Blocking devices are healthy power flow settles at
500MW in GR mode
• If any Blocking device faulty power flow settles at 150MW
• Operator can set the 150MW limit / 500MW limit manually if
required
• During the automatic seq. process power flow follows the
defined curve as shown
• At present 150MW limit is set in GR mode
Electrode Current limitation characteristics
UPGRADATION OF HVDC PROJECT PURPOSE
• Outage of 400 kV transmission lines from
Talcher that requires transmission of maximum
power over this link
• Outage of one Pole which requires maximum
possible transmission of power on the other
pole continuously in metallic return mode due
to the restrictions in the GR mode at Kolar
Basic Components of HVDC Terminal
Converter Xmers
DC Line
Smoothing Reactor
400 kV
AC PLC
DC Filter
AC Filter
Valve Halls
-Thyristors
-Control & Protection
-Firing ckts
-Telecommunication
-Cooling ckt
Control Room
UPGRADATION OF HVDC PROJECT HIGHLIGHTS
• Existing overload capacity of the equipment being
used for long time loads – The overload
characteristics of HVDC are modified in Upgrade
• All the equipment ratings were studied and critical
equipment has been identified for modifications
• Smoothing Reactor, Converter Transformer, LVDC
bushing and PLC reactors (at Kolar) requires
additional modifications / replacement
• Relative ageing of the critical eqpt.- Converter
Transformer and Smoothing reactor are being
monitored in real time
New Over load features of HVDC
Overload
Uac
Ambient Temperature
0-33ºC
Long time
over load
Half – Hour
40ºC
Remarks
50ºC
Normal (380420kV)
1250
1250
1150
Extreme
(360/440)
1150
1110
1050
Normal (380420kV)
1300
1250
1200
Extreme
(360/440)
1300
1200
1200
New long time
overload
Continuous/ New long
time overload
The overload under upgradation is only long time loading of HVDC but
not the continuous loading under which HVDC can operate at 1.25 p.u for
max. of 10 hrs in a day while the rest of the day at 1.0p.u at ambient
<40ºC
Over load features of HVDC
• It is permissible to apply the half-hour overload once in
every 12 hour period
• The five second overload remains unchanged -1470MW
• It is permissible to apply the five second overload power
once in a five minute period and up to at least 5 times
during a two hour period
• The five second overload can be applied during operation
at the long time overload or half an hour overload.
• With Telecom out of service above overloads are not
applicable
Long time limits with redundant cooling
at normal & extreme AC bus voltages at Kolar
Half-hour limits
with redundant cooling
at normal & extreme AC bus voltages at Kolar
Extended long time limit
with redundant Cooling
for extreme ac voltage range
Half hour limit
with redundant Cooling
for extreme ac voltage range
Smoothing Reactor
• Hot spot temperature of the insulation to be within limits at
new extended overload
• The extended overload is achieved without sacrificing the
designed life of the Smoothing reactor
• Forced air cooling ducts are installed to keep the hot spot
temperature within limits
• Overload capacity is monitored by using Relative Ageing
Indication (RAI) and Load Factor Limitation (LFL)
• The status of the SMR forced cooling system decides the
overload limits of the system
• The SMR cooling will be automatically switched ON if the
DC current is >1950A and the ambient temperature is >28
ºC
DEFENCE MECHANISM FOR SR
Operational from March 2006
• Based on absolute power
• Power loss being calculated as
• Loss = Power 2 Secs prior to trip – Power after trip
• Tripping due to line fault is considered –
since during LF, healthy pole power is limited
to 150MW in GR mode
• Signals transmitted through FO instead of
PLCC
• Separate protection couplers installed
DEFENCE MECHANISM FOR SR
Trip generation LOGIC
• Condition 1:
• (500MW<Power loss ≤1000MW) & Pole Block = TRIP I
• Condition 2:
• (1000MW<Power flow ≤1500MW) & Line fault & Pole Block =
TRIP I
• Condition 3:
• (Power loss >1000MW) & Pole Block = TRIP II
• Condition 4:
• (Power flow >1500MW) & Line fault & Pole Block = TRIP II
Whenever Trip II is generated, Trip I also generates
BLOCK DIAGRAM OF DEFENCE MECHANISM FOR SR
Power
HVAC PLCC
Block
P1
TRIP I
Deblock
Line fault
Power
Block
P2
TRIP II
Protection couplers
Protection couplers
PLC
SER
Deblock
Line fault
Fault Recorder
DEFENCE MECHANISM FOR SR
Load relief: TRIP I
Andhra Pradesh
150MW
Trip I
Chinakampalli
Kolar
Chintamani
Hoody
Karnataka
250MW
Tamil Nadu
300MW
Hosur
Sriperambudur
Selam
DEFENCE MECHANISM FOR SR
Load relief: TRIP II
Andhra Pradesh
200MW
Gooty
Anantapur
Somayajulapalli
Kurnool
Karnataka
Trip II
Somanahalli
200MW
Tamil Nadu
200MW
Kerala
200MW
Madurai
Karaikudi
Thiruvarur
Trichy
Ingur
Trichur
Kozhikode
Kannur
Recent cases of SPS non-operation
• The system has worked perfectly in all cases and saved the
SR grid
• Some improvements are being done in following cases
• Pole 2 trip on 11.06.2010
– Problem in the Pole control system selection
– DC power was around 700MW and Pole 1 has taken over the power
immediately after tripping
– Hence inter trip signal need not be generated.
