Download Steady-State and Dynamic Performance Characterization of a

Steady-State and Dynamic Performance
Characterization of a Microturbine
Power System 2002
Impact of Distributed Generation
Conference
March 13-15, 2002
Clemson, SC
Rick Langley
EPRI PEAC Corporation
Knoxville, TN
Microturbine System
Under Test
• Microturbine installed in EPRI PEAC’s
Distributed Resource and Power Quality
Park (DRPQ Park) in January of 2001
• The system was installed for technology
demonstrations and lab testing of DER
technologies.
Microturbine System
Under Test
• Three-phase Inverter-based
DER
– Grid-Dependent
• 400-480Vac, 45-65Hz
– Grid-Independent
• 150-480Vac, 10-60Hz
• Automatic “mode-transfer”
capability allows the unit to
automatically switch from griddependent mode to gridindependent mode and back,
based on the health of the utility
power supply.
Distributed Resource
Type
Microturbine
Generator
Grid-Dependent
Capable
Yes
Grid-Independent
Capable
Yes
Automatic ModeTransfer
Yes
Output kW, kVA –
Grid-Dependent
28, 28
Output kW, kVA –
Grid-Independent
28, 40
(@ 0.7pf min)
Fuel Type / Fuel
Pressure
Low-pressure
Natural Gas / 15 psi
Microturbine System
Under Test
• The microturbine does not have a discrete generator or
combination generator/feeder protection relay.
• The microturbine relies on its own microprocessorbased protection system that is built into the system
controls.
• The system has a separate voltage monitor relay used to
determine if the power grid is suitable for connection
(nominal voltage level and unbalance).
• The microturbine’s grid-dependent and gridindependent protective functions are user-programmed
(undervoltage, overvoltage, over-frequency, and underfrequency).
Microturbine System
Under Test
• The microturbine’s
grid-dependent
protection functions
were set according to
IEEE P1547-Draft 8.
Microturbine Setup
Automatic Mode-Transfer
Enabled
Automatic Restart
Enabled
Grid-Dependent Protection Function Settings
Type
Setpoint
Time-Delay
Undervoltage
Level 1
Undervoltage
Level 2
Overvoltage
Level 1
Overvoltage
Level 2
Under-frequency
424.0V
(88%)
240.0V
(50.0%)
528.0V
(110%)
576.0V
(120%)
59.3Hz
2.0 sec
Over-frequency
60.5Hz
0.010 sec
(not changeable)
1.0 sec
0.010 sec
(not changeable)
0.010 sec
(not changeable)
0.010 sec
(not changeable)
Test Categories
• Grid-Dependent Tests
– Characterization of Nominal Voltage Tolerance Thresholds
• Voltage Unbalance, Overvoltage, & Undervoltage Tests.
– Characterization of Response to Voltage Variations
• Voltage Sags, Swells, Capacitor-Switching Transients.
– Tendency to Island
• Voltage interruptions and Single-Phasing.
• Grid-Dependent Tests
– Characterization of Dynamic Loading Performance
• Resistive Step Loading
• Motor Starting
Characterization of Nominal
Voltage Tolerance Thresholds
• Changes in the Local EPS Nominal Voltage
– Undervoltage
– Overvoltage
– Voltage Unbalance
Characterization of Nominal
Voltage Tolerance Thresholds
• Voltage Unbalance Tests
– Local EPS voltage unbalance was slowly varied until the
microturbine tripped, i.e., ceased to energy the Local EPS.
– The microturbine tripped at 3% voltage unbalance.
• Undervoltage Tests
– Local EPS voltage level was slowly decreased until the
microturbine tripped.
– The microturbine tripped at ~90% of nominal voltage.
• Overvoltage Tests
– Local EPS voltage was slowly increased until the microturbine
tripped.
– The microturbine tripped at ~110% of nominal voltage.
Characterization of Nominal
Voltage Tolerance Thresholds
• Significance
– The IEEE P1547 standard does not
specifically identify these tests.
– However, these issues are important because
they represent of the potential variability in
electric power systems.
– DER systems should be designed so that they
are compatible with the normal variability of
the Local EPS.
Characterization of Response
to Voltage Variations
• Single-phase, two-phase, and three-phase
voltage sags of various magnitudes and
durations were applied to the Local EPS.
Characterization of Response
to Voltage Variations
Load Van
Utility Van
Turbine Ia
500
20
90
400
15
80
300
70
200
Voltage (in Volts)
10
60
50
40
30
100
5
0
0
-100
-5
-200
-10
20
-300
10
-400
-15
0
-500
-20
0.25
0
20
40
60
80
100
Sag Duration
(in cycles)
120
140
160
180
0
0.05
0.1
0.15
Time (in seconds)
0.2
Current (in Amps)
Sag Magnitude
(in % of nominal)
100
Characterization of Response
to Voltage Variations
• Significance
– According to IEEE P1547, a DG system should trip
offline if the magnitude of the Local EPS voltage
falls below 88% for 2 seconds or 50% for 10 cycles.
– It also states that the DG shall not reconnect until
the Local EPS voltage is within Range B of ANSI
C84.1.
