FREQUENCY CONTROL
DURING BLACK START
OPERATIONS
The Isochronous Governor Control
Generator and QSE Remote
Constant Frequency Control
Sydney Niemeyer: NRG Energy
1
Introduction
Frequency Control During Black Start
Operations is intended to provide basic
dos and don’ts of frequency control during
system recovery following a Black out.
Review of Isochronous Governor Control
of a Resource and Constant Frequency
Control of an Island is included.
2
Objectives
At the completion of this course of
instruction you will:
Identify the importance of understanding
the amount of Primary Frequency Control
available during Black Start and Island grid
operations.
Identify the amount of Primary Frequency
Control available on an Island grid.
3
Objectives
Continued:
Identify the effects of cold load pick-up
Identify the importance of one
Isochronous Governor Control Resource
per island.
Identify the importance of having one QSE
on Constant Frequency Control per island.
4
Definitions
Area Control Error (ACE): The
instantaneous difference between a
Balancing Authority’s net actual and
scheduled interchange, taking into account
the effects of Frequency Bias, correction
for meter error, and Automatic Time Error
Correction (ATEC), if operating in the
ATEC mode. ATEC is only applicable to
Balancing Authorities in the Western
Interconnection.
5
Definitions
Area Control Error (ACE): Continued.
Since ERCOT is not synchronously
connected to any other Balancing Authority
the net actual and scheduled interchange
values are always zero.
ERCOT does not correct for meter error in
the measurement of actual interchange.
ERCOT does not utilize ATEC.
QSE’s on Constant Frequency Control (Flat
Frequency Control) implement the ACE
calculation exactly as ERCOT.
6
Definitions
Automatic Generation Control (AGC):
Equipment that automatically adjusts
generation in a Balancing Authority Area
from a central location to maintain the
Balancing Authority’s interchange
schedule plus Frequency Bias. AGC may
also accommodate automatic inadvertent
payback and time error correction.
7
Definitions
Black Start Resource – A generating unit(s) and
its associated set of equipment which has the
ability to be started without support from the
System or is designed to remain energized
without connection to the remainder of the
System, with the ability to energize a bus,
meeting the Transmission Operator’s restoration
plan needs for real and reactive power
capability, frequency and voltage control, and
that has been included in the Transmission
Operator’s restoration plan.
8
Definitions
Frequency Bias: A value, usually expressed in
megawatts per 0.1 Hertz (MW/0.1 Hz),
associated with a Balancing Authority Area that
approximates the Balancing Authority Area’s
response to Interconnection frequency error.
Frequency Bias Setting: A value, usually
expressed in MW/0.1 Hz, set into a Balancing
Authority ACE algorithm that allows the
Balancing Authority to contribute its frequency
response to the Interconnection.
9
Definitions
Frequency Bias Setting: (approved by NERC,
not approved by FERC) A number, either fixed
or variable, usually expressed in MW/0.1 Hz,
included in a Balancing Authority’s Area Control
Error equation to account for the Balancing
Authority’s inverse Frequency Response
contribution to the Interconnection, and
discourage response withdrawal through
secondary control systems.
10
Definitions
Droop governor: a governor that changes
the electricity generated proportionally to
the change in electrical frequency. The
slope of this change represents the ratio of
electricity generated change to the
frequency change.
100% electricity change for a 5% change in
frequency is 5% droop.
11
Definitions
Isochronous governor: 1) a governor that
maintains the same speed in the
mechanism controlled regardless of the
load. 2) The frequency of the electricity
generated is “Flat” or constant and there is
zero generator droop.
RTU – Remote Terminal Unit
12
Content
The Black Start Generator and Frequency
Control
The next Start Generator and Frequency
Control
Sources of Primary Frequency Control
Sources of Load Dampening
Island Frequency Control
13
Black Start Resource
• Must operate with Isochronous governor in
service.
• As electrical load is connected to the Black
Start resource the governor responds to
control the prime mover to maintain
frequency to the frequency reference of
the governor, 60 Hz.
14
Isochronous Governor Controller
Turbine actual speed = 3600 rpm
2 pole generator = 60.00 Hz
Comparator
Device
Increase Prime
Mover if
frequency is low,
Decrease Prime
Mover if
frequency is high.
Reference input equal to
60.00 Hz
15
Isochronous Generator Controls
to Target Frequency
• Load must remain within generator’s
capability.
• The Isochronous Governor Controller does
the rest.
60
57
63
Generator
Frequency
Hz
16
The “Grid”
Black
Start
Black
Start
17
Next
Start
Busses cleared
except for Black
Start plant.
