on load tap changing transformer paralleling simulation and control
Post on 19-Dec-2015
259 views
TRANSCRIPT
![Page 1: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/1.jpg)
On Load Tap Changing
Transformer Paralleling
Simulation and Control
![Page 2: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/2.jpg)
2
OLTC Overview
• Transformer Paralleling
• The need for control
• Current Solutions
• Our Plan and System
![Page 3: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/3.jpg)
3
Parallel Transformers
• Increase Reliability• Improve Power quality• Prevent voltage sag• Meet increased load
requirements
![Page 4: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/4.jpg)
4
Examples
• Illustrate the need for control
• Present Two Calculation Methods– Superposition Method– Admittance Method
![Page 5: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/5.jpg)
5
Grainger Examples
One-Line Diagram Grainger, Example 2.13, pg 78
![Page 6: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/6.jpg)
6
Grainger Examples
Per-Phase Reactance Diagram, Grainger pg 78
![Page 7: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/7.jpg)
7
Superposition Methodj 1 pu 1
tn
n'
Zload 0.8 j 0.6( )pu
V2 1.0 ej 0 deg pu
ZTa j 0.1 pu ZTb j 0.1 pu
ILoad
V2
Zload
0.8 0.6j( ) pu
![Page 8: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/8.jpg)
8
Superposition Method
V t 1 0.05 arg V( ) 0 deg Tap Step Voltage
By Superposition:
IcircV
ZTa ZTb0.25j pu Circulating Current
ITa
ILoad
2Icirc 0.4 0.05j( ) pu
ITb
ILoad
2Icirc 0.4 0.55j( ) pu
![Page 9: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/9.jpg)
9
Superposition MethodEquivalent Circuit
![Page 10: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/10.jpg)
10
Superposition Method
STa V2 ITa
0.4 0.05j
Vars are unbalancedKWs are balancedSTb V2 ITb
0.4 0.55j( ) pu
SLoad V2 ILoad
0.8 0.6j( ) pu
SLoad 1pu
kVA in the circuit thatserves no purpose at the load
STa STb SLoad 0.083pu
![Page 11: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/11.jpg)
11
Admittance Methodt 1.05e
j 0 deg
YTa
Y
Y
Y
Y
10j
10j
10j
10j
pu
YTbt 2
Y
t Y
t Y
Y
11.025j
10.5j
10.5j
10j
pu
Y YTa YTb21.025j
20.5j
20.5j
20j
Grainger, Example 9.7
![Page 12: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/12.jpg)
12
Admittance MethodI1
I2
YV1
V2
V1
I1
Find V1 I1
I1a
I2a
YTa
V1
V2
I2a 0.39 0.049j( ) pu
I1b
I2b
YTb
V1
V2
I2b 0.41 0.551j( ) pu
STa V2 I2a
0.39 0.049j( ) pu
STb V2 I2b
0.41 0.551j( ) pu
![Page 13: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/13.jpg)
13
Problem Definition
• We want to minimize the circulating current.
• Why?– Increased total losses of the two transformers– Unable to fully load one transformer without
over-loading or under-loading the other– This current is parasitic, serving no benefit– The transformer is not operating at optimum
![Page 14: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/14.jpg)
14
Project Objectives
• Build and test an experimental system– Measure the circulating current
• Build a mathematical model of the system• Design a control scheme that utilizes SEL
technology• Refine the System to minimize circulating
current over a variety of conditions
![Page 15: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/15.jpg)
15
Popular Solution Methods.
• Master- Follower Method
• Power Factor Method
• Circulating Current Method
• Var Balancing (∆Var) Method TM
Source: Advanced Transformer Paralleling Jauch, E. Tom: Manager of Application Engineering, Beckwith Electric Co., Inc.
![Page 16: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/16.jpg)
16
Master-Follower
• Desired operation maintains same tap level on all transformers
• Consists of one control commanding transformer tap changes to follow
![Page 17: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/17.jpg)
17
Master-Follower
• Positives:– Appropriate voltage level via load is maintained
• Negatives:– Does nothing to prevent circulating current
![Page 18: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/18.jpg)
18
Power Factor (PF) Method
• Desired tap positions provide equal PF
• Done by comparing angle of currents
• Does not operate controls, Just prevents them from operating in the wrong direction.
![Page 19: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/19.jpg)
19
Power Factor (PF) Method
• Positives:– Keeps PF in desired range.