– The test results show that the microturbine system
under test responded in a manner that was
consistent with the programming of the
microturbine’s grid-dependent protective functions
and the criteria defined by the IEEE draft standard.
Tendency to Island
• Single- and three-phase voltage
interruptions were applied to the Local
EPS at several different durations.
Tendency to Island
Microturbine
Setpoint
Load
Setpoint
Interruptio
n Type
Response
Time
30kW
15kW
SinglePhase
42 cycles
(0.7 sec)
15kW
15kW
SinglePhase
1440 cycles
(24.0 sec)
7.5kW
15kW
SinglePhase
120 cycles
(2.0 sec)
15kW
15kW
Three-Phase
1 cycle
(0.017 sec)
Tendency to Island
• Significance
– Significant variability in detection time to singlephasing conditions based on the microturbine and
load setpoints.
– Single-phasing detection times were greater than the
Voltage Disturbance criteria defined by IEEE P1547
(reference Section 4.2.1) .
• IEEE P1547 criteria for voltage <50% of nominal is 0.16
sec.
– Three-phase interruption detection time was very
fast with little variability in response regardless of
the microturbine and load setpoints.
Tendency to Island
• Significance
– None of the relevant standards (IEEE P1547, IEEE
929, and UL 1741) directly address how three-phase
DER systems should react to single-phasing
conditions .
– There will be many locations where distribution
protection equipment, such as fuses, sectionalizers,
or reclosers, may open only one phase in a threephase system.
– These test results clearly demonstrate the need for
the clarification of the classification of singlephasing in the DER interconnection standards.
Characterization of Dynamic
Loading Performance
• The objective was to characterize the microturbine
system’s grid-independent performance during dynamic
loading conditions:
– Motor Starting
– Resistive Step-Loading
Characterization of Dynamic
Loading Performance
Van
• 30kW to 15kW
Resistive Step Load
– The temporary
voltage rise was less
than 6% of nominal.
300
275
250
225
200
175
150
125
100
75
50
25
0
0
0.05
0.1
0.15
0.2
0.25
Time
(in seconds)
0.3
0.35
0.4
60
55
50
45
40
35
30
25
20
15
10
5
0
0.45
Current
(in rms Amps)
– The temporary
voltage drop was less
than 5% of nominal.
Voltage
(in rms Volts)
• 15kW to 30kW
Resistive Step Load
Ia
Characterization of Dynamic
Loading Performance
• “Line-starting” of a 5-hp
(3.73-kW) three-phase
induction motor.
Voltage
(in rms Volts)
300
275
250
225
200
175
150
125
100
75
50
25
0
0
Ia
120
110
100
90
80
70
60
50
40
30
20
10
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55
Time
(in seconds)
Current
(in rms Amps)
– The voltage on Phase A
was reduced to 28% of its
nominal value.
– Phases B and C were
affected to a lesser degree
at 58% and 81% of
nominal, respectively.
– The system voltage
returned to nominal as
soon as the motor
accelerated to the full
speed.
Van
Characterization of Dynamic
Loading Performance
• Significance
– The ability to operate Distributed Energy Resources
in grid-independent modes can significantly increase
system reliability.
– When grid power is not available, DER systems can
be valuable assets to maintain critical facility loads.
– However, compatibility between the critical loads
and the standby DER can be an issue.
– In some cases, alternative-starting methods, such as
soft-starters for “line-connected” motors, may be
required.
Conclusion
• Distributed energy resources hold great promise for
improving the efficiency and reliability of the nation’s
electric power systems.
• However, before the full benefits of DER can be
realized, a number of potential barriers to
interconnection of DR equipment must be overcome.
• In its recent report, “Making Connections,” DOE’s
National Renewable Energy Laboratory (NREL)
identified a number of technical issues, business
practices, and regulatory rules that can increase the
cost of and unnecessarily delay or even stop viable
projects with potential benefits for both end users and
power-delivery companies.
Conclusion
• EPRI, the utility industry, and the DOE are responding
with initiatives to test and certify DER hardware with
research projects aimed at “breaking down the
barriers” to interconnection by answering technical
questions about DER capabilities for end-users and the
electric utility grid through:
– Developing engineering guides, software tools, and test protocols,
– Conducting field demonstrations and laboratory testing, and
– Supporting education, training, and standards development
activities for DER.
– Testing of this microturbine DER system supports these initiatives.
Conclusion
• The microturbine has operated reliably during many grid voltage
disturbance tests and demonstrations.
• Its built-in protection functions have met most, but not all the
response expectations of IEEE P1547 and utility wires companies.
– The single-phasing issue is still open.
• Analysis of the test results reveals that this system is best suited for
grid-connect that do not have interruption-free power requirements
and standby power applications .
• In grid-independent or standby power applications, load and
microturbine compatibility should be reviewed before installation.
– Alternative load starting and powering methods may be required.
• Testing continues on the microturbine system at the EPRI PEAC
laboratory.
Acknowledgements
• This research was supported in part by
the U.S. Department of Energy, Office of
Power Technologies under Contract DEAC05-00OR22725 with UT-Battelle.
• Member’s of EPRI’s Completing the
Circuit for their support of this research.