Black
Start
Next
Start
Black
Start
18
Next
Start
Black
Start
Next
Start
Black
Start
Second Black Start
unit running. Two
islands.
19
Next
Start
Preparing to Start
the Next Start units.
Black
Start
Next
Start
Black
Start
20
Next
Start
Next Start units on
in the two islands.
Black
Start
Next
Start
Black
Start
21
Island 2
300 MW Capacity
90 MW Output
10 MW
Island 1
20 MW Capacity
8 MW Output
Black
Start 1
10 MW
Next
Start 2
400 MW Capacity
12 MW Output
Next
Start D
15 MW
House
Load
5 MW
Black
Start A
60 MW Capacity
30 MW Output
Island 2:
360 MW Capacity
120 MW Load
100 MW
Island 1:
420 MW Capacity
20 MW Load
22
Island 1
• Next Start 2 generator is operating near
minimum load.
– Unit is typically less stable.
– Risk of over-heating steam turbine from too
little steam flow.
• Minimum flow is 2% to 5% of nameplate
depending on manufacturer.
• Increase Island load if possible.
23
Island 2
• Should start next generator to balance
load on generators. Increases reserves.
• Consider minimum operating conditions on
each generator added to the island.
• Operating above minimum load on
generator provides ability to place controls
in AUTO at plant.
– Improves Primary Frequency Response
delivery.
24
Island 2
300 MW Capacity
70 MW Output
10 MW
Island 1
Next
Start D
15 MW
House
Load
15 MW
Black
Start A
60 MW Capacity
30 MW Output
Island 2:
760 MW Capacity
170 MW Load
400 MW Capacity
70 MW Output
20 MW Capacity
8 MW Output
Black
Start 1
10 MW
Next
Start 2
400 MW Capacity
12 MW Output
Island 2: Now with 3
generators on line. Prepare
for Constant Frequency
Control.
100 MW 40 MW
Island 1:
420 MW Capacity
20 MW Load
25
Island Remote Constant
Frequency Control
• QSE should have MW telemetry from each
generator connected.
• QSE must have frequency telemetry from
the island.
• At least one generator must be capable of
remote dispatch (AGC).
• Black Start generator must be switched to
“droop” governor control from isochronous
control.
26
Preparation for Constant
Frequency Mode
• QSE of the Island generators will not be
following ERCOT Base Points.
• QSE will calculate Base Points for each
controllable generator.
• QSE will calculate Island Area Control
Error (ACE) using Constant Frequency
(Flat Frequency) mode.
– Verify that Scheduled Frequency is set to
60.00 Hz.
27
Determine Island Frequency
Response
• To calculate ACE of the island, the
Frequency Response of the island must
be estimated.
• ACE = (HzActual – HzScheduled ) * -10 * Bias
– Where Bias is the estimated Frequency
Response of the island, a negative number.
– Determine MW capacity of all generators
connected to the island that have a working
“droop” governor.
28
Determine Island Bias
• Sum the island MW generation capacity.
• Divide the capacity by 30.
• The result is the estimated frequency
response of the island in –MW/0.1 Hz.
• Capacity of frequency responsive
generators = 760 MW.
• 760 MW/30 = 25.3 MW/0.1 Hz.
• Bias setting should be -25 MW/0.1 Hz.
29
Bias Setting and Load
Dampening
• Synchronously connected loads provide
some frequency response to the island.
– Synchronous AC motors on fans, pumps etc.
– Florescent lighting.
• Under normal conditions on the ERCOT
grid, the frequency response of load on
the grid can be estimated by multiplying
the load (MW) by 0.00245 to get its
MW/0.1 Hz contribution.
30
Bias Setting and Load
Dampening Continued
• For a 30,000 MW load the frequency response
provided by load dampening would be 30,000 *
0.00245 = 73.5 MW/0.1 Hz.
– During very cold weather with ERCOT load above
42,000 MW, the multiplier will reduce to 0.0015 since
resistive heating load is not frequency responsive.
• During early stages of building an island,
the load dampening contribution will be
very small and can be ignored.
31
Know Your Generator Control
System
• Some QSE Generator Control Systems
require the Bias value to be entered as a
positive number. It is converted to a
negative value within the ACE calculation.
• It is simple to determine if you have Bias
set correctly.
– If frequency is below target, the ACE value should
cause generation to increase output.
– If frequency is above target, the ACE value should
cause generator to decrease output.
32
Bias Setting Lower Better
• Initially set Bias lower than calculated until
several load pickups have been observed.
• Cold Load Pickup will initially appear as 10
times the load increase but will decrease
with time. It is better to under control
(raise generation slowly) to avoid
frequency oscillations as the cold load
pickup will decay with time and aid
frequency recovery to normal.