• Negatives:– Difficult to apply to more than 2 parallel
transformers.– If VAr flow, tap level changed is blocked to
minimize PF difference.– If transformers have different impedances, Highest
KW loaded transformer is forced to have highest VAr load.
![Page 20: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/20.jpg)
20
Circulating Current Method
• Assumes continuous circulating current path
• Controls are biased to minimize Icirc.• Higher tap lowered, as lower tap increased
the same amount to make equivalent tap level.
• Relay used to block operation if tap level variation becomes to great.
![Page 21: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/21.jpg)
21
Circulating Current Method
• Positives:– Icirc is put to a minimum– Initial voltage level maintained– Max difference in tap levels maintained
• Negatives:– Auxiliary CT’s are required– Flow of KW can not be fixed by changing taps
» This causes oscillation of tap levels.
![Page 22: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/22.jpg)
22
Var Balancing (∆Var) Method
• Loads transformers by balanced VAr sharing.
• Ignores KW loading
![Page 23: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/23.jpg)
23
Var Balancing (∆Var) Method
• Positives:– Balanced VArs make Icirc a min or 0– No auxiliary CT’s are needed
• Negatives:– Method is patented by Beckwith Electric Co.
INC.
![Page 24: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/24.jpg)
24
Our Plan
• SEL 3378 SVP assumes control of system• Provided with phasors from the relay• SVP calculates optimal tap levels• SVP directs tap changers through SEL
487E relay
![Page 25: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/25.jpg)
25
Our Plan
• Goals– Appropriate voltage level maintained– Icirc driven to a minimum– Max variation of tap levels met– Avoids tap level oscillation
![Page 26: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/26.jpg)
26
System
• Transformers
• 487E Relay
• 3378 Synchrophasor Vector Processor
![Page 27: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/27.jpg)
27
Transformers
• Two Autotransformers will be used to simulate two parallel power transformers
• Voltage controlled motors on the tap changers
• Transformer secondary will feed an external load from unity to 0.5 lead/lag
![Page 28: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/28.jpg)
28
Transformers
• Superior Electric Type 60M21• Single Phase• Input Voltage: 120V• Output Voltage: 0V-140V• KVA: 0.7• Toroidal Core• Synchronous Motor
– 120VAC, 60Hz, 0.3A, 3.32 RPM
![Page 29: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/29.jpg)
29
Transformers
• Short Circuit Tests– The resistance of the tap contact is larger
than the reactance of the winding– The MVA imbalance of the parallel
combination is expected to be dominantly Watts, rather than Vars
• Verified through no-load Paralleling test
![Page 30: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/30.jpg)
30
T1 X and R Vs Secondary Nominal Voltage
0 20 40 60 80 100 120 140 1600
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
T1 Leakage Reactance Vs Secondary Voltage
X
R
Secondary Nominal Voltage
Ohm
s
![Page 31: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/31.jpg)
31
Transformers
• The autotransformers do not exhibit characteristics similar to a typical power transformer
• Options– Use these transformers– Different Transformers, 5 kVA Motor driven
autotransformers
![Page 32: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/32.jpg)
32
Calculations
• The Superposition method will support the real component while the Admittance method will not– The real component will create a negative
resistance in the PI equivalent
![Page 33: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/33.jpg)
33
487E Relay
• Uses Lateral Logic• 18 Current Channels• 6 Voltage Channels• Synchrophasor data
collected once per cycle, up to 12 Channels
![Page 34: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/34.jpg)
34
487E Relay
• Control transformer tap level
• Receives commands from SVP
• Displays: voltages, currents, Icirc, apparent power, real power, reactive power.
![Page 35: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/35.jpg)
35
3378 SVP
The SVP time aligns synchrophasor messages, processes them with a programmable logic engine, and sends controls to external devices to perform user defined actions.
-SEL 3378 data sheet
![Page 36: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/36.jpg)
36
3378 SVP
• Interface with the 487E Relay via serial connection.
• Phasor input to calculate circulating current.
• Control output to relay to minimize circulating current.
• Display output with real-time circulating current values.
![Page 37: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/37.jpg)
37
![Page 38: On Load Tap Changing Transformer Paralleling Simulation and Control](https://reader031.vdocuments.site/reader031/viewer/2022020712/56649d2e5503460f94a05faf/html5/thumbnails/38.jpg)
38
Conclusion
Proper transformer control results in • reduced losses • increased profits• maximized quality and reliability