• Pole 2 trip on 19.08.2010
–
–
–
–
Problem in the Pole control system selection
The power loss was >500MW
Inter trip signal was not generated in this case
Since both Pole control system 1 &2 of Pole 2 had failed, the Pole
Block signal was not transmitted by the Pole control to the defence
mechanism
– This in turn could not generate the inter trip signal though the power
loss was sufficient for the signal generation.
Proposed modification
• Pole control system generates ESOF (Emergency
Switch OFF) signal to DC protection & SER
• This signal is available even during the complete
power supply failure in both the Pole controls
• One more Binary input for the detection of the Pole
trip in the above cases from each Pole
• This signal can be used with OR logic for the existing
Block /Deblock logic for Pole 1 & 2
• Additionally 2 relays have to be installed in Pole
Control and logic modification has to be carriedout.
Proposed addition of I/O signals
Power
HVAC PLCC
Block
Deblock
Protection couplers
P1
Line fault
"ESOF"
Power
Block
P2
Protection couplers
PLC
SER
Deblock
Line fault
"ESOF"
Fault Recorder
Trip signal -3
•
Addition of Trip signal-3 : Trip signal 3 will be initiated
–
•
OR
–
•
Any one pole / both poles block AND Power loss compared with
power flow 2 secs prior to Pole block is >2000MW
If one of the pole block on line fault AND Power flow just prior to that
instant was >2000MW
List of DTPCs to be wired for the load relief of 500MW for
trip signal -3 has to be provided by SRLDC. The S/w and
H/w modifications in the PLC & DTPC panels will be
carriedout at HVDC Kolar.
Trip Signal-2
• Modified logic:
• Any one pole / both poles block AND Power loss
compared with power flow 2 secs prior to Pole block
is >1000MW and less than or equal to 2000MW
• OR
• If one of the pole block on line fault
AND Power
flow just prior to that instant was >1500MW and less
than or equal to 2000MW.
Trip-1&2 during trip-3
Generation of Trip 1 & Trip 2 signals when
Trip 3 is generated: Modifications will be
carriedout at HVDC Kolar as per the desired
logic.
Trip signal on Line fault
•
Generation of trip signal on Line fault: SRLDC has
suggested following solutions to overcome the problem with
inter trip signal on line fault.
–
–
Generate trip signals -2 after 3 re-tries if set point is >1500MW: The
number of retries may vary depending upon the generator / line
condition at Talcher. Hence, this logic may fail in some cases.
Generate trip signal -2 if (original set point – Current power flow)
exceeds 1500MW in a minute interval: For measuring the power flow
2 secs prior to the Block signal, at present 10 samples for every
200msec are being considered. For 2 minutes we have to take 300
samples and the PLC may hang.
Proposed scheme
• Instead of above suggestions, it is proposed to modify the logic as below:
• The existing logic for line fault is seeing the power flow at the instant the
Line fault signal AND Blocked signal are available. In most of the cases it
is seen that only trip signal-1 on Line fault is generated. Since during line
fault recovery (restart time) of one pole, the power flow on HVDC is
reduced to the capability of the healthy pole (say 1200MW). This power
flow may be less and the Inter trip signal- 1 on line fault is generated.
• To overcome this problem, it is suggested that the logic can be designed
to monitor the power flow 2sec prior to the Line fault signal AND Blocked
signal for both trip signal 1 & 2. The time taken for fault recovery sequence
is <1sec (approx.) and hence 2 sec may be considered.
Power / Current limits due to protection
• One of the advantage of HVDC is
controllability
• On operation of certain protections especially
due to external AC system disturbances
• Current / power limitations are executed
instead of tripping the system immediately
• Improves the transient stability of the system
Single phase faults on AC system
• Single phase faults lasting for >500msec at
Inverter
• Causes severe commutation failures at
Inverter
• After 500msec, power limited by 1/3rd pre fault
power
• After 1200msec, Pole blocks
Reduced short Circuit ratio
•
•
•
•
A reduced short circuit level – Low SCR
Caused by disconnected lines or loss of generators
This produces transient stresses
Over voltages or repeated commutation failures occur during
recovery from external AC system faults or after a change of
power
• The power is limited to a safe power transfer level by pole
control to lead the stable steady state conditions of the HVDC
transmission.
Reduced Short Circuit Ratio
Stage
No. of
commutation
failure / minute
Reduced Current
/power level
Bi pole operation
Stage 1
3
75%
Balanced
Stage 2
6
50%
Balanced
Stage 3
After one minute delay, If again a commutation
failure occurred, the affected Pole will trip. The
time delay of Pole 1 and Pole 2 are set for 200 ms
and 400 ms to avoid Bipole tripping.
DC LINE FAULTS
• DC line faults detected by the DC protection based
on Wave front / under voltage protection
• Line fault recovery seq. initiated
• De-ionisation times
–
–
–
–
–
1st – 200msec
2nd – 250msec
3rd - 300msec
4th – 300msec at RVO
After 300msec Pole block
• Line fault locator – distance accuracy upto one tower
• On one pole trip – healthy Pole in GRM – 150MW
UdL
UdL
IdH
IdH
IdL
IdL
DC-Line
IdN
IdE
Idee1
Idee1
Electrode Line
A
UdN
Idee2
IdE
IdN
Electrode Line
Idee2
B
Power Reversal on HVDC
• Power reversal can only be initiated by the operator
SR  ER
• Pole needs to be Blocked before going for reverse
power operation
• Off-line power reversal can be performed in
monopolar or bipolar operation
• In bipole power control mode the power direction is
changed on a bipolar basis
• Power reversal on a pole basis is provided in current
control mode