33
Cold Load Pick-up
• When adding load remember that cold
load pickup is 10 times the steady state
load and takes up to 30 minutes to decay.
• 1 MW pick up looks like 10 MW and will
cause frequency to drop to 59.96 from 60
Hz with an island Bias of 25 MW/0.1 Hz.
• 3 MW pick up looks like 30 MW and will
cause frequency to drop to 59.88 Hz.
34
Frequency Control in Constant
Frequency Mode
• Will NOT be similar to having the Black
Start Generator on Isochronous control.
– Frequency movement will be much greater.
– Frequency recovery to schedule will be
dependent on the ramp rate of the
generator(s) on AGC.
– Sustained Primary Frequency Response from
all generators connected is critical for stable
frequency control.
35
Keep Operating Margin
• The QSE should closely monitor operating
margins on all the AGC generators.
• If Up or Down margin gets low, manually
adjust non-AGC generators to give AGC
generators more room to operate.
• When moving other generation, consider
the ramp rate of the AGC generators to
avoid excessive ramping demands.
36
Prepare for Tying Islands
Together
• Synchronize smaller island to the larger
island. (Smaller in MW load.)
• Before synchronization, determine MW
capacity of incoming island that will not be
on Constant Frequency Control.
• Calculate new Bias Setting of combined
area by adding capacity of frequency
responsive generators to existing island.
37
Bias Setting For Two Islands
Connected
• Existing Island on Constant Frequency
Mode capacity: 1260 MW.
• Incoming Island on Isochronous governor
control by the Black Start generator.
Capacity 420 MW.
• Combined capacity: 1680 MW.
• Bias Setting: 1680/30 = -56 MW/0.1 Hz.
– Be sure to include only generation capacity
that is frequency responsive.
38
10 MW
300 MW Capacity
70 MW Output
Next
Start D
15 MW
House
Load
Island 2
15 MW
Black
Start A
60 MW Capacity
30 MW Output
Island 2:
1260 MW Capacity
260 MW Load
Island 1
Sync Point
400 MW Capacity
70 MW Output
500 MW Capacity
90 MW Output
20 MW Capacity
8 MW Output
Black
Start 1
10 MW
Next
Start 2
400 MW Capacity
12 MW Output
Preparing to synchronize
Island 1 to Island 2.
100 MW
130 MW
Island 1:
420 MW Capacity
20 MW Load
39
Synchronizing Two Islands
• In the smaller island, take the Isochronous
Black Start generator out of Isochronous
governor control and place it in droop
mode.
• At Sync point, observe island voltages and
match appropriately.
• Observe Sync scope and adjust
generation in smaller island to achieve a
slightly “fast” rotation of the scope. Close
the breaker at the proper phase alignment.
40
Connecting Two Islands When
Both are on Constant Frequency
• The process is the same as the
isochronous generator.
– Take the smaller MW load island (incoming
generation) off Constant Frequency mode.
– Field operator at Sync location should have
contact with QSE of the incoming island to
direct generation up or down to achieve
proper synchronization.
• Only one QSE remains on Constant
Frequency mode after synchronization.
41
10 MW
300 MW Capacity
70 MW Output
Next
Start D
15 MW
House
Load
1 Island
Sync Point
400 MW Capacity
70 MW Output
500 MW Capacity
90 MW Output
15 MW
20 MW Capacity
8 MW Output
Black
Start 1
10 MW
Next
Start 2
400 MW Capacity
12 MW Output
Synchronized
Black
Start A
60 MW Capacity
30 MW Output
100 MW
130 MW
Island:
1680 MW Capacity
280 MW Load
Bias Setting: -56 MW/0.1 Hz
42
After Connecting Islands
• QSE that remains on Constant Frequency
mode adjusts Bias Setting to account for
the additional frequency responsive
generation.
• Communicates through ERCOT for
adjustments in generation operated by the
other QSE.
• Close additional tie lines to strengthen
island connections.
43
10 MW
300 MW Capacity
70 MW Output
1 Island
Next
Start D
15 MW
House
Load
400 MW Capacity
70 MW Output
500 MW Capacity
90 MW Output
15 MW
20 MW Capacity
8 MW Output
Black
Start 1
10 MW
Next
Start 2
400 MW Capacity
12 MW Output
Synchronized
Black
Start A
60 MW Capacity
30 MW Output
100 MW
130 MW
Island:
1680 MW Capacity
280 MW Load
Bias Setting: -56 MW/0.1 Hz
44
One Generator on Isochronous Governor Control per Island or
One QSE on Constant Frequency Control per Island
ONLY ONE BOSS
45
Two Isochronous Governor
Controls Active on One Island
• Each generator will control to a slightly
different frequency.
• The generator controlling to the higher
frequency will increase output.
• The generator controlling to the lower
frequency will decrease output.
46
Isochronous Governor Controller
Small conversion errors can
exist at several locations.
1. Resolution of actual frequency, turbine speed.
Turbine actual speed = 3600 rpm
2 pole generator = 60.00 Hz
Comparator
Increase
Prime Mover if
frequency low,
Decrease
Prime Mover if
frequency
3. Resolution of
high.
the comparator
circuitry/logic.
Device
Reference input equal to
60.00 Hz
2. Resolution of reference frequency, is it an
analog signal or digital.
47
Two Units on Isochronous Control
40
35
30
MW Output
25
Gen A operating at 20
MW output and on
Isochronous Control.
Controlling to 60.008 Hz
Gen B switched to
Isochronous Control and
controlling to 60.002 Hz.
20
15
10
5
Gen B operating at 15
MW output and on Droop
Control.
0
Gen A
Gen B
Total Load
48
Why Only One QSE on Constant
Frequency Mode
• Just like having two Isochronous governor
control generators active on the same
island, Constant Frequency mode will
generally result in undesired actions.
• The problem is that neither control system
will measure the exact same value for the
frequency.
• Neither control system will measure the
exact same value for the frequency
49
reference.
QSE Constant Frequency
Mode
QSE A on
Constant
Frequency
Control
Island ACE = (HzActual – 60.00) * -10 * Bias
Island
Frequency
RTU
Gen 2 MW
and/or
AGC
Telemetry
Bias
RTU
Gen 1
MW, Hz &
AGC
Telemetry
ACE
Target
Frequency
60.00 Hz
50
QSE AGC Control Loop
QSE’s AGC
Generator
Converts Digital Count
to Engineering Units
(Hz) and sends
4
Control Signals to
AGC Generator based
on ACE.
Converts 13.8 KV
1
to 120 VAC
Potential
Transformer
Frequency
Transducer
Converts 120 VAC
to madc or vdc
RTU
Converts madc or vdc
to a Digital Count and
transmits to QSE
when requested.
QSE
Generation
Control
System
2
Data Request
3
Data Reply
Generator
Control
51
Summary
The Isochronous Governor Controlled
generator will manage frequency of the
island.
Don’t ask it to do more than it is
capable of doing.
One Isochronous generator per island.
One Constant Frequency QSE per island.
Consider Generator minimum operating
level before connecting to the island.
52
References
NERC Glossary:
http://www.nerc.com/pa/Stand/Glossary%2
0of%20Terms/Glossary_of_Terms.pdf2
53
Questions
54
1. Initially during the first energization of an island grid,
frequency control in Real Time will be managed by the
___________________.
a)
b)
c)
d)
ERCOT Load Frequency Control (LFC) system.
QSE on Constant Frequency Control.
Resource on Isochronous Governor Control.
Resource on Droop Governor Control.
55
2. When a QSE initially begins controlling the island grid and
places its Control System on Constant Frequency Control,
they should set their Bias in their ACE equation to ________.
a) 699 MW/0.1 Hz, the present ERCOT Bias setting.
b) 698 MW/0.1 Hz, 1% of ERCOT Forecast Peak Load.
c) Total MW Capacity of the island being controlled divided by
30.
d) Sum of the frequency responsive MW Capacity of the island
being controlled divided by 30.
56
3. Cold load pick up will initially appear as _____ times the load
increase but will decrease with time.
a)
b)
c)
d)
5
7
9
10
57
4. Before a QSE places its Control System on Constant
Frequency Control and begins controlling island frequency it
must have _____________________.
a) ERCOT Frequency and ability to control one Resource
connected to the island on AGC.
b) QSE Control System frequency and ability to control one
Resource connected to the island on AGC.
c) Frequency of the island and ability to control one Resource
connected to the island on AGC.
d) Resource on Isochronous Governor Control and one
Resource on AGC, frequency input not needed.
58
5. When synchronizing two islands where both islands have
one Resource on Isochronous Governor Control, what is the
correct procedure in synchronizing the two islands?
a)
b)
c)
Take both units off Isochronous Governor Control after synchronization
to maintain stability, and leave the largest Island on Isochronous
Governor Control.
Take the unit in the smallest Island off Isochronous Governor Control
and place in droop prior to synchronization and leave the largest Island
on Isochronous Governor Control.
Take the unit in the largest Island off Isochronous Governor Control and
place in droop prior to synchronization and leave the smallest Island on
Isochronous Governor Control.
59